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Contents
1. Preface
2. Objectives
3. Main Subjects
3.1 Main Function
3.2 Design Concept
3.3 Steam and Water Flow
3.4 Gas Flow
3.5 Main Equipment Configuration
3.6 Auxiliary Equipment Configuration
3.7 Manufacturing
3.8 Recommended Hydro test Procedure
3.9 Recommended Chemical cleaning Procedure
3.10 Lay up Procedure
3.11 Startup and Operating Procedure
3.12 Recommended Steam Blowing Procedure
3.13 Inspection and Maintenance Procedure
3.14 Input Data for DCS
4. Appendix
4.1 General Arrangement Drawing
4.2 Piping & Instrument Drawing
4.3 Pressure Part Arrangement Darwing
1. Preface
This manual is intended to be used for the comprehensive training of the HRSG operation and maintenance personnel.
Any materials furnished are exclusively for the use of the Owner’s personnel. This material is not resale or to be distributed to third parties, nor is it to be copied or reproduced without the Contractor’s prior written permission.
Any audio or video recording of the lecture material is prohibited unless DOOSAN grants permission in writing in advance of DOOSAN training program.
This course is intended to provide the experienced power plant operator and maintenance technician the information necessary to perform daily operations and routine maintenance of the HRSG.
This course will cover the major components, construction, design theory, start-up, normal shutdown operations and water chemistry.
This course, the student will have been presented with the information necessary to understand the safe operating concepts of a large multi pressure HRSG.
2. Objectives
Operators and engineers will be worked in plant should be understood HRSG, and then those persons involved in operating and maintaining for HRSG can be found easily which items are working as a bad condition or as a good condition and the solution if occur a certain problem during operating. The following items are necessary to understand HRSG.
l Main Subjects
ü Main Function
ü Design Concepts
ü Steam and Water Flow
ü Gas Flow
ü Main Equipment Configuration
ü Auxiliary Equipment Configuration
ü Manufacturing
ü Recommended Hydro Test Procedure
ü Recommended Chemical Cleaning Procedure
ü Recommended Lay up Procedure
ü Startup and Operating Procedure
ü Recommended Steam Blowing Procedure
ü Inspection and Maintenance Procedure
ü Input Data for DCS
l Duration : 1 week
l Location : On Site
l Trainer : HRSG basic designer
3. Main function
ü The plant will be suitable for base load operation and for intermittent part load operation. The power plant will be erected in Chon Buri Province some 80 km Southeast from Bangkok in Thailand.
ü The plant will comprise two(2) GTs(PG6561B) which will be fired with natural Gas as main fuel and light distillate oil as backup fuel, two(2) HRSGs with horizontal gas flow, natural circulation and two pressure and one ST.
ü The plant is designed as a base load system for operation at a design ambient temperature in the range of 15 oC to 43 oC with possibility of daily start stop or weekly standstill.
ü Each steam stage consists of an economizer (HP and LP), evaporator and superheater. The condensate water is heated approximately to boiling temperature in the HP and LP economizer and fed into HP and LP drum. From HP and LP drum, water is fed into the LP evaporator where a portion is evaporated. The resulting water steam mixture returns to the drum, where it is separated by separators. The separated saturated steam of the HP and LP system is fed to the superheater and is heated further to main steam temperature.
ü The HRSG is designed for semi-automatic start-up and shutdown as well as foe daily cycling to cover the load demands.
ü The Gas Turbine exhaust flows through the diffuser and diverter damper into the HRSG.
l General Description
ü Shop assembled pressure parts and structural steel modules
ü Vertical tube arrangement
ü Horizontal gas flow
ü Bottom type pressure part support
ü Direct weld construction for header and tube
ü Self supporting tube
ü Staggered tube arrangement
ü Cold outer casing
ü Natural circulation
l How to transfer the heat energy
ü Fluid / tube metal surface heat transfer by convection
ü Though tube metal surface heat transfer by conduction
ü Radiation from hot gas
l Heat transfer tube arrangement
ü Tube diameter ; 50. 8 mm
ü Staggered tube arrangement
ü The longitudinal space ; 102 mm
ü The lateral space ; 114 mm
ü The assembled HRSG consists of six (6) heat exchanger sections from the inlet transition duct to the exit of HRSG.
ü Each heating surface will be composed of multiple layers tube bank of finned tube.
ü All finned tubing shall be attached a serrated fin which is helical wound onto the tube under tension.
ü The very low penetration of attachment weld minimizes any effects on the physical or chemical characteristics of the tube and/or the fin.
l Casing design
ü Not exposed to high temperature
ü Not exposed to exhaust gas temperature transient
ü Shop fabrication in modules easily possible
ü Shoulder studs (12 mm minimum) will be welded to the inside of the outer casing. Insulating blanket will be impaled on the shoulder studs.
ü An oversize washer will be placed over the insulation and stopped from compressing the insulation by the shoulder of the stud. The liner plate will be installed with studs protruding through oversize washer and a nut welded to the stud. This construction permits the liner plate to expand with respect to the outer casing.
ü Short erection
l Safety valve
ü The purpose of the safety valves is to release the over pressure of the HRSG caused by blinking the steam turbine.
ü HP drum 1 : 83 bara ( design pressure )
ü HP drum 2 : 85.5 bara ( design pressure X 1.03 )
ü Factor 1.03 comes from ASME section I PG-67
ü HPSH : 79.2 barg (drum set pressure - pressure drop)
ü LP drum 1 : 17 bara ( design pressure )
ü LP drum 2 : 17.5 bara ( design pressure X 1.03 )
ü Factor 1.03 comes from ASME section I PG-67
ü LPSH : 14.5 bara (drum set pressure - pressure drop)
ü HP drum 1 : ( total predicted flow rate X 0.4)
ü HP drum 2 : ( total predicted flow rate X 0.4)
ü HP SH : ( total predicted flow rate X 0.2)
ü LP drum 1 : ( total predicted flow rate X 0.4)
ü LP drum 2 : ( total predicted flow rate X 0.4)
ü LP SH : ( total predicted flow rate X 0.2)
l Duct design
ü All duct shall be designed to withstand all loading from wind, seismic, thermal insulation, lagging and the maximum positive and negative pressure to be expected under all operating.
ü Max. Design pressure: 510 mmWG (Diffusor - last row of heating surface) and : 510 mmWG (last row of heating surface - stack outlet)
ü All duct consist of 6.0mm carbon steel outer casing, Insulation, and internal liner. But outlet duct not to be insulated. Only personal protection will be provided bottom side of outlet.
ü The duct will be properly stiffened, reinforced and complete with necessary doors and expansion joint.
l Thermal Insulation
ü The thermal insulation shall be applied to conserve energy, where accessible, and for personal protection.
ü Ambient Temperature : 31℃
ü Cold face Temperature : 65.0℃ below
ü Wind velocity : 0 m/s
ü The floors of modules and filler panels will be provided with drains.
ü Inlet duct and module will be used insulation with ceramic and mineral fiber.
ü All Drum, Header & Link will be used insulation with mineral wool.
ü All Drum, Header & Link will be protected with 1.0mm thick flat aluminum sheet.
3.3 Steam and Water Flow
l HP System Flow Path
ü The source of feedwater flow into the HP system is from the discharge of the HP feedwater pump. The feedwater is transferred into the HP HRSG drum via the HP economizers.
ü The water in the HP drum circulates through the evaporator tube bundle where is heated by the gas turbine exhaust gas and converted into saturated steam in the HP drum.
ü The water in the HP evaporator circulates naturally due to its difference in density.
ü The steam then exits the HP drum after passing through the moisture separator.
ü The dry steam from the HP drum then flows through the HP superheater tube bundles where the steam absorbs additional heat from the highest temperature exhaust gas.
ü This superheated steam flows through the HP main steam piping for admission into the steam turbine.
ü The HP steam is attemperated using the attemperators as needed.
ü The HP system includes valves and overpressure protection relief valves in compliance with the ASME B&PV Codes, Section 1, requirements.
ü The HP steam line from each HRSG is provided with a safety valve, a non return valve, a motor operated main steam isolation valve (by other).
l LP System Flow Path
ü The source of feedwater flow into the LP system is from the discharge of the LP feedwater pump discharge.
ü The water in the LP drum circulates through the evaporator tube bundle where is heated by the gas turbine exhaust gas and converted into saturated steam in the LP drum.
ü The water in the LP evaporator circulates naturally due to its difference in density.
ü The steam then exits the LP drum after passing through the moisture separator.
ü The dry steam from the LP drum then flows through the LP superheater tube bundles where the steam absorbs additional heat from the highest temperature exhaust gas.
ü This superheated steam flows through the LP main steam piping for admission into the steam turbine or for the process steam.
ü The LP system includes valves and overpressure protection relief valves in compliance with the ASME B&PV Codes, Section 1, requirements.
ü The LP steam line from each HRSG is provided with a safety valve, a non return valve, a motor operated main steam isolation valve (by other).
3.4 Gas flow
ü Exhaust gas leaves the gas turbine horizontally and enters diverter damper and an inlet duct where the flow is diverted from the horizontal to the vertical direction.
ü The exhaust gas that enters the HRSG will pass by the pressure sections in the following order:
HPHTSH - HPITSH - HPLTSH - HPEVAP - HPHTECON - LPSH -HPITECON - LPEVAP – HPLTECON2 – LPECON2 – HPLTECON1 – LPECON1.
ü The exhaust will leave the LPECON and exit the HRSG through the main exhaust stack.
3.5 Main Equipment Configuration
l Drum internal
ü Three stages of separation (Spindle blades and Wire mesh in Separator, Dryer).
ü Standard unitized separators include centrifugal separation sections and integral screen drier. The drums have site installed steam separators of sufficient size capacity to limit carryover to the superheater and turbine to the concentration. The separators is centrifugal type.
ü Corrugated plate driers, Dry box
ü Drum volume is sufficient to accommodate drum level fluctuations during startup without “tripping” the boiler due to high or low water level condition
ü Two manways per drum (one each end) are installed. The manways are to be hinged and 406mm diameter round for HP and LP drum.
ü One gauge glass assembly provided at each end of the HP drum (only one side for the LP drum) and have adequate view port length to cover the entire drum level operating range between high and low trip points.
l Harp ass’y
ü Continuous, high frequency welded, spiral finned tubes
ü All tubes enter headers radially
ü Economizers are multi pass for controlled water distribution
ü Economizer final pass is up flow to accommodate steaming at low load
ü Economizers are completely ventable and drainable
ü Permit rapid vertical tube expansion during start-up
ü Steam side pressure drop minimized, but be sufficient to achieve good steam flow distributions.
l Modules
ü Shop assembled
ü Modules are shipped complete with pressure parts and casing
ü Tubes and headers are supported for shipping
ü Module frames are braced for shipping and installation
ü Lifting lugs are included
ü Generous internal access within modules for piping connections to headers
l Inlet Duct Casing Construction
ü Internally insulated cold outer casing
ü Structural steel columns and casing stiffeners are integrated with casing
ü Internal liner
- Protects insulation from gas stream
- Is free to expand in all direction
- Has oversized holes and is secured with studs using large inner and outer washer with nuts
ü Internal insulation
- Ceramic and mineral wool
ü External casing is 6 mm thick
ü In the gas path, liner sections overlap in the direction of gas flow. The liner and attachment studs are so designed to ensure that the insulation will not be exposed to the hot gas flow for any thermal movement.
ü Ducting is sufficiently rigid to avoid vibration and drumming when exposed to gas turbine exhaust flow over the complete flow range.
l Casing Construction
ü Internally insulated cold outer casing
ü Casing stiffeners are attached to casing in the shop
ü No hot casing buckstay beam supports and associated field work is required
ü Internal liner
- Protects insulation from gas stream
- Is free to expand in all direction
- Has oversized holes and is secured with studs using large inner and outer washer with nuts
ü Internal insulation
- Ceramic and mineral wool
ü External casing is 6 mm thick
ü In the gas path, liner sections overlap in the direction of gas flow. The liner and attachment studs are so designed to ensure that the insulation will not be exposed to the hot gas flow for any thermal movement
l Outlet Duct and Stack Construction
ü HRSG outlet duct, expansion joint and stack are provided to deliver the gas turbine exhaust gas from the exit of the HRSG to the atmosphere
ü The outlet transition duct and stack are provided with personnel protection (expanded metal) at ladders, platforms and test ports.
ü Internal liner
l Outlet Duct Casing Construction
ü Internally insulated cold outer casing
ü Structural steel columns and casing stiffeners are integrated with casing
ü Stand-off are provided for attachment of the expanded metal.
l Support Structures
ü This structure also is used to support stairs, platforms, ladders and pipes
ü Stairs, platforms and ladders are supplied to allow easy and safe access into all work areas of the HRSG. The main operating platform must totally encompass the HRSG.
ü Ladder from HRSG operating platform to top of steam drum platforms
ü Stairs and / or ladder to any other HRSG or duct entry door, hatch, water gauges, and maintenance areas are considered to be maintenance area
ü All platforms designed for a live loading of any dead load, wind load and pipe load additives.
ü All ladders have safety cages.
ü Platform elevations to be such that any valve is easily accessible and can be operated from the platforms without the use of ladders or specific operating devices.
.6 Auxiliary Equipment Configuration
l HP SH Attemperators
ü One(1) final-stage attemperator will be provided. The attemperator use water from an extraction of high pressure pump discharge line. The purpose of the attemperator is to limit the steam temperature to as required during operation with gas turbine compressor inlet guide vanes in the low flow position when the gas turbine exhaust gas temperature is higher than the design value.
ü The capacity of the attemperator is such that the steam temperature has setting temperature(511.4 ℃) at the superheater NRV discharge over operating range.
ü The superheater one-stage attemperator system configured as shown on the flow diagram and designed per design criteria.
ü The attemperator configured to atomize and evaporate all water sprayed into the steam.
ü A thermal sleeve is included to permit an erosion resistantance due to water impingement on the steam piping.
l Emission ports in HRSG stacks:
ü Four(4) equally spaced ports for exhaust gas temperature test are installed for each of the main stacks.
ü Four(5) equally spaced ports for emission sampling test ports are installed for each of the main stacks.
ü Four(4) equally spaced ports for emission sampling test ports are installed for each of the bypass stacks.
l Instrumentation
ü HRSG include all required connections, valves, local indicators, thermocouples and connections including those shown in HRSG flow diagram.
ü The HRSG is designed for electrical utility service which includes continuous at base load and loads varying as specified.
l Safety Relief valves
ü To protect the pressure part such as superheater, evaporator, economizer and drum safety relief valves are installed.
ü The installation, equipment, valves and control sequencing meet all the requirements of ASME.
l Level gage
ü All drums have drum water level gage at each side of drum end for HP section and at one side of drum end for LP section.
l Blowdown tank
ü To regulate the HRSG water quality, continuous blow down system and intermittent blow down system are adopted as requirements.
ü The continuous blow down system is cascade system and the HP CBD flow is entered to LP drum.
ü The intermittent blow down water from HP, LP drum enter to BD tank, and the steam flow will vent and the condensate water is drained.
l Steam / Gas Silencers
ü To reduce fluid noise from safety valves, steam silencers are installed at the downstream of the equipment.
ü Also, the gas silencer is installed at the bypass stack.
l Diverter Damper
ü To change the exhaust gas flow direction when start-up, shut down and emergency circumstance from GT to HRSG or to BYPASS STACK, the diverter damper with electrical actuator and sealing air blowing system which is tighten sealing.
ü The bypass stack with internal insulation & liner is installed between G/T and HRSG.
l Flow Correction Device
ü For linear exhaust gas distribution, the gas flow correction device is installed in the inlet duct as shown General Arrange Drawing.
3.7 Manufacturing
DOOSAN HRSG shop manufacturing
ü Dedicated to the manufacture of heat recovery steam generator components
ü ASME approved
ü In house tube finning capability
ü Header manufacture
ü Pressure part module assembly
ü Module shipping structure assembly
ü Casing/insulation/liner system fabrication
ü Tube finning
3.8 Recommended Hydro-Static Test Procedure
l Introduction
After installation of all pressure, except those omitted during chemical cleaning (See Chemical Cleaning Procedure), the unit is subjected to the required initial hydrostatic test of 1-1/2 times the unit design pressure. Depending on insurance requirements, hydrostatic tests following pressure parts repairs are commonly made at the normal operating pressure or the design pressure.
Hydrostatic test procedures depend to great extent on local conditions and provisions. Procedures for initial hydrostatic testing must be in accordance with Boiler Code requirements. The following basic rules should always be followed:
l Preliminary
Before starting to fill the boiler and superheater make sure all drums and headers are cleared of foreign material. Close all drains. Open all vents normally used when filling the unit.
Prior to any hydrostatic test above normal operating pressure, hydrostatic test plugs must be installed in all safety valves in accordance with manufacturer’s instructions. If the hydrostatic test pressure is at or below the normal operating pressure it may be sufficient to merely gag the safety valves. Refer to safety valve manufacturer's instructions.
l Filling
1. Fill the superheater (see Fill Water below) through a suitable outlet connection (such as final superheater outlet header drain or vent) until all elements are filled and the water overflows into the steam drum.
2. Cease filling through the superheater outlet connection when the water overflows into the steam drums. Close superheater fill and vent connections.
3. Proceed filling the boiler (see Fill Water below) through the normal filling connections.
4. Keep filling until water overflows from the drum vents. Then close all vents.
l Filling water
It is the responsibility of the customer to provide properly treated water, as specified below, at 70°F (21°C). If the proper type of water is not available, this Company’s Service Department should be contacted for further information.
l Type of Water To Be Used:
1. Superheater (drainable and non-drainable sections):
Fill with treated condensate or treated demineralized water (see Note). The treatment shall include 10 ppm (10 cm3/m3) of ammonia and 200 ppm (200 cm3/m3) of hydrazine. This treated water will have a pH value of approximately 10.
SYMBOL 70 \f "Wingdings" | NOTE: Demineralized or Condensate quality water is defined as containing no more than 1 ppm (1 cm3/m3) of identifiable solids and essentially a zero concentration (or lowest detectable level) of organic material. |
CAUTION: The use of fill water, treated with solid chemicals, should be avoided. Deposits of solid materials in superheaters can be detrimental from heat transfer and corrosion standpoints. |
2. Remainder of boiler unit:
Fill with treated condensate or treated demineralized water, or, if not available, with a clean source of filtered water with 10 ppm (10 cm3/m3) of ammonia and 200 ppm (200 cm3/m3) of hydrazine.
l Hydrostatic testing
1. Apply hydrostatic test in accordance with Boiler Code requirements.
CAUTION: Hydrostatic test pressure should not be applied to the boiler if the metal temperature of the pressure parts is below 70°F (21°C). |
2. Hydrostatic Test Conditions
Refer to Appendix 1
l Post hydrostatic test procedures
1. Introduce nitrogen through the drum vent to pressurize the unit to approximately 0.3 to 0.6 kg/cm2 g.
2. Remove all hydrostatic test plugs and gags from the safety valves prior to starting up the unit.
SYMBOL 70 \f "Wingdings" | NOTE: Since there is generally some time delay between the hydrostatic test and the initial boiling out and acid cleaning of the boiler, the unit should remain full of water; air should not be allowed to enter. |
SYMBOL 70 \f "Wingdings" | NOTE: If there is a chance of freezing, the water in the drainable circuits can be displaced with nitrogen and the unit can be laid up under nitrogen pressure. Temporary heating equipment should be provided to keep the nondrainable superheater elements above freezing temperature. |
3.8 Recommended Hydro-Static Test Procedure
l Introduction
After installation of all pressure, except those omitted during chemical cleaning (See Chemical Cleaning Procedure), the unit is subjected to the required initial hydrostatic test of 1-1/2 times the unit design pressure. Depending on insurance requirements, hydrostatic tests following pressure parts repairs are commonly made at the normal operating pressure or the design pressure.
Hydrostatic test procedures depend to great extent on local conditions and provisions. Procedures for initial hydrostatic testing must be in accordance with Boiler Code requirements. The following basic rules should always be followed:
l Preliminary
Before starting to fill the boiler and superheater make sure all drums and headers are cleared of foreign material. Close all drains. Open all vents normally used when filling the unit.
Prior to any hydrostatic test above normal operating pressure, hydrostatic test plugs must be installed in all safety valves in accordance with manufacturer’s instructions. If the hydrostatic test pressure is at or below the normal operating pressure it may be sufficient to merely gag the safety valves. Refer to safety valve manufacturer's instructions.
l Filling
1. Fill the superheater (see Fill Water below) through a suitable outlet connection (such as final superheater outlet header drain or vent) until all elements are filled and the water overflows into the steam drum.
2. Cease filling through the superheater outlet connection when the water overflows into the steam drums. Close superheater fill and vent connections.
3. Proceed filling the boiler (see Fill Water below) through the normal filling connections.
4. Keep filling until water overflows from the drum vents. Then close all vents.
l Filling water
It is the responsibility of the customer to provide properly treated water, as specified below, at 70°F (21°C). If the proper type of water is not available, this Company’s Service Department should be contacted for further information.
l Type of Water To Be Used:
1. Superheater (drainable and non-drainable sections):
Fill with treated condensate or treated demineralized water (see Note). The treatment shall include 10 ppm (10 cm3/m3) of ammonia and 200 ppm (200 cm3/m3) of hydrazine. This treated water will have a pH value of approximately 10.
SYMBOL 70 \f "Wingdings" | NOTE: Demineralized or Condensate quality water is defined as containing no more than 1 ppm (1 cm3/m3) of identifiable solids and essentially a zero concentration (or lowest detectable level) of organic material. |
CAUTION: The use of fill water, treated with solid chemicals, should be avoided. Deposits of solid materials in superheaters can be detrimental from heat transfer and corrosion standpoints. |
2. Remainder of boiler unit:
Fill with treated condensate or treated demineralized water, or, if not available, with a clean source of filtered water with 10 ppm (10 cm3/m3) of ammonia and 200 ppm (200 cm3/m3) of hydrazine.
l Hydrostatic testing
1. Apply hydrostatic test in accordance with Boiler Code requirements.
CAUTION: Hydrostatic test pressure should not be applied to the boiler if the metal temperature of the pressure parts is below 70°F (21°C). |
2. Hydrostatic Test Conditions
Refer to Appendix 1
l Post hydrostatic test procedures
1. Introduce nitrogen through the drum vent to pressurize the unit to approximately 0.3 to 0.6 kg/cm2 g.
2. Remove all hydrostatic test plugs and gags from the safety valves prior to starting up the unit.
SYMBOL 70 \f "Wingdings" | NOTE: Since there is generally some time delay between the hydrostatic test and the initial boiling out and acid cleaning of the boiler, the unit should remain full of water; air should not be allowed to enter. |
SYMBOL 70 \f "Wingdings" | NOTE: If there is a chance of freezing, the water in the drainable circuits can be displaced with nitrogen and the unit can be laid up under nitrogen pressure. Temporary heating equipment should be provided to keep the nondrainable superheater elements above freezing temperature. |
Appendix 1 – Hydrostatic Test Conditions
No. | Test Part | Design Pressure (kg/cm2-g) | Test Pressure (kg/cm2-g) | Description |
1 | (HP)BFWP OUTLET →HPLT ECON1 →HPLT ECON2 →HPIT ECON →HPHT ECON →HP DRUM →HP EVAP →HP DRUM →HPLT SH →HPIT SH →HPHT SH →HP MAIN STEAM PIPE | 89.7 | 134.6 | A. First Pressure Up - Recommended Pressure Up : 3~5 kg/cm2-g per minute - Check each part at the design pressure B. Second Pressure Up - Recommended Pressure Up : 3~5 kg/cm2-g per minute - Hold for about 60 minute at test pressure C. Pressure Down - Recommended Pressure Down : 3~5 kg/cm2-g per minute |
2 | (LP) BFWP OUTLET →LP ECON1 →HP ECON2 →LP DRUM →LP EVAP →LP DRUM →LP SH →LP STEAM PIPE | 18.3 | 27.5 | A. First Pressure Up - Recommended Pressure Up : 3~5 kg/cm2-g per minute - Check each part at the design pressure B. Second Pressure Up - Recommended Pressure Up : 3~5 kg/cm2-g per minute - Hold for about 60 minute at test pressure C. Pressure Down - Recommended Pressure Down : 3~5 kg/cm2-g per minute |
3.9 Recommended Pre-operational Chemical Cleaning
l Introduction
Immediately before a new HRSG is put into service, the internal surfaces of the steam generating section should be cleaned to remove oil, grease, and protective coatings by means of an alkaline boilout.
CAUTION: DOOSAN does not recommend the acid cleaning of this unit as an initial clean out of the unit. This initial clean out of the unit is to be accomplished by means of a boilout. If an acid cleaning is performed, the HRSG circulation pumps must be removed. |
There are several methods of boiling out and acid cleaning an HRSG. The recommended procedure outlined in this section has proven to be successful.
l Preliminary to boiling out and acid cleaning
1. In order to minimize the amount of foreign matter that can be introduced into the HRSG from the preboiler system following start-up, the preboiler system should be alkaline flushed prior to boilout of the HRSG. 2. Remove all drum internals before boilout. Inspect and steam clean if necessary prior to installation. 3. Mechanically remove as much oil and grease as possible from the drums and headers before alkaline cleaning. 4. All HRSG instrumentation leads in free communication with the cleaning solution should be isolated during the cleaning process utilizing system isolation valves. 5. Special lines are required from a truck location or remote chemical pumping station: a. Provisions should be made for a 2 inch (50.8 mm) or larger acid fill line to the acid wash connections on the HRSG. b. Provisions should be made for a hot water or steam heating line with facility to regulate temperature between 150 and 180°F (65 and 82°C) at location. c. Provisions should be made for drain lines of adequate size to empty the HRSG rapidly, preferably within 180 minutes. The permanent drain valves provided on the unit are sized to meet this requirement assuming 50% of pressure drop through double valves and 50% through piping to disposal area. d. Provisions should be made for the necessary atmospheric vent lines and nitrogen fill line (tee connection in drum vent line). Vent lines should be tagged and protected against ignition of combustible gases. e. Provisions should be made for valved sampling connections which should be installed and appropriately tagged. f. Provisions should be made to measure boiler metal temperatures. Thermocouples should be peened into headers, drums, and downcomers. A surface pyrometer may be used to confirn the thermocouple readings. Temperature limitations given in the acid cleaning procedures apply to the location with the highest reading. 6. All pressure parts must be carefully inspected for obstructions and the necessary hydrostatic tests made. Internal chemical feed lines should be checked to be certain that they are free and clear. 7. It is important that the operators on duty during the boilout operation are familiar with normal operating procedures and precautions. The normal HRSG trip interlocks should be in operation and functioning properly. The HRSG auxiliaries and the special cleaning equipment should be in good operating condition. 8. Before introducing the cleaning solution into the HRSG, particular care should be taken to eliminate possible leaks, and adequate precautions should be taken to protect personnel in the event leaks occur.
l Boilout
1. A boilout is normally performed to remove oil or preservative which requires the use of a fairly strong caustic solution. The boiler and economizer should be filled to normal operating level with the boilout solution. It is recommended that the boilout solution be formulated with 4 kg of Na2CO3 and 4 kg of Na3PO4 (as Na3HPO4 - 12H2O) per 1000 kg of water and a detergent (0.05 - 0.1% by volume).
Other formulations and combinations of chemicals can be satisfactorily employed for boilout, and in cases where pollution control requirements dictate, changes in formulation can be made. Changes should, however, be reviewed by DOOSAN for suitability prior to use.
2. Pump the dissolved chemicals through the chemical feed line or feed by gravity into the steam drum. 3. After the boilout solution has been added, confirm the drum level in the temporary water gauge glass and prepare for start-up (refer to normal unit start-up procedures). Apply heat slowly, bringing the pressure in the boiler up to 300 psi gauge (20.7 bar), or to 1/5 of design pressure (whichever is lower) within 8 hours. Hold the pressure for 4 hours; observe the temperature of lower headers for an indication of circulation. The water level in the steam drums will rise during this period, however, blowdowns should be restricted only to what is necessary to keep the water level from going out of sight in the temporary gauge glasses. A high water level should be maintained during the boilout process. The gas turbine, controls, vents, drains, etc., should be operated as during normal start-up. 4. After 4 hours, secure heat source and allow the HRSG pressure to decrease. After the pressure has dropped noticeably, at least 150 psig (10.3 bar), blow down the boiler using the bottom blowdown valves, operating them in sequence. Do not allow the water level to go out of sight in the gauge glasses. Restore the water level to normal after the blowdown. 5. Reapply heat, raise the pressure to 300 psig (20.7 bar), or to 1/5 of design pressure (whichever is lower) and hold this pressure for 4 hours. At the end of the 4 hour time period repeat Step 4. 6. Repeat Step 5 two more times. 7. Samples of the boilout solution should be obtained periodically during the boilout period. If the boiler water alkalinity and phosphate concentration have dropped to 1/2 the original values, additional boilout chemicals should be added to restore the original concentrations. The samples should be analyzed for alkalinity, phosphate, and dissolved silica. The samples should also be checked for the presence of oil. Although quantative determinations are preferable, qualitative checks for the presence of oil will be highly satisfactory for monitoring and control purposes. 8. When analysis of the samples show that alkalinity, phosphate and dissolved silica have reached equilibrium levels and oil is no longer detected in samples, the heat source should be shut off. When the steam pressure drops to 25 psig (1.7 bar), the drum vents and superheater header drains should be opened wide. When the steam drum metal temperature falls below 200°F (93°C), the boiler should be drained. 9. Following the complete draining of the alkaline solution, the boiler should be filled to the top of the gauge glasses with clear rinse water heated to 170°F (77°C). While the HRSG is being filled for the boilout rinse, back fill the economizer through the inlet header and back fill the superheaters through the outlet headers with condensate or demineralized water (see Caution below) until water spills over into the respective steam drums. Leave the rinse water in the HRSG until it has sufficiently cooled to allow internal inspection. Drain the HRSG.
CAUTION: The use of fill water treated with solid chemicals should be avoided. Deposits of solid materials in superheaters can be detrimental from a heat transfer and corrosion standpoint. The quality of all fill water should be verified immediately prior to its entry into the superheater circuits. |
10. If the internal inspection of the HRSG indicates unsatisfactory cleaning, the boilout procedure should be repeated. 11. Upon completion of the HRSG boilout and after achieving a clean boiler, if immediate operation of the HRSG is not anticipated, the HRSG shall be laid up utilizing a wet post boilout lay up.
CAUTION: Use of most commercial detergents at concentrations in excess of 0.1% by volume during boilout may cause foaming and carryover of alkaline solution to the superheaters. Since commercial detergents vary in strength (i.e., water diluted) check with the manufacturer if recommended use strengths are higher than 0.1%. |
l Acid cleaning
Periodically during the operating life of any steam generator, chemical cleaning is recommended for the removal of iron oxide, copper, water formed and other deposits which may have accumulated on steam generating surfaces. The frequency of operational cleaning is dependent upon a number of operating conditions. However, three year cleaning appears to be a common and suitable period. This schedule should be altered for units which are subjected to intermittent operation or in cases of system upsets, such as condenser leakage, when feedwater contamination is greater than normal. In cases of tube failures caused by excessive deposits, chemical cleaning is one of the steps to be taken to return the unit to a sound operating condition. The attached curve, Figure 1, may be used as a guide in determining the need for chemical cleaning.
The acid cleaning procedure is based on the use of diluted (about 5% by weight), inhibited hydrochloric acid.
CAUTION: Acid cleaning should be performed only by experienced personnel. The HRSG circulation pumps must be removed prior to cleaning. |
Fill the HRSG with clear water and establish a level near normal in preparation for operation and adjusting metal temperature. Because of considerable heat capacity of the boiler metal and the anticipated heat losses, metal temperature should be adjusted to about 170°F (77°C) prior to introducing the acid to the boiler. Because of the non-uniform rate of cooling between the thin-walled tubes and thick-walled drums and headers, it is necessary to approach metal temperatures from below. This is done by admiting gas turbine exhaust at a very conservative rate. Once the desired metal temperatures [170°F (77°C)] are reached, the HRSG should be drained. All furnace openings must be closed to retain the heat.
Before admitting acid to the HRSG, check to be sure that:
1. The superheaters and economizers are full of condensate or demineralized water. Samples should be obtained from the superheater drains and vents to verify the absence of boilout chemicals. 2. The inspection doors are closed. 3. All drum vent valves are open. Unless specifically mentioned, valves should be positioned as for boiling out. 4. All boiler blowdown and chemical valves are closed. 5. Observe and record metal temperatures. No metal temperature is to exceed 180°F (82°C).
With the metal temperature about 170°F (77°C), fill the HRSG with inhibited acid solution (5–6% hydrochloric acid). It is recommended that 0.25% by weight of ammonia biflouride (NH4HF) be added to the inhibited HCl solution for its intensification and silica removal properties. The temperature of the solvent is maintained between 160 to 170°F (71 to 77°C) by blending the dilution water with steam.
In order to avoid the possibility of acid solution contacting hot steam piping, the steam required for temperature control should be introduced into the dilution water prior to the introduction of acid. There should be a space of at least 10 pipe diameters between these two admission points. Because the initial acid entering the boiler is consumed to some degree during the fill, and is in the HRSG for the longest period of time, it is good practice to blend a slightly higher concentration during the beginning of the fill than at the end. The HRSG should be filled until the level is indicated to have reached the center of the gauge glass. Observe caution, do not allow the level to go out of sight (high in glass). When the solution level has been established, the time should be recorded, a sample of the acid solution should be collected and analyzed for acid strength and iron concentration. Test of samples should be repeated every 30 minutes and tested for acid strength and total iron concentration. The cleaning is continued until the acid solution and total iron concentration approach equilibrium. Normally, this will be accomplished in less than 6 hours.
At the conclusion of the acid soak period, drain the HRSG under a positive pressure of nitrogen 3 to 5 psig (0.2 to 0.35 bar). The HRSG should be drained in as short a time as possible, using the maximum number of drain valves consistent with maintaining a positive nitrogen pressure. Nitrogen should be introduced into the HRSG through the drum vent lines. The pressure regulator should be of adequate size to introduce nitrogen at a volumetric rate capable of displacing all of the acid solution in the HRSG within a period of one hour.
Refill the HRSG with clear water at an approximate temperature of 150°F (66°C) to a slightly higher level than that of the drained acid. Simultaneously feed condensate or demineralized water into the economizers and back flush the superheaters with condensate or demineralized water to discharge any acid which may have inadvertently entered the economizers or the superheaters. The HRSG should then be drained under nitrogen as before. Refill with clear water at approximately 150°F (66°C) for a second rinse. About 0.1% by weight of citric acid should be added to the second rinse under a positive nitrogen pressure to assure more thorough iron removal. Drain the second rinse under a positive nitrogen pressure.
Fill the HRSG to the normal start-up level with a neutralizing solution consisting of 1% by weight of soda ash. Apply heat to the HRSG at a low rate, raising the pressure to 100 psi (6.9 bar) in 2 hours and hold this pressure for about 2 hours. At the end of the 2-hour rinse period, the HRSG should be allowed to cool gradually. During this period, blowdown the HRSG intermittently to reduce turbidity. Re-establish the solution level after each blowdown. The drum vents should be opened when the pressure drops to 25 psi (1.7 bar). When the steam drum and header temperatures fall to 200°F (93°C), the HRSG should be drained.
When the HRSG has cooled sufficiently to allow entrance, open the HRSG for inspection and completion of internal work.
l Notes and Precautions
F | NOTE: Acid cleaning should be performed only by experienced personnel. |
1. Draining of the neutralizing solution need not be under an atmosphere of nitrogen. Nitrogen is a non-toxic gas but will not support respiration. If nitrogen is used during draining of the HRSG, after which access by personnel is required, adequate ventilation must be provided before entrance is permitted. 2. If possible, the acid cleaning should be scheduled so that start-up of the HRSG will proceed immediately following the completion of the cleaning. If there is a delay of more than one or two days, the HRSG and the superheaters should be filled with condensate containing about 200 ppm of hydrazine and the pH adjusted to 10.0 with ammonia. The unit should be pressurized 3 to 5 psig (0.2 to 0.35 bar) with nitrogen. 3. The effectiveness of the inhibitor contained in the acid must be verified before admitting any acid into the HRSG. A simple test would involve submerging an untarnished carbon steel specimen in a sample of the acid which has been adjusted to the proper concentration and heated to 170°F (77°C). If one or more streams of bubbles appear, rather than an occasional isolated bubble, the acid should not be used until additional inhibitor is provided and the acid is proven safe by a repeat test.
A more elaborate test can be made if facilities are available. The loss of weight of a machined sample of boiler steel with a known surface area may be measured for a 30-minute immersion in the inhibited acid, diluted to the strength and maintained at the temperature that is to be used in the acid cleaning. The loss of weight should be no more than a milligram per square centimeter of surface.
4. The only hazard in cleaning a boiler with a properly inhibited acid solution is the possible existence of locally high metal temperatures. Most inhibitors for hydrochloric acid are not effective above 190°F (88°C), and accelerated corrosion will occur if higher metal temperatures are encountered. Since a temperature of at least 150°F (66°C) is recommended for effective cleaning, special care must be taken to establish the proper metal and solvent temperatures. 5. The gas turbine exhaust is capable of delivering significant quantities of heat to local areas of the HRSG. Even with adequate circulation, this may result in locally high, internal tube metal temperatures. For this reason, an HRSG containing hydrochloric acid must never be subjected to gas turbine exhaust or fired. 6. Before any back flushing of superheaters is performed, the water to be used should be chemically analyzed (conductivity, pH) in order to guard against contamination. 7. At the completion of the cleaning operation and prior to any operation of the HRSG, the water in the superheaters, and steam lines should be sampled at all available drains and checked for contamination. 8. In the event alkaline solution or acid should be inadvertently spilled into the superheaters during chemical cleaning, thorough back flushing at adequate flow rates must be done before any HRSG operation is permitted to ensure removal of all traces of acid. 9. As in the handling of any hazardous liquid, extreme care should be exercised to prevent injury to personnel during the acid cleaning.
l Preparations for Putting the HRSG into Service Following Chemical Cleaning
1. Inspect the steam drums. a. Blow out internal gauge glass connections and instrument leads. Remove temporary gauge glasses and install permanent gauge glasses. b. Blow out chemical feed and continuous blowdown piping. c. Flush out any loose sediment from steam drum surfaces and steam separators. Flush with clear water from the drums, draining through the blowdown connections at the bottom of the HRSG. 2. When all internal surfaces are clean, reinstall steam drum internals. Inspect and steam clean drum internals if required prior to installation. 3. Remove temporary piping and/or valves utilized for the boilout process. 4. When all work is completed, a thorough inspection should be made to ensure that no foreign material has been left in the drums. 5. Fill the boiler, economizer, and superheaters. Apply a hydrostatic test at normal operating pressure. Refer to Hydrostatic Testing Procedures provided elsewhere in this manual. If the unit is not to be placed into operation, refer to recommended Lay-Up Procedures. If the HRSG is to be placed into operation continue with Step 6. 6. Reduce the water level in the steam drums to the suggested operating level. 7. Drain the superheaters. The HRSG is now ready for operation. Refer to the HRSG operating procedures elsewhere in this manual.
l Cleaning procedures
All operations performed on the boiler during cleaning should be as outlined in “Recommended Pre-Operational Chemical Cleaning procedures” with the exception that a boilout is rarely used or necessary in a normal operational cleaning. Five percent inhibited hydrochloric acid is recommended for operational cleaning (as for preoperational cleaning).
The basic difference between preoperational and operational cleaning is the additives which are included in the operational cleaning solution to facilitate the removal of specific materials, such as copper and silica, which may be present in the deposit. The choice of additives should be based on the materials contained in deposits, and these should be determined prior to cleaning. If unusual or difficult to remove deposits are encountered, it may be necessary to use multi-step cleaning with special solvents to completely remove scale. It is recommended that one of the reliable chemical cleaning contractors be contacted for operational cleaning. These companies have the experience and technical know-how to properly formulate a cleaning mixture to remove undesired materials.
l NOTES AND PRECAUTIONS
1. All details and precautions outlined for pre-operational cleaning must be strictly followed for operational cleaning. 2. Steam purifying devices and orifices (if so equipped) should not be removed prior to operational cleaning.
l Boilout
1. A boilout is normally performed to remove oil or preservative which requires the use of a fairly strong caustic solution. The boiler and economizer should be filled to normal operating level with the boilout solution. It is recommended that the boilout solution be formulated with 4 kg of Na2CO3 and 4 kg of Na3PO4 (as Na3HPO4 - 12H2O) per 1000 kg of water and a detergent (0.05 - 0.1% by volume).
Other formulations and combinations of chemicals can be satisfactorily employed for boilout, and in cases where pollution control requirements dictate, changes in formulation can be made. Changes should, however, be reviewed by DOOSAN for suitability prior to use.
2. Pump the dissolved chemicals through the chemical feed line or feed by gravity into the steam drum. 3. After the boilout solution has been added, confirm the drum level in the temporary water gauge glass and prepare for start-up (refer to normal unit start-up procedures). Apply heat slowly, bringing the pressure in the boiler up to 300 psi gauge (20.7 bar), or to 1/5 of design pressure (whichever is lower) within 8 hours. Hold the pressure for 4 hours; observe the temperature of lower headers for an indication of circulation. The water level in the steam drums will rise during this period, however, blowdowns should be restricted only to what is necessary to keep the water level from going out of sight in the temporary gauge glasses. A high water level should be maintained during the boilout process. The gas turbine, controls, vents, drains, etc., should be operated as during normal start-up. 4. After 4 hours, secure heat source and allow the HRSG pressure to decrease. After the pressure has dropped noticeably, at least 150 psig (10.3 bar), blow down the boiler using the bottom blowdown valves, operating them in sequence. Do not allow the water level to go out of sight in the gauge glasses. Restore the water level to normal after the blowdown. 5. Reapply heat, raise the pressure to 300 psig (20.7 bar), or to 1/5 of design pressure (whichever is lower) and hold this pressure for 4 hours. At the end of the 4 hour time period repeat Step 4. 6. Repeat Step 5 two more times. 7. Samples of the boilout solution should be obtained periodically during the boilout period. If the boiler water alkalinity and phosphate concentration have dropped to 1/2 the original values, additional boilout chemicals should be added to restore the original concentrations. The samples should be analyzed for alkalinity, phosphate, and dissolved silica. The samples should also be checked for the presence of oil. Although quantative determinations are preferable, qualitative checks for the presence of oil will be highly satisfactory for monitoring and control purposes. 8. When analysis of the samples show that alkalinity, phosphate and dissolved silica have reached equilibrium levels and oil is no longer detected in samples, the heat source should be shut off. When the steam pressure drops to 25 psig (1.7 bar), the drum vents and superheater header drains should be opened wide. When the steam drum metal temperature falls below 200°F (93°C), the boiler should be drained. 9. Following the complete draining of the alkaline solution, the boiler should be filled to the top of the gauge glasses with clear rinse water heated to 170°F (77°C). While the HRSG is being filled for the boilout rinse, back fill the economizer through the inlet header and back fill the superheaters through the outlet headers with condensate or demineralized water (see Caution below) until water spills over into the respective steam drums. Leave the rinse water in the HRSG until it has sufficiently cooled to allow internal inspection. Drain the HRSG.
CAUTION: The use of fill water treated with solid chemicals should be avoided. Deposits of solid materials in superheaters can be detrimental from a heat transfer and corrosion standpoint. The quality of all fill water should be verified immediately prior to its entry into the superheater circuits. |
10. If the internal inspection of the HRSG indicates unsatisfactory cleaning, the boilout procedure should be repeated. 11. Upon completion of the HRSG boilout and after achieving a clean boiler, if immediate operation of the HRSG is not anticipated, the HRSG shall be laid up utilizing a wet post boilout lay up.
CAUTION: Use of most commercial detergents at concentrations in excess of 0.1% by volume during boilout may cause foaming and carryover of alkaline solution to the superheaters. Since commercial detergents vary in strength (i.e., water diluted) check with the manufacturer if recommended use strengths are higher than 0.1%. |
l Acid cleaning
Periodically during the operating life of any steam generator, chemical cleaning is recommended for the removal of iron oxide, copper, water formed and other deposits which may have accumulated on steam generating surfaces. The frequency of operational cleaning is dependent upon a number of operating conditions. However, three year cleaning appears to be a common and suitable period. This schedule should be altered for units which are subjected to intermittent operation or in cases of system upsets, such as condenser leakage, when feedwater contamination is greater than normal. In cases of tube failures caused by excessive deposits, chemical cleaning is one of the steps to be taken to return the unit to a sound operating condition. The attached curve, Figure 1, may be used as a guide in determining the need for chemical cleaning.
The acid cleaning procedure is based on the use of diluted (about 5% by weight), inhibited hydrochloric acid.
CAUTION: Acid cleaning should be performed only by experienced personnel. The HRSG circulation pumps must be removed prior to cleaning. |
Fill the HRSG with clear water and establish a level near normal in preparation for operation and adjusting metal temperature. Because of considerable heat capacity of the boiler metal and the anticipated heat losses, metal temperature should be adjusted to about 170°F (77°C) prior to introducing the acid to the boiler. Because of the non-uniform rate of cooling between the thin-walled tubes and thick-walled drums and headers, it is necessary to approach metal temperatures from below. This is done by admiting gas turbine exhaust at a very conservative rate. Once the desired metal temperatures [170°F (77°C)] are reached, the HRSG should be drained. All furnace openings must be closed to retain the heat.
Before admitting acid to the HRSG, check to be sure that:
1. The superheaters and economizers are full of condensate or demineralized water. Samples should be obtained from the superheater drains and vents to verify the absence of boilout chemicals. 2. The inspection doors are closed. 3. All drum vent valves are open. Unless specifically mentioned, valves should be positioned as for boiling out. 4. All boiler blowdown and chemical valves are closed. 5. Observe and record metal temperatures. No metal temperature is to exceed 180°F (82°C).
With the metal temperature about 170°F (77°C), fill the HRSG with inhibited acid solution (5–6% hydrochloric acid). It is recommended that 0.25% by weight of ammonia biflouride (NH4HF) be added to the inhibited HCl solution for its intensification and silica removal properties. The temperature of the solvent is maintained between 160 to 170°F (71 to 77°C) by blending the dilution water with steam.
In order to avoid the possibility of acid solution contacting hot steam piping, the steam required for temperature control should be introduced into the dilution water prior to the introduction of acid. There should be a space of at least 10 pipe diameters between these two admission points. Because the initial acid entering the boiler is consumed to some degree during the fill, and is in the HRSG for the longest period of time, it is good practice to blend a slightly higher concentration during the beginning of the fill than at the end. The HRSG should be filled until the level is indicated to have reached the center of the gauge glass. Observe caution, do not allow the level to go out of sight (high in glass). When the solution level has been established, the time should be recorded, a sample of the acid solution should be collected and analyzed for acid strength and iron concentration. Test of samples should be repeated every 30 minutes and tested for acid strength and total iron concentration. The cleaning is continued until the acid solution and total iron concentration approach equilibrium. Normally, this will be accomplished in less than 6 hours.
At the conclusion of the acid soak period, drain the HRSG under a positive pressure of nitrogen 3 to 5 psig (0.2 to 0.35 bar). The HRSG should be drained in as short a time as possible, using the maximum number of drain valves consistent with maintaining a positive nitrogen pressure. Nitrogen should be introduced into the HRSG through the drum vent lines. The pressure regulator should be of adequate size to introduce nitrogen at a volumetric rate capable of displacing all of the acid solution in the HRSG within a period of one hour.
Refill the HRSG with clear water at an approximate temperature of 150°F (66°C) to a slightly higher level than that of the drained acid. Simultaneously feed condensate or demineralized water into the economizers and back flush the superheaters with condensate or demineralized water to discharge any acid which may have inadvertently entered the economizers or the superheaters. The HRSG should then be drained under nitrogen as before. Refill with clear water at approximately 150°F (66°C) for a second rinse. About 0.1% by weight of citric acid should be added to the second rinse under a positive nitrogen pressure to assure more thorough iron removal. Drain the second rinse under a positive nitrogen pressure.
Fill the HRSG to the normal start-up level with a neutralizing solution consisting of 1% by weight of soda ash. Apply heat to the HRSG at a low rate, raising the pressure to 100 psi (6.9 bar) in 2 hours and hold this pressure for about 2 hours. At the end of the 2-hour rinse period, the HRSG should be allowed to cool gradually. During this period, blowdown the HRSG intermittently to reduce turbidity. Re-establish the solution level after each blowdown. The drum vents should be opened when the pressure drops to 25 psi (1.7 bar). When the steam drum and header temperatures fall to 200°F (93°C), the HRSG should be drained.
When the HRSG has cooled sufficiently to allow entrance, open the HRSG for inspection and completion of internal work.
l Notes and Precautions
F | NOTE: Acid cleaning should be performed only by experienced personnel. |
1. Draining of the neutralizing solution need not be under an atmosphere of nitrogen. Nitrogen is a non-toxic gas but will not support respiration. If nitrogen is used during draining of the HRSG, after which access by personnel is required, adequate ventilation must be provided before entrance is permitted. 2. If possible, the acid cleaning should be scheduled so that start-up of the HRSG will proceed immediately following the completion of the cleaning. If there is a delay of more than one or two days, the HRSG and the superheaters should be filled with condensate containing about 200 ppm of hydrazine and the pH adjusted to 10.0 with ammonia. The unit should be pressurized 3 to 5 psig (0.2 to 0.35 bar) with nitrogen. 3. The effectiveness of the inhibitor contained in the acid must be verified before admitting any acid into the HRSG. A simple test would involve submerging an untarnished carbon steel specimen in a sample of the acid which has been adjusted to the proper concentration and heated to 170°F (77°C). If one or more streams of bubbles appear, rather than an occasional isolated bubble, the acid should not be used until additional inhibitor is provided and the acid is proven safe by a repeat test.
A more elaborate test can be made if facilities are available. The loss of weight of a machined sample of boiler steel with a known surface area may be measured for a 30-minute immersion in the inhibited acid, diluted to the strength and maintained at the temperature that is to be used in the acid cleaning. The loss of weight should be no more than a milligram per square centimeter of surface.
4. The only hazard in cleaning a boiler with a properly inhibited acid solution is the possible existence of locally high metal temperatures. Most inhibitors for hydrochloric acid are not effective above 190°F (88°C), and accelerated corrosion will occur if higher metal temperatures are encountered. Since a temperature of at least 150°F (66°C) is recommended for effective cleaning, special care must be taken to establish the proper metal and solvent temperatures. 5. The gas turbine exhaust is capable of delivering significant quantities of heat to local areas of the HRSG. Even with adequate circulation, this may result in locally high, internal tube metal temperatures. For this reason, an HRSG containing hydrochloric acid must never be subjected to gas turbine exhaust or fired. 6. Before any back flushing of superheaters is performed, the water to be used should be chemically analyzed (conductivity, pH) in order to guard against contamination. 7. At the completion of the cleaning operation and prior to any operation of the HRSG, the water in the superheaters, and steam lines should be sampled at all available drains and checked for contamination. 8. In the event alkaline solution or acid should be inadvertently spilled into the superheaters during chemical cleaning, thorough back flushing at adequate flow rates must be done before any HRSG operation is permitted to ensure removal of all traces of acid. 9. As in the handling of any hazardous liquid, extreme care should be exercised to prevent injury to personnel during the acid cleaning.
l Preparations for Putting the HRSG into Service Following Chemical Cleaning
1. Inspect the steam drums. a. Blow out internal gauge glass connections and instrument leads. Remove temporary gauge glasses and install permanent gauge glasses. b. Blow out chemical feed and continuous blowdown piping. c. Flush out any loose sediment from steam drum surfaces and steam separators. Flush with clear water from the drums, draining through the blowdown connections at the bottom of the HRSG. 2. When all internal surfaces are clean, reinstall steam drum internals. Inspect and steam clean drum internals if required prior to installation. 3. Remove temporary piping and/or valves utilized for the boilout process. 4. When all work is completed, a thorough inspection should be made to ensure that no foreign material has been left in the drums. 5. Fill the boiler, economizer, and superheaters. Apply a hydrostatic test at normal operating pressure. Refer to Hydrostatic Testing Procedures provided elsewhere in this manual. If the unit is not to be placed into operation, refer to recommended Lay-Up Procedures. If the HRSG is to be placed into operation continue with Step 6. 6. Reduce the water level in the steam drums to the suggested operating level. 7. Drain the superheaters. The HRSG is now ready for operation. Refer to the HRSG operating procedures elsewhere in this manual.
l Cleaning procedures
All operations performed on the boiler during cleaning should be as outlined in “Recommended Pre-Operational Chemical Cleaning procedures” with the exception that a boilout is rarely used or necessary in a normal operational cleaning. Five percent inhibited hydrochloric acid is recommended for operational cleaning (as for preoperational cleaning).
The basic difference between preoperational and operational cleaning is the additives which are included in the operational cleaning solution to facilitate the removal of specific materials, such as copper and silica, which may be present in the deposit. The choice of additives should be based on the materials contained in deposits, and these should be determined prior to cleaning. If unusual or difficult to remove deposits are encountered, it may be necessary to use multi-step cleaning with special solvents to completely remove scale. It is recommended that one of the reliable chemical cleaning contractors be contacted for operational cleaning. These companies have the experience and technical know-how to properly formulate a cleaning mixture to remove undesired materials.
l NOTES AND PRECAUTIONS
1. All details and precautions outlined for pre-operational cleaning must be strictly followed for operational cleaning. 2. Steam purifying devices and orifices (if so equipped) should not be removed prior to operational cleaning.
l Boilout
1. A boilout is normally performed to remove oil or preservative which requires the use of a fairly strong caustic solution. The boiler and economizer should be filled to normal operating level with the boilout solution. It is recommended that the boilout solution be formulated with 4 kg of Na2CO3 and 4 kg of Na3PO4 (as Na3HPO4 - 12H2O) per 1000 kg of water and a detergent (0.05 - 0.1% by volume).
Other formulations and combinations of chemicals can be satisfactorily employed for boilout, and in cases where pollution control requirements dictate, changes in formulation can be made. Changes should, however, be reviewed by DOOSAN for suitability prior to use.
2. Pump the dissolved chemicals through the chemical feed line or feed by gravity into the steam drum. 3. After the boilout solution has been added, confirm the drum level in the temporary water gauge glass and prepare for start-up (refer to normal unit start-up procedures). Apply heat slowly, bringing the pressure in the boiler up to 300 psi gauge (20.7 bar), or to 1/5 of design pressure (whichever is lower) within 8 hours. Hold the pressure for 4 hours; observe the temperature of lower headers for an indication of circulation. The water level in the steam drums will rise during this period, however, blowdowns should be restricted only to what is necessary to keep the water level from going out of sight in the temporary gauge glasses. A high water level should be maintained during the boilout process. The gas turbine, controls, vents, drains, etc., should be operated as during normal start-up. 4. After 4 hours, secure heat source and allow the HRSG pressure to decrease. After the pressure has dropped noticeably, at least 150 psig (10.3 bar), blow down the boiler using the bottom blowdown valves, operating them in sequence. Do not allow the water level to go out of sight in the gauge glasses. Restore the water level to normal after the blowdown. 5. Reapply heat, raise the pressure to 300 psig (20.7 bar), or to 1/5 of design pressure (whichever is lower) and hold this pressure for 4 hours. At the end of the 4 hour time period repeat Step 4. 6. Repeat Step 5 two more times. 7. Samples of the boilout solution should be obtained periodically during the boilout period. If the boiler water alkalinity and phosphate concentration have dropped to 1/2 the original values, additional boilout chemicals should be added to restore the original concentrations. The samples should be analyzed for alkalinity, phosphate, and dissolved silica. The samples should also be checked for the presence of oil. Although quantative determinations are preferable, qualitative checks for the presence of oil will be highly satisfactory for monitoring and control purposes. 8. When analysis of the samples show that alkalinity, phosphate and dissolved silica have reached equilibrium levels and oil is no longer detected in samples, the heat source should be shut off. When the steam pressure drops to 25 psig (1.7 bar), the drum vents and superheater header drains should be opened wide. When the steam drum metal temperature falls below 200°F (93°C), the boiler should be drained. 9. Following the complete draining of the alkaline solution, the boiler should be filled to the top of the gauge glasses with clear rinse water heated to 170°F (77°C). While the HRSG is being filled for the boilout rinse, back fill the economizer through the inlet header and back fill the superheaters through the outlet headers with condensate or demineralized water (see Caution below) until water spills over into the respective steam drums. Leave the rinse water in the HRSG until it has sufficiently cooled to allow internal inspection. Drain the HRSG.
CAUTION: The use of fill water treated with solid chemicals should be avoided. Deposits of solid materials in superheaters can be detrimental from a heat transfer and corrosion standpoint. The quality of all fill water should be verified immediately prior to its entry into the superheater circuits. |
10. If the internal inspection of the HRSG indicates unsatisfactory cleaning, the boilout procedure should be repeated. 11. Upon completion of the HRSG boilout and after achieving a clean boiler, if immediate operation of the HRSG is not anticipated, the HRSG shall be laid up utilizing a wet post boilout lay up.
CAUTION: Use of most commercial detergents at concentrations in excess of 0.1% by volume during boilout may cause foaming and carryover of alkaline solution to the superheaters. Since commercial detergents vary in strength (i.e., water diluted) check with the manufacturer if recommended use strengths are higher than 0.1%. |
l Acid cleaning
Periodically during the operating life of any steam generator, chemical cleaning is recommended for the removal of iron oxide, copper, water formed and other deposits which may have accumulated on steam generating surfaces. The frequency of operational cleaning is dependent upon a number of operating conditions. However, three year cleaning appears to be a common and suitable period. This schedule should be altered for units which are subjected to intermittent operation or in cases of system upsets, such as condenser leakage, when feedwater contamination is greater than normal. In cases of tube failures caused by excessive deposits, chemical cleaning is one of the steps to be taken to return the unit to a sound operating condition. The attached curve, Figure 1, may be used as a guide in determining the need for chemical cleaning.
The acid cleaning procedure is based on the use of diluted (about 5% by weight), inhibited hydrochloric acid.
CAUTION: Acid cleaning should be performed only by experienced personnel. The HRSG circulation pumps must be removed prior to cleaning. |
Fill the HRSG with clear water and establish a level near normal in preparation for operation and adjusting metal temperature. Because of considerable heat capacity of the boiler metal and the anticipated heat losses, metal temperature should be adjusted to about 170°F (77°C) prior to introducing the acid to the boiler. Because of the non-uniform rate of cooling between the thin-walled tubes and thick-walled drums and headers, it is necessary to approach metal temperatures from below. This is done by admiting gas turbine exhaust at a very conservative rate. Once the desired metal temperatures [170°F (77°C)] are reached, the HRSG should be drained. All furnace openings must be closed to retain the heat.
Before admitting acid to the HRSG, check to be sure that:
1. The superheaters and economizers are full of condensate or demineralized water. Samples should be obtained from the superheater drains and vents to verify the absence of boilout chemicals. 2. The inspection doors are closed. 3. All drum vent valves are open. Unless specifically mentioned, valves should be positioned as for boiling out. 4. All boiler blowdown and chemical valves are closed. 5. Observe and record metal temperatures. No metal temperature is to exceed 180°F (82°C).
With the metal temperature about 170°F (77°C), fill the HRSG with inhibited acid solution (5–6% hydrochloric acid). It is recommended that 0.25% by weight of ammonia biflouride (NH4HF) be added to the inhibited HCl solution for its intensification and silica removal properties. The temperature of the solvent is maintained between 160 to 170°F (71 to 77°C) by blending the dilution water with steam.
In order to avoid the possibility of acid solution contacting hot steam piping, the steam required for temperature control should be introduced into the dilution water prior to the introduction of acid. There should be a space of at least 10 pipe diameters between these two admission points. Because the initial acid entering the boiler is consumed to some degree during the fill, and is in the HRSG for the longest period of time, it is good practice to blend a slightly higher concentration during the beginning of the fill than at the end. The HRSG should be filled until the level is indicated to have reached the center of the gauge glass. Observe caution, do not allow the level to go out of sight (high in glass). When the solution level has been established, the time should be recorded, a sample of the acid solution should be collected and analyzed for acid strength and iron concentration. Test of samples should be repeated every 30 minutes and tested for acid strength and total iron concentration. The cleaning is continued until the acid solution and total iron concentration approach equilibrium. Normally, this will be accomplished in less than 6 hours.
At the conclusion of the acid soak period, drain the HRSG under a positive pressure of nitrogen 3 to 5 psig (0.2 to 0.35 bar). The HRSG should be drained in as short a time as possible, using the maximum number of drain valves consistent with maintaining a positive nitrogen pressure. Nitrogen should be introduced into the HRSG through the drum vent lines. The pressure regulator should be of adequate size to introduce nitrogen at a volumetric rate capable of displacing all of the acid solution in the HRSG within a period of one hour.
Refill the HRSG with clear water at an approximate temperature of 150°F (66°C) to a slightly higher level than that of the drained acid. Simultaneously feed condensate or demineralized water into the economizers and back flush the superheaters with condensate or demineralized water to discharge any acid which may have inadvertently entered the economizers or the superheaters. The HRSG should then be drained under nitrogen as before. Refill with clear water at approximately 150°F (66°C) for a second rinse. About 0.1% by weight of citric acid should be added to the second rinse under a positive nitrogen pressure to assure more thorough iron removal. Drain the second rinse under a positive nitrogen pressure.
Fill the HRSG to the normal start-up level with a neutralizing solution consisting of 1% by weight of soda ash. Apply heat to the HRSG at a low rate, raising the pressure to 100 psi (6.9 bar) in 2 hours and hold this pressure for about 2 hours. At the end of the 2-hour rinse period, the HRSG should be allowed to cool gradually. During this period, blowdown the HRSG intermittently to reduce turbidity. Re-establish the solution level after each blowdown. The drum vents should be opened when the pressure drops to 25 psi (1.7 bar). When the steam drum and header temperatures fall to 200°F (93°C), the HRSG should be drained.
When the HRSG has cooled sufficiently to allow entrance, open the HRSG for inspection and completion of internal work.
l Notes and Precautions
F | NOTE: Acid cleaning should be performed only by experienced personnel. |
1. Draining of the neutralizing solution need not be under an atmosphere of nitrogen. Nitrogen is a non-toxic gas but will not support respiration. If nitrogen is used during draining of the HRSG, after which access by personnel is required, adequate ventilation must be provided before entrance is permitted. 2. If possible, the acid cleaning should be scheduled so that start-up of the HRSG will proceed immediately following the completion of the cleaning. If there is a delay of more than one or two days, the HRSG and the superheaters should be filled with condensate containing about 200 ppm of hydrazine and the pH adjusted to 10.0 with ammonia. The unit should be pressurized 3 to 5 psig (0.2 to 0.35 bar) with nitrogen. 3. The effectiveness of the inhibitor contained in the acid must be verified before admitting any acid into the HRSG. A simple test would involve submerging an untarnished carbon steel specimen in a sample of the acid which has been adjusted to the proper concentration and heated to 170°F (77°C). If one or more streams of bubbles appear, rather than an occasional isolated bubble, the acid should not be used until additional inhibitor is provided and the acid is proven safe by a repeat test.
A more elaborate test can be made if facilities are available. The loss of weight of a machined sample of boiler steel with a known surface area may be measured for a 30-minute immersion in the inhibited acid, diluted to the strength and maintained at the temperature that is to be used in the acid cleaning. The loss of weight should be no more than a milligram per square centimeter of surface.
4. The only hazard in cleaning a boiler with a properly inhibited acid solution is the possible existence of locally high metal temperatures. Most inhibitors for hydrochloric acid are not effective above 190°F (88°C), and accelerated corrosion will occur if higher metal temperatures are encountered. Since a temperature of at least 150°F (66°C) is recommended for effective cleaning, special care must be taken to establish the proper metal and solvent temperatures. 5. The gas turbine exhaust is capable of delivering significant quantities of heat to local areas of the HRSG. Even with adequate circulation, this may result in locally high, internal tube metal temperatures. For this reason, an HRSG containing hydrochloric acid must never be subjected to gas turbine exhaust or fired. 6. Before any back flushing of superheaters is performed, the water to be used should be chemically analyzed (conductivity, pH) in order to guard against contamination. 7. At the completion of the cleaning operation and prior to any operation of the HRSG, the water in the superheaters, and steam lines should be sampled at all available drains and checked for contamination. 8. In the event alkaline solution or acid should be inadvertently spilled into the superheaters during chemical cleaning, thorough back flushing at adequate flow rates must be done before any HRSG operation is permitted to ensure removal of all traces of acid. 9. As in the handling of any hazardous liquid, extreme care should be exercised to prevent injury to personnel during the acid cleaning.
l Preparations for Putting the HRSG into Service Following Chemical Cleaning
1. Inspect the steam drums. a. Blow out internal gauge glass connections and instrument leads. Remove temporary gauge glasses and install permanent gauge glasses. b. Blow out chemical feed and continuous blowdown piping. c. Flush out any loose sediment from steam drum surfaces and steam separators. Flush with clear water from the drums, draining through the blowdown connections at the bottom of the HRSG. 2. When all internal surfaces are clean, reinstall steam drum internals. Inspect and steam clean drum internals if required prior to installation. 3. Remove temporary piping and/or valves utilized for the boilout process. 4. When all work is completed, a thorough inspection should be made to ensure that no foreign material has been left in the drums. 5. Fill the boiler, economizer, and superheaters. Apply a hydrostatic test at normal operating pressure. Refer to Hydrostatic Testing Procedures provided elsewhere in this manual. If the unit is not to be placed into operation, refer to recommended Lay-Up Procedures. If the HRSG is to be placed into operation continue with Step 6. 6. Reduce the water level in the steam drums to the suggested operating level. 7. Drain the superheaters. The HRSG is now ready for operation. Refer to the HRSG operating procedures elsewhere in this manual.
l Cleaning procedures
All operations performed on the boiler during cleaning should be as outlined in “Recommended Pre-Operational Chemical Cleaning procedures” with the exception that a boilout is rarely used or necessary in a normal operational cleaning. Five percent inhibited hydrochloric acid is recommended for operational cleaning (as for preoperational cleaning).
The basic difference between preoperational and operational cleaning is the additives which are included in the operational cleaning solution to facilitate the removal of specific materials, such as copper and silica, which may be present in the deposit. The choice of additives should be based on the materials contained in deposits, and these should be determined prior to cleaning. If unusual or difficult to remove deposits are encountered, it may be necessary to use multi-step cleaning with special solvents to completely remove scale. It is recommended that one of the reliable chemical cleaning contractors be contacted for operational cleaning. These companies have the experience and technical know-how to properly formulate a cleaning mixture to remove undesired materials.
l NOTES AND PRECAUTIONS
1. All details and precautions outlined for pre-operational cleaning must be strictly followed for operational cleaning. 2. Steam purifying devices and orifices (if so equipped) should not be removed prior to operational cleaning.
3.10 Lay up procedure
1. Procedure Prior to Initial Operation
a. Pre-operation Period
When the boiler is ready for the hydrostatic test, proceed as follows :
(1) File the superheater with condensate or demineralized water containing 10 ppm (10 ㎤/㎥) of ammonia and 200 ppm (200 ㎤/㎥) of hydrazine. The pH value of the solution should be approximately 10.0. The condensate is added at the superheater outlet to overflow into the boiler drum.
(2) When the condensate overflows from the superheaer into the boiler drum, the addition of condensate at the superheater can be stopped. Fill the boiler through the normal filling connection with hydrazine treated water. Close boiler drains and open boiler vents as during normal filling procedures.
(3) At the conclusion of hydrosratic test, with the boiler filled to overflowing, pressurize the unit to 3-5 psi (21-35 kPa) gage with nitrogen.
Where freezing is a problem, the water in the drainage circuits can be displaced with nitrogen and then the unit is laid up under nitrogen pressure.
b. Post Boil Out Period
If the operation of the boiler is delayed after boiling out or acid cleaning, it should be filled as follows :
introduce condensate containing about 10 ppm (10 ㎤/㎥) of ammonia and 200 ppm (200 ㎤/㎥) of hydrazine to the boiler (and superheater) and pressurize the unit with nitrogen.
2. Methods of Storage
The suggested methods of storage are given as a guide to both the Owner and the Water Treatment Consultant. All protection, both during operation and storage, is the responsibility of the Owner. Internal protection is required if the boiler is out of service for more than 60 hours. Any of the following methods may be used. Steam pressure (minimum of 25 psig) should be maintained in the periods out of service of 60 hours or less.
a. Nitrogen Method Lay-up
This is the simplest method which can be used to protect the internal metal parts of the boiler from corrosion. The nitrogen pressuring system consists of nitrogen bottles under high pressure, a nitrogen pressure reducing and regulating valve and piping to connect the nitrogen bottles to the motor operated valve mounted on the steam drum.
Nitrogen should be introduced into the boiler as soon as it has been removed from service. The boiler must be tightly secured to prevent excessive loss of nitrogen during the storage period.
Open the vent valves and the drain valves mounted on the superheater outlet header and open the nitrogen system shut-off valve. The flow of nitrogen will displace the air in the steam drum above the water level and in the superheater.
After the steam drum and superheater are charged with nitrogen (the superheater is filled with nitrogen when a sizzling sound is heard due to nitrogen escaping from the superheater vents and drain.), close the superheater vent and drain valves and maintain a nitrogen pressure of approximately 5 lbs. (35 kPa) in the boiler.
In some systems it is possible to open the nitrogen supply pressure (5 psi, 35 kPa) in this manner, the boiler will back fill with nitrogen (completely avoiding oxygen contamination) as the unit cools and the remaining steam condenses.
The nitrogen system should be inspected occasionally to ensure proper operation.
The nitrogen system must be placed in operation and maintained properly if corrosion of the internal bare metal surfaces is to be avoided.
The portions of the boiler flooded with water may also require some form of protection. Sufficient alkalizer and oxygen scavenger should be added. As is discussed below under “Wet Method Lay-Up” mixtures of ammonia hydrazine may be used. Frequent checks of nitrogen pressure and tests of the water in the boiler should be made during the idle period to prevent corrosion.
b. Wet Method Lay-up
Boiler not opened for repair work. Where the boiler is removed from service for a period in excess of 60 hours and less then one (1) month.
(1) Fill the boiler with a condensate contain 10 ppm (10 ㎤/㎥) of ammonia and 200 ppm (200 ㎤/㎥) of hydrazine. Fill the superheater first, adding the condensate to the outlet of the non-drainable scetion until overflowing into the boiler.
Then proceed with filling the entire boiler. The treated condensate can be displaced with nitrogen or the entire of the unit can be laid up wet under nitrogen pressure depending upon the temperature of the surrounding area. Maintain a nitrogen pressure of 3-5 psi (21-35 kPa) gage. If the main steam line is not equipped with a stop valve, steps should be taken to blank off the line so the boiler can be pressurized.
(2) If freezing weather conditions arise during the outage means must be provided to keep the elements above freezing temperature.
NOTE
The use of hydrazine (N2H4) has been found acceptable as a reducing agent. Nitrogen purging is important in the complete elimination of oxygen. When the unit is to be put in service, it will be necessary to bring the water level to normal and open the drum (and superheater) vents before lighting off. To conserve nitrogen supply used in pressurizing the unit, shut off the supply before opening the vents.
c. Dry Method Lay-up
(1) Prior to Initial Operation
This method has advantages over the other two when the boiler is to kept out of use for an extended period of time and it will not be required for emergency service.
The one drawback to this system is that the interior of the boiler must be kept absolutely free of moisture. Unless and adequate degree of dryness is maintained, the boiler can suffer extensive damage. Heat may be applied below the boiler body to help dry out the boiler or portable dehumidifiers may also be used to dryout boiler internals prior to dry lay-up. This operation should be carried out under the direct supervision of a responsible engineer and the temperature should be increased slowly and uniformly.
Dry lay-up boiler prior to initial operation is feasible or non-drainable superheater is provided) are shipped in dry condition.
To lay-up the boiler prior to initial operation the following procedures should be followed :
(a) Inspect the unit and thoroughly dry up any visible water which may inadvertently have entered the unit during shipment.
(b) For each 1,000 lbs. Water capacity of the unit, add 0.65 lbs. Of desiccant grade silica gel. The silica gel is to be placed in equal portions to the ends of each boiler drum based upon the water capacity of the generating section. The desiccant should be placed in open deep side pans to avoid spillage.
(c) Tightly close the unit so that the admission of air is minimal. Tag all drum heads
(d) If the unit is held for more then two months, it should be opened to observe the desiccant. If the desiccant is wet, it can be dried by heating or it can be discarded and replaced.
(e) Remove the silica gel from the unit before start-up.
To protect the gas side of the unit, 4 lbs. Of desiccant must be applied for each 100 cubic feet of furnace volume, to be divided into four or more portions, depending on the boiler configuration. After the desiccant is applied, all boiler opening must be sealed.
(2) After Initial operation.
To lay-up (dry) the boiler after initial operation the following procedures should be followed :
After the boiler has been thoroughly cleaned, and dried internally, trays of moisture-absorbing material such as quick lime, silica gel or other suitable commercial desiccant should be placed in the steam drum and the unit tightly secured. Desiccants should be examined frequently for moisture absorption and replaced as required. This procedure should be faithfully followed until the boiler is to be placed in service. Nitrogen may also be used as an added corrosion from the steam generator prior to placing it in operation.
Gas side of boiler should also be protected as outlined in c.(1) above.
3.11 Operating procedure
l Introduction
These procedures are intended to serve as a guide during the initial operating stages of a Heat Recovery Steam Generator (HRSG). They include the proper operating sequences for the steam generator and auxiliary equipment furnished. Refer to the Piping and Instrumentation Diagram. The sequential procedures do not include detailed reference to equipment not furnished, such as the feed pumps.
Because the steam generator is only one part of the power plant, and all equipment must operate in unison, specific procedures and detailed values cannot be included in this manual. As operating experience is gained and the controls are fine-tuned, the characteristics and operating requirements of the unit will become apparent.
Refer to manufacturer's instructions for further operating details for specific equipment supplied by DOOSAN.
l Completion of maintenance prior to operation
Check the HRSG to make sure that all maintenance work has been completed, all tools and debris have been removed, the handhole plates and manhole covers have been installed and secured, and all access doors have been installed and secured.
Check the safety valves to see that the gags have been removed, the lifting levers have been replaced, and the valves are not fouled or hung up.
l Initial filling (When no HRSG is in operation)
This section describes the recommended procedure for fiIIing an empty HRSG with water. If the unit is hot, filling with cold water should be done slowly to avoid severe temperature strains. Deposits of solids in a superheater can cause corrosion or inhibit heat transfer. Introduction of solids by carryover of boiler water from the drum during filling, hydrostatic testing, or chemical cleaning must be avoided.
Proceed as follows:
1. Prepare feedwater pumps and plant feed piping for start-up. 2. Align all HRSG valves as shown under the column labeled “START FROM COLD” on Table 1 and 2. 3. Before the HRSG Feed Pumps are started, the following valves should also be opened to allow for filling of the boiler: ü HP Motor Operated Feedwater Filling Valve ü LP Motor Operated Feedwater Filling Valve 4. Start the LP Feed Pump and slightly open the LP Economizer Vent Valves. Fill the LP Economizer and the LP Evaporator sections until the Low Water Alarm has been cleared. DO NOT OVERFILL THE DRUM. Close the LP Economizer Vent Valves when all the air in the LP Economizer has been displaced. 5. Start the HP Feed Pump and slightly open the HP Economizer Vent Valves. Fill the HP Economizer and HP Evaporator sections until the Low Water Alarm has been cleared. DO NOT OVERFILL THE DRUM. Close the HP Economizer Vent Valves when all the air in the HP Economizer has been displaced.
The HRSG is now ready to be started using the procedure for "START-UP FROM A COLD CONDITION".
l Pre-operational equipment checks
Have all HRSG auxiliary equipment lined up for operation prior to allowing flow of the gas turbine exhaust to the HRSG.
Prior to initial operation:
1. All instrument valves should be lined up for service. 2. All sample line valves should be closed. 3. All chemical feed valves should be closed. 4. All drain valves should be closed. 5. Open and close the following valves to ensure that water level gauges are reading correctly: ü HP Water Level Gauge Drain / Column drain valves (1HAD10AA602 ~ 611) ü LP Water Level Gauge Drain / Column drain valves (1HAD50AA602 ~ 604)
l Start–up from a cold condition
This section describes the recommended procedure for starting the HRSG from a cold condition with no pressure in the HP and LP boiler sections.
1. To allow any condensate in the HP superheaters to drain, open and close the following motor operated valves sequentially for approx. 3 minutes, and the drain cycle to be repeated until HP drum pressure reaches approx. 13.8 barg. ü HP Superheater Drain Valve (1HAH11AA101) ü HP Superheater Outlet Drain Valve (1LBA10AA103) HP drum set-points 13.8 barg will be varied for a draining according to warm-up procedure for HP steam line from HP isolation valve to HP steam turbine inlet.
2. To allow any condensate in the LP superheaters to drain, open and close the following motor operated valves sequentially for approx. 3 minutes, and the drain cycle to be repeated until HP drum pressure reaches approx. 3.5 barg. ü LP Superheater Drain Valve (1HAH51AA101) ü LP Superheater Outlet Drain Valve (1LBA20AA103) LP drum set-points 3.5 barg will be varied for a draining according to warm-up procedure for LP steam line from LP isolation valve to LP steam turbine inlet.
3. Prior to start-up, reset the water level set-points in the feedwater control system to ensure that the water level in the HP and LP Drums is just above the low water alarm point. Use the Evaporator start-up blowdown valves as necessary to reduce the water levels. 4. The motor operated HP Steam Outlet Vent Valve and the motor operated LP Steam Outlet Vent Valve must be opened to vent air out of the system if the pressure in the HP and LP drum is below 13.8 / 3.4 barg respectively. 5. Ensure that the feedwater pumps are running and all feed system valves are lined up. 6. Open the motor operated LP Feedwater Isolation Valve and HP Feedwater Isolation Valve. 7. Open the motor operated LP Steam Outlet Stop Valve and HP Steam Outlet Stop Valve. 8. Allow gas turbine exhaust flow to the HRSG by starting the gas turbine. Reset the water level set–points in the feedwater control system for the HP and LP drums to the normal operating water level settings.
l Start–up from a warm condition
This section describes the recommended procedure for starting the HRSG from a warm condition.
1. To allow any condensate in the HP superheaters to drain, open and close the following motor operated valves sequentially for approx. 3 minutes, and the drain cycle to be repeated until HP drum pressure reaches approx. 13.8 barg. ü HP Superheater Drain Valve (1HAH11AA101) ü HP Superheater Outlet Drain Valve (1LBA10AA103)
2. To allow any condensate in the LP superheaters to drain, open and close the following motor operated valves sequentially for approx. 3 minutes, and the drain cycle to be repeated until HP drum pressure reaches approx. 3.5 barg. ü LP Superheater Drain Valve (1HAH51AA101) ü LP Superheater Outlet Drain Valve (1LBA20AA103)
3. Prior to start-up, reset the water level set-points in the feedwater control system to ensure that the water level in the HP and LP Drums is just above the low water alarm point. Use the Evaporator start-up blowdown valves as necessary to reduce the water levels. 4. The motor operated HP Steam Outlet Vent Valve and the motor operated LP Steam Outlet Vent Valve must be opened to vent air out of the system if the pressure in the HP and LP drum is below 13.8 / 3.4 barg respectively. 5. Ensure that the feedwater pumps are running and all feed system valves are lined up. 6. Open the motor operated LP Feedwater Isolation Valve and HP Feedwater Isolation Valve. 7. Open the motor operated LP Steam Outlet Stop Valve and HP Steam Outlet Stop Valve. 8. Allow gas turbine exhaust flow to the HRSG by starting the gas turbine. Reset the water level set–points in the feedwater control system for the HP and LP drums to the normal operating water level settings.
l Securing to a warm lay–up condition
This section describes the recommended procedure for securing the HRSG to a warm lay–up condition.
1. Prevent any gas turbine exhaust flow to the HRSG by shutting down the gas turbine or closing of the diverter damper. 2. In particular, ensure that the following valves are closed: ü HP Feedwater Isolation Valves. ü LP Feedwater Isolation Valves. ü HP Steam Outlet Stop Valve. ü LP Steam Outlet Stop Valve. ü HP Evaporator Continuous Blowdown Stop. ü LP Evaporator Continuous Blowdown Stop. 3. When the HP Drum pressure falls below 40 psig (2.76 bar), open the HP Nitrogen System Shutoff Valve to maintain a nitrogen blanket. 4. When the LP Drum pressure falls below 40 psig (2.76 bar), open the LP Nitrogen System Shutoff Valve to maintain a nitrogen blanket.
l Securing to drain (without nitrogen lay–up)
This section describes the recommended procedure for securing the HRSG without Nitrogen Lay-up in order to drain the unit prior to performing maintenance.
1. Prevent any gas turbine exhaust flow to the HRSG by shutting down the gas turbine or closing of the diverter damper. 2. When the drum pressure falls to 2 barg, open the motor operated HP Steam Outlet Vent Valve and the LP Steam Outlet Vent Valve. These valves must be opened before the drum pressures fall any lower to prevent a vacuum from developing that may cause leakage of the drum manway gaskets. 3. When the drum pressures have dropped to 1 barg, open the motor operated HP Steam Outlet Drain Valve. 4. The HRSG can be drained when it is completely cooled (when vapor no longer escapes from the vents). 5. Open the vent valves and drain valves for one pressure section at a time to avoid overloading the drain discharge system downstream of the HRSG.
l Controls and instrumentation
Controls
It is beyond the scope of this manual to discuss the design parameters and selection criteria of control systems. Instead we will review the steam generator dynamics involved in tuning these systems and note problems we have found on actual operating units. When we discuss steam generator control, we are actually referring to the drum level controls, all other controls are supplied by others.
The drum level controls will regulate the rate of feedwater flow to maintain a proper drum level throughout the operating range of the steam generator.
To get maximum benefit from a three - element system, feedwater flow should be proportional to steam flow with reset action on drum level. This means that pounds of feedwater entering should always equal pounds of steam leaving, with periodic small corrections made to correct deviations from level set points. The best drum level control is achieved through mass flow balance.
Instrumentation
Even the most sophisticated and well tuned control systems do not take the place of the judgment of an alert, motivated and trained operator. The only means that an operator has to make his judgments is through adequate and calibrated instrumentation.
l Safety valves
Safety valves serve to protect pressure vessels from over pressure. On superheater outlets they serve the additional purpose of protecting the superheater from overheating in the event of a sudden interruption in steam consumption.
The total relieving capacity of the safety valves on a boiler cannot be less than the design steaming capacity. It is a Code requirement that one or more safety valves on the steam drum be set at or below the design pressure of the unit. The discharge capacity of any superheater safety valve or valves can be included in the total relieving capacity of the boiler, provided there is no way to isolate the superheater. Valves are to be designed to operate without chattering and to obtain full lift at no more than 3 percent above their set pressure. Valves are to close within 4 percent of set pressure, but no less than 2 percent of set pressure.
The popping point tolerance shall not exceed:
2 psig (.14 bar) for pressures up to 70 psig (4.83 barg). 3 psig (.21 bar) percent for pressures up to 300 psig (20.68 barg). 10 psig (.69 bar) for pressures up to 1000 psig (68.95 barg). 1 percent for pressures over 1000 psig (68.95 barg).
DOOSAN recommends that all safety valves be lifted to check popping pressure and blowdown prior to annual maintenance outages. During these outages, valves that leaked or had a tendency to simmer or chatter should be disassembled and repaired. During valve testing, it is important to maintain drum level at or below normal water level to prevent water damage to drum valve seats and to prevent high solids boiler water from being drawn into superheaters.
Anytime a valve is disassembled, its seat should be touched up with a lap and 1000 grit lapping compound. If the seat is in poor shape, use a carborundum disc first, then progressively finer grits.
The following are safety tips and helpful hints:
1. Never set safety valves by holding set pressure and lowering the popping pressure setting with a wrench. This is extremely hazardous. Valve setting changes should be made with the boiler pressure considerably lower than set point. After the wrench adjustment is made the lifting gear should be replaced and boiler pressure should be raised to the new popping point.
2. Ring locking pins can vibrate loose when a valve is relieving. The pins should always be wired to each other except when one pin is removed to make a ring adjustment.
3. Entrained water will cause excessive blowdown on drum valves. Set drum valves with the drum water level a few inches below normal water level, if possible.
4. A rule of thumb: Vent pipes should be 2 inches (50.8 mm) larger in diameter than the valve discharge pipe.
5. The discharge pipe should extend no more than 14 inches (356 mm) into the vent pipe from the bottom of the drip pan.
6. A safety valve seat can be damaged by debris and water which enters the valve body through the vent pipe. This debris is blown around when the valve lifts. The problem can be eliminated by covering the vent pipe with a plastic bag.
7. It is occasionally necessary to mount a vent pipe rigidly to the discharge elbow. This should be done only when there is no alternative. Care should be taken that the vent pipe is cut off square, not on the bias.
8. Do not exceed five pops on a valve. If more pops are required, allow valve to cool before proceeding.
9. Do not make adjustments on first pop. Always evaluate the necessary adjustment from two pops.
10. When popping a valve, always have the cap and drop lever assembly in place with a rope affixed. If the valve begins to chatter, it can be manually popped before the seating surfaces are damaged.
11. Observe the popping pressure on a suitable gage mounted in the proximity of the valve being tested. A second gage, preferably a dead weight gage, should be used to validate the calibration of the observed gage.
l Emergency procedures
High or Low Water Levels
Whenever the water level disappears from sight in the water gauges, due to either a high or low level condition, proceed as follows:
1. Secure the flow of gas turbine exhaust. 2. Close the motor operated LP Feedwater Isolation Valve and the motor operated HP Feedwater Isolation Valve. 3. Close the motor operated HP Steam Outlet Stop Valve and the motor operated LP Steam Outlet Stop Valve. 4. If there is any question as to whether the level condition is high or low, blow down the water gauges to determine if the gauge glass is full or empty. 5. As soon as the actual level condition has been determined, take the following appropriate corrective action immediately:
High Water Level
1. Blow the steam generator down until the water is approximately at the normal level. Use the motor operated LP Drum emergency blowdown Valve and the motor operated HP Drum emergency blowdown Valve. 2. Open the motor operated HP Steam Outlet Drain Valve until all condensate in the superheater header has been drained. 3. After correcting the cause of the high water level problem, restart the gas turbine exhaust flow to the steam generator and cut the boiler in on line in the usual manner. Low Water Level 1. Check all systems to determine the cause of the low water level. 2. Re–establish proper drum levels and restart the unit.
CAUTION: Do not attempt to add water until the steam generator has cooled down sufficiently to where the drum metal temperatures are within 60°C of the feedwater temperature, otherwise damage may result due to relatively cool water coming in contact with heated pressure parts. |
Tube Failure 1. Immediately secure the gas turbine exhaust flow. 2. Close the following valves: ü The motor operated HP Feedwater Isolation Valve. ü The motor operated LP Feedwater Isolation Valve. ü The motor operated HP Steam Outlet Stop Valve. ü The motor operated LP Steam Outlet Stop Valve. 3. Open the motor operated HP Steam Outlet Vent Valve after the drum pressure falls below 13.8 barg. No water should be fed to the steam generator. 4. Open the motor operated LP Steam Outlet Vent Valve after the drum pressure falls below 3.4 barg. No water should be fed to the steam generator. 5. After the pressure has decreased, allow the boiler to cool off slowly. Loss of Feedwater Supply
The loss of feedwater supply is a rare occurrence in a properly maintained steam plant. However, loss of the feedwater supply can happen and it is to be treated as an extreme emergency.
A steady persistent drop in the steam drum level indicates problems with the feed pump, feed pump recirculation control, steam generator feedwater valve control or a tube leak. By quickly comparing system pressures and flows with data taken at comparable loads during normal operation, operators should be able to identify the problem area.
If feedwater flow is increasing relative to steam flow and the drum water level is still falling, a tube leak can be assumed. Secure the gas turbine exhaust flow and proceed with tube failure emergency procedures.
If the problem is with the feed pump or controls, restrict steam generator steam flow to balance the ability of the crippled feedwater system to maintain drum level.
If it is not possible to stabilize drum levels by reducing load, secure the gas turbine exhaust flow and bottle up the steam generator, keeping all vents closed. When the feedwater system is repaired, restart the unit as detailed under the procedure titled "START-UP FROM A WARM CONDITION".
In any case, the first consideration must be the protection of the steam generator pressure parts from operation with low water.
As is true of any emergency situation with a steam plant, events do not always follow an orderly pattern. The procedures above may or may not fit the pattern for every circumstance. The intent is to emphasize what should be done in order to protect the steam generator and bring the plant back in operation as soon as possible.
TABLE 1. VALVE ALIGNMENT : HIGH PRESSURE SECTION
VALVE NO. | VALVE DESCRIPTION | START FROM COLD | START FROM WARM | NORMAL OPERATING | SECURE TO WARM | SECURE TO DRAIN |
By other | HP Feed control | Auto | Auto | Auto | Auto | Auto |
By other | HP FW Control Valve Isolation | Open | Open | Open | Open | Open |
By other | HP Feedwater Isolation | Open | Open | Open | Closed | Closed |
1HAC11AA603 | HP Economizer Vent | Closed | Closed | Closed | Closed | Closed |
1HAD10AA101 | HP Evap. Vent (MOV) | Closed | Closed | Closed | Closed | Closed |
1HAD20AA101 | HP Evap. Start-up Blowdown (MOV) | Open | Open | Closed | Closed | Closed |
1HAD20AA351 | HP Evap. Start-up Blowdown Control | Auto | Auto | Closed | Closed | Closed |
1HAD14AA351 | HP Cascade Blowdown Control | Closed | Closed | Closed | Closed | Closed |
1HAD13AA101 | HP Evap. Emergency Blowdown (MOV) | Closed | Closed | Closed | Closed | Closed |
1HAD20AA601 1HAD20AA602 | HP Evap. Intermitt. Blowdown | Closed | Closed | Closed | Closed | Closed |
1HAH11AA101 | HP SH Drain ( MOV) | Auto | Auto | Closed | Closed | Closed |
1LBA10AA103 | HP SH Steam Outlet Drain (MOV) | Auto | Auto | Closed | Closed | Closed |
1HAD10AA003 1HAD10AA004 | HP Nitrogen System Shutoff | Closed | Closed | Closed | Closed | Closed |
1LAB11AA351 | HP Spraywater Control | Auto | Auto | Auto | Auto | Auto |
By other | HP SH Steam Outlet Stop (MOV) | Auto | Auto | Open | Closed | Closed |
TABLE 2. VALVE ALIGNMENT : LOW PRESSURE SECTION
VALVE NO. | VALVE DESCRIPTION | START FROM COLD | START FROM WARM | NORMAL OPERATING | SECURE TO WARM | SECURE TO DRAIN |
By other | LP Feed control | Auto | Auto | Auto | Auto | Auto |
By other | LP FW Control Valve Isolation | Open | Open | Open | Open | Open |
By other | LP Feedwater Isolation | Open | Open | Open | Closed | Closed |
1HAC51AA603 | LP Economizer Vent | Closed | Closed | Closed | Closed | Closed |
1HAD50AA101 | LP Evap. Vent (MOV) | Closed | Closed | Closed | Closed | Closed |
1HAD60AA101 | LP Evap. Start-up Blowdown (MOV) | Open | Open | Closed | Closed | Closed |
1HAD60AA351 | LP Evap. Start-up Blowdown Control | Auto | Auto | Closed | Closed | Closed |
1HAD54AA351 | LP Continuous Blowdown Control | Closed | Closed | Closed | Closed | Closed |
1HAD53AA101 | LP Evap. Emergency Blowdown (MOV) | Closed | Closed | Closed | Closed | Closed |
1HAD60AA601 1HAD60AA602 | LP Evap. Intermitt. Blowdown | Closed | Closed | Closed | Closed | Closed |
1HAH51AA101 | LP SH Drain ( MOV) | Auto | Auto | Closed | Closed | Closed |
1LBA20AA103 | LP SH Steam Outlet Drain (MOV) | Auto | Auto | Closed | Closed | Closed |
1HAD50AA002 | LP Nitrogen System Shutoff | Closed | Closed | Closed | Closed | Closed |
By other | LP SH Steam Outlet Stop (MOV) | Auto | Auto | Open | Closed | Closed |
3.12 Recommended Steam Blowing Procedure
1. Introduction
It is necessary to clean the steam line (main steam pipe, superheater section, etc.) prior to admitting the steam to turbine.
For this purpose, the high velocity steam would be introduced to the pipes, tubes and exhausted to remove and blow off the mil-scale or another foreign materials in the tubes or pipes.
The energy of steam which is accumulated as pressure in the steam drum shall be changed to velocity by exhausting the steam to atmosphere through superheater, main steam pipe and silencer which shall be done, by open or close the temporary motor operated stop valve. This kinetic energy will act as cleaning force of the superheater, etc.
The cleaning force is defined as mass-velocity of steam. Blowing out should be planned on temporary piping of blowing steam pressure to get same mass-velocity or more as unit shall be operated at maximum continuous rate.
Blowing out should be carried out by following route and step.
(1) HP steam system (refer to Fig-1)
HP steam drum →SH →HP main steam pipe →HP steam stop valve
↓
Silencer ←Temporary stop valve←Temporary piping←HP steam turbine stop valve
(2) HP by-pass line (refer to Fig-2)
HP steam drum →SH →HP main steam pipe →HP steam stop valve
↓
Silencer ←Temporary stop valve←Temporary piping←HP by-pass valve stop valve
(3) LP steam system (refer to Fig-3)
LP steam drum → SH → LP steam pipe → LP steam stop valve
↓
Silencer ←Temporary stop valve←Temporary piping←LP steam turbine stop valve
(4) LP by-pass line (refer to Fig-4)
LP steam drum → SH → LP steam pipe → LP steam stop valve
↓
Silencer ←Temporary stop valve←Temporary piping←LP by-pass valve stop valve
2. Preparation
2.1 Temporary piping and instrument
① Temporary piping should be made according to the schematic diagram or drawing.
② Welding of temporary piping should be done as same grade as high pressure pipe welding by qualified welders.
③ The support of the temporary piping should have enough strength for the reaction of steam blowing of vibration. And it should also be free for thermal expansion.
④ Disassembling and reassembling of turbine stop valves and protective work for the valves shall be done under supervision of turbine manufacture.
⑤ HP/LP turbine by-pass valves are connected to temporary piping, and blinded to condenser side.
⑥ It is necessary to install drain line where drain is able to stay and all drain lines should be opened to atmosphere.
⑦ Pressure gauge, thermometer and target plate should be installed on the free end of the temporary pipe.
⑧ The temporary stop valve should be prepared to be operated its full stroke at one minute more or less.
2.2 Personal arrangement and communication
Personnel for following items shall be provided.
① Unit operator
② Temporary stop valve operator, temporary drain valve operator
③ Worker for target plate
④ Personnel for instrument reading
⑤ Safety guard
Note : Communication system which is used temporary telephone among the blow end, temporary stop valve operator and the control room.
2.3 HRSG interlock test should be completed prior to Gas-in.
3. HRSG water treatment during blowing out
HRSG water quality should be controlled by volatile treatment, considering carry-over from steam drum.
If silica in the drum water is very high, blow down shoul be made on each interval the blowing out.
PH (at 25℃) | Conductivity (㎲/cm) | N2H4 (mg/l) | Turbidity | Cl (mg/l) | |
Feed Water | ≥9.0 (Target) | - | 30 ~ 50 | - | - |
Drum Water | ≥9.0 | - | - | ≤5 | - |
Make-Up water | - | ≤1 | - | - | ≤0.1 |
4. Blowing out procedure
4.1 Principal of steam blowing
A. The corresponding gas turbine is operated under minimum load or no load.
B. The LP steam pressure during HP steam line blowing is regulated by their drain valves.
When the drain valves cannot control the steam pressure, try to control by the divert damper.
C. Typical blowing out conditions
① HP steam system
Drum pressure : 25 ~ 35 barg
SH outlet steam temperature : 270 ~ 350 deg C
② LP steam system
Drum pressure : 4 ~ 6 barg
SH outlet steam temperature : 200 ~ 230 deg C
4.2 Pressurizing
A. Confirm the start-up preparation of the HRSG.
B. Confirm that the steam turbine is in the condition recommended by the steam turbine side.
C. Confirm that the temporary stop valve is in fully closed position.
D. Confirm the drain valves on the temporary pipings.
These drain valves should be opened during the line warming & pressuring, and be closed or nearly closed during the steam blowing.
E. Start up gas turbine (GT) and synchronize. Load shall be minimum.
F. Open the diverter damper to rise temperature and pressure.
In order to check the expansion of each part, temperature rising rate should be as follows;
0 ~ 20 barg …………..55℃/Hr
20 ~ 30 barg …………..30℃/Hr
G. Operate the drain valves to control the HP drum pressure during the pressurizing. Then, LP line drain valves should be fully opened to keep the pressure less than (5 ) kg/cm2.
If HP/LP pressures are expected to over (30/5) barg under all drain valves open condition, decrease the diverter damper position.
H. Adjust the HP/LP drum level at N.W.L. –50 mm.
4.3 Warming
A. When the HP drum pressure is reached to (20) barg, maintain the HP drum pressure by operating the drain valves on the HP steam line. If necessary, fully close the diverter damper when the LP drum pressure is over (5) barg with the full open of drain valves on the LP steam line.
B. Open the temporary stop valve by-pass valve to warm the temporary pipings with the fully opened drain valves on them.
C. When temperature at blow end is come up over 90℃, the warming is completed.
D. Check the expansion of temporary piping with the supports and further fasten the bolts on the flanges.
4.4 Test blow
A. the test blows should be carried out before the steam blows to confirm the vibration, the thermal expansion and reaction force of the temporary piping to their supports.
B. The test blow conditions is as follows.
① Drum pressure : 20 ~ 25 barg (HP)
4 ~ 5 barg (LP)
② Opening of the temporary : Step 1: 30% of the full open
Stop valve Step 2: 60% of the full open
③ Holding time at the : 0 sec.
Specified opening
④ Number of the test blows : 2 ~ 3 times
4.5 HP line blowing out
The blowing out is made by opening the temporary stop valve completely, keeping this opening about 30s ~ 60s, and then closing this valve completely.
A. Drum water level should be controlled between NWL and NWL -100 mm before blowing out.
B. When drum pressure has reached the specified valve (30 kg/cm2), open the temporary stop valve.
C. After starting the blowing out, increase the feed water flow up to 25% MCR flow (X% + 20%MCR).
D. Keep the full opening of temporary stop value about 30 ~ 60 sec.
Keeping time shall be decided according to cleaning factor and operating conditions (HP drum press. Dropped to 10 ~ 15 kg/cm2).
E. After starting the blowing out, drum water level suddenly rise and scale over the level gauge.
But at this time, keep the feed water flow, and pay attention to occurring of carry over.
And when the drum water level once come in sight of level gauge as closing the temporary stop valve and begin to rise again, decrease the feed water flow rapidly to prevent over rising of drum water level.
F. After the temporary stop valve is closed and drum water level is stable, raise again the drum pressure at the specified value.
G. Above procedure should be done several times until the surface of target plate is free from foreign material.
4.6 HP turbine by-pass line steam blows
Blowing out procedure is same as HP line.
4.7 LP line blowing out
A. Control the LP drum pressure at the blowing pressure of 5 barg.
B. Open the temporary stop valve to blow LP line with the same operation procedure as the HP line blows. (LP drum pressure dropped to 2~3 barg)
4.8 LP turbine by-pass line steam blows
Blowing out procedure is same as LP line.
5. Measuring items
Measuring items are as follows.
A. Pressure
HP/LP drum
SH outlet
Blow end
B. Temperature
SH outlet
Blow end
C. Drum level
D. Feed water flow
E. Temporary stop valve opening time
6. Note
If necessary, the following interlock shall be released during the blowing out,
A. A. Drum level abnormal low → HRSG trip
B. B. Drum level abnormal high → HRSG trip
7. Completion judgment of steam blowing-out
7.1 Target plate
A. Soft material like brass are recommendable to apply as a target plate and it will be fitted into the temporary blowing pipe close to the existing pipe. And the indication of the target plate (soft material) which will be given by foreign particles are inspected for judging a cleanness of the pipe.
B. The size of the test pieces is as follows.
⊙ Thickness : 3 ~ 5 mm
⊙ Width : approx. 30 mm
⊙ Length : approx. 85 % length of pipe normal diameter
7.2 Judgment
A. More than 10 (ten) times blowing-out have to be applied including test blowing as a practice.
B. The steam blowing-out can be terminated in case of that the following conditions are satisfied.
a) The indication of the target plate is less than 0.5 Φmm as a diameter.
b) The number of indications is less 1 (one) against 24.5 mm x 24.5 mm area of the target plate.
c) The indication on the target plate is not raised pit.
d) The above condition a), b) & c) is to continue 3 times at least.
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3.13 Inspection and Maintenance Procedure
l HRSG External Inspection
After the HRSG has been shut down and sufficiently cooled, the HRSG external components must be inspected.
The tubes shall be cleaned carefully and checked for corrosion, deformation, bulging, burning and cracking.
The HRSG proper walls, especially the casing and doors, must be inspected for potential leak of flue gas.
l HRSG Internal Inspection
HRSG interior shall be examined during every periodical inspection.
The following items represent a specific check list :
¨ Drum inspection
ü Take off the manhole cover and check whether steam drum internals are securely fixed. Also verify possible contamination.
ü Confirm that the steam stop, feed water, blow down and chemical injection valves are completely and firmly closed and locked in "Closed" position.
ü Provide all the isolation valves with appropriate holding tags, so that other persons will not inadvertently open them.
ü Seals around manway doors
ü Inside around manway doors
ü Upon entering into the HRSG drum, check for corrosion and pitting, if the HRSG water properties during the HRSG wet layup are appropriate, pitting will rarely occur inside the steam drum.
ü The main cause is the presence of dissolved oxygen in feed water, so Pitting can be completely prevented if the feed water and HRSG water control is performed correctly.
ü When mounting the internals, pay attention to the following :
(1) Fully understand beforehand the assembling procedure and the internals configuration.
(2) Because the internals are composed of a large number of parts, it is recommended to sort them into two separate groups :
Those to be mounted above water level and those to be mounted below water level.
This recommendation will help avoiding re-installation mistakes.
(1) During the time of re-assembly, fully inspect all parts to check whether there is any future possibility of steam water mixture, dry steam and feed water, etc., leaking from joints and being mixed with each other.
(2) In particular, the portion near the dry steam outlet should be completely tight.
(3) When new packings have been inserted in bolted joints, the bolts should be finally retightened after a preliminary tightening.
(4) The joints that do not use any packing should be well fitted prior to the bolts tightening.
ü The internals must be fully inspected also during their reassembly.
ü After reassembly completion, it is impossible to check the correct reassembly of all components.
ü An incomplete tightness of the internals will cause damage to the superheater tubes, due to carry-over. Even only one missing bolt or incomplete or damaged packing can allow above carry-over to occur. Therefore, careful attention shall be provided when reassembling the drum internals.
¨ Superheater Inspection
ü The inspection and maintenance of the superheater shall comply with the following requirements :
1. When inspecting the drum, be sure to inspect the superheater also.
2. Check the superheater for alignment, deformation and bulging.
3. Inspect the condition of superheater supports and repair the defective parts, if any, immediately.
4. Check the superheater, header and steam drum interior for carried over solids and, if present, clean them immediately. Also, determine and eliminate the source.
ü The superheater must be correctly operated, inspected and subjected to proper maintenance.
ü Superheater cleaning
1. External cleaning
When operated for a long period of time, keep the exterior of the superheater as clean as possible.
If the superheater is contaminated, the flue gas will not have an uniform flow. Therefore, the heat transfer drops causing local overheating against which precautions should be taken.
2. Internal cleaning
To keep the interior of the superheater clean, the feed water and the related water treatment must be performed correctly.
Also, the steam humidity and the solid content of the steam entering the superheater shall be kept within the specified limits.
The following are causes of adhesion of scales to the superheater inside wall :
a) Operation in over load conditions / parameters or sudden load fluctuation, high water level, priming or increase of HRSG water concentration values, etc.
b) Adhesion of scale generates a reduction of superheater heat rate and a steam pressure drop. Therefore, the superheater could be damaged, unless the scales are removed.
c) The HRSG manufacturer shall be consulted prior the scales removal. When the superheater steam pressure drop is measured periodically, the adhension of scales can be judged. However, the pressure measurements have to be made under the same load.
Notes :
1. A periodic measurement of superheater steam pressure drop will allow a scales deposit evaluation
2. The pressure measurements shall be performed under the same HRSG load conditions, for evaluation consistency.
¨ Economizer Inspection
Before the HRSG startup, the economizer must be externally inspected and cleaned, as required.
¨ Miscellaneous Inspections
1. Inspect and clean the flue gas side of HRSG heating surfaces.
2. The following inspections, but not limited to, must be performed annually :
a) Complete inspection of HRSG interior
b) Remove(eliminate) the scale deposits, if required
c) Verify the superheater and economizer performances
d) Tubes detailed inspection, especially after tube failures and/or expected tube failures.
e) Metallurgical examination and analysis of tube sections. (see Note 1)
f) Tube sections chemical analysis of deposits. (see Note 1)
Notes :
1. Inspection items must be performed when tube failures have occurred, or are expected to occur, and no reasons have been clearly identified.
2. Scales inspection shall be performed by qualified persons for this area of expertise.
3. Separate records shall be kept for each inspection in accordance with Owner approved procedure.
4. The records shall be kept and compared with the actual conditions, at different operation intervals.
¨ Table Of Maintenance Inspections
(Periodic Maintenance Inspections)
Interval/ Frequency | Item | Standard inspection items | Standard measures |
Interval/ Frequency | Item | Standard inspection items | Standard measures |
Interval/ Frequency | Item | Standard inspection items | Standard measures |
Interval/ Frequency | Item | Standard inspection items | Standard measures |
3.15 Input Data for DCS
HP steam isolation valves: (Not in HRSG Scope)
Close at HHA level in the drum.
Close at LLA level in the drum.
HP Drum level
(Drum level will be corrected by the drum pressure).
Normal Level: (Drum centerline)
The drum level controls will regulate the rate of feed water flow to maintain a proper drum level throughout operation range of the steam generator.
To get the maximum benefit from a three-element system, feedwater flow should be proportional to steam flow with reset action on drum level. This means that the mass of feed water entering should always equal the mass of steam leaving, with continuous corrections made for deviations from level set points. The best drum level control is achieved through the mass flow balance.
HHHA Level (205 mm above DRUM centerline).
If HP steam header valve is not closed, ST should trip.
GT Protective load shedding and closing of diverter valve.
Feedwater stop /control valve remain closed.
HHA Level: (180 mm above DRUM centerline)
Sound the alarm.
Close the feedwater stop valve.
Close the feedwater control valve.
Close the steam isolation valve.
Open the emergency blowdown valve.
HA level: (130 mm above DRUM centerline)
Sound the alarm.
Open the start-up blowdown valve.
LA level: (545 mm below DRUM centerline)
Sound the alarm.
Check closing of cascade blowdown Valve.
Close the start-up blowdown valve.
Close the emergency blowdown valve.
LLA Level: (645 mm below DRUM centerline)
GT protective load shedding.
GT trip (after 2 min. of total elapsed time).
Close the HP steam isolation valve.
Note
GT trip if diverter damper(MBR80AA101) is still full open at LLA level or HHHA level after 10 seconds.
GT trip if diverter damper(MBR80AA101) not full closed after 2 minutes.
If HP steam stop Valve is not closed, ST should trip. .
Caution
Do not attempt to add water until the steam generator has cooled down sufficiently to where the drum metal temperature are within 60 oC of the feedwater temperature, otherwise damage may result due to relatively cool water coming in contact with heated pressure parts.
HP Drum Cascade Blowdown valve: (1HAD14AA351)
Open if the steam quality > Controlled conductivity.
Close if the drum level < LA Level.
Close if HRSG is shut down.
HP Start-up Blowdown valve: (1HAD20AA101)
Open if the drum level > HA Level.
Close if the drum level < LA Level.
Feedwater control valve setpoint during normal operating : NWL
Open if the drum level > NWL during startup.
Close if the drum level <-150 mm during startup.
Feedwater control valve setpoint during startup : -200 mm
Close if HRSG is shutdown.
HP Emergency Blowdown Valve: (1HAD13AA101)
Open if the drum level > HHA Level.
Close if the drum level < LA Level.
Close if HRSG is shutdown.
HP Feedwater Stop Valve: (Not in HRSG Scope)
Open during start-up.
Close at HHA level in the drum.
HP Feedwater Control Valve : (Not in HRSG Scope)
Open during start-up.
Close at HHA level in the drum.
HP Overpressure:
1. If HP steam pressure (1LBA10CP001) ≥ 79.2 bara, GT protective load shedding.
2. GT trip if HP steam pressure (1LBA10CP001) > 83.0 bara.
3. Automatically mechanical open HP super heater safety valve (1LBA11AA401) if steam
pressure > 79.2 bara.
4. Automatically mechanical open HP drum 1 safety valve (1HAD12AA401) if steam pressure
≥ 83.0 bara.
5. Automatically mechanical open HP drum 2 safety valve (1HAD11AA401) if steam pressure
≥ 85.5 bara.
6. Close by-pass damper to 70% gas flow, if HP superheater steam pressure exceeds SH safety valve setting pressure (79.2 bara)
Notes : Condition number 4 should only occur after condition number 3 has occurred.
HP Final stage steam temperature control: (1LAB11AA351)
Open if steam temperature (1LBA10CT001) is > set temperature = 511.4 deg C
Close if steam temperature (1LBA10CT001) is < set temperature = 511.4 deg C
HP Overtemperature:
1. If 2 of 2 HP steam temperature (1LBA10CT002, 1LBA10CT003) ≥ 528 deg C,
Close diverter damper
2. GT trip if the diverter damper fails to close and 528 deg C of HP steam temperature will be maintained total delay time180 seconds.
Comment; These two values should be confirmed by FORTUM to match the allowable steam temperature in steam turbine.
HP Start-up vent valve: (Not in HRSG Scope)
Open to 10% open position if HP drum pressure < 13.8 barg during start-up
**% open position of this valve will be adjusted during start-up
Close if HP drum pressure > 13.8 barg
HP Drum vent valve: (1HAD10AA101)
Open to vent air during start-up
Close if HP drum pressure > 3.5 barg
HP Economizer vent valve: (1HAC11∼21AA602, 1HAC11AA603, 1HAC30AA601)
Open during initial filling water
Close during operation
HP Super heater drain valve: (1HAH11AA101)
Open if HP drum pressure < 13.8 barg during start-up
Close if HP drum pressure > 13.8 barg
HP Super heater pipe line drain valve: (1LBA10AA103)
Open if HP drum pressure < 13.8 barg during start-up
Close if HP drum pressure > 13.8 barg
* During start-up, 1HAH11AA101 will be opened and remained for 3 minutes. After 3 minutes open, 1HAH11AA101 will be closed and LBA10AA103 will be opened for 3 minutes, then closed. The drain cycle will be repeated until HP drum pressure reaches 13.8 barg (END OF STARTUP). When HP drum pressure reaches above 13.8 barg, the drain cycle will be deactivated, and the control of these drain valves will be up to the operator’s decision.
* The valve opening of 1HAH11AA101, LBA10AA103 can be adjusted by the DCS programmed logic or by the operator according the HP drum pressure using the remote position feedback signal.
* HP drum set pressure (13.8 barg) of draining during start-up will be adjusted according to warm-up procedure.
LP steam isolation valve: (Not in HRSG Scope)
Close at HHA level in the drum.
Close at LLA level in the drum.
LP Drum Level:
(Drum level will be corrected by the drum pressure).
Normal Level: (Drum centerline)
The drum level controls will regulate the rate of feed water flow to maintain a proper drum level throughout the operation range of the steam generator.
To get the maximum benefit from a three-element system, feed water flow should be proportional to steam flow with reset action on drum level. This means that the mass of feed water entering should always equal the mass of steam and water leaving, with continuous corrections made for deviations from level set points. The best drum level control is achieved through the mass flow balance.
HHHA Level (205 mm above DRUM centerline).
If LP steam header valve is not closed, ST should trip.
GT Protective load shedding and closing of diverter valve.
Feedwater stop /control valve remain closed.
HHA Level: (180 mm above DRUM centerline)
Sound the alarm.
Close the feedwater stop valve.
Close the feedwater control valve.
Close the steam isolation valve.
Open the emergency blowdown valve.
HA level: (130 mm above DRUM centerline)
Sound the alarm.
Open the start-up blowdown valve.
LA level: (200 mm below DRUM centerline)
Sound the alarm.
Close continuous blowdown Valve.
Close the start-up blowdown valve.
Close the emergency blowdown valve.
LLA Level: (300 mm below DRUM centerline)
GT protective load shedding.
GT trip (after 2 min. of total elapsed time).
Close the LP steam isolation valve.
Note
GT trip if diverter damper(MBR80AA101) is still full open at LLA level or HHHA level after 10 seconds.
GT trip if diverter damper(MBR80AA101) not full closed after 2 minutes.
If LP steam stop Valve is not closed, ST should trip. .
Caution
Do not attempt to add water until the steam generator has cooled down sufficiently to where the drum metal temperature are within 60 oC of the feedwater temperature, otherwise damage may result due to relatively cool water coming in contact with heated pressure parts.
LP Drum continuous blowdown: (1HAD54AA351)
Open if the steam quality > Controlled conductivity.
Close if the drum level < LA Level.
Close if HRSG is shutdown.
LP Start-up blowdown valve: (1HAD60AA101)
Open if the drum level > HA Level.
Close if the drum level < LA Level.
Feedwater control valve setpoint during normal operating : NWL
Open if the drum level > NWL during startup.
Close if the drum level <-150 mm during startup.
Feedwater control valve setpoint during startup : -200 mm
Close if HRSG is shutdown.
LP Emergency blowdown valve: (1HAD53AA101)
Open if the drum level > HHA Level and heat supply to HRSG.
Close if the drum level < LA Level.
Close if HRSG is shutdown.
LP Feedwater main stop valve: (Not in HRSG Scope)
Open during start-up.
Close at HHA level in the drum.
LP main feedwater control valve: (Not in HRSG Scope)
Open during start-up.
Close at HHA level in the drum.
LP Overpressure:
1. If LP steam pressure (1LBA20CP001) ≥ 14.5 bara, GT protective load shedding.
2. GT trip if LP steam pressure (1LBA20CP001) > 17.0 bara.
3. Automatically mechanical open LP super heater safety valve (1LBA21AA401) if steam pressure
> 14.5 bara.
4. Automatically mechanical open LP drum 1 safety valve (1HAD51AA401) if steam pressure
> 17.0 bara.
5. Automatically mechanical open LP drum 2 safety valve (1HAD52AA401) if steam pressure
> 17.5 bara.
6. Close by-pass damper to 70% gas flow, if LP superheater steam pressure exceeds SH safety valve setting pressure (14.5 bara)
Notes : Condition number 4 should only occur after condition number 3 has occurred.
LP startup vent valve: (Not in HRSG Scope)
Open to 10% open position if LP drum pressure < 3.4 barg during start-up.
**% open position of this valve will be adjusted during start-up
Close if LP drum pressure > 3.4 barg.
LP Drum vent valve: (1HAD50AA101)
Open to vent air during start-up
Close if LP drum pressure > 2.5 barg.
LP economizer vent valve: (1HAC51AA602, 1HAC60AA601, 1HAC51AA603)
Open during initial filling water.
Close during operation.
LP Superheater drain valve: (1HAH51AA101)
Open if LP drum pressure < 3.4 barg during start-up
Close if LP drum pressure > 3.4 barg
LP Superheater pipe line drain valve: (LBA20AA103)
Open if LP drum pressure < 3.4 barg during start-up
Close if LP drum pressure > 3.4 barg
* During start-up, 1HAH51AA101 will be opened and remained for 3 minutes. After 3 minutes open, 1HAH51AA101 will be closed and 1LBA20AA103 will be opened for 3 minutes, then closed. The drain cycle will be repeated until HP drum pressure reaches 3.5 barg (END OF STARTUP). When HP drum pressure reaches above 3.5 barg, the drain cycle will be deactivated, and the control of these drain valves will be up to the operator’s decision.
* The valve opening of 1HAH51AA101, 1LBA20AA103 can be adjusted by the DCS programmed logic or by the operator according the HP drum pressure using the remote position feedback signal.
* HP drum set pressure (3.4 barg) of draining during start-up will be adjusted according to warm-up procedure.
EXHAUST GAS ADMITTION
Cold Start:
Admit 70% exhaust gas mass flow for minimum 30 minutes.
Admit 100% exhaust gas mass flow (after 45 minutes).
Warm Start: (minimum 4 bara pressure in HP drum)
Admit 70% exhaust gas mass flow for minimum 20 minutes.
Admit 100% exhaust gas mass flow (after 25 minutes).
Hot Start: (after no more than 4hr shutdown)
Admit 70% exhaust gas mass flow for minimum 15 minutes.
Admit 100% exhaust gas mass flow (after 20 minutes).
Boiler protection:
The water level is kept constant in two drums. During normal operation the signal for the feed water control valve is derived from the feed water flow minus boiler water extraction, the steam flow and the drum water level (three element control). Signal use for the equipment protection must be two out of three configuration (3 level transmitters).
HP Drum level below LLA level, GT protection load shedding.
Trip GT after 2 minutes.
LP Drum level below LLA level, GT protective load shedding.
Trip GT after 2 minutes.
HP Overpressure, GT protective load shedding. Trip GT after 2 minutes.
If HRSG inlet gas temperature > 562 deg C, GT protection load shedding.
Trip GT after 3 minutes.
If HRSG inlet gas pressure > +/- 510 mmWG, GT protection load shedding.
Trip GT after 3 minutes.
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