REGULAR AND PREVENTIVE MAINTENANCE
The maintenance presented in this subsection is intended as a guide for regular and preventive
maintenance which is required for a stable operation of the unit.
Regular maintenance
Internal & External part
Check that there is no rusting or deterioration on any parts of the evaporator.
Clean and paint if necessary.
Flash chamber
Check the condition of the demister for scaling, clogging or dropping. Repair
or replace if necessary.
Check the internal surface of the flash chamber.
Tube and Tube bundles Check for defective tube and tube bundles. Plug or replace if necessary.
Check tube ends for scaling. Perform acid cleaning if necessary.
Joint
Check sealing of tube to tube sheet joints for leakage.
Conduct an airtight test.
Water boxes
Check the internals of the water boxes for corrosion, hard scale precipitation
or blocking by debris or foreign material.
Repair if necessary applying weld repair procedure
Regular maintenance
Manhole
Nozzles
Check the manhole and the sealing gaskets of manholes installed on the
distillate trough.
Remove the sludge of the evaporator internal and clean the nozzles of the
Orifice
instruments.
Check orifice setting condition.
Bottom plate Check internal surface of bottom plate.
Gaskets Check the gaskets for crack or tear.
Sacrificial anodes Check anodes in the water boxes.
Remove corrosion
SPECIAL MAINTENANCE
Replacement of faulty tubes
Replacement parts
Gasket, bolts, nuts, thermal insulation material, paint
and tools for external painting, new tubes.
a.
Preparation for disassembly
1) Remove any pipes connected to and above the
water box.
2) Remove any instruments and the wiring to such
instruments.
3) Drain the water from the water boxes and open the
manholes for inspection.
4) Close the valves on the suction side of the brine
recirculation pump, brine blow down pump,
6) Prepare to make vacuum condition inside of the
evaporator shell. Fill the evaporator brine and
distillate chamber with water by 400 500mm
distillate pump.
5) Close the valves on the lines of the above pumps.
Also close any others on the piping connected to
th t
~
water level.
7) Use the hogging ejector to make vacuum condition
inside of the evaporator
4
e evapora or. .
Disassemble of water box
1) Set wires, shackles and chain blocks to the water
box as shown in the figure. In this case, chain
blocks are useful to adjust a water box horizontally.
2) Remove the bolts and nuts to the water box
connection.
3) Remove the water box by using a mobile crane.
4) Put the water box on wooden supports as shown in
the figure
Reassemble of water box.
1) Perform the procedure of disassemble in reverse order.
2) After completion of the reassemble of the water box, all
dismantled thermal insulation and damaged external
painted surfaces must be repaired.
3) If required, apply hydro. Test to ensure that the water
box is satisfactorily sealed.
4) Tighten the bolts on the shell flange of the water box by
using a proper torque wrench as specified below.
The first bolt tightening circuit shall be performed until
60-70% f f ll i l t h b hi d of following normal torque has been achieved.
5) If leakage occurs from the flanges, gradually increase
tightening torque for the bolts around the leakage area,
up to the maximum torque indicated above.
Detection of Faulty tubes.
- Air Leakage Test.
1) Inside of the water box, check suspected tube bundles if
there is any sound of air leakage using sound detector.
If there is any faulty tube(s), it could be detected by air
l k d eakage sound.
2) Supply service air to the evaporator and raise the air
pressure up to 0.4 barg. Close the air inlet valve.
Tube Plugging of faulty tubes.
1) Normally, the faulty tubes can be plugged with teflon
plugs on both sides unless the plant performance is
appreciably affected.
2) However when it is necessary to replace the defective
tube with a new tube
Removal of tubes.
1) Cut off both ends of the faulty tube with a drill, at about
30mm from the tube end. A special drill with guide is
provided for this work. The drilling must be done very
carefully so as not to cut or scrape the tube hole surface.
2) Drive out the tube by a knock out punch.
3) When the tube sticks out at the opposite side, set a clamp
collar on it and draw out by hammering.
Insertion of New Tube.
1) Clean the tube sheet holes Foreign matter or scratches , Foreign matter or scratches
on the surface of the hole can cause leaking.
2) Use a reamer of appropriate size or fine emery paper to
smooth the hole surface radial.
3) Fix the tube guide on top of the new tube. Insert the tube
into the hole until it comes out from the opposite side.
Rotating the tube will help to give smooth insertion.
Replacement of the demister.
1) Set up the portable ladder inside demister.
2) Knock the J-bolts body with impact hammer to remove
the scale.
3) Unfasten J-bolts and nuts which are tightening the
d i i h emister with spanner.
(If the wire is applied, cut the wire.)
4) Detach the demisters from demister support.
5) Take out the detached demister through the manhole.
Cleaning of demister.
1) Clean scaled demisters with diluted sulphuric acid by
using the acid cleaning system.
2) After cleaning fl sh the demisters thoro ghl ith h dro , flush the demisters thoroughly with hydro
- jetting (water and caustic soda solution).
3) After flushing, dry the demisters with steam as necessary.
Reassemble of demister
1) Return the cleaned or new demister to its original position
after cleaning or replacement.
2) Securely tighten demister with J-bolt and nut or wire