This presentation gives simple understanding of Chemical Cleaning of Pressure Parts of the Boiler in a Thermal Power Plant.

1. CHEMICAL CLEANING OF
BOILER
KARTHICK POOBATHI,
KALYANAM SUDHEER KUMAR
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2. Purpose of Chemical Cleaning of Pressure
Parts:
To remove dirt, grease, oil, rust etc. which are present
in the pressure parts of boiler.
 Advantages of Chemical Cleaning of Boiler:
1) Quality of steam can be maintained at the turbine
inlet.
2) Corrosion of the metal surface of boiler can be
minimized.
3) Under deposit corrosion of metal can be avoided.
4) Heat transfer of the system can be improved.
5) Plant Outage due to boiler tube failures can be
minimized.

3. Chemical Cleaning Alkali Boil Out
Acid Cleaning
Precaution: During this process normally steam drum
internals are removed and a temporary gauge glass is
fitted .
Alkali Boil Out Process:
1) Tri Sodium Phosphate(TS 0.1%) , Di Sodium
Phosphate (DSP 0.05%), caustic soda and soda ash are
dozed to DM Water.

4. 2) Light up the boiler as per instructions and raise the
temperature of solution up to 130 to 140 deg C by setting
the LDO oil pressure.
3) Boiler level to be monitored and care to be taken to
open the Economizer R.V.
4) At 100 deg C Eco. outlet temp. steaming is started in
the boiler. At 110 deg C Eco. outlet temp. the boiler drum
pressure is 2Kg/sq.cm. Close all the vents.
5) At 5kg/sq.cm trip the boiler by withdrawing all LDO
guns. Keep ID fan & FD fan running slowly. At 110 deg C
open all the vents.
6) At 90 deg C boiler drum temp. open all the drains and
completely drain the solution to specially prepared
disposal tank.

5.  Hot Water Rinse:
1) After the draining the alkali sol. completely fill the boiler with
fresh DM water using ELP from Boiler Filling Tank.
2) Again the light up the boiler and raise the boiler pressure and
temp. to 5 to 6 kg/sq.cm and 130 deg to 140 deg C. Now trip
the boiler and drain the boiler when the temp reaches 100 deg
C.
3) Values of pH & PO4 should be less than 7.5 and 10 ppm
respectively.
ACID CLEANING [EDTA CLEANING]:
What is EDTA?
Ethylene Di- amine Tetra Acetic Acid is a strong chelating agent
having ability to form stable complexes with transition metal

6. Advantages of EDTA over HCL Cleaning
Process:
1) DM Water and fuel consumption is less.
2) Shorter Cycle time(5 days).
3) Less Temporary Piping required.
4) Less no. of chemicals required.
5) Effluent Treatment is easy.
6) No usage of Nitrogen.

7. Preparation of EDTA Solution:
Keep the required amounts of EDTA solution ready in EDTA in
EDTA storage tank. Keep the inhibitors BHEL Max & BHEL Sol
and Hydrazine ready for adding in chemical mixing tank.
Ammoniated EDTA : 40% wt/vol
BHELMAX(inhibitor) : 0.15-0.2% wt/vol
BHELSOL (inhibitor) : 0.15-0.2% wt/vol
Hydrazine Hydrate : 1000 ppm
Ammonia : For setting pH of sol. as 9.5 to 9.8.
 EDTA Cleaning Process:
Precaution: Normally acid cleaning is not done to the non
drainable parts of super heater.
1) Thoroughly mix all the above chemicals in the chemical
mixing tank with DM Water and inject this solution to the
bolier upto 3 port level.

8. 2) Light up the boiler by taking LDO guns into service and raise the
boiler drum pressure to 5 to 6kg/sq.cm and 130 to 140 deg C
temperature.
3) Kill the flame & keep the fans running and note down the time
taken for the water to reach 110 deg C.
4) The EDTA Acid reacts with iron oxide of the inner surface of boiler
tube . So the concentration of Iron in the solution increases.

9. 6) The Cleaning process us repeated till the iron concentration
in
consequent samples show equilibrium status.
7) At 90 deg C temperature remove the disposal to the deposit
tank. However EDTA content once after attaining 110 deg C
shall not be allowed more than 8 hours to stay in boiler.
 Passivation or Magnetite Layer Formation:
 Magnetite is a combination of FeO & FeO3 is protective layer
on the water touched metal surfaces which stops further
corrosion of the base metal.
 During the EDTA Cleaning process the removal of deposit
constituents and subsequent passivation of metal surfaces
will occur in a single step.

10. Treated DM Water Rinsing:
1) Prepare a blended solution of NH3 , Hydrazine and DM
Water with calculated quantities in the dissolving tank in
order to achieve a solution of pH of 9.0 to 9.5 & Hydrazine
content of 50 ppm and to be filled in boiler 100mm above
the normal level.
2) Light up the boiler and raise the boiler water temperature up
to 120 deg C and kill the flame. Allow the boiler to cool
down naturally.
3) When the boiler water temperature comes to 95 deg C drain
the water to the effluent pit and allow the system to cool by
natural aeration.
4) Open the inspection drain manually and clean the drum if
required.

11. Superheater Back Flushing:
Super Heater is filled with a solution of hydrazine of 50 ppm &
Ammonia of 9.0 to 9.5 pH in DM Water through Super Heater
drain header.
When the solution comes through Superheater openings to the
Boiler Drum, the back flushing is continued for 10 to 30 minutes
and drained.

12. Conclusion:
After the Alkali Boil Out and Acid Cleaning the Magnetite
Layer is formed on the metal surfaces of water touching
surfaces of boiler thus increasing the boiler efficiency and
decreasing the boiler tube failures.