Transcript chemicalcleaningofboiler-141221013159-conversion-gate01

CHEMICAL CLEANING OF
W
BOILER
E
L
C
O
M
E
KARTHICK POOBATHI,
KALYANAM SUDHEER KUMAR
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.
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.
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.
 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 ions present in
Boiler such as Iron & Copper.
Advantages of EDTA over HCL Cleaning Process:
1)
2)
3)
4)
5)
6)
DM Water and fuel consumption is less.
Shorter Cycle time(5 days).
Less Temporary Piping required.
Less no. of chemicals required.
Effluent Treatment is easy.
No usage of Nitrogen.
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
BHELMAX(inhibitor)
BHELSOL (inhibitor)
Hydrazine Hydrate
Ammonia
: 40% wt/vol
: 0.15-0.2% wt/vol
: 0.15-0.2% wt/vol
: 1000 ppm
: 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.
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.
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.
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.
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.
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.