Chemical Cleaning of Boiler
Content
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
1.0
PLANT DETAILS
2.0
OBJECTIVES
3.0
PROPOSALS
4.0
SERVICES REQUIRED
5.0
SAFETY PRECAUTIONS
6.0
EMERGENCY PROCEDURES
7.0
STATE OF THE PLANT
8.0
METHOD
9.0
COMPLETION CRITERIA
10.0
WASTE TREATMENT & DISPOSAL
11.0
APPENDICES
LOG SHEET FORMATS
ANALYTICAL PROCEDURES
DRAWING
Sheet
1 of 25
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
2 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
1.0
PLANT DETAILS
The steam generator is a controlled circulation Radiant Reheat (Type CC + RQ)
Boiler. The furnace consists of water cooled tubes complete with down comers,
water and steam headers, bottom hoppers, drains, vents, sampling line
connections etc.
2.0
OBJECTIVE
The objective of this procedure is to chemically clean and passivate the internal
surfaces of the steam generating portion (water touched surfaces) and pre
heating surfaces (Economiser) using specified chemicals employing a single
step process. This will render the above mentioned surfaces free of mill scale
and other deposits and form uniform & smooth protective layer of magnetite to
resist corrosion.
3.0
PROPOSAL
The objectives are achieved by carrying out the following proposals. By
carrying out one Alkali Flushing, one Hot water flushing followed by cold DM
water rinsing. Generally loose rust, debris, deposits and other materials left in
the Boiler are removed.
Then, it is subjected to ammoniated EDTA cleaning for the removal of patchy
mill scale and adherent rust. The acid pickled surface is passivated for the
formation of uniform and adherent magnetite layer. Both chemical cleaning and
passivation process are completed in a single step in the EDTA cleaning
process.
4.0
SERVICES REQUIRED
4.1
Prior to the commencement of chemical cleaning all the DM water storage
tanks should be kept full and the DM water generating units kept in regenerated
condition. Approximately 3200 m3 of DM water will be consumed during the
entire process. At any time of acid cleaning a minimum of two Boiler volumes
(approximately 700 m3) of DM water should be available in ready stock to
facilitate rapid flushing of the system in the event of Chemistry upset.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
3 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
4.2
All the required quantities of chemicals as given below should be made
available prior to the commencement of the process:
Quantity
Name of Chemicals
Tri Sodium Phosphate
(NA3PO4,12H2O as perIS573:1992))
400 kgs
2. Disodium Hydrogen Phosphate
(Na2HPO4 12H2Oas per IS566-1991)
200 kgs
3. Ammoniated EDTA
40% wt/wt as active EDTA
ammoniated solution (pH = 9.5 to 9.8)
(EDTA : Ethylene diamine tetra acetic acid)
Sp gravity : 1.17- 1.18
% of active EDTA(W/V)- 47% to 48%
4. Ammonia solution (20% Min as NH3,
sp gr : 0.91) as per IS 799 / 1990
40 tons
1800 litres
5. Hydrazine Hydrate
(80% Min. conc). IS 12086/1991
1800 litres
6.
Bhelmax
690 kg
7.
Bhelsol
690 litres
4.3
Temporary drum water level gauge glass and (Tell-tale lamp indication) at
control room and low point drain area.
4.4
HT / LT power supply to be available.
4.5
Instrument / service Air to be available.
4.6
Chemical Testing laboratory should be available for testing during the process.
4.7
Flood lights, Telephones / walkie-talkie are available.
4.8
For effluent treatment compressed air facility and suitable perforated Carbon
Steel / polythene tubing arrangement shall be made available
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
4 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
4.9
SAFETY EQUIPMENTS
1. Gum boots (Various sizes)
6 Pairs
2. Rubber gloves
6 Pairs
3. Rubber or Polythene aprons
6 Nos
4. Helmets
12 Nos
5. Safety goggles plain glass
6 Nos
6. Face mask (Transparent, plastic)
4 Nos
7. First aid box (containing dilute ammonium hydroxide, 50% sodium
bicarbonate solution, eye lotion, bandages, tincture iodine, cotton, Burnol
etc)
5.0
SAFETY PRECAUTIONS
5.1
Flushing and washing water supplies should be available.
5.2
Ample supplies of tepid flushing and washing water supplies should be
provided at all possible points of discharge, spillage or escape of chemicals.
5.3
Adequate provisions should be made for emergency treatment of the eyes,
comprising eye wash bottles, located conveniently to places where discharge,
spillage or escape of chemicals can occur.
5.4
Safety shower should be provided.
5.5
A suitable first aid treatment room with outside telephone facilities should be
provided within a reasonable distance of the place where chemicals are being
used.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
5 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
5.6
The protective clothing and apparatus required for emergency use should be
made available near the acid cleaning area.
5.7
FIRST AID TREATMENT
5.7.1
Splashes of the eye
5.7.1.1
Immediately flood the eye with water. To be effective the eyelids must be
opened. The eyelids should be pushed apart using the thumb and index finger
of the left hand. The casualty will probably not be able to open the eye
himself because of painful spasms.
5.7.1.2
If an eye wash bottle is used the jet should not be directed at the front of the
eye. It should be directed in from the side so that flow is over the surface of
the eye.
5.7.1.3
Irrigation should be continued for 5 – 10 minutes after which the casualty
should be taken to the first aid room.
5.7.1.4
Irrigation should be continued in the first aid room. Remember vision is saved
by thorough irrigation. No other treatment can prevent damage if this is
omitted.
5.7.1.5
After thorough irrigation the eye should be covered with a pad. The patient
should be referred for medical opinion.
5.7.2
5.7.2.1
IRRITATION OF THE SKIN
If signs of skin irritation occur the person should be removed from location
and referred for medical opinion. In the event of splashing of chemicals on
the skin the affected area should be thoroughly washed.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
6 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
5.8
GENERAL
5.8.1
Test area will be cordoned off and unauthorized entry should not be allowed.
Suitable signboard should be displayed.
5.8.2
Whenever any inspection is done during the cleaning process the location
should be adequately ventilated.
5.9
SAFETY OF PLANT
5.9.1
The Boiler should be suitably preserved after chemical cleaning if the light up
for the subsequent activity could not be done within 4 weeks of completion of
chemical cleaning.
5.9.2
Temperature limitations specified for various steps should not be exceeded.
6.0
EMERGENCY PROCEDURES
6.1
The testing team should be aware of the operating procedures of fire
extinguishers to be used for quenching minor or major fires.
6.2
The testing team should be aware of the procedure to be followed in case of
accidents involving personnel injury.
6.3
In case of failure of running pump the stand by pump should be started
immediately without delay.
6.4
An operator posted at the pump area, should be instructed to stop the pumps
and properly isolate the system in the event of emergency. All operators should
be well conversant with the emergency operating instructions.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
7 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
7.0
STATE OF THE PLANT
7.1
Readiness of the following is to be ensured:
7.2
During the acid cleaning process all the permanent Boiler instruments are
isolated except providing a temporary pressure gauge of 0 to 10 kg/ cm2 in the
drum for monitoring pressure in the drum during acid cleaning.
Provisions should be made at the following locations for the measurement of
temperature:
Two locations in the drum (left & right) for the measurement of Boiler water
temperature. Long thermocouples of around 400 mm length shall be installed
directly in the spare / unused stubs in the drum. Alternatively; metal
temperature measuring thermo couple with suitable adopter can be used. (Refer
enclosed drawing).
A)
B) Water wall metal temperature measurements as given below:
4 number thermocouples shall be installed at AB elevation on corner water
wall tubes (outside the furnace) and 2 numbers thermocouples shall be
installed at GH elevation in the front and rear water wall (outside the
furnace) at accessible locations.
C) Two more thermocouples with pads one each at left and right side of ECO
coil shall be welded at suitable locations inside the boiler (or penthouse) to
measure the metal temperature in the gas side.
(Total 6 nos. thermocouples will be used for measurement of water wall tube
metal temperature and 2 nos. for economizer tube temperature)
Peening type temporary thermocouples are to be provided in the measurement
points on the water walls and economizer. Provision should be made for
monitoring of temperatures in the control room.
Light up of boiler for steam blowing to be done within 4 weeks after EDTA
cleaning. To achieve this, erection of MS, CRH AND HRH piping has to be
planned accordingly. Further delay in light up leads to corrosion in boiler
tubes.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
8 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
7.3
SAMPLING DURING PROCESS
To get representative samples of the process solution, sampling points
with sample coolers are to be provided at the following locations: 25mm dia
pipe shall be used for sampling line.
CC pump suction through temporary cooler. The sampling line from cooler
outlet shall be extended to zero meter with an isolation valve.
One number of sampling point is to be provided from bottom ring header as
shown in the drawing through temporary cooler. The sampling line from cooler
outlet shall be extended to zero meter with an isolation valve.
7.4
For alkali flushing, rinsing, chemical cleaning and passivation processes,
essential control and instruments viz. protections, interlock, alarms,
measurement, annunciation etc. required for safe light-up of boiler are made
available as per mutually agreed list between NTPC and BHEL at site.
7.5
One set of boiler auxiliaries are made ready and available for boiler light up. A
checklist, containing minimum requirements to be made ready prior to
commencement of Chemical cleaning is enclosed at 7.15.
7.6
All Drum internals including Primary separators, screen driers and secondary
separators are to be installed in the upper drum.
7.7
In the bottom drum the screen plates shall be retained and orifices are not to be
installed.
7.8
The economizer recirculation valve shall be kept open throughout the chemical
cleaning process. Economiser inlet valve shall be kept closed.
7.9
O & M instruction for the Boiler and other auxiliaries are to be available well in
advance of the commencement of the cleaning process.
7.10
All the safety measures discussed and implemented in advance with suitable
instruction / caution tags provided at strategic places / equipment.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
9 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
7.11
Boiler water wall test tube coupons are placed at two ends inside the drum and
bottom ring header to see the effectiveness of the cleaning. It is to be ensured
that the test coupons placed in the boiler upper drum are properly kept
immersed in the solution. Test coupons shall be kept suspended vertically and
tied with stainless steel/thick steel wire to withstand the temperature during the
EDTA process.
7.12
Proper effluent treatment arrangement is to be made available at site. A
cemented neutralizing pit of volume 800 m3 approx. with compressed air
scouring arrangement is to be made.
7.13
Chemical cleaning system / equipment should be complete as per the approved
scheme.
7.14
Inhibitor efficiency test certificate shall be produced by BHEL.
7.15
MINIMUM OPERATIONAL REQUIREMENTS
1. Ensure the commissioning of the following including their protections,
interlocks, measurements, alarms and annunciations:
One ID Fan
One FD Fan
One SAPH & its SOOT BLOWER
All CC Pumps
Steam Coiled Air Pre Heater
Light Oil Firing System
FSSS
SADC
Scanner Air System
Boiler filling system
Measurements, alarms, annunciations pertaining to secondary air flue
gas, feed water, steam & Boiler metal temp
CC pumps purge line to be ready and continuous water supply at 15kg/cm2 for
purging of CC pumps. One fill pump should be available on emergency supply
to continue purging of CC pump even incase of normal supply failure.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
10 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
2. Ensure free expansion of the furnace and duct and provision of expansion Status
markers.
3. Blow-down system of Boiler
4. Proper drainage system of boiler area
5. Air in leak test of two passes of ESP
6. Mechanical readiness of two passes of ESP
7. Adequate quantity of light oil & readiness of light oil handling system
8. Temporary sampling system along with the cooling arrangement for
collecting samples from the header drains and CC pump casing during
chemical cleaning is ready
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
Water and steam systems are ready for operation
Air and flue gas system ready for operation
Effluent treatment pit to hold approximately 800 m3 is ready
Drainage line to effluent treatment is ready
Readiness of MDBFP and Feed system (optional)
Drum water sampling system along with sample cooling arrangement
Availability of emergency supply for
• Scanner air Fan
• Emergency lighting
UPS
Fire fighting system of concerned equipments
Equipment cooling water system shall be made ready.
Availability of adequate quantity of DM water.
Adequate capacity of instrument air and service air system
Availability of HP dozing system.
Availability of test coupons & their fixing arrangements.
Emergency operating instructions viz. AC power failure, DC. Power
failure, APH fire etc.
Adequate lighting in operating areas.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
11 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
25. Public address system at all operating locations, including telephone & Status
walkie-talkies at all working areas
26. Readiness of staircases, hand railings and platforms
27. Personal safety equipment.
28. Easy access and approaches to all the operating equipments.
29. SH metal temperature measurement shall be made ready for continuous
monitoring in the control room.
30. Data logging printer at control room shall be made available to record the
boiler parameters periodically.
31. Proper isolation of Air Pre heater, which will not be taken into service, will
be ensured. Alternately, the same be kept running.
32. Ensure availability of APH soot blowing system, fire detection and fire
fighting system, rotor stoppage alarm, oil carry over probe.
8.0
METHOD
8.1
ALKALI FLUSHING
8.1.1
Requisite quantities of Tri-sodium Phosphate (TSP) & Di Sodium Hydrogen
Phosphate are added to the mixing tank along with DM Water and the solution
is thoroughly mixed by recirculation so that final solution in the Boiler
contains 0.1 % TSP and 0.05 % DSP. The solution will be injected into the
Boiler through the bottom ring header drain and economizer drain operating the
chemical filling pump. Further DM water will be taken in the Boiler up to
normal level.
8.1.2
Light up the boiler as per O&M instructions and gradually raise the boiler
water temp. to 130-140 deg C. Trip the boiler and keep the fans running for
cooling. Keep one CC pump running.
Note: All the three CC pumps shall be put into operation on rotation
periodically
8.1.3
When the boiler water temperature comes down to 95 deg.C, stop the CC pump
and drain the boiler in the hot condition to the plant’s water disposal system, by
keeping open the drain valves fully.(without throttling).The effluent is diluted
with plenty of service water.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
12 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
8.2
HOT WATER RINSE
8.2.1
Once the draining is complete Boiler is refilled with DM water. Boiler is lit up
and the Boiler water temperature is gradually raised to 130-140 0C. Then the
Boiler is tripped and Fans are kept running for cooling.
8.2.2
During all rinsing operations (hot & cold) all the CC pumps are to be made
ready and operated in rotation.
8.2.3
The running CC pump is stopped after 30 minutes and Boiler is drained in hot
condition to the plant drain system by keeping the drain valves wide open
(without any throttling). The effluent is diluted with service water so as to bring
pH and PO4 in the effluent below 7.5 and 10 ppm respectively.
8.3
COLD WATER RINSE
8.3.1
Cold water rinsing is done using fill and dump method. Draining is done in the
plant drain system. pH of the rinsed effluent is monitored during draining. The
rinsing operation is continued until pH of the effluent is almost equal to pH of
inlet water used for rinsing. All CC pumps are run one by one for proper
rinsing.
8.3.2
All sampling and blow down lines are flushed. All temperature / pressure
measurements relevant to the process are monitored in UCB for their reliability.
8.4
ACID CLEANING & PASSIVATION
8.4.1
Required quantity of ammoniated EDTA (40% wt / wt) solution is kept ready in
the EDTA storage tank.
8.4.2
The inhibitors “BHELMAX” & “BHELSOL”, Hydrazine hydrate and ammonia
for addition in the Chemical dissolving tank are also made available near the
mixing tank.
8.4.3
All the Boiler Blow down valves are kept shut and drum vent valves & start up
vent are kept open during Boiler filling.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
13 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
8.4.4
40 Cu.m of DM water is drawn in the mixing tank. The temporary chemical fill
pump is started and system put into recirculation. Required quantity of
Ammoniated EDTA (40% wt/wt) solution is transferred from the EDTA
storage tank to the mixing tank. The EDTA concentration in the mixing tank is
checked. Transferring of the EDTA solution is stopped when the EDTA
concentration reaches 3 + 1% by weight. Required quantity of Hydrazine
hydrate and inhibitors (BHELMAX & BHELSOL) are also added.
Recirculation is done till all the chemicals are uniformly mixed up. With this
one batch of EDTA Chemical solution is ready for filling into the Boiler.
8.4.5
The approximate quantities of various chemicals that are to be mixed per batch
of 40 m3 is :
1. EDTA ammoniated (40 % ) concentrate : 3 to 4 m3
2. BHELMAX
: 60 kgs
3. BHELSOL
: 60 lit
4. N2H4.H2O (80%)
: 60 litres
8.4.6
Ammonia is added if required to adjust the pH between 9.0 and 9.8. DM water
is used to make up to 40 m3.
8.4.7
This solution is filled into the Boiler through Low Point drain header with the
temporary chemical fill pump. Fill the boiler up to +200 mm from the normal
working level in the drum. Start the middle CC pump for thorough mix up of
the chemical solution for 30 minutes. Check the boiler water sample.
8.4.8
The cleaning solution is quite harmless in respect of corrosion and hence there
is no time limitation for filling the Boiler and retaining the solution inside the
Boiler.
8.4.9
Preparation of Chemical solution and batch filling is repeated as explained in
point no 8.4.4 till the solution level in the Drum reaches the center line of the
gauge glass.
The composition of the filling solution is:
EDTA content
:
3 + 1% W/v
Hydrazine
:
1000 ppm (min)
pH
:
9.0 to 9.8
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
14 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
8.4.10
The Boiler is lighted up as per normal operating procedure with minimum
firing rate (say 2 oil guns in AB elevation)
8.4.11
The Drum and super heater vents are closed when steaming starts, say at 1 kg /
sq. cm. pressure in the Drum. SH start up vents are kept crack open.
8.4.12
The drain valve in SH Header # 1 is kept in crack opened condition.
8.4.13
The time at which the temperature of Boiler water reaches 110 0C is noted.
8.4.14
Raising of Boiler water temperature is continued till temp reaches140 0C.
8.4.15
Once the temperature of Boiler water reaches 140 0C, the firing rate is
controlled in such a way that the Boiler water temperature is maintained at 140
- 145 0C, for a minimum period of 4 hours. Then the Boiler is tripped but
running of CC pump is continued.
8.4.16
The ID & FD Fans are allowed to run to bring down the Boiler water
temperature. In case it appears that the results of iron concentration may not
level out when temperature is expected to be 110 0C, ID/FD fans are stopped
suitably during the cooling down phase & Boiler is boxed up with CC pump
running and kept in this condition to achieve the EDTA contact period of 8
hours with temperature exceeding 1100C.
8.4.17
Samples are taken at every 30 minutes interval from the sampling points at
locations given in article 7.3 from the time when the temperature in the system
had reached 1100 C and analysed for pH, EDTA concentration and Iron content.
8.4.18
After attaining the completion criteria of pickling process, as per article 9.0, the
system is allowed to cool with the ID & FD Fans in operation (ID & FD Fans
are to be restarted, in case they have been stopped to meet the completion
criteria, to bring down the Boiler water temperature). Open the Drum air vents
when the pressure reaches 1 kg/sq.cm.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
15 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
8.4.19
Boiler water temperature & Water Wall metal temperature at the locations
indicated as per 7.2 are to be measured and logged.
8.4.20
When the temperature comes down to 950C the running CC pump is stopped
and the system is drained completely in hot condition to the effluent pit by
opening all the drain valves.
8.5
8.5.1
8.5.2
TREATED DM WATER RINSE
Prepare a blended solution of ammonia & Hydrazine with calculated
quantities in the dissolving tank in order to achieve a solution pH 9.0 to 9.5
and hydrazine content 50 ppm in the DM water being filled in the boiler.
Fill the boiler with the above treated DM water through low point drains
and economizer as practiced earlier, up to just above the centre gauge glass.
8.5.3
Start the middle CC pump and light up the boiler as per O&M Instruction.
Drum level will drop after starting the CC pump. Again fill the boiler with
treated DM water solution to make up the level up to 100 mm above NWL.
8.5.4
Raise boiler water temperature up to 110 deg .C and then shut down the
boiler. Allow the boiler to cool down naturally. When the boiler water
temperature comes down to 95 deg C. drain the boiler in hot condition to
plant drain and allow the system for natural aeration
8.5.5
Boiler Drum manhole is opened for removal of Coupons. Manually clean the
drums if required.
8.5.6
Lower drums manholes are opened for inspection and cleaned manually, if
required.
8.5.7
Restore the boiler and prepare it for regular operation for steam blowing,
safety valve floating etc.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
16 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
8.6
INSPECTION
8.6.1
The test coupons placed at identified locations are taken out. All coupons
should be free of deposits and should have uniform coating of the protective
layer.
8.6.2
The Drum internal surface is visually inspected for uniform smooth coating of
protective layer.
8.6.3
The ring headers will be inspected and loose debris if any, will be removed.
9.0
COMPLETION CRITERIA
9. 1
COLD RINSE AFTER ALKALI FLUSHING
9.1.1
The rinsing operation is continued until pH of the effluent is almost equal to pH
of inlet water used for rinsing.
9.2
EDTA CLEANING
9.2.1
Cleaning process is to be continued till iron concentration in three consecutive
samples show equilibrium status.
9.2.2
When the iron concentration in the cleaning solution is constant it indicates that
all the oxides have been dissolved. However, a minimum EDTA contact period
of 6 hours from the time of attaining the required temperature (110 0C) shall be
allowed.
9.2.3
If the iron concentration values do not level out and attain equilibrium status,
regardless of analytical results, the EDTA contact period with temperature
exceeding 1100C shall not be allowed for more than 8 hours (approx).
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
17 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
10.0
WASTE TREATMENT & DISPOSAL
10.1
Treatment and disposal of the waste and effluents of the chemical cleaning
process should comply with the requirements / stipulations of State Pollution
Control Board norms.
10.2
Effluent of Hot DM water flushing should be drained into plant normal drain.
10.3
The spent EDTA chemical solution after the cleaning process is drained into the
designated pit. The pH of the effluent will be in the range of 8.5 to 9.0 and
hence no treatment for pH adjustment is required as it would meet the pH
requirement for disposal.
10.4
Compressed air is used to destroy the residual Hydrazine & organics and the
effluent may be disposed after aeration for 10 days, as per state pollution
control board norms. Effluent may be disposed to ash dyke in installments
through existing ash slurry system (The organic chemical is completely biodegradable).
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
18 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
11.0
APPENDIX
11.1
NOTE
11.1.1
Drains should be provided at lowest points of temporary piping.
11.1.2
All temporary connections to Boiler should be of good quality. They will be
hydraulically tested at 14 kg/cm2 with the temporary boiler filling pump.
11.1.3
Service water supply should be available near the pump operating areas.
1.1.4
Additional Check lists / Modifications in the layout, if found necessary, may
be made at site in consultation with site Commissioning In-charge.
11.1.5
All the sampling points along with sample coolers and the temperature
measurement points with necessary thermocouples shall be provided as
indicated in 7.3 & 7.2 respectively.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
LOG SHEET
PROJECT :
DATE :
/
/
UNIT NO. :
ACTIVITY :
I.
EDTA ACID CLEANING AND PASSIVATION
ADDITION OF CHEMICALS
____________________________________________________________________
Sl. No. DATE TIME
NAME OF CHEMICAL ADDED
QUANTITY
_____________________________________________________________________
II.
ANALYTICAL DATA
_____________
Sl.
DATE
No.
1.
2.
3.
4.
5.
_________________________________________________
TIME
SAMPLE POINT
TOTAL EDTA
IRON
pH
hrs.
%
ppm
____________________________________________________________________
Signatures.
BHEL
NTPC
Sheet
19 of 25
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
20 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
PROCEDURE FOR DETERMINATION OF TOTAL EDTA CONCENTRATION IN PROCESS
SOLUTION DURING CHEMICAL CLEANING
1. PRINCIPLE
EDTA reacts with Zirconium ions under strong acid conditions to form a chelate. The end
point of the titration is indicated by a Xylenol orange indicator.
2. REAGENTS AND APPARATUS REQUIRED
APPARATUS
1.
2.
3.
4.
Erlenmeyer flask 300 ml capacity
Pipettes
Hot plate
Magnetic stirrer
REAGENTS
1. Hydrochloric acid (conc.)
2. Standard Zirconium oxy chloride (ZrOCl2. 8H2O) 0.1 M solution in 1 N HCl
(Take a 1000 ml volumetric flask and add 32.25 gram of ZrOCl2.8 H2O and add
DM water to about 500 ml. To this add 85 ml of conc. HCl. Make up to 1000 ml mark with
DM water and mix well)
3. Ascorbic acid
4. Xylenol orange indicator
3. TEST PROCEDURE
1.
2.
3.
4.
Pipette out 10 cc of the water sample into a 300 ml Erlenmeyer Flask.
Add 10 ml of conc. HCl ( the pH value is about 1.0)
Add a spatula of ascorbic acid.
Boil of the solvent on the heating plate for about 5 minutes.(The yellow colour of the ferric
ion should disappear due to reduction to ferrous iron.
5. Immediately after the addition of 0.05 ml of 0.05 % xylenol orange indicator the sample is
titrated with 0.1M ZrOCl2 until the colour changes from yellow to red violet; The colour
changes from yellow to red violet. The colour change shall remain constant for at least 3 min.
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
21 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
4.
CALCULATION
The total EDTA concentration
% = Volume of 0.1M ZrOCl2 consumed x 0.292
PROCEDURE FOR THE DETERMINATION OF IRON CONCENTRATION
IN WATER SAMPLES DURING CHEMICAL CLEANING.
1. APPARATUS REQUIRED
1. Spectrophotometer.
2. Hot plate
3. Volumetric flasks
4. Pipettes
2. REAGENTS REQUIRED
1. Thioglycolic acid (pure Grade)
2. Ammonia solution (25%) AR Grade
3. TEST METHOD
1.
2.
3.
4.
pipette out 25 ml of the water sample into a 50 ml capacity volumetric flask.
Add 2 ml of Thioglycolic acid using pro-pipette. Mix well
Heat it to 70 – 80 deg C for about 10 minutes.
Cool it to room temperature and make it up with DM water to the 50 ml mark and mix
well.
5. Measure the extinction of the sample against a blank using DM water treated as the
sample at 532.5 nm using Spectrophotometer.
6. Plot a curve taking standard iron solution and measuring the extinction in the same way as
that of the water sample.
7. Read the iron concentration of the sample from the calibration graph plotted.
Alternatively,
Pre-calibrated spectrophotometer (HACH USA/ Lovibond ) with appropriate reagent for iron can be
used.
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
22 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
ESTIMATION OF HYDRAZINE
1. REAGENTS
Standard Potassium bromate 0.1 N
Dissolve 2.7836 gram of Potassium bromate (KbrO3) and 10 gram of Potassium
bromide (KBr) in DM / Distilled water and make up to 1000 ml.
0.1 % Methyl orange indicator solution.
Hydrchloric acid (conc.) AR.
2. PROCEDURE
o Place 10 ml of sample in a titration flask.
o Add 10 ml of conc. HCl.
o Add about 5 drops of Methyl orang indicator.
o Titrate with standard KbrO3 titrant to the first appearance of yellow colour.
3. CALCULATION
Hydrazine as N2H4 in ppm
= Titre value x 80
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
1.0
PLANT DETAILS
2.0
OBJECTIVES
3.0
PROPOSALS
4.0
SERVICES REQUIRED
5.0
SAFETY PRECAUTIONS
6.0
EMERGENCY PROCEDURES
7.0
STATE OF THE PLANT
8.0
METHOD
9.0
COMPLETION CRITERIA
10.0
WASTE TREATMENT & DISPOSAL
11.0
APPENDICES
LOG SHEET FORMATS
ANALYTICAL PROCEDURES
DRAWING
Sheet
1 of 25
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
2 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
1.0
PLANT DETAILS
The steam generator is a controlled circulation Radiant Reheat (Type CC + RQ)
Boiler. The furnace consists of water cooled tubes complete with down comers,
water and steam headers, bottom hoppers, drains, vents, sampling line
connections etc.
2.0
OBJECTIVE
The objective of this procedure is to chemically clean and passivate the internal
surfaces of the steam generating portion (water touched surfaces) and pre
heating surfaces (Economiser) using specified chemicals employing a single
step process. This will render the above mentioned surfaces free of mill scale
and other deposits and form uniform & smooth protective layer of magnetite to
resist corrosion.
3.0
PROPOSAL
The objectives are achieved by carrying out the following proposals. By
carrying out one Alkali Flushing, one Hot water flushing followed by cold DM
water rinsing. Generally loose rust, debris, deposits and other materials left in
the Boiler are removed.
Then, it is subjected to ammoniated EDTA cleaning for the removal of patchy
mill scale and adherent rust. The acid pickled surface is passivated for the
formation of uniform and adherent magnetite layer. Both chemical cleaning and
passivation process are completed in a single step in the EDTA cleaning
process.
4.0
SERVICES REQUIRED
4.1
Prior to the commencement of chemical cleaning all the DM water storage
tanks should be kept full and the DM water generating units kept in regenerated
condition. Approximately 3200 m3 of DM water will be consumed during the
entire process. At any time of acid cleaning a minimum of two Boiler volumes
(approximately 700 m3) of DM water should be available in ready stock to
facilitate rapid flushing of the system in the event of Chemistry upset.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
3 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
4.2
All the required quantities of chemicals as given below should be made
available prior to the commencement of the process:
Quantity
Name of Chemicals
Tri Sodium Phosphate
(NA3PO4,12H2O as perIS573:1992))
400 kgs
2. Disodium Hydrogen Phosphate
(Na2HPO4 12H2Oas per IS566-1991)
200 kgs
3. Ammoniated EDTA
40% wt/wt as active EDTA
ammoniated solution (pH = 9.5 to 9.8)
(EDTA : Ethylene diamine tetra acetic acid)
Sp gravity : 1.17- 1.18
% of active EDTA(W/V)- 47% to 48%
4. Ammonia solution (20% Min as NH3,
sp gr : 0.91) as per IS 799 / 1990
40 tons
1800 litres
5. Hydrazine Hydrate
(80% Min. conc). IS 12086/1991
1800 litres
6.
Bhelmax
690 kg
7.
Bhelsol
690 litres
4.3
Temporary drum water level gauge glass and (Tell-tale lamp indication) at
control room and low point drain area.
4.4
HT / LT power supply to be available.
4.5
Instrument / service Air to be available.
4.6
Chemical Testing laboratory should be available for testing during the process.
4.7
Flood lights, Telephones / walkie-talkie are available.
4.8
For effluent treatment compressed air facility and suitable perforated Carbon
Steel / polythene tubing arrangement shall be made available
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
4 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
4.9
SAFETY EQUIPMENTS
1. Gum boots (Various sizes)
6 Pairs
2. Rubber gloves
6 Pairs
3. Rubber or Polythene aprons
6 Nos
4. Helmets
12 Nos
5. Safety goggles plain glass
6 Nos
6. Face mask (Transparent, plastic)
4 Nos
7. First aid box (containing dilute ammonium hydroxide, 50% sodium
bicarbonate solution, eye lotion, bandages, tincture iodine, cotton, Burnol
etc)
5.0
SAFETY PRECAUTIONS
5.1
Flushing and washing water supplies should be available.
5.2
Ample supplies of tepid flushing and washing water supplies should be
provided at all possible points of discharge, spillage or escape of chemicals.
5.3
Adequate provisions should be made for emergency treatment of the eyes,
comprising eye wash bottles, located conveniently to places where discharge,
spillage or escape of chemicals can occur.
5.4
Safety shower should be provided.
5.5
A suitable first aid treatment room with outside telephone facilities should be
provided within a reasonable distance of the place where chemicals are being
used.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
5 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
5.6
The protective clothing and apparatus required for emergency use should be
made available near the acid cleaning area.
5.7
FIRST AID TREATMENT
5.7.1
Splashes of the eye
5.7.1.1
Immediately flood the eye with water. To be effective the eyelids must be
opened. The eyelids should be pushed apart using the thumb and index finger
of the left hand. The casualty will probably not be able to open the eye
himself because of painful spasms.
5.7.1.2
If an eye wash bottle is used the jet should not be directed at the front of the
eye. It should be directed in from the side so that flow is over the surface of
the eye.
5.7.1.3
Irrigation should be continued for 5 – 10 minutes after which the casualty
should be taken to the first aid room.
5.7.1.4
Irrigation should be continued in the first aid room. Remember vision is saved
by thorough irrigation. No other treatment can prevent damage if this is
omitted.
5.7.1.5
After thorough irrigation the eye should be covered with a pad. The patient
should be referred for medical opinion.
5.7.2
5.7.2.1
IRRITATION OF THE SKIN
If signs of skin irritation occur the person should be removed from location
and referred for medical opinion. In the event of splashing of chemicals on
the skin the affected area should be thoroughly washed.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
6 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
5.8
GENERAL
5.8.1
Test area will be cordoned off and unauthorized entry should not be allowed.
Suitable signboard should be displayed.
5.8.2
Whenever any inspection is done during the cleaning process the location
should be adequately ventilated.
5.9
SAFETY OF PLANT
5.9.1
The Boiler should be suitably preserved after chemical cleaning if the light up
for the subsequent activity could not be done within 4 weeks of completion of
chemical cleaning.
5.9.2
Temperature limitations specified for various steps should not be exceeded.
6.0
EMERGENCY PROCEDURES
6.1
The testing team should be aware of the operating procedures of fire
extinguishers to be used for quenching minor or major fires.
6.2
The testing team should be aware of the procedure to be followed in case of
accidents involving personnel injury.
6.3
In case of failure of running pump the stand by pump should be started
immediately without delay.
6.4
An operator posted at the pump area, should be instructed to stop the pumps
and properly isolate the system in the event of emergency. All operators should
be well conversant with the emergency operating instructions.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
7 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
7.0
STATE OF THE PLANT
7.1
Readiness of the following is to be ensured:
7.2
During the acid cleaning process all the permanent Boiler instruments are
isolated except providing a temporary pressure gauge of 0 to 10 kg/ cm2 in the
drum for monitoring pressure in the drum during acid cleaning.
Provisions should be made at the following locations for the measurement of
temperature:
Two locations in the drum (left & right) for the measurement of Boiler water
temperature. Long thermocouples of around 400 mm length shall be installed
directly in the spare / unused stubs in the drum. Alternatively; metal
temperature measuring thermo couple with suitable adopter can be used. (Refer
enclosed drawing).
A)
B) Water wall metal temperature measurements as given below:
4 number thermocouples shall be installed at AB elevation on corner water
wall tubes (outside the furnace) and 2 numbers thermocouples shall be
installed at GH elevation in the front and rear water wall (outside the
furnace) at accessible locations.
C) Two more thermocouples with pads one each at left and right side of ECO
coil shall be welded at suitable locations inside the boiler (or penthouse) to
measure the metal temperature in the gas side.
(Total 6 nos. thermocouples will be used for measurement of water wall tube
metal temperature and 2 nos. for economizer tube temperature)
Peening type temporary thermocouples are to be provided in the measurement
points on the water walls and economizer. Provision should be made for
monitoring of temperatures in the control room.
Light up of boiler for steam blowing to be done within 4 weeks after EDTA
cleaning. To achieve this, erection of MS, CRH AND HRH piping has to be
planned accordingly. Further delay in light up leads to corrosion in boiler
tubes.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
8 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
7.3
SAMPLING DURING PROCESS
To get representative samples of the process solution, sampling points
with sample coolers are to be provided at the following locations: 25mm dia
pipe shall be used for sampling line.
CC pump suction through temporary cooler. The sampling line from cooler
outlet shall be extended to zero meter with an isolation valve.
One number of sampling point is to be provided from bottom ring header as
shown in the drawing through temporary cooler. The sampling line from cooler
outlet shall be extended to zero meter with an isolation valve.
7.4
For alkali flushing, rinsing, chemical cleaning and passivation processes,
essential control and instruments viz. protections, interlock, alarms,
measurement, annunciation etc. required for safe light-up of boiler are made
available as per mutually agreed list between NTPC and BHEL at site.
7.5
One set of boiler auxiliaries are made ready and available for boiler light up. A
checklist, containing minimum requirements to be made ready prior to
commencement of Chemical cleaning is enclosed at 7.15.
7.6
All Drum internals including Primary separators, screen driers and secondary
separators are to be installed in the upper drum.
7.7
In the bottom drum the screen plates shall be retained and orifices are not to be
installed.
7.8
The economizer recirculation valve shall be kept open throughout the chemical
cleaning process. Economiser inlet valve shall be kept closed.
7.9
O & M instruction for the Boiler and other auxiliaries are to be available well in
advance of the commencement of the cleaning process.
7.10
All the safety measures discussed and implemented in advance with suitable
instruction / caution tags provided at strategic places / equipment.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
9 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
7.11
Boiler water wall test tube coupons are placed at two ends inside the drum and
bottom ring header to see the effectiveness of the cleaning. It is to be ensured
that the test coupons placed in the boiler upper drum are properly kept
immersed in the solution. Test coupons shall be kept suspended vertically and
tied with stainless steel/thick steel wire to withstand the temperature during the
EDTA process.
7.12
Proper effluent treatment arrangement is to be made available at site. A
cemented neutralizing pit of volume 800 m3 approx. with compressed air
scouring arrangement is to be made.
7.13
Chemical cleaning system / equipment should be complete as per the approved
scheme.
7.14
Inhibitor efficiency test certificate shall be produced by BHEL.
7.15
MINIMUM OPERATIONAL REQUIREMENTS
1. Ensure the commissioning of the following including their protections,
interlocks, measurements, alarms and annunciations:
One ID Fan
One FD Fan
One SAPH & its SOOT BLOWER
All CC Pumps
Steam Coiled Air Pre Heater
Light Oil Firing System
FSSS
SADC
Scanner Air System
Boiler filling system
Measurements, alarms, annunciations pertaining to secondary air flue
gas, feed water, steam & Boiler metal temp
CC pumps purge line to be ready and continuous water supply at 15kg/cm2 for
purging of CC pumps. One fill pump should be available on emergency supply
to continue purging of CC pump even incase of normal supply failure.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
10 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
2. Ensure free expansion of the furnace and duct and provision of expansion Status
markers.
3. Blow-down system of Boiler
4. Proper drainage system of boiler area
5. Air in leak test of two passes of ESP
6. Mechanical readiness of two passes of ESP
7. Adequate quantity of light oil & readiness of light oil handling system
8. Temporary sampling system along with the cooling arrangement for
collecting samples from the header drains and CC pump casing during
chemical cleaning is ready
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
Water and steam systems are ready for operation
Air and flue gas system ready for operation
Effluent treatment pit to hold approximately 800 m3 is ready
Drainage line to effluent treatment is ready
Readiness of MDBFP and Feed system (optional)
Drum water sampling system along with sample cooling arrangement
Availability of emergency supply for
• Scanner air Fan
• Emergency lighting
UPS
Fire fighting system of concerned equipments
Equipment cooling water system shall be made ready.
Availability of adequate quantity of DM water.
Adequate capacity of instrument air and service air system
Availability of HP dozing system.
Availability of test coupons & their fixing arrangements.
Emergency operating instructions viz. AC power failure, DC. Power
failure, APH fire etc.
Adequate lighting in operating areas.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
11 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
25. Public address system at all operating locations, including telephone & Status
walkie-talkies at all working areas
26. Readiness of staircases, hand railings and platforms
27. Personal safety equipment.
28. Easy access and approaches to all the operating equipments.
29. SH metal temperature measurement shall be made ready for continuous
monitoring in the control room.
30. Data logging printer at control room shall be made available to record the
boiler parameters periodically.
31. Proper isolation of Air Pre heater, which will not be taken into service, will
be ensured. Alternately, the same be kept running.
32. Ensure availability of APH soot blowing system, fire detection and fire
fighting system, rotor stoppage alarm, oil carry over probe.
8.0
METHOD
8.1
ALKALI FLUSHING
8.1.1
Requisite quantities of Tri-sodium Phosphate (TSP) & Di Sodium Hydrogen
Phosphate are added to the mixing tank along with DM Water and the solution
is thoroughly mixed by recirculation so that final solution in the Boiler
contains 0.1 % TSP and 0.05 % DSP. The solution will be injected into the
Boiler through the bottom ring header drain and economizer drain operating the
chemical filling pump. Further DM water will be taken in the Boiler up to
normal level.
8.1.2
Light up the boiler as per O&M instructions and gradually raise the boiler
water temp. to 130-140 deg C. Trip the boiler and keep the fans running for
cooling. Keep one CC pump running.
Note: All the three CC pumps shall be put into operation on rotation
periodically
8.1.3
When the boiler water temperature comes down to 95 deg.C, stop the CC pump
and drain the boiler in the hot condition to the plant’s water disposal system, by
keeping open the drain valves fully.(without throttling).The effluent is diluted
with plenty of service water.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
12 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
8.2
HOT WATER RINSE
8.2.1
Once the draining is complete Boiler is refilled with DM water. Boiler is lit up
and the Boiler water temperature is gradually raised to 130-140 0C. Then the
Boiler is tripped and Fans are kept running for cooling.
8.2.2
During all rinsing operations (hot & cold) all the CC pumps are to be made
ready and operated in rotation.
8.2.3
The running CC pump is stopped after 30 minutes and Boiler is drained in hot
condition to the plant drain system by keeping the drain valves wide open
(without any throttling). The effluent is diluted with service water so as to bring
pH and PO4 in the effluent below 7.5 and 10 ppm respectively.
8.3
COLD WATER RINSE
8.3.1
Cold water rinsing is done using fill and dump method. Draining is done in the
plant drain system. pH of the rinsed effluent is monitored during draining. The
rinsing operation is continued until pH of the effluent is almost equal to pH of
inlet water used for rinsing. All CC pumps are run one by one for proper
rinsing.
8.3.2
All sampling and blow down lines are flushed. All temperature / pressure
measurements relevant to the process are monitored in UCB for their reliability.
8.4
ACID CLEANING & PASSIVATION
8.4.1
Required quantity of ammoniated EDTA (40% wt / wt) solution is kept ready in
the EDTA storage tank.
8.4.2
The inhibitors “BHELMAX” & “BHELSOL”, Hydrazine hydrate and ammonia
for addition in the Chemical dissolving tank are also made available near the
mixing tank.
8.4.3
All the Boiler Blow down valves are kept shut and drum vent valves & start up
vent are kept open during Boiler filling.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
13 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
8.4.4
40 Cu.m of DM water is drawn in the mixing tank. The temporary chemical fill
pump is started and system put into recirculation. Required quantity of
Ammoniated EDTA (40% wt/wt) solution is transferred from the EDTA
storage tank to the mixing tank. The EDTA concentration in the mixing tank is
checked. Transferring of the EDTA solution is stopped when the EDTA
concentration reaches 3 + 1% by weight. Required quantity of Hydrazine
hydrate and inhibitors (BHELMAX & BHELSOL) are also added.
Recirculation is done till all the chemicals are uniformly mixed up. With this
one batch of EDTA Chemical solution is ready for filling into the Boiler.
8.4.5
The approximate quantities of various chemicals that are to be mixed per batch
of 40 m3 is :
1. EDTA ammoniated (40 % ) concentrate : 3 to 4 m3
2. BHELMAX
: 60 kgs
3. BHELSOL
: 60 lit
4. N2H4.H2O (80%)
: 60 litres
8.4.6
Ammonia is added if required to adjust the pH between 9.0 and 9.8. DM water
is used to make up to 40 m3.
8.4.7
This solution is filled into the Boiler through Low Point drain header with the
temporary chemical fill pump. Fill the boiler up to +200 mm from the normal
working level in the drum. Start the middle CC pump for thorough mix up of
the chemical solution for 30 minutes. Check the boiler water sample.
8.4.8
The cleaning solution is quite harmless in respect of corrosion and hence there
is no time limitation for filling the Boiler and retaining the solution inside the
Boiler.
8.4.9
Preparation of Chemical solution and batch filling is repeated as explained in
point no 8.4.4 till the solution level in the Drum reaches the center line of the
gauge glass.
The composition of the filling solution is:
EDTA content
:
3 + 1% W/v
Hydrazine
:
1000 ppm (min)
pH
:
9.0 to 9.8
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
14 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
8.4.10
The Boiler is lighted up as per normal operating procedure with minimum
firing rate (say 2 oil guns in AB elevation)
8.4.11
The Drum and super heater vents are closed when steaming starts, say at 1 kg /
sq. cm. pressure in the Drum. SH start up vents are kept crack open.
8.4.12
The drain valve in SH Header # 1 is kept in crack opened condition.
8.4.13
The time at which the temperature of Boiler water reaches 110 0C is noted.
8.4.14
Raising of Boiler water temperature is continued till temp reaches140 0C.
8.4.15
Once the temperature of Boiler water reaches 140 0C, the firing rate is
controlled in such a way that the Boiler water temperature is maintained at 140
- 145 0C, for a minimum period of 4 hours. Then the Boiler is tripped but
running of CC pump is continued.
8.4.16
The ID & FD Fans are allowed to run to bring down the Boiler water
temperature. In case it appears that the results of iron concentration may not
level out when temperature is expected to be 110 0C, ID/FD fans are stopped
suitably during the cooling down phase & Boiler is boxed up with CC pump
running and kept in this condition to achieve the EDTA contact period of 8
hours with temperature exceeding 1100C.
8.4.17
Samples are taken at every 30 minutes interval from the sampling points at
locations given in article 7.3 from the time when the temperature in the system
had reached 1100 C and analysed for pH, EDTA concentration and Iron content.
8.4.18
After attaining the completion criteria of pickling process, as per article 9.0, the
system is allowed to cool with the ID & FD Fans in operation (ID & FD Fans
are to be restarted, in case they have been stopped to meet the completion
criteria, to bring down the Boiler water temperature). Open the Drum air vents
when the pressure reaches 1 kg/sq.cm.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
15 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
8.4.19
Boiler water temperature & Water Wall metal temperature at the locations
indicated as per 7.2 are to be measured and logged.
8.4.20
When the temperature comes down to 950C the running CC pump is stopped
and the system is drained completely in hot condition to the effluent pit by
opening all the drain valves.
8.5
8.5.1
8.5.2
TREATED DM WATER RINSE
Prepare a blended solution of ammonia & Hydrazine with calculated
quantities in the dissolving tank in order to achieve a solution pH 9.0 to 9.5
and hydrazine content 50 ppm in the DM water being filled in the boiler.
Fill the boiler with the above treated DM water through low point drains
and economizer as practiced earlier, up to just above the centre gauge glass.
8.5.3
Start the middle CC pump and light up the boiler as per O&M Instruction.
Drum level will drop after starting the CC pump. Again fill the boiler with
treated DM water solution to make up the level up to 100 mm above NWL.
8.5.4
Raise boiler water temperature up to 110 deg .C and then shut down the
boiler. Allow the boiler to cool down naturally. When the boiler water
temperature comes down to 95 deg C. drain the boiler in hot condition to
plant drain and allow the system for natural aeration
8.5.5
Boiler Drum manhole is opened for removal of Coupons. Manually clean the
drums if required.
8.5.6
Lower drums manholes are opened for inspection and cleaned manually, if
required.
8.5.7
Restore the boiler and prepare it for regular operation for steam blowing,
safety valve floating etc.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
16 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
8.6
INSPECTION
8.6.1
The test coupons placed at identified locations are taken out. All coupons
should be free of deposits and should have uniform coating of the protective
layer.
8.6.2
The Drum internal surface is visually inspected for uniform smooth coating of
protective layer.
8.6.3
The ring headers will be inspected and loose debris if any, will be removed.
9.0
COMPLETION CRITERIA
9. 1
COLD RINSE AFTER ALKALI FLUSHING
9.1.1
The rinsing operation is continued until pH of the effluent is almost equal to pH
of inlet water used for rinsing.
9.2
EDTA CLEANING
9.2.1
Cleaning process is to be continued till iron concentration in three consecutive
samples show equilibrium status.
9.2.2
When the iron concentration in the cleaning solution is constant it indicates that
all the oxides have been dissolved. However, a minimum EDTA contact period
of 6 hours from the time of attaining the required temperature (110 0C) shall be
allowed.
9.2.3
If the iron concentration values do not level out and attain equilibrium status,
regardless of analytical results, the EDTA contact period with temperature
exceeding 1100C shall not be allowed for more than 8 hours (approx).
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
17 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
10.0
WASTE TREATMENT & DISPOSAL
10.1
Treatment and disposal of the waste and effluents of the chemical cleaning
process should comply with the requirements / stipulations of State Pollution
Control Board norms.
10.2
Effluent of Hot DM water flushing should be drained into plant normal drain.
10.3
The spent EDTA chemical solution after the cleaning process is drained into the
designated pit. The pH of the effluent will be in the range of 8.5 to 9.0 and
hence no treatment for pH adjustment is required as it would meet the pH
requirement for disposal.
10.4
Compressed air is used to destroy the residual Hydrazine & organics and the
effluent may be disposed after aeration for 10 days, as per state pollution
control board norms. Effluent may be disposed to ash dyke in installments
through existing ash slurry system (The organic chemical is completely biodegradable).
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
18 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
Status
11.0
APPENDIX
11.1
NOTE
11.1.1
Drains should be provided at lowest points of temporary piping.
11.1.2
All temporary connections to Boiler should be of good quality. They will be
hydraulically tested at 14 kg/cm2 with the temporary boiler filling pump.
11.1.3
Service water supply should be available near the pump operating areas.
1.1.4
Additional Check lists / Modifications in the layout, if found necessary, may
be made at site in consultation with site Commissioning In-charge.
11.1.5
All the sampling points along with sample coolers and the temperature
measurement points with necessary thermocouples shall be provided as
indicated in 7.3 & 7.2 respectively.
Signatures
NTPC
BHEL
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
LOG SHEET
PROJECT :
DATE :
/
/
UNIT NO. :
ACTIVITY :
I.
EDTA ACID CLEANING AND PASSIVATION
ADDITION OF CHEMICALS
____________________________________________________________________
Sl. No. DATE TIME
NAME OF CHEMICAL ADDED
QUANTITY
_____________________________________________________________________
II.
ANALYTICAL DATA
_____________
Sl.
DATE
No.
1.
2.
3.
4.
5.
_________________________________________________
TIME
SAMPLE POINT
TOTAL EDTA
IRON
pH
hrs.
%
ppm
____________________________________________________________________
Signatures.
BHEL
NTPC
Sheet
19 of 25
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
20 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
PROCEDURE FOR DETERMINATION OF TOTAL EDTA CONCENTRATION IN PROCESS
SOLUTION DURING CHEMICAL CLEANING
1. PRINCIPLE
EDTA reacts with Zirconium ions under strong acid conditions to form a chelate. The end
point of the titration is indicated by a Xylenol orange indicator.
2. REAGENTS AND APPARATUS REQUIRED
APPARATUS
1.
2.
3.
4.
Erlenmeyer flask 300 ml capacity
Pipettes
Hot plate
Magnetic stirrer
REAGENTS
1. Hydrochloric acid (conc.)
2. Standard Zirconium oxy chloride (ZrOCl2. 8H2O) 0.1 M solution in 1 N HCl
(Take a 1000 ml volumetric flask and add 32.25 gram of ZrOCl2.8 H2O and add
DM water to about 500 ml. To this add 85 ml of conc. HCl. Make up to 1000 ml mark with
DM water and mix well)
3. Ascorbic acid
4. Xylenol orange indicator
3. TEST PROCEDURE
1.
2.
3.
4.
Pipette out 10 cc of the water sample into a 300 ml Erlenmeyer Flask.
Add 10 ml of conc. HCl ( the pH value is about 1.0)
Add a spatula of ascorbic acid.
Boil of the solvent on the heating plate for about 5 minutes.(The yellow colour of the ferric
ion should disappear due to reduction to ferrous iron.
5. Immediately after the addition of 0.05 ml of 0.05 % xylenol orange indicator the sample is
titrated with 0.1M ZrOCl2 until the colour changes from yellow to red violet; The colour
changes from yellow to red violet. The colour change shall remain constant for at least 3 min.
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
21 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
4.
CALCULATION
The total EDTA concentration
% = Volume of 0.1M ZrOCl2 consumed x 0.292
PROCEDURE FOR THE DETERMINATION OF IRON CONCENTRATION
IN WATER SAMPLES DURING CHEMICAL CLEANING.
1. APPARATUS REQUIRED
1. Spectrophotometer.
2. Hot plate
3. Volumetric flasks
4. Pipettes
2. REAGENTS REQUIRED
1. Thioglycolic acid (pure Grade)
2. Ammonia solution (25%) AR Grade
3. TEST METHOD
1.
2.
3.
4.
pipette out 25 ml of the water sample into a 50 ml capacity volumetric flask.
Add 2 ml of Thioglycolic acid using pro-pipette. Mix well
Heat it to 70 – 80 deg C for about 10 minutes.
Cool it to room temperature and make it up with DM water to the 50 ml mark and mix
well.
5. Measure the extinction of the sample against a blank using DM water treated as the
sample at 532.5 nm using Spectrophotometer.
6. Plot a curve taking standard iron solution and measuring the extinction in the same way as
that of the water sample.
7. Read the iron concentration of the sample from the calibration graph plotted.
Alternatively,
Pre-calibrated spectrophotometer (HACH USA/ Lovibond ) with appropriate reagent for iron can be
used.
NTPC - SIMHADRI
Stage – II (2 X 500 MW)
BHEL Ref no.: PS:TSX :180 : 00 :10
NTPC Ref no :COS-COMM-SIM-Commg-PRO/036
Sheet
22 of 25
Plant Area: BOILER
PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA
ESTIMATION OF HYDRAZINE
1. REAGENTS
Standard Potassium bromate 0.1 N
Dissolve 2.7836 gram of Potassium bromate (KbrO3) and 10 gram of Potassium
bromide (KBr) in DM / Distilled water and make up to 1000 ml.
0.1 % Methyl orange indicator solution.
Hydrchloric acid (conc.) AR.
2. PROCEDURE
o Place 10 ml of sample in a titration flask.
o Add 10 ml of conc. HCl.
o Add about 5 drops of Methyl orang indicator.
o Titrate with standard KbrO3 titrant to the first appearance of yellow colour.
3. CALCULATION
Hydrazine as N2H4 in ppm
= Titre value x 80
