Chemical Cleaning of Boiler

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

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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



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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: 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 5. Hydrazine Hydrate

Quantity

40 tons

1800 litres



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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



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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



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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.



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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/ cm 2 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



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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

7.5

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. 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



Sheet 9 of 25


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 3 cemented neutralizing pit of volume 800 m 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



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Plant Area: BOILER PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA 2. Ensure free expansion of the furnace and duct and provision of expansion 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. Water and steam systems are ready for operation 10. Air and flue gas system ready for operation 3

11. Effluent treatment pit to hold approximately 800 m is ready 12. Drainage line to effluent treatment is ready 13. Readiness of MDBFP and Feed system (optional) 14. Drum water sampling system along with sample cooling arrangement 15. Availability of emergency supply for

Status



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Plant Area: BOILER PROCEDURE OF CHEMICAL CLEANING OF BOILER USING EDTA 25. Public address system at all operating locations, including telephone & 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

Status



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8.2

HOT WATER RINSE

8.2.1

Once the draining is complete Boiler is refilled with DM water. Boiler is lit up 0 and the Boiler water temperature is gradually raised to 130-140 C. 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 8.3.1

COLD WATER RINSE

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



Sheet 13 of 25


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 3 of 40 m is : 3 1. EDTA ammoniated (40 % ) concentrate : 3 to 4 m

8.4.6

2. BHELMAX

: 60 kgs

3. BHELSOL

: 60 lit

4. N2H4.H2O (80%)

: 60 litres

Ammonia is added if required to adjust the pH between 9.0 and 9.8. DM water 3 is used to make up to 40 m .



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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 C is noted.

8.4.14

Raising of Boiler water temperature is continued till temp reaches140 C.

8.4.15

Once the temperature of Boiler water reaches 140 C, the firing rate is controlled in such a way that the Boiler water temperature is maintained at 140 0 - 145 C, 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 0 level out when temperature is expected to be 110 C, ID/FD fans are stopped

0

0

0



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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 95 C 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

8.5.3

0

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. 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.



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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



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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).



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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 2 hydraulically tested at 14 kg/cm 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.



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

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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



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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



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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 (KbrO 3) 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.

Chemical Cleaning of Boiler

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