Chemical Analysis During EDTA Activity

7/30/2019 Chemical Analysis During EDTA Activity

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TECHNICALDOCUMENT

ONCHEMICALANALYSISDURINGCHEMICALCLEANINGOF

BOILERUSINGEDTA

DocumentNo.:PWR/TSX/BLR/02/269/00/12

BHARATHEAVY

ELECTRICALS

LIMITED

POWERSECTORTECHNICALSERVICESKribhcoBhawan,A810,Sector1,

Noida201301.


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TECHNICALDOCUMENTONCHEMICALANALYSISDURING

CHEMICALCLEANINGOFBOILERUSINGEDTA

BHARATHEAVYELECTRICALSLIMITEDPOWER

SECTOR

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DOCUMENTNO:PWR/TSX/BLR/02/269/00/12


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PROCEDUREFORCHEMICALANALYSISDURING



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DOCUMENTNO.:PWR/TSX/BLR/02/269/00/12 1

Introduction

BHEL has adopted procedure of Ammoniated EDTA with initial concentration of 4 1%

for Chemical Cleaning of Boiler. The chemical cleaning process and chemicalformulations used for each step is, as outlined below:

S. No. Step Chemical Formulation Completion Criteria

1 Preliminary Cleaning Step

1.1 Alkali Flushing Tri Sodium Phospahte (1000 ppm)

Di Sodium Phospahte (500 ppm)

Achieving drum watertemperature of 140C

1.2 Hot Water Flushing Nil Achieving drum watertemperature of 140C

1.3 Cold Water Flushing Nil Phosphate < 10 ppm

and

pH 7.0

2 Acid Pickl ing Step

2.1 EDTA Pickling Ammoniated EDTA (4 1%)

Hydrazine (1000 ppm)

BHELmax (0.15% w/w)

BHELsol (0.15% w/v)

Ammonia (to maintain pH: 9.2 9.8)

Iron Conc. stabilizes inthree concurrent values

or

EDTA contact time of 8hrs. at temperature

above 110C

2.2 Treated DM WaterRinsing

Hydrazine (200 ppm)

Ammonia (to maintain pH: 9.2 9.8)

None

The quality and quantity of chemicals required for Chemical Cleaning of Boiler using

EDTA is as per Appendix I.


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Chemical Analysis

Chemical analysis is carried out to monitor and control the chemical parameters of the

chemical cleaning process for ensuring safe and efficient chemical cleaning of boiler.Following chemical parameters are monitored during the process:

Phosphate Concentration

pH

Total EDTA Concentration

Hydrazine Concentration

Iron Concentration

The chemical analysis to be carried out during various steps of Chemical Cleaning of

Boiler using EDTA is listed as below:

Chemical Cleaning Step

1. Cold Water Rinsing

2. EDTA solution batches for Boiler

filling

3. EDTA Pickling step

4. Boiler filling for Treated DM

Water Rinsing

Chemical Analysis to be carried out

a) Phosphate Concentration

b) pH

a) Total EDTA Concentration

b) Hydrazine Concentration

c) pH

a) Total EDTA Concentration

b) Iron Concentration

c) pH

a) Hydrazine Concentration

b) pH

The quality and quantity of chemicals required for chemical analysis during Chemical

Cleaning of Boiler using EDTA is as per Appendix II.

The list of lab wares and other materials required for chemical analysis during Chemical

Cleaning of Boiler using EDTA is as per Appendix III.


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Chemical Analysis Procedures

1. Determination of Phosphate Concentration

(Using Spectrophotometer)

1.1. Significance:

It can be measured to estimate phosphate concentration in the system during

Alkali Flushing, Hot Water Rinsing and Cold Water Rinsing. Its measurement is

significant during Cold Water Rinsing for declaring its completion i.e. PO43-

< 10

ppm.

1.2. Principle:

Spectrophotometer works on the principle of absorption of light by elements/ions present in a solution when it passes through the solution. Each element/

ion absorbs a specific wavelength of light which is characteristic to it. Thus

when a light beam passes through a solution, element/ ion present in the

solution absorbs its particular wavelength of light and thus intensity of that

particular wavelength of light decreases after passing through the solution. The

change in intensity indicates the amount of the particular element present in the

solution.

1.3. Apparatus and Reagents Required:

1.3.1. Apparatus:

a. Spectrophotometer Instrument with its kit; preferably HACH DR890

b. Pipette

c. Volumetric Flask

1.4. Procedure:

1.4.1. Take the sample and dilute it 10 times. The dilution factor has to be

chosen to get the value in the range of 0.5 2.9 ppm.

1.4.2. Take Spectrophotometers sample bottle and fill it with DM Water up tothe 20 ml mark.

1.4.3. Place it in Spectrophotometer and put its cap.


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1.4.4. Switch on the Spectrophotometer and choose Function for

determination of Phosphate concentration (in case of other

spectrophotometer than HACH DR 890; kindly refer the procedure

provided by the instrument manufacturer).

1.4.5. Press 0 (or test button) for tare setting.

1.4.6. Take out the sample bottle and dont switch off the Spectrophotometer.

1.4.7. Now take the diluted sample in the sample bottle up to the 20 ml mark.

1.4.8. Place it in the Spectrophotometer and put its cap.

1.4.9. Now press the test button and allow it for 3 minutes of testing time.

1.4.10. After that, Phosphate concentration of the diluted sample will be

displayed in the Spectrophotometer display.

1.4.11. If the value is in the range of 0.5 2.9 ppm, then it should be multiplied

with the dilution factor and we will get the Phosphate concentration for

the sample.

1.4.12. If the value is either less than 0.5 ppm or more than 2.9 ppm then the

dilution factor of the sample has to be changed and testing to be

repeated.

1.5. Calculation:

Phosphate Concentration, ppm = Spectrophotometer X DilutionReading Factor


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2. Determination of Total EDTA Concentration

2.1. Significance:

It signifies the total active EDTA available in the solution. It includes free EDTA

as well as EDTA that has reacted with iron present in the system. It is checked

during batch making to ensure initial EDTA concentration and during the

pickling step to ensure sufficient active EDTA is available in the solution.

2.2. Principle:

EDTA reacts with Zirconium ions under strong acidic conditions to form a

chelate. Thus, total EDTA concentration is determined by complexometric

titration of EDTA solution with Zirconium Oxy-chloride solution and Xylenol

Orange solution as an indicator for indicating the end point of this titration.

2.3. Titrant & Indicator:

a. Titrant : 0.1 M Standard Zirconium Oxy-chloride solution in 1 N HCl

b. Indicator: 0.05% Xylenol Orange solution


2.4.1. Apparatus:

a. Erlenmeyer flask (250 ml capacity)

b. Pipette

c. Hot plate

d. Test tube

e. Spatula

f. Burette

g. Filter paper

2.4.2. Reagents:

a. Hydrochloric acid (conc.)

b. Ascorbic acid

c. 0.1 M Standard Zirconium Oxy-chloride solution in 1 N HCl

d. 0.05% Xylenol Orange solution


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2.5. Titration Procedure:

2.5.1. Take about 100 ml of DM water into a 250 ml Erlenmeyer flask.

2.5.2. Pipette 5 ml of the sample to the flask.2.5.3. Add 5 ml (or half test tube) of conc. HCl (1:1) to the flask.

2.5.4. Add a spatula of ascorbic acid to the flask.

2.5.5. Boil off the solvent on the heating plate for about 5 minutes (yellow

colour of the ferric ion should disappear due to reduction to ferrous iron).

2.5.6. Allow the solution to cool.

2.5.7. Add 5 to 6 drops of 0.05% Xylenol Orange indicator to the flask and

immediately titrate it with 0.1M ZrOCl2 until the colour changes from

yellow to red violet (colour change shall persist for at least 3 min).

2.6. Calculation :

EDTA (w/v), % = Titre Value X 0.584


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3. Determination of Iron concentration

(Using Spectrophotometer)

3.1. Significance:

It signifies the iron picked up by the EDTA solution. It is important to monitor

iron concentration as it tells the completion of the process as well as indicates

the healthiness of the process. If iron concentration increases very rapidly and

is continuing to increase rapidly, then it indicates failure of inhibitors and EDTA

solution should be drained immediately to save the boiler.

3.2. Principle:

Spectrophotometer works on the principle of absorption of light by elements/

ions present in a solution when it passes through the solution. Each elementabsorbs a specific wavelength of light which is characteristic to it. Thus when a

light beam passes through a solution, element present in the solution absorbs

its particular wavelength of light and thus intensity of that particular wavelength

of light decreases after passing through the solution. The change in intensity

indicates the amount of the particular element present in the solution.


3.3.1. Apparatus:

a. Spectrophotometer Instrument with its kit; preferably HACH DR890

b. Pipette

c. Volumetric Flask

3.3.2. Reagents:

a. Ferrover reagent

3.4. Procedure:

3.4.1. Take the sample and dilute it 1000 times. The dilution factor has to be

chosen to get the value in the range of 0.5 2.9.

3.4.2. Take Spectrophotometers sample bottle and fill it with DM Water up to

the 20 ml mark.

3.4.3. Place it in Spectrophotometer and put its cap.


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3.4.4. Switch on the Spectrophotometer and choose Function for determination

of Iron concentration (in case of other spectrophotometer other than

HACH DR 890; kindly refer the procedure provided by the instrument

manufacturer).

3.4.5. Press 0 (test button) for tare setting.

3.4.6. Take out the sample bottle and dont switch off the Spectrophotometer.

3.4.7. Now take the diluted sample in the sample bottle up to the 20 ml mark.

3.4.8. To it add a pouch of Ferrover reagent and shake well to mix it. A brown

color in the sample should be observed.

3.4.9. Place it in the Spectrophotometer and put its cap.

3.4.10. Now press the test button and allow it for 3 minutes of testing time.

3.4.11. After that, Iron concentration of the diluted sample will be displayed in

the Spectrophotometer display.

3.4.12. If the value is in the range of 0.5 2.9, then it should be multiplied with

the dilution factor and we will get the Iron concentration for the sample.

3.4.13. If the value is either less than 0.5 or more than 2.9 then the dilution

factor of the sample has to be changed and testing to be repeated.

3.5. Calculation:

Iron Concentration, ppm = Spectrophotometer X DilutionReading Factor


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4. Determination of Hydrazine concentration

4.1. Significance:

Hydrazine concentration is measured during EDTA batch making and Treated

DM Water Rinse filling to maintain the required level of hydrazine in the system.

4.2. Titrant & Indicator:

a. Titrant : 0.1 N Standard Potassium Bromate solution

b. Indicator: 0.1% Methyl Orange solution


4.3.1. Apparatus:

a. Erlenmeyer flask (250 ml capacity)

b. Pipette

c. Test tube

d. Burette

e. Filter paper

4.3.2. Reagents:

a. Hydrochloric acid (conc.)

b. 0.1 N Standard Potassium Bromate solution

c. 0.1 % Methyl Orange solution

4.4. Procedure:

4.4.1. Pipette 10 ml of the sample into a 250 ml Erlenmeyer flask.

4.4.2. Add 5 ml (or half test tube) of conc. HCl (1:1) to the flask.

4.4.3. Add 5 to 6 drops of 0.1% Methyl Orange indicator to the flask and

immediately titrate it with 0.1N KBrO3 until the colour changes from pink

to yellow.

4.5. Calculation:

Hydrazine as N2H4, ppm = Titre value X 80


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5. Determination of pH

5.1. Significance

It indicates the pH or acidity/ basicity of the system as chemical cleaning is to

be carried out in basic medium with pH around 9.2 9.8. It is measured to

verify and maintain the required basicity in the system. pH is one of the

completion criteria for Cold Water Rinsing step.


5.2.1. Apparatus:

a. pH meter

b. Beaker (50 ml)

5.2.2. Reagents:

a. Buffer solutions

5.3. Procedure:

5.3.1. Take sample in beaker up to around half level of the beaker.

5.3.2. Take out the pH meter probe from the buffer solution and wash it with

DM water.

5.3.3. Dip the pH meter probe into the sample solution.

5.3.4. Note the reading for pH.

5.3.5. Take out the pH meter probe from the sample solution and wash it with

DM water and then put it back into the buffer solution.


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Appendix I

List of Chemicals required for Chemical Cleaning of Boiler using EDTA

S.No. Chemicals&ChemicalFormulae Standard 500MW 250MW 210MW 125M

1. Trisodium Phosphate (TSP)

Na3(PO4).12H2O

IS 566 1991 400 kg. 250 kg. 250 kg. 125 kg

2. Disodium Phosphate (DSP)

Na2H(PO4).7H2O

IS 573 1992 200 kg. 125 kg. 125 kg. 65 kg

3. Ammoniated EDTA

C6H12N2O8(NH4)4

---- 42 M.T. 22 M.T. 21 M.T. 18 M.T

4. Ammonia

NH3

IS 799 1990 1500 ltrs. 1000 ltrs. 1000 ltrs. 600 ltr

5. Hydrazine

N2H4.H2O

IS 12086 1992 1500 ltrs. 1000 ltrs. 1000 ltrs. 600 ltr

6. BHELmax ---- 700 kg. 350 kg. 350 kg. 250 kg

7. BHELsol ---- 700 ltrs. 350 ltrs. 350 ltrs. 250 ltr


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Appendix II

List of Chemicals/ Reagents required for chemical analysis purpose

S. No. Chemicals/ Reagents Grade Quantity

1. Ascorbic Acid AR 100 g

2. Conc. HCl AR 500 ml

3. Buffer Solutions for pH meter -- 100 ml

4. Ferrover Reagent -- 60 pouches

5. Zirconium Oxy-chloride AR 100 g

6. Xylenol Orange AR 25 g

7. Hydroxylamine Hydrochloride AR 50 g

8. Potassium Bromate AR 50 g

9. Potassium Bromide AR 50 g

10. Methyl Orange AR 100 g


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Appendix III

List of Lab wares required for chemical analysis purpose

S. No. Apparatus Capacity Quantity

1. Spectrophotometer; preferably HACHDR 890

-- 1

2. pH meter -- 1

3. Electronic Mass Balance -- 1

4. Erlenmeyer flask 250 ml 6

5. Pipettes, graduated 10 ml 2



8. Burette 50 ml 3

9. Beaker 100 ml 3

10. Volumetric flask 1000 ml 2



13. Measuring Cylinder 50 ml 2



16. Wash bottles 500 ml 3

17. DM water carboys 5 L 3

18. Plastic buckets 20 L 2

19. Plastic bottles (for DM Water) 500 ml/ 1000 ml 6


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S. No. Apparatus Capacity Quantity

20. Sample Bottles 500 ml 6

21. Funnel -- 2

22. Burette stand -- 2

23. Hot plate -- 1

24. Spatula -- 2

25. Filter paper (qualitative) -- 1 box

26. Electrical extension box 5 A sockets 3 points


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ED, PS-ER, Kolkata

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GM (Projects II), PS- SR, Chennai

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Engineering Heads

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Management Representatives

GM (Quality, Safety & MM), PS-HQ, Noida

AGM (Quality & SCT), PS-NR, Noida

Sr.DGM (Quality), PS-WR, Nagpur

AGM (Quality), PSER Kolkata

AGM (Quality & BE) SR Chennai

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CM (Ukai)

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CM (NTPC Mauda)

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CM (Avantha Power, J abua)

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Chemical Analysis During EDTA Activity

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