paper 6 chem cleaning edta bhel

Bharat Heavy Electricals Limited Power Sector: Technical Services

Advance Techniques in Boiler Chemical Cleaning

Chemical Cleaning of Boilers with EDTA

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By: HC MadanSS ChauhanDhruv Garg


Agenda

Need for Chemical Cleaning of Boilers1

What is EDTA Cleaning?

BHEL’s Experience with EDTA Cleaning

EDTA Cleaning Process

EDTA vis-à-vis HCl Cleaning– Advantages

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6 Conclusion

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Need for Chemical Cleaning of Boilers


Need for Chemical Cleaning of Boilers?

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Pre-operative• Maintaining steam quality at the turbine inlet.• Minimizing corrosion of the metal surface of

boiler.

Post-operative• Improving heat transfer in the system.

• Enhancing efficiency of the power plant.

• Minimizing under-deposit corrosion of the metal surface of boiler.

• Minimizing plant outage due to boiler tube failures.



Pre-operative Chemical Cleaning System• Evaporator System

EconomizerDowncomersBottom Ring HeadersWater WallsBoiler Drum (Only water touched surface)

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Iron metal surface with corrosion layers


What is EDTA Cleaning?

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What is EDTA?

EDTA or Ethylene Di-amine Tetra acetic Acid is a strong chelating agent having ability to form stable complexes with transition metal ions present in boiler such as of Iron and Copper etc.


EDTA and EDTA-Fe Complex Structure

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EDTA EDTA-Fe Complex


EDTA Pickling & its Reaction

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Magnetite Layer

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• A protective layer of Magnetite (Fe3O4) is formed on the water touched metal surfaces in the steam generator.

• Magnetite layer acts as a coherent media that stops further corrosion of the base metal.

• Magnetite is a combination of FeO and Fe2O3.


BHEL’s Experience with EDTA Cleaning

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• EDTA process is at present executed by : Dow chemical Co – USAHalliburton Services – UKAlstom, MHI, & Siemens

• Process details & chemical formulations especially inhibitor for the process are being held under proprietary rights by these companies.

EDTA Process - World Scenario


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• BHEL has joined the select band of few companies in the world to possess & establish this advanced cleaning process.

• BHEL has marked the giant leap by developing its own inhibitors and chemical formulations for EDTA Cleaning Process.

EDTA Process - World Scenario


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• EDTA Process developed by R&D Centre of BHEL-Trichy; involved in-house development of inhibitors:

BHEL MAXBHEL SOL

• These inhibitors are patented by BHEL:Patent Nos.: 177 & 332 / 2004

• These inhibitors act by forming an invariable layer between the base metal surface and the chemical solution as the deposits are removed.

Inhibitors


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• EDTA Cleaning Process was introduced in BHEL in 2003-2004.

• Chemical cleaning of boilers with EDTA completed in 43 projects of different ratings, till Feb 2009.

Year No. of Projects

2003 – 2004 1

2004 – 2005 3

2005 – 2006 3

2006 – 2007 7

2007 - 2008 13

2008 - 2009 16

Total 43

Experience with EDTA Cleaning


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Experience with EDTA Cleaning

Rating No. of Projects

500 MW 4

250 MW 22

210 MW 9

75 / 120 / 125 MW 8

Total 43

Rating wise –2003-04 to 2008-09 (upto Feb 2009)


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Exceptions during reigns of EDTA Process

Besides EDTA Cleaning, BHEL has also conducted HClcleaning at following 7 projects during the same period.

Rihand # 4 (500 MW)

Vindhyachal # 9 (500 MW)

Vindhyachal # 10 (500 MW)

Sipat # 4 (500 MW)

Sipat # 5 (500 MW)

Kahalgaon # 6 (500 MW)

Kahalgaon # 7 (500 MW)


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Projects expected in 2009-10

Rating No. of Projects

500 MW 9

250 MW 11

210 MW 1

125 MW 6

Total 27



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Alkali FlushingAlkali FlushingHot Water FlushingCold Water Rinse

EDTA CleaningEDTA Pickling & PassivationTreated DM Water Rinsing

Inspection

SH Back Flushing


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Alkali Flushing - PurposeAlkali Flushing

– Removes polar organic materials such as oil, grease etc. from the metal surface.

– Alkali reacts with polar organic materials to form soluble glycerols and salts.

– Loose deposits, dust etc. are also removed.– TSP and DSP is used as alkali.

Hot Water Flushing

Cold Water Rinse


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Alkali Flushing- Procedure

Alkali FlushingAlkali solution made by adding TSP(0.1%) & DSP (0.05%) with DM water.Solution is filled into boiler through bottom ring header & economizer drains up to NWL.Boiler is fired. Water temperature is raised to 140ºC and boiler tripped.Solution is allowed to cool till 95ºC and then drained.


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Alkali Flushing- Procedure (Contd..)

Hot Water FlushingSystem is filled with DM water and temperature raised to 1400C and allowed to cool to 950C and drained subsequently.

Cold Water RinseSystem is filled with DM water and drained. The process is repeated till phosphate level is less than 10 ppm.


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Preparing EDTA Solution

EDTA solution is prepared for total boiler volume by mixing.

1.EDTA Ammoniated (40%) : 4%2.BHEL MAX (inhibitor) : 0.15-0.2% w/v3.BHEL SOL (inhibitor) : 0.15-0.2% v/v4.Hydrazine hydrate : 1000 ppm5.Ammonia : for setting pH as 9.5-9.8


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EDTA Pickling and Passivation

The system is filled with EDTA solution upto drum NWL

The boiler is lighted up and temperature raised to 1400C and maintained for 4 hours and sample solution checked for iron, pH and EDTA concentration every ½an hour.

The boiler is tripped on achieving 3 consecutive readings of iron concentration.

The solution is allowed to cool till 950C and drained.


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Treated DM Water Rinsing

A solution of hydrazine (0.01-0.02%) and ammonia with DM water is prepared (pH 9.5 – 9.8) and the system is filled with this solution.

Boiler is fired and temperature raised to 120⁰C.

Boiler is tripped and allowed to cool. When the temperature comes down to 95⁰C, the solution is drained.


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InspectionBoiler drum Bottom ring headersWater wall tubes

Super heater back flushingSuper heater is filled with a solution of hydrazine (N2H4 >50 ppm) & Ammonia (pH>9.5) in DM water through SH drain header. When the solution comes through SH openings in the drum, the back flushing is continued for 10-30 minutes and drained.


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EDTA Cleaning Results


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EDTA vis-à-vis HCl Cleaning-Advantages

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EDTA vis-à-vis HCl Cleaning–Advantages

HCl Cleaning Process• Preliminary Cleaning – Alkali Cleaning

Hot Water FlushingAlkali Boil-outCold Water Rinsing

• Acid Cleaning HCl CleaningDM Water RinsingCitric Acid RinsingDM Water RinsingNeutralization Passivation (1st and 2nd Stage)

• Inspection


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EDTA vis-à-vis HCl Cleaning–Advantages

Disadvantages of HCl Cleaning Process• Lot of temporary piping required.

• More number of chemicals (12 Nos.) required.

• Nitrogen gas in huge volume & its piping system required.

• Auxiliary steam required in huge quantity, which is a problem ingreen field projects.

• DM water and fuel consumption is very high.

• Process handling is difficult and hazardous due to corrosive nature of chemicals.

• Large cycle time (17 days).

• Effluent treatment & disposal requires huge investments.


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EDTA Cleaning– Advantages

• Technological advantagesEDTA is a strong chelating agent with transition metal ions and hence has an efficient action as metal remover.

• Process advantagesUse of Nitrogen & its system is eliminated. Auxiliary steam is not required at all.DM water and fuel consumption is less.Shorter cycle time (5 days).



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EDTA Cleaning– Advantages

• Process advantages (contd.)Less temporary piping requiredLess number of chemicals required.Ease of handling.Effluent treatment easy.

• Other advantagesEconomical.



Conclusion

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• EDTA cleaning process ensures efficient cleaning and passivation of boiler internal surfaces.

• Inhibitor for EDTA cleaning process being used has been developed by BHEL. Inhibitors are patented as – “BHEL MAX” and “BHEL SOL”.

• EDTA Cleaning has obvious advantages over conventional HCl Cleaning with minimum effect on the base metal surface.

Conclusion


Thank you

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paper 6 chem cleaning edta bhel

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