Paper 6 Chem Cleaning Edta Bhel

Advance Techniques in Boiler Chemical Cleaning

Chemical Cleaning C leaning of o f Boilers w ith EDTA E DTA

By: HC Madan SS Chauhan Dhruv Garg Bharat Bha rat Hea Heavy vy Ele Electr ctrica icals ls Lim Limite ited d

1

Agenda 1

Need for Chemical C hemical Cleaning C leaning of Boilers

2

W hat is EDTA ED TA Cleaning? Cle aning?

3

BHEL’s Experience w ith EDTA EDT A Cleaning

4

EDTA ED TA Cleaning Clea ning P rocess

5

E DT DTA A visv is-àà-vi vis s HC HCll Clea leaning– ning– Adva Advanta ntages ges

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Conclusion 2

Bharat Bha rat Hea Heavy vy Ele Electr ctrica icals ls Lim Limite ited d

Need for Chemical C hemical Cleaning C leaning of Boilers

Bharat Bha rat Hea Heavy vy Ele Electr ctrica icals ls Lim Limite ited d

Need for Chemical Cleaning of Boilers? 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. Bharat Heavy Electricals Limited

4

Need for Chemical Cleaning of Boilers? P re-operative Chemical Cleaning System •

Evaporator System  Economizer  Downcomers  Bottom Ring Headers  Water Walls  Boiler Drum (Only water touched surface)

Bharat Heavy Electricals Limited

5

Need for Chemical Cleaning of Boilers? Iron metal surface with corrosion layers


6

W hat is EDTA Cleaning?


7

W hat 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.


8

EDTA and EDTA-Fe Complex Structure EDTA


EDTA-Fe Complex

9

EDTA P ickling & its Reaction


10

Magnetite Layer •

•

•

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.


11

BHEL’s Experience w ith EDTA Cleaning


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EDTA P rocess - W orld Scenario • EDTA process is at present executed by : 

Dow chemical Co – USA Halliburton Services – UK



Alstom, MHI, & Siemens



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


13

EDTA P rocess - W orld Scenario • 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.


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Inhibitors • EDTA Process developed by R&D Centre of BHEL-Trichy; involved in-house development of inhibitors:  BHEL MAX  BHEL 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. Bharat Heavy Electricals Limited

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Experience w ith EDTA Cleaning • 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. Y ear

No. of P rojects

2003 – 2004

1

2004 – 2005

3

2005 – 2006

3

2006 – 2007

7

2007 - 2008

13

2008 - 2009

16

Total

43


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Experience w ith EDTA Cleaning Rating wise – 2003-04 to 2008-09 (upto Feb 2009) Rating

No. of P rojects

500 MW

4

250 MW

22

210 MW

9

75 / 120 / 125 MW

8

Total

43


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Exceptions during reigns of EDTA P rocess Besides EDTA Cleaning, BHEL has also conducted HCl cleaning 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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P rojects expected in 2009 -10

Rating

No. of P rojects

500 MW

9

250 MW

11

210 MW

1

125 MW

6

Total

27


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EDTA Cleaning P rocess


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EDTA Cleaning P rocess 

Alkali Flushing   



Alkali Flushing Hot Water Flushing Cold Water Rinse

EDTA Cleaning  

EDTA Pickling & Passivation Treated DM Water Rinsing



Inspection



SH Back Flushing


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EDTA Cleaning P rocess Alkali Flushing - P urpose 

Alkali 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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EDTA Cleaning P rocess Alkali Flushing- P rocedure 

Alkali Flushing  Alkali 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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EDTA Cleaning P rocess Alkali Flushing- P rocedure (Contd..) 

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



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


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EDTA Cleaning P rocess P reparing EDTA Solution EDTA solution is prepared for total boiler volume by mixing. 1.EDTA Ammoniated (40%) 2.BHEL MAX (inhibitor) 3.BHEL SOL (inhibitor) 4.Hydrazine hydrate 5.Ammonia


: : : : :

4% 0.15-0.2% w/v 0.15-0.2% v/v 1000 ppm for setting pH as 9.5-9.8

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EDTA Cleaning P rocess EDTA P ickling and P assivation 

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 ½ an 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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EDTA Cleaning P rocess Treated DM W ater 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 120 C.



Boiler is tripped and allowed to cool. When the temperature comes down to 95 C, the solution is drained.

⁰

⁰


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Inspection   



Boiler drum Bottom ring headers Water wall tubes

Super h eater back flushing Super 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 P rocess EDTA Cleaning Results


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EDTA Cleaning P rocess EDTA Cleaning Results


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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 P rocess • Preliminary Cleaning – Alkali Cleaning  Hot

Water Flushing  Alkali Boil-out  Cold Water Rinsing

• Acid Cleaning  HCl

Cleaning  DM Water Rinsing  Citric Acid Rinsing  DM Water Rinsing  Neutralization  Passivation (1st and 2nd Stage)

• Inspection Bharat Heavy Electricals Limited

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EDTA vis-à-vis HCl Cleaning–Advantages Disadvantages of HCl Cleaning P rocess • 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 in green 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 vis-à-vis HCl Cleaning– Advantages EDTA Cleaning– Advantages •



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

•

Process advantages



Use 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 vis-à-vis HCl Cleaning– Advantages EDTA Cleaning– Advantages •

Process advantages (contd.)



Less temporary piping required



Less number of chemicals required.



Ease of handling.



Effluent treatment easy.

•

Other advantages



Economical.


36

Conclusion


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Conclusion • 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.


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Paper 6 Chem Cleaning Edta Bhel

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