Edta Cleaning Process

Advance Techniques in Boiler Chemical Cleaning

Chemical Cleaning of Boilers with EDTA (Ethylene Diamine Tetra Acetic Acid)

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By: BRIJRAJENGINEER (ABHIJEET PROJRCTS LTD,

| POWER | MINING | STEEL | FERRO ALLOYS | ROADS |

AgendaNeed for Chemical Cleaning of Boilers?1

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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1Need for Chemical Cleaning of Boilers?


Need for Chemical Cleaning of Boilers?

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Pre-operative• Maintaining steam quality in the system.

• Minimizing corrosion of the metal surface of the boiler.

Post-operative• Improving heat transfer in the system.

• Enhancing efficiency of the power plant.

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

• Minimizing plant outage due to boiler tube failures.



Pre-operative Chemical Cleaning System

• Evaporator System Economizer Down comers Bottom Ring Header Water Walls Boiler Drum (Only water touched surface)

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Iron metal surface with Corrosion layer


2What 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 metal ions present in the boiler such as of Iron and

Copper etc.

C10H16O8N2


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 is coherent in nature that stops further corrosion of the base metal.

• Magnetite is a combination of FeO and Fe2O3.

Fe + O2 FeO

4FeO + O2 2Fe2O3

6Fe2O3 + N2H4 4Fe3O4 + N2 + 2H2O


3BHEL’s Experience with EDTA Cleaning

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• 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.

EDTA Process - World Scenario


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

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

Inhibitors | POWER | MINING | STEEL | FERRO ALLOYS | ROADS |

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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

2009 - 2010 15

2010 – 2011 20

Total 78

Experience with EDTA Cleaning | POWER | MINING | STEEL | FERRO ALLOYS | ROADS |

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Experience with EDTA Cleaning

Rating No. of Projects

500 MW 24

250 MW 26

210 MW 10

75 / 120 / 125 MW 8

Total 78


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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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Exceptions during reigns of EDTA Process

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)


4EDTA Cleaning Process

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1. Alkali Flushing Alkali Flushing Hot Water Flushing Cold Water Rinsing

2. EDTA Cleaning EDTA Pickling & Passivation Treated DM Water Rinsing

3. Inspection

4. SH Back Flushing


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1. Alkali Flushing – Purpose

Alkali Flushing (TSP and DSP is used as alkali) Removes polar organic material such as oil,

grease etc. from the metal surface. Alkali reacts with polar organic materials to

form soluble glycerols and salts. Dirt & loose debris etc. are also removed.

Hot Water Flushing

Cold Water Flushing


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1. Alkali Flushing - Procedure

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 drum NWL. Boiler is fired. Water temperature is raised to

140ºC and boiler tripped. Solution is forced cool till 95ºC and then

drained.


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1. Alkali Flushing - Procedure (Contd.)

Hot Water Flushing System is filled with DM water and temperature

raised to 140ºC and then forced cool to 95ºC and drained subsequently.

Cold Water Rinsing System is filled with DM water and drained. The

process is repeated till phosphate level is less than 10 ppm and pH around 7 to 8.


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Preparing EDTA Solution

EDTA solution is prepared for total boiler volume by mixing.

1.Ammoniated EDTA (40%) : 4% (approx.)2.BHEL MAX (inhibitor) : 0.15-0.2% w/v3.BHEL SOL (inhibitor) : 0.15-0.2% v/v4.Hydrazine hydrate : 1000 ppm (min.)5.Ammonia : for achieving pH 9.5-9.8

2. EDTA Cleaning


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EDTA Pickling and Passivation

The system is filled with EDTA solution up to 100 mm below NWL of drum.

The boiler is lighted up and temperature raised to 140ºC and maintained for maximum 4 hours. Sample solution is checked for Iron, pH and EDTA concentration every 45 minutes.

The boiler is tripped either on achieving 3 consistent consecutive readings of Iron concentration or completion of 4 hours, whichever is earlier.

The solution is allowed to cool till 95ºC and drained.

2. EDTA Cleaning



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(Typical)



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EDTA Storage Tank



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EDTA Mixing Tank & Pumps


EDTA Cleaning ProcessSample Analysis of EDTA Solution


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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 120ºC.

Boiler is tripped and natural cooled. When the temperature comes down to 95ºC, the solution is drained.

2. EDTA Cleaning


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4. Super heater back flushing Super heater is filled with a solution of hydrazine

(N2H4 > 0.005 %) & 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.

3. Inspection Boiler Drum and Coupons Bottom ring header (Only for 500 MW units)


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EDTA Cleaning ProcessEDTA Cleaning Results


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EDTA Cleaning ProcessEDTA Cleaning Results


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EDTA Cleaning Results



EDTA Effluent Pit



EDTA Effluent Treatment by Aeration


5EDTA vis-à-vis HCl Cleaning - Advantages

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EDTA vis-à-vis HCl Cleaning–AdvantagesHCl Cleaning Process

1. Preliminary Cleaning – Alkali Cleaning Hot Water Flushing Alkali Boil-out Cold Water Rinsing

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

3. Inspection


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Parameter EDTA Cleaning HCl Cleaning

Iron pick-up mechanism

Strong chelating agent for metal ions

Dissolution action

Technological Advantage

Process Advantage


Viability for Green Field Project

Suitable as auxiliary steam is not required

Not suitable as auxiliary steam required

Cycle time 5-6 days 14-17 days

Magnetite layer More adherent Less adherent


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Chemicals required 7 chemicals 12 chemicals

DM Water consumption

Less More (4 times)

Fuel consumption Less More

Nitrogen & its systems

Not required Required

Temporary pipes & tanks

MS/CS piping and tanks required

Extensive piping and tanks required with Rubber lining

Process Advantage (contd.)


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Acid Handling Pumps

Not required Required

Process Handling Easy due to less hazardous chemicals

Difficult due to hazardous chemicals

Effluent treatment

Easy as volume of effluent is less and requires aeration only

Difficult as volume of effluent is more and requires chemical treatment

Process Cost Economical Costly

Process Advantage (contd.)


6Conclusion

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

• Inhibitors 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 | POWER | MINING | STEEL | FERRO ALLOYS | ROADS |

Thank you

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Edta Cleaning Process