Post on 14-Apr-2015
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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,
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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?
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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.
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Need for Chemical Cleaning of Boilers?
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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Need for Chemical Cleaning of Boilers?
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Iron metal surface with Corrosion layer
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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
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EDTA and EDTA-Fe Complex Structure
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EDTA EDTA-Fe Complex
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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
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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)
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4EDTA Cleaning Process
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EDTA Cleaning Process
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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EDTA Cleaning Process
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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EDTA Cleaning Process
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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EDTA Cleaning Process
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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EDTA Cleaning Process
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 Cleaning Process
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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EDTA Cleaning Process
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(Typical)
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EDTA Cleaning Process
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EDTA Storage Tank
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EDTA Cleaning Process
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EDTA Mixing Tank & Pumps
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EDTA Cleaning ProcessSample Analysis of EDTA Solution
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EDTA Cleaning Process
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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EDTA Cleaning Process
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 Process
EDTA Cleaning Results
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EDTA Cleaning Process
EDTA Effluent Pit
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EDTA Cleaning Process
EDTA Effluent Treatment by Aeration
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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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EDTA vis-à-vis HCl Cleaning– Advantages
Parameter EDTA Cleaning HCl Cleaning
Iron pick-up mechanism
Strong chelating agent for metal ions
Dissolution action
Technological Advantage
Process Advantage
Parameter EDTA Cleaning HCl Cleaning
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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EDTA vis-à-vis HCl Cleaning– Advantages
Parameter EDTA Cleaning HCl Cleaning
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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EDTA vis-à-vis HCl Cleaning– Advantages
Parameter EDTA Cleaning HCl Cleaning
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.)
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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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