Frequent Tube Failure in Grid Panel of CFBC

7/30/2019 Frequent Tube Failure in Grid Panel of CFBC

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Case Study onFrequent tube Failure of Grid

panel in CFBC Boiler

Presented by

S. SivakumarAGM- O&M Contracts

Cethar Vessels Ltd, Trichy


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CETHAR VESSELS LIMITED

Leading manufacture of AFBC , CFBC , WHRB for sponge iron kilnGas, cement kiln gas ,DG exhaust gas & supply of power plant onEPC basis for more than two decades .

Tied up with Riley Power Inc, USA for PC fired boilers of sub critical &super critical pressure. Collaboration with Riley / Siemens Benson

Technology for super critical PC boilers.

Collaboration with Siemens for Super Critical CFBC boilers.

Tied up with OJSC power machineries , Russia for turbine design andManufacturing.

Executing O & M contracts of captive power plants of any Capacitythrough Cethar energy ltd.


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Major projects under execution:

2x 135 MWe IPP with CFBC Boiler - M/s.Aryan Coal Beneficiation

2 x 350 MWe PF Fired Boiler - M/s.Ind Barath energy Ltd.

2 x 300 MWe PF Fired Boiler - M/s.Meenakshi energy Ltd.

2 x 150 MWe IPP with CFBC Boiler - M/s.Shree cement

2 x 135 MWe IPP with PF Fired Boiler - M/s.Vandana vidhuyut

2 x 60 MWe CFBC Boiler - M/s.Jayprakash associates

65 Boilers are under execution for IPP, CPP & Co-gen

10 IPP & Captive power plants are under execution


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Credentials

CVL had designed, manufactured, erected andcommissioned more than 1000 FBC boilers.

Based on our versatile experience duringoperation and maintenance, we have listed fewproblems faced and the causes, solution given

for the information to this elite league


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Case study I :

Reported issue:

Tube failure of grid panel in CFBC boiler


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BACKGROUND :

Plant capacity : 2 X 25MW CPP

Boiler capacity : 114 TPH

Type of firing : CFBC

Steam pressure : 88 Kg/cm

Steam temperature : 520 5 C

Grid tube size : 51.0 X 4.0 mm

location : 1,2,17,18,19,20,21,24,25,26th row from

combustor left side


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BACKGROUND :

Approx. service temperature : 300C

Boiler commissioned on : 20.08.2009

Tube failed on : (a) Tube No : 1, 2 -23.01.10

(b) Tube No : 19, 20, 21 -12.01.10

(c) Tube No: 24, 25, 26 -12.11.2009

(d) Tube No: 16, 17 -13.11.2009.

Approx. service period : 4 Months


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Observations

(A)Sample No. 17& 24 :

On inspection it is found that severe erosion withpuncture.

Transverse cracks with ID grooving were also noticed.

Transverse crack at

inner surface

Crack noticed by LPI

test


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ObservationsSample No. 20, 16, 1 & 2 :

Severe puncture with erosion was noticed


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ObservationsSample No. 19, 21 :

Erosion is found at 25 mm from one end.


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ObservationsSample No 26:

This tube length 320 mm have no crack indication.


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Failure Analysis

Dimensional Measurements :Diameter and thickness of grid panel tube sample

measured at various location and given below


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Failure Analysis

Chemical Analysis :

Spectroscopically chemical analysis of failed tubesample carried out. Values are given below


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Failure Analysis

Deposit analysis (24,26,19 & 21) :

F il A l i


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Failure Analysis

Hardness measurement :Hardness measurement using Rockwell B scale

was done on failed tubes. The values given below


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Failure Analysis

Metallographic Examination (Micro) :

Metallographical polishing is done in the region closer

& away from failure region and examined under

microscope


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Reasons for Failure

(A) Sample No. 24 & 17 :

Overheating of tube around Ac1 for prolonged period.

Fluctuating load.

Thermal Cyclic variation.


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Reasons for Failure

(B) Sample No. 19,20,21, 1 & 2 :

Erosion on outer surface of the tubes.

Secondary failures caused from other primary sources.


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Solution

Refractory was laid on the entire grid panel tube to a thickness of100mm to withstand thermal load variation.


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Conclusion

There is no grid panel tube failure till date after refractory laying.


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Case study 2:

Reported issue:

Excess coal consumption


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Plant design details:

Plant capacity : 1 X 8 MWe co-gen plant

Boiler capacity : 40 TPH

Type of firing : AFBC

Steam pressure : 68 ata

Steam temperature : 495 C


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Design Fuel Analysis

Moisture : 13.98%GCV : 6100 kcal/kg


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Plant visit was made, boiler operating data, fuel input were

collected and analyzed


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Boiler data:

Boiler operating capacity : 37.5 TPH

Steam pressure : 68.007 ata

Steam temperature : 495 C

Feed water temperature : 122C

Flue gas temperature leaving APH : 132C

O2 in flue gas : 4%


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Fired fuel analysis and efficiency

GCV : 3950 Kcal/kg

Moisture : 31.50%

Efficiency achieved : 81.7%

Reasons for lower Efficiency:

Excess fired fuel moisture comparing to design fuel

moisture

Lower GCV of fuel comparing to design

Loss in efficiency due to the above was 3.501%


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Conclusion:

Corrected efficiency is 85.2%

Fuel moisture to be controlled for achieving theguaranteed thermal Efficiency of the boiler

Expected Fuel saving by controlling moisture is 7.6TPD


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Any questions

please?

THANKSCVL

Documents

Frequent Tube Failure in Grid Panel of CFBC