Posted By: Vivek Gharote

June 18, 2016
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Overview

Unit Capacity and Details: 4x61.5 MW, Boiler: 250 TPH Wuxi make (Chinese) Turbine: 61.5 MW Dongfang make (Chinese) Issue: Sever problems were faced after commissioning of all the four units: 1. The un-burnt carbon % through bed ash and fly ash was significantly high. 2. Low Flue Gas ESP inlet temperature was testified, which in turn specified high boiler efficiency. 3. Station Heat Rate was on the higher side. Observation: 1. There was a huge difference between the inlet and outlet air pre-heater oxygen % in flue gas. The difference showed that there was more than 50 % of air ingress in air pre-heater. 2. Insufficient quantity of Primary and Secondary air was being supplied by the PA and SA fans; also the balance of Primary and Secondary air from right and left side of the furnace was unequal. 3. The achieved Primary and Secondary air temperatures were less than the design temperatures after APH. 4. There was improper fluidization in boiler, resulting in high specific coal consumption. 5. Insufficient Primary air flow to the furnace was leading to clinker formation causing frequent chocking at inlet pipe of bed ash coolers and failure of bed ash conveying system. Problem Rectification: In purview of the tribulations, decision was made to conduct APH leak test in all boilers. Following outcomes were attained: 1. Several tubes were found in damaged condition in all the four units (See Attached Photos) 2. Welding of all Air pre-heater bundles were incomplete at all four sides. Near about 256 meters out of 356.48 meters for all four Units. (See Attached Photos) 3. There were many holes at all the corners of the APH Rectification: 1. Tubes which were found in damaged condition were dummied from both ends. 2. Tube bundles were welded at all four sides. 3. Holes at the corners were repaired. Results after Rectification: 1. Improvement in Station Heat rate from around, 3300 Kcal/kwh to around 2750 Kcal/kwh 2. Decline in percentage of un-burnt in bed ash and fly ash from around 2.7 % to less than 1% and from 2.7% to less than 2 % respectively. 3. Increase in Primary air temperature from around 169 Deg Celsius to around 190 Deg Celsius 4. With same coal flow, reduction in power consumption of PA and SA fans, leading to energy saving of an average of 3444 kwh/day. 5. Improved PA and SA loading, leading to improvement in combustion profile. 6. Reduction in air ingress across APH from around 50 % to less than 2%. 7. Increase in Primary air temperature from around 230 Deg Celsius to around 240 Deg Celsius 8. Improvement in fluidization resulted in less clinker formation, which further improved bed ash cooler performance. 9. Improvement in combustion resulted in less usage of emergency drain.

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Armin

July 18, 2018
Greetings I am a mechanical engineer working on boilers faults (problems and solutions) in steam power plants with fuel oil and natural gas fuel, would you let me know whether there are any useful documents (papers, books, reports) in the above subject. Sincerely Armin Farvizi
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