Coal burners in coal fired boilers get damaged mainly due to erosion and burn out.
Erosion of coal burners
Erosion in a coal burner is mainly due to the inorganics in coal. The higher the percentage of inorganics, the higher will be the erosion. Designers adopt an optimal coal air mixture velocity and erosion resistant materials to design coal burners. There are number of methods to reduce the metal loss due to erosion. Depositing high hardness material on coal burner surfaces by various methods is the prime one adopted by many. It is seen that operating the running mills with very high mill air flow increases erosion and hence metal loss on the coal burners.
Erosion in a coal burner can be minimized by adhering to design coal for firing and operating with the recommended parameters. If coal deviates from the design coal, then proper tuning of various parameters will have to be done. This will reduce the undue erosion of coal burner tips. Firing with coarser coal particles will increase erosion, hence checking operating mill fineness and adjusting it to optimal level is important.
Coal burner burnout
Coal burners are made of high alloy steels with wear resistant material deposited or pasted on it. The primary air and burner air cool the tip or burner nozzle from radiation heat from coal flame. Coal burner burning out can be because of inadequate cooling of tip, and this can be attributed to many reasons.
- Flame front too close to the burner tip due to high volatiles in coal and inadequate burner air to keep the flame front about one meter away
- Low amount of cooling air for the burner tip
- High intensity flame due to high reactives in coal
- Higher than required swirl setting in burner leading to high intensity flame
- Low coal pipe coal-air mixture velocity – keeps the flame too close to the burner
- Improper burner damper adjustment
- Very high fineness of pulverized coal
- Maintaining support fuel for higher load than required leads to intense flame near burner tip
Minimizing coal burner burnout can be achieved by regular checking of flame front of each burner and adjusting the same to be about one meter away from the coal burner tip. Check all operating mill fineness and maintain little coarser than being operated. This will shift the flame front away from the burner. Make sure all the burner air flows are properly proportioned with in burner and between burners. Check the primary air flow for ensuring the required fuel-air mixture velocity. Check the burner during turn around and repair or replace if any sign of overheating or erosion is noticed.
About the Author
Dr V T Sathyanathan is a boiler consultant with 35 years of experience in various areas of high pressure boiler trouble shooting. He holds a PhD in coal combustion in boilers.
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