A well tuned burner gives the optimum performance of the boiler. This requires a careful setting of air flow, fuel flow and the swirl level which ensures air fuel mixing.
Tuning a front wall fired burner firing any fuel, gas or oil or coal, first requires the air flow equalization in all burners. This is carried out by equalizing the pressure after the individual burner isolating damper in the windbox or the air inlet duct to the burner.
The steps involved:
- First look at the above two figures in the O & M manual of the boiler you are tuning and understand the steps fully
- Note the burner setting details for start-up
- The Tertiary Air swirl position for all burners and all vanes set at the recommended open position (Many burner manufactures use 30 degree open) to moderate swirl
- The Secondary Air swirl position are normally factory set at a specified open position (here also burner designers prefer 30 degree open) to moderate swirl
- Generally the SA flow control damper positions are all set at fully open position
- All shrouds are set uniformly at the same position to produce approximately the recommended windbox to furnace differential pressure, better to keep any variation within plus minus 15 % deviation
- Igniter to be set as per manufacturer guide lines.
- As the boiler load increases the windbox to furnace drop increases from a lower value to the required maximum value from a load of 50% to 100%
- The flame in burner will be approximately as shown in the figure. In the case of coal burner the coal stream extends only 1 to 3 inches before rapid ignition occurs.
Manual biasing can be done in most of the coal burners to modify the relative position of each shroud with respect to the other. This is required to be provided by the operator
- The ability to balance air flow on burners in service at each burner level. This is done by observing the air velocity indication at each burner and individually biasing the shroud in each burner
- Capability to manually adjust the total burner level air flow to attain a certain degree of off-stoichiometry with respect to mill load at that level
Many burner designers prefer to provide two airflow measurement: one upstream of the secondary and the other upstream of the tertiary air.
Any deviation in burner setting can be evaluated from the performance changes that occur during continuous operation. The parameters like unburned carbon in ash, the CO levels, the flame colour, and the smoky tail of the burner are some of the indications that need the operator attention. The flame length variation and the NOx level variations are the other parameters that need to be addressed.
Coal Burner Flame
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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