Posted By: Madhu Bafna

June 18, 2016
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Overview

Operational optimization of Boiler involves the following: 1. Burner tilting and flow bias along elevations: Using the rich fire ball technique NOx emission can be controlled. This technique ensures volatile combustion under rich conditions and subsequent completion of combustion by providing sufficient excess air. 2. Pulverizer performance: High mill outlet temperatures result in mill fires while low temperatures result in reduced capacity. High moisture in raw coal can lead to clogging of the mill. Besides moisture and air temperatures, classifier settings must be set at the optimal level. 3. Air and flue gas pressure: The secondary air differential pressure between the wind box and furnace may be reviewed and increased if required. The furnace draft must be maintained as close to the atmospheric pressure as possible (- 5 mm WC) for minimal air ingress and stable operation. 4. Coal flow: Equalizing coal flow between the various burners (in an elevation) to within 10 % of the mean flow rate. 5. Air flow: Proportioning of primary to secondary air in the ratio of 35:65. When the secondary air flow is increased, if the flue gas temperature increases it indicates that carbon conversion efficiency is increasing. If it decreases, it indicates that the carbon conversion efficiency has reached its optimal value. 6. Excess air levels and flue gas temperatures: If the excess air is too low, unburnt carbon losses will increase and if it is too high, the dry flue gas losses will increase. 7. Bias control between main-steam and re-heat by alternative control modes. 8. Control of MS & RH sprays by burner tilting downwards or flue gas flow control. 9. Operation intervals of soot blowers, wall de-slaggers and bottom ash removal. 10. When the furnace temperature crosses over the ash fusion temperature (AFT 1200-1300 Deg C), either the load is reduced (fuel control - remote manual) or the total air supply is increased keeping the load constant. If the carbon conversion efficiency is low, it does not provide relief and slagging persists. If the carbon conversion efficiency is optimal, then furnace temperature decreases thereby bringing slagging under control. But high gas velocity increases the metal erosion rate as well as leads to more spray requirement due to excessive heat pickup in the convective zones. Hence, under slagging conditions it is necessary to lower the load on the plant.

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