The report gives results of a study of the effects on pollutant emissions of extensive combustion modifications on two industrial boilers. Staged combustion, variable excess air, and variable air preheat were evaluated while firing natural gas or No. 6 fuel oil in a watertube boiler rated at 16 MW thermal input (55 million Btu/hr). Reductions in NOx of 31% for natural gas and 42% for No. 6 fuel oil were obtained when excess air was optimized and staged air was introduced through injection ports in the furnace side, as far downstream from the burner as practical. Combined lowered air preheat and staged combustion reduced NOx by 70% while firing natural gas. In a watertube boiler rated at 6.5 MW thermal input (22 million Btu/hr), flue gas recirculation, staged combustion, and variable excess air were evaluated while firing natural gas, No. 2 fuel oil, or No. 6 fuel oil. The maximum NOx reduction for natural gas was 79% with flue gas recirculation and lowered excess air. A 77% NOx reduction was obtained for No. 2 fuel oil with combined modifications. Since NOx reduction for heavy fuel oil has been very difficult to achieve, the most significant result in the program was a 55% NOx reduction, obtained with a combination of modifications while firing No. 6 fuel oil. Trace species and organics emissions were measured while firing No. 6 fuel oil.

Prepared by KVB under Contract no. 68-02-2144, program element no. EHE624A. Issued May 1978. Includes bibliographical references.