Minimization of selective non-catalytic reduction (SNCR) operational concerns

Several combustion and post-combustion techniques are common for the control of NO{sub x} emissions. These include low NO{sub x} burners, overfire air, reburning, selective catalytic reduction and selective non-catalytic reduction. The use of selective non-catalytic reduction (SNCR) for the post-combustion control of these emissions is rapidly gaining popularity in a variety of applications, including circulating fluidized bed boilers and traveling grate MSW incinerators. Existing coal fired combustors in ozone non-attainment areas may be forced to install RACT for NO{sub x} control, especially in the Northeastern US. These RACT requirements will likely involve the installation of post combustion controls for major sources. The ease of retrofitting today`s SNCR technology can be of significant appeal to these facilities. However, due to the boiler load swings and short residence times of these combustors, some design considerations must be carefully reviewed to ensure optimum operation of the SNCR process. This paper discusses the use of the NOxOUT process to control emissions from existing coal fired combustors. NOxOUT is an in-furnace SNCR technology, using urea based chemicals to convert NO{sub x} to nitrogen, carbon dioxide and water. Special emphasis is placed on minimization of ammonia slip, ammonium sulfate formation, air heater deposition and pressure drop,more » ammonia in the collected flyash and SNCR effects on downstream pollution control equipment such as electrostatic precipitators, fabric filters and spray dryer/fabric filter combinations.« less