Impact of NOx Selective Catalytic Reduction Processes on Flue Gas Cleaning Systems

摘要

The report gives results of a study of the impact of the ammonia leaving a nitrogen oxide (NOx) selective catalytic reduction (SCR) process on downstream flue gas cleaning processes. (NOx emissions from electric utility boilers may be reduced 80-90% by the application of pollution control technology based on the SCR of NOx with ammonia; however, some unreacted ammonia may be emitted from the control system.) These processes include electrostatic precipitators (ESPs), baghouses, and flue gas desulfurization (FGD) systems. In normal operation, most ammonia leaving the SCR system will be removed, either as particulate salts by the particulate removal system or as free ammonia by the FGD system. Very little ammonia should be emitted at the stack. The operation of ESPs and FGD systems will, in most cases, be improved by the presence of ammonia in the flue gas. The effects of ammonia and ammonia salts on baghouse operation are not known. At normally expected emission levels, no adverse environmental impacts are projected; however, at high ammonia emission levels, the potential exists for problems with ammonia in the waste streams from fly ash and SO2 collection devices. Potential adverse environmental impacts exist in the ash and sludge ponds where collected ammonia may be concentrated and emitted as a gaseous pollutant.