Emissions Control Technology

Three-Way Catalysts

Overview

Three-way catalysts are employed primarily on natural gas reciprocating engines that operate in a rich-burn mode. This is the most cost effective method for control of emissions of NOx, CO and VOCs at the same time. In order for this control technology to work, the engine must be operated in a rich-burn mode at less than 0.5% oxygen in the exhaust, as the catalyst will not function properly at higher oxygen levels. Engines operating with NSCR require tight air-to-fuel control to maintain high reduction effectiveness without high hydrocarbon emissions. This technology has been proven in various commercial applications to be able to meet the current California BACT (Best Available Control Technology) for engines less than 2064 brake horsepower (bhp) of 0.15 grams/bhp-hr for NOx and VOC, and 0.6 g/bhp-hr for CO at a capital cost estimate of $50 - $100/KW. There is an electrical efficiency penalty for operating a natural gas reciprocating engine in a rich-burn mode of 3-5%. In addition, to achieve the 0.15 g/bhp-hr levels, a premium catalyst is necessary that is more efficient in reducing NOx emissions than the standard catalysts. Catalyst efficiency must be monitored with catalyst replacement often required every five years.