Engines, including diesel engines, gasoline engines, natural gas engines, and other engines known in the art, may exhaust a complex mixture of air pollutants. The air pollutants may be composed of gaseous and solid material, including particulate matter, nitrogen oxides (“NOx”), and sulfur compounds.
Due to heightened environmental concerns, exhaust emission standards have become increasingly stringent over the years. The amount of pollutants emitted from an engine may be regulated depending on the type, size, and/or class of engine. One method that has been implemented by engine manufacturers to comply with the regulation of particulate matter and NOx exhausted to the environment has been to remove these pollutants from the exhaust flow of an engine with filters. However, using filters for extended periods of time may cause the pollutants to buildup in the components of the filters, thereby causing filter functionality and engine performance to decrease.
One method of improving filter performance may be to implement filter regeneration. For example, International Publication No. WO 01/51178 (the '178 publication) to Campbell et al., describes a method and apparatus for removing nitrogen oxides (NOx) and gaseous sulfur compounds such as SO2 and H2S from engine exhaust using a catalyst filter system with regeneration capabilities. The catalyst filter system of the '178 publication is designed for use in lean burn internal combustion engines and comprises two identical catalyst sections arranged in parallel. Each catalyst section includes a sulfur selective catalyst and a NOx selective catalyst. Exhaust flow is directed through a first catalyst section to remove sulfur and NOx from the exhaust flow, while a second catalyst section undergoes a regeneration process. During the regeneration process, gas containing a reducing agent passes through the second catalyst section in a direction opposite the normal direction of flow. The gas flows through the NOx and sulfur selective catalysts and desorbs nitrogen and sulfur compounds collected thereon through regeneration. In this reverse flow direction, the gas contacts the NOx selective catalyst before the sulfur selective catalyst.
Although the catalyst filter system of the '178 publication may reduce the amount of NOx released to the environment, in order to avoid collecting sulfur on the NOx absorber of the second catalyst section during regeneration, the filter system requires a separate catalyst section for filtering the exhaust flow. Incorporating a second catalyst section may substantially increase the overall cost of the filter system and may double the space requirements of the system.
The present disclosed filter system is directed to overcoming one or more of the problems set forth above.