13-01-2011, 12:22 PM
INTRODUCTION
Internal combustion (IC) engines are used in a variety of stationary applications ranging from power generation to inert gas production. Both spark ignition and compression ignition engines can be found. Depending on the application, stationary IC engines range in size from relatively small (~50 hp) for agricultural irrigation purposes to thousands of horsepower for power generation. Often when used for power generation, several large engines will be used in parallel to meet the load requirements. A variety of fuels can be used for IC engines including diesel and gasoline among others. The actual fuel used depends on the owners/operators preference but can be application dependent as well.
The operation of IC engines results in the emission of hydrocarbons (NMHC or VOC), carbon monoxide (CO), nitrogen oxides (NOx), and particulate matter (PM). The actual concentration of these criteria pollutants varies from engine to engine, mode of operation, and is strongly related to the type of fuel used.
Various emission control technologies exist for IC engines which can afford substantial reductions in all four criteria pollutants listed above. However depending on whether the engine is being run rich, lean, or stoichiometrically and the emission control technology used, the targeted emissions vary as do the levels of control. For example, an oxidation catalyst can be used to control NMHC, CO, and PM emissions from diesel engines which inherently operate in a lean environment, whereas selective catalytic reduction (SCR) could be used to additionally control NOx emissions. More recently, lean-NOx catalysts have been demonstrated to provide greater than a 80 percent reduction in NOx emissions from a stationary diesel engine, while providing significant CO, NMHC, and PM control as well.
PM emissions from stationary diesel engines are more of a concern than those for IC engines using other fuels. Several emission control technologies exist for diesel engine PM control. Oxidation or lean-NOx catalyst can be used to not only reduce the gaseous emissions associated with the use of diesel engines but further provide significant PM control. Likewise, diesel particulate filter systems can be used to achieve up to and greater than 90 percent PM control while in some instances, also providing reductions in the gaseous emissions.
Additionally, special ceramic coatings applied to the combustion zone surfaces of the piston crown, valve faces, and head have shown the ability to significantly reduce NOx and PM emissions in diesel engines. These ceramic coatings can be used by themselves or combined with an oxidation catalyst to give even greater reduction of PM. Ceramic engine coatings change the combustion characteristics such that less dry, carbon soot, is produced. Also, when combined with an oxidation catalyst, ceramic coatings allow retarding of the engine to reduce NOx, while CO and particulates are maintained at low levels.
Emission Control Technology for Stationary Internal Combustion Engines
In the case of gaseous fuels, ceramic coatings have shown the ability to allow the user to operate their engines with timing significantly advanced generating higher power levels. Also, wider ranges of fuel composition and ambient air temperature fluctuations are tolerated without the deleterious effects of precombustion. Tests are currently underway to evaluate the effects of the coatings on specific emissions from gaseous fueled engines.
Emission control technology for stationary IC engines is currently available and can be used to provide substantial reductions in the CO, NMHC, NOx, and PM emissions from these sources in a cost-effective manner.
Read more
