Selective catalyst reduction and its dominant role in reducing NOx emissions
Selective catalyst reduction (SCR) is a proven and reliable method in the reduction of nitrogen oxide emissions from the exhaust of a coal-fired power plant. Nitrogen is naturally present in coal and during the combustion process, nitrogen and water combine to form nitrogen oxide. Nitrogen oxide reacts with the catalyst and anhydrous ammonia so that it will be converted into harmless hydrogen and water. Anhydrous ammonia is a compressed liquefied gas that is stored in the power plant but when it is released into the environment, it can become hazardous.
Nitrogen oxide and how it forms ground level ozone
Nitrogen oxide is one of the diesel engine emissions that contribute to the formation of ground-level ozone. On a hot sunny day, complex chemical reactions between nitrogen oxide and volatile organic compounds can produce ground-level ozone. The primary manmade source of nitrogen oxide is electrical utilities that burn fossil fuel but motor vehicles and industries also contribute to the nitrogen oxide found in the environment. Motor vehicles are also the primary sources of volatile organic compounds that is why diesel engine manufacturers are exploring SCR technology in vehicles after its success in stationary applications.
EGR in the reduction of diesel engine emissions
Exhaust gas recirculation (EGR) is an effective technology used in the reduction of diesel engine emissions particularly nitrogen oxides. EGR reduces NOx by lowering oxygen concentrations in the combustion chamber or through heat absorption on most types of diesel engines. However, the reduction of nitrogen oxides through EGR comes with a cost since other measures are usually required to avoid increase in fuel consumption, the emissions of particulate matter and carbon monoxide, engine wear and reduction in engine durability. The range of changes includes:
- Reductions in the consumption of lubricating oil
- Fuel injection pressure increases
- Increase in diesel oxidation catalyst
- Increase in the intake of manifold boost pressure
Diesel particulate filter in the reduction of diesel engine emissions
Diesel particulate filter is a device that is usually installed in the exhaust system of the diesel engine so that soot and particulate matter can be trapped. These particles are too tiny to be seen by the naked eye but the larger particles can be seen as black smoke coming out from the exhaust. The range of particles that are trapped by DPF are about 2.5 microns in diameter. This reduction in diesel engine emissions has obvious health and environmental benefits. However, diesel particulate filters do not work like magic to transform diesel engines into zero emissions since there are significant pollutants that cannot be trapped.