Selective catalytic reduction is the process used to lessen NOx emissions hence controlling air pollution rates. The process involves the conversion of emissions into water and nitrogen gas. The process uses a catalyst in the form of ammonia or air, which is injected into the exhaust pipes hence holding the NOx gases. Once the gases have mixed thoroughly as the emissions pass through the catalytic bed NOx is reduced. The catalysts used are only meant to reduce the NOx but do not affect it. The by-product resulting from the reaction between urea and the emissions is carbon dioxide. Selective catalytic reduction usually reduces NOx emissions by 70 to 95%.
Power plants normally emit large volumes of NOx because they obtain power from the ignition of fuels. The SCR catalyst technique has helped in the considerable reduction of these emissions. The process comprises of a reactor chamber, a catalyst bed that contains catalyst modules and the ammonia injection grid system.
The moment the Ammonia steam gets fed into the exhaust pipes containing the emissions, it then passes all the way through the catalyts . This reduces the oxides of Oxygen as well as the toxic Nitrogen gas. This system makes use iof Urea, aqueous Ammonia together with anhydrous ammonia. Though all the catalysts used have their own disadvantages, urea is more popular. This technique has been accredited for its capability in reducing these toxic emissions at a great percentage.
One major disadvantage of this technique is the ammonia slip, which is the release of unused ammonia. This takes place maintenance of the necessary temperatures is not carried out or when excess ammonia is injected into the system. Another setback is the emission of ammonium bisulphate and ammonium sulfate. These are as a result of the combination of the excess ammonia with sulfates that are found in the air. The sulfates are linked to respiratory inflammations and coughs.
Proper use of the SCR catalysts has been acknowledged for the successful removal of 90 % and above levels of NO x. A number of coal fired boilers based in Virginia possessing the catalyst systems have been able to reduce the emissions by 60 to 65 %. The gas fired utilities have achieved more than 90 %.
This system originally began in the United States with the Engelbert Corporation in 1957, by then it was not tested. This system then continued with developments in Japan and United States in the early ’60s, where the research mainly focused on catalyst agents that were more durable and cost friendly. In 1978, the IHI Corporation installed the first system.
The most favored reducing agents are produced from different ceramic materials, which are used as carriers. Such include titanium oxide. However, the active catalytic components are obtained from metals like vanadium and zeolites. They can also be obtained from precious metals. Catalysts from vanadium and other base metals are not highly durable but those obtained from zeolites can withstand high temperatures. Plate type catalysts are the best when it comes to withstanding temperatures. However, they are very expensive.
Best content writer in association with Cormetech Inc., the leading producer of titania-based ceramic honeycomb catalyst for NOx emissions control and NOx reduction used in Selective Catalytic Reduction (SCR) systems for air pollution control.
