NOx and SCR (Selective Catalytic Reduction)
Presently, part of the energy generated by the combustion process is wasted as nitrogen oxide (NOx) emissions into the atmosphere. The problem of NOx emissions is so significant that in the future, power plant operators must comply with newly established environmental regulations and accept limits to the amount of NOx they release into the environment. Currently, the most efficient process of decreasing NOx emissions is known as Selective Catalytic Reduction, or SCR.
The SCR method is a two-step process to reduce nitrogen oxide (NOx) emissions released into the atmosphere by a power plant. The first step is the oxidation of nitrogen oxides (NOx) to nitrogen and oxygen. This can be achieved through the addition of an oxidising agent, such as a fuel. The second step is the actual reduction of nitrogen oxides to nitrogen and water using a catalytic converter that contains zeolites or transition metal oxides. The catalytic converter carries out the reduction of NOx emissions to nitrogen and water by a process of chemisorption, where the nitrogen oxides are adsorbed into the catalytic converter and then reduced.
In order to ensure optimal reduction of NOx emissions, there must be a sufficient and balanced supply of an oxidising agent and a reducing agent. Depending on the plant’s operating conditions, an oxidising agent such as hydrogen, carbon monoxide, or methane, can be introduced into the process. Hydrogen is most commonly used, and is the oxidising agent of choice for many power plants, as it offers the highest nitrogen oxide reduction efficiency with the lowest fuel consumption. The most commonly used reducing agents are ammonia, urea, and ammonia-urea compounds. Depending on the plant’s application, the specific reducing agent can be adjusted to maximize the reduction efficiency while minimizing the cost.
In addition to reducing NOx emissions, SCR systems can also increase the efficiency of the combustion process. This efficiency is usually achieved by higher temperatures, improved thermal performance, and better fuel utilisation. With the use of a SCR system, plants can increase their net output and reduce their fuel consumption, making them more economically and environmentally efficient.
The use of SCR technology has become increasingly popular for power plants and industrial processes to reduce their NOx emissions due to its ability to efficiently convert nitrogen oxides to nitrogen and oxygen. This method is a relatively cost-effective solution for controlling NOx emissions and reducing their effect on the environment. Additionally, SCR technology has enabled power plants to increase their efficiency and reduce fuel consumption. With the continued enforcement of environmental regulations, SCR will become even more important in the future as a solution for meeting the increasingly stringent requirements of power plants.
