A CFD Study on Flow Control of Ammonia Injection for Denitrification Processes of SCR Systems in Coal-Fired Power Plants

Abstract

The selective catalytic reduction method is a useful method for the denitrification process of exhaust gas emitted from industrial facilities. The distribution of the ammonia–nitrogen oxide mixing ratio at the inlet of the catalyst layers is important in the denitrification process. In this study, a computational analysis technique was used to improve the uniformity of the NH3/NO molar ratio by controlling the flow rate of the ammonia injection nozzle according to the flow distribution of nitrogen oxides in the inlet exhaust gas of the denitrification facility. The application model was simplified to the two-dimensional array adopted from the existing selective catalytic reduction (SCR) process in the large-scaled coal-fired power plant. As the inlet conditions, four (4) types of flow pattern were simulated, i.e., parabolic, upper-skewed, lower-skewed, and random. The flow rate of the eight (8) nozzles installed in the ammonia injection grid was controlled by Design Xplorer as the optimization tool. In order to solve the two-dimensional steady, incompressible, and viscous flow fields, the commercial software named ANSYS Fluent was used with the κ-ε turbulence model. The root mean square of NH3/NO molar ratio at the inlet of the catalyst layer has been improved from 84.6% to 90.1% by controlling the flow rate of the ammonia injection nozzles. From the present numerical simulation, the operation guide could be drawn for the ammonia injection nozzles in SCR DeNOx facilities.

Integrated Gas and Solid Model to Determine the Flow Performance in the SCR Reactor

“…1−3 Selective catalytic reduction (SCR) denitration systems are widely used in power plants to treat NO x . 4,5 Catalysts are the key to SCR denitration technology. 6 Controlling the deactivation rate of the catalyst is of great significance for the long period stable operation of the SCR denitration system.…”

“…Coal combustion for thermal power generation is the most conventional way to use coal. Coal combustion will produce a large number of pollutants, such as gaseous NO x and fly ash. − Selective catalytic reduction (SCR) denitration systems are widely used in power plants to treat NO x . , Catalysts are the key to SCR denitration technology . Controlling the deactivation rate of the catalyst is of great significance for the long period stable operation of the SCR denitration system .…”

Adaptive Internal Model Control of SCR Denitration System Based on Multi-Objective Optimization

“…The combustion of fossil fuels, especially in coal-fired power plants, is one of the main sources of x NO in the atmosphere [1]- [3]. Currently, thermal power plants have two ways to reduce x NO emissions.…”

Numerical Simulation and Optimization of SCR-DeNOx Systems for Coal-Fired Power Plants Based on a CFD Method

“…Sohn et al also suggested placing the AIG and mixer away from the catalyst layer to enhance the NH 3 mixing and flow uniformity together [17]. Moreover, Kim et al used a computational analysis technique to improve the uniformity of the NH 3 /NO molar ratio by controlling the flow rate of the ammonia injection nozzle according to the flow distribution of the nitrogen oxides in the inlet exhaust gas of the denitrification facility [18]. Based on the response surface methodology (RSM), Ye et al studied the effect of three factors on denitration efficiency, including catalyst inlet gas velocity, reaction temperature, and the NH 3 /NO molar ratio.…”