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.
Highlights
Published: 2 March 2021The harmful substances emitted from coal-fired power plants are mainly composed of nitrogen oxides (NOx ), sulfur oxides (SOx ), and particulate matter
The nitrogen oxides (NOx ) of the exhaust gas, which has been evenly mixed with the ammonia (NH3 ) emitted from the ammonia injection grid (AIG), is decomposed into nitrogen and water through a chemical reaction in the catalyst layer, as expressed in the following equation: Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
The effect of AIG flow control on the uniformity of the NH3 /NO molar ratio was analyzed by modifying the amount of NH3 injected through the AIG nozzle according to the NO distribution pattern of the inlet flue gas
Summary
The harmful substances emitted from coal-fired power plants are mainly composed of nitrogen oxides (NOx ), sulfur oxides (SOx ), and particulate matter. To reduce the concentration of these harmful substances, coal-fired power plants utilize denitrification and desulfurization facilities and dust collectors. Most plants adopt a selective catalytic reduction (SCR) system or a selective noncatalytic reduction (SNCR) system for denitrification. The SNCR system is cheaper than the SCR system, its reduction reaction is less stable, and it has a lower reduction capacity. To comply with recently reinforced environmental regulations, most large thermal power plants use the SCR system [1]. The nitrogen oxides (NOx ) of the exhaust gas, which has been evenly mixed with the ammonia (NH3 ) emitted from the ammonia injection grid (AIG), is decomposed into nitrogen and water through a chemical reaction in the catalyst layer, as expressed in the following equation: Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations
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