By the end of 2010, China had approximately 650 GW of coal-fired electric generating capacity producing almost 75% of the country's total electricity generation. As a result of the heavy reliance on coal for electric...By the end of 2010, China had approximately 650 GW of coal-fired electric generating capacity producing almost 75% of the country's total electricity generation. As a result of the heavy reliance on coal for electricity generation, emissions of air pollutants, such as nitrogen oxides (NOx), are increasing. To address these growing emissions, the Ministry of Environmental Protection (MEP) has introduced new NOx emission control policies to encourage the installation of selective catalytic reduction (SCR) technologies on a large number of coalfired electric power plants. There is, however, limited experience with SCR in China. It is therefore useful to explore the lessons from the use of SCR technologies in other countries. This paper provides an overview of SCR technology performance at coal-fired electric power plants demonstrating emission removal rates between 65% and 92%. It also reviews the design and operational challenges that, if not addressed, can reduce the reliability, performance, and cost-effectiveness of SCR technologies. These challenges include heterogeneous flue gas conditions, catalyst degradation, ammonia slip, sulfur trioxide (SO3) formation, and fouling and corrosion of plant equipment. As China and the rest of the world work to reduce greenhouse gas emissions, carbon dioxide (CO2) emissions from parasitic load and urea-to-ammonia conversion may also become more important. If these challenges are properly addressed, SCR can reliably and effectively remove up to 90% of NOx emissions at coal-fired power plants.展开更多
Ammonia (NH<sub>3</sub>) dissociation and oxidation in a cylindrical quartz reactor has been experimentally studied for various inlet NH<sub>3</sub> concentrations (5%, 10%, and 15%) and reacto...Ammonia (NH<sub>3</sub>) dissociation and oxidation in a cylindrical quartz reactor has been experimentally studied for various inlet NH<sub>3</sub> concentrations (5%, 10%, and 15%) and reactor temperatures between 700 K and 1000 K. The thermal effects during both NH<sub>3</sub> dissociation (endothermic) and oxidation (exothermic) were observed using a bundle of thermocouples positioned along the central axis of the quartz reactor, while the corresponding NH<sub>3</sub> conversions and nitrogen oxides emissions were determined by analysing the gas composition of the reactor exit stream. A stronger endothermic effect, as indicated by a greater temperature drop during NH<sub>3</sub> dissociation, was observed as the NH<sub>3</sub> feed concentration and reactor temperature increased. During NH<sub>3</sub> oxidation, a predominantly greater exothermic effect with increasing NH<sub>3</sub> feed concentration and reactor temperature was also evident;however, it was apparent that NH<sub>3</sub> dissociation occurred near the reactor inlet, preceding the downstream NH<sub>3</sub> and H<sub>2</sub> oxidation. For both NH<sub>3</sub> dissociation and oxidation, NH<sub>3</sub> conversion increased with increasing temperature and decreasing initial NH<sub>3</sub> concentration. Significant levels of NO<sub>X</sub> emissions were observed during NH<sub>3</sub> oxidation, which increased with increasing temperature. From the experimental results, it is speculated that the stainless-steel in the thermocouple bundle may have catalysed NH<sub>3</sub> dissociation and thus changed the reaction chemistry during NH<sub>3</sub> oxidation.展开更多
文摘By the end of 2010, China had approximately 650 GW of coal-fired electric generating capacity producing almost 75% of the country's total electricity generation. As a result of the heavy reliance on coal for electricity generation, emissions of air pollutants, such as nitrogen oxides (NOx), are increasing. To address these growing emissions, the Ministry of Environmental Protection (MEP) has introduced new NOx emission control policies to encourage the installation of selective catalytic reduction (SCR) technologies on a large number of coalfired electric power plants. There is, however, limited experience with SCR in China. It is therefore useful to explore the lessons from the use of SCR technologies in other countries. This paper provides an overview of SCR technology performance at coal-fired electric power plants demonstrating emission removal rates between 65% and 92%. It also reviews the design and operational challenges that, if not addressed, can reduce the reliability, performance, and cost-effectiveness of SCR technologies. These challenges include heterogeneous flue gas conditions, catalyst degradation, ammonia slip, sulfur trioxide (SO3) formation, and fouling and corrosion of plant equipment. As China and the rest of the world work to reduce greenhouse gas emissions, carbon dioxide (CO2) emissions from parasitic load and urea-to-ammonia conversion may also become more important. If these challenges are properly addressed, SCR can reliably and effectively remove up to 90% of NOx emissions at coal-fired power plants.
文摘Ammonia (NH<sub>3</sub>) dissociation and oxidation in a cylindrical quartz reactor has been experimentally studied for various inlet NH<sub>3</sub> concentrations (5%, 10%, and 15%) and reactor temperatures between 700 K and 1000 K. The thermal effects during both NH<sub>3</sub> dissociation (endothermic) and oxidation (exothermic) were observed using a bundle of thermocouples positioned along the central axis of the quartz reactor, while the corresponding NH<sub>3</sub> conversions and nitrogen oxides emissions were determined by analysing the gas composition of the reactor exit stream. A stronger endothermic effect, as indicated by a greater temperature drop during NH<sub>3</sub> dissociation, was observed as the NH<sub>3</sub> feed concentration and reactor temperature increased. During NH<sub>3</sub> oxidation, a predominantly greater exothermic effect with increasing NH<sub>3</sub> feed concentration and reactor temperature was also evident;however, it was apparent that NH<sub>3</sub> dissociation occurred near the reactor inlet, preceding the downstream NH<sub>3</sub> and H<sub>2</sub> oxidation. For both NH<sub>3</sub> dissociation and oxidation, NH<sub>3</sub> conversion increased with increasing temperature and decreasing initial NH<sub>3</sub> concentration. Significant levels of NO<sub>X</sub> emissions were observed during NH<sub>3</sub> oxidation, which increased with increasing temperature. From the experimental results, it is speculated that the stainless-steel in the thermocouple bundle may have catalysed NH<sub>3</sub> dissociation and thus changed the reaction chemistry during NH<sub>3</sub> oxidation.