外文翻译--石灰石脱硫对循环流化床中NOX排放的影响.docVIP

- PAGE 10 - - PAGE 15 - 英文原文 Limestone Effects on NOx Formation in CFB Combustors Abstract Circulating Fluidized Bed (CFB) combustion technology has been widely used in power generation with the considerations of its advantages in economically controlling SO2 and NOx emissions. However, it is found that NOX emission increased up to 30% when limestone is added into the combustor for desulphurization, especially with rather high Ca/S ratio. The phenomenon of NOx augment was discussed based on associated mechanisms and chemical kinetics. The catalytic oxidization effect, preferential conversion effect from HCN to NH3, and reduction effect on NOx were analyzed. It is found limestone can act as a catalyst, increasing the reaction rates for the reaction associated with NOx formation. Furthermore, CaO decomposed CaCO3 favors the conversion of HCN to NH3 when they are release in de-volatilization process. Due to preferential oxidization of NH3 to NO rather than the unstable N2O, NOX emission increases with limestone injection. When high Ca/S is used, the reduction effect becomes dominated and reduces the overall NOX emission. Keywords CFB, limestone, desulphurization, NOX formation, chemical kinetics 1. Introduction Circulating Fluidized Bed (CFB) combustion technology has been widely used in power generation, because of its advantages in such as the high fuel flexibility for burning various kinds of coals and the high feasibility in economical emission control. Given that the combustion temperature in CFB combustors, e.g., boilers, is usually between 1020~1120K and secondary air can be injected at different ports along the axial direction, the NOX concentration in the flue gas can be controlled to be much lower than those using other combustion technologies. Shown in Fig. 1, NOx emission from a CFB combustors are lowest, in the range of 100-220 ppm, compared with other kinds of combustors [1]. Fig. 1 NOX emissionlevel for differen