| In recent years,environmental pollution has become more and more serious.Nitrogen oxides(NOx)are one of the main air pollutants,and are also the main causes of acid rain,photochemical smog and ozone layer destruction.Activated lime rotary kiln technology is mature,advanced and widely used,which occupies a considerable proportion in the lime industry.Influenced by such factors as higher combustion temperature and relatively concentrated high temperature area,the NOx produced in the calcination process of lime rotary kiln ranks first among all kinds of lime kilns.The emission concentration of nitrogen oxides from lime kiln flue gas tends to be strict.Some places put forward the standard of 100 mg/m~3 emission concentration of nitrogen oxides from lime kiln.At present,the NOx emission concentration of most domestic lime kilns can not meet the standard requirements.There are no systematic control measures for flue gas denitrification of lime kilns at home and abroad.It is of great significance to put forward the purification process of flue gas denitrification of lime kilns.Taking 800t/d active lime rotary kiln production line as an example,the flue gas field inside the kiln preheater was analyzed by computational fluid dynamics(CFD)method.On this basis,the process of flue gas preheating and denitrification in lime rotary kiln is emphatically analyzed,and the low temperature SCR flue gas denitrification purification process is proposed at the end of lime rotary kiln.At the same time,according to different influencing factors,the technical route of flue gas denitrification and purification suitable for lime rotary kiln is determined.The low temperature SCR flue gas denitrification system of lime rotary kiln was simulated numerically.According to the simulation results,the low temperature SCR reactor was optimized and the following results were obtained:(1)The numerical simulation of the gas flow field in the preheater of 800t/d active lime rotary kiln was carried out to provide reference for the selection of flue gas denitrification purification process and feasibility analysis of lime rotary kiln.The results show that the estimated residence time of the selected denitrification area in the preheater of lime rotary kiln is 1.0-1.52 s due to the structure of the equipment.(2)On the basis of studying the distribution of air flow and NOx in the preheater of lime kiln,the influence of various factors on the denitrification reaction was investigated,and the feasibility and limitation of SNCR and SCR denitrification technology in the flue gas denitrification of lime rotary kiln were discussed emphatically.The low temperature SCR denitrification process was proposed at the end of lime rotary kiln.(3)According to the layout,temperature,dust and other factors of low-temperature SCR denitrification system,different technological routes of flue gas denitrification and purification were compared and demonstrated,and the technological route of flue gas denitrification and purification suitable for"low nitrogen combustion+electrostatic precipitator+low-temperature SCR"of active lime rotary kiln was determined.(4)The numerical simulation and optimization design of 800t/d low-temperature SCR flue gas denitrification system for lime rotary kiln are carried out.The structural optimization scheme of a set of straight-arc guide plates at the bend 1 and 2 of the SCR flue gas denitrification system is proposed,respectively,and a set of straight-arc guide plates above the rectifying grid of the SCR reactor.The simulation results show that after optimization,the relative standard deviation of flue gas velocity at the first catalyst inlet section of SCR flue gas denitrification unit decreases from 31.7%to 8.52%after optimization,which meets the control target of no more than 15%.The flue gas incidence angle of catalyst inlet section basically meets the requirement of maximum deviation<10 degrees.The uniform distribution of flue gas velocity effectively improves the uniformity of the flow field at the entrance section of the first catalyst layer.The total pressure drop of the optimized SCR flue gas denitrification unit is 742 Pa,which meets the design requirements. |
