| The Standard for Emission of Air Pollutants in Thermal Power Plants(GB 13271-2014)clearly stipulates that NOx emissions are not higher than 200 mg/m3,in some areas no more than 100 mg/m3.In order to meet increasingly stringent environmental requirements,Most coal-fired units use the selective catalytic reduction denitration technology(SCR)that dominates the market.After the SCR denitration unit was installed in the coal-fired unit,the reductant NH3 not fully involved in the reaction in the SCR reactor reacts additionally with SO3 and H2O in the flue gas to form highly viscous and corrosive ammonium bisulfate(ABS).The ABS causes the rotary air preheater disposed behind the SCR to be seriously clogging,resulting in the inlet and outlet differential pressure of the flue gas and air in the air preheater being large,and the furnace pressure fluctuates greatly,which seriously affects the safety and economic operation of the boiler.By combining the actual case of No.3 furnace of Datang Huayin Zhuzhou Power Plant,firstly,this article conducts the performance test and numerical simulation of the SCR denitration system,and then do research on the numerical simulation of the air preheater.Based on actual data of Zhuzhou Power Plant Project,the SCR denitration systems is studied by online performance test and CFD numerical simulation.lt is found that the velocity of gas,ammonia concentration distribution in the flow field of the denitration system is uneven.After analyzing the simulation and test results,the optimization scheme of adding the deflector and changing the angle of the static vortex mixer is obtained.After the optimization,the relative standard deviation of the speed is reduced to 13.6%,and the flow field uniformity is greatly improved.If the NO concentration of the SCR denitration systems outlet is controlled above 10 ppm,the NH3 escape concentration is basically reduced to 3 ppm,which can alleviate the problem of rotary air preheater blocking caused by ABS.Because,ammonia escape problem cannot be avoided for Zhuzhou Power Plant SCR denitration system so that it is very necessary to study the air preheater.Firstly,the numerical simulation calculations are carried out on the four types heat exchange element of the air preheater,obtained the flow distribution of the unit passage section and the heat transfer distribution of the components,and then calculate the heat transfer characteristics and resistance characteristics of the heat exchange elements.Using the simulation data of DU and NU heat exchanger plate,and combined with the simulation results of Zhuzhou Power Plant SCR denitration system,the overall simulation of the rotary air preheater is carried out.The simulation results of the air preheater are consistent with the air preheater performance test results.According to the three-dimensional temperature distribution of the simulation results of the air preheater,the deposition range of ABS in the air preheater is analyzed,and the deposition range of ABS in the air preheater is analyzed.Further simulations were carried out to study the effects of variable speed conditions,inlet velocity gradient distribution and air inlet temperature on the overall performance of the air preheater,on ABS deposition area and acid corrosion location in the air preheater.In this paper,the SCR denitration system is optimized to reduce ammonia slip and air preheater operation and structural adjustment.Active control through the source and passive management measures make the air preheater more suitable for SCR denitrification,which has important application value for ensuring the safety,stability and economic operation of SCR denitration unit. |
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