Study On Optimization And Regulation Of Flue Gas Temperature For SCR Reaction In A 600MW Coal-Fired Power Plant

As the environmental problems become increasingly serious, more and more domestic large coal-tired power plants have installed SCR (selective catalytic reduction) denitration apparatus. However, when the units are under low load operation, economizer outlet flue gas temperature become lower, and SCR denitration efficiency will be decreased. In this paper, a 600MW supercritical unit is studied. Thermal calculation method is used to analyse the influence factors of SCR inlet flue gas temperature at low load, and several optimization schemes are studied. The obtained results can provide valuable reference for solution of similar issues in power plants.The reaction principle and effects of low load operation on SCR denitrification system are firstly analyzed in this paper, including SCR denitrification efficiency, NOx emission concentration and NH3 escape rate. Bblocking of the air prcheatcr caused by both solid state and liquid state of NH4HSO4 are furtherly been studied. To analyse the impact of boiler load change on the SCR inlet flue temperature, the boiler thermal calculation program is written. And effects of coal variation, environment temperature, ratio of front and rear flue gas flow, and furnace leakage at 50% THA on SCR inlet temperature are analysed by using single-variable checking method. The results show that the change of load, coal variation and the ratio of front and rear flue gas flow affects more on the SCR inlet flue gas temperature. In the design and operation of the boiler, issues above should be taken care to ensure that SCR inlet flue gas temperature is in the allowable range when the boiler is at low load.Focusing on the problems above, detail thermal calculations of 3 existed optimization schemes arc performed at 50%THA with designed coal. The ability of SCR inlet flue gas regulation, change of economizer outlet water temperatre, exhaust gas temperature, economical efficiency and the reform work are contrasted of the 3 schemes. Comprehensive comparison and analysis of the advantages and disadvantages of each scheme, the bypass-low temperature heater combined scheme is proposed, the thermal calculation results show that, with the area of low temperature heater 20% of the economizer area, when the rear flue gas bypass share is 10.72%, the SCR inlet flue gas temperature will be increased from 310.57? to 320? to meet the requirements of SCR. At the same time, exhaust gas temperature is dropped by 2.39? and the standard coal consumption is decreased nearly 0.4g/(kWh).