Researches On Low-Load SCR Operation And Reheat Steam Temperature Enhancement Based On Straw After-Burning

In this paper,in order to solve the universal problem of reheat steam temperature on the low side and the failure operation of SCR under low load,a technical program for coupling a straw adiabatic direct-fired furnace or gasifier in a power station boiler and supplementing it in the tail flue is proposed.When the straw direct burning furnace is set,the high-temperature flue gas burned by the straw is directly sent to the flue of the boiler tail,and the flue temperature of the boiler tail is raised.When the straw gasifier is set,the uncooled or cooled and pressurized gasification gas is directly sent to the flue of the boiler tail to directly burn,and the chemical heat of the straw gas is used to raise the flue temperature of the boiler tail.The flue gas temperature at the inlet of SCR can be directly raised due to the afterburning at the economizer.And at the inlet of low temperature reheater,the temperature and volume of the flue gas can be improved due to the afterburning to achieve the purpose of increasing the temperature of reheat steam temperature at boiler outlet.A 350 MW supercritical coal-fired boiler(double tail flue)was taken as the research object.The thermal calculation,resistance calculation and economic analysis under rated load and 50% load conditions,and FLUENT numerical simulation software was used for straw numerical simulation to study on the reburning denitrification effect of straw gas in tail flue environment.According to the calculation results,the selection of the optimal parameters of the afterburning scheme and the comparison of different schemes are carried out.The results show that the source of the direct-fired furnace is the hot secondary air of the boiler,and the optimum outlet temperature of the direct-fired furnace is 1000?.For the gasification and refueling scheme,the use of uncooled or cooled to normal temperature straw gas has its own advantages.Under 100% load condition,Afterburning before the low temperature reheater to rais the reheat steam temperature to the design value.Afterburning of direct combustion and gasification respectively require consumption straw 3749kg/h,4850kg/h and 5750kg/h.respectively reduce the coal consumption of power supply by 1.85g/(kW·h),2.15g/(kW·h)? 2.12g/(kW·h).The afterburning will reburning to restore about 28% of NOX.Under the 50% load condition,Afterburning will raise the reheat steam temperature from 526.9 to 560.3?,560.6 ? and 561.1?.reduce the coal consumption of power supply by 7.39g/(kW·h),8.12g/(kW·h)? 8.28g/(kW·h).Afterburning before the SCR to raise the flue gas temperature to 320? require consumption straw 580kg/h?640kg/h and 730kg/h.When raise the reheat temperature to 579? require consumption straw 5900kg/h?7610kg/h ? 8990kg/h.It will reduce the coal consumption of power supply by 4.06g/(kW·h),4.57g/(kW·h)? 4.54g/(kW·h).Compared with different Afterburning schemes,the amount of straw required for gasification and combustion can be about 1.3 to 1.5 times that of the direct combustion scheme.The amount of flue gas generated by direct combustion supplemental combustion and the required amount of air are about 2-2.5 times that of the gasification refueling scheme.The diameter of the high-temperature flue gas conveying pipe is 1.8-2 times the diameter of the gasification gas conveying pipe.However,gasification and Afterburning requires a booster fan,and the number of pipes is large.