| As the country has increased its efforts to control environmental protection,environmental protection agencies have increasingly strict requirements on the discharge of pollutants from power plants.The ultra-low emission standard stipulates that the NOx(nitrogen oxide)emission concentration of coal-fired power plants shall not be higher than 50mg/Nm3,which puts forward higher requirements on the equipment,production technology and operation level of coal-fired units.SCR(Selective Catalytic Reduction)flue gas denitrification technology with advantages of simple structure,low cost and high denitrification efficiency,widely used in newly built domestic coal-fired generating units.During the actual operation of the SCR denitrification system,due to improper adjustment of ammonia spraying in the denitrification control system and uneven distribution of NOx in the denitrification reactor,part of ammonia gas fails to react.As the flue gas enters the equipment after SCR denitrification reactor,it reacts with sulfur trioxide in the flue gas to produce ammonium bisulfate.With the gradual decrease of the flue temperature at the end of the boiler,ammonium bisulfate gas gradually liquefied,and the fly ash in the flue gas adhesion led to the blockage of the air preheater,which resulted in the increase of flue resistance,the reduction of heat exchange efficiency,the increase of energy consumption of the fan and the reduction of boiler efficiency,which seriously affected the safe and economic operation of the unit.Reasonable control of ammonia escape plays an important role in the safe,economic and environmental operation of power generation enterprises,and puts forward higher requirements for the control system of field equipment and operation level of operators.Based on this background,this project relied on the "Research and Application of Automatically Optimized Ammonia Injection System Based on Boiler Combustion Adjustment and Grid Method Multi-point Measurement of Ammonia Escape Rate"scientific and technological project of a power generation company to measure the ammonia escape amount of coal-fired units that have been put into operation.The improvement of the device,the modification of the ammonia injection control valve and the optimization design of the control system based on DCS(Distributed Control System)have realized the optimization of the ammonia injection control of coal-fired units.The following three aspects are mainly carried out.One is to lay the hardware foundation for closed-loop automatic control by changing the ammonia injection valve from traditional manual control to electric valve adjustment;the second is to carry out grid-type transformation of ammonia escape measurement facilities to realize the ammonia escape measurement in the entire flue area and solve the problem of data fluctuation and poor representativeness caused by the single-point measurement of ammonia escape at the outlet of the traditional SCR reactor;third,through the combination of traditional control model based on theoretical analysis and optimization model based on big data analysis,a relatively independent optimization control system is established,forming a full-process intelligent closed-loop control from parameter input,optimized target output,and automatic control.The research results of this subject have realized the friendly docking with the DCS system,can directly output instructions to the DCS system,ensure seamless switching between DCS control and ammonia injection optimization system control,and improve the reliability and intelligent level of system operation.After the actual production and operation,the results of this research have reached the expected goal.Under stable working conditions,it can be ensured that the average value of NOx concentration is controlled at 43-46mg/Nm3,and it can be controlled at 38-48mg/Nm3 during load rise and fall.Under the premise of meeting the ultra-low emission index,the coupling control of environmental protection and energy saving is realized,which has high promotion value. |
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