Optimization Research Of 660MW Supercritical Unit Denitration Control System

Along with the rapid development of the national economy,the domestic electricity demand amount and total installed capacity are gradually increasing,the thermal power units has held the dominant position in China energy structure f or ages.Therefore,NO_x and other atmospheric pollutants as the result of combustion of thermal power units put a huge pressure on the environment.Now,coal-fired boiler mainly adopts Low NO_x combustion technology and SCR technology to control the NO_x emissions.While the use of low nitrogen burner greatly reduced the generation of the NO_x in total,it is still difficult to achieve environmental protection standards,at the same time it leads to the low-temperature corrosion of the water wall.The SCR technology can make coal-fired units to achieve high denitration efficiency,and requires low industrial regulation,so it is widely used in thermal power units.The SCR technology generally adopts PID cascade regulation to control the denitration spray amount of ammonia which can better control the export of the NO x generated when the unit operated stably.However,the operating condition changes,the SCR technology system presents nonlinear and has a large inertia,at this rate,it is difficult to ensure the best mole ratio of ammonia nitrogen.If the system spray ammonia too little,it is difficult to guarantee the emission NO_x of the outlet gas.On the contrary,if more,not only causing the waste of liquid ammonia,but also increasing the amount of ammonia escape,and seriously can lead to the blockage of the air pre-heater.To ensure the NO_x emission concentration in accordance with the existing environmental standards is of great significance,hence,the control optimization of the SCR is looming ahead.By taking the Jingneng Ningdong Power Generation Co.Ltd660 mw supercritical unit as an example,this paper introduces the denitration system and the various problems occurred in the process of the "ultra low emissions".Based on the data correlation we found the problem of the denitration flow field uneven,and use d the spraying ammonia flow field uniform online test to solve this problem.In the process of analyzing the denitration system historical trend,we found the control characteristic of the denitration ammonia injection control system was relatively poor,so we determinet transform the denitration CEMS system pipeline to solve the high sample delay of the system.By reforming the spraying ammonia logic of scavenging system,we improved the control precision.By the analysis of the original denitration system control scheme,we found the error defect of the spraying ammonia logic and optimized it.By conducting large numbers of experiments,we added the Smith predictor for the cascade control loops of denitration system to optimize it and reset the PID parameters,thus the control quality of the denitration system was greatly improved.Last but certainly not least,by optimizing the feed-forward loop of denitration system,we made the ammonia spraying more reliable and finally realized the NO_x ultra-low emissions of the units.