DCS Based On The Technology Of Coal-fired Power Plant NO_x Ultra-low Emissions

In the process of burning of coal for power generation in the power plants, series of pollutants (including sulfur dioxide (SO2), nitrogen oxides (NOx) and dust particles) creat great harm to the atmospheric environment. In order to ensure the pollutants of coal-fired power generating units under or near to the atmospheric pollutant emissions limits (the emission concentration of dust, sulfur dioxide, nitrogen oxide are not more than 10,35,50 mg/m3 under the condition of 6% oxygen content) of gas turbine units, we conducted a series of technical innovation of ultra low emission (near zero emissions). The mainly discussed is the technology of ultra-low NOx emissions in this article. In the example of super-low NOx emissions technology and process of the capacity of 330 mw unit #5 in Shiheng power plant, combined with the actual working condition, we designed a set of corresponding denitration control system based on DCS, mainly includes the data acquisition and processing system, modulating control system, sequence control system and important interlock protection, etc.In the first of this article, we choose the low nitrogen burner alteration technology from the perspective of the generation mechanism of NOx, and control the boiler combustion NOx concentration about 200 mg/m3. Secondly, we choose the Selective Catalytic Reduction technology (SCR) after boiler and set the reactor to ensure export NOx concentration is lower than 50 mg/m3. On the basis of the reconstruction of the equipment to design a set of match the unit with the DCS system, and in the view of the actual complex and changeable working environment, we optimized the control strategy and the operating mode of DCS, and use cascade control to ammonia area within the public system of liquid ammonia evaporator pressure and temperature control to solve the single loop control leads to stress and the problem of large temperature fluctuations. In the use of SCR inlet ammonia flow by robust control, we solved the problem of the low rate of automatic investment and poor quality in the SCR export NOx control system. And also we can reduce the workload of the operators, improve the control level and efficiency of denitration system, effectively ensure the safety of the power grid and stability of the unit operation.