Research On The Control Method Of The Ammonia Gas Flow System Of Power Plant Denitrification Based On Fuzzy Theory

Along with more strict national standard of NOx emission, all power plants are forced to face the problem of denitrification transformation, selective catalytic reduction(SCR) technology become the first choice of domestic power plants. Ammonia gas flow system work as the most important part in the SCR denitrification system, its control effect will directly determine the emission of NOx in power plants. Considering the disadvantages of slow respond speed, poor robustness as well as poor anti-interference performance, the conventional control schemes of ammonia gas flow system are insufficient, which buries the hidden trouble for the stable and economic operation of SCR system.In order to improve the control quality of ammonia gas flow and NOx emission in power plants, the control system of ammonia gas flow is studied in this paper, which includes the formulation of the control scheme, the establishment of forecast models as well as the design and implementation of the advanced controller.Based on detailed analysis of the SCR denitrification system and conventional control schemes of ammonia gas flow system, the variable ammonia nitrogen mass ratio scheme with fuzzy Smith controller is proposed by using the fuzzy control theory. Considering the ill effects caused by the lag of NOx concentration measurement and the change of the ammonia nitrogen mass ratio, the influence factors of inlet NOx concentration and ammonia nitrogen mass ratio are analyzed and the forecast mode1 s are established with the principal component analysis method and multivariate linear regression theory. TO guaran tee the accuracy and precision, established models are inspected and corrected by the goodness of fit test, the overall significance test as well as the variable significance test.The bi-fuzzy Smith controller is designed considering the large lag and time-varying characteristics of ammonia gas flow system. In the design, Smith arithmetic and fuzzy theory are combined, the control rules are formulated. By simulating, the control effect of the variable ammonia nitrogen mass ratio scheme with bi-fuzzy Smith controller to NOx emission concentration is analyzed. Considering that there are two kinds of schemes to put the denitrification contol system into the power plant control system, which are DCS and PLC, the idea of PLC implementation of bi-fuzzy Smith controller based on the method of look-up table and interpolation algorithm is analyzed, which guarantees the industrial application of the designed controller.By the research and simulating, it is validated that the ammonia gas flow control scheme based on the fuzzy theory, which owns better dynamic performance and robustness, can steadily control the export NOx concentration in the ideal range under the operating condition of SCR system with alterative condiction and multi disturbance, which meets the control requirements of the ammonia gas flow of power plants.