Research And Application On The Control Of Adding Acid To Circulating Water Based On Fuzzy Control

In a thermal power plant, the circulating water system has the distinct characters such as high consumption of water, high pollution, etc. Recently, water-saving and emission-reduction of the circulating water system has aroused the universal attentions of the researchers since the water resource is lacking increasingly. Therefore, most thermal power plants try various kinds of advanced methods to treat with the circulating water. One of the most economical and effective approaches is the combination method of adding acid and inhibitor, in which the control of adding acid is one key step of the entire process. At present, the manual control or PID control is adopted extensively to regulate the amount of acid to be added. The accuracy and the uniformity can not be guaranteed in the above two control methods, which will cause that the pH value fluctuates evidently. This may affect the stable operation of the generating units.In this paper, the fuzzy controller is applied to regulate the amount of the acid to be added. The error and its variance rate are adopted as the input of the fuzzy controller. The frequency of the convertor is employed as the output of the fuzzy controller. To counteract the effect of seasons on the amount of acid to be added, various output universes are designed in the fuzzy controller for different seasons to satisfy the requirement of low rotating speed of the adding acid pump in winter and the high rotating speed of the adding acid pump in summer. Consequently, the fuzzy control of adding acid for different seasons is realized without changing the membership functions and fuzzy rules. In the conventional fuzzy control strategy, the membership functions are determined based on the experiences of the operators, which is vulnerable to the subjective consciousness of the operators. This often causes the subjectivity and the blindness in the design process of the fuzzy controllers. For this reason, the PSO algorithm is introduced to optimize the membership functions of the fuzzy controller in this paper. Simulation results are given to demonstrate the effectiveness of the proposed control method.The control system of adding acid to the circulating water in Tieling thermal power plant is analyzed detailedly in this paper. Moreover, the corresponding fuzzy controller is designed and realized in the form of programmable logic controller. The strategy that computation online and table lookup offline is adopted in the proposed control algorithm in order to reduce the online computation. In addition, the functional design of the upper computers is carried out and the online supervisory control is implemented in this paper. The satisfactory control effects are derived by analyzing the operating curves of the considered system.