Research On Dosing System Control Of Water Treatment Plant

Water is very important for people’s life. With the development of our society, people’s requirements on the quality of water is increasing correspondingly, which result in a higher requirements to the water treatment process. Coagulant dosing is one of the most critical processes in water treatment process. If the dosage is not enough, the quality of water can’t reach the standard, on the other hands, if the dosage is too much, not only the effect of coagulation being affected, but the medicine is wasted, which will inevitably result in the increase of the operating cost.This paper is about ensuring the effect of coagulation by adjusting the dosage to the changes of factors such as water quality and quantity etc. of the raw water quickly and accurately. The survey found most of the water current dosing control system uses feed forward-feedback control structure, when the raw water quality and quantity changes, feed forward controller is used to reduce or eliminate the interference, feedback controller is used for bias correction. The feed forward controller mainly adopts flow proportional control, which is only control the increase in drug based on the change of raw water flow. The impact of changes in water quality is mainly fixed by the feedback controller. Changes in water quality affect the dosage is an important factor, however, coagulation process is a course that have time delay, using feedback to correct the water quality is often timely enough. In this paper, least-squares method has been used to improve feed-forward controller, take water quality factors into consideration, so that the amount of feed-forward become more accurate. Currently, water treatment company mainly use traditional PID control algorithm in feedback controller. If the water quality and quantity is stability, traditional PID has relatively better result in control effect. If the water quality and quantity is changed, it will lead to increased interference and changes in the coagulation process model, the traditional PID controller, which use unchanged control parameters, have difficulty to respond well to these changes, system shock intensified, flow of current SCD of the system to track setting ineffective. To solve the above problem, this paper designed IMC-PID controller and Expert-PID controller respectively, and compared with the traditional PID controller. Simulation results show that, feed forward dosage that fitted out by least squares is similar with the best dose that fitted out by beaker test. When the changes of water quality and quantity lead to interference and changes in the coagulation process model, IMC-PID controller and Expert-PID controller perform better than the traditional PID controller in tracking, anti-stability, capacity and interference robustness are also improved.