Research On PH Value Control In Reclaimed Water Reverse Osmosis System

In recent years, with the rapid development of China’s national economy, the increasing number of industrial enterprises and the constantly population growth, the contradiction between water resource supply and demand is increasingly prominent. The application of reverse osmosis technology, as the most advanced and effective water treatment technique is playing significant role in various water reuse technologies, and pH value of the water treatment is one of the most important test indicator in reverse osmosis system.This thesis, on the basis of a water treatment plant as background, makes a deep research on reclaimed water process flow and reverse osmosis system. According to water treatment requirement, if only pH value get between7.0～9.0, water from reverse osmosis treatment uses for boiler. By researching on the pH value control method domestic and overseas, researching on different acid and alkali neutralization titration curve, analyzing the widely-used piping and instruments diagram management that most of water treatment plant employed, the thesis makes conclusion that in the acid and alkali neutralization titration progress, pH value shows nonlinearity and lagging to some degree and easy to be affected by temperature and other outside factors, which makes it is hard to establish mathematical model of the pH value; the neutralization of pH value in real operation is simplified to continuous stirred tank system in this thesis, according to theoretical analysis in the feature and parameter characteristics of acid and alkali neutralization progress, and the law of conservation of the materials and the law of electric charge conservation in chemical reaction, the author establishes a mathematical model of the controlled plant. On the basis of real data and expert experience, the input of the control system is under fuzzification as well as the establishment of fuzzy controller. PH value fuzzy PID controller is designed by making use of fuzzy control possessing the feature of strong robustness, good dynamic response, and small overshoots, and its design is also combined with the reliability of conventional PID control. Taking advantage of fuzzy inference method, the pH value fuzzy PID controller realizes the on-line setting of pH data, which figure out the nonlinearity during the acid and alkali neutralization process.In conclusion, the stability of pH value fuzzy PID controller, which makes pH value of water flow fit requirement, embodies the rationality of the design in this thesis.