Study Of Blending Control System Based On Fuzzy Algorithm

The blending problems are always met in the control fields of petroleum chemical industry. Some research is done and presented in theory and application. The blending of some materials will be implemented by controlling the flow of each component. The pneumatic electrical regulating valves or chutes are used to control the flow of liquid in most of control systems, so that the proportional of blending can be controlled under allowed range easily. In these control systems, it will come true easily according to the common traditional control technology, like PD. However, the wide using of ethanol-gasoline makes it difficult to distribute and blend in the tank farm. Because the gasoline and ethanol are the combustibles and explosive materials, in terms of explosion-prevention, electrical regulating actuator is unsuitable in this control system. In the actual blending control systems, electro-hydraulic valves are used as the regulating devices to complete the distributing and blending of the ethanol gasoline. However, the control character of electro-hydraulic valve is nonlinear, so it is difficult to complete the blending control of the ethanol gasoline. To meet the technical requirement, these problems will be solved, by using PLC fuzzy control technology after studying the blending of the ethanol gasoline deeply. This system is not only low cost, but also the accuracy of blending proportion and distributing oil can meet the requirement of national criterion. It can be used in other plants of petroleum chemical to control blend gasoline.To ensure the reliability and exchange the information expedite, the system is designed a system with information management, besides to supply the interface to operators and automatic control. The system is divided into two levels. One is the monitor level, another is the measurement and control level to measure the field parameters and control the distributing course alone. In monitor level, it supplies operating and monitoring platform, and communicates with PLC. The software is divided into two parts. One is the management part. Another is the monitor part. Main duty of low level is to realize the automatic control of distributing and blending course. It’s the essential of this system too. All measurement, control calculation and regulation are done by PLC in this part. So, PLC is the most important element in this system.The proportion of 1 to 9 of ethanol and gasoline means the proportion of volume of ethanol and gasoline under 20℃. To meet this requirement, the flow of 1 to 9 of ethanol and gasoline will be kept in distributing course by fuzzy control.The control accuracy of distributing oil quality is other aim of this control system. The Nation Criterion prescribes that the accuracy must be controlled in the range of 0.2 %.The proposed method is used to complete the technological reform of many tank farms in northeast region of PetroChina and SINOPEC, and the system has already been put into operation. By testing the quality, the precision of the blending proportion and the distributing oil both can meet the requirements of the national criterion. The result is shown that this method is efficiently to solve the control of complex nonlinear system.