Design And Realization Of Control Systems For Mixed Gas Station In The Cold Roll Factory

Mixed gas pressure station of Xinyu Iron & Steel Co. Ltd. Cold Roll Factory is designed for supplying mixed gas for the Continuous Annealing Line. It requires when mixed gas in the furnace is ranged from 0 to 20000Nm3/h, the calorific value must be limited in the range of ± 4%, the pressure must be limited in the range of ± 5%.For the current metallurgical industry, there are so many uncertain and unpredictable factors in the process of mixing blast furnace gas and coke oven gas. The mathematical model is nonlinear and difficult to be established. Pressure and flow of the gas interact with each other, they are coupled strong. Because of user’s operating continuous, the mixed gas changes strongly, which causes the calorific value and the pressure of the mixed gas be unstable. The instability of the pressure and the calorific value becomes a "bottleneck" which restricts the steel products of the metallurgical field. The steady of the calorific value and the pressure of the mixed gas are studied. This research has important significance to guarantee the quality of the products.The article is talked about how to optimize the technics and the program of the control system about the calorific value and the pressure, researching on the mixed gas pressure station of Xinyu Iron & Steel Co. Ltd. Cold Roll Factory, based on the investigation of the mixed pressure control system, pointing at the requirement to the calorific value and the pressure of the mixed gas. The method of realizing the steady of the calorific value and the pressure is studied in order to meet the need of the requirement of technics and production.In the respect of technics improving, there are two solutions. The first one is the plan applied mostly in the current steel factory, this plan is simple and mature, but the investments are too large and construction is too long, so it is not fit for the current situation of the factory. The another option is to change small on the basis of the production process, a simple upgrade for part of the equipment, in order to meet the control requirements. This plan is quite difficult relatively, and there is no example to refer. But it is good to meet the company’s current production requirements the because of the few investments and the short construction. Therefore, the final selection is the second solution.In the respect of optimizing to control system, there are several control difficult points. According to the difficulty, the five control loops are designed. Five parts are the control loop of the calorific value, the control loop of mixed gas pressure, the control loop of the pressure behind the blast furnace gas compressor, the control loop of pressure behind the coke gas compressor and the control loop of the few flow of mixed gas. Combined with the production process and equipment characteristics, most of the control loops are put to use subsection-PID compound control as control algorithm. The method of work overcomes difficulty that the calorific value and the pressure are unstable when flow of mixed gas fluctuate or run on the condition of the flow is few. It not only realizes the stability of the calorific value and the pressure but also meet the requirement of production.