| Rotary kiln is the key equipment in metallurgical industry. Product quality, energy consumption, production safety and cost are directly related to the running state of rotary kiln. Calcination temperature in rotary kiln is an important process parameter to reflect the running state that plays a decisive role to ensure product quality, achieve safe and stable operation and reduce labor intensity. As rotary kiln is a typical complex controlled object with the characteristics of multi-variables, nonlinear, time-varying and large inertia, it is difficult to obtain the satisfactory control effect by traditional control methods. Currently, many rotary kilns are still controlled by work experience of the site operators. It suffers many troubles, such as low automation, low productivity, high energy consumption and unstable product quality. Therefore, the research on the control method of calcination temperature in rotary kiln has great significance.Under the background of the lime kiln of Tiantie group, this paper draws a conclusion that calcination temperature can be effectively controlled by adjusting gas flow and secondary air flow through analyzing the process characteristics and the influencing factors on calcination temperature. According to lime kiln historical data of Tiantie group, T-S model between calcination temperature and gas flow is established by applying the T-S fuzzy modeling method. Antecedent and consequent of T-S model are identified apart. Fuzzy c-means clustering algorithm is used to identify antecedent parameter and structure. Consequent parameter is identified by least square method. Further more, T-S model is transformed to a linear time-varying state space model for the following control algorithm.Due to the complex characteristics of rotary kiln, synthesis approach of predictive control is used to control calcination temperature. Synthesis approach of predictive control has became a mainstream of predictive control theory in nowadays with optimal control as the most important theoretical reference system, Lyapunov stability analysis method as a performance guarantee, invariant set and linear matrix inequality as basic tools. There are two problems with synthesizing state feedback predictive control. First, the method steers system state without offset only at the origin. The second is the method can not achieve a wide range of control with the limitation of the feasible region. Aiming at the problems, methods are proposed to improve synthesizing state feedback predictive control. Synthesizing predictive control with target tracking can track changing given set points by calculating steady states associated to the given output and modifying the terminal constraint. Scheduled Synthesizing predictive control achieves a wide range of control by introducing the idea of scheduling. Offline, a set of controllers are designed with their regions of stability overlapped each other. Online, scheduling of the controllers can move the state through the intersections of the regions of stability of different controllers to the desired operating point.Finally, a calcination temperature control system in rotary kiln is designed. The results of simulation show the effectiveness of synthesis approach of predictive control. |
