The Study And Application Of The Advanced Process Control For Styrene Plants

Styrene is an important organic chemical material and has wide applications. On the whole, the world styrene production capability is superfluous, but the consumption in china is increased. As a result, more foreign products will go to our country, and this will threaten the styrene development in china. Hence, the scale and technology of the plants should be enhanced using the advanced technology. Many factories have purchased the advanced process control software package (APCSP) for styrene plants to improve economic benefit. These plants had good performance by applying those packages in early days, but the APCSP can't be used for a long time in china. By analyzing the reason, we find that the robust of the APCSP is not strong, and its maintenance is complicated. In fact, the plants have changed after a long time, but the model in those APCSP can't be updated on time or is difficult to be updated. Finally the APCSP can't be used.How to resolve the above problems is the emphasis in this thesis. The model accuracy is the key for the long time and effective running of the APCSP, while the simple and effective model identification method must be performed to reduce the complexity of maintenance. Hence the IMC-PID and MODEL-PID method based on the model identification are proposed. The accurate model is the keystone for applying the advanced process control, and the simplest method is by using optimal method based on the dynamic response of the plant. To simply and effectively get the model, collect data by using the OPC/DDE data traffic technique and get the dynamic characteristic of the control loop by adding test signal to it; to reduce the algorithm complexity, identify the model parameters by using the NLJ optimization method.For the industry plants with longer time constant which difficultly get the stable state because of the larger disturbance and time-delay, the novel closed-loop model identification method called Model Parameters and State Equation Initial Values Identified simultaneously (MPSEIVI) is proposed; for the model error because of larger dead-time, an improved method for resolve the dead-time called M-Pade method is performed.To ensure effective running for a long time, reduce the investment and sufficiently mine the potential of the original system, the model PID technique based on the classical PID control is presented. It uses the existing PID controllers and doesn't change them. If only the model parameters can be identified, the parameters of the PID controller can be resolved.The results of the classical PID controller are unsatisfactory for some complex control loops. For them, the IMC-PID method has applied in some literatures. However, when we apply the IMC-PID controller, it is too difficult to choose optimal parameters of the PID controller because many results can be found by using the complex mathematics method. Hence, the new method from IMC controller to IMC-PID controller based on the theory of identical step response is proposed.When applying the IMC-PID control the existing PID controller form should be changed, but some control system can not be changed. For these control loops, the model PID method is performed to implement the optimal control.Based on the above theories and methods, a novel advanced process control software package for the Styrene plant is developed, and has a successful application on styrene process. Practical applications show that the IMC-PID and the IMC-MOD-PID APC software based on NLJ,IMC and MPSEIVI algorithms are advantageous of being simple, practicable, economical and easy to perform for the PID optimization of the complex process system.