Control of the temperature in a petroleum refinery heating furnace based on a robust modified Smith predictor

Multivariable non-singular terminal composite sliding mode control of gas-water-coal mixture lifting system

In order to ensure the stability of flow rate and valve pressure difference during gas-water-coal mixture lifting, a multivariable non-singular terminal composite sliding mode (MNTCSM) controller based on accurate feedback linearization is proposed. The multi-input multi-output nonlinear system with time delay and coupling is transformed into a multi-input multi-output uncoupled linear system by using an improved Smith predictor and accurate feedback linearization. At the same time, the MNTCSM controller is designed to make the flow and pressure tracking errors of the decoupling system converge to zero in a finite time. Finally, simulations and experiments are designed for different control methods to verify the feasibility and effectiveness of the proposed scheme.

Data-driven approach for time-delay estimation of industrial processes

An accurate estimate of time delay is of crucial importance for control tasks such as performance assessment and controller design. In this paper, a novel data-driven approach to time-delay estimation is developed for a process subject to industrial background disturbances, in which the closed-loop output data under the routine operating conditions is only required. The practical solutions are proposed to estimate the time delay based on the estimated impulse response of the closed loop that is estimated online by utilizing the output data. Without relying on system identification and any prior knowledge of the process as well, the time delay is estimated directly for a large time delayed process; while for a small time delayed process, the time delay is estimated by means of the stationarilized filter, the pre-filter and the loop filter. The effectiveness of the proposed approach is validated by various numerical and industrial examples including a distillation column, a petroleum refinery heating furnace and a ceramic dryer.

Design of a Dead-Time Compensator Robust H∞ State Feedback Temperature Controller for a Precalciner of a Cement Rotary Kiln

A dead-time compensator robust H∞ state feedback controller (DTC-H∞-SFC) for the temperature control in a precalciner of a cement rotary kiln is designed. A mathematical model of the process under study with ARMAX structure was obtained. A dead-time compensator robust H∞ state feedback controller is therefore designed. The results of the comparative evaluation of the DTC-H∞-SFC vs. DTC+PI designed controllers showed that the DTC-H∞-SFC gives improved performance of the control system.

Optimization of the Countercurrent Continuous Reforming Process Based on Equation-Oriented Modeling and the SQP Algorithm

Catalytic reforming is a key technology in the petroleum refining and petrochemical industry. In recent years, countercurrent continuous reforming has put forward and practiced the new concept of matching the activity of the catalyst with the difficulty of the reaction. Based on the equation-oriented method, the steady-state model for the reactor-regenerator section of countercurrent continuous reforming was established, including the reactor module, the regenerator module, the compressor model, the heat exchanger model, the heating furnace model, and the oil property model. The inlet and outlet of each module are connected according to the actual technological process, and the model conforms to the requirement of real-time optimization (RTO). The sequential quadratic programming (SQP) algorithm is used for calculation in this study. The model is calibrated to make the calculated value more consistent with the actual value. The model simulation showed the trend of the reforming reaction and the difference between countercurrent reforming and cocurrent reforming. Finally, the process model was optimized for different goals such as the yield of aromatics, the yield of high-octane gasoline, and the yield of C₇ ⁺ aromatics. These results indicate that the established model can simulate the actual industrial process, which can meet the requirements of RTO, and obtain considerable profits for different optimization objectives.

Application of the Modified Fuzzy-PID-Smith Predictive Compensation Algorithm in a pH-Controlled Liquid Fertilizer System

An appropriate pH value of liquid fertilizer can enable crops to better absorb nutrients from fertilizers. However, the mixed liquid fertilizer with high concentration of liquid fertilizer and irrigation water has a high pH value, which affects the absorption of nutrients by crops. Therefore, the precise regulation of liquid fertilizer pH value is an important link to realize the integration of water and fertilizer in modern agriculture. Due to pipeline transportation and diffusion of the regulating liquid and liquid fertilizer, the pH value control system has the characteristics of time-varying, non-linear and time-delayed models, and it is difficult for ordinary controllers to accurately control the pH value of liquid fertilizer. Therefore, modern agriculture urgently needs a controller that can adapt to non-linear and uncertain systems. According to the characteristics of the pH regulation process of liquid fertilizer, this study proposes and designs a modified fuzzy-PID-Smith predictive compensation algorithm, which adds the fuzzy-PID algorithm to the predictor of the conventional Smith algorithm to compensate for the error between the actual and theoretical models in order to reduce the decline of control quality caused by the model mismatch to the control system. To verify the practicability and robustness of the algorithm in practical applications, a liquid fertilizer pH value control system with STM32F103ZET6 as the control core was developed. The pH control system with fuzzy-PID and Smith algorithm as controller was used as the control group. The model was simulated and tested under two conditions of exact matching and imprecise matching, and performance tests were carried out under different output flow rates. The results showed that the maximum overshoot of the modified fuzzy-PID-Smith predictive compensation algorithm was significantly less than that of the other two algorithms at different output flow rates, with an average of 0.23%. The average steady-state time of adjusting the pH value of liquid fertilizer from 7.3 to 6.8 was 72 s, which was superior to the 145 s and 3.2% of fuzzy-PID and 130 s and 1.4% of the Smith controller.