CSTR反应器抗扰动能力的稳态模拟与动态模拟

本文以环氧丙烷PO水合法制1,2-丙二醇为例,对CSTR抗扰动能力进行了稳态及动态模拟的对比研究,分析了进料温度扰动对PO转化率的影响。结果表明:若进料温度升高,稳态与动态模拟结果一致,PO转化率增幅较小;当进料温度降温幅度4.00K时,稳态与动态模拟结果一致,PO转化率减幅较小;当进料温度降温幅度≥4.00K但高于熄火温度时,稳态模拟结果显示CSTR仍处于较高PO转化率状态,转化率变化较小,但动态模拟结果表明此时CSTR已从高PO转化率状态跌至低PO转化率状态,稳态与动态模拟结果不符;当进料温度降至熄火温度以下时,稳态与动态模拟结果一致,CSTR均从高PO转化率状态跌至低PO转化率状态。通过对比可知,动态模拟比稳态模拟能更真实地反映CSTR的抗扰动能力。     

Dynamic analysis and linear control strategies for proton exchange membrane fuel cell using a distributed parameter model

To satisfy high power density demand in proton exchange membrane fuel cells (PEMFCs), a robust control strategy is essential. A linear ratio control strategy is examined in this work. The manipulated variables are selected using steady-state relative gain array (RGA) analysis to be the inlet molar flow rates of hydrogen and coolant, and the controlled variables are average power density and average solid temperature, respectively. By selecting proper manipulated variables, the PEMFC does not exhibit sign change in gain and hence can be controlled by using a linear controller. Transfer function models obtained from step tests on the distributed parameter PEMFC model are used to design controllers for the multiple input–multiple output (MIMO) system. In addition, a ratio control strategy is proposed and evaluated, where the inlet molar flow rate of oxygen is used as a dependent manipulated variable and changed in a constant ratio with respect to the inlet molar flow rate of hydrogen. Simulation results show that the ratio control strategy provides a faster response than a MIMO control strategy. This ratio control strategy is able to circumvent the problem of oxygen starvation, and the increase in average solid temperature is small as compared to the MIMO control strategy.     

基于小波变换的非线性广义预测控制

提出了基于小波变换的非线性广义预测控制算法。预测模型采用Hammerstein模型,对于其静态非线性部分采用小波网络来辨识,动态线性部分用最小二乘法来辨识。这种辨识方法比传统的多项式拟合的模型误差要小得多。基于这种预测模型广义预测控制器弥补了传统广义预测控制的模型失配问题。以CSTR为例对所设计的控制器进行仿真研究,结果表明控制器能够取得良好的控制效果。     

Power-shaping control of reaction systems: The CSTR case

Power-shaping control is a recent approach for the control of nonlinear systems based on the physics of the dynamical system. It rests on the formulation of the dynamics in the Brayton-Moser form. One of the main obstacles for using the power-shaping approach is to write the dynamics in the required form, since a partial differential equation system submitted to sign constraints has to be solved. This work comes within the framework of control design approaches that could possibly generate a closer link between the notions of energy that are specific to reaction systems as derived from thermodynamics concepts, and the dynamic system stability theory. The objective of this paper is to address the design of power-shaping control to reaction systems, and more particularly the step of solving the partial differential equation system. In order to illustrate the approach, we have selected the classical yet complex continuous stirred tank reactor (CSTR) as a case study. We show how using the power-shaping approach leads to a global Lyapunov function for the unforced exothermic CSTR. This Lyapunov function is then reshaped by means of a controller in order to stabilize the process at a desired temperature.     

基于反馈线性化的CSTR自适应模糊控制

本文应用输入一输出反馈线性化方法和李雅普诺夫方法,研究了一类非线性系统的自适应模糊输出跟踪控制问题,并将其应用于带噪声干扰的连续搅拌反应釜.仿真结果表明,该算法不仅能克服外界干扰对系统的影响,而且具有跟踪精度高,收敛速度快的优点.     

Improved fractional augmented control strategies for continuously stirred tank reactors

Controlling concentration and temperature of continuously stirred tank reactor (CSTR) is an extremely challenging task in chemical process industries. This is because conventional unity feedback schemes do not guarantee stable operating conditions for the CSTR process. Therefore, fractional calculus is augmented with multi-loop control to achieve enhanced stability and closed-loop performance than unity feedback structure in this work. Accordingly, three different fractional-order-based novel multi-loop control structures are proposed based on time domain analysis. In two of the proposed strategies, fractional-order PID controller (FOPID) and internal model control (IMC)-based FOPID controller with fractional filter are used in the inner-loop. Moreover, fractional-order-based Lyapunov stability rule of model reference adaptive control (MRAC) is used in outer-loops for both of the above mentioned methods. Finally, an advanced multi-loop predictor with FOPD controller in the inner-loop and FOIMC controller in the outer-loop is also proposed. In this work, fractional-order, filter parameters, and FOPID settings are obtained by minimizing multi-objective functions using modified particle swarm optimization (PSO) algorithm. Closed-loop responses and control efforts of the proposed control strategies are compared with that of FO-Lyapunov-based MRAC scheme. Quantitative performance analysis is also carried out on all proposed methods based on error metrics and total variation of the control signal.     

Segregated regions in continuous laminar stirred tank reactors

Using visualization techniques, including acid/base reactions and UV fluorescence, we provide experimental evidence of segregated regions (islands) during mixing of viscous Newtonian fluids under laminar flow conditions in continuous stirred tank reactors (CSTRs). The effect of inlet/outlet stream position and Reynolds number on the dynamics of the mixing processes is examined. Numerical experiments in 3-D map were able to capture the main features of the CSTR flow by perturbing a Batch system using an imposed axial flow. Asymmetric flow patterns produced by off-center positioning of inlet and outlet pipes cause a reduction in size of the segregated region, enlarging the chaotic region and leading to more efficient mixing. Under dynamic inlet flow conditions, the laminar steady flow is perturbed, giving rise to an asymmetric flow pattern that is able to destroy toroidal segregated regions. Counter-intuitively, higher agitation speed (higher Re) did not enhance overall mixing efficiency. Faster agitation stabilized the toroidal regions, making it harder to destroy them. In addition, dynamic mixing protocols are investigated to enhance mixing performance. We demonstrate that time-dependent pumping and stirring protocols are able to efficiently destroy long-lasting toroidal regions.     

CMAC网络建模在非线性预测控制中的应用

CMAC是一种具有线性结构、算法简单的局部化设计网络。将 CMAC网络应用到具体非线性系统的预测控制研究中。对一类 CSTR系统的仿真结果表明 ,该预测控制策略响应快且容易实现 ,具有较强的鲁棒性 ,对于改善非线性预测控制性能不失为一种有益的尝试     

Evaluation of residence time distribution and mineralogical characterization of the biooxidation of sulfide minerals in a continuous stirred tank reactor

The residence time distribution (RTD) of the liquid phase and the mineralogical characterization of the biooxidation of refractory gold mineral was studied in a continuous stirred tank reactor. The latter was achieved using a native mixed culture of acidophilic mesophiles. The RTD was assessed using a mathematical model of stirred tanks in parallel. The oxidation of sulfide and the phases generated through the biooxidation process were evaluated via X-ray diffraction (XRD).The results indicated that the experimental RTD fit to the model. The reactor has a high tendency to behave as a completely mixed reactor. However, the mixed flow inside the reactor has disturbances such as by-pass and dead zones. The estimated mean residence time for the model was approximately 36% greater than the theoretical residence time. It was probably caused by the delay in the outflow of the tracer due to gas hold-up, foaming at the top and the design of the reactor outlet structure. The XRD outcomes showed that the oxidation of arsenopyrite was greater than that of pyrite. Similarly, the formation of jarosite and brushite was observed. It was concluded that the dead zones could increase the probability of jarosite precipitations.