Two-dimensional modeling of pinane cracking tubular reactor

为了研究蒎烷在裂解管式反应器中内主要变量沿管程的分布,基于自由基链式机理,结合质量、能量和动量守恒,本文建立蒎烷在管式反应器中的二维模型.通过反应器内的温度分布、出口转化率和产品选择性与工业数据的对比,发现计算值与工业实际值吻合良好,验证了该模型的准确性.模拟分析了蒎烷进料量、入口温度和管径对反应的转化率、选择性的影响,结果表明最佳的工艺条件是蒎烷进料量为0.36 kmol.h-1,进料温度为646 K,裂解管管径(0.3～0.4)m,为蒎烷热裂解反应器的优化设计提供理论依据.     

蒎烷裂解管式反应器二维模拟

为了研究蒎烷在裂解管式反应器中内主要变量沿管程的分布,基于自由基链式机理,结合质量、能量和动量守恒,本文建立蒎烷在管式反应器中的二维模型。通过反应器内的温度分布、出口转化率和产品选择性与工业数据的对比,发现计算值与工业实际值吻合良好,验证了该模型的准确性。模拟分析了蒎烷进料量、入口温度和管径对反应的转化率、选择性的影响,结果表明最佳的工艺条件是蒎烷进料量为0.36 kmol.h~(-1),进料温度为646 K,裂解管管径(0.3～0.4)m,为蒎烷热裂解反应器的优化设计提供理论依据。     

光气合成反应器一维二维模型的对比研究

基于光气合成反应的动力学机理,分别建立了管式光气合成反应器的一维和二维数学模型。对两种数学模型分别采用不同的数值计算方法,得出反应器的床层温度和氯气转化率分布图。改变进料流量和催化剂的装填量,研究两种模型的特征表达和变化规律,对比分析两种模型计算结果。     

基于神经网络的加氢反应器温度优化控制

根据加氢反应器的特点，提出了一种加氢反应器出口温度神经元网络优化控制方法，给出了作为模型预估器的神经网络GA－BP算法流程及GA算法实现，提出了最优控制指标选择原则及控制指标表达式，经计算机对四床层一段加氢裂化装置进行仿真研究表明，该控制方法具有良好的跟踪性能及抗干扰能力。     

数学软件Mathematica在化学反应工程中的应用

化学反应工程中会遇到大量复杂的数学模型求解和数学模型参数估值问题,以往依靠手工或编写计算机程序计算.本文采用数学软件Mathematica求解了若干化学反应工程中的数学问题,例如用FindRoot命令求取非理想反应器的轴向扩散模型中彼克列(Pe)准数,NonLinearFit命令进行反应动力学模型中的参数估值,符号计算和数值计算求反应器模拟中的定积分和微分方程的解.求解过程表明Mathematica强大的计算功能可以避免编程工作,且具有可视和图形化的特点,是求解化学反应工程中的数学问题的先进工具.     

参数化模型预测空间实现及递推预测算法

本文给出线性时不变离散系统的参数化模型的预测空间实现的表达式，利用该表达式将传统的参数化模型预测算法化为状态空间递推形式，可大大减小参数化模型预测的在线计算量。为工程上实现自适应参数化模型预测控制带来很大方便。     

环氧乙烷非催化水合制乙二醇反应器的数值模拟

为深入了解环氧乙烷水合管式反应器的操作与性能,采用交错网格上的SIMPLE算法,选择4种典型的反应动力学模型对环氧乙烷非催化水合制乙二醇反应器进行了数值模拟,并与文献数据进行了比较,确定了适宜于水合反应器模拟的动力学模型。利用该模型模拟得到了反应器在流动充分发展后的截面温度和转化率分布,考察了入口温度及水合比等工艺条件对产品分布的影响。     

基于FD-NOMA的无人机通信系统容量分析

为了提高无人机与地面用户的通信质量，提出了一种基于全双工和非正交多址接入技术的无人机通信系统模型，并分析了城市和郊区两种场景下该系统模型的遍历容量。首先，推导出两种场景下该系统模型的精确容量表达式；然后，通过引入Q函数和利用截断方法解决了式中指数积分函数的计算问题，得到了容量的近似闭式表达式，并在城市场景下，采用取系数因子的方法得到了更精确的容量近似闭式表达式；最后，仿真和数值结果表明，莱斯因子对系统容量存在一定影响，增加无人机数量或非正交多址接入功率向量都可以获得更好的容量性能。     

光气合成反应器动态仿真

该文对光气合成管式反应器的动态仿真技术进行了研究.根据物料及焓守恒方程建立了管式反应器的动态机理模型,并根据模型的形式和特点选择了适当的数值计算方法,开发了光气反应器的动态模拟程序模块.模块应用结果表明,达到稳态时的结果能比较真实地反映生产实际情况,动态过程能很好地反映生产的变化趋势,并能完成对非正常工况的模拟.该模型对光气合成反应器动态特性和控制方式的研究以及光气合成相关工艺仿真培训系统软件的开发等都有重要的意义.     

RG——MOSFET的IDS特性分析

以普通长沟道MOSFET的电流模型为基础，推导出RG—MOSFET一级近似下电流模型的解析表达式，并对其物理机制进行了较详细的分析讨论。     

Increasing the reactant conversion through induced oscillations in a continuous stirred tank reactor by using PI control

We report a strategy to increase the reactant conversion in a continuous stirred tank reactor (CSTR) to produce propylene glycol through induced oscillations generated by two controllers PI₁ and PI₂ that manipulate the reactor outlet flow and the coolant flow rate respectively. It is shown that an adequate parameter choice for the PI controllers allows one to derive sustained oscillations in the concentrations and reactor temperature, which in turn allows increasing the propylene glycol production. For a suitable choice of the PI₁ and PI₂ controller parameters, we use a complete reactor model that provides with physically feasible parameters. The issues of external disturbance rejection, self-oscillations and stability have also been discussed. The analytical calculations are verified by means of full numerical simulations.     

Free radical polymerization in multilaminated microreactors: 2D and 3D multiphysics CFD modeling

This paper investigates the modeling of styrene free radical polymerization in two different types of microreactor. A multiphysics model which simultaneously takes into account the hydrodynamics, thermal and mass transfer (convection, diffusion and chemical reaction) is proposed. The set of partial differential equations resulting from the model is solved with the help of the finite elements method either in a 2D or a 3D approach. The different modeled microreactors are on one hand an interdigital multilamination microreactor with a large focusing section, and on the other hand a simple T-junction followed by a straight tube with three different radii. The results are expressed in terms of reactor temperature, polydispersity index, number-average degree of polymerization and monomer conversion for different values of the chemical species diffusion coefficient. It was found that the 2D approach gives the same results as the 3D approach but allows to dramatically reduce the computing time. Despite the heat released by the polymerization reaction, it was found that the thermal transfer in such microfluidic devices is high enough to ensure isothermal conditions. Concerning the polydispersity index, the range of diffusion coefficients over which the polydispersity index can be maintained close to the theoretical value for ideal conditions increases as the tube reactor radius decreases. The interdigital multilamination microreactor was found to act as a tubular reactor of 0.78 mm ID but with a shorter length. This underlines that the use of microfluidic devices can lead to a better control of polymerization reactions.     

Numerical modeling of polystyrene synthesis in coiled flow inverter

Recent studies show that microfluidic devices are gaining importance as micromixer in chemical and bio-chemical analysis systems. However, little attention has been paid to investigate chemical reactions such as polymerization reaction process in microreactors. In the present study, numerical modeling of the free-radical polymerization of styrene was carried out in novel coiled flow inverter (CFI) microreactor. The concept of CFI is based on the technique developed by Saxena and Nigam (AlChE J 30:363–368, 1984). This device is made up of helical coiled tube which is bent periodically to 90° at equidistant length. The CFD modeling for polymerization reaction taking place in coiled tube reactor was also performed in order to understand the influence of secondary flows on reactor performance for fluid flowing with very low flow rate. Its performance was compared with CFD results obtained in a straight tube reactor having identical length and operating under the same process conditions. The results showed that monomer conversion in the coiled tube reactor was higher than that of the straight tube reactor. Further work was carried out in the novel CFI reactor to study the effect of diffusion coefficient and number of bends on different parameters such as monomer conversion, number-average degree of polymerization (DP _n ), and polydispersity indexes (PDI). It was found that the performance of CFI as reactor increased when the diffusion coefficients of reactants was decreased. Thus, CFI was found to be an efficient microfluidic device for controlling the free-radical polymerization.     

双曲型动力学模型催化剂内扩散有效因子的数值计算

采用数值分析方法对反应动力学方程为复杂的双曲型动力学方程时催化剂颗粒内扩散有效因子进行了严格计算。采用弦位法、Ｇａｕｓｓ－Ｌｅｇｅｎｄｒｅ求积公式和Ｒｏｍｂｅｒｇ加速求积公式等数值计算方法,解决出催化剂颗粒中心处反应物浓主ＣＡ０,进而求内扩散有效因子。     

Temperature control in catalytic cracking reactors via a robust PID controller

The stabilization of fluid catalytic cracking reactors is tackled in this paper. A robust PID control law is developed in order to control the outlet reactor temperature. The suggested control is based on a reduced order model of the reactor given by a system of ordinary differential equations. The controller is synthesized using an input/output linearizing control law coupled to a proportional-derivative reduced order observer to infer on-line the unknown heat of reaction. The proposed control algorithm leads to a classical PID structure. New tuning rules are given, based on the system structure, estimations and closed-loop time constants. This control strategy turns out to be robust against model uncertainties, noisy temperature measurements and set point changes. The performance of the reaction temperature in a tubular riser reactor is numerically compared when the proposed control scheme and standard PID controllers are applied.     

Computation of optimal feed rates and operation intervals for tubular reactors

We consider mathematical models for tubular reactors in the form of dynamic distributed parameter systems. The goal is to maximize the overall profit over a fixed time horizon, where the number of cleaning operations, the length of the reactor operation between successive cleanings, and the reactor feed rates for each time interval are to be computed. We assume that product prices and consumer demands are time-dependent. It must be guaranteed that the decrease of the free cross-sectional area of the tube caused by coke deposition never exceeds a certain limit. Moreover, there are time and position dependent constraints for the state and control variables such as a maximum bound for the temperature. The mathematical model and the applied discretization scheme are outlined in detail. Numerical results are presented for a case study, where optimal input feeds and maintenance times of an acetylene reactor are computed. Of special interest is the behaviour of the program under real-time conditions, when changes in the process data or price and user demand functions require a restart of the calculation.     

Positive Polynomial Constraints for POD-based Model Predictive Controllers

This paper presents an application of positive polynomials to the reduction of the number of temperature constraints of a proper orthogonal decomposition (POD)-based predictive controller for a non-isothermal tubular reactor. The objective of the controller is to maintain the reactor at a desired operating condition in spite of disturbances in the feed flow, while keeping the maximum temperature low enough to avoid the formation of undesired byproducts. The controller is based on a model derived by means of POD, which reduces the high dimensionality of the discretized system used to approximate the partial differential equations that model the reactor. However, POD does not lead to a reduction in the number of temperature constraints which is typically very large. If we use univariate polynomials to approximate part of the basis vectors derived with the POD technique, it is possible to apply the theory of positive polynomials to find good approximations of the temperature constraints by linear matrix inequalities and to get a reduction in their number. This is the approach that is followed in this paper. The simulation results show that the predictive controller presented a good behavior and that it dealt with the temperature constraints very well.      

Steady state optimization of an ammonia reactor

A hybrid simulation technique for identification and steady state optimization of a tubular reactor used in ammonia synthesis is presented. The parameter identification program finds the catalyst activity factor and certain heat transfer coefficients that minimize the sum of squares of deviation from simulated and actual temperature measurements obtained from an operating plant. The optimization program finds the values of three flows to the reactor to maximize the ammonia yield using the estimated parameter values. Powell's direct method of optimization is used in both cases. The results obtained here are compared with the plant data.     

Model Predictive Control for Nonlinear Distributed Parameter Systems based on LS‐SVM

This paper presents a novel model predictive control configuration for nonlinear distributed parameter systems based on least squares support vector machine. First, a data‐based modeling methodology for an unknown nonlinear distributed parameter system is introduced. Subsequently, the model predictive control framework based on the aforementioned model is presented at the measured point. To verify the effectiveness and feasibility of the control arithmetic, simulation results from a tubular reactor with the controller designed by the presented procedure are given.     

Robust actuator fault isolation and management in constrained uncertain parabolic PDE systems

This paper presents a methodology for the design of an integrated robust fault detection and isolation (FDI) and fault-tolerant control (FTC) architecture for distributed parameter systems modeled by nonlinear parabolic Partial Differential Equations (PDEs) with time-varying uncertain variables, actuator constraints and faults. The design is based on an approximate finite-dimensional system that captures the dominant dynamics of the PDE system. Initially, an invertible coordinate transformation-obtained through judicious actuator placement-is used to transform the approximate system into a form where the evolution of each state is excited directly by only one actuator. For each state, a robustly stabilizing bounded feedback controller that achieves an arbitrary degree of asymptotic attenuation of the effect of uncertainty is then synthesized and its constrained stability region is explicitly characterized in terms of the constraints, the actuator locations and the size of the uncertainty. A key idea in the controller synthesis is to shape the fault-free closed-loop response of each state in a prescribed fashion that facilitates the derivation of (1) dedicated FDI residuals and thresholds for each actuator, and (2) an explicit characterization of the state-space regions where FDI can be performed under uncertainty and constraints. A switching law is then derived to orchestrate actuator reconfiguration in a way that preserves robust closed-loop stability following FDI. Precise FDI rules and control reconfiguration criteria that account for model reduction errors are derived for the implementation of the FDI-FTC structure on the distributed parameter system. Finally, the results are demonstrated using a tubular reactor example.