连续搅拌槽式反应器定态绝热操作的热稳定性

本文研究了连续搅拌槽式反应器(CSTR)定态绝热操作的临界条件及其有关问题.讨论了分析这类放热反应器操作条件中热灵敏区间的新方法,导出了点火(飞温)和熄火这两个重要的热灵敏边界的数学表达,并从理论上指出了这类反应器的一个新的概念:跃迁状态,即热灵敏区间的消失,提出了跃迁条件的数学表达.还讨论了在十分接近热灵敏边界(点火点)的操作条件下,反应系统到达点火的时间(延滞期).     

移热速率对稳态非等温理想反应器效率的影响

以正丁烷的液相异构化反应为例,探究了移热速率对稳态非等温理想连续搅拌釜式反应器(CSTR)和活塞流反应器(PFR)效率的影响。研究结果表明:从反应器绝热操作到具有一定换热速率,再到冷却介质温度不变的情况,随换热速率增大,达到一定转化率时所需的CSTR和PFR反应体积曲线由一个交点、到两个交点,再到相切,最终无交点,即随换热速率增大,在不同阶段两种理想反应器效率的相对大小不同。此结果可为理想反应器的选型提供指导。     

以玉门直馏七碳烃馏份铂重整制取甲苯的中型多段绝热反应

为了提供铂重整工业装置的设计数据及操作指标,进行了三个和四个串联绝热反应器的中型试验。铂重整中型装置的处理量为每日200—350公斤。原料油为玉门直馏汽油中85—125℃七碳烃馏份,以生产甲苯为主。采用三个反应器时,合理的操作条件为进口温度,490℃;压力,30气压;汽油分子循环比,6-7∶1;空速,3.稳定重整油的液收率为92％（重量）,甲苯产率为25％（重量）,副产品氢气纯度为95％,氢气产率为1.8％（重量,对原料油）。每个反应器催化剂容量的比例为1∶1∶1。采用四个反应器时,在同样的操作条件下,液收率为86％（重量）。甲苯产率为28％（重量）。由于第四反应器的平均床层温度过高,催化剂积炭较快,催化剂的活性不能持久。但如将第四反应器进口温度降至470℃,第四反应器即会失去效用。因此不宜采用四个反应器。在试验过程中,用热平衡方法证明中型反应器能达到绝热的条件,因此保证了工业装置设计数据的代表性。试验时,并测定了各反应器的温度降。反应系统内反应物和生成物的总热容量,以及各反应器内生成芳香烃的反应热是按照热力学基本数据计算而得的。     

实验室绝热反应器的开发和设计

在绝热反应器中进行工程动力学的研究是一种有益的方法。本文介绍了实验室绝热反应器的设计方法及其结构。实验测定了反应器的绝热效果，并计算了在操作条件改变后，反应器的非稳态传热情况。计算结果表明，对本实验装置操作条件获得重新稳定所需时间为０．８４７ｈ。     

甲烷化反应工艺流程和反应器模拟

通过分析绝热反应曲线和反应过程CO转化率曲线,设计可行的多级绝热固定床甲烷化工艺流程,得到了一个第一甲烷化反应器循环比为3.0,反应器个数为3的甲烷化反应系统。建立绝热固定床反应器的一维拟均相数学模型,在工业操作条件下,分析了该流程中3个甲烷化反应器内的温度和摩尔分数分布规律。在合成气的进料速度800 kmol/h,进料温度553 K,操作压力为3.0 MPa,氢碳物质的量比约为3.0,循环比为3.0的条件下,模拟结果表明:物料在3个反应器出口的温度分别为879,725,611 K;甲烷干基摩尔分数分别为53.48%,79.24%和95.49%;CO在3个反应器出口的转化率分别为82.18%,99.41%和100%。第3反应器出口CH4干基摩尔分数为95.49%,满足了工业生产要求。     

管式固定床反应器多态的研究 Ⅱ.反应动力学对多态的影响

本文通过对具有轴向返混拟均相一维模型参数分析,研究了管式固定床反应器的多态问题。计算结果示出在非等温非绝热管式固定床反应器中在较宽的 Peclet 数范围内存在着3个定态。反应级数 L—H 机理的吸附平衡常数明显地影响反应器操作的多态范围。     

非绝热式固定床反应器的参数敏感性及热失控临界参数

寻找安全有效的反应条件一直是绿色化工的重要研究内容之一。采用邻二甲苯氧化的反应动力学模型,分析了非绝热式固定床反应器的参数灵敏性和热失控行为,考察了非绝热式固定床反应器温度对冷却介质流量、进料温度和初始压力的敏感性。模拟计算结果表明,当反应进入敏感性区域后,反应器对冷却介质流量、进料温度和初始压力的改变极其敏感。采用系统散度判据（div>0）计算该反应的热失控临界操作参数,计算结果与文献中的判据进行了分析比较,得到类似的结果,但计算更简单。考虑冷却介质的影响,修正了div判据,得到更准确的热失控临界操作参数。研究结果表明,此判据能为反应器的设计及过程控制提供重要的参考依据。     

堰上清液高度的计算问题

骪++本文对各种板式塔中,平直堰和齿形堰的堰上清液高度的计算问题分别进行讨论.对于平直堰提出了用简化公式计算液流收缩系数E: E=1+[0.00012-0.00386 ln(lw/D)](L_h)/(l_w~(2.5))上式对Bolles公式的平均误差为0.576%,由此可以用Francis公式计算出堰上清液高度。对于齿形堰,当堰上清液层超过齿顶时,可以用下式计算堰上清液高度h_(ow): h_(ow)=(O.23+2.47 h_n)(L_s/l_w)~[0.3-0.0326ln(h_n)]上式的平均误差为0.48%。     

绝热固定床反应器的研究——(Ⅱ)床内定态温度分布

本文运用一维非均相动态模型,研究了绝热固定床反应器床内定态温度分布问题.由于床内温度分布直接关系到反应器内高温区长度,因而对温度分布影响因素的研究甚为重要.本研究分别阐明了催化剂层、气体及器壁导热对床层温度分布的影响,并以实例予以说明.研究表明,实验型反应器器壁导热的影响不容忽视,因而将实验数据用于放大时必须考虑器壁导热的影响.     

绝热轴向固定床中气流均布的数学模型

以前文为基础,在 0.4m、0.535×0.535 m 以及1.32×1.32 m 的装置中,对侧向进、出口绝热轴向固定床反应器的气流均布问题作了进一步的研究。采用瓷球促使反应器内气流均匀分布,根据理论分析和实验结果提出了数学模型,得到气流不均匀度的表达式:s=[k_1-k_2(H/D)~(k3)][1-exp(-1/k_4Eu)]     

Data mining macrokinetic approach based on ANN and its application to model industrial oxidation of p-xylene to terephthalic acid

Considering that kinetics and thermodynamics are coupled with heat and mass transfer effects being present in the liquid-phase catalytic oxidation of p-xylene to terephthalic acid (OXTA) in an industrial type of continuous stirred tank reactor (CSTR) and that the time evolution of the concentration of all the interest intermediate and final products of OXTA in the industrial CSTR cannot be obtained to estimate macrokinetic parameters, a novel data mining macrokinetic approach based on artificial neural network (ANN) was proposed to develop the macrokinetic model of OXTA in the industrial CSTR, which mines intrinsic kinetics and transport phenomena information from the sample data collected from OXTA in the industrial CSTR. Firstly, the reaction orders of OXTA are estimated by the mass transfer-free experiment data in the laboratory semi-batch stirred tank reactor. The kinetics of OXTA in the industrial CSTR is assumed to be zeroth-order with respect to gaseous reactants, 0.65-order with respect to p-xylene, and first-order with respect to the other liquid reactants, respectively. Secondly, ANN is employed to model the influence of the reaction parameters on the rate constants of OXTA in the industrial CSTR. Based on the sample data collected from OXTA in the industrial CSTR, heuristic differential evolution algorithm is employed to adjust the weights and thresholds of the rate constant ANN in such a way that it minimizes the prediction error of the macrokinetic model, and thus the optimal weights and thresholds are obtained and the macrokinetic model of OXTA in the industrial CSTR is developed. The reliability of the macrokinetic model was investigated and the satisfactory results were obtained. Further, a generalized macrokinetic approach for multi-phase reaction in industrial reactor was suggested too.     

Parametric sensitivity of a CSTR

It is shown that the generalized sensitivity criterion recently developed in the context of thermal explosions and tubular reactors can be easily applied in the case of a CSTR as well. An illustrative example concerning sensitivity analysis of a single nth order irreversible exothermic reaction in a nonadiabatic CSTR is presented. A generalized region of parametric sensitivity is identified where the reactor temperature is parametrically sensitive simultaneously to all the input parameters. Asymptotic analysis for large heats of reaction is performed to investigate limiting behaviour, which leads to the classical Semenov limit in the case of large activation energies. It is shown that parametric sensitivity can occur even when unique steady states exist for all Damköhler number (Da) values. Furthermore, if operating conditions are chosen so as to avoid completely the possibility of parametric sensitivity for all Da, then the possibility of steady-state multiplicity is automatically avoided.     

Emulsion polymerization and copolymerization in continuous reactor systems

Continuous reactors are important for commercial production of latex products and they can be useful tools for fundamental polymerization kinetics studies. Results are presented for four projects: (i) elimination of conversion oscillations in continuous stirred-tank reactors (CSTR) by use of a tubular prereactor; (ii) use of a seed-fed CSTR to measure free radical transport from monomer-swollen latex particles; (iii) development of a continuous process as an alternative to a commercial batch process; and (iv) determination of copolymerization kinetic parameters with a steady-state CSTR system.     

The stirred tank forced

We examine the response of a continuous stirred tank reactor (CSTR), in which a simple irreversible reaction A → B occurs, to periodic variations of the coolant temperature. The amplitude and the frequency of the forcing are used as control parameters. The remaining operating conditions are chosen so that the unforced CSTR exhibits a single stable oscillation; this means that for small forcing amplitudes the system behaves like a typical forced oscillator: its response consists of alternating entrainment and quasi-periodicity. As the forcing amplitude grows, more characteristic traits of the CSTR and the particular forcing variable become apparent, and a complicated picture develops, involving the co-existence of multiple periodic, quasi-periodic and even chaotic oscillations, period doublings and global bifurcations. We track several of these traits numerically, placing special emphasis on the mechanisms by which such features branch out from the well-defined low-amplitude region. Several algorithms based on shooting methods for boundary value problems are used in this task, and some appropriate ways of tackling the simple initial value problem of simulation are also employed. In particular, the need for efficient algorithms to tackle global bifurcations is stressed. Such algorithms seem to be indispensable tools in the systematic study of the forced CSTR and, more generally, of periodically forced oscillators.The qualitative traits discovered for the forced CSTR are compared with other known results for model systems, and several questions present themselves as possible subjects of further research, both for the CSTR and for a wide class of periodically forced and/or coupled reactor models.     

FUZZY GAIN SCHEDULED CSTR WITH GA-BASED PID

In this article, a new control scheme, the gain scheduled genetic algorithm (GA)-based PID is proposed for a continuous stirred tank reactor (CSTR). A CSTR is a highly nonlinear process that exhibits stability in certain regions and instability in other regions. The proposed control scheme implements the characteristics of the genetic algorithm's (GA) global optimization to optimize the PID's three control parameters, k_p, k_i, k_d, to obtain the best control effect by minimizing the integral square error online. The PID controller parameters tuned by the GA for each region are gain scheduled by a fuzzy logic scheduler. Fuzzy gain scheduling is a special form of fuzzy control that uses linguistic rules and fuzzy reasoning to determine the controller parameter transition policy for the dynamic plant subject to large changes in its operating state. Simulation results show the feasibility of using the proposed controller for the control of the dynamical nonlinear CSTR.     

Molecular weight distribution in low-density polyethylene polymerization; impact of scission mechanisms in the case of a tubular reactor

It has been shown that scission kinetics strongly affects the molecular weight distribution (MWD) of low-density polyethylene (ldPE) in a continuous stirred tank reactor (CSTR). The present paper focuses on the effects of different chemical scission mechanisms, linear and topological scission, as well as mechanical scission on MWD in batch and tubular reactors. In contrast to the CSTR, a batch reactor MWD does not show bimodalities or long tails. The tubular reactor was modeled as an industrially representative system with four initiator injection points and a proper ‘cocktail’ of different initiators. Calculated MWD was compared to one experimentally determined with SEC-MALLS for a commercial tubular product and fair agreement was found. Typically, these MWDs are broad, but not bimodal. Sensitivity studies were performed as to scission kinetics and the effect of chain transfer agent (CTA). Both batch and tubular reactor were observed to be less sensitive to scission kinetics than a CSTR. In addition, alternative CTA injection strategies (downstream positions) were tested. These showed interesting behavior leading to very broad and bimodal MWD. The model allows following the MWD broadening along the tube. We conclude that batch and tubular ldPE reactors lead to completely different MWD behavior than a CSTR and that it is possible to manipulate it to a great extent.     

The use of momentum ratio to evaluate the performance of CSTRs

In this study, the residence time distribution of a CSTR was measured and analysed for variations in CSTR feed geometry, impeller speed and inlet flow rate. The measured residence time distributions were also used to characterise the degree of plug flow behaviour and short-circuiting. The data showed that the performance of a CSTR could not be evaluated using the ratio of the mean residence time to the batch-mode mixing time (τ/t_M), and that this approach can lead to process over-design and excessive energy requirements. Instead, it was shown that all process parameters could be correlated using the ratio of the inlet jet momentum to the impeller discharge momentum. The prediction of the degree of short-circuiting and plug flow in the CSTR could be used to improve process control. In addition, the results can be used to identify whether the inlet position or diameter of an existing CSTR should be modified to improve process performance.     

The use of krasovskii's stability technique for control strategy evaluation and system design

Krasovskii's stability method for generating Lyapunov functions for the prediction of regions of asymptotic stability (RAS) is applied to a second-order chemical reaction in an adiabatic CSTR. Three conclusions are drawn from this study. Firstly, that the stability areas predicted by the method are too conservative for use as criteria for control system design. Secondly, that the method fails to predict valid regions of asymptotic stability under some circumstances. Thirdly the results are shown to be sensitive to changes in system parameter values.     

Thermal regimes of exothermic processes in continuous stirred tank reactors

Thermal regimes of a CSTR are analysed from the standpoint of the thermal explosion theory. Critical phenomena and time characteristics of the process are considered. It is shown that for appropriately chosen dimensionless parameters the critical conditions of the thermal explosion and induction period in a CSTR slightly differ from those for non-flow (batch) systems. These corrections may be performed by using an additional parameter which is characteristic for flow systems. In the region of multiplicity of steady states, the critical condition of thermal explosion is characterized by a jump of self-heating, while in the non-flow systems such phenomenon occurs only for a zero order reaction. For a unique steady state the transition through the critical condition is continuous.