THE EFFECT OF MACROMIXING ON OSCILLATORY BEHAVIOR IN RECOMBINANT FERMENTATION IN A CONTINUOUS STIRRED TANK REACTOR

A general model is presented for recombinant fermentation in a chemostat in which micromixing may be imperfect. Using the production of tryptophan synthetase as an example and the dilution rate, D, as the bifurcation parameter, conditions are first derived for Hopf bifurcation in a perfectly mixed chemostat. The bifurcation surfaces in three-dimensional space are such that oscillatory solutions exist above the surfaces and washout conditions below. A similar analysis is done for imperfect mixing. The bifurcation region is a concave hyperboloid in the [D,f, n]-space, where f and n ; are model parameters. It is argued that poor macromixing reduces the range of D over which bifurcation to periodic solutions is possible.     

CSTR处理含五氯酚废水的运行特性研究

采用连续流搅拌槽式反应器(CSTR)处理含五氯酚(PCP)废水,探讨了中温(35±1)℃下CSTR的启动和运行情况.结果表明,中温条件下,CSTR在35d左右可完成反应器的启动运行.在稳定运行过程中,CSTR具有良好的缓冲能力,对处理含低负荷PCP的废水具有较好的效果,PCP和COD平均去除率分别达到64%和42%.而高负荷的PCP会造成反应器处理效果的下降,运行过程中应控制PCP负荷在30×103kg·m3·d-1以下.     

EFFECT OF REACTOR HEAT CAPACITY ON THE STABILITY AND START-UP TIME OF A DIABATIC CONTROLLED-CYCLED STIRRED TANK REACTOR

A simple model was written to simulate a first-order exothermic reaction taking place in a diabatic controlled-cycled stirred tank reactor (CCTR) in which the reactor jacket heat capacity is not infinitely larger than the reacting fluid heat capacity. The simulations have shown tpthat including the reactor heat capacity in the model tends to stabilize oscillatory states to a unique steady state. A further result is that a smaller reactor heat capacity results in a shorter transition time to the final steady state. The study shows the possibility that reactor stability and short start-up times may be achieved by simple changes in the reactor design rather than through complex control systems.     

AN EXOTHERMIC CONTINUOUS STIRRED TANK REACTOR IS FEEDBACK EQUIVALENT TO A LINEAR SYSTEM

This brief paper demonstrates the concept of linear feedback equivalence for an exothermic eontinu-ous stirred tank reactor with first order kinetics. Feedback control is achieved by finding a transformation for the nonlinear system which carries this system into a linear controllable system in Brunovsky canonical form. A linear state feedback controller is then designed which achieves control over a broad range of operating conditions. This example demonstrates how recent developments in nonlinear control theory can be applied to chemical systems without relying on the usual methods of local linearization.     

COMPARISON OF KINETIC MODELS FOR THE AQUEOUS SOLID-LIQUID EXTRACTION OF TILIA SAPWOOD IN A CONTINUOUS STIRRED TANK REACTOR

The kinetic study of the aqueous extraction of Tilia sapwood was based on temperature, while all the other factors were kept constant. Several models were used and compared to explain the kinetics of the aqueous solid-liquid extraction of Tilia sapwood. For each model, the rate constant, the equilibrium extraction capacity, and the initial extraction rate were evaluated to analyze the suitability of these kinetic models to describe the leaching process for temperatures ranging from 313 to 363 K. The pseudo first-order model could not be applied during the whole of the process. The Elovich model provided a good degree of correlation (from 0.929 to 0.988) and could be applied all along the extraction process. The pseudo second-order model was satisfactorily applied, with coefficients of correlation over 0.998, showing that it perfectly described the process. A physical explanation of these models was finally proposed.     

ON THE PARAMETER-SPACE CLASSIFICATION OF THE DYNAMIC BEHAVIOR OF A CONTINUOUS MICROBIAL FLOW REACTOR

Recently Agrawal et al.¹ classified the dynamic behavior of continuous stirred tank fermentor for the Monod's model and the two parameter hump function model with variable yield coefficient in the parameter space. We employed the more general three parameter substrate inhibition model which includes the Monod's model as a limiting case, derived the boundary equations which rigorously divide the parameter space of different dynamic behavior, and showed the interesting phenomenon that a limit cycle suddenly vanished for the slight change in the Damköhler number by computer simulation.     

BIFURCATIONS AND CHAOS APPEARING IN A PERIODICALLY CONTROLLED CSTR

Bifurcations of periodic states in a CSTR subject to a periodic control which are caused by changes in the parameter values contained in the control input are investigated on the basis of the bifurcation theory. Principles which give a classification of basic possible bifurcations are briefly surveyed. Then a numerical example in which the period and switching ratio of a bang-bang periodic control are changed is worked. Most of the basic possible bifurcations appear. The chaotic phenomena are also observed and the structure of the strange attractor corresponding to a chaotic state is analysed in some detail,     

气液固三相浆态搅拌反应器中管式内过滤器的过滤特性研究

探讨了在气液固三相浆态搅拌反应器中设置管式内过滤器，以实现气液固三相分离及浆态反应器的连续化。冷模研究表明：在强烈搅拌下，存在一种动态平衡过滤。即在滤饼沉积速率及剥离速率达到平衡条件下，可实现液相进料及滤液排料的连续化。在确定适宜过滤元件结构及过滤介质后研究了搅拌速度 、固含率、体系性质等因素对气液固三相浆态搅拌釜中管式中管式内过滤器的过滤速率的影响。气相按一定比例随液相通过过滤介质 ，其比例大小取决于过滤器的压降大小。实验表明：对颗粒平均直径在（0.8-1.0)10^-4m的α一氧化铝及硅铝氧化物细粒可获得较满意的分离效果。     

液固搅拌槽中固、液相停留时间分布

本文以海沙和自来水为介质研究了在标准搅拌槽内影响固液两相停留时间分布的主要因素,以便比较两相之间的差异,并利用双区模型描述出口流体中固体和液体的停留时间分布。对所建立模型中的参数进行估值后,建立了模型参数与搅拌雷诺数、固体颗粒浓度及搅拌槽几何参数之间的关联式。     

A NOVEL SPINNING DISC CONTINUOUS STIR TANK AND SETTLER REACTOR (SDCSTR) MODEL FOR CONTINUOUS SYNTHESIS OF TITANIA: A PHENOMENOLOGICAL MODEL

A novel phenomenological spinning disc continuous stir tank and settler reactor (SDCSTR) has been modeled for continuous synthesis of titania from its chloride precursor and water in which the desired polymorph, particle size, and distribution are controlled by the characteristics of the atomized inlet reagents, disc, and tank stir rate. This energy-efficient reactor generates seeding nuclei in the aerosol reacting volume that are then deployed for heterogeneous nucleation and particle growth in the metastable reacting volume of the aqueous (sol) process. Once at steady state, the enhanced TiO₂ nanoparticles due to the OH^?–H⁺ chemisorbed on the surface (with surface energy 0.5 < σ < 2.11 N/m) are continuously withdrawn at a rate equivalent to the particle settling rate from the settler. This reactor model eliminates the energy intensity required in traditional chemical vapor deposition (CVD) and aerosol reactors and provides better control for particle growth and size distribution by increasing particle residence time in the metastable zone of the aqueous (sol) reaction stage.     

连续搅拌釜式丙烯聚合反应器的模拟（Ⅰ）反应器的定态模拟

以实际工业装置为背景，建立了丙烯液相本体聚合连续搅拌釜式反应器的定态数学模型。通过模拟计算，考察了诸工艺参数──进料温度、进料流量、夹套冷却水人口温度和流量、丙烯蒸汽冷凝量、催化剂浓度以及反应器中的氢浓度对聚合反应釜反应结果的影响，并对其定态操作行为作了理论上的解释和分析。     

PRODUCT FORMATION PATTERNS AND THE PERFORMANCE IMPROVEMENT FOR MULTISTAGE CONTINUOUS STIRRED TANK FERMENTORS

The relationship between the product formation patterns and the performance improvement was studied for the multistage chemostat system. The performance evaluation was made based on the noninferior sets defined for the productivity and the product concentration. It is shown that when the strong product inhibition or the substrate inhibition occurs, the significant improvement can be attained by increasing the number of stages. It is also shown that the maximum product concentration attainable can be increased by increasing the number of stages for the case where either the cell maintenance coefficient or the product decomposition rate is nonzero. If the productivity is the only performance criterion, the performance improvement cannot be attained by increasing the number of stages for the growth-associated type of product formation, while it can be expected for the non-growth-associated type.     

EFFECT OF SUSPENDED FIBRES ON MACRO-MIXING AND MICRO-MIXING IN A STIRRED TANK REACTOR

The effects of suspended fibre on macroscale and microscale mixing in a small stirred tank reactor were studied under batch conditions using the competitive, consecutive azo coupling between 1-naphthol and diazotized sulfanilic acid. The mixing quality was determined from the distribution between the mono and bis substituted reaction products. Nylon (2 and 3 millimeters in length) and fully bleached softwood kraft pulp (FBK) fibre suspensions were examined at volumetric concentrations up to the limit that complete suspension motion could be maintained in the vessel at impellet rotational speeds of 7 and 10s^-1. The adsorption of the product dyes on the fibre was found to be proportional or very nearly proportional to their concentrations in the aqueous phase and did not interfere with the assessment of mixing in the suspension.

Suspended fibres were found to slightly increase the 'critical feed time' of the diazotized sulfanilic acid, corresponding to an increase in the macromixing or bulk blend lime of the vessel. Continued increase in the fibre concentration led to the formation of a well mixed cavern centered on the impeller and the creation of stagnant regions adjacent to the vessel walls. The departure from the Newtonian fibre-free case is due to changes in the flow through and distribution of the energy dissipative regions in the vessel. The most effective location for chemical addition to ensure good microscale mixing remains in the impeller vicinity.     

OPERATION POLICIES FOR A GAS—LIQUID STIRRED TANK REACTOR

The operation of a gas-liquid stirred tank reactor is simulated, including batch operation, steady and unsteady state, continuous operation and cyclic variable volume operation. A pseudo first order reaction is considered. Analytical expressions for the enhancement factor of gas absorption rate are derived for each case, and productivity obtainable under different operation policies is evaluated. Results obtained are shown graphically for specific cases for the purpose of demonstrating the influence of some of the parameters on the system

The equations as presented can be easily extended to other kinetics, and serve as a useful guide for optimum operational policies in a gas-liquid stirred tank reactor.     

A SIMPLE METHOD FOR STUDYING THE KINETICS OF GAS-SOLID REACTIONS IN A FLUIDIZED BED REACTOR

A methodology for studying the kinetics of gas-solid reactions in a fluidized bed reactor is presented. This procedure is based on the analysis of the response of the system (flue gases) when batches of solids of different weight are added to the reactor. The method has been applied to the study of limestone particle calcination. The calcination rate constants obtained are in good agreement with those found in the literature. The method offers the advantage of simplicity and avoids the use of model assumptions or empirical correlations.     

CHAR GASIFICATION: PARTICLE MODEL COMPARISON IN A STIRRED TANK REACTOR

A simple well mixed model is developed to study the effect of single particle models for the gasification of char in a reactor. Two models, a lumped model and a distributed model, are used to describe the processes in the particle. The model consists of the conservation equations along with the residence time distributions and population balance equations. It is found that neglecting the conversion distribution function in the bed causes considerable differences at high temperatures and large particle sizes. The lumped model is rather insensitive to the mean residence time of the particles and the pressure, compared to the dependence observed in the distributed system. The difference in the design parameters predicted by the models is large and further, the particle size influences these parameters to a greater extent in the distributed system, the lumped system being almost independent of the particle size.     

HYDRODYNAMIC MODEL FOR THE IMPELLER REGION IN AN AERATED AND STIRRED TANK

The radial and axial distribution of mean 1iquid velocity were measured by a.hot-filmanemometer at the impeller region in an aerated and stirred tank 0.287m in diameter.The tangentialjet model for impeller discharge flow used for single phase flow was modified to conform with thecharacteristics of gas-liquid flow.The radial and axial velocity profiles at the impeller region in thegas-liquid stirred tank were calculated by the model The results predicted by the model were in goodagreement with those obtained in experiment.     

MODEL PREDICTIVE CONTROL AND DYNAMIC OPERABILITY STUDIES IN A STIRRED TANK: RAPID TEMPERATURE CYCLING FOR CRYSTALLIZATION

A stirred-tank reactor was built with the objective of rapid and accurate temperature control in the reaction vessel. A first-principles heat transfer model was developed for the jacketed batch system, with the jacket inlet temperature used to control the vessel temperature. A model predictive controller was implemented to follow a rapidly changing temperature profile that cycled between steep heating and cooling motifs, and it was tested experimentally at progressively shorter temperature cycles. For a water-solvent-water-jacket system, a cycle consisting of increasing and decreasing the temperature by 15°C over a period of 20 min was achieved in practice. The performance of the MPC controller was explained by calculating the dynamic operability characteristics of the process.     

Casson流体层流反应器中连串反应的产品分布

引　言目前化工流体力学涉及的范围已由传统的牛顿流体发展到非牛顿流体 .常见的非牛顿流体包括幂律流体、Bingham流体和Casson流体 .有许多高聚物反应物系和生化反应物系属于非牛顿流体 .特别是某些生化反应系统 ,所处理的物系常由各种天然物质组成 ,因而表现出典型的非牛顿流