合成甲醇基元过程瞬态动力学的模型化(Ⅱ)——合成甲醇瞬态动力学

在基元过程序列结构判识的基础上,以傅立叶变换红外光谱仪(FTIR)气体池作为检测器,采用动态响应技术,进行了合成甲醇过程瞬态动力学的实验研究,得到了微型反应器尾气中各主要物种的浓度对反应器进料浓度阶跃变化的动态响应数据。基于瞬态速率模型对实验数据的拟合,得到了由H_2/CO/CO_2合成甲醇初步的瞬态动力学关系。     

MODELING OF ELEMENTARY PROCESS KINETICS FOR METHANOL SYNTHESIS (Ⅱ )A TRANSIENT KINETIC MODEL OF METHANOL SYNTHESIS FROM CO/CO_2/H_2

在基元过程序列结构判识的基础上,以傅立叶变换红外光谱仪(FTIR)气体池作为检测器,采用动态响应技术,进行了合成甲醇过程瞬态动力学的实验研究,得到了微型反应器尾气中各主要物种的浓度对反应器进料浓度阶跃变化的动态响应数据。基于瞬态速率模型对实验数据的拟合,得到了由H_2/CO/CO_2合成甲醇初步的瞬态动力学关系。     

聚酯装置酯化生产过程动态模拟

动态模型是进行生产过程动态优化的基础。本文采用链段法建立了聚酯装置酯化生产过程反应器和工艺塔相互影响的动态模型,分析了基本控制系统作用下过程操作工况的动态阶跃响应特性。模拟结果表明,酯化反应器进料摩尔配比及反应器温度、压力、液位的调整显著影响了酯化过程气相流的变化,且对反应产物中端羧基含量和聚合度等指标的响应比较灵敏;控制系统对稳定酯化生产过程操作起着显著的作用。     

Temperature control of the water gas shift reaction in microstructured reactors

Microchannel reactors offer unique possibilities for temperature control of chemical reactions due to the strong coupling of channel and wall temperatures. This may be applied to all chemical reactions which require a certain temperature profile to achieve an optimum yield. For the reformation of hydrocarbons for fuel cell applications a low CO concentration of the product gas is desired. In conventional systems, this is achieved by sequentially processing the reformate through a high and low temperature water gas shift reactor because increased temperature enlarges the reaction rate while lower temperature shifts the equilibrium to the desired small CO concentrations. However, for every gas composition arising during the reaction process an optimum temperature exists at which the reaction rate is highest. We will demonstrate that this optimum temperature profile to a good approximation can be achieved in a single step WGS reactor by controlling the temperature via cooling gas flowing in counter current to the reformate. Furthermore, the effect of water addition (steam injection) is analysed for a conventional two-step adiabatic reactor system and the possible size reduction in an integrated heat-exchanger reactor under comparable conditions is validated. Finally, the effect of diffusion limitations at various channel dimensions is investigated applying a two-dimensional model which allows a trade-off between pressure drop or respective reactor size and performance when dimensioning a real system in future.     

Dynamic Matrix Control of a Bubble‐Column Reactor for Microbial Synthesis Gas Fermentation

A spatiotemporal metabolic model of a representative syngas bubble‐column reactor was applied to design and evaluate dynamic matrix control (DMC) schemes for regulation of the desired by‐product ethanol and the undesired by‐product acetate. This model was used to develop linear step response models for controller design and also served as the process in closed‐loop simulations. A 2 × 2 DMC scheme with manipulation of the liquid and gas feed flows to the column provided a superior performance to proportional integral (PI) control due to slow process dynamics combining the multivariable and constrained nature of the control problem. Ethanol concentration control for large disturbances was further improved by adding the flow of a pure hydrogen stream as a third manipulated variable. The advantages of DMC for syngas bubble‐column reactor control are demonstrated and a design strategy for future industrial applications is provided.     

Numerical simulation of horizontal jet penetration in a three-dimensional fluidized bed

The introduction of reactant gas as a jet into a fluidized bed chemical reactor is often encountered in various industrial applications. Understanding the hydrodynamics of the gas and solid flow resulting from the gas jet can have considerable significance in improving the reactor design and process optimization. In this work, a three-dimensional numerical simulation of a single horizontal gas jet into a cylindrical gas-solid fluidized bed of laboratory scale is conducted. A scaled drag model is proposed and implemented into the simulation of a fluidized bed of FCC particles. The gas and particles flow in the fluidized bed is investigated by analyzing the transient simulation results. The jet penetration lengths of different jet velocities have been obtained and compared with published experimental data as well as with predictions of empirical correlations. The predictions by several empirical correlations are discussed. A good agreement between the numerical simulation and experimental results has been achieved.     

The effect of carbon dioxide during the desulfurization of flue gas with Mardin–Mazıdagı phosphate rock

The effects of temperature, CO₂ concentration and particle size on simultaneous calcination/sulfation of Mardin–Maz?dag? phosphate rock in fluidized-bed reactor were investigated. For this, a raw sample was exposed to calcination and sulfation processes in a fluidized-bed reactor to determine the effects of parameters by using a model gas mixture similar to the flue gas composition. The calcination ratio increased with increasing temperature and decreasing particle size, but decreased with increasing CO₂ concentration. In sulfation process, however, sulphate conversion ratio increased with increasing CO₂ ratio and decreased with decreasing particle size. The sulfation reaction is well represented by the shrinking core model and can be divided into two regions with different rate controlling step. For low conversions, the controlling step was found to be chemical reaction at the interface, but the diffusion through the product layer for high conversion. The activation energies for the chemical reaction at the interface and diffusion through the product layer cases were calculated as 100 and 296 kJ mol^?1, respectively.     

Development and testing of an interconnected multiphase CFD-model for chemical looping combustion

An interconnected multi-phase CFD model is developed capable of describing the transient behavior of a coupled chemical looping combustion systems comprising of both air and fuel reactors. The air reactor is modeled as a high velocity riser, the fuel reactor as a bubbling fluidized bed. The models of both reactors are implemented as separate CFD simulations allowing for an exchange of solid mass through time-dependent inlet and outlet boundary conditions as well as mass, momentum, heat and species sinks. The developed framework is applied to a chemical looping combustion system based on Mn₃O₄ as carrier material in combination with CH₄ as fuel gas. Starting from a base case, different system configurations are investigated. The results indicate clearly that interconnected multi-phase CFD models are well suited for the design process of coupled chemical looping systems.     

Simulation of catalytic fluidized bed reactors by a transient axial dispersion model with invariant physical properties and nonlinear chemical reactions

This paper presents a transient axial dispersion model for an isothermal, catalytic fluidized bed reactor, which is frequently employed in synthetic production processes including coal gasification and liquefaction. A non-linear chemical reaction is considered to occur in the reactor. This model of a fluidized bed reactor takes into account the axial dispersion in the three phases, bubble, cloud-wake and emulsion. The physical properties along the axial coordinate are invariant in the model. Transient characteristics of the gas reactant, and the length of the transient period have been examined based on the model. The model compares favorably with experimental data in the steady state condition.     

Thermal transport model of a sorbent particle undergoing calcination–carbonation cycling

A numerical model coupling transient radiative, convective, and conductive heat transfer, mass transfer, and chemical kinetics of heterogeneous solid–gas reactions has been developed for a semitransparent, nonuniform, and nonisothermal particle undergoing cyclic thermochemical transformations. The calcination–carbonation reaction pair for calcium oxide looping is selected as the model cycle because of its suitability for solar‐driven carbon dioxide capture. The analyzed system is a single, porous particle undergoing thermochemical cycling in an idealized, reactor‐like environment. The model is used to investigate two cases distinguished by the length of the calcination and carbonation periods. The calcination–carbonation process for a single particle is shown to become periodic after three cycles. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2647–2656, 2015     

Self-adaptive predictive functional control of the temperature in an exothermic batch reactor

In this paper we study a self-adaptive predictive functional control algorithm as an approach to the control of the temperature in an exothermic batch reactor. The batch reactor is located in a pharmaceutical company in Slovenia and is used in the production of medicines. Due to mixed discrete and continuous inputs the reactor is considered as a hybrid system. The model of the reactor used for the simulation experiment is explained in the paper. Next, we assumed an exothermic chemical reaction that is carried out in the reactor core. The dynamics of the chemical reaction that comply with the Arrhenius relation have been well documented in the literature and are also summarized in the paper. In addition, the online recursive least-squares identification of the process parameters and the self-adaptive predictive functional control algorithm are thoroughly explained. We tested the proposed approach on the batch-reactor simulation example that included the exothermic chemical reaction kinetic model. The results suggest that such an implementation meets the control demands, despite the strongly exothermic nature of the chemical reaction. The reference is suitably tracked, which results in a shorter overall batch-time. In addition, there is no overshoot of the controlled variable T, which yields a higher-quality production. Finally, by introducing a suitable discrete switching logic in order to deal with the hybrid nature of the batch reactor, we were able to reduce the switching of the on/off valves to a minimum and therefore relieve the wear-out of the actuators as well as reduce the energy consumption needed for control.     

铜基催化剂上甲醇合成的动态反应动力学

Adsorption, surface reaction and process dynamics on the surface of a commercial copper-based cata-lyst for methanol synthesis from CO/CO2/H2 were systematically studied by means of temperature programmed desorption (TPD), temperature programmed surface reaction (TPSR), in-situ Fourier transform-inferred spectroecopy(FTIR) and stimulus-response techniques. As a part of results, an elementary step sequence was suggested and a group of ordinary differential equations (ODEs) for describing transient conversations relevant to all species on the catalyst surface and in the gas phase in a micro-fixed-bed reactor was derived. The values of the parameters referred to dynamic kinetics were estimated by fitting the solution of the ODEs with the transient response data obtained by the stimulus-response technique with a FTIR analyzer as an on-line detector.     

Studies on the inhomogeneous nature of the silent discharge reactor: Part 3. A multi-zoned flow model

The reaction space of a silent discharge reactor consists of two distinct components, viz. (1) the collection of primary reaction zones (PRZ) or discharge streamers where, under the influence of free electron avalanches, primary electron molecule collisions take place and (2) the remaining reaction space which provides for secondary or quenching reactions between activated species and gas molecules. A flow model based on this concept has been proposed which accounts for the intrinsic chemical activity of the PRZs as well as their random distribution, spatial location, transient nature, and temperature field. Experimental results obtained on laboratory ozonizers have been examined to show the validity of the proposed model.     

Useful experimental technique for the study of heterogeneous reactions

The heterogeneous CaO/SO₂ reaction has been thoroughly investigated by developing a series of new experimental techniques including the TGA reactor, the volulmetric reactor and the entrained flow reactor. The heterogeneous system is designed in such a way that most of the gas film and pore diffusion resistances are reduced. The modelling of each step related to the reaction is discussed while the chemical reaction and product layer diffusion are emphasized as the main influences on the SO₂removal. The unchanging size shrinking core model is used to describe the reaction progress with a two stage assumption which has been confirmed in the TGA reactor: first, a very fast surface reaction, followed by a product layer diffusion controlled reaction. It was found from the experiments that the SO₂-partial pressure aat the very beginning is very important for a high removal efficiency during the initial reaction period.     

下行床反应器内催化裂化过程的CFD模拟

耦合湍流气粒多相流模型和催化裂化集总动力学模型,建立了描述下行床内多相流动和催化裂化过程的反应器数学模型,并利用计算流体力学单元模拟软件CFX4.3对下行床内的催化裂化过程进行了数值模拟及分析.模型能预测出在工业应用中反应器内最受关注的诸多参数,如固含率、相间滑移速度、压降、气固相的加速区以及各组分浓度的分布情况.预测结果表明,气相反应的进行将导致反应器内的气粒流动行为发生较大变化,充分考虑反应与流动行为的耦合十分重要;而反应器床径的增大将导致转化率和各产物收率的下降.     

Gas Absorption with Chemical Reaction and Desorption in a Foam-bed Reactor

A general model of a foam-bed reactor involving simultaneous gas absorption, reaction, and desorption has been developed. The model considers all coupled processes in the reactor. The reactive gas absorption and desorption in the foam section have been simulated via analysis of a single foam film surrounded by limited gas pockets. The model includes a sub-model to find out concentration profiles inside the surface element. A modular approach has been used to simulate a single foam film to obtain transient concentration profiles of the gas-phase reactant A and product P. Effects of various kinetic, physicochemical, operating, and system parameters like reaction velocity, diffusion coefficient, solubility, contact time, and holdup on fractional absorption and desorption of gas are studied.     

Vapour phase chemical reaction in spouted beds: A theoretical model

A theoretical model of a spouted bed chemical reactor, involving vapour phase reaction in the presence of catalyst or heat carrier particles, is proposed. The hydrodynamic features relevant to the model are described in as generalized a manner as permitted by the available information. The application of the model is then demonstrated by making certain predictions concerning the effect of the major variables on gas conversion for a first order reaction, as well as on the relative performance of spouted, fixed, and fluidized bed systems.     

Dynamic operation of a three-phase upflow reactor for the hydrogenation of phenylacetylene

The selective catalytic hydrogenation of phenylacetylene to styrene presents an attractive and interesting process both from scientific and industrial viewpoints. The process mechanism consists of two consecutive reaction steps in which a high selectivity towards the intermediate product is desired.

There have been many papers published so far, that report an increase in the selectivity of adsorption-desorption-based gas-phase processes performed on solid catalysts, due to a periodic (pulsing) operation of the reactor system. Pulsing the gas feed is believed to create more preferential adsorption conditions for the required reactant (transient conditions).

This paper presents the results of a theoretical and experimental study concerning the influence of forced periodic oscillations of the gas-phase component on the performance of a three-phase reactor. The theoretical results are based on a heterogeneous mathematical reactor model considering both the transient mass balance over the reactor length as well as accumulation inside the catalyst pellets.

Numerical dynamic reactor simulations with a simplified model neglecting accumulation of components within the catalyst pellet showed little improvement in conversion and selectivity when compared to results of the steady-state model. These results were supported by dynamic experiments in a bench scale reactor. It is shown that due to mass transfer limitations, the original square wave shape of the oscillation in the gas-phase concentration was almost completely faded into a smooth and rather flat oscillation at the catalyst surface. Simulations with a model in which accumulation of the relevant components inside the particles was considered showed no further improvement in performance at transient conditions, but demonstrated the impact of accumulation capacity of the pellets on the shape of oscillation present at the catalyst surface.

The study is a result of direct cooperation between Politecnico di Torino, where the modelling and calculations were performed, and DSM Research. Its aim was to offer an attractive alternative to the conventional approach.     

Temperature control of highly exothermic batch polymerization reactors

In this article a highly exothermic batch polymerization reactor is considered. The reactor is simplified as a mixing tank with the internal heat generation treated as a disturbance. A fuzzy-hybrid-PID-feedback (FH-PID) control structure is developed in which the output of fuzzy hybrid portion is used to adjust the set point of a PID controller to compensate for the effect of the major disturbance, the heat of reaction. In this way, the hybrid portion of the controller does not influence the stability of the original PID control system. A fuzzy model was constructed to estimate the heat of reaction inside the fuzzy hybrid block. The fuzzy parameters of the hybrid portion do not depend on the process model and can be estimated from the transient response obtained with a conventional PID controller. This FH-PID control strategy has been applied to the temperature control of batch solution and batch inverse emulsion polymerizations of acrylamide in a 1 gallon pilot scale reactor. The results show that this fuzzy hybrid—PID-feedback control strategy improves the control performance of the batch polymerization reactor.