Digital simulation of an industrial ammonia reactor

A mathematical model for the steady-state simulation of a commercial system formed by a countercurrent tube cooled fixed bed ammonia reactor coupled to a heat exchanger has been developed. The heterogeneous model approximates closely the actual reactor. The results indicate that the phenomenon of multiple steady states occurs. Good agreement was observed between the computer calculated values and the plant data. The model is used to predict a good approximate value for the catalyst activity. The model developed is then used to carry out a parametric study for the converter performance under various conditions.     

Multivariable correlation analysis and its application to an industrial polymerization reactor

The correlation analysis (CRA) theory is an important tool in the system identification field. Among its utilities, the correlation analysis enables the mathematical modeling of a process, through the estimate of its impulse response. This model can be used directly, as in some control algorithms, or, at least, can allow the attainment of important preliminary dynamic information that is valuable in constructing a parametric model of the system. This paper presents the mathematical development of the multivariable correlation analysis and its application to simulated and experimental data. Results show that the present method is effective in identifying an industrial polymerization reactor and overperforms the one commonly used, that suggests the use of the monovariable correlation analysis even for multivariable systems. A numeric analysis of the problem is also done and some guidelines are proposed to overcome possible problems.     

工业级错流列管式固定床反应器的CFD模拟

工业级大型列管式固定床反应器壳程温度场与流场的均匀程度与反应的转化率及选择性密切相关。通过添加阻力源项和分散热源项,对工业级全尺寸错流列管式固定床壳程流场及温度场进行了CFD模拟研究,并进一步考察了折流板窗口区大小及其位置对壳程压降与温度分布的影响。结果表明,模拟得到壳程压降与由经验公式计算得到的压降较为接近,且壳程温度分布与工业实际数据吻合;增大窗口区面积,壳程压降呈现指数下降,同时高温差区（径向温差大于2 K）的范围与径向温差变大;随着第1块折流板位置降低,高温差区范围及径向温差均减小,但压降并不呈现规律性变化。模拟方法可用于工业级大型列管式固定床反应器的优化及设计。     

The effect of mixing on reactor performance: an application of perturbation technique

The effect of local mixing on the performance of a reactor system is derived by the perturbation technique. It is found that the sign of the inner product of the adjoint vector λ and the acceleration vector ? is the only indicator as to whether or not local mixing at a certain point of a reaction path is desirable. A complex reaction system with competing side reactions of different order is treated as an example. The possibility of applying the results in this work to the selection of the optimal type of reactor is also discussed.     

CFD simulation of mixing in tall gas-liquid stirred vessel: Role of local flow patterns

In this work, we have used the computational fluid dynamics (CFD)-based models to investigate the gas-liquid flows generated by three down-pumping pitched blade turbines. A two-fluid model along with the standard k-ε turbulence model was used to simulate the dispersed gas-liquid flow in a stirred vessel. Appropriate drag corrections to account for bulk turbulence [Khopkar and Ranade, 2005. CFD simulation of gas-liquid flow in a stirred vessel: VC, S33 and L33 flow regimes. A.I.Ch.E. Journal, accepted for publication] were developed to correctly simulate different flow regimes. The computational snapshot approach was used to simulate impeller rotation and was implemented in the commercial CFD code, FLUENT4.5 (of Fluent. Inc., USA). The computational model has successfully captured the flow regimes as observed during experiments. The particle trajectory simulations were then carried out to examine the influence of the different flow regimes on the circulation time distribution. The model predictions were verified by comparing the predicted results with the experimental data of [Shewale and Pandit, 2006. Studies in multiple impeller agitated gas-liquid contactors. Chemical Engineering Science 61, 489-504]. The computational model and results discussed in this study would be useful for explaining the implications local flow patterns on the mixing process and extending the applications of CFD models for simulating large multiphase stirred reactors.     

Modeling and simulation of an industrial slurry-phase catalytic olefin polymerization reactor series

In the present study, a comprehensive mathematical model is developed to simulate the dynamic behaviour of an industrial slurry-phase olefin catalytic polymerization loop reactor series. More specifically, the effects of various operating conditions on the dynamic reactor behaviour (i.e., reaction temperature and pressure, inflow rates of catalyst, monomers and diluent, etc.) as well as the on the molecular and rheological polyolefin properties (i.e., M_n, M_w, MWD, complex viscosity, etc.) are fully assessed. According to the proposed modeling approach, each loop reactor (i.e., consisting of the loop reactor and the settling legs) is modeled as an ideal CSTR in series with a semi-continuous product removal unit. Dynamic macroscopic mass species and energy balances are derived to calculate the dynamic evolution of the concentrations of the various molecular species as well as of temperature profiles and heat removal in the two loop reactors. The polymer molecular properties (i.e., number- and weight-average molecular weights and molecular weight distribution) are determined by employing a generalized multi-site, Ziegler–Natta (Z–N) kinetic scheme in conjunction with the well-known method of moments. All the thermodynamic calculations, regarding the equilibrium species concentration in the various phases (i.e., solids and liquid), are carried out using the Sanchez–Lacombe Equation of State (S–L EOS). It is shown that the proposed comprehensive model is capable of simulating the dynamic operation of an industrial slurry-phase cascade-loop reactor series under different plant operating policies (i.e., start-up, grade transition, etc.).     

Downer reactor: From fundamental study to industrial application

Downer reactor, in which gas and solids move downward co-currently, has unique features such as the plug-flow reactor performance and relatively uniform flow structure compared to other gas-solids fluidized bed reactors, e.g., bubbling bed, turbulent bed and riser. Downer is therefore acknowledged as a novel multiphase flow reactor with great potential in high-severity operated processes, such as the high temperature, ultra-short contact time reactions with the intermediates as the desired products. Typical process developments in industry have directed to (1) the new-generation refinery process for cracking of heavier feedstock to gasoline and light olefins (e.g., propylene) as by-products; and (2) coal pyrolysis in hydrogen plasma which opens up a direct means for producing acetylene, i.e., a new route to synthesize chemicals from a clean coal utilization process. This paper is to give a comprehensive review on the development of fundamental researches on downer reactors as well as the particular industrial demonstrations for the fluid catalytic cracking (FCC) of heavy oils and coal pyrolysis in thermal plasma.     

Two-phase flow simulation of reactor clarifiers

In this work, hydrodynamic behavior of flow in three different reactor clarifiers was simulated by three-dimensional, multiphase flow model. The primary construction of reactor clarifier was based on the Bansin Water Treatment Plant, Taiwan. This is the traditional construction, and we call it Type A. The other two were designed in such a way as to improve effluent water quality. The traditional clarifier construction was varied in these to make a large well angle (Type B) and a gradually larger inlet pipe (Type C). Solid effluent flux can be calculated directly from this model. The simulation results showed that under the same daily throughput, the Type C construction of clarifier could decrease upflow fluid velocity in the clarifier and, therefore, reduce effluent water turbidity.     

Modeling and simulation of an industrial slurry phase ethylene polymerization reactor: effect of reactor operating variables

A hierarchical and computationally efficient mathematical model was developed to explain the polymerization of high-density polyethylene (HDPE) in an isothermal, industrial, continuous stirred tank slurry reactor (CSTR). A modified polymeric multi-grain model (PMGM) was used. Steady-state macroscopic mass balance equations were derived for all species (namely, monomer, solvent, catalyst and polymer) to obtain the final particle size and the required monomer and solvent input rates for a given catalyst input and the reactor residence time. The interphase mass transfer coefficients were calculated for the industrial CSTR using the operating data on the reactor. The present model was tuned with some data on an isothermal industrial reactor and the simulation results were compared with data on another set of industrial reactor. The comparison revealed that the present tuned model is capable of predicting the productivity and the polymer yield at various catalyst feed rates and the mean residence times. The effects of variation of two operating variables (catalyst feed rate and mean residence time) on the productivity, the polymer yield, the polydispersity index (PDI) and the operational safety were analyzed. The present study indicated that an optimal value of the reactor residence time (for maximum productivity per catalyst particle) exists at any catalyst feed rate.

     

CFD simulation of liquid-phase mixing in solid-liquid stirred reactor

A comprehensive CFD model was developed to gain an insight into solid suspension and its implications on the liquid-phase mixing process in a solid-liquid stirred reactor. The turbulent solid-liquid flow in a stirred reactor was simulated using a two-fluid model with the standard k-ε turbulence model with mixture properties. The multiple reference frames (MRFs) approach was used to simulate impeller rotation in a fully baffled reactor. The computational model with necessary sub-models was mapped on to a commercial solver FLUENT 6.2 (of Fluent Inc., USA). The predicted solid concentration distribution was compared with the experimental data of Yamazaki et al. [1986. Concentration profiles of solids suspended in a stirred tank. Powder Technology 48, 205-216]. The computational model was then further extended to simulate and understand the implications of the suspension quality on liquid-phase mixing process. The computational model and the predicted results discussed here will be useful for understanding the liquid-phase mixing process in stirred slurry reactors in various stages of solid suspension.     

Modeling and simulation for an industrial reactor on hydroisomerization of C8-aromatics

将3个二甲苯异构体集总为一个组分,提出一个新的异构化三角反应网络,建立工业异构化反应器模型。基于多组平衡的工业数据,采用传统的优化方法估计动力学参数,然后对不同操作条件下的大量工业数据进行仿真,结果表明模型估计值与观测值相当吻合。与其他模型相比,文中开发的模型在相对误差、相对均方误差和参数估计时间等性能指标上均体现出优越性。     

Modelling, simulation and control of an industrial, semi-batch, emulsion-polymerization reactor

This paper presents an emulsion-polymerization model that is designed for an industrial, semi-batch reactor. The model consists of a reaction model and a calorimetry model, and as such enables us to predict the reactor temperature and the batch-output parameters, i.e., the conversion, the solids content and the viscosity. The model was validated on real-plant data and used in the analysis and design of the reactants dosing control. The control strategy proposed is valid for cases where evaporative cooling is either the only or an additional way to remove the heat of the reaction. It consists of an initiator and monomer dosing control, using the reactor temperature as a controlled variable. The simulation results and the real-plant testing show that the proposed reactants dosing control significantly reduces the variations in the reactor temperature and at the same time results in more uniform batch results.     

超短接触旋流反应器混合腔内气固混合特性的数值模拟

采用欧拉双流体模型对超短接触旋流反应器内的气固两相流场进行了数值模拟,主要研究了混合腔内固相的体积分数分布情况。计算结果表明：混合腔内的气流在切向进气的作用下得到了一定的混合加速效果,切向的高速射流有效地缩短了气固停留时间,保证短接触反应效果。通过对两种不同混合腔结构反应器的对比计算发现,在相同入口速度条件下结构2（切向进气管位于混合腔顶部）较结构1（切向进气管位于混合腔下部）气固停留时间短,由于切向气流的迅速作用,增加了混合腔内的湍动强度,使催化剂颗粒迅速有效扩散、增强气固接触效果而更有利于催化裂化反应的进行,更易实现短接触操作要求。计算结果与实验测量结果的比较表明模型能有效地描述超短接触旋流反应器内气固两相流动形态。     

The distribution of residence-times in an industrial fluidised reactor

The distribution of residence-times of the gas flowing through a fluidised catalyst regenerator has been determined by using helium as a tracer. Only about 5% of the gas spends less than half, and about 5% more than twice, the mean residence-time in the regenerator. It appears that the flow through the fluidised bed itself is much closer to piston-flow than to complete mixing, the hold-back being less than 0·1.     

The influence of mixing on lysozyme renaturation during refolding in an oscillatory flow and a stirred-tank reactor

Protein refolding is a key unit operation in many processes that produce recombinant biopharmaceuticals using Escherichia coli. Yield in this step generally controls overall process yield, and at industrially relevant protein concentrations is limited by aggregation. While most refolding operations are optimised with respect to chemical environment, the physical processes affecting yield have been neglected. In this study, we demonstrate that refolding yield for the model protein lysozyme is dependent on mixing intensity during dilution refolding. This is shown for two different reactor configurations: a standard stirred-tank reactor and a novel oscillatory flow reactor. We further show that the effect of mixing is dependent on the type of chaotrope employed for denaturation. Yield falls significantly when mixing intensity is decreased following urea denaturation, while the effect of mixing is not apparent when guanidine hydrochloride is employed as the denaturant. In batch tests we further confirm that, for urea, the “path” of dilution affects yield, and hence the observed sensitivity to mixing is not unexpected. We conclude that mixing is a critical parameter that must be optimised in industrial reactors, along with the usual chemical and protein-specific parameters.     

A mass-transfer study of two-phase flow in an electrochemical reactor

The electrodeposition of Cu²⁺ ions from a solution of 1 M H₂SO₄ has been studied in a parallel plate cell with two-phase (liquidgas) flow. The results are interpreted in terms of the LevichLandau and TaylorPrandtl models. The conclusion is reached that the mass-transfer enhancement observed results mainly from increase in linear velocity of the liquid phase due to a reduction of the effective cross-sectional area of the cell caused by the bubbles. The industrial prospects for such a system are discussed.     

Chemical reactor network application to predict the emission of nitrogen oxides in an industrial combustion chamber

A new chemical reactor network model is developed to predict the emission of nitrogen oxides in an industrial combustion chamber operating on liquefied petroleum gas. The boundary conditions and operating parameters used for this model are typical operating conditions of an industrial combustion chamber. The global mechanism is developed by GRI-MECH 3.0 in the UW code. The model predictions are compared with experimental data. The chemical reactor network model provides an accurate estimation of nitrogen oxide emission.     

Modeling, simulation and control of dimethyl ether synthesis in an industrial fixed-bed reactor

Dimethyl ether (DME) as a clean fuel has attracted the interest of many researchers from both industrial communities and academia. The commercially proven process for large scale production of dimethyl ether consists of catalytic dehydration of methanol in an adiabatic fixed-bed reactor. In this study, the industrial reactor of DME synthesis with the accompanying feed preheater has been simulated and controlled in dynamic conditions. The proposed model, consisting of a set of algebraic and partial differential equations, is based on a heterogeneous one-dimensional unsteady state formulation. To verify the proposed model, the simulation results have been compared to available data from an industrial reactor at steady state conditions. A good agreement has been found between the simulation and plant data. A sensitivity analysis has been carried out to evaluate the influence of different possible disturbances on the process. Also, the controllability of the process has been investigated through dynamic simulation of the process under a conventional feedback PID controller. The responses of the system to disturbance and setpoint changes have shown that the control structure can maintain the process at the desired conditions with an appropriate dynamic behavior.     

Startup of an industrial adiabatic tubular reactor

The dynamic behaviour of an adiabatic tubular plant reactor during the startup is demonstrated, together with the impact of a feed-pump failure of one of the reactants. A dynamic model of the reactor system is presented, and the system response is calculated as a function of experimentally-determined, time-dependent, manipulated variables. The values of model parameters are estimated by using the SimuSolv (1991) computer program. The data set collected during the reactor start-up is used for the parameter estimation procedure. An excellent agreement is obtained between the experimental and the calculated system response. Many continuously-operated commercial reactors require a complete conversion of one of the main reactants at the reactor exit. It is shown that for an industrial tubular reactor a much higher initial reactor temperature is required during the startup, compared to the reactor inlet temperature during normal steady-state operation, to ensure a complete reactant conversion. Much more research is necessary to determine whether this is a generally valid rule.     

液体连续相撞击流反应器中流体混合时间的数值模拟

在混合时间理论计算基础上利用CFD技术模拟连续操作的LISR混合过程, 数值计算与验证混合时间的变化规律。结果表明, 随着输入比有效功率增大, 混合时间先急剧减小后逐渐趋于平稳;LISR撞击区一次撞击局部混合时间在0.25 s以内, 与经验公式或理论公式计算所得结果在数量级上完全一致, 证明数值方法分析一次撞击局部混合时间是可行的, 而且可以弥补实验无法测定中间过程参量的不足;进一步数值分析宏观混合时间与微观混合时间发现, 二者大小相差1个数量级, 但二者变化规律处于一种联动平衡状态, 该结果与前期理论分析结果一致;本研究所得结论可为后续LISR混合强化机理与性能研究提供定量参考。