Optimal design of a thermally coupled fluidised bed heat exchanger reactor for hydrogen production and octane improvement in the catalytic naphtha reformers

The present study combines simultaneously the definition of fluidisation and process intensification (thermally coupled heat exchanger reactor) concept and determines the optimum operational conditions in both sides of the reactor, using Differential Evolution (DE) optimisation approach. The exothermic hydrogenation of nitrobenzene to aniline takes place in a set of tubular reactors which is placed inside the naphtha reactors and thermally handle the endothermic reaction of reforming. A single objective function consists of four terms including aromatic mole fraction of the reformate and hydrogen production from each reactor in the endothermic side as well as the total molar flow rate of aniline and nitrobenzene conversion in the exothermic side is defined. Seven decision variables such as inlet temperature of exothermic and endothermic sides, exothermic molar flow rates for the first and the second reactors and the number of tubes are considered during the optimisation procedure. Temperature constraints have been considered in both sides during the optimisation in order to reduce the possibility of rapid catalyst deactivation by sintering. Results show approximately 464.4 and 598.9 kg/h increase in aromatic and aniline production rates in optimised thermally coupled fluidised bed naphtha reactor (OTCFBNR) compared with non‐optimised case (TCFBNR), respectively. Such a theoretical study is necessary prior to designing new pilot plants and revamping industrial units. © 2011 Canadian Society for Chemical Engineering     

操作参数对余热回收甲醇水蒸气重整制氢过程的影响

以模拟汽车尾气供热的甲醇水蒸气重整（MSR）制氢反应为研究对象,设计了集余热加热与MSR制氢反应于一体的肋式微反应器,考察了反应器进口热风速度、温度,反应物进口速度、温度、水醇比及顺逆流情况对MSR制氢过程的影响。计算结果表明,逆流、水醇比1.3、热风进口速度1.1 m/s、温度773 K、反应物进口速度0.1 m/s、温度493 K为该反应过程的最佳工况参数,此时甲醇转化率为99.4%,模拟汽车尾气余热的热效率为28%,反应器出口氢气的体积分数为69.6%。研究结果对开展余热综合利用及发动机尾气重整制氢掺氢燃烧的研究有借鉴意义。     

Operational optimisation of centrifugal compressors in multilevel refrigeration cycles

Low-temperature energy systems are processes that require cooling at temperatures below ambient, which are accomplished using refrigeration cycles. Little research has addressed the operational optimisation of refrigeration cycles considering the performance of existing equipment. This work develops a methodology for operational optimisation of refrigerated processes, taking into account existing centrifugal compressors. For the optimisation of multilevel cycles, the evaporation temperatures of each level are varied to find a set of operating conditions that minimise shaft work demand. The optimisation takes into account equipment constraints, including compressors on a common shaft, minimum and maximum allowable inlet flow rates, etc. Two examples are presented; the first represents a three-level refrigeration cycle and the second a cascade cycle. For the two examples, the conditions of the base case are optimised, identifying improvements of around 3% in shaft work demand. In addition, both cycles were also optimised for a range of process cooling demands.     

Steady State Modeling and Optimization of Styrene Production in an Industrial Axial Flow Adiabatic Reactor

In this study, the performance of industrial axial flow adiabatic reactors to produce styrene through ethylbenzene dehydrogenation on the potassium-promoted iron catalyst studied at steady state condition. The dehydrogenation reactors have been modeled heterogeneously based on the one-dimensional mass and energy governing laws and considering a detailed kinetic model. The catalytic and thermal kinetic models have been applied in the mathematical model of process. To prove the accuracy of the considered model and assumptions, the simulation results are compared with the plant data at the same process condition. Also, Genetic algorithm as a powerful method in the global optimization has been considered to maximize styrene production as the objective function. The inlet feed temperature to each reactor is selected as attainable decision variables due to severe effect of temperature on the equilibrium and kinetic constant. This configuration has enhanced styrene production rate by 1.2% compared to industrial adiabatic reactor.     

溶液浓差能驱动的逆电渗析反应器制氢实验研究

低品位热能制氢技术首先是将热能转换为溶液浓差能,然后通过逆电渗析（RED）反应器将溶液浓差能转换成氢能。为了验证RED反应器能将溶液浓差能转换为氢能,探索关键运行参数变化对能量转换过程的影响。设计了一个由40个膜对所构成的RED反应器,以NaCl水溶液为工作溶液,NaOH水溶液为电极液的制氢系统。通过改变浓/稀溶液入口浓度,溶液过膜流速以及输出电流来考察对RED反应器产氢率、制氢效率和能量转换效率的影响。实验结果发现,浓/稀溶液入口浓度,过膜流速变化均会影响RED反应器的输出电流。在外电路短接条件下,输出电流越大,反应器产氢率和制氢效率越高,但能量转换效率越低。     

Simulation and thermodynamic analysis of an integrated process with H2 membrane CPO reactor for pure H2 production

A one-dimensional steady-state heterogeneous model has been used to simulate the H₂ membrane reactor. The simulation work is the basis for the thermodynamic analysis of the integrated pure H₂ production process. The simulation and analysis also provide a quantitative tool for insight into and understanding the process.The simulation and thermodynamic analysis results indicate that increasing the inlet ratio H₂O/CH₄ cannot enhance the pure H₂ production rate. With increasing the inlet ratio H₂O/CH₄, the overall exergy efficiency of the process decreases, because a large amount of energy is required to obtain the steam.When the geometric parameters of membrane reactor and inlet temperature are given, there is a maximum feeding rate of methane for the integrated process. The pure hydrogen production rate increases with the inlet methane rate increasing, while the overall exergy efficiency decreases as inlet methane rate increases.For the same inlet rate of methane, operating the process at higher inlet temperature increases hydrogen production rate. Whereas, the overall exergy efficiency is lowered.Three suggestions are discussed to improve the overall exergy efficiency. All of them require more equipment investment. There will be an optimal point to balance equipment investment, pure hydrogen production rate and overall exergy efficiency. To find the optimum, thermo-economic analysis will be helpful.     

Membrane/sorption-enhanced methanol synthesis process: Dynamic simulation and optimization

In this study, a dynamic mathematical model of a Membrane-Gas-Flowing Solids-Fixed Bed Reactor (Membrane-GFSFBR) with in-situ water adsorption in the presence of catalyst deactivation is proposed for methanol synthesis. The novel reactor consists of water adsorbent and hydrogen-permselective Pd-Ag membrane. In this configuration feed gas and flowing adsorbents are both fed into the outer tube of the reactor. Contact of gas and fine solids particles inside packed bed results in selective adsorption of water from methanol synthesis which leads to higher methanol production rate. Afterwards, the high pressure product is recycled to the inner tube of the reactor and hydrogen permeates to the outer tube which shifts the reaction towards more methanol production. Dynamic simulation result reveals that simultaneous application of water adsorbent and hydrogen permeation in methanol synthesis process contributes to a significant enhancement in methanol production. The notable advantage of Membrane-GFSFBR is the continuous adsorbent regeneration during the process. Moreover, a theoretical investigation has been performed to evaluate the optimal operating conditions and to maximize the methanol production in Membrane-GFSFBR using differential evolution (DE) algorithm as a robust method. The obtained optimization result shows there are optimum values of inlet temperatures of gas phase, flowing solids phase, and shell side under which the highest methanol production can be achieved.     

Optimization of methane reforming in a microreactor—effects of catalyst loading and geometry

In this paper, the effect of the catalyst surface site density (catalyst amount) and reactor geometry on the reforming process of methane in a wall-coated, single-channel microreactor is investigated numerically. Such a reactor, consisting of a tubular flow channel and a thermal conductive channel wall, is a good representation of microfabricated channels and monoliths. It is found that the hydrogen selectivity changes significantly with varying catalyst loading, which is a noteworthy result. Thus, the reaction path leading to higher hydrogen production becomes more important by increasing the catalyst surface site density on the active surface. This is due to the splitting rate of methane and water, which is a function of catalyst density. Furthermore, this study shows the significance of scaling the inlet volume flow not only with the reactor volume (gas space velocity) but also with the catalyst amount (catalyst space velocity). Another unexpected result is the presence of an optimum channel geometry and an optimum catalyst amount if the gas space velocity and the catalyst space velocity are constant. This underlines the necessity of coordinating the channel diameter, the inlet volume flow rate, and the catalyst amount in order to obtain a maximum reformer performance. Furthermore, it is necessary to specify the catalyst amount, the inlet conditions and the geometry in order to characterize sufficiently a catalytic reactor.     

A comparison of conventional and optimized thermally coupled reactors for Fischer–Tropsch synthesis in GTL technology

In this research, the conditions at which a thermally coupled reactor – containing the Fischer–Tropsch synthesis reactions and the dehydrogenation of cyclohexane – operates have been optimized using differential evolution (DE) method. The proposed reactor is a heat exchanger reactor consists of two fixed bed of catalysts separated by the tube wall with the ability to transfer the produced heat from the exothermic side to the endothermic side. This system can perform the exothermic Fischer–Tropsch (F–T) reactions and the endothermic reaction of cyclohexane dehydrogenation to benzene simultaneously which can save energy and improve the reactions' thermal efficiency. The objective of the research is to optimize the operating conditions to maximize the gasoline (C₅⁺) production yield in the reactor's outlet as a desired product. The temperature distribution limit along the reactor to prevent the quick deactivation of the catalysts by sintering at both sides has been considered in the optimization process. The optimization results show a desirable progress compared with the conventional single stage reactor. Optimal inlet molar flow rate and inlet temperature of exothermic and endothermic sides and pressure of exothermic side have been calculated within the practicable range of temperature and pressure for both sides.     

Analysis of a fluidized bed membrane reactor for butane partial oxidation to maleic anhydride: 2D modelling

The partial oxidation of butane to maleic anhydride in a membrane reactor with improved heat transfer through the wall has been studied in this work. The reactor consisted of a catalytic fixed bed with sintered metal membrane wall that allows the gradual feed of air from the external fluidized bed. The influence of the most important design and operation variables (reactor length, gas flow rate, inlet temperature, butane inlet concentration, and air gas flow rate) on butane conversion and maleic anhydride selectivity has been studied by means of computer simulations using an experimentally-validated detailed 2D model. The performance of this reactor was systematically compared to the corresponding conventional fixed bed reactor. The membrane reactor has been found to provide slightly higher selectivity than the fixed bed reactor. Moreover, in the membrane reactor, the mixing of butane and air takes place through the wall directly inside the catalytic bed. Since solid beds avoid flame propagation, the process can be operated with higher butane inlet concentrations under safety conditions. Hence, the fluidized bed membrane reactor represents an interesting alternative for industrial-scale operation.     

Application of response surface methodology for optimization of purge gas recycling to an industrial reactor for conversion of CO2 to methanol

Nowadays, by the increasing attention to environment and high rate of fuel production, recycling of purge gas as reactant to a reactor is highly considered. In this study, it is proposed that the purge gases of methanol production unit, which are approximately15.018 t·h~(-1) in the largest methanol production complexes in the world, can be recycled to the reactor and utilized for increasing the production rate. Purge gas streams contain 63% hydrogen,20% carbon monoxide and carbon dioxide as reactants and 17% nitrogen and methane as inert. The recycling effect of beneficial components on methanol production rate has been investigated in this study. Simulation results show that methanol production enhances by recycling just hydrogen, carbon dioxide and carbon monoxide which is an effective configuration among the others. It is named as Desired Recycle Configuration(DRC) in this study. The optimum fraction of returning purge gas is calculated via one dimensional modeling of process and Response Surface Methodology(RSM) is applied to maximize the methanol flow rate and minimize the carbon dioxide flow rate. Simulation results illustrate that methanol flow rate increases by 0.106% in DRC compared to Conventional Recycle Configuration(CRC) which therefore shows the superiority of applying DRC to CRC.     

Incorporation of Flexibility in the Design of a Methanol Synthesis Loop in the Presence of Catalyst Deactivation

This paper presents the incorporation of process flexibility into a methanol synthesis loop operating under catalyst deactivation. A design methodology is discussed with regard to catalyst deactivation, and some limitations are identified. In the current flexibility study the size of the reactor and recycle ratio have been fixed. Attempts to maintain methanol production at the rates observed with fresh catalyst included increased pressure, increased make up gas flow rate, and the injection of carbon dioxide into the make up gas at optimized inlet temperature. In order to provide flexibility and produce a design compatible with increased production rates, the effect of interrelating equipment had to be considered. As a result of catalyst deactivation, an increased flow rate is necessary and the altered process streams entering the preheater disturb the reactor inlet temperature. These issues should be considered in the design stage and may be resolved by the flexible designs presented.     

管式反应器中苯乙烯连续本体热聚合过程模型化和数值模拟

建立了管式层流反应器中苯乙烯本体热聚合过程的模型。数值模拟了反应介质流速和温度沿反应器的轴向和径向的分布,考察了反应器的几何尺寸、壁温、反应介质入口温度和流量对反应器出口转化率和产物相对分子质量的影响。结果表明,反应器的几何尺寸和反应器壁温及进料质量流量对单体转化率影响较大,而入口温度影响不大。     

煤等离子气化反应器优化模拟

介绍了煤等离子气化的工艺过程及煤等离子气化反应器装置的结构形式,建立了等离子体反应器的热流场计算流体力学模型,将此模型应用于单入口、双入口及带保护气的双入口等离子反应器模拟,采用不完全乔勒斯基共轭梯度法对热流体耦合场进行求解。结果表明,采用双入口结构,可提高反应器负荷,在等离子反应器的等离子入口周边设置保护气可降低壁面结焦,当保护气的入口流速为70 m/s左右时,效果较好。     

Raney-Ni催化剂甘油蒸气重整制氢研究

采用管式固定床流动反应器,以Raney-Ni为催化剂,对甘油蒸气重整制氢进行了研究,考察了常压下不同温度、料液浓度和催化剂装载量对催化活性和氢气选择性的影响。结果表明:当进料浓度合适,催化剂Raney-Ni可在较低温度下呈现出对蒸气重整制氢反应较好的催化活性和选择性。当温度为280℃、料液浓度为5%(质量分数)、流量为0.5 mL/min时,碳转化率和H_2产率分别可达99.9%和93.21%,H_2和CO选择性分别为80.70%和0.20%。     

Dynamic simulation of a parallel-plate electrochemical fluorination reactor

A time-dependent mathematical model of a parallel-plate reactor was developed to study the electrochemical fluorination of organic compounds dissolved in anhydrous hydrogen fluoride. The model incorporates two-phase flow with differential material, energy and pressure balances. Dynamic results are presented that show the effect of disturbances to the whole reactor or one of the cells of the multicell reactor. The effect of disturbances in the cell current and inlet electrolyte flow rate on the cell voltage, molar flow rates, and current efficiency is studied. Also, the effect of a blockage in inlet flow to one cell in the cell pack is studied for cases when heat transfer is either present and absent between the adjoining cells.     

Modelling-based Optimisation of the Direct Synthesis of Dimethyl Ether from Syngas in a Commercial Slurry Reactor

In the present study, we developed a multi-component one-dimensional mathematical model for simulation and optimisation of a commercial catalytic slurry reactor for the direct synthesis of dimethyl ether (DME) from syngas and CO₂, operating in a churn-turbulent regime. DME productivity and CO conversion were optimised by tuning operating conditions, such as superficial gas velocity, catalyst concentration, catalyst mass over molar gas flow rate (W/F), syngas composition, pressure and temperature. Reactor modelling was accomplished utilising mass balance, global kinetic models and heterogeneous hydrodynamics. In the heterogeneous flow regime, gas was distributed into two bubble phases: small and large. Simulation results were validated using data obtained from a pilot plant. The developed model is also applicable for the design of large-scale slurry reactors.     

An optimisation approach for increasing the profit of a commercial VGO hydrocracking process

In this paper, an optimisation approach is proposed to increase the profit of a commercial hydrocracking unit called Isomax. To represent the system, a full‐lump kinetic model incorporating the flow rate of fresh vacuum gas oil (VGO), bed temperatures, recycle flow rate and the catalyst life is developed. This model is capable of predicting the yield of all products, and it improves with respect to the previous works by considering LPG and light gases, fresh VGO and recycle streams as separate lumps. After developing and validating the model, the profit function of the plant, including the value of the products, fresh feed and hydrogen, as well as energy expenses, is optimised by manipulating the bed temperatures, flow rate of fresh VGO and combined feed ratio (CFR) whilst all process limitations and operating constraints are taken into account. During two years of study and considering all mechanical and operational constraints, the results confirm that the decision variables, generated by the optimisation package, can increase the gross profit of the Isomax process to about 8.17%, which is equal to $5.6 million of net profit annually. © 2012 Canadian Society for Chemical Engineering     

Studies of gas–liquid flow through reactors internals using VOF simulations

Two-phase flow through reactor internals have been experimentally and numerically studied. Experiments have been carried out with a setup running under ambient pressure for two configurations. The first configuration consists of a mixing box orifice inlet through which liquid flows as a film sheared by a gas flow. The liquid height at orifice inlet is documented over a wide range of liquid and gas flowrates. The second configuration consists of the two-phase flow through a downcomer of a distributing tray. Two and three dimensional computational fluid dynamic (CFD) simulations using the volume of fluid approach have been used to compute both flows for similar flow conditions as used in the experiments. It is shown that the agreement between experiments and calculations is very good. Based on this good agreement, it is finally discussed how CFD can be used to achieve better design rules for gas liquid reactor internals via simulations carried out for industrial process conditions.     

Ethylene selectivity variation in acetylene hydrogenation reactor with the hydrogen/acetylene ratio at the reactor inlet

Variation in the selectivity of ethylene produced by acetylene hydrogenation in an integral reactor was analyzed as a function of the hydrogen/acetylene ratio in the reaction stream at the reactor inlet. The analyses were made for two sample catalysts, which showed different dependence of the ethylene selectivity on the reactant composition. Even a small mismatch between the hydrogen/acetylene ratio at the reactor inlet and the ratio for converted reactants caused a large change in the ethylene selectivity along the reactor position, particularly when the conversion was high. The results of this study indicate two important factors to be considered in the design and operation of acetylene hydrogenation process: the hydrogen/acetylene ratio in the reactor inlet should be controlled close to the ratio for converted reactants; and catalysts showing high ethylene selectivity over a wide range of the hydrogen/ acetylene ratio are required for the design of a highly selective hydrogenation process. This paper is dedicated to Professor Wha Young Lee on the occasion