耦合传质的羰基化固定床反应器传热模拟分析

固定床反应器中进行强放热反应时, 反应器的热点温度对操作参数变化敏感,容易引起飞温,导致转化率下降,影响催化剂寿命。为强化羰基化固定床反应器内热质传递与化学反应的协同性,建立考虑颗粒内扩散影响的羰基化固定床反应器拟均相一维传热模型,考察操作参数对床层热点温度、反应转化率、床层温升的影响。不仅体现传热传质和反应的协同作用,而且影响关系明晰、求解方便。为保证反应转化率,本实验条件下确定催化剂颗粒直径小于等于1.5 mm。反应器入口温度/冷却剂油温既要满足床层热稳定性需求,又要使反应转化率和床层温升都在合理范围内。模拟结果表明在床层入口温度升高的同时,可通过降低冷却剂油温获得良好的反应转化率和较小的床层温升。在此基础上,考察入口环氧乙烷浓度对反应转化率和床层温升的影响。本研究可为固定床反应器满足转化率要求、床层合理温升而选择催化剂颗粒直径、床层入口温度、冷却剂油温和床层入口浓度等操作参数提供计算依据。     

工艺条件对碳二前加氢催化剂性能的影响

以α-Al2O3为载体,钯为活性组分,银为助剂制备了前加氢催化剂,并在750 mL工业侧线装置上与进口催化剂进行了对比评价。考察了入口温度、空速和CO含量三个工艺参数对碳二前加氢催化剂性能的影响,结果表明:提高入口温度,催化剂乙炔转化率、MAPD转化率升高,乙烯增量先增加后降低;和入口温度相比,空速对催化剂性能的影响稍小;CO含量对催化剂性能影响较大。     

基于COMSOL Multiphysic的CO变换反应的数值模拟与优化

利于多物理场耦合软件COMSOL Multiphysic,建立一个耦合CO变换反应传质、传热、动量传递和化学反应的二维轴对称拟均相固定床反应器模型。采用COMSOL Multiphysicl默认的反应流,稀物质传递(rfcs)模型和传热(ht)模型,通过内置的模型输入将二个模型耦合起来。催化动力学采用Langmuir-Hinshelwood方程,催化剂的性质及操作条件以Wei-Hsin Chen等的实验为基础。采用有限元法对模型进行稳态模拟,得到反应器内的速度场、浓度场、温度场,对反应床层内组分浓度、速度及温度进行可视化分析。将所得的结果与文献值进行对比,从而验证了模型的准确性。最后,采用COMSOL Multiphysic对催化反应条件进行灵敏度分析,分析了入口温度、催化剂失活因子、入口组成对床层温度及CO转化率的影响。     

XNC-98催化剂甲醇合成本征动力学

在等温积分反应器中研究了XNC-98催化剂上甲醇合成反应本征动力学.实验压力为4~8MPa,空速7000~13000h-1,反应温度200~260℃.实验采用粒度为0.154~0.198mm的细颗粒催化剂.选取以各组分逸度表示的CO、CO2加氢合成甲醇的Langmuir-Hinshelwood本征动力学模型.采用正交实验设计,实验测定了25组数据,用全局通用算法结合马夸特算法确定动力学模型参数.残差分析和统计检验表明,动力学模型是适宜的.随温度升高,反应器出口甲醇浓度、CO和CO2转化率先增加后降低,在4~8MPa下,230~245℃为较佳反应温度范围:随着反应压力的提高,反应器出口甲醇浓度、CO和CO2转化率都有显著增加,提高反应压力能够有效提高反应器的生产能力.     

煤基合成气制SNG反应工艺的研究

采用2个模拟绝热反应器串联的模试装置,对自主研发的NCJ-1宽温型催化剂与NCJ-2低温型催化剂进行了活性评价,研究了煤基合成气制SNG的反应工艺。试验采用的原料气组成(φ)为:H268.4%,CO 19.6%,CO_23.0%,CH_49.0%,考察了空速、入口温度、新鲜气中CO_2体积分数、循环比、反应压力、一反入口加水量等条件对甲烷合成的影响。试验结果表明:空速上升对反应转化率和气体出口浓度的影响不太明显,但热点位置会下移;入口温度在高于250℃的前提下,随着温度的升高热点温度急剧上升;CO_2入口体积分数上升,CO_2转化率上升;通过改变循环比可以有效控制一反入口CO_x体积分数,使反应热点温度控制在催化剂允许的范围内;随着压力升高,热点温度、CH_4出口体积分数、CO转化率、CO_2转化率均上升;一反入口加水有利于控制床层温度,并有效保护催化剂,防止积炭。     

甲醇水蒸气重整制氢固定床反应器的数学模拟

建立二维拟均相固定床反应器数学模型用于描述Cu₅₀Zn₃₀Ce₁₀Al₁₀催化剂颗粒的甲醇水蒸气重整制氢反应过程，该模型由流体相的质量、热量和动量传递方程组成，耦合催化剂颗粒内部的扩散-反应模型。通过将模型预测值与实验数据进行比较，验证反应器数学模型的准确性。在此基础上，分析关键组分CO₂和CO的效率因子随床层轴向的变化规律以及催化剂床层的轴径向温度分布。结果表明：催化剂床层的轴径向温差较大，导致CO₂效率因子变化较大，而CO由于浓度低，反应速率慢，其效率因子变化不明显。     

催化重整固定床径向反应器结构的优化研究

催化重整固定床反应器（Catalytic Reforming Fixed Bed Reactor,以下简称CRFBR）传递及反应过程的综合数学模型是以流体力学的基本微分方程为基础,考虑了流体的湍流流动,多孔介质内流体流动、传热、传质等过程,结合催化重整集总反应动力学模型而建立的。采用该模型对工业催化重整径向反应器进行数值模拟计算,考察了反应器入口分配器设置、催化剂床层空隙率分布情况、催化剂填装比、反应器底部结构四个因素对产物组成的影响,从而确定优化的反应器结构和理想的催化剂填装情况。结果表明,反应器入口分配器采用单层效果较好,并确定了分配器的最佳位置;分析了催化剂床层空隙率分布不均对床层轴向温度、压力、组份浓度分布的影响;确定了最佳的催化剂填装比为1：1：2：4;针对反应器底部床层温度分布不均的情况改善了反应器底部结构,效果较好。     

乙烯氧化固定床反应器温度场模拟研究

针对乙烯氧化制环氧乙烷固定床反应器,利用YS-7型银催化剂的宏观反应动力学模型和固定床反应器拟均相二维数学模型方法,建立了催化剂床层的质量、热量平衡方程组,并采用Crank-Nicholson差分法对该偏微分方程组进行了数值计算。在模拟计算中,通过改变反应器汽包温度、反应器入口原料气温度、空速以及反应器入口原料气中乙烯、氧气、1,2-二氯乙烷的摩尔分数等工艺条件,系统地研究了以上各工艺条件单因素变化时对整个银催化剂床层温度场的影响。结果表明:随着固定床反应器汽包温度、入口原料气中乙烯、氧气摩尔分数的升高,以及固定床反应器中空速、入口原料气的温度及1,2-二氯乙烷摩尔分数的降低,银催化剂床层温度均有所升高,特别是床层"热点"区域的温度升高较明显。     

气体氨浓度自动分析仪

一、前言在复合成催化剂研制工作中,为了获得性能比较理想的催化剂,要进行广泛的活性筛选,这种筛选一般是在活性评选装置中,于不同温度、压力条件下,通过对反应器前后气体氨浓度变化的测定来完成的。同样,在氨合成反应动力学研究工作中,为求得动力学模型和参数,予示催化剂在工业反应器内的动力学行为,也要求对气体氨浓度变化进行精确的测定。     

大庆石化乙烯装置应用数学建模估算碳二加氢催化剂反应活性方法研究

乙炔前加氢反应系统中,催化剂活性与物料中的CO浓度密切相关。通过应用数学建模方法,提出一种三角函数来描述CO浓度对催化剂活性的影响程度,能够根据CO浓度对催化剂活性进行定量分析,并根据CO的波动范围提供操作依据,进而指导生产。     

Effects of system parameters on the performance of CO2-selective WGS membrane reactor for fuel cells

Performing water gas shift (WGS) reaction efficiently is critical to hydrogen purification for fuel cells. In our earlier work, we proposed a CO₂-selective WGS membrane reactor, developed a one-dimensional non-isothermal model to simulate the simultaneous reaction and transport process and verified the model experimentally under an isothermal condition. Further modeling investigations were made on the effects of several important system parameters, including inlet feed temperature, inlet sweep temperature, feed-side pressure, feed inlet CO concentration, and catalyst activity, on membrane reactor performance. The synthesis gases from both autothermal reforming and steam reforming were used as the feed gas. As the inlet feed temperature increased, the required membrane area reduced because of the higher WGS reaction rate. Increasing the inlet sweep temperature decreased the required membrane area more significantly, even though the required membrane area increased slightly when the inlet sweep temperature exceeded about 160 °C. Higher feed-side pressure decreased the required membrane area as a result of the higher permeation driving force and reaction rate. A potentially more active catalyst could make the membrane reactor more compact because of the enhanced reaction rate. The modeling results have shown that a CO concentration of less than 10 ppm is achievable from syngases containing up to 10% CO.     

Optimal temperature policies for catalytic transport reactors under periodic operation

The influence of inlet gas concentration cycling on the optimal temperature policy of catalytic transport reactors is studied theoretically. The model considered is based on plug flow of gas and catalyst particles with negligible interand intra-particle diffusional resistances and concentration dependent deactivation kinetics. To utilise the concentration of the reactant and the activity of the deactivating catalyst fully a proper temperature sequence along the reactor is needed. Thus, a general optimal temperature policy using the continuous minimum principle is derived for the reactor under periodic operation. The model equations are solved analytically for gas concentration, activity and temperature profiles. Resonance behaviour (maximum in conversion with pulse width) is obtained using the optimal temperature policy for certain sets of parameters. The effects of activation energy groups, reaction and deactivation constant groups and inlet temperature on the optimal temperature policy under periodic operation are evaluated. In all cases an improvement in conversion with the optimal temperature policy under periodic operation over that with an isothermal policy under periodic operation is obtained. A suboptimal policy, comprising constant temperature over different reactor sections, which is useful for implementation purposes is also discussed.     

Operating strategies for Fischer-Tropsch reactors: A model-directed study

A comprehensive parametric study for a Fischer-Tropsch (FT) synthesis process has been conducted to investigate the relation between process parameters and reactor characteristics such as conversion, selectivity, multiplicity, and stability. A flexible model was employed for this purpose, featuring the dependence of Anderson-Shultz-Flory (ASF) factor on composition and temperature. All variable process parameters in industrial FT reactors were subject to variation, including reaction temperature, reactor pressure, feed ratio, inlet mass flux, feed temperature, heat transfer coefficient, catalyst concentration, catalyst activity, etc. While typical trade-off was encountered in most cases, i.e., the change of a parameter in one direction enhances one aspect but deteriorating another, the change of feed conditions gave some promising results. It has been found that decreasing the feed rate (or increasing the residence time) and/or lowering the feed concentration can successfully enhance the conversion up to more than 90% for our specific case, without hurting the product selectivity as well as effectively condense the region of multiple steady states. The benefits and limitations accompanied with the variation of the parameters were discussed in detail and a rational start-up strategy was proposed based on the preceding results. It is shown that the decrease of inlet mass flux (say, 85% decrease of the feed rate or 60% decrease of the feed concentration from the nominal condition chosen here) or the decrease of H₂/CO ratio (specifically, below about 0.25), or their combination can eliminate multiple steady states. The resulting unique relation between temperature and manipulated variable (i.e., coolant flow rate) appears to assure a safe arrival at the target condition at the start-up stage. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

密闭空间CO消除的Pd/Al_2O_3催化剂合成及其催化性能研究

采用浸渍法制备不同PdCl_2含量的贵金属催化剂,并对反应前后催化剂进行傅里叶红外和物理结构表征。结果表明,PdCl_2质量分数为3%的催化剂活性最高,可在70℃实现低浓度CO的完全转化。反应后,催化剂表面没有明显变化,催化剂比表面积增大,孔容及平均孔径呈减小趋势。研究进口CO浓度和空速对CO转化率的影响,结果表明,在一定浓度范围,提高进口CO浓度对CO转化率没有影响,浓度超过1 000×10~(-6)时,CO转化率下降;空速升高,CO转化率下降,温度越低,空速对CO转化率影响越大。     

An experimental study of instability in a non-adiabatic multi-reaction tubular reactor

An experimental study of instability in a non-adiabatic packed bed reactor using NO reduction with CO over a fiber glass supported Ru catalyst is presented. A 2-reaction kinetic model is used. The results are compared to the predictions of two different TRAM ignition criteria which are expanded to cover the non-adiabatic, single reactant but multireaction case. Although there were difficulties in experimentally evaluating some of the transport parameters, the results show that one of the expanded ignition criteria in particular does satisfactorily model the data. Data are also presented which show how the temperature profile in an ignited bed moves as the inlet temperature is lowered to the quench point. Additional quench data are provided which show that the quench point is strongly affected by the feed concentration of the reactant and only a mild function of gas velocity.     

B112催化剂上一氧化碳变换反应工业过程动力学研究

采用“沿程积分拟合法”,在某小合成氨厂变换工段引出的支线上,利用绝热固定床反应器,对B112催化剂上一氧化碳变换反应进行了常压及加压工业过程的动力学研究。通过对不同操作条件下的床层轴向温度分布进行积分拟合,得到了适用于工业条件的过程动力学方程。一氧化碳变换反应 CO+H_2~O(?)CO_2+H_2 是石油化工和煤化工重要的化学反应。国内外学者对许多种铁系催化剂上的该反应进行了动力学研究,推荐了各自的本征或宏观动力学方程。本文采用“沿程积分拟合法”对国产B112催化剂上的一氧化碳变换反应进行工业过程动力学研究。按照该法的要求,实验中需采用与工业实际反应器(绝热固定床反应器)型式相同的小型反应器,在工业条件下,测定不同进口条件的反应器轴向温度分布及出口浓度,通过积分拟合获得工业过程动力学方程。     

Low-Temperature CO Oxidation over a Pt/Al2O3 Monolith Catalyst Investigated by Step-Response Experiments and Simulations

The ignition–extinction processes for CO oxidation over a Pt/Al₂O₃ monolith catalyst have been studied by flow-reactor experiments and simulations. The study was performed by stepwise changes of the inlet O₂ concentration ranging 0–20 vol% while the CO concentration and the inlet gas temperature were kept constant at 1.0 vol% and 423 K, respectively. Several features observed experimentally are qualitatively simulated with our model: (i) the ignition of the CO oxidation demands 8.0vol% O₂ (ii) corresponding to a catalyst ignition temperature of 433 K (due to the exothermicity of the reaction) and (iii) occurs in the rear part of the monolith where (iv) a local reaction zone is formed which (v) moves towards the reactor inlet as a function of time on stream. Additionally, the simulations show first order kinetic phase transitions, i.e. rapid adsorbate concentration changes, where the catalyst surface is predominantly CO covered in the low reactive state and almost completely oxygen covered in the high reactive state. For the ignition process the kinetic phase transition occurs after the actual catalytic ignition. However, the extinction process is more difficult to simulate dynamically without changing the model parameters for O₂ adsorption in the low and high reactive state, respectively. The influence of diffusion limitations and the role of formation of a less reactive Pt state under oxidising conditions is discussed.     

Experimental study of traveling waves in nonadiabatic fixed bed reactors for the oxidation of carbon monoxide

An experimental study of axial temperature profiles in a nonadiabatic tubular fixed bed reactor has been made under the transient operation. The catalytic carbon monoxide oxidation occuring on a Pt/alumina catalyst has been used. Unlike the adiabatic conditions the velocity of a traveling temperature wave in a nonadiabatical arrangement depends on its axial position. In certain regions of inlet concentration multiple temperature fronts have been observed. For low inlet CO concentration a downstream temperature wave results and the lower (kinetic) steady state is dominant. For high inlet CO concentration an upstream propagating front results and the upper steady state is dominant. For a downstream moving wave oscillations of wave velocity, hot spot temperature and exit conversion have been measured. For certain operating conditions periodic behavior of temperature profiles in the reactor has been observed.     

催化剂颗粒形状对甲烷水蒸气重整反应的影响及工业反应器模拟

甲烷水蒸气重整工艺是现阶段最主要的工业制氢技术,催化剂颗粒形状和反应器操作条件是影响重整反应器性能和产物组成的重要因素。首先从颗粒尺度研究催化剂形状对甲烷水蒸气重整反应的影响,在不同的反应温度和压力下,计算并比较了球形、柱形和环形催化剂的效率因子,其大小顺序为:柱形 < 球形 < 环形。其次,将反应器床层的质量、热量和动量传递与环形催化剂颗粒的扩散-反应方程相结合,建立了用于描述甲烷水蒸气重整工业反应器的一维轴向数学模型。计算并分析了反应器进口温度和压力对反应器床层的温度和压力分布、催化剂效率因子以及甲烷转化率和各组分浓度分布的影响,确定了适宜的工业反应器进口温度和压力,分别为773 K和3 MPa。