基于CFD-DEM的异形催化剂径向床反应器数值模拟

为研究催化剂颗粒形状对床层流场均匀度的影响,应用计算流体力学-离散元耦合方法(CFD-DEM)对异形催化剂颗粒随机堆积径向床反应器内的流场进行数值模拟,分别建立柱形、小孔环柱形、大孔环柱形、3孔柱形以及5孔柱形颗粒床层模型,分析反应器床层孔隙率、速度场和压力场的变化。结果表明,不同形状颗粒床层的流场均匀度从高到低的顺序为柱形、3孔柱形、5孔柱形、大孔环柱形和小孔环柱形,柱形颗粒床层主流道径向压差最高,床层孔隙率最低,床层径向速度及压降沿轴向变化最小,流体分布最均匀。     

异形催化剂床层中Sabatier反应的微-介尺度模拟

采用离散元方法（DEM）建立随机堆积球形、柱形催化剂床层,计算流体力学（CFD）方法模拟Sabatier反应床层介尺度和催化剂微尺度的温度和物质浓度分布,并探讨了催化剂形状、壁温和入口条件对反应特征的影响。结果表明：床层中会出现球形热点区,并随反应进行向出口移动,催化剂外层反应物浓度比内层高且呈环状分布。柱形催化剂单颗粒中心CO₂转化率较球形高,但棱角和床层壁面会出现低转化率区,床层流体会出现回流、滞留和沟流现象,最终导致CO₂转化率为球形>柱形（径高比=1.3）>柱形（径高比=1）。球形催化剂床层中,时间t=200s时,CO₂转化率达到峰值26%,若此时将壁温降低50K,时间t=500s时,较降温前CO₂转化率增大2%、热点温度降低10K;增加惰性球层、减小入口流速和温度,能提高催化剂内CO₂转化率。     

热等离子体催化耦合重整CH_4和CO_2制合成气

常压下,利用实验室制备的Ni-Ce/Al2O3催化剂,进行了热等离子单独重整与热等离子体催化耦合重整CH4和CO2制合成气的实验研究。实验中,催化剂被放置在等离子体反应区,催化剂床层由高温等离子射流气体加热。固定原料气配比V(CO2)/V(CH4)=1、等离子体工作载气流量0.8 m3/h及放电功率3.5 kW不变,考察了原料气总流量对原料转化率、产物选择性、化学能效和催化剂积碳速率的影响;并探讨了助剂Ce在重整反应中的作用。结果表明:随原料气总流量的增加,CH4和CO2转化率降低,H2和CO选择性无明显变化,C2H2选择性和催化剂积碳速率增加。热等离子催化耦合重整比热等离子单独重整具有较高的原料转化率、H2和CO选择性、化学能效值和较低的C2H2选择性。     

气固反应多孔填充床反应特性的多尺度模拟

采用孔隙网络方法建立了颗粒堆积多孔填充床内细观孔隙结构、微观气固反应及宏观传输过程交互耦合的多尺度孔道网络数学模型.以铁矿石间接还原反应为例,计算分析了床层孔道结构特征及颗粒孔结构对传递过程和反应特性的影响规律.结果表明,床层孔道结构特征对流动气体浓度分布和固体物料转化程度影响显著,正态分布的孔结构孔径沿气体流动方向降低时,床层各横截面的平均固体转化率最高,与均匀分布的孔结构计算结果的最大相对误差为29.5%;计算粒级分布范围较窄的颗粒物料时,可采用均匀分布孔结构近似代替实际正态分布孔结构.颗粒孔结构变化引起的转化率最大相对误差随反应进行持续增大,固体转化率为0.5时,颗粒两种孔结构分布的最大相对误差达14.6%.     

耐硫甲烷化催化剂的研究

煤制天然气采用耐硫甲烷化催化剂,减小了反应设备体积,对节省投资和降低能耗有积极意义。采用等体积浸渍法制备系列Mo-Ni/γ-Al2O3耐硫甲烷化催化剂,并对催化剂活性及耐硫性进行评价,考察浸渍液中不同Co和W元素添加量对催化剂活性的影响。结果表明,耐硫甲烷化催化剂活性中心MoS2和WS2的生成有利于提高CO转化率和CH4选择性,促进合成气生成CH4,Co的添加不利于提高催化剂的CO转化率和CH4选择性,而W元素的添加有利于提高催化剂的CO转化率和CH4选择性。在反应温度550℃、压力2 MPa和空速1 800 h-1条件下,n（H2）∶n（CO）=1∶1时,CO转化率为64.24%,CH4选择性为52.00%。n（H2）∶n（CO）=3∶1时,CO转化率为77.90%,CH4选择性为68.41%。     

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。     

丙烯氧化制丙烯酸催化剂单管试验研究

通过研究,得到了丙烯氧化制丙烯酸的最佳反应条件。由于采用了不同颗粒大小和活性的催化剂,使床层热点与熔盐温差降低,床层轴向温度分布和反应过程稳定性得到改善。研究结果表明,丙烯总转化率为 94.23％,丙烯酸收率为 84.17％,按丙烯酸计的催化剂时空产率为 143.3克/升催化剂·小时。     

浆态床中二氧化碳加氢合成甲醇

研究了浆态床中自行开发的LP201甲醇合成催化剂上二氧化碳加氢合成甲醇的过程。探讨了不同操作条件,如温度、压力、气体空速、原料气配比等对反应的影响;考察了该催化剂在浆态床二氧化碳加氢合成甲醇过程中的稳定性。实验结果表明,浆态床二氧化碳加氢合成甲醇过程中主要产物为甲醇、CO和水;随温度的增加,CO2的转化率和甲醇产率呈现上升的趋势,但甲醇的选择性明显下降;压力的升高有利于CO2的转化率、甲醇产率以及甲醇的选择性提高;原料气空速的提高会增大甲醇产率,但同时降低CO2的转化率以及甲醇的选择性;CO2的转化率、甲醇收率以及甲醇的选择性在氢碳摩尔比4～5获得极大值。LP201催化剂的寿命考察结果表明,该催化剂具有较好的催化活性和稳定性。     

工艺条件对Ni/A12 O3和Ni/CeO2-A12O3催化剂在甲烷自热重整制氢反应中催化性能的影响

采用共沉淀法制备γ-A12O3载体和不同Ce添加量的CeO2-A12O3载体,然后用浸渍法制备Ni负载质量分数10%的Ni/γ-A12O3和Ni/CeO2-A12O3催化剂.在固定床微反装置中考察了反应温度、原料气配比和CH4空速等工艺条件对Ni/γ-A12O3和Ni/Ce30A170Oδ催化剂在甲烷自热重整制氢反应中催化性能的影响.结果表明,添加Ce的催化剂催化性能有较大提高,在Ni/Ce30A170O3催化剂上,反应温度750 ℃时,CH4转化率94.3%,与Ni/A12O3催化剂相比,提高20%.Ni/γ-A12O3和Ni/CeO2-A12O3催化剂的CH4转化率均随反应温度的升高而增大.原料气中n(O2):n(CH4)和n(H2O):n(CH4)的增加均能提高各催化剂的CH4转化率.但n(O2):n(CH4)和n(H2O):n(CH4)的变化对各催化剂的催化性能的影响不同.随着n(O2):n(CH4)的增大,产物中n(H2):n(CO)降低,n(CO2):n(CO CO2)升高;而n(H2O):n(CH4)增大时,产物n(H2):n(CO)和n(CO2):n(CO CO2)均升高.随着CH4空速的增加,Ni/A12O3催化剂上CH4转化率、n(H2):n(CO)和n(CO2):n(CO CO2)均较大程度下降;而在Ni/Ce30A170Oδ催化剂上,随着CH4空速的增加,CH4转化率、n(H2):n(CO)和n(CO2):n(CO CO2)变化不大.     

循环流化床生物质颗粒掺混流动特性CPFD模拟

针对循环流化床(CFB)燃煤锅炉掺混生物质颗粒对床内颗粒流动特性的影响,文中基于计算颗粒流体动力学(CPFD)方法对CFB内煤炭颗粒掺混生物质颗粒的混合流动特性进行模拟研究,考察床层压降,并分析生物质掺混比以及不同的掺混方式对颗粒流动特性的影响。结果表明：掺混质量分数15%生物质的混合颗粒最小流化速度为0.7 m/s;生物质掺混比例的增加使最小流化速度有所提升,但提升程度不大;此外,2种颗粒的堆积方式对颗粒流动特性存在影响,当生物质堆积在煤炭上方时,会阻碍床层内颗粒的正常流化,出现节涌现象。     

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.     

Experimental and modeling analysis of the effect of catalyst aging on the performance of a short contact time adiabatic CH4-CPO reactor

Catalytic partial oxidation of methane at short contact time was studied in a lab-scale packed bed reactor over a 0.5 wt% Rh/A₂O₃ catalyst. Experiments were focused on the investigation of catalyst stability and durability upon repeated start-up/shut-down tests at different inlet temperatures and flow rates. Measurements of the axial temperature profiles evidenced a high sensitivity of the steady state thermal behavior of the reactor on catalyst activity: a decrease of the intrinsic catalytic activity was interpreted as the cause of a progressive over-heating of the bed which, in turn, moderated the loss of methane conversion and syngas productivity. At sufficiently high flow rate the observed temperature rise spread along the whole catalytic bed. Under such conditions both steady state and dynamic reactor performances were affected by the progressive decay of catalyst activity. A rationalization of the observed results was pursued by applying a one dimensional (1D) heterogeneous model of the reactor to the quantitative analysis of experimental results. Model predictions revealed the occurrence of operating surface temperatures up to 1100 °C and allowed to quantify the progressive worsening of reactor performances in terms of a loss of reforming activity localized in correspondence of the catalyst hot spot.     

Pyrolysis of wood in vibro-fluidized beds of catalysts and inert materials

Pyrolysis of wood in vibro-fluidized beds of disperse packings of deep oxidation catalysts and inert materials is investigated. It is shown that the properties of the disperse packing material of vibro-fluidized beds do not have a significant effect on the rate and degree of conversion of wood to volatiles. The presence of catalysts in the vibro-fluidized bed leads to an increase in the amount of CO₂, CO, H₂, and CH₄ in the gas phase compared to the pyrolysis of wood in vibro-fluidized beds of inert materials. The greatest activity in the conversion of volatiles to CO₂, CO, H₂, CH₄ was found for the catalyst IK-12-73 (Mg_0.5Cu_0.5Cr₂O₄/Al₂O₃). The accumulation of carbon in IK-12–73 catalyst has little effect on the conversion of volatile substances to gaseous products. The degree of burnout of wood particles under conditions of a vibro-fluidized bed of IK-12-73 catalyst is 99.7%, which is consistent with data on the catalytic combustion of wood in the fluidized bed.     

Modelling of fluidized bed reactors—II: Uniform catalyst temperature and concentration

A model based on the simple two phase theory of fluidization including the catalyst particles as a third phase has been developed for a nonisothermal fluidized bed catalytic reactor with continuous circulation of catalyst particles. The dilute phase is assumed to be in plug flow, the emulsion phase gas is considered to be perfectly mixed and the particles are assumed to be perfectly mixed and uniform.Exact criteria for uniqueness and multiplicity of the steady state solutions are presented and some conclusions derived therefrom. Several examples illustrating the influence of some parameters on the steady state multiplicity are reported. The steady states are analyzed for local asymptatic stability using Liapunov's direct method, but the sufficient conditions for stability are found to be rather conservative.Numerical examples illustrating the transient behavior of the system are presented, and it has been found that the initial temperature of the catalyst particles is a predominant factor in determining which steady state will be approached.     

Coupling exothermic and endothermic reactions in adiabatic reactors

The steady state and the dynamic behavior of coupling exothermic and endothermic reactions in directly coupled adiabatic packed bed reactors (DCAR) are analyzed using one-dimensional pseudo-homogeneous plug flow model. Two different configurations of DCAR (simultaneous DCAR—SIMDCAR and sequential DCAR—SEQDCAR) are investigated. In SIMDCAR, the catalyst bed favors both exothermic and endothermic reactions and both reactions occur simultaneously. SEQDCAR has alternating layers of catalyst beds for exothermic and endothermic reactions and hence the exothermic and endothermic reactions occur in a sequential fashion. The performance of both reactors, in terms of conversion achieved and manifested hot spot behavior, is compared with that of the co-current heat exchanger type reactor. Various possible operational regimes in SIMDCAR have been classified and the conditions for the existence of hot spots or cold spots in SIMDCAR are obtained analytically for the first order reactions with equal activation energies. The reactor behavior for the reactions with non-equal activation energies is also presented. The preliminary criteria for the selection of suitable reactor type and the general bounds on the reaction parameters to obtain the desired conversion for endothermic reaction with minimal temperature rise are proposed. The dynamic behavior of these reactors is important for control applications and we have reported some of the transient behavior.     

CH_4-CO_2重整转化反应器热平衡和流体阻力特性的研究

基于炭催化剂特性、原料气组成和重整转化反应器的尺寸参数,建立了重整反应器体系的物料平衡和热平衡方程;并针对形状不规则炭催化剂粒度分布的特点,研究了重整转化反应器内流体阻力特性。研究结果表明:1)CO和H2O的生成热量是系统的主要放热源,占系统热量收入的71.03%,吸热的主要反应为CH4和CO2的转化反应,其吸热量占系统热量支出的33.54%,高温气体带走的大量热量占54.11%,散热量占13.51%;2)炭催化剂床层的流体阻力是重整转化反应器流体阻力的主要部分,炭催化剂粒度越大,炭催化剂床层的阻力越小,最适宜粒度组成是25～35mm的占80%,15～25 mm的占15%,5～15 mm的占5%,此时炭催化剂床层的流体阻力为313.5Pa/m。     

变换工段水气比的选择与节能

根据QDB-04型催化剂在各企业的应用数据,研究了原料气中的CO含量和水气比对变换反应深度、催化剂床层热点温度、催化剂反硫化的影响,分析了QDB-04型催化剂对不同气化工艺制取的不同水气比原料气的适应性。针对高CO含量、高水气比原料气变换系统存在的问题,开发了废热锅炉+两段低水气比耐硫变换专利技术和分层进气的反应器专利技术,稳定了变换操作,显著降低了蒸汽用量,确保装置连续长周期运行。     

流化床甲烷化基础与应用最新进展

由于CO甲烷化的快速表面反应、强放热特性,相比固定床,采用小颗粒催化剂的流化床甲烷化技术在反应活性和催化剂稳定性方面具有明显的技术优势。从高耐磨催化剂、流化床反应器及其创新、短流程两段甲烷化技术构建及其验证等方面总结了流化床甲烷化技术开发的最新进展。优化催化剂前体制备方法、调变催化剂组成可获得具有较高骨架强度和均匀性的催化剂一次微粒,进而通过优化的喷雾造粒工艺和填充黏结剂,制备出具有可调变粒度分布、高强度和高球形度的流化床用粉末催化剂,但其黏结剂的添加明显影响催化剂的低温活性。通过改性如Al₂O₃和FCC催化剂的球形颗粒,进而负载活性组分,开发了制备高活性、磨损指数小于1.5的流化床甲烷化Ni基催化剂的另一种技术方法。实验室研究证实了流化床甲烷化反应速率极快,在分布板上数毫米处即可实现可能的最高转化率,且在转化率和催化剂稳定性方面明显优于固定床,不仅由于流态化催化剂床层温度均匀,而且催化剂在床层内不停循环,加快了颗粒表面的更新。增大空速和表观气速,流化床的催化剂床层膨胀,反应气体与催化剂颗粒表面间的有效接触面积增加,使得流化床甲烷化对空速和表观气速的可调范围大。操作在更高气速条件的输送床甲烷化避免了操作气速的上限限制,可大幅降低反应器尺寸,有效提高单位截面的原料气负荷能力。输送床甲烷化可采用高热导率的催化剂颗粒传递反应热,相对于气体移热效率高、能力大。流化床甲烷化已在生物废弃物利用和焦炉煤气甲烷化方面开展了侧线示范,形成了相对多段绝热固定床工艺更简单的短流程两段甲烷化新工艺。     

Multidimensional modeling of a microfibrous entrapped cobalt catalyst Fischer‐Tropsch reactor bed

Thermal management of highly exothermic Fischer‐Tropsch synthesis (FTS) has been a challenging bottleneck limiting the radial dimension of the packed‐bed (PB) reactor tube to 1.5 in. ID. A computational demonstration of a novel microfibrous entrapped cobalt catalyst (MFECC) in mitigating hot spot formation has been evaluated. Specifically, a two‐dimensional (2‐D) model was developed in COMSOL^®, validated with experimental data and subsequently employed to demonstrate scale‐up of the FTS bed from 0.59 to 4 in. ID. Significant hot spot of 102.39 K in PB was reduced to 9.4 K in MFECC bed under gas phase at 528.15 K and 2 MPa. Improvement in heat transfer within the MFECC bed facilitates higher productivities at low space velocities (≥1000 h^?1) corresponding to high CO conversion (≥90%). Additionally, the MFECC reactor provides an eightfold increase in the reactor ID at hot spots ≤ 30 K with CO% conversions ≥ 90%. This model was developed for a typical FTS cobalt‐based catalyst where CO₂ production is negligible. © 2017 American Institute of Chemical Engineers AIChE J, 64: 1723–1731, 2018