二甲醚水蒸气重整制氢的模型和数值模拟

为研究二甲醚的水蒸气重整制氢过程,设计了一种带有隔热套、瓦片式加热通道和催化反应床的重整反应器。建立了反应器的数学模型,并利用COMSOL软件对其仿真。试验研究了反应气体温度、水蒸气与二甲醚的物质的量比和反应器结构参数对二甲醚转化率、氢产率的影响。模拟结果显示了二甲醚水蒸气重整制氢过程中的各组分质量分布及不同温度、不同水醚物质的量比下二甲醚转化率和制氢率情况,给重整器的研究提供了参考。通过试验验证了模型的可行性,获得了微型催化重整床反应器的设计数据。结果显示较高的进口温度可以提升反应速率,从而提高二甲醚转化率;水醚物质的量比的提高促进了正反应,加快了二甲醚的消耗,提高了二甲醚的转化率和氢产率。     

泡沫金属微反应器内二甲醚水蒸汽重整制氢的研究

在自制的泡沫金属微结构反应器中,以多孔泡沫镍为载体,负载Cu6Zn3Al0.5Ce0.5/HZSM-5双功能催化剂,用于二甲醚水蒸汽重整制氢的研究。考察负载方法、水醚比、空速、反应温度以及催化剂焙烧温度等条件对二甲醚水蒸汽重整反应的影响。通过X射线衍射(XRD)、程序升温还原(H2-TPR)等手段对催化剂负载方法与催化性能的关系进行探索。结果表明:直接将催化剂Cu6Zn3Al0.5Ce0.5/HZSM-5涂覆在泡沫镍上的催化效果最好,催化剂的最适宜煅烧温度为450℃。在275℃,空速5180 m L/(g·h),水醚比为5的反应条件下,二甲醚转化率和氢收率分别可达99%和95%,反应进行40 h催化剂活性没有明显降低,二甲醚的转化率保持在97%以上。     

木炭催化甘油重整制氢研究

以木炭为催化剂,在固定床反应器中对甘油水蒸气重整制氢进行研究。结果表明:随着空速的增大,氢产率、潜在氢产率和碳转化率逐渐减小;随着温度的升高,氢产率、潜在氢产率和碳转化率增大;S/C的增大在一定程度上有助于促进氢产率、潜在氢产率和碳转化率的增大。在温度为800℃,S/C为4∶1,空速为1.5 h~(-1)时,氢气产率、潜在氢产率分别为114.31 g/kg和128.30 g/kg,碳转化率为89.08%。     

二甲醚水蒸气重整制氢Cu-Zn-Al-Cr/ZSM-5双功能催化剂研究

用共沉淀耦合机械混合法制备Cu-Zn-Al-Cr/ZSM-5双功能催化剂,与Cu-Zn-Al/ZSM-5催化剂进行对比研究,并考察其在二甲醚水蒸气重整制氢反应中的催化性能,研究ZSM-5在二甲醚水解反应以及铜基催化剂Cu-Zn-Al-Cr在甲醇水蒸气重整制氢反应中的活性,同时采用热重、X射线衍射、H2程序升温还原等手段对催化剂的焙烧温度、物相结构、还原性能等进行分析。结果表明,Cu-Zn-Al-Cr/ZSM-5双功能催化剂的性能明显优于Cu-Zn-Al/ZSM-5催化剂,同时Cu-Zn-Al-Cr/ZSM-5双功能催化剂在二甲醚水蒸气重整制氢反应中有较好的低温活性和CO选择性,当反应温度为280℃,水醚比为7∶1时,二甲醚转化完全,氢气收率达到85.7%,反应温度低于240℃时,无CO生成;同时催化剂之间的耦合作用使Cu-Zn-Al-Cr/ZSM-5催化剂在较高温度下具有较好的活性和稳定性。     

整体式催化剂上甘油水蒸气重整制氢

为改善甘油重整制氢反应在转化率、氢产率以及抑制积碳方面都与热力学平衡存在较大差距的问题,设计开发了整体式重整催化剂.考察了涂层组分、比例对整体式催化剂理化特性及其在甘油水蒸气重整制氢反应中催化性能的影响.通过考察Ce-Zr物质的量比及La的添加对催化剂活性的影响,确定了Ce-Zr-La物质的量比为1∶1∶1为最优条件.整体式催化剂的活性得到明显改善,在甘油质量分数为10%,空速为3.07,h-1时,在温度考察范围内甘油完全转化为气相产物,氢气选择性递增,并趋于平稳,最高可达90.85%;随着空速增大,甘油质量分数的增加,氢气选择性减小,甘油气相转化率降低,但仍可保持较好的转化效果.     

甘油水蒸气重整制氢及其CO_2原位吸附强化的研究

文章采用共沉淀方法合成了不同配比的Ni O/Al2O3催化剂,采用固定床反应器研究了不同配比的催化剂对甘油水蒸气重整制氢的影响。通过气体产品含量、甘油及水蒸气转化率等指标的分析得出:甘油和水蒸气转化率及氢气产率在450~650℃时随温度升高而增加,其中Ni O/Al2O3(Ni O=27.43%,Al2O3=72.57%)催化剂由于Ni含量较高,表现出高制氢催化活性,其氢气产率在650℃时达到最高的12.7%,甘油转化率也达到最高值96.9%。进行CO2原位吸附的甘油重整吸附强化制氢时,得到了更高纯度的氢。进行多次循环再生实验时,随着循环次数的增多,由于吸附剂再生不完全,氢气纯度会随着循环次数增多有所下降。     

微细腔内甲烷-湿空气重整特性试验与数值模拟

针对甲烷-湿空气在微细腔内的自热重整,建立了直径为2mm的微细直管试验系统,采用试验研究和三维数值计算两种方法分析了微反应器内甲烷-湿空气自热重整转化特性,并重点分析了反应温度、原料气组分比例变化对重整反应中甲烷转化率和氢气产率的影响.结果表明：在相同的甲烷流量工况下,随着温度的升高以及空/碳比和水/碳比的增大,甲烷转化率和氢气产率均增大,其中空-碳比对甲烷转化率的影响比对氢气产率的影响大;进气质量流量较小的体系比较大的体系在重整产氢方面的效果好.试验和数值模拟得到的结果比较一致.     

Cu-Ni/γ-Al2O3催化剂上二甲醚水蒸气重整制氢工艺条件的研究

采用沉积沉淀法制备了Cu-Ni/γ-Al2O3催化剂,在连续流动的固定床反应器内,进行了二甲醚水蒸气重整制氢反应的研究,考察了还原温度、反应温度、系统压力、气体空速以及催化剂的粒径大小等工艺条件对Cu-Ni/γ-Al2O3催化剂上二甲醚水蒸气重整制氢反应性能的影响。实验结果表明,较优的工艺条件为:催化剂还原温度为400℃,粒径为0.45～0.90mm,反应温度为350℃,常压,气体进料空速为3240mL.(gcat.h)-1。     

甘油水蒸气重整制氢热力学分析

采用吉布斯自由能最小化原理计算甘油水蒸气重整制氢过程的平衡组成,该模型经实验结果验证,吻合良好。考察温度、压力、水/甘油物质的量之比对H_2、CO、CO_2、CH_4组成及选择性,积碳,原料平衡转化率及系统耗能的影响。计算结果表明:在高温低压及高水/甘油物质的量之比条件下有利于提高H_2产率,水/甘油物质的量之比大于4时可有效避免积碳,在873 K下,水/甘油物质的量之比大于20时即可完全消除CH4;结合各反应条件对上述关键反应过程参数的影响,推荐反应温度为823～1023 K,反应压力为常压,水/甘油物质的量之比6∶1～46∶1。甘油水蒸气重整反应过程在反应温度1023 K及水/甘油物质的量之比为9的典型工况下系统耗能占系统产生总能量的30%以上。     

微反应器内催化剂分布对甲醇蒸气重整的影响

甲醇重整制氢具有多方面的优势,是制取氢气的重要途径.传统固定床反应器受到传热传质的限制,导致床层中颗粒催化剂的效率降低.本文设计了一种微型板式反应器,开展了固定床催化剂在床层中不同分布形式对甲醇蒸气重整制氢反应性能影响的研究.结果表明,催化剂床层中沿反应物流动方向上的温度分布出现了冷点温差.通过催化剂合理分布可以降低冷点温差并可提高甲醇蒸气重整反应的氢气产量.在最佳催化剂分布条件下获得了微反应器轴向最小冷点温差的温度分布,其甲醇转化率和氢气产率也较高.     

Design and optimization of reforming hydrogen production reaction system for automobile fuel cell

Mathematical modeling and simulation analysis of the dimethyl ether steam reforming reaction system were carried out in the study. The numerical results of simulation and experiment were consistent. The effects of reaction conditions on the conversion of dimethyl ether and hydrogen production were analyzed. The internal structure of the reforming reactor was adjusted to obtain higher hydrogen production efficiency. The study established the reforming hydrogen production industry system, and analyzed the thermal efficiency of the system. The results show that when the temperature of the conversion bed is 673 K, the inlet flow rate of the mixture gas is 0.5 ms^?1 and the ratio of water to ether is 3, the dimethyl ether steam reforming reaction system could obtain the dimethyl ether conversion rate of 90%, the hydrogen production rate of 88% and system thermal efficiency of 74%.     

Modeling and simulation of hydrogen production from dimethyl ether steam reforming using exhaust gas

In this paper, hydrogen production from steam reforming of DME (dimethyl ether) has been modeled and simulated using a CFD (computational fluid dynamics) method. The reformation chemistry occurs in a porous catalytic bed where exhaust gas is supplied through the EGR (exhaust gas recycling) valve of the engine to drive the endothermic reaction system. The tightly coupled system of mass, energy, and momentum equations are used to describe the complex physical and chemical process of DME steam reforming. The global reaction kinetics for the reforming is adopted in the CFD model. The mathematical models are introduced into the commercial software Comsol, and then numerical simulations are also performed based on this model. The model predictions are quantitatively validated by experiment data. The simulation results indicate the temperature distribution, mass distribution, DME conversion, and hydrogen production from steam reforming of DME. In addition, the fuel to steam ratio and velocity of exhaust gas are manipulated as operating parameters. These simulation results will provide helpful data to design and operate a bench scale catalytic fluidized bed reactor. Copyright © 2015 John Wiley & Sons, Ltd.     

Thermodynamic analysis of high‐temperature helium heated fuel reforming for hydrogen production

In order to take full advantage of the heat from high temperature gas cooled reactor, thermodynamic analysis of high‐temperature helium heated methane, ethanol and methanol steam reforming for hydrogen production based on the Gibbs principle of minimum free energy has been carried out using the software of Aspen Plus. Effects of the reaction temperature, pressure and water/carbon molar ratio on the process are evaluated. Results show that the effect of the pressure on methane reforming is small when the reaction temperature is over 900 °C. Methane/CO conversion and hydrogen production rate increase with the water/carbon molar ratio. However the thermal efficiency increases first to the maximum value of 61% and then decreases gradually. As to ethanol and methanol steam reforming, thermal efficiency is higher at lower reaction pressures. With an increase in water–carbon molar ratio, hydrogen production rate increases, but thermal efficiency decreases. Both of them increase with the reaction temperature first to the highest values and then decrease slowly. At optimum operation conditions, the conversion of both ethanol and methanol approaches 100%. For the ethanol and methanol reforming, their highest hydrogen production rate reaches, respectively, 88.69% and 99.39%, and their highest thermal efficiency approaches, respectively, 58.58% and 89.17%. With the gradient utilization of the high temperature helium heat, the overall heat efficiency of the system can reach 70.85% which is the highest in all existing system designs. Copyright © 2014 John Wiley & Sons, Ltd.     

Hydrogen production by glycerol reforming in a two-fixed-bed reactor

A two-stage fixed bed system was used in the hydrogen production from glycerol reforming. The calcined dolomite catalyst was used in the first fixed bed, and the Nickel-based catalyst was used in the second fixed bed to produce hydrogen from the glycerol steam reforming. The results showed that the hydrogen yield and carbon conversion gradually increased with the temperature increasing. When the temperature exceeded 800 °C, the growth rate of hydrogen yield and carbon conversion decreased. As the space velocity increased, the hydrogen yield and carbon conversion gradually decreased. When the space velocity was greater than 2 h^?1, the decline rate of hydrogen yield and carbon conversion decreased rapidly. As the water-to-carbon ratio (S/C) increased, the hydrogen yield and carbon conversion gradually increased. The growth rate of hydrogen yield and carbon conversion became smaller when the S/C was more than 5. Compared with the single-stage fixed-bed reactor, the utilization of two-stage fixed-bed catalytic reaction system can not only increase the hydrogen yield and carbon conversion, but extend the life of the Nickel-based catalyst. Under the optimal reaction conditions, the hydrogen yield is as high as 84.3%, and the carbon conversion is as high as 88.23%.     

Thermal analysis of a micro tubular reactor for methanol steam reforming by optimizing the multilayer arrangement of catalyst bed for the catalytic combustion of methanolr

Packed bed tube reactors are commonly used for hydrogen production in proton exchange membrane fuel cells. However, the hydrogen production capacity of methanol steam reforming (MSR) is greatly limited by the poor heat transfer of packed catalyst bed. The hydrogen production capacity of catalyst bed can be effectively improved by optimizing the temperature distribution of reactor. In this study, four types of reactors including concentric circle methanol steam reforming reactor (MSRC), continuous catalytic combustion methanol steam reforming reactor (MSRR), hierarchical catalytic combustion methanol steam reforming reactor (MSRP) and segmented catalytic combustion reactor with fins (MSRF) are designed, modeled, compared and validated by experimental data. It was found that the maximum temperature difference of MSRC, MSRR, MSRP and MSRF reached 72.4 K, 58.6 K, 19.8 K and 11.3 K, respectively. In addition, the surface temperature inhomogeneity U_f and CO concentration of the MSRF decreased by 69.8% and 30.7%, compared with MSRC. At the same reactor volume, MSRF can achieve higher methanol conversion rate, and its effective energy absorption rate is 4.6%, 3.9% and 2.6% higher than that of MSRC, MSRR and MSRP, respectively. The MSRF could effectively avoid the influence of uneven temperature distribution on MSR compared with the other designs. In order to further improve the performance of MSRF, the influences of methanol vapor molar ratio, inlet temperature, flow rate, catalyst particle size and catalyst bed porosity on MSR were also discussed in the optimal reactor structure (MSRF).     

Mathematical simulation of hydrogen production via methanol steam reforming using double-jacketed membrane reactor

The hydrogen production and purification via methanol reforming reaction was studied in a double-jacketed Pd membrane reactor using a 1-D, non-isothermal mathematical model. Both mass and heat transfer behavior were evaluated simultaneously in three parts of the reactor, annular side, permeation tube and the oxidation side. The simulation results exhibited that increasing the volumetric flow rate of hydrogen in permeation side could enhance hydrogen permeation rate across the membrane. The optimum velocity ratio between permeation and annular sides is 10. However, hydrogen removal could lower the temperature in the reformer. The hydrogen production rate increases as temperature increases at a given Damköhler number, but the methanol conversion and hydrogen recovery yield decrease. In addition, the optimum molar ratio of air and methanol was 1.3 with three air inlet temperatures. The performance of a double-jacketed membrane reactor was compared with an autothermal reactor by judging against methanol conversion, hydrogen recovery yield and production rate. Under the same reaction conditions, the double-jacketed reactor can convert more methanol at a given reactor volume than that of an autothermal reactor.     

Experiments on hydrogen production from methanol steam reforming in fluidized bed reactor

A novel approach for the hydrogen production which integrated methanol steam reforming and fluidized bed reactor (FBR) was proposed. The reaction was carried out over Cu/ZnO/Al₂O₃ catalysts. The critical fluidized velocities under different catalyst particle sizes and masses were obtained. The influences of the operating parameters, including that of H₂O-to-CH₃OH molar ratio, feed flow rate, reaction temperature, and catalyst mass on the performance of methanol steam reforming were investigated in FBR to obtain the optimum experimental conditions. More uniform temperature distribution, larger surface volume ratio and longer contacting time can be achieved in FBR than that in fixed bed reactor. The results indicate that the methanol conversion rate in FBR can be as high as 91.95% while the reaction temperatures is 330 °C, steam-to-carbon molar ratio is 1.3, and feed flow rate is 540 ml/h under the present experiments, which is much higher than that in the fixed bed.     

Application of aspen plus to renewable hydrogen production from glycerol by steam reforming

Steam reforming is the most favored method for the production of hydrogen. Hydrogen is mostly manufactured by using steam reforming of natural gas. Due to the negative environmental impact and energy politics, alternative hydrogen production methods are being explored. Glycerol is one of the bio-based alternative feedstock for hydrogen production. This study is aimed to simulate hydrogen production from glycerol by using Aspen Plus. First of all, the convenient reactor type was determined. RPlug reactor exhibited the highest performance for the hydrogen production. A thermodynamic model was determined according to the formation of byproduct. The reaction temperature, water/glycerol molar feed ratio as reaction parameters and reactor pressure were investigated on the conversion of glycerol and yield of hydrogen. Optimum reaction parameters are determined as 500 °C of reaction temperature, 9:1 of water to glycerol ratio and 1 atm of pressure. Reactor design was also examined. Optimum reactor diameter and reactor length values were determined as 5 m and 50 m, respectively. Hydrogen purification was studied and 99.9% purity of H₂was obtained at 25 bar and 40 °C. The obtained results were shown that Aspen Plus has been successfully applied to investigate the effects of reaction parameters and reactor sizing for hydrogen production from glycerol steam reforming.     

A CFD approach on simulation of hydrogen production from steam reforming of glycerol in a fluidized bed reactor

Hydrogen production from steam reforming of glycerol in a fluidized bed reactor has been simulated using a CFD method by an additional transport equation with a kinetic term. The Eulerian–Eulerian two-fluid approach was adopted to simulate hydrodynamics of fluidization, and chemical reactions were modelled by laminar finite-rate model. The bed expansion and pressure drop were predicted for different inlet gas velocities. The results showed that the flow system exhibited a more heterogeneous structure, and the core-annulus structure of gas–solid flow led to back-mixing and internal circulation behaviour, and thus gave a poor velocity distribution. This suggests the bed should be agitated to maintain satisfactory fluidizing conditions. Glycerol conversion and H₂ production were decreased with increasing inlet gas velocity. The increase in the value of steam to carbon molar ratio increases the conversion of glycerol and H₂ selectivity. H₂ concentrations in the bed were uneven and increased downstream and high concentrations of H₂ production were also found on walls. The model demonstrated a relationship between hydrodynamics and hydrogen production, implying that the residence time and steam to carbon molar ratio are important parameters. The CFD simulation will provide helpful data to design and operate a bench scale catalytic fluidized bed reactor.     

Enhancement of hydrogen production in a novel fluidized-bed membrane reactor for naphtha reforming

In this work, a novel fluidized-bed membrane reactor (FBMR) for naphtha reforming in the presence of catalyst deactivation has been proposed. In this reactor configuration, a fluidized-bed reactor with perm-selective Pd–Ag (23 wt% Ag) wall to hydrogen has been used. The reactants are flowing through the tube side which is a fluidized-bed membrane reactor while hydrogen is flowing through the shell side which contains carrier gas. Hydrogen penetrates from fluidized-bed side into the carrier gas due to the hydrogen partial pressure driving force. Hydrogen permeation through membrane leads to shift the reaction toward the product according to the thermodynamic equilibrium. This membrane-assisted fluidized-bed reactor configuration solves some drawbacks of conventional naphtha reforming reactors such as pressure drop, internal mass transfer limitations and radial gradient of concentration and temperature. In FBMR the hydrogen which is produced in shell side is a valuable gas and can be used for different purposes. The two-phase theory of fluidization is used to model and simulate the FBMR. Industrial packed bed reactor (PBR) for naphtha reforming is used as a basis for comparison. This comparison shows enhancement in the yield of aromatic production in FBMR for naphtha reforming. Although using FBMR reduces hydrogen mole fraction in reaction side and enhances catalyst deactivation due to coking, but this effect can be compensated using advantages of FBMR such as suitable hydrogen to hydrocarbon molar ratio, lowering deactivation rate due to lower temperature, control of permeation rate by adjusting shell side pressure and shifting the equilibrium reactions. The impacts of hydrogen to hydrocarbon molar ratio, pressure, membrane thickness, flow rate and temperature have been investigated in this work.