制氢转化炉内甲烷蒸汽重整模拟及影响因素分析

考虑40 000m~3/h顶烧式常压加热制氢转化炉的结构特点,建立了制氢转化炉辐射室流体的三维有限元模型,采用有限体积法计算辐射室温度场,得到了转化管外壁面轴向温度的分布规律,并以外壁面温度为边界条件,以多孔介质模型表征催化剂床层,模拟了催化剂床层在转化管内的甲烷蒸汽重整制氢过程,研究了不同入口速度、入口温度的变化对甲烷转化率的影响规律。结果表明:入口速度的下降和入口温度的增加都会提高甲烷转化率。     

基于ASPEN模拟计算的甲烷二氧化碳重整反应研究

使用ASPEN对甲烷二氧化碳重整反应进行模拟计算,研究反应温度、压力以及原料气中二氧化碳浓度对重整反应影响。结果表明,提高反应温度,增加原料气中二氧化碳浓度可以提高甲烷转化率,降低合成气中氢碳比。同时,对现有工业化项目的转化合成气的氢碳比进行了模拟计算,结果与实际运行值吻合,模型有良好的预测性。     

用于吸/放热反应耦合的金属基整体式催化反应器性能模拟

利用计算化学工程方法,针对甲烷催化燃烧和甲烷水蒸气重整的模型反应体系,研究了一种结构较复杂的金属基整体式催化反应器用于吸/放热反应耦合时的性能.模拟结果表明,这种金属基整体式催化反应器应用于吸/放热反应耦合具有很大的研发潜力.初步分析了操作参数的影响,重整侧与燃烧侧入口气体速度的比值、气体入口温度以及燃烧部分和重整部分的甲烷体积流量比都是影响反应器性能的重要因素.     

苯酚低温催化水蒸气重整制氢

以Raney Ni为催化剂,在温和条件下(523～723 K)实现了苯酚催化水蒸气重整制氢反应。研究表明,反应温度、液体空速和原料浓度等反应条件是影响苯酚转化率和H₂选择性的重要因素,较高的反应温度和较低的液体空速有利于提高苯酚转化率,但不利于提高H₂选择性。对比苯酚水相重整制氢过程发现,尽管水蒸气重整反应温度相对较高,且需要汽化原料使反应在气相中进行,但该过程具有比水相重整更高的H₂选择性(93%～100%)。此外,Raney Ni催化剂上苯酚水蒸气重整反应与现有的文献结果比较还具有反应条件温和、催化剂稳定性好(60h)以及CO含量低(CO/CO₂摩尔比为0.01～0.2)等优点。将该技术应用于工业含酚有机废水的资源化处理制备的H₂可以直接作为氢源使用。     

热解-重整-燃烧解耦的煤气化特性

采用热解、重整、燃烧解耦分离的解耦三床气化(decoupled triple bed gasification,DTBG)系统,以橄榄石为原位焦油裂解催化床料,进行了煤催化气化实验。研究了煤种、煤进料速率、重整器温度以及水碳比(S/C)对煤热解焦油裂解/重整反应的影响。结果显示:随着煤挥发分含量增加,气体产率、碳转化率、冷煤气效率以及产气中的H_2含量增加。由于半焦不参与气化反应,导致碳转化率和冷煤气效率偏低。煤和催化剂比例的改变会影响气体产率和产气组成,当煤的进料速率从0.12 kg/h增加到0.30 kg/h时,气体产率从0.28 m~3/kg增加到0.46 m~3/kg,H_2含量从28.4%增加到50.5%。重整器温度的升高有利于促进煤焦油裂解转化,从而增加气体产率。当重整器温度为850℃、S/C为1.0时,气体产率达到了0.60 m~3/kg,橄榄石催化剂有效地降低了焦油含量,焦油产率仅为2.11g/m~3。S/C的升高增强了焦油水蒸气重整反应,但引入过量的水蒸气会导致反应器内气体的流速加快,缩短了反应物的停留时间和反应时长,减缓了焦油水蒸气重整反应的反应程度。     

二甲醚水蒸汽重整制氢反应平衡组成模拟计算

对比了二甲醚水蒸汽重整过程中由外部供热和燃烧反应尾气供热两种方式下的热效率,并对体系进行了热力学分析,模拟考察了反应温度、压力、原料组成等因素对体系平衡组成的影响,探讨了二甲醚转化率、氢气和一氧化碳等产物的变化情况.分析发现,反应器温度在200 ℃,压力为0.1 MPa时可以获得最佳的原料转化率.研究认为二甲醚水蒸气重整制氢的副产物甲烷可显著降低氢气的含量,一氧化碳在高温、低水/二甲醚进料比的情况下产生.催化剂应具有选择性催化功能,同时应具有低温高活性.     

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。     

正丁烷水蒸气重整中热裂解的研究

在无催化剂作用下，对正丁烷水蒸气重整中的热裂解行为进行了研究，采用常压固定床管式反应器，考察了反应温度、水碳比等因素对正丁烷水蒸气重整中热裂解过程的影响。结果表明，随着温度的升高，正丁烷热裂解加剧，达到750℃时裂解完全，750℃是考察催化剂的蒸汽转化活性的适宜温度，水碳比增加，使丁烷分压下降，反应产气量、正丁烷转化率和C1选择性下降。     

微型流化床中焦油热裂解和水蒸气重整的反应特性及动力学对比

采用微型流化床反应分析仪(MFBRA)考察了不同温度(T,750~950℃)和水蒸气分压(SP,10%~30%)下生物质焦油水蒸气重整过程中的气体生成、气体产物中总碳转化和焦油转化等反应特性,求算反应动力学,并与焦油热裂解特性进行比较。在热裂解过程中,随温度增加,各气体(H₂、CH₄、CO、CO₂)产率和气体产物中的总碳转化率增加,反应时间缩短。而在焦油水蒸气重整过程中,等温下的反应时间明显延长,且H₂、CH₄、CO产率和气体产物中的总碳转化率显著提升,而CO₂产率在850℃时有最大值。在焦油水蒸气重整过程中,不仅有焦油裂解,还有裂解产物与水蒸气的反应,促进碳转化。在950℃、SP=30%条件下,气体产物中的总碳转化率达到92.34%。水蒸气作用下,气体组分的产率和气体产物中的总碳转化率增加,而等温条件下的反应速率下降。水蒸气分压对各气体组分的影响具有差异性。随分压增加,CO、CH₄的生成速率和气体产物中的总碳转化的反应速率增加;H₂生成速率逐渐下降,速率稳定段扩大;CO₂生成速率在850℃时有最大值。采用均相模型求取焦油水蒸气重整反应过程中的活化能,气体产物的生成活化能(H₂、CO、CO₂和CH₄)、气体产物中的总碳转化及焦油转化的活化能明显偏低,分别为90.10、42.01、58.56、64.92、61.44和63.26 kJ/mol,对应数值明显小于焦油热裂解,说明水蒸气对焦油重整反应的促进作用。最后,将焦油热裂解动力学数据与文献数据对比,验证了MFBRA对焦油水蒸气重整反应测试的可行性和分析结果的准确性。     

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。     

CFD study on partial oxidation of methane in fixed-bed reactor

Partial oxidation of methane (POM) is a preferred method for synthesis gas, which usually occurs in fixed bed reactors. In this paper, the discrete element method (DEM) is used to reconstruct the structure of a reactor bed via simulating the process of filling the reactor with catalyst. The particle resolved CFD physical model with the detailed micro-kinetcis of the POM reaction was established to study the interaction among reactant flow, heat and mass transfer, and reaction in the fixed bed. The gas composition and temperature distribution in the reactor were obtained based on the simulation results. The effects of the space velocity and the reaction temperature on the CH₄ conversion, catalyst selectivity, and catalyst surface coke formation were analyzed. The simulation results show that the temperature hot spots of the catalyst in the bed occur at the inlet and the temperature increases further near the wall. With the increase in space velocity, the conversion rate of CH₄ decreases gradually, and the selectivity does not change significantly. As the temperature increases, the conversion rate of CH₄ gradually increases and the selectivity decreases. The risk of coke formation on the catalyst surface rises axially and the C species concentration is relatively higher near the outlet. Appropriately increasing the gas velocity and increasing the temperature helps to reduce the surface coke accumulation of the catalyst.     

Novel multi-scale diffusion model for catalytic methane combustion

A multi-scale model of methane catalytic combustion was built by a series of balance equations and diffusion equations, and these equations were solved through the computational fluid dynamics (CFD) software. The difference between this work and previous model is the diffusion process in catalyst coating was considered. By analyzing the methane conversion, temperature distribution and mass fraction contours of every component, the performance of multi-scale model was compared with that of the pure CFD model without diffusion. The effects of diffusion, methane concentration, flow rate on the methane conversion and temperature distribution of monolithic reactor were also evaluated and discussed by the multi-scale model. The multi-scale model showed better accuracy than the pure CFD model without diffusion process. Different methane concentrations and gas flow rates had enormous effects on the methane conversion and temperature. Therefore, it was beneficial to the reaction process to adjust the methane concentration and gas flow rate appropriately.     

焦炉煤气非催化部分氧化制合成气实验研究与数值模拟

在带有单孔喷嘴石英管反应器实验的基础上,对焦炉煤气非催化部分氧化工艺制合成气进行了研究,分析了O_2/GAS比对合成气各组分含量的影响,反应器中反应过程和温度分布及出口产品组成.实验结果表明CH4转化率随O_2/GAS比增大而增大,O_2/GAS比调节到0.22～0.26时,CH_4转化率达到95%～97%,此时合成气CH_4含量低于1%.利用CFD软件平台对转化反应器进行了数值模拟.模拟结果显示,流量一定时出口气体组分H_2与CH4分别随着进气氧气与焦炉煤气体积流量比值的增加而减少.CO和CO_2分别随着比值的增加而增加.出口气体有效组分摩尔分数随进气流量的变化不是非常明显.在壁面温度为1 100 K时转化效果最好.     

Enhanced model predictive control of a catalytic flow reversal reactor

The combustion of lean methane air mixtures in a catalytic flow reversal reactor (CFRR) is studied using a two dimensional heterogeneous continuum model, based on mole and energy balance equations for the solid (the inert and catalytic sections of the reactor) and the fluid phases. Following a design of experiments (DOE), many simulations were carried out to investigate the reactor performance. The results show the impact on the methane conversion and the maximum temperature in the reactor of key process parameters such as the methane inlet concentration, the superficial gas velocity, the switching time, and the mass extraction rate. A simple empirical model is deduced to predict the maximum temperature and conversion of methane in the reactor at stationary state. This model is combined with a model predictive control (MPC) strategy in the form of a terminal constraint to improve the controller performance. Results show that the control of the reactor is improved.     

Tube flow of a particulate-filled thermosetting polymer

The conservation equations of momentum, energy, and mass are numerically solved for the flow of filled thermosets reacting In a tube. The flow is assumed to be laminar and adiabatic with a constant volumetric flow rate. The critical radii are parameters that define the processability limits. The lower one is the value of the radius where an undesirable advance in the reaction extent takes place at the wall or where viscous heating leads to degradation. The upper critical radius is the radius where wall velocity is low and gelation takes place. The effects of filler volumetric fraction, wall slip velocity, and different inlet conditions are taken into account. Increasing wall slip velocity or filler fraction and decreasing inlet temperature or tube length amplify the processability zone.     

Chemical reactions catalysed on a tube wall

The progress of a reaction catalysed on a tube wall is analysed for an assigned radial pattern of axial velocity. A procedure is given for mathematically transforming an observed axial profile of cross-section average reactant concentrations into a plot of the instantaneous reaction rate vs. the wall concentration at which the reaction is proceeding. It is also shown how to calculate the average conversion at any contact time for an arbitrary reaction rate function.     

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.     

A study of Nusselt and Sherwood numbers in a monolith reactor

A two-dimensional model of a single channel of a monolith reactor is used to evaluate the values of the Nusselt and Sherwood numbers under reaction conditions. The circular channel is assumed to have axisymmetry with a first-order reaction occurring at the wall. The values of the Nusselt and Sherwood numbers do not correlate uniquely with the Graetz number but rather depend on the reaction rate at the wall. Hence they depend on such variables as gas velocity, inlet temperature and reactant concentration.