Mathematical Modeling of Methane Air Conversion on a Structured Porous Metal Catalyst

A one-dimensional two-phase mathematical model of an ideal plug-flow reactor for methane air conversion on a Ni–MgO monolith catalyst on porous nickel was proposed. The model describes the methane air conversion as the result of three simultaneous reaction stages: methane deep oxidation, methane steam reforming, and reverse shift reaction. The effect of the external gas–solid mass transfer is taken into account in two variants: (i) independent diffusion and (ii) multicomponent diffusion for all mixture components. The results of modeling were used to analyze the experimental data (obtained in our previous work) on the dependence of the temperature of the front layer of the catalyst on the pressure and excess air coefficient. The best agreement between the calculation and experiment was obtained under conditions of complete external diffusion control of the exothermic stage for oxygen and the transition (between the kinetic and external diffusion) region of the endothermic stage, the kinetic effect of the endothermic stage being further limited by internal pore-diffusion resistance of the rate of this stage for methane.     

Modeling and Simulation of an Integrated Micro Packed Bed Reactor-Heat Exchanger Configuration for Direct Dimethyl Ether Synthesis

The application of an integrated micro packed bed reactor-heat exchanger for highly exothermic syngas conversion to dimethyl ether was investigated by numerical simulation. A three-dimensional pseudo-homogeneous model was developed to describe concentration and temperature distributions inside a single reaction slit. The model was adopted at low Reynolds numbers (small catalyst particles and long residence times). The simulation results reveal that the micro packed reaction slit is close to isothermal, and a negligible temperature gradient is predicted also for a doubling of the critical reaction slit dimension, i.e. the reaction slit height. The flow in the reaction slit was modelled by Brinkman??s equation and it was found that the pressure drop in wide range of gas velocity was not significant. The reactor simulation showed good agreement with experimental results and could be further developed to assess the potential of microstructured packed bed reactors to intensify large-scale industrial processes.     

天然气催化燃烧催化剂的研究进展

分析了以天然气作能源燃烧时,催化燃烧具有火焰燃烧不可比拟的优越性;进而对天然气催化燃烧使用的催化剂进行了研究探讨;提出了今后研究开发燃烧催化剂的努力方向。     

Experimental Study of the Temperature Rise in the Frontal Layer of a Structured Porous Metal Catalyst in Air Conversion of Methane

Heat-resistant Ni/MgO block catalysts have been developed on porous nickel carriers for the air conversion of natural gas to synthesis gas. The catalysts were tested under normal pressure, which allowed one to select of a number of samples that demonstrate relatively the low temperature of the frontal layer of the catalytic block of 880–940°C at the inlet temperature of the mixture of 20°C and excess air factor of 0.3. The composition of the mixture at the outlet remained close to thermodynamic equilibrium at a volumetric flow rate of up to 49 000 h^–1. It was experimentally established that the temperature of the frontal layer decreases with increasing pressure (2–6 atm), an increase in the frontal layer temperature with an increasing coefficient of excess air (0.31–0.42) and the rate of the inlet mixture (0.30–0.74 m/s). This made it possible to obtain approximate estimates of the areas of exothermic and endothermic reaction stages taking into account external diffusion inhibition based on the analysis of the heat balance equation for the frontal layer of the catalyst.     

Filtration Gas Combustion in an Inhomogeneous Porous Medium

Mathematical modeling is performed of the transition of a filtration gas combustion wave through the interface between two porous media with different thermodynamic characteristics. Trends and mechanisms of changes in the structure of the filtration gas combustion wave and its propagation velocity in transition through the interface are considered. It is established that the transition process can end not only with the formation of a steady-state combustion wave that corresponds to conditions in the new porous medium but also with the stabilization of the combustion wave at the interface or quenching. It is shown that, in some cases, transition of a filtration gas combustion wave through the interface is accompanied by a sudden transfer of the flame zone for a few millimeters or even centimeters. Because of the thermal inertia of the porous medium, in the experiment this can look like disintegration of the combustion zone into two coexisting regions.     

气体流动条件下钴基催化剂固定床的传热

在气体流量4~8 Nm3/h、气体分布器进口温度190~210℃、加热管壁温约240℃的条件下,对气体流动时活性组分呈蛋壳型分布的钴基催化剂固定床的传热进行了实验研究,建立了二维拟均相传热模型,利用正交配置法和Levenberg-Marquardt法对其求解,得到了钴基催化剂床层径向有效导热系数及壁给热系数的关联式,并将传热参数与由气体处于静态时固定床的有效导热系数计算而得的固定床传热参数值进行了比较,在气体入口温度范围内考察了其对固定床传热参数的影响. 结果表明,实验所得传热参数与文献值的最大偏差绝对值均在15%以内.     

Some Stability Aspects of Gas Combustion in Porous Media

Some aspects of the stability of hot-spot and oblique gas-combustion fronts in porous media are considered using a thermal model. A general expression for the velocity of a curved wave front of filtration gas combustion is obtained taking into account the curvature and local slope of the front. It is shown that curvature always promotes stabilization of the front. The slope of the front, in principle, can have a destabilizing effect. However, because this effect is weaker than the curvature effect, it does not cause development of instability. The roles of convective heat and mass transfer between the hot spot and the ambient gas flow and selective diffusion in the development of local instability are analyzed. Criteria are found for the development of hot-spot instability, and the ranges of system parameters in which instability is possible are determined. The effect of variation in the length of the front during wave propagation on the development of instability of an oblique front is considered. Accounting for this factor gives a criterion for instability development that coincides with the experimental one.__________Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 4, pp. 39–49, July–August, 2005.     

天然气富氧燃烧特性分析

随着全球各个国家对能源需求的不断增长和对环境保护意识的逐渐增加,我国以煤炭为主要消耗能源的现状已不符合可持续发展的理念。现阶段我国正在对清洁能源天然气大力推行,使得天然气在我国能源消耗中占比越来越大。如何提高能源燃烧效率的同时使污染物的排放得到减少,已成为了目前全球各个国家迫切需要解决的问题之一。富氧燃烧一种是利用助燃气体以高于空气中的氧气浓度进行燃烧的技术。能降低燃料的燃点,加快火焰的燃烧速度,燃烧过程中烟气含量减少,传热能力增强,从而大幅度提高燃烧效率,节约能源。但是在富氧燃烧过程中,必定产生比空气燃烧高得多的高温。这些高温会使空气中以及燃料中的N_2反应生成污染物NO_x,如何减少NO_x的生成量,就是富氧燃烧目前需要解决的问题。在建立好燃烧器,并完成网格划分之后,进行了富氧燃烧的模拟分析,从而得到了天然气在不同条件下的燃烧特性。并且分别研究了当助燃气体氧气氮气比例不同以及氧气和二氧化碳配比不同的NO的生成量,从而得到富氧燃烧时,减少NO_x生成量的最佳燃烧条件。     

Metal Organic Frameworks for Natural Gas Storage in Vehicles

With the increasing demand for alternative fuels the storage of natural gas (NG) in adsorbents like metal organic frameworks (MOFs) will become more important. In order to use MOFs as storage media in fuel delivery systems, the optimization of mass and energy transfer of the system is crucial. For rapid NG filling of a tank, molecules need to reach the adsorption sites within a reasonable time while the heat of adsorption should be dissipated to the environment. In this article, mass transfer in shaped bodies of MOFs was determined by permeability measurements and pulsed field gradient (PFG) NMR spectroscopy. The heat dissipation was also experimentally measured and both data sets were used to set up a theoretical density function theory model to predict the behavior of MOFs for NG storage.     

贵金属催化剂用于VOCs催化燃烧的研究进展

催化燃烧技术因具有起燃温度低、处理效率高和无二次污染等优点,在挥发性有机物(VOCs)净化处理过程中得到了广泛地应用。文章分别对Pt、Pd和Au等贵金属催化剂用于VOCs催化燃烧的研究进展进行了总结。并对贵金属催化剂用于VOCs催化燃烧的研究方向提出了展望。     

Reduction of Devolatilization Rate of Fuel During Bubbling Fluidized Bed Combustion Using Porous Bed Material

Plastic waste combustion in bubbling fluidized bed combustors (BFBC) is characterized by the rapid devolatilization of the fuel. Noncombusted hydrocarbons are often formed, which have been reported to promote the formation of dioxins. In this work, porous bed material was employed instead of commonly used non‐porous sand to reduce the devolatilization rate. We measured (1) the heat transfer coefficient between an immersed object (brass sphere) and the bed and (2) the time required for the devolatilization of a plastic pellet after dropping it into the bed at 943 K. For porous particles we found a 30 % lower heat transfer coefficient, delayed onset of devolatilization and prolonged devolatilization time, compared with quartz sand. Therefore, porous particles were found to be effective in suppressing the rapid devolatilization of plastic waste.     

贵金属负载型核壳结构催化剂的制备及其催化性能

以十六烷基三甲基溴化铵(CTAB)为表面活性剂,尿素为碱源,正硅酸四乙酯(TEOS)为硅源,在环己烷和正戊醇组成的微乳体系中制备了以微孔ZSM-5分子筛为核,树枝状介孔SiO_2为壳的多级孔核壳结构分子筛。考察制备温度、时间、尿素添加量以及TEOS添加量等制备条件对制备催化剂所需载体的影响,并采用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和N2吸附-脱附等手段对分子筛样品进行了表征。结果表明,制备温度为100~120℃,时间为4 h,尿素与TEOS物质的量之比为1和TEOS与ZSM-5物质的量之比为0.9~1.2时,得到的核壳结构分子筛呈现出优良的单分散性、完整性以及水热稳定性。最终在树枝状介孔SiO_2壳层负载高分散贵金属Pt,得到的双功能催化剂Pt/ZSM-5@MS在催化丙酮一锅法制备甲基异丁基酮(MIBK)反应中表现出较高的活性及良好的循环使用性能。     

固定床中天然气与煤联合气化制合成气反应过程的实验研究

用固定床反应器模拟合成气制备炉,对天然气与煤联合气化反应过程进行了研究. 实验结果表明,在合成气制备炉下部主要发生甲烷和碳的氧化反应,氧气完全消耗. 合成气在制备炉内上升过程中,未转化完的甲烷继续裂解,中间产物水蒸汽和CO2被还原. 出口合成气在离开制备炉时整个炉内体系接近反应平衡.     

Porous Adsorbents for Vehicular Natural Gas Storage: A Review

Methane adsorption data (both experimental and simulated) under conditions of direct relevance for vehicular natural gas storage, i.e., at 500 psig and ambient temperature, has been compiled from the literature for various microporous adsorbents and discussed in this work. Characterization of microporosity has been briefly reviewed, followed with a discussion on the porous structure of natural gas adsorbents. A common trend of gravimetric methane adsorption capacity scaling with surface area among the diverse microporous adsorbents (viz., coals, carbons, zeolites, silica gel and an MCM-41 type material) is demonstrated. Further, it is substantiated and emphasized that increasing the adsorbent surface area on a volumetric basis is very important for vehicular natural gas storage where the fuel storage volume is a constraint. The effect of other adsorbent properties such as heat of adsorption and heat capacity on the natural gas storage capacity is also discussed.     

Z型天然气蒸汽转化催化剂弯曲因子的测定

设计了一种能测量环状、柱状或片状催化剂弯曲因子的实验装置.采用这套设备和定总压稳态技术,以及CH_4-He、N_2-He和N_2-CH_4气体体系在常温常压下,测定了Z型天然气蒸汽转化催化剂的弯曲因子.不同气体体系所得的结果彼此十分接近,该催化剂的弯曲因子大约为2.3.     

FCP-1型催化剂催化燃烧PTA尾气性能研究

研究了FCP-1催化剂对PTA尾气的催化燃烧性能。FCP-1催化剂对PTA尾气具有良好的催化燃烧活性,在反应温度280℃,PTA尾气的转化率可达98%以上,出口净化气中非甲烷总烃和苯满足国家排放标准;反应空速从23 000 h-1增加至50 000 h-1,FCP-1催化剂的活性基本保持不变,出口非甲烷总烃60 mg/m3,苯≤6 mg/m3:甲苯未检出;500 h的催化剂稳定性试验运行期间,出口非甲烷总烃60 mg/m3,苯7 mg/m3,甲苯10 mg/m3。     

规整丝网填料旋转填充床的气相压降特性及脱硫性能

采用空气-水体系,对装有4种不同规格规整丝网填料的旋转填充床的压降特性进行了实验研究,考察了转速、气体流量、液体流量等操作参数及填料特性对气相压降的影响规律,并与传统不锈钢波纹丝网填料旋转填充床压降进行了比较. 结果表明,装有规整丝网填料的旋转填充床压降可降低35%~70%. 进一步采用压降较低的规整丝网填料以(NH4)2SO3为吸收剂进行氨法脱硫性能研究,结果表明,随转子转速和(NH4)2SO3浓度增大,SO2脱除率升高;随进气口SO2浓度升高及气液比增大,SO2脱除率降低;SO2脱除率最高可达97%,可满足国家排放标准.     

Cotton Stalk Combustion in a Circulating Fluidized Bed

The basic properties of cotton stalk (CS) of length 10–100 mm and its ash were investigated. Studies concerning the combustion characteristics of CS were performed in a circulating fluidized bed (CFB) test facility with a heat input of 0.5 MW. According to previous cold tests, there is very little segregation during the mixing of CS with this size profile and bed material at a fluidization number of N > 7, but the hot experimental results indicate that slight segregation has a small effect on the steady combustion of the dense region. Experiments were carried out with the aim of investigating the effects of operating conditions on the axial temperature and gas concentration profiles along the combustor height, as well as the emission performance and combustion efficiency of the CFB. The experimental results indicate it is difficult to react alumina bed material with alkali metals from CS ash following 26 h of combustion. The overall conclusions appear to indicate that the application of circulating fluidized bed boilers to fire pure CS of length 10–100 mm, is feasible.     

天然气水合物注热水分解径向数学模型

在一半无限大区域水合物分解过程描述基础上,建立了Stefan移动边界径向拟稳定传热数学模型,利用Paterson指数积分函数求解了分解带和水合物带的温度精确解,结合Deaton方法和Clausius-Clapeyron分解热方程确定水合物分解前缘位置。对一给定物性参数的稳定水合物储层例子进行计算,得出了水合物径向分解规律:随着径向距离增加温度急剧下降到分解温度8.416℃,再降到储层温度5.33℃,分解前缘位置变化趋势变缓;随着时间增加温度从5.33℃缓慢上升到8.416℃后急剧上升,时间足够长接近注入热水温度100℃;随着时间增加径向半径增加趋势减缓,分解时间到150 d时80～100℃温度变化为27.3℃,100～150℃温度变化为49.3℃。