Steam reforming of biogas over a Rh/Al2O3 catalyst in an annular microreactor

The article deals with the catalytic steam reforming of biogas of model composition into hydrogen and carbon monoxide over a Rh/γ-Al₂O₃ catalyst in an annular microchannel reactor. The reforming of biogas consisting of 60% methane and 40% carbon dioxide in a steam medium has been experimentally investigated under isothermal conditions while activating the reactions on the inner convex wall of the annular microchannel with a thin catalyst layer. The experiments have been performed at a residence time of 0.12 s, reactor temperatures of 750 and 860°C, and a water: biogas molar ratio of 0.8 to 3.1 in the feed. The range of water: biogas molar ratios maximizing the hydrogen yield has been determined for the model biogas. By changing the reactor temperature and water: biogas molar ratio, it is possible to widely vary the hydrogen: carbon monoxide molar ratio in the resulting synthesis gas.     

生物质燃气变换-甲烷化双功能催化剂研究进展

生物质燃气在达到居民使用标准前必须进行提质,变换-甲烷化工艺单元可同时降低CO含量和提高燃气热值,因此研发适合生物质燃气的变换-甲烷化双功能催化剂显得尤为重要。在已广泛研究的单功能水气变换和甲烷化催化剂基础上,近年来国内外对变换-甲烷化双功能催化剂也开展了诸多探究。本文从催化剂组成、制备方法和反应机理三方面对变换-甲烷化双功能催化剂进行了综述,详细介绍了适用于该种催化剂的活性组分、助剂与载体,比较分析了浸渍法、共沉淀法等传统制备方法与火焰喷雾燃烧法、等离子体分解法等新颖制备方法,并对变换-甲烷化双功能催化剂进行了总结和展望,指出未来制备催化剂时助剂可根据具体要求选择性添加,廉价的矿石可替代成为有竞争力的催化剂载体,变换-甲烷指出化机理可借助多种材料表征以及理论计算而获悉。     

Ni-CeO2-K/γ-Al2O3催化剂上沼气联合重整制合成气

采用超声波辅助等体积浸渍法制备Ni-CeO₂-K/γ-Al₂O₃催化剂用于沼气联合重整反应,采用 BET、XRD、TG/DTG等技术对催化剂性质进行了表征,在微型固定床反应装置中研究了反应温度、体积空速、原料气组成等对沼气联合重整反应特性的影响,并对催化剂的稳定性进行了研究。结果表明,助剂CeO₂的加入,提高了催化剂中Ni的分散度,降低了催化剂还原温度。升高反应温度和减小体积空速,能够提高沼气中CH₄和CO₂的转化率;原料气中加入水蒸气,能够明显提高H₂/CO体积比;加入的O₂容易与H₂、CO发生反应,CH₄转化率稍有提高。在常压、反应温度850℃、体积空速为100000h^-1、摩尔比CH₄∶CO₂∶H₂O∶O₂∶Ar=1∶0.5∶0.5∶0.1∶0.01的优化条件下,沼气中CH₄转化率超过95%,CO₂转化率超过75%,生成合成气H₂/CO体积比约为1.6,反应48h后,催化剂未见积炭,保持稳定的活性。与沼气干重整相比,沼气联合重整不利于沼气中CO₂的转化。     

A Comparison Between Monolithic and Wire Gauze Structured Catalytic Reactors for CH4 and CO Removal from Biogas-Fuelled Engine Exhaust

The application of the wire gauzes as the catalytic supports can provide a number of advantages in biogas exhaust abatement. In this paper, a model of wire gauze structured reactor for biogas exhaust removal is proposed and model based calculations are performed to compare the wire gauze catalytic reactor with the classic monolith. The modelling bases on kinetic data experimentally obtained in a small-scale tubular reactor for cobalt and palladium (as reference) oxide catalysts doped with promoters (Ce, Pd). The heat and mass transfer characteristics of the wire gauze reactor are taken from the former studies by the authors. The simulations show that for assumed reactor parameters, a combination of the promoted cobalt oxide catalyst and the wire gauze support can give high conversion of methane and carbon monoxide.     

Anaerobic Digestion Process of Food Waste for Biogas Production: A Simulation Approach

Anaerobic digestion (AD) involves a series of biological processes in which organic material is broken down and transformed into biogas. A simulation model of the AD process in treating food waste to produce biogas was developed using Aspen Plus software. The components list, thermodynamic property package, reaction list, reactor model, and process condition were specified in Aspen Plus. Sensitivity analysis was performed to study the effect of hydraulic retention time and changes in food waste composition on the biogas production. The methane composition in biogas decreased when the hydraulic retention time was increased which is due to the reduction of substrate consumption during the AD process. The process model is able to represent the AD process and provides a good approximation on the production of biogas under various process operating conditions.     

Heat and mass transfer limitations in pre-turbocharger catalysts

The use of the Diesel engine is increasing, while at the same time emission limits are becoming more stringent. To reduce emissions, novel catalyst converter designs have been proposed, including the placement of a small converter before the turbocharger. The role of this catalyst is to provide some reduction of the pollutant level prior to the main catalyst. This catalyst is typified by high flow rates. In this paper the performance of small catalytic converters operated at high flowrate is examined using computer simulation. The oxidation of CO is used as a model reaction. It is shown that for a typical oxidation catalyst, conversions of the order of 30% can be achieved at typical temperatures and a GHSV of 5 million h⁻¹.     

Biogas Catalytic Reforming Studies on Nickel‐Based Solid Oxide Fuel Cell Anodes

Heterogeneous catalysis studies were conducted on two crushed solid oxide fuel cell (SOFC) anodes in fixed‐bed reactors. The baseline anode was Ni/ScYSZ (Ni/scandia and yttria stabilized zirconia), the other was Ni/ScYSZ modified with Pd/doped ceria (Ni/ScYSZ/Pd‐CGO). Three main types of experiments were performed to study catalytic activity and effect of sulfur poisoning: (i) CH₄ and CO₂ dissociation; (ii) biogas (60% CH₄ and 40% CO₂) temperature‐programmed reactions (TPRxn); and (iii) steady‐state biogas reforming reactions followed by postmortem catalyst characterization by temperature‐programmed oxidation and time‐of‐flight secondary ion mass spectrometry. Results showed that Ni/ScYSZ/Pd‐CGO was more active for catalytic dissociation of CH₄ at 750 °C and subsequent reactivity of deposited carbonaceous species. Sulfur deactivated most catalytic reactions except CO₂ dissociation at 750 °C. The presence of Pd‐CGO helped to mitigate sulfur deactivation effect; e.g. lowering the onset temperature (up to 190 °C) for CH₄ conversion during temperature‐programmed reactions. Both Ni/ScYSZ and Ni/ScYSZ/Pd‐CGO anode catalysts were more active for dry reforming of biogas than they were for steam reforming. Deactivation of reforming activity by sulfur was much more severe under steam reforming conditions than dry reforming; a result of greater sulfur retention on the catalyst surface during steam reforming.     

以单体酸为原料制备生物柴油

研究了以单体酸为原料制备生物柴油的方法,反应以对甲苯磺酸为催化剂,单体酸与甲醇进行酯化反应获得脂肪酸甲酯。分别考察了酯化反应条件如甲醇与脂肪酸的摩尔比、反应时间、催化剂浓度以及反应温度对酯化率的影响。通过正交实验得到最佳酯化反应参数：醇酸摩尔比3∶1,反应时间3 h,对甲苯磺酸用量6%,反应温度60 ℃,该条件下单体酸酯化率达98.25%。实验制得的单体酸甲酯生物柴油的主要性能指标符合ASTM质量标准,并与0^#柴油性质接近。     

Power Generation from Biogas using SOFC – Results for a 1 kWe Demonstration Unit

A stand‐alone system for power generation from biogas‐based on a commercial SOFC module in the 1 kW_e range shall demonstrate its applicability to biogas, quantify the efficiency gain compared to conventional combined heat and power technology and justify further development toward SOFC modules in the hundreds of kilowatt range. The system includes biogas cleaning, combined dry and steam reforming, electrochemical oxidation of synthesis gas, offgas burning, and heat usage for steam generation and support of the endothermic reforming reaction. The system demonstrated a performance of 1 kW_e at 52% gross efficiency for a synthetic biogas containing 55 vol.% CH₄ during 500 h in the lab. In addition, the performance using real biogas derived from the wastewater treatment process of a sugar plant was demonstrated for different operating points. Based on the experimentally validated results, it is possible to predict the benefit of operating larger SOFC biogas systems. Investment costs of 2.5 times compared to the conventional technology of a 75 kW_e biogas unit get paid off due to higher electricity revenues over time.     

微绿球藻去除沼液氮、磷研究

微绿球藻对环境变化适应性较强,若用沼液培养既能节约成本,又可以避免沼液所含N、P导致水体富营养化。论文主要研究在微藻培养过程中,高温灭菌、盐度、pH值以及沼液稀释倍数等因素对微藻生长及N、P去除率的影响。研究表明,高温灭菌使TN、TP降低,对微藻生长不利;较高的pH值对生长不利,而且盐度为5％0时,微藻呈现负增长趋势。使用原沼液直接培养,体积分数为20％时,微藻生长最优,此时N、P去除率分别为71．96％和72．40％。TP去除率最高的是100％的沼液培养。去除率为80．63％,TN去除率最高的是40~,6的沼液培养,去除率为82．74％。     

Prospective Catalytic Structured Converters for NH3-SCR of NOx from Biogas Stationary Engines: In Situ Template-Free Synthesis of ZSM-5 Cu Exchanged Catalysts on Steel Carriers

The main objective of this study is to develop highly active catalyst and its preparation method that would meet the requirements of steel carriers for short-channel structured converters for NO_x abatement from stationary biogas engines. The in situ synthesis was applied to deposit a series of Cu-exchanged MFI zeolite (ZSM-5) on kanthal sheets. The samples differ in preparation conditions: organic template assisted and template-free synthesis, Si/Al ratio and catalyst carrier pretreatment (calcined vs. non-calcined). Dip-coating method was used as a reference to compare loading efficiency. In order to evaluate preparation quality and purity of resulting structure the samples were examined by XRD and SEM/EDS at various stages of preparation. For the assessment of mechanical endurance of the deposited catalyst layers the ultrasonication method was used. The results demonstrated high depositing efficiency of the in situ synthesis as well as high activity and selectivity of the Cu-exchanged MFI samples prepared without costly organic template.     

介质阻挡放电等离子体脱除沼气中硫化氢的实验研究

介质阻挡放电（DBD）等离子体技术是一种有效的气体污染物控制技术。开展了利用DBD等离子体技术脱除模拟沼气中硫化氢的实验研究,考察了放电能量密度、硫化氢初始体积浓度、停留时间以及含氧量对硫化氢脱除效果的影响,并分析了DBD等离子体反应器中脱除硫化氢的产物。结果表明,DBD等离子体能有效脱除模拟沼气中的硫化氢气体,脱除效率随放电能量密度、停留时间和含氧量的增大而提高,并且随硫化氢初始体积浓度的增加而下降;当模拟沼气处理气量为382mL／min、硫化氢初始体积浓度为4000×10^-6、氧气体积浓度为2％、能量密度为24．1kJ／L时,硫化氢气体被完全脱除,同时氧气的体积含量也低于0．5％,达到了国家规定的车用天然气标准内的硫化氢和氧气含量标准。根据产物分析,硫化氢的脱除产物主要为二氧化硫,少量的单质硫粉。     

沼气机驱动的风冷热泵系统变工况性能

为高效利用沼气资源并减轻环境污染,构建了基于沼气机驱动的风冷热泵能源综合利用实验装置,重点研究了蒸发温度、冷却水量、沼气机转速等参数对系统性能的影响。实验测试结果表明:冷凝器总负荷随蒸发温度及冷却水量的增加而增大,但增幅较小;回收的沼气机余热随蒸发温度的升高而降低,但降幅较小,通过增大冷却水量可以提高沼气机余热的回收率,同时也增大了系统总供热量;冷却水量对系统性能系数(COP)的影响不具有单调性,在同一工况下,存在一个最佳冷却水量;冷却水量对系统一次能源利用率(PER)的影响幅度不同,冷却水量大时,PER的增幅反而较小。实验工况下,系统COP最高可达5.15,PER最高可达1.68。     

Synthesis of Light Hydrocarbons from Biogas and Hydrogen: Investigation of a Fe-Mn-K/MgO Catalyst

Fischer-Tropsch synthesis of the CO₂ in biogas aims at producing light hydrocarbons and increasing its calorific value for feeding into the grid. Fe catalysts with Mn and K as promoters are supposed to yield high amounts of light hydrocarbons. Using a Fe-Mn-K/MgO catalyst, a parameter screening and long-term experiments were carried out. The catalyst shows, within the examined range, the highest selectivity to C₂–C₄ hydrocarbons at 450 °C, 8 bar(a), and a gas hourly space velocity of 350 h⁻¹. Calcination of the catalyst resulted in a significant drop of activity and an almost complete loss of selectivity to hydrocarbons. Admixture of steam to the reactant gas lowers the tendency to carbon deposition but also promotes the water-gas shift reaction and results in lower yields of hydrocarbons.     

Improving performances of a lean burn cogeneration biogas engine equipped with combustion prechambers

Tests of the unscavenged prechamber ignition system on a 150 kW cogeneration engine fed with biogas are presented. The objective was to reach at least 36% in fuel conversion efficiency with exhaust gas emissions lower than the Swiss regulations limits (NO_x, CO: 400 and 650 mg/Nm³, 5% O₂ and 0% relative humidity) without exhaust gas after treatment. With a compression ratio of 12.0, it is shown that 40% of CO₂ induces a CO reduction of 15% and an HC reduction of 8% for the same NO_x emissions, but with a slight reduction of 1% in fuel conversion efficiency compared to pure natural gas. The results for the compression ratio of 13.3, a spark timing of 8 ca_BTDC, an air factor λ of 1.57 and 39.5% CO₂ are a fuel conversion efficiency of 37.7% while keeping the NO_x and CO emissions below the Swiss limit. This study shows that using unscavenged prechambers in biogas engines is particularly beneficial to reach interesting conversion efficiencies with low emissions. It allows a significant boost in energy conversion from biogas compared to existing systems.     

生物气射流内循环厌氧流化床中复杂化工有机废水的催化还原过程

针对集约化化工园区排放的高浓度、高色度、高时变性及难降解性复杂化工废水，自行研制了处理能力为24 m³·d^-1、内置Fe⁰作为生物催化剂的生物气射流内循环厌氧流化床，研究了新型反应器及其工艺对该废水预处理的催化还原过程及运行参数。结果表明：以射流的方式使生物气和废水在反应器内主动循环，使催化剂、活性炭、污泥与废水之间保持良好的接触传质，通过产氢、絮凝和提供营养等方式强化厌氧反应过程。在回流比为2、环境温度为23～34℃及水力停留时间（HRT）为12～24 h的条件下，当进水容积负荷为0. 874～2. 996 kg COD·m^-3·d^-1和色度为250～2000倍时，其COD和色度的平均去除率分别达到26. 2%和70. 8%;出水pH稳定在6～8之间，原废水BOD/COD值由0. 26±0. 04提高到0. 43±0. 03。该新型反应器及工艺在实现部分有机负荷去除的同时明显改善了废水的可生化性，可作为复杂化工有机废水的高效预处理技术。     

Promotion effect of Re additive on the bifunctional Ni catalysts for methanation coupling with water gas shift of biogas: Insights from activation energy

The cheap manganese sand was first modified by H₂O₂ and was further creatively utilized as Ni-based catalyst support. In order to enhance the catalytic performance, Re was added into the Ni-based catalyst and the promotion effect of Re on the methanation coupling with water gas shift of biogas was investigated from the perspective of activation energy. It was found that CH₄ and CO₂ formation rates, which separately represented the reaction rate of methanation and water gas shift, were both enhanced after Re addition compared to non-added catalyst. Two kinetics models including empirical model and K-model were employed and from the results of calculation, it showed that Re selectively decreased the activation energy of methanation reaction and had little impact on the activation energy of water gas shift. The increased CO₂ formation rate was owing to the assistance of accelerated H₂O production from methanation rather than the activation energy change in water gas shift.     

水稻秸秆渗滤床半固态厌氧发酵性能研究

以水稻秸秆为原料,利用自行设计的渗滤床反应器,对比研究了不同温度（20、25、30和35℃）及不同预处理方式（NaOH、生物试剂和沼液）对秸秆厌氧发酵产气性能、物能转化率、发酵后沼液性能和产气成本等方面的影响。实验结果表明：发酵后总固体（TS）质量分数稳定在13%~15%之间,属于半固态厌氧发酵,同时累积产气量与温度、发酵后COD及NH₃-N的变化量均呈极显著正相关。相同温度（20~30℃）条件下,经预处理后的水稻秸秆TS产气率较空白均有所提高;其中沼液预处理效果最为明显,35℃条件下,TS产气率及挥发性固体（VS）产甲烷率分别为154.0和55.2 mL/g,较空白样品分别提高25.1%和52.5%。同时,沼液预处理可显著提升厌氧发酵产气中的甲烷体积分数。各预处理样品TS产甲烷率及VS产甲烷率呈随温度（20~30℃）上升而增加的趋势,但产甲烷提升率随温度的上升而逐渐下降,将系统温度从20℃提升至25℃,各处理产甲烷率可提高90%以上。考虑到沼气工程罐体增温及产能收支平衡等因素,温度控制在25℃是经济性最好的策略模式。从产气成本上分析,自产沼液具有较佳的处理效果和较低的生产成本,每生产1 m³沼气的可变成本1.62元。     

概述沼液综合利用

利用沼气发酵处理畜禽养殖场废水是综合治理畜牧业污染的主要途径之一,但大量沼液出路问题亟待解决,通过阐述沼液在沼液浸种、沼液叶面施肥、沼液灌溉以及沼液防治病虫害上的合理应用,减少作物化肥和药物的施用量,增加收入。