Biogas upgrading technologies:Energetic analysis and environmental impact assessment

Biogas upgrading for removing CO2 and other trace components from raw biogas is a necessary step before the biogas to be used as a vehicle fuel or supplied to the natural gas grid. In this work, three technologies for biogas upgrading, i.e., pressured water scrubbing (PWS), monoethanolamine aqueous scrubbing (MAS) and ionic liquid scrubbing (ILS), are studied and assessed in terms of their energy consumption and environmental impacts with the process simulation and green degree method. A non-random-two-liquid and Henry's law property method for a CO2 separation system with ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf2N]) is established and verified with experimental data. The assessment results indicate that the specific energy consumption of ILS and PWS is almost the same and much less than that of MAS. High purity CO2 product can be obtained by MAS and ILS methods, whereas no pure CO2 is recovered with the PWS. For the environmental aspect, ILS has the highest green degree production value, while MAS and PWS produce serious environmental impacts.     

二段式吸收塔强化水洗技术提纯沼气过程

压力水洗技术已成为提纯沼气的关键技术之一。采用填料吸收塔进行CO₂脱除实验研究,考察了液气比、吸收压力、吸收温度、CO₂初始含量、填料层高度对CO₂脱除率的影响,以及液气比、沼气流量对总体积吸收系数的影响,并运用填料塔与喷雾塔结合的二段式吸收塔进行压力水洗提纯沼气的过程强化实验。实验结果表明,吸收压力和液气比的增大、吸收温度的降低、填料层高度的增加有利于CO₂的脱除,体积总吸收系数随着液气比及沼气流量的增加而增大。二段式吸收塔能够提高CO₂吸收效果,当沼气处理量为10 L·min^-1,填料层高度为100 cm,CO₂含量小于3%时,与填料塔相比二段式吸收塔可以减少约12%的吸收液用量,并且采用110 cm填料的二段式吸收塔获得最佳的提纯效果,CO₂脱除率达到97.4%。     

Updates on biogas enrichment and purification methods: A review

The market for biogas production has been increasing every year all over the world. The use of biogas as an energy vector is accomplished through the most diverse applications, such as direct burning (thermal energy), internal combustion engines, and fuel cells. Besides direct applications, biogas can be used as a raw material for producing high added-value products, such as molecular hydrogen and renewable hydrocarbons, through a new enterprise concept, the biorefineries. Purity and quality control are determinant factors that enable the decision-making regarding the end use of biogas. Physical, chemical, and biological methods can be used in biogas upgrading processes as well as a combination of different techniques. This review aims to deepen the knowledge about relevant technologies for biogas purification. It also addresses the most efficient and feasible methods, challenges to be overcome, and main demands for future studies. Therefore, the presentation, in a detailed way, of the synergistic effects caused by components contained in natural biogas and the combinatorial methods for removing these contaminants, differentiates this from other works that approach only the purification techniques but do not point out their problems and causes more comprehensively. Thus, studies related to the combined effects of contaminants would be interesting in future works.     

Comparison of Various Alkaline Solutions for H2S/CO2‐Selective Absorption Applied to Biogas Purification

Biogas is a common renewable energy resource. A very important stage of biogas upgrading, studied in the present work, is its purification from H₂S traces. The selective absorption of H₂S and CO₂ into oxido‐alkaline solutions containing hydrogen peroxide and into amine solutions was compared by performing absorption test runs in a cables‐bundle scrubber at 293.15 K and atmospheric pressure. The absorption rate and selectivity for H₂S over CO₂ were determined for various solute partial pressures, different alkaline absorbents and hydrogen peroxide concentrations in the scrubbing liquid, and different pH values. Higher H₂S‐selective absorption performances with oxido‐alkaline solutions than with amine solutions could be observed provided that the solution is at a low pH value (9.5) and contains a sufficient hydrogen peroxide concentration.     

Development of a Model for Water Scrubbing‐Based Biogas Upgrading and Biomethane Compression

Biomethane is an easily storable, renewable energy source that is applicable to the sectors electricity, heat, and transport. It is mostly obtained from biogas by different upgrading technologies. At present, the most common technology is water scrubbing because of its reliability and simplicity. A methodology for designing as well as for evaluating and optimizing water scrubbing plants including biomethane compression is introduced. To demonstrate possible applications of this methodology, a zero‐emission water scrubbing process characterized by under‐pressure regeneration of washing water is modeled and investigated by a sensitivity analysis.     

沼气重整制氢方法选择

生物质经厌氧发酵产生的沼气富含甲烷与二氧化碳,两者都是主要的温室气体,然而经适当净化后,沼气又是可再生的清洁能源,可以有多种利用方式。从沼气中分离出甲烷并通过催化重整可以制取氢气,具有环境与经济的双重效益。本文对比了沼气重整制氢的各种方法,指出通过干重整是沼气重整制氢的最优途径。     

Treatment of odorous sulphur compounds by chemical scrubbing with hydrogen peroxide—Application to a laboratory plant

Hydrogen peroxide (H₂O₂) has proved its efficiency when it is used as an oxidant in chemical scrubbing towers. The important H₂O₂ decomposition in basic solutions has been investigated and slowed down by addition of a stabiliser: poly-α-hydroxyacrylic acid. The objective of this work is to implement this alternative in a laboratory scrubbing pilot. H₂S and CH₃SH removals were studied in order to characterise the performances of the process. The consumption of reactants (H₂O₂ and NaOH) was quantified in continuous working with recycling of the scrubbing solution or not. Using hydrogen peroxide in a scrubbing tower gave quite satisfactory results for hydrogen sulphide, and encouraging ones for methylmercaptan. Hydrogen peroxide decomposition observed was economically acceptable, even if compared with the chlorine process. However, sodium hydroxide consumption was found important because of the carbon dioxide competitive absorption.     

Optimization of the Sodium Hydroxide–Assisted Hydrogen Sulfide Selective Removal from Natural Gas

Scrubbing of hydrocarbon-based gases such as natural gas or biogas is essential prior to its use. These gas mixtures when contaminated with hydrogen sulfide cause safety, environmental, and corrosion problems in pipelines. There are several methods of reducing the content of hydrogen sulfide in sour gases, but few of these are selective as well. Selectivity is important to avoid unnecessary chemical usage. Chemisorption in sodium hydroxide solution by applying a special spray technique appears to be an efficient and selective method for hydrogen sulfide removal. This study aims to determine the characteristic of system and thereby facilitating the design of gas-cleaning parameters. The studied parameters include the contact time, concentration of sodium hydroxide, absorbent volumetric flow rate, and gas composition. Model gas mixtures of hydrogen sulfide, carbon dioxide, and nitrogen were used for experiments. To define the optimal experiment setup, the Box–Behnken design (BBD) method was applied. Based on the method, the number and the condition of necessary absorption experiments were constructed. To rank the operating parameters of the absorption process from the point of view of which effect is more significant on the scrubbing performance, statistical analysis of variance (ANOVA) was done. The analysis shows contact time and concentration of sodium hydroxide as the two most influential factors in the absorption process. Carbon dioxide content of sour gas as influencing factor was examined for efficiency and order of priority parameters of process. An extended model has been created to support the optimization of operating conditions in the investigated removal system.     

农村沼气的净化及资源化利用研究进展

沼气的净化提纯技术是沼气资源化利用中非常重要的一个环节.介绍了农村沼气的组成,并总结了现有的沼气净化提纯的主要方法及其特点.目前沼气的净化提纯技术主要是脱硫、脱碳、脱水及脱除其它不助燃的杂质.其中,脱硫技术主要有干法、湿法及生物法脱硫等;脱碳主要有液体吸收法、固体吸附法和膜分离法等;脱除水分主要有冷凝法、溶剂吸收和固体...     

Evaluation of Bioelectromethanogenesis Part II: Environmental Impact

As already mentioned in part I bioelectromethanogenesis is a power to gas technology that is used to convert electrical power to chemical energy carriers. In this case carbon dioxide is converted to methane by electroactive microorganisms. Part I of this study reviewed the theoretical energetic demand and showed the general reaction process. This part observes the technology's environmental impact by regarding the global warming potential (GWP). According to the contemplated purpose of the reviewed technology there is a comparison to common biogas upgrading techniques.     

CFD simulation of chemical reaction between sulfur dioxide and water in a venturi scrubber

ABSTRACT

The use of fossil fuel, i.e., coal, was first initiated in 1880s for electricity generation. It was used extensively worldwide due to its cheap rate. Consequently, there is an adverse effect on the environment that results in a climate change. Many industries were working on cleaning flue gases emitted from coal power plants according to Environmental Protection Agency (EPA) standards by using different scrubbing technologies and venturi scrubber is one of them having ability to remove particulates and toxic gases simultaneously. Industries were using computational fluid dynamics (CFD) techniques to fully understand the gases behavior inside scrubbing technologies prior employed in the project. This research represents CFD simulation to study abatement process of sulfur dioxide through chemical reaction with water in a venturi scrubber. Parameters such as mass concentration of sulfurous acid formation, sulfur dioxide and water mass content distribution inside venturi scrubber were analyzed. The sulfur dioxide removal efficiency was also investigated. The results show that water mass content distribution was greatly influenced by sulfur dioxide mass flow rates. Desulfurization efficiency depreciates with an increase in sulfur dioxide mass flow rate, whereas efficiency increases with accession in liquid to gas ratio. Maximum sulfur dioxide removal was observed at lower sulfur dioxide concentration comparatively to higher concentration of sulfur dioxide.     

对垃圾填埋场生物气体控制的研究

垃圾的处理是世界各国的重要问题.在各种处理技术中,填埋是处理最为经济的方法.填埋场对环境的潜在危害之一就是其生物气体(主要包括二氧化碳和甲烷)的逸出.甲烷是一种主要的温室气体,同时也是一种可燃气体.旧式垃圾填埋场对环境的负面影响及人们对可再生能源的认识使填埋场生物气体的回收利用引起了越来越多的关注.以抚顺市榆林垃圾填埋场为研究对象,对其生物气的成份,含量进行了分析,对结果进行了讨论,并对其作为能源的潜在性进行了评估.     

酸性气体脱除单元副产二氧化碳中夹带甲醇的去除方案研究

酸性气体脱除单元副产的二氧化碳可作为粉煤气化装置载气循环利用,但其夹带微量甲醇,需经过处理才能达标排放。以某二氧化碳需求量为20000 m³/h的粉煤气化装置为例,分析对比了压缩机段间洗涤和压缩前洗涤两种水洗法脱除二氧化碳中微量甲醇的方案,结果发现水洗法脱除甲醇的方案可行,且压缩机段间洗涤方案较压缩前洗涤方案安全性更高,设备费用更低,能耗低15.5%,每小时可省操作费用105.1元。初步探讨了吸附法用于脱除二氧化碳中微量甲醇的可行性。     

Simultaneous absorption with reaction in a slurry containing fine particles

The simultaneous absorption of two gases accompanied by chemical reaction into a slurry of fine suspended particles was numerically analysed using the model obtained with some extension of the corresponding single gas absorption.Experiments were performed for the simultaneous absorption of sulfur dioxide and carbon dioxide with a plane gas—liquid type stirred tank absorber. The experimental results were satisfactorily elucidated by the proposed model and it is suggested that when accompanied by sulfur dioxide absorption, carbon dioxide may almost be regarded as an inert gas.     

水合物法提纯沼气技术研究进展

沼气是一种重要的可再生能源,对沼气进行充分高值利用对于缓解我国能源需求和环境压力具有重要意义。沼气在高值利用前必须进行脱碳提纯处理,本文介绍了一种可用于沼气提纯的新技术--水合物分离技术。介绍了水合物分离技术的基本理论,调研总结了水合物法提纯沼气和可用于沼气体系（CH₄/CO₂）的水合物分离技术研究进展,包括相平衡研究、热力学促进剂、动力学促进剂、机械强化、外场强化、添加多孔介质/纳米流体等和采用油/水乳液促进技术,并对各种水合物分离促进技术进行了分析：相平衡研究为水合物法提纯沼气提供了理论基础;合理地选用热力学和动力学促进剂能够有效改善气体水合物相平衡条件,促进水合物生成,增加储气效果和提高分离效率;机械强化及外场作用通过强化水合反应过程的传质传热效果促进水合物生成;添加多孔介质和纳米流体等能够增大气液接触面积,对水合过程发挥促进作用;采用油/水乳液不但能够强化气液接触,而且微乳状态下的水合物具有很好的流动性,具有良好工业应用前景。最后对水合物法提纯沼气技术进行了展望,水合物提纯沼气研究虽处在起步阶段,但随着研究的不断深入,该技术凭借操作条件温和,对原料气要求低,并且具有操作简单灵活、安全性高、环保无污染等优点,必将在我国沼气产业发展过程中发挥作用。     

Fuel Gas Purification with Permselective Membranes

Abstract

Production of fuel gas from biomass and recovery of flared gas from landfills, oil fields, coal mines, is hampered by the high cost of gas purification for the removal of C02 and H2S. Membranes offer a potentially simple and attractive technique for on-site gas purification. Two membrane approaches have been considered for fuel gas purification-polymer films and facilitated transport-each with its own unique advantages. Polymer films can be made extremely thin (<500Å), and thus have high gas throughput and a very low membrane area requirement. Ultrathin polymer membranes have been found to be extremely attractive for purification of gas produced from waste or in remote site applications. Of particular interest is biogas produced from anaerobic digestion of sewage, municipal waste, agricultural waste, and landfills. Membrane purification is expected to cost less than half of that for conventional scrubbing processes. Additionally, the gas is purified and dried at the same time. Laboratory tests confirm that membrane performance projections can be met. Facilitated transport membranes in which reversible chemical reactions with a carrier species occur, have nearly perfect selectivity for CO₂ and other reactive gases. However, permeation rates are relatively low, and they are less attractive for flared gas/biogas purification.     

Gasification of Green River oil shale kerogen

Green River oil shale kerogen when reacted with a sodium tetra-chloroaluminate melt, gasifies efficently under a low pressure of hydrogen. The function of the tetrachloroaluminate melt is to promote radical formation and rearrangement of aliphatic units through chemical effects in addition to the role the solvent plays as a thermal transfer agent. The mechanism of gasification appears to involve the generation of electron deficient sites, which either undergo bond breakage or rearrange resulting in the formation of low-molecular-weight hydrocarbons, normally gases or near gases at ambient temperatures. The product gases are sufficiently clean that conventional scrubbing techniques may be used and that the process may be operated on a semi-continuous basis.     

Improved rate-based modeling of carbon dioxide absorption with aqueous monoethanolamine solution

This paper focuses on modeling and simulation of a post-combustion carbon dioxide capture in a coal-fired power plant by chemical absorption using monoethanolamine. The aim is to obtain a reliable tool for process simulation: a customized rate-based model has been developed and implemented in the ASPEN Plus® software, along with regressed parameters for the Electrolyte-NRTL model worked out in a previous research. The model is validated by comparison with experimental data of a pilot plant and can provide simulation results very close to experimental data.     

Katalytische Methanisierung von Kohlenstoffdioxid

Power‐to‐Methane is a technically feasible process that can store large amounts of electrical energy for a long time period. The produced gas of the process can be fed into the natural gas grid or used as fuel. An essential part of the process chain is the catalytic methanation of carbon dioxide. In the methanation process, carbon dioxide and hydrogen are converted into methane and water vapor. Carbon dioxide can be won from industrial processes, ambient air or biogas plants. In this paper, fundamentals and process developments of methanation of carbon dioxide are described.     

磷石膏生产建筑石膏的工艺探讨

介绍磷石膏综合利用的主要技术和方法：磷石膏洗涤净化预处理,洗涤水循环利用回收大部分的可溶性磷;采用两段沸腾煅烧工艺先预烘干脱除游离水,后脱除结晶水生产建筑石膏。