Methane and carbon dioxide in dual-porosity organic matter: Molecular simulations of adsorption and diffusion

Shale gas, which predominantly consists of methane, is an important unconventional energy resource that has had a potential game-changing effect on natural gas supplies worldwide in recent years. Shale is comprised of two distinct components: organic material and clay minerals, the former providing storage for hydrocarbons and the latter minimizing hydrocarbon transport. The injection of carbon dioxide in the exchange of methane within shale formations improves the shale gas recovery, and simultaneously sequesters carbon dioxide to reduce greenhouse gas emissions. Understanding the properties of fluids such as methane and methane/carbon dioxide mixtures in narrow pores found within shale formations is critical for identifying ways to deploy shale gas technology with reduced environmental impact. In this work, we apply molecular-level simulations to explore adsorption and diffusion behavior of methane, as a proxy of shale gas, and methane/carbon dioxide mixtures in realistic models of organic materials. We first use molecular dynamics simulations to generate the porous structures of mature and overmature type-II organic matter with both micro- and mesoporosity, and systematically characterize the resulting dual-porosity organic-matter structures. We then employ the grand canonical Monte Carlo technique to study the adsorption of methane and the competing adsorption of methane/carbon dioxide mixtures in the organic-matter porous structures. We complement the adsorption studies by simulating the diffusion of adsorbed methane, and adsorbed methane/carbon dioxide mixtures in the organic-matter structures using molecular dynamics.     

Electricity,methane and liquid carbon dioxide production from landfill gas

Landfill gas, which has a typical composition of 40–60% methane, 40–50% carbon dioxide, and a wide range of impurities, has historically been recovered solely for its heating value. After only minor impurity removal, landfill gas has been used as medium Btu industrial fuel or to generate electricity; after significant impurity and carbon dioxide removal, landfill gas has been used as a source of pipeline quality methane. For both cases, the value of the substantial amount of contained carbon dioxide has not been realized. This has been due to the impurities which present a significant obstacle to the economic production of merchant grade carbon dioxide.This paper presents two processes¹ which make use of an oxygen fed combustion step to reduce both the quantity and variety of impurities which must be removed to meet carbon dioxide product specifications. The two processes produce carbon dioxide and electricity or carbon dioxide and pipeline quality methane, respectively. In both oxygen based coproduction processes, the combustion step is integrated into the overall process to maximize energy efficiency. The two processes are described and anticipated net liquid carbon dioxide manufacturing costs are presented.     

城市垃圾污染监测用二氧化碳中甲烷气体标准物质的研制

城市垃圾填埋法由于会释放大量二氧化碳和甲烷温室气体而受到广泛关注。研制了城市垃圾污染监测用气体标准物质,该标准物质以垃圾场填埋气为背景气,避免了影响填埋场释放的甲烷及二氧化碳气体监测结果的基体效应。同时还可以模拟不同环境下的垃圾场填埋气,确保城市垃圾污染监测用气体分析仪器监测数据的准确性。采用称量法制备了一系列浓度为1%~65%(mol/mol)二氧化碳中甲烷气体标准物质,并对该气体标准物质的均匀性、稳定性及随压力变化的实验结果进行了分析与考察。结果表明,研制的气体标准物质量值准确,均匀性、稳定性好。该标准物质已获批为国家二级标准物质GBW(E)061757。     

初始压力对冰冻石英砂中CO2水合物生成特性的影响

利用冰冻石英砂模拟冻土水合物的赋存条件，研究了压力对二氧化碳水合物生成特性的影响，在300 mL高压水合物反应釜中于271 K下进行了多组CO2液化压力以上及以下的霰状冰粉包裹的石英砂中水合物生成实验。结果表明，充入的CO2未液化时，初始压力越大，水合反应速率越快，压力越早达稳定状态；充入压力达液化压力后，注入的CO2越多，水合反应速率越快。压力作为水合反应的驱动力，压力越高水合物生成越多，冰的最终转化率越高。采用CO2置换冻土区中甲烷水合物时，控制压力低于液化压力或注入过量的CO2，置换效果更好。     

Multiphase CFD Modeling for a Chemical Looping Combustion Process (Fuel Reactor)

There are growing concerns about increasing emissions of greenhouse gases and a looming global warming crisis. CO₂ is a greenhouse gas that affects the climate of the earth. Fossil fuel consumption is the major source of anthropogenic CO₂ emissions. Chemical looping combustion (CLC) has been suggested as an energy‐efficient method for the capture of carbon dioxide from combustion. A chemical‐looping combustion system consists of a fuel reactor and an air reactor. The air reactor consists of a conventional circulating fluidized bed and the fuel reactor is a bubbling fluidized bed. The basic principle involves avoiding direct contact of air and fuel during the combustion. The oxygen is transferred by the oxygen carrier from the air to the fuel. The water in combustion products can be easily removed by condensation and pure carbon dioxide is obtained without any loss of energy for separation. With the improvement of numerical methods and more advanced hardware technology, the time required to run CFD (computational fluid dynamic) codes is decreasing. Hence, multiphase CFD‐based models for dealing with complex gas‐solid hydrodynamics and chemical reactions are becoming more accessible. To date, there are no reports in the literature concerning mathematical modeling of chemical‐looping combustion using FLUENT. In this work, the reaction kinetics models of the (CaSO₄ + H₂) fuel reactor is developed by means of the commercial code FLUENT. The effects of particle diameter, gas flow rate and bed temperature on chemical looping combustion performance are also studied. The results show that the high bed temperature, low gas flow rate and small particle size could enhance the CLC performance.     

Investigation of carbon dioxide photoreduction process in a laboratory-scale photoreactor by computational fluid dynamic and reaction kinetic modeling

The production of solar fuels via the photoreduction of carbon dioxide to methane by titanium oxide is a promising process to control greenhouse gas emissions and provide alternative renewable fuels. Although several reaction mechanisms have been proposed, the detailed steps are still ambiguous, and the limiting factors are not well defined. To improve our understanding of the mechanisms of carbon dioxide photoreduction, a multiphysics model was developed using COMSOL. The novelty of this work is the computational fluid dynamic model combined with the novel carbon dioxide photoreduction intrinsic reaction kinetic model, which was built based on three-steps, namely gas adsorption, surface reactions and desorption, while the ultraviolet light intensity distribution was simulated by the Gaussian distribution model and Beer-Lambert model. The carbon dioxide photoreduction process conducted in a laboratory-scale reactor under different carbon dioxide and water moisture partial pressures was then modeled based on the intrinsic kinetic model. It was found that the simulation results for methane, carbon monoxide and hydrogen yield match the experiments in the concentration range of 10⁻⁴ mol·m^–3 at the low carbon dioxide and water moisture partial pressure. Finally, the factors of adsorption site concentration, adsorption equilibrium constant, ultraviolet light intensity and temperature were evaluated.     

A farm level approach to define successful mitigation strategies for GHG emissions from ruminant livestock systems

Ruminant livestock systems are a significant source of greenhouse gases (GHGs). Thus far, mitigation options for GHG emissions mainly focused on a single gas, and are treated as isolated activities. The present paper proposes a framework for a farm level approach for the full accounting of GHG emissions. The methodology accounts for the relevant direct and indirect emissions of methane, nitrous oxide and carbon dioxide, including carbon sequestration. Furthermore, the potential trade-off with ammonia volatilisation and nitrate leaching are taken into account. A ruminant livestock farm is represented with a conceptual model consisting of five pools: animal, manure, soil, crop and feed. The carbon and nitrogen inputs, throughputs and outputs are described, and the direct emissions are related to the carbon and nitrogen flows. The indirect emissions included in the methodology are mainly carbon dioxide emissions from energy use and nitrous oxide emissions related to imported resources and nitrogen losses. The whole farm approach is illustrated with a case of two dairy farms with contrasting livestock density and grassland management. It is shown that the inclusion of carbon sequestration and all indirect emissions have a major impact on the GHG budget of the farm. For one farm, the effect of four mitigation options on the GHG emissions was quantified. It was concluded that a whole farm approach of full accounting contributes to a better insight in the interactions between the carbon and nitrogen flows and the resulting emissions, within and outside the farm boundaries. Consequently, the methodology can be used to develop efficient and effective mitigation strategies.     

CH4掺混H2的燃烧数值模拟及掺混比合理性分析

本工作针对天然气掺氢燃烧技术在燃气锅炉的最佳掺混比开展数值模拟研究,以小火焰燃烧器为研究对象,计算了在空气氛围、恒定过氧系数、不同甲烷掺混氢气比条件下,掺氢比对燃料燃烧温度、燃烧速率、主要污染物排放浓度的影响.其中燃烧机理采用GRI-MECH 3.0简化机理,该反应包含24个基元反应,涉及17种组分.计算结果表明,随掺...     

Shortcut Evaluation of Chemical Carbon Dioxide Utilization Processes

Chemical utilization of carbon dioxide seems to be an attractive option for the mitigation of greenhouse gas emissions. However, the respective processes themselves cause substantial greenhouse gas emissions. To achieve a good CO₂ balance, it is necessary not only to fix carbon but also to do this efficiently in terms of reactant supply and energy demand. An evaluation of the CO₂ balance requires detailed process simulation for the utilization reaction and the supply chain. To allow a quick evaluation of the potential to mitigate emissions, a number of estimation methods are presented.     

Molecular dynamics study on growth of carbon dioxide and methane hydrate from a seed crystal

In the current work, molecular dynamics simulation is employed to understand the intrinsic growth of carbon dioxide and methane hydrate starting from a seed crystal of methane and carbon dioxide respectively. This comparison was carried out because it has relevance to the recovery of methane gas from natural gas hydrate reservoirs by simultaneously sequestering a greenhouse gas like CO₂. The seed crystal of carbon dioxide and methane hydrate was allowed to grow from a super-saturated mixture of carbon dioxide or methane molecules in water respectively. Two different concentrations (1:6 and 1:8.5) of CO₂/CH₄ molecules per water molecule were chosen based on gas–water composition in hydrate phase. The molecular level growth as a function of time was investigated by all atomistic molecular dynamics simulation under suitable temperature and pressure range which was well above the hydrate stability zone to ensure significantly faster growth kinetics. The concentration of CO₂ molecules in water played a significant role in growth kinetics, and it was observed that maximizing the CO₂ concentration in the aqueous phase may not result in faster growth of CO₂ hydrate. On the contrary, methane hydrate growth was independent of methane molecule concentration in the aqueous phase. We have validated our results by performing experimental work on carbon dioxide hydrate where it was seen that under conditions appropriate for liquid CO₂, the growth for carbon dioxide hydrate was very slow in the beginning.     

Determining the air excess in the heating of coke furnaces. 3. Calculation of the air excess

The chemical mechanism by which coke-oven gas burns in the heating ducts of coke ovens is considered. A formula is obtained for the air excess. In contrast to the existing formula, the proposed version takes account of not only the content of oxygen, carbon monoxide, and carbon dioxide in the combustion products but also the content of sulfur dioxide, hydrogen, methane, nitrogen oxides. Analysis of the combustion products in the heating ducts of a coke battery with 30.9-m³ ovens shows that the content of incombustible components in the coke-oven gas may reach 3%. Calculation of the air excess by means of the proposed formula permits improvement in the uniformity of the temperature distribution in the heating system, the prevention of specific lining defects, and decrease in atmospheric emissions when the coke battery is heated by means of coke-oven gas. The proposed method of determining the air excess may be used not only in equipment for coke production but also in other metallurgical systems where coke-oven gas is burned.     

A 300 W laboratory reactor system for chemical-looping combustion with particle circulation

Chemical-looping combustion (CLC) is a method to burn gaseous fuels with inherent separation of carbon dioxide. A continuously operated laboratory reactor system for chemical-looping combustion with two interconnected fluidized beds was designed and built. This chemical-looping combustor was designed to operate with a fuel flow corresponding to 100–300 W. The CLC system was operated successfully using a highly reactive nickel-based oxygen-carrier. Furthermore, tests were carried out to determine the degree of gas leakage between the reactors. Although there was some leakage between the fuel and air reactors, it is low enough to enable evaluation of the combustion results. The combustion tests showed a high conversion of the natural gas to carbon dioxide, indicating that the particles are suitable for chemical-looping combustion. No methane was detected in the gas from the fuel reactor, and the fraction of carbon monoxide was in the range 0.5–3%.     

Carbon capture from stationary power generation sources: A review of the current status of the technologies

The world will need greatly increased energy supply in the future for sustained economic growth, but the related CO₂ emissions and the resulting climate changes are becoming major concerns. CO₂ is one of the most important greenhouse gases that is said to be responsible for approximately 60% of the global warming. Along with improvement of energy efficiency and increased use of renewable energy sources, carbon capture and sequestration (CCS) is expected to play a major role in curbing the greenhouse gas emissions on a global scale. This article reviews the various options and technologies for CO₂ capture, specifically for stationary power generation sources. Many options exist for carbon dioxide capture from such sources, which vary with power plant types, and include post-combustion capture, pre-combustion capture, oxy fuel combustion capture, and chemical looping combustion capture. Various carbon dioxide separation technologies can be utilized with these options, such as chemical absorption, physical absorption, adsorption, and membrane separation. Most of these capture technologies are still at early stages of development. Recent progress and remaining challenges for the various CO₂ capture options and technologies are reviewed in terms of capacity, selectivity, stability, energy requirements, etc. Hybrid and modified systems hold huge future potentials, but significant progress is required in materials synthesis and stability, and implementations of these systems on demonstration plants are needed. Improvements and progress made through applications of process systems engineering concepts and tools are highlighted and current gaps in the knowledge are also mentioned. Finally, some recommendations are made for future research directions.     

Biogenic versus abiogenic emissions from agriculture in the Netherlands and options for emission control in tomato cultivation

In this paper, present-day emissions of greenhouse gases and acidifying compounds from agriculture are analysed at the farm level. Quantitative estimates are given for these emissions from three nested systems in the Netherlands: the agricultural sector, greenhouse horticulture, and tomato cultivation under glass. Total emissions are subdivided into emissions from biogenic sources and abiogenic sources. We conclude that, although most of the emissions from the agricultural sector have biogenic sources, those from abiogenic sources should not be neglected. Abiogenic emissions are mainly from greenhouse horticulture. The cost-effectiveness of options to reduce carbon dioxide (CO₂) and nitrogen oxides (NO_x) emissions from on-farm combustion of natural gas in tomato cultivation under glass is analysed. An inventory is given of technical reduction options that are presently available in practice. Based on information about the costs and the reduction potential of each option, cost-efficiency curves are derived for both types of emissions. Relative to a situation where none of the described options were applied (early nineties), CO₂ and NO_x emissions from tomato cultivation can be reduced at most by about 70% and 75%, respectively, by combinations of technical options. This revised version was published online in August 2006 with corrections to the Cover Date.     

Catalytic activation of CO2: Use of secondary CO2 for the production of synthesis gas and for methanol synthesis over copper-based zirconia-containing catalysts

Consumption of fossil fuel resources throughout the industrial era has resulted in an enormous increase in carbon dioxide concentration in the atmosphere. Developed countries have committed to reducing the atmospheric load of greenhouse gases and ratified the Kyoto Protocol. Chemical utilization of carbon dioxide captured from large scale stationary sources is one possible pathway to decrease the rate of emissions. Catalysis plays a crucial role in these carbon dioxide utilization reactions. In this paper, the production of synthesis gas from carbon dioxide-containing secondary gases and carbon dioxide hydrogenation to methanol over copper-based zirconia-containing catalysts have been investigated. Pathways of carbon dioxide utilization are outlined, research done on carbon dioxide hydrogenation over copper-based zirconia-containing catalysts is reviewed, and the challenges of these reactions are reported. It is argued that direct utilization of secondary carbon dioxide from industrial sources can be a significant step toward developing sustainable industrial practices and a critical part in sustainable energy strategies.     

基于链式循环二氧化碳重整的甲烷制甲醇过程火用分析

二氧化碳重整制甲醇过程对碳源高效利用和环境保护具有重要意义，可作为替代传统高能耗、高排放水蒸气重整过程的途径。用Aspen Plus软件模拟链式循环二氧化碳重整的甲烷制甲醇过程。结果表明，该过程的?损失主要集中在化学过程，占总?损的76.47%，其中燃烧反应与重整反应分别占41.62%和27.69%，而甲醇合成反应与水汽变换反应分别占3.55%与3.61%。与传统水蒸气重整制甲醇过程相比，在原料甲烷输入量一定情况下，二氧化碳重整制甲醇系统的重整过程比水蒸气重整过程?损失减少21.44%，水蒸气消耗量减少77.02%，整体系统二氧化碳排放量降低了25.89%，甲醇的产量提高了12.03%。随着重整反应温度的提高，?效率和甲醇产量均出现先升高、后平稳的趋势，并在980℃达到最大值。此外，较低的重整反应压力有利于提高甲醇产量。     

SHS-produced Ni-Co-Al-Mg-O catalysts for dry reforming of methane

Oxide catalysts Ni-Co-Al-Mg-O, Ni-Al-Mg-O, Co-Al-O, and Co-Mg-O have been prepared by combustion synthesis and characterized by XRD, Fourier transform IR spectroscopy (FTIR), SEM/EDS, TEM, and nitrogen porosimetry. Their catalytic activity in the process of dry (carbon dioxide) reforming of methane was studied by gas chromatography at different temperatures. Feed gas contained equal amounts of methane, carbon dioxide, and nitrogen and the effect of catalyst composition and temperature on the catalytic activity, selectivity, and product yields were recorded.     

碳中和目标下石油与化学工业绿色低碳发展路径分析

石油与化工行业是高耗能、高污染、高碳排的“三高”行业,在碳达峰、碳中和的目标下,促进石油与化学工业和生态环境的协调可持续发展成为亟需解决的热点问题。本文从国家层面和企业层面总结典型国家及其石油与化学工业面对“双碳”目标采取的措施行动,对乙烯、成品油等石油与化工产品不同生产路径的能耗及二氧化碳排放情况进行比较分析,概述中国的区域能源分布特点、各省份的石油与化学工业产值及二氧化碳排放情况,明确提出作为碳排放的大户,石油与化工行业有可能在“十四五”期间被纳入全国碳市场。文中指出石油与化工行业必须在借鉴发达国家先进碳减排经验的基础上,立足本国国情,综合考虑本国的能源分布情况和石油与化工产品生产的能耗及二氧化碳排放情况,建构清洁低碳、节能高效的工艺流程体系,促进石油与化学工业的高质量发展。石油与化学工业二氧化碳减排的核心是区域能源结构的调整和工艺流程的优化,并以此为前提建设绿色集成化工园区,辅之以可再生能源如风能、太阳能等的综合利用,研发碳捕集、利用与封存技术进行碳固定。还提出值得注意的是,由于其他温室气体如甲烷等的减排已经提上日程,我国也应加快相关技术储备。     

Methane and nitrous oxide emissions: an introduction

Methane and nitrous oxide are important greenhouse gases. They contribute to global warming. To a large extent, emissions of methane and nitrous oxide are connected with the intensification of food production. Therefore, feeding a growing world population and at the same time controlling these emissions is a great challenge. Important anthropogenic sources of biogenic methane are wet rice fields, cattle, animal waste, landfills and biomass burning. Important anthropogenic sources of biogenic nitrous oxide are land-use change, fertilizer production and use and manure application. The ultimate objective of the Framework Convention on Climate Change implies a stabilization of greenhouse gas concentrations in the atmosphere. As a small first step towards achieving this objective, the Convention requires the industrialized countries to bring their anthropogenic emissions of greenhouse gases by 2000 back to 1990 levels. It was also agreed that all parties would make national inventories of anthropogenic greenhouse gas emissions and programmes for control (UN, 1992).In this context, in February 1993 an international workshop was held in Amersfoort in the Netherlands to discuss methods in national emission inventories for methane and nitrous oxide, and options for control (Van Amstel, 1993). A selection of the papers presented in Amersfoort that focus on agricultural sources is published in this volume. This introductory chapter gives background information on biogenic sources and sinks of methane and nitrous oxide and options for their control. The goal of the Climate Convention is described as well as the IPCC effort to develop an internationally accepted methodology for the monitoring of greenhouse gas emissions and sinks. Finally, some preliminary results from country inventories are given. It is concluded that a common reporting framework and transparency of the inventories are important to obtain comparable results that can be used for complying with the requirements of the Climate Convention and for facilitating the international debate about appropriate response strategies.     

Simulation of a calcium looping CO2 capture process for pressurized fluidized bed combustion

The Canadian regulations on carbon dioxide emissions from power plants aim to lower the emissions from coal-fired units down to those of natural gas combined cycle (NGCC) units. Since coal is significantly more carbon intensive than natural gas, coal-fired plants must operate at higher net efficiencies and implement carbon capture to meet the new regulations. Calcium looping (CaL) is a promising post-combustion carbon capture (PCC) technology that, unlike other capture processes, generates additional power. By capturing carbon dioxide at elevated temperatures, the energy penalty that carbon capture technologies inherently impose on power plant efficiencies is significantly reduced. In this work, the CO₂ capture performance of a calcium-based sorbent is determined via thermogravimetric analysis under relatively high carbonation and low calcination temperatures. The results are used in an aspenONE™ simulation of a CaL process applied to a pressurized fluidized bed combustion (PFBC) system at thermodynamic equilibrium. The combustion of both natural gas and coal are considered for sorbent calcination in the CaL process. A sensitivity analysis on several process parameters, including sorbent feed rate and carbonator operating pressure, is undertaken. The energy penalty associated with the capture process ranges from 6.8–11.8 percentage points depending on fuel selection and operating conditions. The use of natural gas results in lower energy penalties and solids circulation rates, while operating the carbonator at 202 kPa(a) results in the lowest penalties and drops the solids circulations rates to below 1000 kg/s.