中国煤层气资源及中长期发展趋势预测

与常规天然气相比,煤层气在组成上并无太大的差别,中国埋深2000m以浅煤层气资源总量为34.5万亿m3,可采约10万亿m3,人口密集、工业集中的华北聚气区占资源总量的62%,这对于建设煤层气生产基地,规模利用极为有利。长期以来,人们发现煤层中蕴含有一种可燃的伴生气体,称为瓦斯气或沼气,一直把煤矿中的这种气当作有毒、易燃、易爆、危害极大的有害气体,都没有很好地开发利用。近30多年来,随着科学技术的快速进步,能源问题、环境问题和煤矿安全问题的日益突出,人们认识到煤层气的开发利用,可以较好地改善煤矿安全、保护生态环境,并能增加一种优质洁净的新能源。我国一些地区煤层气抽放利用和地面勘探开发成果,显示了煤层气良好的开发利用前景。通过对中国煤层气发展的中长期预测表明:伴随着技术进步和能源结构的调整,煤层气将形成独立的产业体系,将在我国未来一次能源中占有重要地位,成为常规天然气的战略补充资源。文中最后提出了加快煤层气发展具体建议,认为这些措施的实施会对我国煤层气的发展起到关键性的作用。     

Hydrogen and syngas production from biomass gasification for fuel cell application

Gasification process is being developed to produce a clean and efficient gas flue from fuels such as coal, biomass, and solid/liquid wastes for power generation. In this work, a biomass gasification kinetic model that can predict reaction temperature, gasification performance, and gas composition has been developed for a circulating fluidized bed (CFB). Experimental data from a CFB power plant have been used to validate the model. It is confirmed that the addition of steam is important for increasing the hydrogen concentration and syngas caloric value. Based on the predicted results, an optimal condition is suggested for air and steam gasification in the CFB gasifier.     

Australian coal mine methane emissions mitigation potential using a Stirling engine-based CHP system

Methane, a major contributor to global warming, is a greenhouse gas emitted from coal mines. Abundance of coal mines and consequently a considerable amount of methane emission requires drastic measures to mitigate harmful effects of coal mining on the environment. One of the commonly adopted methods is to use emitted methane to fuel power generation systems; however, instability of fuel sources hinders the development of systems using conventional prime movers. To address this, application of Stirling engines may be considered.Here, we develop a techno-economic methodology for conducting an optimisation-based feasibility study on the application of Stirling engines as the prime movers of coal mine CHP systems from an economic and an environmental point of view. To examine the impact of environmental policies on the economics of the system, the two commonly implemented ones (i.e. a carbon tax and emissions trading scheme) are considered. The methodology was applied to a local coal mine. The results indicate that incorporating the modelled system not only leads to a substantial reduction in greenhouse gas emissions, but also to improved economics. Further, due to the heavy economic burden, the carbon tax scheme creates great incentive for coal mine industry to address the methane emissions.     

煤层气发动机CO排放量数值模拟及试验

根据化学反应动力学原理，建立了火花点火武变组分煤层气发动机CO的生成模型，该模型由碳氢燃料高温氧化生成CO以及CO在火焰中及火焰后氧化两部分组成。以MATLAB程序设计语言为应用平台，对CO的瞬时排放量进行了模拟计算，得到了发动机缸内CO的变化规律。同时，计算和分析了煤层气组分变化对CO排放的影响，并与实验结果进行了比较。研究结果证实．所建立的CO排放模型是合理的。理论和试验结果表明，提高煤层气中的甲烷浓度和发动机的负荷有利于降低发动机的CO排放量。     

Development of a Solid Oxide Fuel Cell for the utilization of coal mine gas

Apart from natural gas there is another important natural source of methane. The so-called coal mine gas is a by-product of the geochemical process of the carbonization of sediments from marsh woods of the Earth's Carboniferous Period. Methane evaporates from the coal and has to be removed out of the active mines where it represents one of the main safety risks. Methane also evaporates in abandoned coal mines. In the federal state Saarland in Germany exists above ground a more than 110 km pipeline for the drained coal mine gas from 12 different sources. The content of methane varies between 25 and 90%, the oxygen content (from air) is in the range up to 10%. This wide range or variation, respectively, of fuel and oxygen content, causes a lot of problems for the use in conventional engines. Therefore the company Evonik New Energies GmbH is interested in using SOFC with coal mine gas as efficient as possible to produce electric power. For that purpose at Forschungszentrum Jülich the available SOFC technology was adapted to the use with coal mine gas and a test facility was designed to operate an SOFC stack (approximately 2 kW electrical power output) together with a pre-reformer.This paper presents the results of the coal mine gas analysis and the effect on the pre-reformer and the fuel cell. The composition of the coal mine gas was determined by means of micro-gas chromatography. The results obtained from preliminary tests using synthetic and real coal mine gas on the pre-reformer and on the fuel cell are discussed.     

煤矿通风气燃气轮机系统控制试验仿真

提出了一种用于煤矿通风气的燃气轮机系统并设计了系统的控制策略;建立了系统的仿真模型,利用模型对系统进行了动态控制仿真试验,结果表明采用设计的控制策略,燃气轮机系统的热效率以及系统的动态特性都有所提高。采用把甲烷作为辅助调节燃料,根据机组负荷的变化调节以煤矿瓦斯气、煤层气为主的预混气体中甲烷含量,可以达到系统平稳运行的目的。     

Production of synthesis gas by co-gasifying coke and natural gas in a fixed bed reactor

The production of synthesis gas has gained increasing importance because of its use as raw material for various industrial syntheses. In this paper synthesis gas generation during the reaction of a coal/methane with steam and oxygen, which is called the co-gasification of coal and natural gas, was investigated using a laboratory scale fixed bed reactor. It is found that about 95% methane conversion and 80% steam decomposition have been achieved when the space velocity of input gas (oxygen and methane) is less than 200 h⁻¹ and reaction temperature about 1000 °C. The product gas contains about 95% carbon monoxide and hydrogen. The reaction system is near the equilibrium when leaving the reactor.     

李阳煤业瓦斯综合利用的实践与探索

中国煤矿瓦斯治理和利用的政策体系基本形成,根据李阳煤业瓦斯抽采及利用现状,结合当前瓦斯综合利用技术,提出了李阳煤业“高浓度瓦斯并网销售+低浓度瓦斯发电+余热利用+掺混燃烧”的瓦斯综合利用方案,分析了所能产生的环境效益、社会效益和经济效益,并对煤矿瓦斯综合利用的发展提出了建议。     

All CO2 is equal in the atmosphere—A comment on CDM GHG accounting standards for methane recovery and oxidation projects

Greenhouse gas (GHG) accounting with respect to two categories of methane recovery and oxidation activities (coal bed or coal mine methane recovery and landfill gas (LFG) recovery) within the Clean Development Mechanism (CDM) is analysed. It is found that baseline methodologies approved by the CDM Executive Board apply systematically inconsistent assumptions concerning the global warming impact of carbon dioxide emissions from the oxidation of methane. One important implication of the results is that applying the baseline methodologies approved for project activities involving LFG recovery will lead to overestimation of the net GHG abatement effect of such CDM project activities.     

Thermochemical analysis of ACFB-based gas and power cogeneration

A first- and second-law analysis is presented for a process developed for simultaneous generation of a fuel gas and electric power (gas and power cogeneration) based on atmospheric circulating-fluidized-bed (ACFB) combustion of coal. The mathematical model has a zone structure, multi-species equilibrium calculations for applicable zone conditions at high temperatures (50 gas-phase and seven solid-phase chemical species) and the concept of freezing of the gas composition at low temperatures. Our analysis shows that the process utilizes coal in a simple, effective and environmentally clean manner. The first- and second-law efficiencies of the process are, respectively, 35.0 and 27.6% for gas generation, 15.4 and 14.6% for power generation, 50.4 and 42.2% overall. The heating value of the gas is 11 MJ/Nm³ (medium). Desulphurization is achieved by using CaS-based sulphur capture during limestone addition to the gasifier bed. Results are compared with data from a 150 kg of coal/h experimental plant.     

Reducing life‐cycle environmental impacts of coal‐power by using coal‐mine methane

The exploitation of coal‐mine methane is analysed to reduce the environmental impact from coal power systems. The analyses are based on a life cycle assessment, and the results were compared with carbon‐capture and storage technologies. The results suggest that by increasing the use of coalmine methane, the environmental impacts of coal power plants could be clearly reduced. Although the CO₂ reduction is much less than through sequestration of CO₂, increased use of coal‐mine methane in Poland could potentially reduce greenhouse gas emissions up to 9 million tonnes of CO₂ per year, which corresponds to about 2.5% of the emissions of Poland. Copyright © 2012 John Wiley & Sons, Ltd.     

Estimation of hydrogen release and conversion in coal-bed methane from roof extraction in mine goaf

In order to effectively utilize the coal bed methane (CBM) resources extracted from underground coal mines, an evaluation method of hydrogen production capacity from CBM is established by means of experiments and theoretical models. The main components of CBM collected from coal working face are measured by gas chromatography, and the release law of trace hydrogen is obtained. Considering gas extraction technology in goaf roof, a computational fluid dynamics model for seepage problem in porous media is presented. The law of gas migration in goaf under extraction conditions is obtained by simulation, and the extraction rate of CBM and methane/hydrogen content are predicted. The technology of producing hydrogen from CBM extracted from goaf under low gas concentration is discussed, and the effect of methane content on auto-thermal conversion efficiency is analyzed. Under the condition of this study case, the theoretical estimation of pure hydrogen produced from goaf extraction can reach more than 10,000 m³ per day. The presented results could provide a new route for the utilization of CBM by underground extraction.     

A mathematical model for exit gas composition in a 10 MW fluidized bed coal combustion power plant

A mathematical model has been developed for the oxygen mass balance for a 10 MW fluidized bed coal combustion power plant operated at Jamadoba (TISCO, India). Assuming the three phase theory of fluidization, the fluid bed is considered to consist of a number of equivalent stages in series. Within each stage, an exchange of gas takes place between the bubble, cloud-wake, and emulsion phases. An effective chemical reaction rate of char combustion has been derived considering the single film theory of char combustion for shrinking particles. The model has been used to predict the consumption of oxygen in the fluidized bed combustor, the outlet gas composition, variation of oxygen concentrations in different phases and also the variation of average oxygen concentration along the bed height. Model predictions were compared with plant data, and reasonable accuracy was obtained.     

Role of natural gas in meeting an electric sector emissions reduction strategy and effects on greenhouse gas emissions

With advances in natural gas extraction technologies, there is an increase in the availability of domestic natural gas, and natural gas is gaining a larger share of use as a fuel in electricity production. At the power plant, natural gas is a cleaner burning fuel than coal, but uncertainties exist in the amount of methane leakage occurring upstream in the extraction and production of natural gas. At higher leakage levels, the additional methane emissions could offset the carbon dioxide emissions reduction benefit of switching from coal to natural gas. This analysis uses the MARKAL linear optimization model to compare the carbon emissions profiles and system-wide global warming potential of the U.S. energy system over a series of model runs in which the power sector is required to meet a specific carbon dioxide reduction target across a number of scenarios in which the availability of natural gas changes. Scenarios are run with carbon dioxide emissions and a range of upstream methane emission leakage rates from natural gas production along with upstream methane and carbon dioxide emissions associated with production of coal and oil. While the system carbon dioxide emissions are reduced in most scenarios, total carbon dioxide equivalent emissions show an increase in scenarios in which natural gas prices remain low and, simultaneously, methane emissions from natural gas production are higher.     

From coal towards renewables: Catalytic/synergistic effects during steam co-gasification of switchgrass and coal in a pilot-scale bubbling fluidized bed

Recent environmental sharp curbs on fossil fuel energy systems such as coal power plants due to their greenhouse gas emissions have compelled industries to include renewable fuels. Biomass/coal co-gasification could provide a transition from energy production based on fossil fuels to renewables. A low-ash coal and switchgrass rich in potassium were selected on the basis of previous thermogravimetric studies to steam co-gasify 50:50 wt% coal:switchgrass mixtures in a pilot scale bubbling fluidized bed reactor with silica sand as the bed material at ∼800 and 860 °C and 1 atm. With the switchgrass added to coal, the hydrogen and cold gas efficiencies, gas yield and HHV of the product gas were enhanced remarkably relative to single-fuel gasification. The product gas tar yield also decreased considerably due to decomposition of tar catalyzed by switchgrass alkali and alkaline earth metals. Switchgrass ash therefore can act as inexpensive natural catalysts for steam gasification and assist in operating at lower temperatures without being penalized by an increase in product tar yield. An equilibrium model over-predicted hydrogen and under-predicted methane concentrations. However, an empirically kinetically-modified model was able to predict the product gas compositions accurately.     

Microbial consortium in a non-production biogas coal mine of eastern China and its methane generation from lignite

A coal bed water in Zhaolou coal mine of eastern China contained abundant microbial consortia, which could convert Baiyinhua native lignite to biogenic methane. The major microbes in coal bed water were bacteria (88%) including Proteobacteria and Firmicutes, and the rest of it were assigned to Methanobacterium. Methane generation rate with this microbial consortium was up to 72 μmol/g coal in 28 d culture. After treatments with the enriched culture, the ash, volatility contents, and hydrophobicity of residual lignite decreased, while its active functional groups containing oxygen and hydrogen increased.     

Bounding the climate viability of natural gas as a bridge fuel to displace coal

Natural gas has significant potential carbon benefits over coal when used for electricity generation, but these benefits can be offset by emissions of fugitive methane or delays in the adoption of near-zero carbon technologies. We analyze the time-evolution of radiative forcing from both natural gas and coal-based electricity generation by calculating average radiative forcing over an interval of time from greenhouse gas emissions under a range of assumptions for fugitive methane leakage, electricity generation efficiency, and delays in the adoption of near-zero carbon technologies. We find that leakage rates of between 5.2% and 9.9% are required for natural gas to result in greater mean forcing than coal over the next 100 years. We show that natural gas infrastructure with modest leakage could remain in place for 1.5–2.4 times the time interval that coal generation would have persisted prior to replacement with near-zero carbon technologies before the climate benefits of replacing coal with natural gas are negated. Natural gas can serve a viable bridge away from coal-based generation if avoiding longer-term climate impacts is prioritized, fugitive methane emissions are minimized, and the large-scale transition to near-zero carbon alternatives is unlikely to happen in the near-term.     

Progress in developing an innovative lean burn catalytic turbine technology for fugitive methane mitigation and utilization

Approximately 2.8 × 10¹⁰ m³ of methane is emitted per year to the atmosphere from coal mining activities around the world. Mitigation and utilization of the fugitive coal mine methane is very difficult because its concentration is very low and varies from 0.1% to1%, and the methane is contained in a large air flow rate of 150–400 m³/s. This paper overviews existing and developing technologies for the mitigation and utilization of the fugitive mine methane, and then presents research progress in developing an innovative lean burn catalytic turbine technology for fugitive methane mitigation and utilization. This turbine system can be powered with about 1% methane in air.     

煤矿通风瓦斯在燃气轮机中的催化燃烧特性

在不同进口温度、工作压力和当量比条件下,研究了煤矿通风瓦斯气在燃气轮机催化燃烧室内部的燃烧特性,对数值模拟结果与试验结果进行了对比,并分析了催化燃烧对超低浓度瓦斯气性能的影响.结果表明:增加甲烷浓度(或当量比)可促进超低浓度甲烷的催化燃烧;提高催化燃烧室进口温度或工作压力可相应提高煤矿通风瓦斯燃气轮机系统的效率.