Status of worldwide coal mine methane
emissions and use
Underground coal mines worldwide liberate an estimated 29–41×109 m3 of methane annually, of which less than 2.3×109 m3 are used as fuel. The remaining methane is emitted to the atmosphere, representing the loss of a valuable energy resource. Methane is also a major greenhouse gas and is thus detrimental to the environment when vented to the atmosphere. Coal mine methane recovery and use represents a cost-effective means of significantly reducing methane emissions from coal mining, while increasing mine safety and improving mine economics.
The world’s ten largest coal producers are responsible for 90% of global methane emissions associated with the coal fuel cycle. China is the largest emitter of coal mine methane, followed by the Commonwealth of Independent States, or CIS particularly Russia, Ukraine and Kazakhstan, the United States, Poland, Germany, South Africa, the United Kingdom, Australia, India and the Czech Republic. Most of these countries use a portion of the methane that is liberated from their coal mines, but the utilization rate tends to be low and some countries use none at all. Coal mine methane is currently used for a variety of purposes. Methane is used for heating and cooking at many mine facilities and nearby residences. It is also used to fuel boilers, to generate electricity, directly heat air for mine ventilation systems and for coal drying. Several mines in the United States sell high-quality mine gas to natural gas distributors. There are several barriers to decreasing methane emissions by increasing coal mine methane use.
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Many of the same barriers are common to a number of the subject countries. Technical barriers include low-permeability coals; variable or low gas quality, variations in gas supply an demand and lack of infrastructure.
Economic and institutional barriers include lack of information pertinent to development of the resource, lack of capital and low natural gas prices. A possible option for encouraging coal mine methane recovery and use would be international adoption of a traceable permit system for methane emissions. 1 Introduction
In recent years, coalbed methane has gained attention as a saleable natural gas resource. Methane can be extracted either from coal seams which will never undergo mining, or it can be produced as a part of the coal mining process. This paper focuses on methane which is produced in conjunction with coal mining operations（ coal mine methane） . According to the United States Environmental Protection Agency （USEPA, 1994a） , underground coal mines liberate an estimated 29 to 41×109 m 3of methane annually, of which less than 2.3×109 m3 are used as fuel. The remaining methane is vented to the atmosphere, representing the loss of a valuable energy resource. This paper examines the potential for recovering and using the methane which is currently being emitted from coal mines.
There are three primary reasons for recovering coal mine methane. The first reason is to increase mine safety. Worldwide, there have been thousands of recorded fatalities from underground mine explosions in which methane was a contributing factor. Using methane drainage
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systems, mines can reduce the methane concentration in their ventilation air, ultimately reducing ventilation requirements.
The second reason is to improve mine economics. By reducing emissions and preventing explosions and outbursts, methane drainage systems can cost effectively reduce the amount of time that the coal mine must curtail production. Moreover, recovered methane can be used either as fuel at the mine site or sold to other users.
The third reason for coalbed methane recovery and use is that it benefits the global and local environment. Methane is a major greenhouse gas and is second in global impact only to carbon dioxide; methane thus is detrimental to the environment if vented to the atmosphere. Although the amount of carbon dioxide accumulating in the atmosphere each year is orders of magnitude larger than that of methane, each additional gram of methane released to the atmosphere is as much as 22 times more effective in potentially warming the Earth’s surface over a 100-year period than each additional gram of carbon dioxide (USEPA, 1994a) . Compared with other greenhouse gases, methane has a relatively short atmospheric lifetime. The lifetime of methane (defined as its atmospheric content divided by its rate of removal) is approximately 10 years. Due to its short lifetime, stabilizing methane emissions can have a dramatic impact on decreasing the buildup of greenhouse gases in the atmosphere. Coal mine methane recovery and use represent a cost-effective means of significantly reducing methane emissions from coal mines. Methane, moreover, is a remarkably clean fuel. Methane combustion
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produces no sulfur dioxide or particulates and only half the amount of carbon dioxide that is associated with coal combustion on an energy equivalent basis.
Because of the environmental impact of coal mine methane emissions, the USEPA, the International Energy Agency’s Coal Advisory Board (CIAB), and others have investigated methane emissions from coal mining worldwide. The USEPA (1994a) estimates that the coal fuel cycle (which includes coal mining, post-mining coal transportation and handling, and coal combustion) emits 35 to 59×109 m3 of methane to the atmosphere annually. Table 1 shows methane emissions from the world’s ten largest coal producers, which are responsible for 90% of global methane emissions associated with the coal fuel cycle. Underground coal mining is the primary source of these emissions, accounting for 70 to 95% of total emissions. There are many opportunities for decreasing coal mine methane emissions by increasing recovery of this abundant fuel. Section 2 examines the status of methane recovery and use in key countries worldwide.
2 Coal mine methane recovery and use in selected countries
2.1 China
The Peoples Republic of China (China) produces about 1.2×109 raw tons of hard coal annually (EIA, 1996). In 1990, coal mining activities in China emitted an estimated 14 to 24×109 m3 (10 to 16×106 ton) of methane to the atmosphere, contributing one-third of the world’s total from this source. Not only is China the largest coal producer in the
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world; it is unique in that underground mines produce over 95% of the nation’s coal. Because of the great depth and high rank of China’s coals, underground coal mines have higher methane emissions than surface mines.
There are currently 108 Coal Mining Administrations (CMAs) in China, which manage more than 650 mines. These state-owned mines are responsible for most of China’s methane emissions, but there are numerous gassy local, township, and private mines that cumulatively produce over one-half of China’s coal. However, these non-states owned mines are not gassy (International Energy Agency or IEA, 1994).
2.1.1 Methane recovery and use in China
China has a long history of coal mine methane drainage, and the volume of methane drained has increased markedly during the past decade. Nationwide, coal mine methane drainage at state-run mines nearly doubled in 14 years, increasing from 294×106 m3 in 1980 to more than 561×106 m3 in 1994 .However, this is still less than 11% of the total methane liberated annually. Approximately 131 state-owned mines currently have methane drainage systems. Less than one-half of these mines are set up to distribute and use recovered methane. China’s state-run coal mining administrations use about 70% of the methane they drain (USEPA, 1996a).
Most of the methane recovered from Chinese mines is used for heating and cooking at mine facilities and nearby residences. Methane is also used for industrial purposes, in the glass and plastics industries,
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and as a feedstock for the production of carbon black (an amorphous form of carbon used in pigments and printer’s ink). Methane is also being used, to a lesser extent, for power generation. In 1990, the Laohutai Mine at the Fushun Coal Mining Administration built a 1200 kW methane-fired power station, the first in China.
Several barriers currently prevent China from developing economic methane recovery from coal mining to its full potential. Critical barriers include the lack of an appropriate policy framework, limited capital for project investments and equipment, the need for additional information and experience with technologies and the lack of a widespread pipeline network. Artificially regulated low gas prices and difficulty with repatriation of profits, create barriers to foreign investment in joint ventures for production of domestic energy resources (USEPA, 1993).
2.1.2 The future of methane development in China
Recognizing the need for a unified effort in advancing coalbed methane development, China’s highest governing body, the State Council, established the China United Coalbed Methane Company (China CBM) in May 1996. As a single, trans-sectoral agency, China CBM is responsible for developing the coalbed methane industry by commercializing
the
exploration,
development,
marketing,
transportation and utilization of coalbed methane. The State Council has also granted China CBM exclusive rights to undertake the exploration, development and production of coalbed methane in coopera- tion with foreign partners (China Energy Report, 1996).
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More than 20 coalbed methane projects are underway or planned in China, and at least half of them are taking place at active mining areas. Some of the projects are state-sponsored, while others involve joint ventures with foreign companies. The future of the coalbed methane industry in China appears bright. The government recognizes coalbed methane’s potential for meeting the nation’s burgeoning energy needs and is generally supportive of efforts to develop this resource. With deregulation of energy prices, increased capital investment in pipeline infrastructure, and ongoing research efforts, China can likely overcome its remaining barriers to widespread coalbed methane use. 2.2 Russia, Ukraine and Kazakhstan
In 1994, Russia produced more than 169×106 ton of hard coal; Kazakhstan produced nearly 104×106 ton and Ukraine more than 90×106 ton. The coal mining regions of these republics liberate approximately 5.3×109 m3 of methane annually, of which less than 3% is utilized. This amount represents about 20% of world methane emissions from underground coal mining.
The energy sectors of these Republics are at a turning point. The coal mining industry, in particular, is undergoing restructuring, a process which includes decreasing or eliminating subsidies, and closing many of the most unprofitable mines. The industry is being compelled to become more efficient in order to increase profitability. Mining regions are also seeking to mitigate environmental problems resulting from producing and using coal. Thus, there is an impetus to utilize more natural gas and decrease dependency on low grade coal.
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Increasing recovery and use of coalbed methane is a potential means of improving mine safety and profitability while meeting the regions’ energy and environmental goals.
There are five coal basins in the Commonwealth of Independent States where hard coal is mined and which have the potential for coalbed methane development.
They are: (1) the Donetsk Basin (Donbass) , located in southeastern Ukraine and western Russia, (2) the Kuznetsk Basin Kuzbass , located in western Siberia (south-central Russia) , (3)the L’vov-Volyn Basin, located in western Ukraine, which is the southeastern extension of Poland’s Lublin Basin, (4)the Pechora Basin, located in northern Russia and (5) the Karaganda Coal Basin, located in Kazakhstan. Of the five basins, the Donetsk and Kuznetsk Basins appear to have the largest near-term potential for coalbed methane development （USEPA, 1994b）. Both of these regions are heavily industrialized and present many opportunities for coalbed methane use. 2.2.1 Options for methane use in the CIS
2.2.1.1 Heating mine facilities. Currently, most mines use coal-fired boilers to produce steam heat for drying coal, heating mine facilities and heating ventilation air. In some cases, mine boilers also supply thermal energy to the surrounding communities. Boilers can be retrofitted to co-fire methane with coal, a relatively simple and low-cost procedure. More than 20 mines in the Donetsk and Pechora Basins use methane to fuel boilers and several mines also use it for directly heating air for the mines’ ventilation systems and for coal
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drying (Serov, 1995; Saprykin et al., 1995).
2.2.1.2. Use in furnaces in the metallurgical industry. Another viable market for methane use is the metallurgical industry. For example, the city of Novokuznetsk, in the southern portion of the Kuznetsk Basin, contains numerous gassy mines and is one of the biggest centers of metallurgy in Russia. The region’s metallurgical industry consumes about 54 PJ of natural gas annually, which is equivalent to about 1.4×109 m3 of methane (USEPA, 1996b) .
2.2.1.3. Power generation at mine facilities. Most mines purchase electricity from the power grid. Co-firing coalbed methane with coal to generate electricity on-site may be a more economical option for these mines. Coalbed methane can be used, independently of or in conjunction with coal, to generate electricity using boilers, gas turbines and thermal combustion engines (USEPA, 1994b).
2.2.1.4. Use as a motor vehicle fuel. The Donetskugol Coal Production Association in Ukraine is draining methane in advance of mining using surface boreholes. The recovered methane is compressed on-site and used as fuel for the Association’s vehicle fleet. The refueling station, which has been operating for more than three years, produces about 1,000 m3 of compressed gas per day. Based on estimated gas reserves it is expected to operate for a total of eight years ( Pudak, 1995 ).
While many mines in the CIS are utilizing their methane resources, the majority are not. Certain barriers must be overcome before recovery and use of coal mine methane becomes widespread. These
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barriers and their potential solutions are discussed in greater detail in Section 3 of this paper. 2.3 The United States
There are five major coal producing regions in the United States from which hard coal is mined and which have the potential for coalbed methane development. They are: （1）the Appalachian Basin, located in Pennsylvania, Ohio, West Virginia, eastern Kentucky and Tennessee, （2） the Warrior Basin, located in Alabama, （3） the Illinois Basin, located in Illinois, Indiana and western Kentucky, （4）the Southwestern region, including the Uinta, Piceance, Green River and San Juan Basins located in Colorado, Utah and New Mexico and （5）the Western Interior region, including the Arkoma Basin of Oklahoma and Arkansas.
In 1994, an estimated 4.2×109 m3 of methane were liberated by underground mining in these regions, of which less than 0.7×109 m3 were used（USEPA, unpublished data）.
Currently in the United States, at least 17 mines in six states（ Alabama, Colorado,Ohio, Pennsylvania, Virginia and West Virginia）recover methane for profit, primarily through sale to gas distributors. In 1995, the total methane recovered from these mines, including vertical wells draining methane in advance of mining, exceeded 1×109 m3.By maximizing the amount of gas recovered via drainage systems, these mines have greatly reduced their ventilation costs, improved safety conditions for miners and have collected and sold large quantities of high-quality gas. Following is a brief
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description of selected coal mine methane recovery activities in the United States.
2.3.1 Warrior basin: Alabama
Six of the seventeen US mines with commercial methane recovery systems are located in the Warrior Basin of Alabama. Today, energy companies recover methane from the Warrior Basin by horizontal wells, gob wells（ in areas being mined ）and vertical wells（in both mined and unmined areas） . Most of this gas is sold to regional natural gas distributors, although there is some on-site mine use. In 1995, four mines operated by Jim Walter Resources produced more than 380×106 m3 of methane for pipeline sale and USX’s Oak Grove Mine recovered an estimated 117×106 m3 of methane for use. 2.3.2 Appalachian region
Eight mines in Virginia and West Virginia have developed successful methane recovery and use projects. The Consol mines in Virginia are the most well-documented examples. Consol produces gas from a combination of vertical wells that are hydraulically stimulated, horizontal boreholes and gob wells drilled over longwall panels. In 1995, Consol produced approximately 688×106 m3 of saleable methane from three mines. Methane recovery efficiency at these mines is higher than 60%.
2.3.3 Southwestern region
The Soldier Canyon Mine in Utah recovered about 10.9×106 m3 of methane for sale annually until early 1994, when production was curtailed and gas sales ended due to low market prices.
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2.3.4 Summary
While methane recovery has been economically implemented at the above-described mines, safety and high coal productivity remain the impetus for their degasification efforts. Methane drainage at many gassy mines in the United States is limited or nonexistent. Section 3 of this paper discusses potential avenues for increasing methane recovery and use in the United States and other countries. 2.4 Germany
Germany produced nearly 54 million tons of hard coal in 1995, all from underground mines （Schiffer, 1995）. Of this total, 43 million tons were mined from the Ruhr Basin in northwestern Germany （Von Sperber et al., 1996） and most of the remainder was mined from the Saar Basin in southwestern Germany. Until recently, hard coal mining was heavily subsidized in Germany, and the industry’s future is in question （Schiffer, 1995） . Even mines that are closed, however, can continue to liberate methane for long periods of time. An estimated 1.8×109 m3 of methane are liberated annually from underground mining activities in Germany, of which 520×106 m3, or 30%, are drained（63 IEA, 1994）. About 371×106 m, or 71% of all drained methane is used, primarily for heating or power generation.
Government officials suggest that as much as 45% of the methane emitted from coal mining activities could be drained and used in a variety of applications. The primary barrier to increased methane recovery is low methane concentrations in the gas mixture.
Safety regulations in Germany prohibit any utilization if the
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methane content is less than 25%. If the average recovery efficiency at German mines is to be increased, it will be necessary to adopt practices that will recover methane in a more concentrated form. 3 Barriers to decreasing coal mine methane emissions
There are several barriers to decreasing methane emissions by increasing coal mine methane use. Some are technical, such as low coal permeability, while others are Institutional, such as low gas prices. In a few cases, certain barriers are country orregion specific, but most cases, many of the same barriers exist in a number of countries. This section discusses obstacles to increased coal mine methane use, and potential ways to overcome these obstacles. 3.1 Technical issues
3.1.1 Low-permeability coals
Coal seams that exhibit low permeability pose special problems for developing
successful methane drainage and recovery systems. Methane desorbs and flows through natural pores and fractures until the gas reaches the mine face or borehole. Stimulation technology that enhances the flow of gases from the seam into a recovery system has been successfully used in the past several years. Early efforts to modify fracturing techniques for application in coal seams were largely unsuccessful （IEA, 1994） . The current practice of hydraulic stimulation in coals, however, minimizes roof damage while achieving extensive fracturing. Under ideal conditions, 60 to 70% of the methane contained in the coal seam can be removed using vertical
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degasification wells drilled more than 10 years in advance of mining. These efforts have been successful in the United States and other industrialized countries. Transfer of this technology to other countries can help increase coal mine methane recovery. 3.2 Economic and institutional issues
In addition to the technical obstacles described above, there are a variety of other issues that have prevented coal mine methane recovery from becoming more widespread.
These issues include lack of information, lack of capital, low natural gas prices and risks associated with foreign investment. Some issues are explored below.
The key strategy for overcoming informational barriers in the United States has been to develop outreach programs. Outreach programs work well when companies are shown that they can profit while at the same time reducing emissions or improving mine safety. Examples of outreach programs include the USEPA’s Coalbed Methane Outreach Program, which is conducted in the United States, and the Coalbed Methane Clearinghouses in Poland, China and Russia. These institutions distribute information and link together interested parties, provide technical training, and in some cases perform pre-feasibility assessments for specific projects. 3.2.1 Lack of information
In the United States and other countries, one of the problems that has slowed coal mine methane project development is that some coal mine operators do not have adequate information regarding coal mine
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methane projects. While much has been published on the subject, methane recovery is still seen as a relatively new concept to many coal operators. A related constraint is that some coal operators simply do not have the time or resources to investigate the potential to develop a profitable project at their own coal mine. 3.2.2 Lack of capital
Even when a pre-feasibility assessment has demonstrated that the economics of a coal mine methane project are attractive, a lack of financing may prevent projects from taking place. Coal companies often do not have surplus capital available to invest in coalbed methane recovery and use projects because available capital must be invested in their primary business of coal production. Additionally, some lending organizations may be unfamiliar with the relatively new concept of coal mine methane recovery and use, and project developers may thus be unable to secure the necessary up-front financing needed to cover the large capital investments required for such projects.
3.2.3 Low natural gas prices
In some countries natural gas prices are held at artificially low rates. Even in countries whose gas prices are at market levels, prices may be low due to low demand. In such cases, special types of incentives to encourage coal mine methane recovery could be implemented. For example, legislation could be enacted requiring local distribution companies to purchase recovered coal mine methane if it is sold at a competitive price. China has recently established preferential policies
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for projects which involve gas recovery and use from coal mines. The government has also passed a law exempting coalbed methane producers from royalties and land occupation fees for production of up to 2×109 m3 of methane per year. 4 Conclusions
As discussed above, coal mines worldwide emit large volumes of methane, much of which could be recovered and used as fuel. In many instances, countries whose mines emit large quantities of methane are in critical need of a domestic energy source, particularly one which is clean-burning. In countries whose economies are in transition, such as China, the former Soviet Union and the Eastern European nations, coal mine methane recovery offers economic benefits as a new industry that can help provide jobs for displaced coal miners or other workers. In countries whose economies are established, such as the United States, the United Kingdom and Australia, coal mine methane recovery may help increase the profit margin of mining enterprises.
The reduction of methane emissions can have a significant global impact, but incentives are needed to encourage more widespread recovery of coal mine methane. An incentive program offered on an international level would probably be the most effective means of stimulating development of the coal mine methane industry. Of the various options for international-level incentives, a system of tradeable permits for methane emissions would likely be the most cost effective. Due to various technical, economic and institutional barriers, it will never be possible to completely eliminate emissions of methane from
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coal mines. However, a worldwide coal mine methane utilization rate of 25% may be realizable, particularly if an international incentive program is implemented. This would reduce the estimated emissions of coal mine methane to the atmosphere by 7 to 10×109 m3 annually, substantially reducing greenhouse gas emissions and curtailing the waste of a valuable energy source.
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附录Ｂ
全球煤矿瓦斯涌出及利用现状
全球煤矿每年释放瓦斯29～41×109 m3 ，其中少于2.3×109 m3
的瓦斯用作燃料，其余的被直接排放到大气中，这是能源的一种浪费。并且瓦斯是造成温室效应的主要气体之一，当它被释放到大气，会对环境造成危害。矿井瓦斯的利用现状要求有一个节约成本且减少瓦斯涌出的方法，同时还要可以提高采煤的安全性及经济效益。
由于世界上十大煤生产国家燃烧煤、利用循环煤而排放的瓦斯占全球的90%，中国是排放矿井瓦斯的最大国家，紧随其后是独联体尤其是俄罗斯、乌克兰、哈萨克斯坦，美国，波兰，德国，南非，英国，澳大利亚，印度，捷克斯洛伐克。大部分国家利用煤矿瓦斯的一部分，但是其利用效率低，甚至一些国家根本没有利用。通常，利用煤矿瓦斯的目的不一。如用于家庭取暖、做饭，加热锅炉，发电，或直接为煤矿通风系统的空气加热和干燥服务。美国的许多煤矿向天然气开发商出售高质量瓦斯。通过提高煤矿瓦斯利用降低瓦斯排放存在重重困难，在许多未独立的国家存在同样的困难。技术方面的难题包括煤层底渗透率、瓦斯性质的多变、瓦斯质量低、市场供求多变、缺少基础设施。经济和体制方面的困难有开发瓦斯能源的信息不足、资金馈乏、价格低廉。国际部门发放煤矿瓦斯排放准许证鼓励煤矿瓦斯回收利用是一个可选择的方法。
1 前言
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近几年，煤矿瓦斯作为赢利资源越来越引起人们的关注。事实上如果瓦斯在煤矿不经开采情况下没有抽出，那么在煤开采过程中将产生瓦斯。本论文重点关注煤矿开采中产生的瓦斯。据美国环境保护署（USEPA，1994年）调查，认为地下矿井每年释放出19－40×109m3瓦斯，其中仅有少于2.3×109 m3的瓦斯被用作燃料。其余全部被排放到大气中，这无疑是资源浪费。论文审查目前煤矿抽放的瓦斯中可回收利用的潜力。
回收再利用矿井瓦斯主要有三个原因，第一是可以提高煤矿安全性，全世界范围内，由于瓦斯导致致命严重煤矿爆炸事故的记录不下千余起。煤矿利用瓦斯抽放系统可以降低通风中的瓦斯浓度，进而减少通风需要。第二个原因是可以提高煤矿经济效益。瓦斯抽放系统的利用通过减少瓦斯涌出而避免爆炸和突出，进而实现高产高效。另外回收的瓦斯即可在煤矿用作燃料还可以售出。
第三个原因是，煤矿瓦斯回收利用有利于全球及地方环境。瓦斯是造成温室效应的主要气体之一，仅次于二氧化碳。如果瓦斯排放到大气，会破坏环境。虽然每年大气中增加的瓦斯少于二氧化碳，但大气中每增加1千克瓦斯对地球表面温度升高的潜在影响远超过二氧化碳22倍。（美环境保护署1994a）与其它温室效应气体相比，瓦斯在大气中的存在时间相对短暂。瓦斯生命（定义为它在大气中的含量除以其运移速率）大约10年。由于瓦斯生命短暂，稳定的瓦斯涌出对大气中温室气体的减少有显著的影响。
矿井瓦斯的回收利用是一种显著减少矿井瓦斯的有效方法。更重要的是瓦斯是洁净燃料，瓦斯燃烧不产生二氧化硫等物，且生成获得同样能量燃烧煤所产生二氧化碳的半量
由于煤矿瓦斯涌出对环境的影响，美环保署、CIAB及其它部
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门对全球范围的煤矿瓦斯涌出情况进行了调查。美环保署（1994文件）强调煤作为燃料循环（包括采煤、运煤、加工、燃烧）每年放出35－59×109 m3 瓦斯到大气中图表1显示世界十大产煤地的瓦斯涌出情况，其中全球90%的瓦斯涌出由煤燃烧循环造成。地下采煤是瓦斯涌出的主要来源，占70－95%，有很多的机会可以通过增加回收利用丰富的瓦斯以减少煤矿瓦斯涌出。本文第二部分讨论一些主要国家的瓦斯回收利用情况。
2 中国煤矿瓦斯的回收利用
2.1 中国
每年中国产原生煤大约1.2×109吨（EIA，1996）.1990年，中国采煤向大气排放14－24×10 m即10-16×10吨瓦斯，占全世界总量的1/3。中国不仅是世界上最大的产煤基地，尤其95%的煤是地下开采煤。由于中国煤矿越采越深以及高瓦斯矿具多，地下采煤便会比露天开采涌出较多瓦斯。
目前中国有108个煤矿管理机关，他们管理650多个矿井。中国的瓦斯涌出主要是国有矿井造成的，而中国有无数的地方煤矿、乡镇煤矿、私人煤矿，并且它们累计生产中国一半的煤。然而这些非国有煤矿一般不是高瓦斯矿。（国际能源署1994）
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3
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2.1.1 中国的瓦斯利用情况
中国在瓦斯抽放方面有很长的历史，并且在过去10年间瓦斯抽放量有显著增加。在14年里，全国的国营煤矿的瓦斯抽放量几乎翻倍。由1980年的294×10m上升至1994年的561×10m。然而这仍少于每年瓦斯释放总量的11%。大约131个国有煤矿有抽放系统。而仅有少于一半的抽放系统是为了出售回收利用瓦斯的。中
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63
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3
国国有煤矿管理机构用了他们抽放瓦斯的70%。
中国煤矿回收的大部分瓦斯被用作加热煤矿设备及周遍居民做饭。在工业方面，瓦斯可用于玻璃和塑料工业。瓦斯还可以在一定范围内用作发电。1990年，抚顺劳扶山煤矿建立一座1200kw的瓦斯-火力发电厂。
目前，各种彰碍使中国难于回收利用潜能巨大的煤矿瓦斯来发展经济，其中关键的障碍包括缺少适当的政策框架、工程项目资金和设备受限，信息和技术不足、缺少广泛的网状管道。人为规定造成瓦斯价格低廉、销售取利困难，这使国内外联合生产中国的能源遇到许多困难。
2.1.2 在中国瓦斯利用的前景
中国国务院（中国的最高管理部门）认识到共同努力开发煤层气的必要性，于是国务院于1996年五月成立中联煤层气瓦斯开发公司。作为一个独立的对外部门，中联煤层气瓦斯开发公司通过商业手段运转发展煤层气勘探、开发、经营、运输、利用。中国国务院赋予中联煤层气开发公司特权以便其与外国合作管理煤层气勘探、开发、生产。（中国能源报，1996）
中国规划至少20多个煤层气方面的项目，并且至少一半以上的项目在高瓦斯矿井区。一部分项目是国家投资赞助的，其它的项目有与外国公司联合经营的。在未来不久，中国煤层气产业的将来更加光明。中国政府认识到煤层气开发解决能源短缺的潜能，并且支持对能源开发的努力。由于能源价格的调整、管道基础设施的投入增加以及正在进行的项目努力等原因，中国很可能克服推广煤层气利用的种种障碍。
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2.2 俄罗斯、乌克兰瓦斯利用的前景
这些国家的能源部门正在经历转折。尤其它们的煤炭产业正在经历结构重组，这一过程包括降低或免征税收、关闭多数亏损煤矿。为了增加利润，煤产业部门被迫提高效益。采煤地区也寻求减小由于开采应用煤而造成的环境污染。因而，这对天然气的应用和减少对低瓦斯的依靠是一种激励。回收利用煤层瓦斯气体是一个提高矿井安全、利润的潜在措施。并且可以达到地区能源利用、保护环境的目标。在独联体有五个煤盘地，那里开采硬煤并且有发展煤层气的潜力。
它们别分是:1)顿涅茨克盆地(顿)坐落于乌克兰东南部,俄罗斯西部;2) 库兹涅茨克盆地坐落于西伯利亚西部(俄罗斯中南部);3) 乌克兰盆地坐落于乌克兰西部,它的东南部延展到波兰的卢布林;4)伯朝拉河盆地坐落于俄罗斯北部;5)卡拉干达州煤盆地坐落于哈萨克斯坦镜内。五个煤盆地中的顿涅茨克 看起来有最大的短期开发煤层气的潜力美环保署1994）。这两个地区的重工业比较发达，现在这有很多开发利用煤层气的机会，表3中列出了五个煤盆地的瓦斯涌出及利用比较。
2.2.1 CIS瓦斯利用
a.用于加热矿井设备。
目前，很多煤矿都采用燃煤锅炉来制造热蒸汽以干燥煤，加热矿井设备，加热通风空气。某些情况下，煤矿锅炉还用于为周遍社区提供热能。煤矿锅炉还可以改造成低豪资煤气设备。CIS地区的瓦斯在燃烧锅炉方面的利用比顿涅茨克和伯朝拉河的煤盆地高20倍，在加热矿井通风系统空气和干燥煤方面比顿涅茨克和伯
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朝拉河的煤盆地高很多倍。
b.冶金工业炉利用瓦斯
冶金工业是有利于瓦斯利用市场化的另一优势。例如，库兹涅茨克煤盆地南部的新库兹涅茨克城市，有无数的瓦斯矿井，它是俄罗斯的最大冶金城市之一，每年，这一地区的冶金工业消费了大约天然气的54 PJ，那相当于1.4×10 m的瓦斯。（美环保署1996b）
c.用于发电
许多煤矿从电力网购买电。不过对于煤矿，煤和煤层气用于现场发电是一种比较经济的方法。煤层气可以单独利用，也可以和煤结合利用用于锅炉发电、燃气涡轮发电、热燃机发电等。（美环保署1996b）
d.用于动力燃料
乌克兰的顿涅茨克煤矿生产协会利用地表打转孔预先抽放瓦斯。回收的瓦斯被现场压缩并用作协会的交通、运输燃料。供应站已经经营了三年多，每一天制造了大约1000 m3的压缩瓦斯。根据估计的瓦斯储量，此供应站可以大约可运营8年左右。
然而在独联体的一些煤矿在利用瓦斯资源，但是大部分煤矿没有这样做。如果想瓦斯回收利用得到普及，那么某些障碍是必须得到解决的。在论文的第三部分将对这些障碍和其有可能被用的解决方法进行讨论。
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2.3 美国的情况
美国有五个主要产煤地区，那里开采硬煤并且有发展煤层气的潜力。五个主要产煤地分别区是:1)阿巴拉契亚盆地,坐落在宾西法尼亚州、俄亥俄州、西弗吉尼亚州和田纳西州,肯塔基州东部
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之间;2)战士盆地,坐落在阿拉巴马州,伊利诺斯州盆地;3),位于伊利诺斯州、印第安纳州和肯塔基州西部之间;4)西南部地区,包括皮申斯格林河和坐落于科罗拉多州、犹他州和新墨西哥之间的圣胡安盆地;5)西部内陆地区,包括俄克拉荷马的阿卡玛盆地和阿肯色州。
在这些地区，仅1994年地下开采煤释放了大约4.2×10m的瓦斯，其中只有0.7×109m3的瓦斯被回收。（美国环保署非公开数据）。
目前，在美国有6个州（阿拉巴马州、科罗拉多州、俄亥俄、宾夕法尼亚、弗吉尼亚州和西弗吉尼亚州）至少17个煤矿回收瓦斯，他们主要通过出售回收的瓦斯给销售商取的利润。1995年，包括开采前预先抽放的瓦斯，回收瓦斯的总量达到了1×109 m3。这些地区的矿井已经通过最大化瓦斯抽放系统的瓦斯抽放量大大降低了通风成本，提高了矿井安全条件，并且收集、出售了大量高质量瓦斯。下面简单描述一下在美国的煤矿瓦斯回收利用活动的情况。
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2.3.1战士盆地:阿拉巴马州
美国有17个煤矿有商业回收瓦斯系统，其中的6个都在阿拉巴马州的战士盆地。现在，该地区，能源公司从平硐、正在开采的矿井的采空区、正在开采和已经开采的立井中回收瓦斯。虽然被回收的瓦斯的一部分用于煤矿现场，但大部分的瓦斯都卖给瓦斯销售商。1995年，吉姆·沃尔特所经营的4个煤矿通过管道销售了380×106 m3的瓦斯，并且美国的橡树林煤矿回收了大约117×106 m3的可用瓦斯。
2.3.2阿巴拉契亚地区
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弗吉尼亚州和西弗吉尼亚州的8个煤矿已经成功开发了瓦斯回收利用工程。维吉尼亚州的康索尔煤矿最有见证的例子。在1995年，康索尔的3个煤矿生产了大约688×106m3的可销售瓦斯。在这些煤矿的瓦斯回收率高达60%。
2.3.3 西南部地区
直到1994年瓦斯市场价格走低，犹他州的士兵峡谷煤矿煤矿每年都回收大约10.9×106 m3的瓦斯用于销售。
2.3.4 小结
以上描述的矿井已经和高效率的、经济的回收瓦斯，但为了安全地、高量地生产的目的，分离瓦斯的努力依然很有诱惑。在美国，许多瓦斯矿井被限制抽放瓦斯甚至不允许。
2.4 德国
1995年，德国生产将近540万吨硬煤，全部来自地下开采。 其中的430万吨由德国西北部的鲁尔区盆地开采得到，并且其余的大部分由德国西南部的萨尔河盆地开采得到。直到最近，在德国硬煤开采得到大量补贴，煤炭业的将来成为问题。即使煤矿被关闭，在相当一段时间里，它们依然会释放瓦斯。粗略估计，在德国每年由于地下采煤活动释放1.8×109 m3的瓦斯。其中的520×106m3，即其中的30%是抽放出来的。（63 IEA, 1994）大约371×106 m（即抽放瓦斯的71%）主要用于加热或发电。
政府部门提议：由于开采煤而涌出的瓦斯的45%都可以抽放并以各种形式利用。目前，提高瓦斯回收利用的主要障碍是混合气体中瓦斯浓度低。
德国安全规程规定：如果瓦斯浓度低于25%，那么禁止了利用。
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如果想进一步提高德国的瓦斯利用效率，那么有必要采取一些措施以高浓度瓦斯形式回收利用。
3 降低瓦斯释放量的障碍
通过增加煤矿瓦斯利用来降低瓦斯释放的障碍重重。有技术因素，如煤的渗透性差，还有一些传统因素，像瓦斯价格低廉。许多年来，一些国家或地区面临特殊障碍，但大多的情况是许多国家面临着共同的困难。这一部分将探讨增加煤矿瓦斯利用方法及克服种种障碍的可行方法。
3.1 技术困难
3.1.1 煤的渗透性低
煤层的渗透性低给瓦斯的抽放和回收利用造成了很大的困难。瓦斯通过天然微孔及裂隙不断解吸、流动造成瓦斯到达工作面或大巷。很多年以前，增加由煤层而形成的瓦斯流，使其进入回收系统的模拟技术已经获得成功。在煤层早中应用改变其裂隙的技术也获得了巨大成功（IEA, 1994）。然而在矿上，目前的水力挤压模拟实验扩展裂隙的同时还使顶板的破坏最小化。在理想的情况下，在煤层开采前的10年多，它们中的60-70%的瓦斯就可以通过竖直钻孔进行预先抽放。在美国和一些工业化国家这些努力已经获得了成功。如果这些技术得以传播将有利于增加矿井瓦斯的回收利用。
3.1.2 基础设施缺乏
许多矿区都因缺乏收集瓦斯、运输瓦斯的收集系统、管道系统。在一些情况下，如压缩、长距离运输瓦斯不很必要时，当地直接利用会是很经济的。
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3.2 经济和体制问题
不但存在以上描述的技术难题，还有很多阻碍矿井瓦斯回收利用推广的问题。这些问题包括信息不畅通、资料不全资金匮乏、天然气价格低、国内外共同投资的风险。下面将阐述一些问题。
3.2.1 信息不畅、资料不全
在美国和一些国家，减缓瓦斯利用工程发展的一个原因是煤矿管理者没有关于矿井瓦斯利用工程的充分资料。虽然相关瓦斯利用的资料、信息已经出版，但对许多的煤矿管理者来讲，瓦斯回收利用仍然是一个相对新的概念。煤矿管理者仅仅因为时间紧张、资料不足而没有调查研究他们自己的煤矿发展瓦斯利用项目的可取利润。
在美国，克服信息信息不畅、资料不全的困难的关键因素是发展极限伸距项目。伸距项目非常有效，他们取得利润的同时还降低了瓦斯涌出量、提高了矿井的安全性。
极限伸距项目的例子如已经启动的美国环境保护署的煤层气项目，在波兰、中国和俄罗斯的项目。这些机构出售信息、资料并且联系盈利部门，提供技能培训，有时还对特殊项目进行预可行性评估。
3.2.2 资金匮乏
即使煤矿瓦斯项目的预评估结果是很经济的、诱人的，但如果资金匮乏，那么项目可能难以实施。煤矿公司很少增加煤矿瓦斯回收利用工程方面的投资，因为可用资金大都投入到煤产品的买卖中。另外，一些借贷组织机构对相对较新的瓦斯回收利用概念不很了解，项目开发者也不能确保资金补进需要源源不断资金
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的项目。
3.2.3 瓦斯价格低廉
在一些国家认为控制天然气价格致使其价格低廉。即使在一部分国家天然气价格市场化了，但因为由于对天然气的需求不足其价格依然不高。在这种情况下，必须采取一些特殊措施刺激鼓励煤矿瓦斯回收利用工程的实施。例如，颁布法规规定：在自由竞争情况下，要求当地的经销公司收购煤矿回收的瓦斯。最近中国已经颁布了特惠政策以利于矿井瓦斯回收利用。政府还通过一向法规：凡年产2×109 m3瓦斯的天然气生产者免征矿山使用费用和占地税。
4 结论
如上所述，全球的煤矿放出大量瓦斯，其中被回收的大部分都是用作燃料。例如，在一些国内能源短缺并且瓦斯涌出量大的国家主要把瓦斯用于清洁燃料。在一些经济转型的国家例如中国、前苏联和东欧，煤矿瓦斯回收利用作为一个新型产业可以为下岗矿工和其他人员提供工作岗位，创造了经济效益。在一些发达国家例如美国、英国、澳大利亚，矿井瓦斯回收利用有利于增加煤矿企业的利润率。
瓦斯涌出量减少有全球性的重大影响，但是为了鼓励矿井瓦斯回收利用更加广泛，激励政策还很需要。一个国际性的激励项目将是刺激瓦斯回收利用发展的最有效方法。所有的国际性的激励措施中，瓦斯释放准许制度可能是最有效的方法。
因为种种的技术、经济、体制障碍，所以完全消除煤矿瓦斯涌出几乎是不可能的。不过，矿井瓦斯回收利用达到25%是可能的，
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尤其如果国际性激励项目得以实施情况下。这将使每年矿井向大气中涌出的瓦斯量减少到7-10×109m3，大大降低温室气体的涌出量并且节约了可回收能源的浪费。
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