为了正常的体验网站,请在浏览器设置里面开启Javascript功能!

煤直接液化和间接液化的比较

2011-06-09 27页 pdf 293KB 75阅读

用户头像

is_032572

暂无简介

举报
煤直接液化和间接液化的比较 A comparison of direct and indirect liquefaction technologies for making fluid fuels from coal Robert H. Williams and Eric D. Larson Princeton Environmental Institute, Princeton University Guyot Hall, Washington Road, Princeton, NJ 08544-1003, USA E-mail (Willia...
煤直接液化和间接液化的比较
A comparison of direct and indirect liquefaction technologies for making fluid fuels from coal Robert H. Williams and Eric D. Larson Princeton Environmental Institute, Princeton University Guyot Hall, Washington Road, Princeton, NJ 08544-1003, USA E-mail (Williams): rwilliam@princeton.edu Direct and indirect liquefaction technologies for making synthetic liquid fuels from coal are com- pared. It is shown that although direct liquefaction conversion processes might be more energy- efficient, overall system efficiencies for direct and indirect liquefaction are typically comparable if end-use as well as production efficiencies are taken into account. It is shown that some synfuels derived via indirect liquefaction can outperform fuels derived from crude oil with regard to both air-pollutant and greenhouse-gas emissions, but direct liquefaction-derived synfuels cannot. De- ployment now of some indirect liquefaction technologies could put coal on a track consistent with later addressing severe climate and other environmental constraints without having to abandon coal for energy, but deploying direct liquefaction technologies cannot. And finally, there are much stronger supporting technological infrastructures for indirect than for direct liquefaction tech- nologies. Prospective costs in China for some indirect liquefaction-derived fuels are developed but not costs for direct liquefaction-based synfuels, because experience with the latter is inadequate for making meaningful cost projections. Especially promising is the outlook for the indirect lique- faction product dimethyl ether, a versatile and clean fuel that could probably be produced in China at costs competitive with crude oil-derived liquid fuels. An important finding is the potential for realizing, in the case of dimethyl ether, significant reductions in greenhouse gas emissions relative to crude oil-derived hydrocarbon fuels, even in the absence of an explicit climate change mitigation policy, when this fuel is co-produced with electricity. But this finding depends on the viability of underground storage of H2S and CO2 as an acid gas management strategy for synfuel production. Many ‘‘megascale’’ demonstration projects for underground CO2 storage and H2S/CO2 co-storage, along with appropriate monitoring, modeling, and scientific experiments, in alternative geological contexts, are needed to verify this prospect. It is very likely that China has some of the least-costly CO2 sources in the world for possible use in such demonstrations. It would be worthwhile to explore whether there are interesting prospective demonstration sites near one or more of these sources and to see if other countries might work with China in exploiting demonstration oppor- tunities at such sites. 1. Introduction China, with its rapidly growing demand for transportation fuels, scant domestic oil and natural gas resources but abundant coal, is likely to turn to coal as a basis for pro- viding synthetic fluid fuels for transportation, cooking, and other applications that are not easily served by elec- tricity. Two very different approaches to providing fluid fuels from coal are described and compared in this paper: direct coal liquefaction (DCL) and indirect coal liquefaction (ICL). For both approaches a major challenge is to in- crease the hydrogen-carbon ratio. For finished hydrocar- bon fuels such as gasoline and diesel, H/C ~ 2 (molar basis). For petroleum crude oil, the ratio ranges from 1.3 to 1.9. For typical bituminous coals, H/C ~ 0.8. Making a comparison of DCL and ICL technologies is not an easy task because of the very different stages of development for these two classes of technologies. ICL technologies (Fischer-Tropsch (F-T) liquids, methanol (CH3OH or MeOH) and dimethyl ether (CH3OCH3 or DME)) are either commercially proven or made up of proven modules, and there is an extensive literature on these technologies and modules. In contrast, DCL tech- nologies are not yet commercially proven, and informa- tion available in the public domain is limited -- with quite different findings coming from the few assessments that have been made. Despite this difficulty, enough is known about DCL technologies to offer policy-makers guidance in understanding the fundamental distinguishing aspects of these two classes of coal conversion technologies. DCL technology involves making a partially refined synthetic crude oil from coal, which is then further refined Energy for Sustainable Development l Volume VII No. 4 l December 2003 Articles 103 kozinsky Reproduced with permission from Energy for Sustainable Development into synthetic gasoline and diesel as well as LPG -- hy- drocarbon fuel products similar to hydrocarbon fuels de- rived from petroleum crude oil. ICL technology involves first gasifying coal to make synthesis gas (‘‘syngas’’, mainly carbon monoxide (CO) and hydrogen (H2)) and then making synthetic fuels from this syngas; the label ‘‘indirect’’ refers to the intermediate step of first making syngas. ICL technology can also pro- vide hydrocarbon fuels that resemble crude oil-derived products. One possibility is synthetic middle distillates de- rived via the F-T process that can either be used directly as diesel or in blends with petroleum-derived diesel. An- other possibility is gasoline via the route of first making MeOH from syngas and then converting MeOH into gaso- line via the Mobil process. But MeOH can also be used directly as a fuel, and other oxygenates (fuels containing some oxygen) such as DME can also be provided via ICL process technology and used directly as fuels. Making conventional hydrocarbon fuels from coal via either DCL or ICL processes has the advantage that the fuel infrastructures already in place for petroleum crude oil products can be used unchanged when a shift is made to coal-derived fuels. However, prospective air-pollutant regulatory constraints worldwide give high value to clean synthetic fuels with emission characteristics superior to those for petroleum crude oil-derived fuels. Moreover, the oft-cited advantage of fuel infrastructure compatibility of- fered by synthetic hydrocarbon fuels is not so great in China at present, where a liquid hydrocarbon fuel infra- structure for transportation fuels is at an embryonic state of development. For these reasons and because some oxy- genates offer performance and emission characteristics su- perior to those for hydrocarbon fuels, the focus of ICL analysis in this paper is on the oxygenates MeOH and DME. 1.1. Direct coal liquefaction With DCL technology the H/C ratio is increased by adding gaseous H2 to a slurry of pulverized coal and recycled coal-derived liquids in the presence of suitable catalysts to produce synthetic crude oil. A slate of partially refined gasoline-like and diesel-like products, as well as propane and butane, are recovered from the synthetic crude oil mainly by distillation. Each of the products is made up of not one but many different large molecules that are recovered via distillation in different temperature ‘‘cuts’’. Hydrogen is needed in the DCL process both to make synthetic crude oil (which might be represented in a sim- plified manner as CH1.6) and to reduce the oxygen, sulfur, and nitrogen in the coal feedstock. These elements are removed from the liquid fuel products in the forms of H2O, H2S, and NH3. The oxygen is removed so that hy- drocarbon fuels can be obtained. The nitrogen and sulfur compounds are removed because they would otherwise poison the cracking catalysts in the refining operations downstream of the DCL plant. The amount of H2 needed is crudely estimated as fol- lows for Yanzhou bituminous coal[1], which can be repre- sented as CH0.81O0.08S0.02N0.01: CH0.81 + 0.395 H2 ® CH1.6 (1a) 0.04 O2 + 0.08 H2 ® 0.08 H2O (1b) 0.02 S + 0.02 H2 ® 0.02 H2S (1c) 0.005 N2 + 0.015 H2 ® 0.01 NH3 (1d) Thus 0.5 kmol (1.0 kg) of H2 plus 1 kmol (14.9 kg) of coal are required to produce 1 kmol (13.6 kg) of synthetic crude oil. The H2 might be made from natural gas via steam reforming or from coal via gasification; the latter is a suitable option for China, where natural gas is scarce. The DCL products are only partially refined. They must be further refined into finished liquid fuel products at con- ventional refineries, where additional H2 is added (to bring the H/C up to ~ 2 for the final products), and energy is consumed to provide the refinery’s heat and power needs. DCL technology was invented by Friedrich Bergius in 1913 and commercialized in Germany and England in time to provide liquid fuels for World War II. The activity was abandoned when low-cost Middle East oil became available in the early 1950s. R&D was revived in the United States, Germany, and Japan after the Arab oil em- bargo of 1973. Interest in DCL declined again in the mid- 1980s with the decline of the world oil price. None of the industrialized countries are now pursuing DCL technology to meet their own liquid fuel needs. Most global interest in alternatives to crude oil is focused on gas-to-liquids (GTL) technology, which aims to exploit low-cost ‘‘stranded’’ natural gas resources in various parts of the world. However, the Clean Coal Technology Program of the US Department of Energy is pursuing several projects that involve liquid fuel production via indirect coal lique- faction (ICL). Modern DCL technology is not proven at commercial scale. The largest scale at which there has been experience with DCL in the United States is a Process Development Unit at the Hydrocarbon Technology, Inc. (HTI) R&D fa- cility that consumes 3 tonnes (t) of coal per day. In 2002, China announced a $ 2 billion investment for a DCL plant in Inner Mongolia based on HTI technology. The plant was expected ultimately to produce 50,000 bar- rels per day (b/d) (1 barrel = 0.1364 t) of partially refined gasoline and diesel and was to be made up of three reactor trains, each processing 4,300 t of coal daily. The first re- actor train, which represents a scale-up by a factor of 1400 from the previous largest plant, was to start up in 2005. However, as this article was going to press in early De- cember 2003, it was announced that construction of the plant is being suspended. The future of the project is now uncertain, but at the very least the project will be scaled down and its timing stretched out. 1.2. Indirect coal liquefaction The first step in indirect liquefaction is to gasify coal in oxygen (partial oxidation) to produce syngas. The CO and H2 molecules in the syngas are then combined catalyti- cally to produce compounds that can be used as fuels -- either hydrocarbon fuels such as synthetic gasoline or syn- thetic diesel, or oxygenated fuels. The challenge of in- creasing the H/C ratio is addressed by using the water-gas-shift (WGS) reaction (CO + H2O ® H2 + CO2) and removing the CO2 thereby produced from the system. Energy for Sustainable Development l Volume VII No. 4 l December 2003 Articles 104 At present the most important options are hydrocarbon fuels synthesized via the F-T process, MeOH, and DME. 1.2.1. Fischer-Tropsch liquids The F-T process for making synthetic hydrocarbons can be summarized, in a simplified manner, by the following two catalytic reactions that build up large hydrocarbon molecules from the small CO and H2 molecules produced by gasification, with the oxygen in the CO feed being rejected in steam: n CO + 2n H2 ® n H2O + CnH2n (olefins) (2a) n CO + (2n + 1) H2 ® n H2O + CnH2n+2 (paraffins) (2b) The slate of products generated depends on the catalysts used and reactor operating conditions. Olefin-rich prod- ucts with n in the range 5 to 10 (naphtha) can be used for making synthetic gasoline and chemicals in high-tem- perature F-T processes. Paraffin-rich products with n in the range 12 to 19 (distillates) are well suited for making synthetic diesel and/or waxes in low-temperature F-T processes. Development has emphasized making synthetic diesel because the raw distillate product is an excellent diesel fuel, whereas the raw naphtha product requires sub- stantial subsequent refining to make an acceptable gaso- line. F-T technology is well established commercially and is the focus of global GTL efforts to exploit low-cost ‘‘stranded’’ natural gas to make synthetic liquid transpor- tation fuels. Sasol in South Africa has extensive construc- tion and operating experience with F-T technology based on coal gasificaton and converts annually about 42 million t (Mt) of coal into 6 billion liters (Gl) of synthetic fuels and 2 Gl of chemicals [Geertsema, 1996]. And there is growing interest in coal-based F-T technology in the United States. Sasol F-T synthesis technology along with a Shell gasifier will be used in a $ 0.6 billion US Depart- ment of Energy-sponsored demonstration project in Gil- berton, Pennsylvania, that will make from coal waste materials 5,000 b/d of F-T liquids plus 41 MWe of elec- tricity. Recently, a detailed assessment was carried out for the US Department of Energy of the co-production of F-T liquids and electricity from coal via gasification at large scales [Bechtel et al., 2003a; 2003b]. This study, based on the E-Gas gasifier (now owned by PhillipsConoco) and slurry-phase reactors for F-T liquids synthesis, estimated that for an optimized plant[2] built in the US Midwest, the internal rate of return would be 10 % if the electricity were sold for $ 0.04/kWh and the F-T liquids for $ 30 per barrel; the equivalent crude oil price would be up to $ 10 per barrel less than this $ 30 per barrel cost (de- pending on refinery configuration and relative oil product demands), because the F-T liquids would already be partly refined [Marano et al., 1994]. Sulfur and aromatic-free F-T middle distillates are al- ready being used as blend stock with conventional crude oil-derived diesel in California to provide fuel that meets that state’s stringent specifications for diesel. 1.2.2. Methanol MeOH is a well-established chemical commodity used throughout the world. It can potentially also be used in- directly or directly (see Box 1) as a fuel. The primary reactions involved in making MeOH from syngas are: CO + H2O ® CO2 + H2 (water gas shift) (3a) CO + 2 H2 ® CH3OH (methanol synthesis) (3b) The MeOH produced can be further processed to make gasoline by the Mobil process (a commercial technology that can provide gasoline at attractive costs from low-cost stranded natural gas [Tabak, 2003]) or DME by MeOH dehydration (see below), or the MeOH can be used Box 1. MeOH as a synthetic fuel for transportation Because of its high octane rating[28], MeOH is well- suited for use in SIE vehicles (see discussion in main text)[29]. It can be used in such vehicles with rela- tively modest modifications of the basic vehicle. Used in SIE vehicles, MeOH offers air-quality bene- fits that are thought to be comparable to those of- fered by reformulated gasoline [Calvert et al., 1993]. The ozone formation potential from formaldehyde emissions of MeOH is thought to be less than the ozone formation potential of unburned hydrocarbon emissions; NOx emissions from MeOH engines op- erated at the same compression ratio as for gasoline would be less than for gasoline, because of the lower flame temperature, but when the compression ratio is increased to take advantage of MeOH’s higher oc- tane rating, thereby improving engine efficiency, this advantage may be lost [Wyman et al., 1993]. And just as some of the unburned hydrocarbon emissions for gasoline are carcinogenic, the US Environmental Protection Agency has classified formaldehyde as a probable human carcinogen, on the basis of evidence in humans and in rats, mice, hamsters, and monkeys [EPA, 1987]. The major drawbacks of MeOH as a transport fuel are its low volumetric energy density (half that of gasoline -- see Table 4), its affinity for water, its cor- rosiveness, and its toxicity -- a fatal dose is 2-7 % MeOH in 1 litre (l) of water, which would defy de- tection by taste. Drawing upon HEI [1987] and Malcom Pirnie [1999], the following provides a perspective on the MeOH toxicity issue: MeOH is classified as a poison (it is rated as slightly more toxic than gasoline), and it is infinitely miscible with water (forms mixtures in all concentrations), allowing ready transport in the environment. Chronic low-dose MeOH vapor expo- sure from normal vehicle operations is not likely to cause health problems. However, exposure through MeOH-contaminated drinking water is a concern. In the event of a spill, MeOH would probably be less likely to reach drinking water supplies than gasoline, because natural processes would degrade it more quickly, but if MeOH-contaminated drinking water had to be treated (which it might if an underground MeOH tank leaked into groundwater), remediation would be more difficult than with gasoline. Energy for Sustainable Development l Volume VII No. 4 l December 2003 Articles 105 IBMUSER 附注 烯烃 IBMUSER 附注 脂肪烃 IBMUSER 附注 致癌的 IBMUSER 附注 甲醛 directly as fuel. This last option is the focus of the present study (see also companion paper in this issue by Larson and Ren [2003]). In most parts of the world MeOH is made by steam reforming of natural gas, but in gas-poor regions such as China it is made mainly from coal-derived syngas via gasification. Under the US Department of Energy’s Clean Coal Tech- nology Program, Air Products and Chemicals, Inc., has brought to commercial readiness slurry-phase reactor technology for MeOH production [Heydorn et al., 2003]. Following successful proof-of-concept in 7,400 hours of test operation at a scale of 12,000 l/day at the DOE-owned process development unit at LaPorte, Texas, the technol- ogy has been demonstrated successfully at near-commer- cial scale (300,000 l/day rated capacity) at the Eastman Chemical Company’s coal gasification facility in King- sport, Tennessee; during the 69-month demonstration pro- gram since start-up in April 1997 the plant availability averaged 97.5 %. 1.2.3. Dimethyl ether DME is a non-carcinogenic and virtually non-toxic chemi- cal produced at a rate of 143,000 t/year for chemical proc- ess uses and one significant final consumer market: as an aerosol propellant that replaced fluorinated hydrocarbons phased out because of concerns about ozone-layer dam- age[3]. It is also usable as a fuel (see Box 2). Currently DME is made by MeOH dehydration: 2 CH3OH ® CH3OCH3 + H2O. But DME can also be made (prospectively at lower cost) in a single step by combining mainly three reactions in a single reactor [Lar- son and Ren, 2003]: CO + H2O ® CO2 + H2 (water gas shift) (4a) CO + 2 H2 ® CH3OH (methanol synthesis) (4b) 2 CH3OH ® CH3OCH3 + H2O (methanol dehydration).(4c) Haldor Topsoe in Denmark [Bøgild-Hansen et al., 1995; 1997] is developing a single-step process for making DME from natural gas. NKK Corporation in Japan [Ohno, 1999; Adachi et al., 2000] and Air Products and Chemi- cals, Inc., in the United States [Peng et al., 1997; APCI, 2002; Heydorn et al., 2003] are developing single-step processes for large-scale DME manufacture from coal-de- rived syngas using slurry-phase reactors. In China, the Institute of Coal Chemistry (ICC) of the Chinese Academy of Sciences together with the Shanxi New Style Fuel and Stove Company constructed a 500 t/year DME plant in Xi’an based on MeOH dehydration for use as a domestic cooking fuel as an alternative to LPG (see Box 2); also, since 1995, the ICC has been car- rying out R&D on one-step DME synthesis based on slurry-phase reactor technology [Niu, 2000]. The Ningxia Petrochemical Industry Lingzhou Group, Ltd., is pursuing plans to build a 830,000 t/year DME production plant in Lingwu City, Ningxia Province, based on use of a Chevron-Texaco coal gasifier and the slurry- phase reactor technology of Air Products and Chemicals, Inc. [Lucas and Associates, 2002]. The proposed plant would be built in two phases: during the
/
本文档为【煤直接液化和间接液化的比较】,请使用软件OFFICE或WPS软件打开。作品中的文字与图均可以修改和编辑, 图片更改请在作品中右键图片并更换,文字修改请直接点击文字进行修改,也可以新增和删除文档中的内容。
[版权声明] 本站所有资料为用户分享产生,若发现您的权利被侵害,请联系客服邮件isharekefu@iask.cn,我们尽快处理。 本作品所展示的图片、画像、字体、音乐的版权可能需版权方额外授权,请谨慎使用。 网站提供的党政主题相关内容(国旗、国徽、党徽..)目的在于配合国家政策宣传,仅限个人学习分享使用,禁止用于任何广告和商用目的。

历史搜索

    清空历史搜索