考研英语历年真题来源报刊阅读(17)

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Can coal be clean?NO.10

                         10Can coal be clean?



COAL has several advantages as a fuel. It is abundant. It is widely distributed: countries that are short of other fossil fuels, such as Germany and South Africa, have mountains of it. As a result, it is cheap. Even though the price has risen in the past few years, it is still less expensive to run a power plant on coal than on almost anything else.


But coal is also dirty. It releases lots of soot and various noxious chemicals as it burns, and so has fallen out of favour in many Western countries. Worse, coalired plants produce roughly twice as much carbon dioxide per unit of electricity generated than those that run on natural gas.


The obvious solution is to make coalired generation cleaner. And that’s what utilities in Western countries have been doing for years, to comply with ever stiffer airollution standards.


Reducing emissions of carbon dioxide, however, is another matter. In Britain, as in most rich countries, the average efficiency of coalired power stations is about 35%. But Mitsui Babcock, an engineering firm, says its most recent designs can achieve efficiencies as high as 46%. It reckons that switching from an old design to a new one can cut fuel consumption and emissions by 23%.


Many methods can reduce the various emissions produced by coalired power stations, so that they are at least no worse than gasired stations. But technologies also exist to make coal cleaner still, by filtering out carbon dioxide from the flue gas and storing it somehow. This is theoretically possible, but expensive. Moreover, unlike modifications that improve efficiency, there are no savings to be had by adding carbonapture technology to a power plant. As a result, no such plants have been built.


How does carbon capture work? Most utilities are eyeing one of three basic designs. The simplest, and easiest to bolt on to existing plants, treats carbon dioxide like any other pollutant, and extracts it from the flue gas. Many firms already use this “amine scrubbing” approach to remove carbon dioxide from natural gas, for example. But it is not so practical for largecale uses, since the amines are expensive, as is heating them to release the captured carbon dioxide.


“Oxyuel” plants sidestep the difficulties of separating oxygen and nitrogen in the flue gas by ******* coal in pure oxygen rather than air. The resulting flue gas is almost pure carbon dioxide. But the energy used to separate oxygen from air before ******* is almost as great as that needed to filter out nitrogen afterwards, leading to a similar loss of efficiency.
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The third approach, called “integrated gasification combined cycle” (IGCC), also requires oxygen, but for use in a chemical reaction rather than for *******. When heated in oxygen, coal reacts to form carbon dioxide and hydrogen. An amine solution then absorbs the carbon dioxide, while the hydrogen is burnt in a modified furnace. The amine scrubbing is cheaper than usual, since the reaction generates carbon dioxide in a more concentrated form. Engineers are also experimenting with membranes that would allow hydrogen to pass, but not carbon dioxide.


There are four IGCC demonstration plants operating in America and Europe, although none currently captures carbon dioxide permanently; instead, it is simply released into the atmosphere. AEP’s planned new plants will follow a similar design.


George Bush is a believer, at any rate. In 2003 he unveiled a subsidised scheme to build a zeromissions IGCC plant called “FutureGen” by 2013. The European Union, for its part, is giving money to utilities dabbling in oxyuel, among other schemes. Handouts from the taxpayer are needed, power firms argue, since the technology in question is still young. But it is hard to believe that it will ever grow up unless subsidies give way to stronger measures, such as longerm caps or taxes on carbonioxide emissions. The technology to eliminate such emissions from coalired plants exists, but it will not be adopted without regulatory incentives from governments.


distribute［dis5tribju(:)t］


v.①分发，分配；②分布；③配（电）；④（over）散布


［真题例句］ For example, a grandmotherly woman staffing an animal rights booth at a recent street fair was distributing (①) a brochure that encouraged readers not to use anything that comes from or is tested in animals—no meat, no fur, no medicines.［2003年阅读2］


［例句精译］ 例如，在近期的一次集市上，一位老奶奶站在动物权利宣传点前散发小册子，规劝人们不要使用动物制品和动物实验制品——肉类，毛皮，药物。


utility［ju:5tiliti］


n.效用，有用


［真题例句］ Decisions based on utility as opposed to lack of utility are straightforward.［1996年翻译］


［例句精译］ 根据项目是否有效来做决策简单明了。


capture［5kAptFE］


n.捕获，俘虏；v.①吸引（注意）；②记录；③俘虏


［真题例句］ Few creations of big technology capture (v.①) the imagination like giant dams.［1998年阅读1］


［例句精译］ 重大科技创造中很少能像大型水坝这样让人痴迷的。


［真题例句］ While even the modestly educated sought an elevated tone when they put pen to paper before the 1960s, even the most well regarded writing since then has sought to capture (v.②) spoken English on the page.［2005年阅读4］


［例句精译］ 在60年代以前，甚至仅受过一般教育的人在下笔时都要寻求一种更高雅的腔调，但在那之后，即使是最受关注的文章也开始把口语用于写作。


absorb［Eb5sC:b］


v.①吸收；②吸收，使专心


eliminate［i5limineit］


v.消除


［真题例句］ If the products is in short supply relative to the demand, the price will be bid up and some consumers will be eliminated from the market.［1994年阅读1］


［例句精译］ 如果商品供不应求，价格就上升，有些消费者就会被排挤出市场。


由于世界石油和天然气价格居高不下，全球发电能源构成正出现重大转变，煤炭将重新成为新建电厂的首选燃料。当前世界发电燃料再度转为以煤为主决非偶然，而是由多种因素促成的。其中最重要的是清洁煤技术的研究发明，使煤炭利用更加环保、更为经济。这不仅是产业界的重大转变，更证明了科学技术对于世界能源利用的推进作用。


煤炭可能干净吗？


作为燃料，煤炭兼备多项优势。首先，它的储量丰富、分布广泛：缺乏其他化石燃料的国家，如德国和南非，却拥有堆积如山的煤炭。因此，煤炭的价格也很低廉。尽管煤炭的价格在过去几年里有所上浮，但燃煤发电站的运营成本仍低于几乎任何一种其他类型的发电站。


但煤炭也是种污浊不堪的燃料。它会随着燃烧释放大量煤烟和有害化学物质，因此许多西方国家已经不再钟情于它了。更糟的是，燃煤发电站的单位发电产生的二氧化碳量几乎是天然气发电站的两倍。


直接的解决之道是令燃煤发电变得更加清洁，而且这正是西方国家里的那些公用事业公司们多年来为达日渐苛刻的空气污染的标准所不断努力的方向。


然而，减少二氧化碳的排放量则需另辟蹊径。同大多数富国一样，英国燃煤发电站的平均燃烧效率在35%左右。但是三井巴布科克（Mitsui Babcock）能源有限公司（一家工程公司）宣称其最新设计的发电站可以将燃烧效率提升到46%。该公司预计新设计比起旧设计可以令燃料消耗和污染物排放减少23%。


许多方法均能减少燃煤发电站制造的各类排放物，所以这类燃煤发电站对环境的污染至少不会超出燃气发电站的水平。但是借由滤除烟道气体中的二氧化碳并将其储存起来从而令煤炭更加清洁的各类技术已然出世。虽理论可行，但代价高昂。另外，不同于提升燃烧效率的各种改进，给电站追加捕碳技术根本无利可图。结果，人们至今没有建造一座此类电站。


捕碳究竟如何进行呢？大多数公用事业公司都将目光聚焦在三种基本设计上。同其他污染物一样对待二氧化碳并将其从烟道气体中分离出来是改造现有发电站的设计中最简单易行的方案。许多企业已经采用这种“氨净化”途径，例如从天然气中去除二氧化碳。但是，该法还不适于大规模使用，因为用以吸收并加热后释放溶解的二氧化碳的氨溶液较昂贵。


“燃料增氧（Oxyuel）”电站则通过其他途径避开了将氧和氮从烟道气体中分离的难题，即用纯氧而非空气燃烧煤炭，产生的管道气体几乎仅仅是二氧化碳。但是燃烧前将氧气从空气中分离所需的能源几乎不亚于上述将氮气过滤所需的耗费，这就使得两者在效率损失上不相上下。


第三种途径称为“结合气化的综合循环途径（IGCC）”。该途径同样需要氧气，但这是作为化学反应之用而不是燃料。当煤炭在氧气中加热时经化学反应会形成二氧化碳和氢气。二氧化碳经氨溶液吸收，而氢气则送往改进型熔炉燃烧。如此，氨净化的成本将低于普通方法，因为之前化学反应产生的二氧化碳是高浓度的。工程师们也正在用允许氢气而不允许二氧化碳通过的半透膜做实验。在美国和欧洲，现有四座IGCC示范电站，尽管目前为止任何一家都无法将碳永久性地封存起来；相反，很容易释放而进入大气。AEP计划的新电站将采用类似的设计。


乔治·布什是一个忠实的信徒。2003年他公布了一项补贴计划用以建造一座零排放的IGCC电站，该电站名为“FutureGen”，该计划将历时十年。就其他方案而言，欧盟正在给予涉足燃料增氧的公用事业公司财力支持，这是方案中的一部分。电力公司们强调政府的宣传报道也是必须的，因为这种存在疏漏的技术还很不成熟。但是，很难相信没有强有力的措施，如制定长期减排目标或对二氧化碳排放征税等，而仅凭苍白无力的宣传就能够促使该技术不断成长和发展。除去燃煤电厂产生的排放物的技术已经出现，但是离开政府的监管和激励后将无人问津。