经济学人_英文阅读_009

Natural gas Difference Engine Fuel for the future May 27th 2013 21 13 by N V LOS ANGELES Tweet AMERICA S unexpected and most welcome bonanza of natural gas from its vast shale deposits seems to be doing as much to reduce pollution as many of the efforts introduced over the years to restrict emissions from vehicles power stations and other sources The biggest breakthrough the energy industry has seen in decades hydraulic fracturing fracking combined with horizontal drilling has released unprecedented quantities of gas from this shale As a consequence the spot price of domestically produced natural gas has tumbled from a high of over 12 per million British Thermal Units in 2008 to less than 2 in 2012 before settling at around 4 today a million BTUs is roughly equivalent to a gigajoule of energy Increasing use of this cheap clean gas means power stations across the country have reduced their carbon dioxide emissions to levels not seen since 1992 despite serving a population that has grown by almost a quarter since then On a per capita basis carbon dioxide emissions from power stations are now at their lowest since President Eisenhower left office in 1961 This is because when purged of impurities natural gas which is more or less pure methane is the cleanest fossil fuel around It produces 30 less carbon dioxide per unit of heat than petrol does and 45 less than coal Conventional coal fired power stations churn out 900kg 1 980 pounds of the gas for every megawatt hour of electricity they generate Natural gas plants emit little more than half that amount Given such remarkably cheap natural gas the outlook for coal is dire On average coal fired power stations still produce the cheapest electricity And between them they still account for 37 of the electricity generated in America compared with 30 from natural gas 19 from uranium 7 from hydro 5 from renewables and 1 from oil But coal fired stations with their belching smokestacks are notorious polluters and face tough new air quality standards that will render many older ones uneconomic At present natural gas plants have lower operating costs than only 9 of coal fired stations But the tougher emission standards proposed by the Environmental Protection Agency EPA will make natural gas plants as economically attractive as 65 of existing coal fired stations according to researchers at Duke University in Durham North Carolina The EPA s more stringent standards include lower emissions of nitrogen oxides sulphur dioxide soot and mercury At present natural gas plants produce only one class of emission nitrogen oxides that exceeds the new EPA thresholds Many coal fired plants exceed all the proposed thresholds says Lincoln Pratson leader of the study team at Duke That will make it more expensive prohibitively so in many cases for them to comply Industry has got the message A year ago Southern Company of Atlanta Georgia long one of America s biggest operators of coal fired power stations generated more electricity from natural gas than it did from coal In 2010 power plant owners across America announced plans to retire over 40 gigawatts roughly 12 of their coal fired capacity in favour of natural gas As the transition to gas gathers pace the need for a more comprehensive network of pipelines and storage facilities has become apparent Such infrastructure would also assist a second and in some ways more radical shift in the way gas is used For it may be the future of road transport too American commercial vehicles already use a lot of natural gas For several decades now local delivery vans buses and rubbish collectors which rarely stray far from their refuelling stations and operate mainly within towns have been switching to compressed natural gas CNG to lower fuel costs and to minimise their impact on the environment Long distance hauliers would do likewise if there were more highway filling stations with CNG pumps All of which is encouraging for natural gas producers But for real change to happen private motorists will have to follow suit They might be tempted At an equivalent in energy terms of around 2 20 a US gallon CNG costs a little over half what Americans pay for petrol But making the change is not easy First only one car model designed to run on CNG the Honda Civic GX is currently available in America And it is not cheap The basic model costs 26 300 compared with 18 200 for a comparable petrol engined Civic The two models have similar fuel economy 31 32 mpg ie 7 6 7 4 litres 100km on the combined city highway cycle but the GX is nowhere near as spritely as its petrol powered twin Second enthusiasts wishing to retrofit existing vehicles to burn the stuff face enormous hurdles Kits to do so cost anything from 12 000 to 18 000 and have to be installed by a licensed technician That is because it is illegal in America for private individuals to tamper with a vehicle s emission system which is what has to be done to enable a petrol or a diesel engine to run on natural gas Third it is not just the up front cost that puts many motorists off CNG The paucity of filling stations is an even bigger deterrent America has around 600 natural gas stations open to the public compared with 118 000 petrol stations The Honda GX s pressurised natural gas tank holding the energy equivalent of an eight gallon petrol tank is good for about 240 miles 380km Trips out of town have therefore to be planned strategically via CNG filling stations spaced few and far between This third objection could be overcome if CNG vehicles were hybrids able to run on petrol as well as natural gas That is one of the goals of America s Natural Gas Alliance ANGA a trade group in Washington DC ANGA has had popular models from half a dozen manufacturers including BMW Ford Chrysler and General Motors retrofitted to run on both fuels A number of these bi fuel demonstrators were previewed at a Southern California Gas facility in Los Angeles on May 21st To drum up further in