<P> Today, national and state legislation require refineries to meet stringent air and water cleanliness standards . In fact, oil companies in the U.S. perceive obtaining a permit to build a modern refinery to be so difficult and costly that no new refineries were built (though many have been expanded) in the U.S. from 1976 until 2014, when the small Dakota Prairie Refinery in North Dakota began operation . More than half the refineries that existed in 1981 are now closed due to low utilization rates and accelerating mergers . As a result of these closures total US refinery capacity fell between 1981 and 1995, though the operating capacity stayed fairly constant in that time period at around 15,000,000 barrels per day (2,400,000 m / d). Increases in facility size and improvements in efficiencies have offset much of the lost physical capacity of the industry . In 1982 (the earliest data provided), the United States operated 301 refineries with a combined capacity of 17.9 million barrels (2,850,000 m) of crude oil each calendar day . In 2010, there were 149 operable U.S. refineries with a combined capacity of 17.6 million barrels (2,800,000 m) per calendar day . By 2014 the number of refinery had reduced to 140 but the total capacity increased to 18.02 million barrels (2,865,000 m) per calendar day . Indeed, in order to reduce operating costs and depreciation, refining is operated in less sites but of bigger capacity . </P> <P> In 2009 through 2010, as revenue streams in the oil business dried up and profitability of oil refineries fell due to lower demand for product and high reserves of supply preceding the economic recession, oil companies began to close or sell the less profitable refineries . </P> <P> Raw or unprocessed crude oil is not generally useful in industrial applications, although "light, sweet" (low viscosity, low sulfur) crude oil has been used directly as a burner fuel to produce steam for the propulsion of seagoing vessels . The lighter elements, however, form explosive vapors in the fuel tanks and are therefore hazardous, especially in warships . Instead, the hundreds of different hydrocarbon molecules in crude oil are separated in a refinery into components which can be used as fuels, lubricants, and as feedstocks in petrochemical processes that manufacture such products as plastics, detergents, solvents, elastomers and fibers such as nylon and polyesters . </P> <P> Petroleum fossil fuels are burned in internal combustion engines to provide power for ships, automobiles, aircraft engines, lawn mowers, dirt bikes, and other machines . Different boiling points allow the hydrocarbons to be separated by distillation . Since the lighter liquid products are in great demand for use in internal combustion engines, a modern refinery will convert heavy hydrocarbons and lighter gaseous elements into these higher value products . </P>

Why does crude oil need to be refined
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