Technology
Energy: how best to use coal, other sources Economic constraints, effects on the environment, efficiency of methods of conversion all affect choice of future fuel economy A standard undergraduate chemical engineering problem used to be to make compound X starting with coal, water, salt, and air. It was always a test of the student's ingenuity to come up with a reasonable scheme, keeping in mind the appropriate economic constraints. The energy fraternity now faces a similar test of ingenuity but the stakes are much higher and the constraints are more demanding. Coal is the most abundant energy source available in the near future. But a consensus of the energy fraternity voiced last week in Chicago at the 69th annual meeting of the American Institute of Chemical Engineers seems to rule out direct combustion of coal as an energy source except in a few special cases. The optimum use of coal depends not only on economics, but also on such constraints as environmental pollution and the convertibility of coal to liquid and gaseous fuels and feedstocks. Two of the options considered at the AIChE meeting would be to convert coal to electricity or to secondary fuels. But, if coal is the fuel of the next generation, oil and gas still may be the key elements in deciding how coal will be used, largely because of their firmly entrenched position and existing distribution system. A protagonist for converting coal to synthetic fuel is R. Bruce Foster of the Institute of Gas Technology. Foster notes that if direct use of coal is chosen it will have to be in refined form. Environmental laws have relegated coal to the status of a raw material rather than a primary fuel. Because the use of stack gas cleanup is technically and economically undesirable, Foster says the environmental impetus is toward better means of combustion and in turn to upgraded coal. Some of the better means of combustion are fluid-bed combustion and combustion of solventrefined coal, coal emulsions, and slurries. These means are suitable for large installations, but there is less confidence that they can be applied to small ones, Foster says. In small installations, liquid or gaseous fuels are the only reasonable choices since they would permit the use of existing combustion equipment.
The biggest disadvantage in going the coal-to-synthetic-fuel route, Foster says, is the high cost of conversion facilities. However, this would be the only additional cost necessary since existing distribution and combustion equipment could be retained. At present, construction of coal conversion facilities is stalled by financial barriers. Foster says that only the existence of cheap natural gas prevents synthetic fuels from being offered as a relatively low-cost alternative to electricity. The cost of heat from coal, via synthetic gas, is less than the cost of heat from electricity, according to Foster. Even using the less efficient first-generation gasification processes, he estimates the cost of gas heat would be $4.29 per million Btu less than the same heat from electricity, a saving of about one third. If the second-generation processes now being piloted are considered, an additional 15% would be saved. However, because heat cannot provide all the energy, an appropriate thermal-electric mix would have to be designed. But economics, although important, are really a secondary consideration to Dr. J. L. Gaddy of the University of Missouri, Rolla. He notes that economics have dictated energy policies in the past, and the results have been good. However, with limited energy resources in the future he advocates energy policies based on maximizing the efficiency of the resource rather than the economics. This may be costly initially, he admits, but in the long run it will be best. The problem, of course, is determining which technical mix will maximize efficiency. Of all the possible forms of coal conversion, Gaddy sees the coal-to-electricity route as the most efficient use of the resource, with coal gasification and liquefaction being inherently wasteful. Petroleum, he claims, should be reserved for petrochemical feedstocks. The upshot is a plea for putting the national energy eggs in the electric basket. In either event, the ultimate coal reserves figure prominently in the plans of the energy fraternity. According to T. Reed Scollon of the Bureau of Mines, there were 219 billion tons of coal technically and economically recoverable as of Jan. 1,1974. That is a 300-year supply at the present rate of consumption and represents about 90% of identified U.S. fossil fuel reserves. The highest estimate of undiscovered reserves has been placed by the U.S. Geological Survey at about 4 trillion tons. As with oil reserves, these estimates are subject to much speculative interpretation, but there is no doubt that
Synthane process, currently being tested in this pilot plant near Pittsburgh, is one candidate for coal-to-fuel route more than 219 billion tons of reserves are there. With attention shifting to coal, however, natural gas may stage a comeback and further confound the energy picture. In an address to the Institute of Gas Technology's annual meeting in midNovember, U.S. Geological Survey director V. E. McKelvey noted that natural gas from offshore wells has increased in volume every year since 1955. Dr. McKelvey regards this situation as encouraging because only 4% of the offshore lands have been leased. Demonstrated offshore reserves are about 15% of onshore reserves, not an encouraging number for the long run. However, there are unused gas reserves available. The biggest problem is getting the gas to the consumer. He says that it typically takes from four to eight years between well completion and delivery of gas to a consumer. What may be the last gasp for U.S. natural gas production could come from Alaska, particularly the North Slope, which is projected to supply from 6 to 8% of the nation's requirements by 1985. That still will leave a shortfall of 1 trillion to 2 trillion cu ft. As is the case with offshore gas, the problem in using Alaskan gas is getting it to the consumer. Pipelines, either to the Gulf of Alaska for cryogenic transshipment, or across Canada, have yet to be built. If and when this gas does become available, it is expected to cost consumers from $2.50 to $2.75 per thousand cu ft in 1975 dollars. D Dec. 6, 1976C&EN
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