Coal : energy for the future

Coal is by far the largest fossil fuel resource in the U.S. with known reserves adequate to meet expected demand without major increases in production cost well beyond the year 2010. In contrast, domestic natural gas, its principal fossil fuel competitor for power generation, is a more limited resource and increases in production cost and decreased availability are projected to occur after the year 2000, thus weakening its ability to compete with coal for power generation in the U.S. Renewable and nuclear energy sources are not expected to displace coal to a major extent during the 1995–2040 time period considered here. For manufacture of liquid and gaseous fuels, coal is projected to become competitive with other resources (petroleum, oil shale and bitumen) in the 2021–2040 time period. Increasingly strict requirements for environmental management of coal-generated waste streams are also anticipated with a growing incentive to reduce CO2 production through increased efficiency. This planning model imposes demanding requirements for conversion of coal to electricity and to clean gaseous and liquid fuels and, thus, for a strategic program of research, development and commercialization to most efficiently utilize coal resources in the 21st century. This review is based on an assessment of DOE's coal research, development, demonstration and commercialization programs for the time period 1995–2040. This assessment was conducted under the auspices of the National Research Council, in response to a request from the Acting Assistant Secretary for Fossil Energy. For the above time period, electric power generation is expected to dominate the use of coal, although a growing production of merchant medium Btu gas and liquid transportation fuels is anticipated during the period 2021–2040. The current DOE coal program emphasizes activities through 2010 and is focused almost exclusively on power generation technologies with small programs on other uses. Funding for many of the latter programs has been reduced significantly in recent years. The present study, with its longer time horizon, proposes an increasing emphasis on clean fuels research and on advanced research that addresses the barriers to higher efficiency in both power generation and fuels production to reduce CO2 emissions. Improvements will also be needed in control of air pollutants and the discharge of solid wastes. The power generation program addresses both near term goals that do not offer significantly higher efficiency, and also more ambitious goals based on combined cycles utilizing high performance gas turbines or fuel cells to potentially provide a 10–15 point increase in efficiency. These increases in efficiency will require extensive RD high temperature air/furnace heat exchanger for indirect fixed systems; hot gas cleanup system for PFBC and for gasification-based systems; high temperature turbine blades compatible with trace impurities that may escape the high temperature gas cleanup system; and high thermal efficiency gasification. Solution of these challenging problems will require a continued program of advanced research and component development. The choice of winners from the large array of technologies will also require augmented use of systems studies and development of realistic commercialization strategies. As natural gas prices rise, production of cleaned coal-based medium Btu gas for use in existing natural gas fueled-combined cycles and for industrial heat becomes economic and could relieve the pressure on the supply of natural gas for other uses. Conversion of this coal-based medium Btu gas to methane (SNG) might follow towards the end of the 2021–2040 time period. For this use, high efficiency oxygen blown-cold gas clean up gasification is needed. At present, however, the DOE gasification program is concentrated on air blown processes specifically aimed at integration with power generation. Production of medium Btu (synthesis gas) will allow concurrent production of hydrogen or Fischer-Tropsch liquids. The use of simplified once through processes with production of electric power from unconverted feed and low value products (such as methane) could bring costs of premium liquid fuels to a level competitive with 25–30 $/bbl imported crude oil (DOE financing basis). Current projections indicated that the price of imported crude oil could be in this range in the 2021–2050 time frame. Direct liquefaction costs, with continued R&D, are believed to be approximately the same as indirect liquefaction, but with 5–10% higher efficiency and correspondingly less production of CO2. Given the long-term nature of opportunities for production of coal-derived gaseous and liquid fuels, DOE has a special role to play in supporting technology development aimed at cost reduction and efficiency improvement for these potentially important uses of coal.