摘要
China depends for most of its energy on coal – a situation that is likely to persist in the light of the abundance of its coal resources, the paucity of its oil and gas resources, and the reluctance of the government to allow China to become overly dependent on energy imports. The challenge is to find ways to use coal without the enormous air pollution damage caused by current conversion technologies and with greatly reduced carbon dioxide (CO2) emissions. A coal energy system for China is proposed that could ultimately be characterized by near-zero emissions of both air pollutants and greenhouse gases.The key enabling technology is oxygen-blown (O2–blown) gasification to generate synthesis gas from coal. This technology is used in commercially ready integrated gasification combined-cycle power plants that can provide electricity with air pollutant emissions as low as emission levels for natural gas combined-cycle plants. O2-blown gasification is not yet used in China's energy sector, although the technology is well-established in China's chemical process industry.The key enabling strategy, which would often lead to attractive energy costs without further technological advances, is “polygeneration” – the co-production from synthesis gas of at least electricity and one or more clean synthetic fuels (e.g., dimethyl ether (DME), Fischer-Tropsch (F-T) liquids, hydrogen (H2)) and often also chemicals, town gas, and/or industrial process heat. The products of polygeneration could be used in the near term to serve a wide range of energy needs with extremely low levels of air pollutant emissions.In such polygeneration configurations CO2 can often be produced in relatively pure streams as a co-product as a result of processing to increase the synthetic fuel's hydrogen-to-carbon ratio. In the near term this CO2 might be used profitably for enhanced oil recovery or enhanced recovery of methane from deep beds of unminable coal where resource recovery opportunities exist.For the longer term the potential exists for evolving the coal energy system to the co-production primarily of electricity and H2 for serving urban areas, with most of the carbon in the coal ending up as CO2 that is sequestered in geological reservoirs such as in depleted oil and natural gas fields and deep saline aquifers at low incremental cost – even where there are no opportunities for using the CO2 for enhanced resource recovery. The H2 so produced would be used for fueling zero-polluting fuel-cell vehicles, for distributed cogeneration (combined heat and power) applications in stationary fuel cells, and for cooking and heating applications as well.A third clean carbon-based synthetic fuel might also be needed for serving rural markets that would be difficult to serve with H2, unless there are breakthroughs in H2 storage technology. DME is a strong candidate for becoming the “third” clean energy carrier for China.Evolving a coal-based energy system that would be characterized ultimately by near-zero emissions of air pollutants and greenhouse gases would probably involve shifting the center of gravity for central-station power generation to the chemical process industries that would ultimately be co-producing as their major products electricity, H2, and (perhaps) DME. Ongoing structural reforms in the electric power sector that encourage greater competition in power generation would facilitate the realization of this vision for coal.