Historical shifts of the four main energy resources-from wood, to coal, to petroleum, and to natural gas-have been investigated from the viewpoints of technology, energy efficiency and environment. It is concluded that the driving force for the energy shifts is desire of human beings to get resources with higher thermal value, or higher hydrogen content, and that technology is a tool or measure-rather than restriction-by which human beings pursue that desire. Having the highest hydrogen to carbon ratio and the lowest carbon to hydrogen ratio, natural gas is stated as the ultimate energy resources, both in terms of energy efficiency and in the environmental issues.
The role of natural gas in the 21st century has been examined from four viewpoints: resources and reserves, global warming, energy efficiency, and transportation and delivery. It is concluded that the ultimate recoverable reserves of natural gas will probably be increased and meet the world demand for energy in the next century. The effects of natural gas in reducing CO
2 are stressed together with the importance of carbon sequestration to stabilize the emission of global warming gases. The efficiency, present state and future outlook are demonstrated by various gas utilizing technologies, such as cascade use of energy in combined cycle power generation and co-generation, natural gas vehicles, fuel cells, and combination technology with other types of energy. The importance of constructing world gas supply networks is emphasized in order that as many people as possible can enjoy the merits of natural gas.
It is proposed that hydrogen will be an ideal and ultimate energy in the
22
nd century and beyond, providing the highest energy efficiency and absolutely no environmental damage, and that natural gas, which has the lowest CO
2 emission, is a reasonable bridge to it as the most economic source, reservoir and carrier of hydrogen.
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