MULTI-CHANNEL EVALUATION OF CO{sub}2 MITIGATION TECHNOLOGIES

摘要

The overall objective of the present study is to compare and evaluate various measures for global warming problem, especially carbon dioxide problem, classified as follows. a) Primary energy: changes from fossil fuel resources to renewable or nuclear energies and from higher carbon content fossil fuels to lower ones. b) Secondary energy system: energy conservation, material and energy recycling, change in life style, and improvement in efficiencies of energy use. c) CO{sub}2 from other than energy. d) CO{sub}2 recovery and storage: separation system, ocean disposal, subterranean storage, and biological and chemical fixation. e) CO{sub}2 absorption from atmosphere: afforestation, rock weathering, and ocean absorption. f) Policy and economic options: carbon, energy and environmental taxes, emissions market, etc. First of all, various organic chemical and biological processes so far proposed were evaluated as total systems. It was clarified that these systems with energy use (usually, the energy is solar, which can be used as other primary energy source instead) should be evaluated from the energy point of view as primary and secondary energy systems; i.e. they should be classified into the categories of a) and b). On the other hand, the measures in category d) are to be evaluated as those of carbon fixation processes, because they essentially require no artificial energy. Secondly, the various measures as above were classified into two categories; regrettable and no-regrettable. In the course of the present evaluation, we should take resources problems and other environmental problems into account. The measures which give positive effects on the resources and/or other environmental problems are classified into non-regrettable measures: those that will not be regretted if global warming does not in the end take place, or if its effect is minimal. For example, the measure of change from coal to natural gas or nuclear fuel is classified into regrettable one from the viewpoints of resources, because the amount of natural gas or uranium resources is much less than that of coal. On the other hand, the measure of the afforestation is classified into no-regrettable one from the viewpoint of environment, though small amount of additional energy should be input. Other evaluation factors are their scale and stability. The larger scale or capacity of the measure is of course preferable. In addition, the measures with large ratio of CO{sub}2 reduction to input energy are regarded as stable and reliable ones. It is obvious that no-regrettable measures with larger capacity and reliability should be undertaken, as early as possible, however, most of these measures have their own difficulties, from technological, economical, and/or international points of view. The evaluation from these points of view was also conducted in the present study. Various policy and economic options have also been proposed. However, we should consider the effects of these options on the energy utilization system. For example, when a kind of carbon tax is introduced, the regrettable measure of the change from coal to natural gas or nuclear fuel will be proceeded. The energy tax will not cause the problem, however, the introduction of renewable energy will not be enhanced by the tax. Some additional options such as subsidy should be introduced together with the energy tax. Taking these conditions into account, a tax to all virgin resources is thought to be most suitable, though critical evaluation of amount of resources is essential. Furthermore, to make the taxation fair among domestic and imported goods, accumulation of LCI (life cycle inventory) data is essential.