The contribution of thermochemical biomass conversion to the greenhouse effect

The objective is to convert or upgrade the biomass into a more useful and hence more valuable energy product which, in turn, can be converted into an even more valuable end-product such as electricity or a motor fuel, and in all cases the carboniferous energy products are eventually converted into carbon dioxide in order to release the maximum amount of energy. The main thermochemical processes are outlined by reference to the operational parameters and products. Two examples of utilization of biomass are used to show how carbon dioxide emissions vary with technology - transport fuels and electricity generation. A system may be selected as optimised using the ultimate product or effect for comparison with gross or net carbon dioxide emission/absorption and minimum cost of this change in carbon dioxide as the criteria. It is claimed that the use of biomass is carbon dioxide neutral, and even that new biomass resulting from use absorbs carbon dioxide at a greater rate than the old biomass that is consumed. On this basis it is shown that the least efficient overall biomass conversion process is the most effective at reducing carbon dioxide levels. Further, it is shown that the most economically effective way of reducing carbon dioxide levels is that of the lowest cost to efficiency-of-conversion ratio. For transport fuels methanol is the clear choice for both criteria while for electricity generation, air gasification with integrated combined cycles is preferred for short to medium term opportunities. 2 refs., 3 figs., 6 tabs