Due to limited reserves of crude oil and natural gas, it is generally accepted that fuel prices will continue to rise. Associated with cost increase is a strong possibility that quality of petroleum distillate fuels will deteriorate, particularly for power generation. Several techniques are available or are being developed to produce fuels from non-petroleum sources, including liquids and gases from coal and vegetation. Liquid fuels will fall into two categories: a synthetic distillate with lower hydrogen content and a significant amount of fuel-bound nitrogen unless further hydrogenation is carried out; and light alcohol fuels with lower calorific values than present distillates. Gases produced will vary considerably dependent on the process and original material, but a common factor will be medium to low calorific values in terms of Btu/scf and a tendency to have high inert gas content. The efficiency of energy conversion of various materials is higher when gas is produced (70–85%) than liquid (40–65%). The efficiency of conversion being the ratio of the available energy from the products to the input energy of the feed.

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