Methanol synthesis from flue-gas CO_2 and renewable electricity: a feasibility study

摘要

The twin requirements of reducing CO_2 emission levels and increasing the level of penetration of renewable energy will involve innovative technical and operational solutions. This paper describes a novel but proven process (CO_2 + 3 H_2 → CH_3OH + H_2O) which could be adapted to use, as input reagents, CO_2 emitted from fossil-fuelled power stations and hydrogen from electrolysis of water by a zero-emissions electricity source, e.g. renewable and/or nuclear energy. This approach, in addition to addressing the above two issues, would produce methanol for which there is a ready and expanding market. A preliminary analysis is presented of the process economics and operational regimes necessary in the UK Electrical Supply Industry to accommodate the methanol plant. Four different designs are assessed, all based on a supply of renewable energy limited to 16 h/day when demand is off-peak. Option 'A' relies on a variable 100―500 MW supply, whereas Option 'B' makes use of a steady 100 MW during the availability period. Option 'C' is identical to 'B', except for the use of pressurised electrolysers at 30 bar instead of conventional ones. Option 'D' departs from 'B' with the use of hydrogen-powered fuel cells for power generation during the period of no availability. In the absence of a market for the electrolytic oxygen, Option 'B' is found to be the most economical, and it should be profitable if a favourable taxation regime applies on zero-emission automotive fuels. However, if the oxygen can be sold to a local industry via pipeline, Option 'C' could be potentially viable, even in the absence of tax breaks. It is claimed that significant benefits might accrue from successful development of a methanol process and that it may ease the absorption of increasing levels of embedded generation into the electricity supply network.