Chapters authored
Minimising CO2 Emissions from Coal Gasification
Traditional coal-to-liquid processes use gasification with excess steam to obtain hydrogen-rich syngas for downstream manufacturing of methanol or Fischer-Tropsch liquids. Such processes are shown to produce very large amounts of CO2 directly by the Water-Gas-Shift (WGS) reaction or, indirectly, by combustion in raising steam. It is shown how any coal gasifier can operate under auto-thermal conditions with methane as source of hydrogen instead of steam. This co-gasification system produces syngas for a poly-generation facility while minimising the formation of process CO2. It is shown that minimal steam is required for the process and a limit on the maximum amount of H2:CO can be obtained. Co-gasification of coal is shown to have a major advantage in that a separate WGS reactor is not required, less CO2 is formed and methane is reformed non-catalytically within the gasification unit. Furthermore, regions of thermally balanced operations were identified that enabled a targeting approach for the design of co-gasification systems. The method will guide gasification practitioners to incorporate fossil fuels and renewable-H2 into coal-to-liquids processes that require syngas with H2:CO ratio of 2. An important result shows that low-grade coals can be co-gasified with methane to obtain CO2-free syngas ideal for power generation.
Part of the book: Clean Energy Technologies