Feedstock choice Coal gasification

Biomass is similar to some coals with respect to total ash content as discussed in Chapter 3, but because of the diversity of biomass, several species and types have relatively low ash and also low sulfur contents. Woody biomass is one of the feedstocks of choice for thermal gasification processes. The ash contents are low compared to those of coal, and the sulfur contents are the lowest of almost all biomass species. Grasses and straws are relatively high in ash content compared to most other terrestrial biomass, and when used as feedstocks for thermal conversion systems, such biomass has been found to cause a few fouling problems. 

The most important factor for the choice of process layout is, of course, the type of feedstock. Before the Second World War coke dominated (see Sect. 6.3.6). During the war several plants based on natural gas were constructed in the USA [522], and natural gas has since then been the preferred feedstock in the USA as well as in other parts of the world. There has, however, also been a significant production based on partial oxidation of heavy fuel oil or gasification of coal, especially in Europe and in countries like India and China also naphtha has been a preferred feedstock in some areas. During the 1970s there was, due to the oil crises, a renewed interest, especially in the USA, in coal as feedstock for ammonia production, but an expected major change to coal-based production of ammonia did not materialize. Comparisons of the economics of ammonia production from different feedstocks may be found in [160, 676-691]. 

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