Evaluation of a Coal Gasification Process towards Hydrogen Production: An integrated assessment

This paper explores the (energetic and exergetic) thermodynamic efficiency as well as the environmental sustainability (mass flow accounting and emergy accounting) of syngas production from several types of coal (lignite, anthracite, bituminous and sub-bituminous coals). Syngas production is an intermediate step towards hydrogen production, accomplished by means of CO2 sequestration and trace element removal. The basic model investigated in this work is the Koppers-Totzek gasification process, the performance of which is assessed by means of selected literature data. The task is performed by means of an in-house developed software, adjusted to match the specificity of the investigation, according to the environmental quality requirements issued by the International Standardization Office (norms ISO 14040/1997 to ISO 14043/2000). A set of efficiency and environmental sustainability indicators for each kind of coal used is calculated, in order to provide useful operational suggestions for further research and policy. A comparison with hydrogen production by steam reforming of natural gas and alkaline water electrolysis is also performed. The results have shown a relative independence of the efficiencies on the kind of feedstock coal used, whereas the two environmental indicators exhibit opposite but equally marked trends, the meaning of which is discussed in the paper. Calculated transformities for syngas range from 4.0E+04 to 7.5E+04, depending on the type of feedstock.