Energy and exergy analysis of hydrogen-oriented coal gasification with CO2 capture

Coal gasification is seen as an attractive way for hydrogen production. The main advantage of this approach is the low fuel price compared to reforming of natural gas. On the other hand, considering the EU climate policy, the emission of CO2 has to be reduced. The CO2 capture from the raw syngas should be thus considered. The main purpose of this work is to propose implementation of a fully “zero-emission” plant by introduction of biomass into the gasifier. The structure of the plant has been proposed and modeled. It is composed basically of gasifier, water gas shift reactors, acid gas removal units, pressure-swing adsorption process for hydrogen separation, combined cycle for power production and essential auxiliary components. The analyzed installation has been evaluated from the energy and exergy points of view by calculation of energy utilization factor and relative exergy losses occurring in main components of the system. Such an approach enables determination of the contribution of each component to the total system irreversibility. The results indicate that the highest exergy loss takes place in the gasifier. The overall exergy efficiency of the coal-to-hydrogen system is equal to ca. 57%, while the energy utilization factor is close to 65%.