Performance and exergy analysis of the current developments in coal gasification technology

The present paper addresses the recent developments in coal gasification regarding the commercial Shell, Siemens, GE, ConocoPhillips (CoP), and HTW systems. Based on literature verification data, generic thermodynamic models were developed for the state-of-the-art systems integrating deviations from equilibrium. After extension of the models to the proposed new concepts, uniform boundary conditions were introduced processing bituminous Pittsburgh#8 coal and a South African coal with an elevated ash content (25 wt.%(wf)). Subsequently, an evaluation of the state-of-the-art gasification processes in comparison to new concepts was carried out in terms of cold gas efficiency, syngas yield and exergetic efficiency. The results are illustrated in ternary gasification diagrams for each coal which reveal the existence of clear maxima for cold gas efficiency between 965 and 980 °C and for syngas yield at 1135 and 1178 °C. The graphical approach leads to the conclusion that the proposed concepts of the internal circulation fluid-bed gasifier (INCI) and the entrained slagging transport reactor (E-STR) show the potential to operate close to the identified maxima especially for high-ash coal. In the exergy analysis, the influence of the different gas cooling techniques was assessed before investigation of the overall systems. Amongst the traditional systems, CoP (79.2%) and Shell (78.9%) exhibit the highest exergetic efficiencies for Pittsburgh#8 coal while Siemens (76.8%) offers the highest efficiency for the South African coal. The new concepts of GE, ConocoPhillips and INCI have the potential to exceed 80% exergetic efficiency for Pittburgh#8 coal. In case of the ash-rich South African coal, only the INCI fluid-bed approach holds the potential to exceed 80% significantly.