This paper presents simulation results of air-blown coal gasification-based combined cycles when using low-rank coals, by means of a previously realized thermodynamic model. In detail, besides considering a sub-bituminous coal, attention is also paid to a brown coal, pre-dried to reduce its high moisture content.
When gasifying a sub-bituminous as received coal the results highlight a slight reduction in IGCC LHV efficiency, with an absolute difference less than 1 percentage point if compared to the case with bituminous coal. This result is accomplished with an increase in net power output (almost 8 percentage points).
As concerns the brown coal, a pre-drying before gasification is considered because of its significant moisture content (65 wt%). In particular, three cases with different pre-drying levels are analyzed, with the highest residual moisture content limited to 30 wt%. Even considering an energy-saving technology as the fluidized bed dryer with integrated waste heat recovery, the specific demand for coal drying amounts to 2.1–2.3 percentage points referred to the (pre-dried) coal thermal input, seriously affecting both the final IGCC efficiency and its power output in comparison with the case of bituminous coal. Higher residual moisture in coal leads to lower IGCC efficiency, whereas the net power is always less than the one delivered by the plant with the sub-bituminous coal. However, comparing the cases with sub-bituminous coal and brown coal with the minimum moisture content (10 wt%), LHV and HHV efficiencies present opposite trends, since HHV efficiency for the case with brown coal is even better than with sub-bituminous coal.