Use of Low-Volatile Solid Fuels in a 100 kW Chemical-Looping Combustor

Abstract

Carbon capture and storage (CCS) can be used to mitigate climate change. Chemical-looping combustion (CLC) is an innovative carbon-capture technology with potential to drastically reduce the capture cost. In CLC, oxygen is transported from combustion air to fuel by means of metal-oxide particles, called oxygen carrier. This work presents findings from a 100 kW CLC reactor system, which is designed as interconnected fluidized beds. The 100 kW unit was operated with ilmenite as the oxygen carrier. Swedish wood char and Mexican petcoke, both having low volatile content, were used as fuel. High gas conversion was achieved with both fuels. The carbon capture efficiency was high with wood char, but not as high with petcoke. The duration of operation was 34.5 h with fuel, of which the majority, 31 h, was achieved with wood char. Oxygen demand was strongly correlated with the solids inventory in the fuel reactor, as has been observed in previous works. Using wood char as fuel, gas conversion was 90–95.3%, except during high fuel power, and carbon capture efficiency was 93–97%, except during high fuel power. The gas conversion should be compared to what has previously been observed in the 100 kW unit, where the highest gas conversion was 84%, using a bituminous coal. Furthermore, comparatively high solid fuel conversion was seen in many tests with wood char—the highest value was 89%. Using petcoke as fuel, high gas conversion was achieved even when employing very high fuel power, 148 kW. The highest gas conversion for petcoke was 89%. The carbon capture efficiency was, however, much lower than what has been observed with pulverized coal and wood char. In summary, this study shows that important improvements can be achieved regarding gas conversion in the 100 kW unit by using low-volatile fuels.