Influence of AAEM species in coal and biomass on steam co-gasification of chars of blended coal and biomass

This study investigated effects of blending ratio and alkali and alkaline earth metallic (AAEM) species in the feedstock on char reactivity and producer gas composition in steam co-gasification of chars of blended coal and biomass. Experiments were conducted on a bench-scale fixed bed gasifier in which lignite was used as coal and radiata pine was used as biomass. The blending ratios of lignite to pine (L/P) were, respectively, 0:100 (pure pine), 20:80, 50:50, 80:20 and 100:0 (pure lignite). Lignite and radiata pine were first separately ground to fine particles which were then blended based on pre-set ratios. After this, the blends were pelletized and charred at 900 °C. In order to investigate the effect of AAEM in the coal, experiments were also performed using blended pine and acid-washed lignite from which most of AAEM species were effectively removed. The co-gasification operation temperature was 950 °C. From the experimental results, it was found that the ratios of H2/CO, H2/CO2 and CO/CO2 in the producer gas were nonlinearly related to L/P ratio in the lignite blended chars; however, these gaseous ratios were linearly correlated to the L/P ratio in co-gasification of acid-washed lignite blended chars. In addition, by removing the AAEM species in lignite, yields of H2 and CO2 were reduced while CO yield was increased. The char reactivity of acid-washed lignite and pine blends was decreased and this decrease became more significant with increase in coal to biomass blending ratio.