Catalytic effect of alkali metal in biomass ash on the gasification of coal char in CO2

Biomass ash rich in alkali metals has been proven as a natural and disposable catalyst for the thermal conversion of carbon-containing materials. The application of biomass ash as a catalyst for coal gasification shows an economic and promising scenario. The effects of addition ratio of biomass ash, alkali metal compounds in biomass ash and mineral matter in the coal on anthracite char gasification were studied with a thermogravimetric analyzer under CO2 atmosphere. The chemical fractionation method was used to prepare three kinds of biomass ash with different alkali metals containing chemicals. The morphology and elemental composition of solid samples were analyzed with a scanning electron microscope coupled with an energy-dispersive X-ray spectrometer. The achieved results revealed that the gasification conversion of anthracite char increased with the addition of biomass ash. However, it was also observed that 50% biomass ash addition resulted in the agglomeration of the co-gasification ash. The majority of the catalytic effect of alkalis in biomass ash was attributed to the H2O-soluble forms of alkali metal containing chemicals. Co-gasification of demineralized coal char and biomass ash showed that the catalytic activity of 2.5% biomass ash addition to demineralized coal char is similar to the 30% biomass ash addition to coal char. The mineral matter in the coal was observed to decrease the catalytic activity of the biomass ash. The catalytic mechanism of biomass ash on coal char gasification was elucidated.