keywords: Coal bottom ash; Treatment; Gasification; Palm kernel shell; TGA
Utilization of coal bottom ash (CBA) as catalyst in biomass gasification is an effective and promising route that will provide alternative ways for utilizing the waste and reducing the cost of gasification process. This study optimised the leaching of CBA in water and performed gasification of palm kernel shell with the treated waste. Response surface methodology (RSM) of central composite design (CDD) was used to design the leaching experiment and to vary the ratio of volume of water to mass of CBA (L/s ratio), leaching time and temperature. This was applied to determine the influence of the parameters on the physicochemical properties of the ash and the yield of CH4 and CO2 in steam gasification of palm kernel shell in a thermogravimetric analyser setup incorporated with mass spectrometer and a steam generator (TG-MS). Field Emission Scanning Microscopy/Energy Dispersive X-ray (FESEM-EDX) micrograph of the ash samples show that the pore of the treated ash are clearer and free of debris which may clog the pores and cause fusion and agglomeration easily. Chemical analysis from Energy Dispersive X-ray (EDX) spectra indicated a fall in carbon content (38.76 to 20.60 wt%) and a rise in Fe, Ca, and Al increased from 6.78 to 10.63 wt%, 6.92 to 15.03 wt% and 2.37 to 5.21 wt%, respectively. The increase in metal content increased the catalytic potential of the treated ash. Response surface 3D plots were used to analyse the results. The yields of CH4 and CO2 in the gasification process carried out in a thermogravimetric analyser attached to a mass spectrometer and a steam generation setup are as low as 27.5 and 0.94 vol% with an optimum of of 29.65 ± 0.06 and 1.02 ± 0.01 vol%, respectively. Syngas yield at optimum condition is 69.35 ± 0.05 vol%. This was obtained using L/s ratio 3, 10 hours leaching time and 56°C temperature as optimized CBA leaching parameters. The most influential variables on CH4 and CO2 yields as indicated are L/s ratio and temperature, respectively. Result of the study shows that water-leached CBA can be used effectively in gasification and it reduces the yield of CH4 and CO2 thus potentially increasing syngas (H2 and CO).