Production of hydrogen-rich syngas from steam gasification of blend of biosolids and wood using a dual fluidised bed gasifier

A study was undertaken on steam gasification of mixtures of wood pellets and biosolids (dried sewage sludge). The gasification experiments were conducted in a fast circulating dual fluidised bed gasifier. In the experiments, the gasification temperature was set at 720 °C and the fuel feeding rate to the gasifier was 15.5 kg/h (as received). The biosolids was blended with wood pellets, with biosolids to wood pellet mass proportion being controlled at 0% (or 100% wood pellets), 10%, 20%, 40%, 60%, 80% and 100%. From the results, the syngas produced from the biosolids had higher H2 content (28%) compared with that from pure wood (23%), with the H2 content increasing with biosolids fuel loadings. In addition, the ratio of H2/CO increased from 0.6 to 0.9 as the biosolids loading increasing from 0% to 100%. However, the syngas yield and the cold gas efficiency of the gasification decreased dramatically by 53% and 43%, respectively, at 100% biosolids loading compared with 100% pure wood loading. Nevertheless, the increase from 10% to 20% loading of biosolids in the fuel did not diminish the yields and the cold gas efficiency. For gasification of pure biosolids, the gas concentrations of H2 and CO in this study were found to be 40% higher than that produced by other researchers using air, O2 or CO2/N2 as the gasification agent.