The influence of calcite loading on producer gas composition and tar concentration of radiata pine pellets in a dual fluidised bed steam gasifier

This study has investigated the influence of calcite loading on the producer gas composition and the tar concentrations on a 100 kWth dual fluidised bed (DFB) steam gasifier. In the experiments, wood pellets of radiata pine were used as the feedstock and the operating temperature in the bubbling fluidised bed reactor (BFB) was set at 710–750 °C while that in the fast fluidised bed reactor (FFB) was controlled at 800 °C. In the first part of the experiments, the calcite loading was varied at 0%, 50% and 100% at constant steam to biomass (S/B) ratio of 0.8 kg/kgdry. In the second part of the experiment, the influence of S/B ratio was examined at 50% and 100% calcite loadings. The present study has concluded that the ratio of H2/CO can be varied from 0.9 to 4.2 by increasing the calcite loading and the S/B ratio only at 100% calcite loading. In addition, the total tar concentration decreased exponentially from 5.0 to 0.7 g/Nm3 with the calcite loading. This method provides the flexibility to meet the required H2/CO in target downstream applications. However, the disadvantage of increasing calcite loading was that the attrition rate increased exponentially from 0.5% at 0% loading to 4.1 kg/h at 100% loading. The tar reduction from 0% to 50% calcite loading was found to be higher than that from 50% to 100% calcite loading. This could be mainly due to the suppressing effect of high partial pressure of H2 on the steam reforming of those tar compounds.