Co-pyrolysis of sewage sludge and sawdust: Synergistic effects of product yield and synthetic gas calorific value

Abstract

Co-pyrolysis of sludge and sawdust, which are two renewable and abundant biomass resources, offers a promising environmental-friendly way to produce valuable energy products. In this study, the synergistic effect between sludge and sawdust was quantified by fixed bed reactor and thermogravimetric experiments. The product yield and product quality were also studied. The results showed that both temperature and sawdust addition significantly affected the distribution of co-pyrolysis products. Biochar yield decreased with increasing temperature, with the highest yield at 700 °C. With the addition of sawdust, the yield of biochar first increased and then decreased. The highest biochar yield was 58.1 wt% after adding 10 wt% sawdust. The yield of bio-oil initially decreases and then increases with temperature. With the addition of sawdust, the yield of bio-oil first decreased and then increased. The process condition of a temperature of 700 °C–800 °C and a sawdust addition ratio of less than 30 wt% is more favorable for the production of bio-oil. Increasing temperature and the addition of sawdust boosteded syngas production and calorific value. When the sawdust ratio was 10 wt%, it exhibited the most pronounced influence on gas yield and demonstrated less susceptibility to temperature variations. The most obvious increase in the calorific value of syngas was observed at 700 °C and 10 wt% sawdust ratio. Taking into account the product yield and product quality, the optimum conditions for co-pyrolysis were determined to be 750 °C and a sawdust ratio of 10 wt%.