Equilibrium Modeling of Sorption-Enhanced Cogasification of Sewage Sludge and Wood for Hydrogen-Rich Gas Production with in Situ Carbon Dioxide Capture

Sewage sludge disposal is troublesome because of the presence of microbes, toxins, and heavy metals in it. Co-gasification of sewage sludge with wood is a promising pathway to dispose of sewage sludge and generate usable syngas, simultaneously. By using a sorbent for in situ sorption of CO 2, H 2 fraction in the generated syngas can be enhanced considerably. An equilibrium model was developed taking wood and sewage sludge as the model compounds and CaO as the sorbent. This evaluation was performed by employing ASPEN PLUS (V 8.8) software. Principle of Gibbs free-energy minimization was adopted to predict the outlet gas composition and gas yield. The impact of reactor temperature (600 to 900 °C) and sludge content (0 to 100 wt % at 700 °C) in the feedstock on syngas yield and constituents were assessed. With 30 wt % sludge, maximum gas yield was observed as 0.526 kg h –1 at 900 °C while minimum CO 2 fraction was achieved at 700 °C. At 700 °C, the highest gas yield of 0.251 kg h –1 was recorded at 50 wt % sludge, whereas minimum CO 2 concentration was observed at 30 wt % sludge. The model predictions were in good agreement with the experimental findings. The study reflects that CO 2 -sorption enhanced gasification of sewage sludge with other biomass such as wood is an attractive option to dispose of sewage sludge in an environmental friendly manner and to generate hydrogen-rich fuel gas.