Syngas analysis by hybrid modeling of sewage sludge gasification in downdraft reactor: Validation and optimization

In general, sewage sludge obtained from the municipal wastewater treatment plant is one of the significant sources of waste for renewable energy production. In this article, the thermochemical conversion of sewage sludge through a downdraft gasifier is addressed. Two-zone equilibrium and one-zone kinetic model as the hybrid modeling of the sewage sludge gasification is proposed. Three zones of drying & pyrolysis, oxidation, and (char) reduction are modeled by using an integrated thermodynamic stoichiometric equilibrium and Langmuir-Hinshelwood kinetic model. Through the validation and sensitivity analysis, the syngas compositions and cold gas efficiency show to be sensitive to the variations of inlet flow rates of gasifying agents (air and steam), the inlet flow rate of feedstock (sewage sludge), and the temperature and pressure of the gasifier. Through the response surface methodology-based optimization algorithm, the proper operating conditions of the process can be found under the prescribed operating constraints.