Advancing Sewage Sludge Valorization: Sustainable Biofuel Production through First-Principles Modeling and Process Simulation

Abstract

Sewage sludge is a challenging waste to valorize. Hydrothermal carbonization offers a potential solution, concentrating the sludge’s dry matter into a solid product called hydrochar, which can be further processed through thermal conversion. However, current models for hydrochar thermal conversion lack accuracy, as they rely on thermodynamics or sample-specific kinetic models. This work presents a novel approach using GasDS, a generalized first-principles suite for dynamic and steady-state modeling. The study first simulates hydrochar combustion in a bubbling fluidized bed, tracking the temperature and pollutant concentration. GasDS is then applied to analyze the feasibility of hydrochar gasification, optimizing the process, and sizing the gasifier. Additionally, the study introduces a new method for converting gasification-derived biosyngas into bio-DME, a sustainable fuel for diesel engines. Using Aspen HYSYS, a process simulation is modeled, demonstrating improved performance in mass yield, energy yield, and CO₂ emissions compared to conventional combustion.