Species transport model and custom field function algorithm for computational fluid dynamics-based design and exergy analysis of downdraft biomass gasifiers

Abstract

Biomass gasification holds great promise as a technology for generating renewable energy from biomass feedstocks. Ensuring efficient operation necessitates the evaluation of energy efficiency within the gasification process. However, traditional energy-based analysis has limitations as it fails to account for the impact of inherent irreversibilities in the process. In contrast, exergy-based analysis offers a more rigorous technique that considers these irreversibilities, providing a comprehensive assessment of the process. In this study, a laboratory-scale downdraft biomass gasifier was modelled and simulated using computational fluid dynamics (CFD). The model incorporated a species transport model to predict concentrations of different species and reaction rates occurring within the gasifier. To evaluate the gasifier's performance comprehensively, an exergy analysis algorithm was integrated into the model through a custom field function, assessing three types of exergy: physical exergy, chemical exergy, and mixing exergy. The developed model achieved superior results compared to a previously reported model, achieving a syngas composition of 1:1.55 and a gasification temperature of 1100 °C. The application of the exergy analysis algorithm enabled a more comprehensive evaluation of the gasifier's performance, revealing areas for improvement that were not apparent in traditional energy-based analyses. The findings of this study highlight the potential of combining CFD simulations, species transport models, and exergy analysis algorithms to enhance the efficiency and sustainability of biomass gasification processes. This approach provides valuable insights into the intricate physical and chemical processes taking place within the gasifier, thereby facilitating the development of more efficient and sustainable biomass gasification technologies.