Energy and exergy analysis of gasification of solid fuels by optimization of chemical kinetics

Abstract

A three-zone kinetic model is developed for thermodynamic analysis of the gasification of two solid fuels, rubber wood and refused devised fuel (RDF), by optimizing the chemical kinetics for five reduction zone reactions. With the help of the kinetic model, syngas composition and temperatures are determined for pyrolysis, oxidation, and reduction reactions. The chemical kinetics for reduction zone reactions are considered as control variables in the Taguchi optimization technique with the objective functions of maximum calorific value and maximum exergy efficiency. Optimization results obtained for refused derived fuel (RDF) indicate that the methanation reaction has the most influence, with a 65 % contribution on calorific value and a 71 % contribution for maximizing exergy efficiency. However, for rubber wood, the Boudouard reaction was found to have the most influence on calorific value with a 49 % contribution, while the water-gas reaction had the most influence on exergy efficiency with a 46 % contribution. Based on the findings from Taguchi optimization on the influential chemical kinetics coefficients, further analysis is carried out on the relevant equilibrium constants for both materials. The research outcome of the study is helpful for understanding the relative influence of biomass composition and reaction conditions on the chemical kinetics of gasification for maximizing energy output from the process.