PHD-Department of Agriculture and Biosystem engineering

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    Thermodynamic modelling and optimization of biomass gasification system for fischer-tropsch synthesis
    (Kenyatta University, 2023) Kombe, Emmanuel Yeri; Nickson K. Lang’at; Paul M. Njogu
    Biomass is a feasible route for producing transport fuels through Fischer-Tropsch synthesis (FTs). Production of transport fuels from biomass gasification output gas by FTs has become more attractive due to its ability to substitute fossil fuel in the energy market. Gasification technology is at the forefront of biomass conversion among other technologies due to its high flexibility in utilizing various biomass materials. In this work, a thermodynamic model of air gasification of rice husk in a downdraft gasifier was developed using Aspen Plus software and Engineering Equation Solver at various operating conditions. Experiments were conducted to validate the model. The influence of gasification temperature, equivalence ratio (ER), and moisture content (MC) on the composition of syngas, hydrogen to carbon monoxide ratio (H2/CO), and lower heating value of syngas was studied. Response surface methodology was applied to study the combined effects of the main operating parameters and thus determine the optimized zone of the operating conditions for Fischer-Tropsch synthesis. The R2 values of the generated regression models from the ANOVA tool were observed to be 98.47% for LHVSyngas, 98.93% for H2, 96.94% for CO and 89.91% for H2/CO molar ratio with corresponding Adj-R2 values of 98.28%, 98.80%, 96.56%, and 88.64%, respectively. This result indicates that the regression models determined the response variables with a high accuracy level. By using Response Surface Methodology (RSM), an optimization of the parameters was achieved. The RSM analysis results showed optimal conditions at gasification temperatures between 720 oC and 780 oC, ER in the range of 0.06 and 0.095, and MC in the range of 10% and 16%. The findings of this study reveal that a blend of simulation with advanced optimization tools can indeed achieve optimal operating conditions of a gasification system at a more refined precision. These analyses could form a basis for future practical development and implementation of biomass-based gasification systems through the selection of the best possible conditions in on-field plant operations