Thermo-chemical design and parametric analysis of an Imbert downdraft fixed-bed gasifier for decentralized electricity generation in Malawi

Biomass gasification has emerged as a viable option for decentralized electricity generation in regions with limited access to reliable grid infrastructure. This study presents the design, development and evaluation of a 100 kWe Imbert downdraft gasifier for decentralized electricity generation using locally available agricultural residues in Malawi. The methodology combines empirical correlations, experimental data, and computational modelling to optimize system performance and produce engine-grade syngas. The gasifier performance was evaluated through syngas composition, lower heating value (LHV), gas yield, cold gas efficiency (CGE), and carbon conversion efficiency (CCE). The optimized gasifier design achieved a reactor diameter of 998 mm, a reactor height of 2800 mm, a biomass consumption rate of 110 kg h⁻¹, and an air flow rate of 117.7 kg h⁻¹. The resulting producer gas consisted of 23% CO, 18% H₂, 5% CH₄, 43% N₂, and 10% CO₂. The performance study shows that under operating temperatures of 800-850°C and an optimum equivalence ratio of 0.212, the system produced a gas yield of 2.29 Nm³ kg⁻¹, an LHV of 6.46 MJ Nm⁻³, a CGE of 72%, a CCE of 94.8%, thermal efficiency of 68.4%, and a tar concentration below 7.39 g Nm⁻³, indicating its suitability for internal combustion engine applications. The proposed framework offers a technically robust, economically viable, and scalable approach for deploying biomass gasification systems to support sustainable and decentralized electricity generation in developing regions.