Syngas Quality Optimisation, Tar Reduction and Engine Performance of Downdraft Biomass Gasification System Using Agro-Residues in Rural India

Biomass gasification — the thermochemical conversion of solid organic matter to a combustible producer gas (syngas) through partial oxidation — offers a technically mature and economically viable pathway for decentralised electricity generation in India's rural and peri-urban areas where grid connectivity is unreliable, grid tariffs are unaffordable for agricultural and agro-processing loads, and agricultural residues represent an abundant zero-cost energy feedstock whose open-field burning causes severe air quality deterioration across the Indo-Gangetic Plain. India generates an estimated 500 million tonnes of agricultural residues annually, of which only 40% is currently utilised as animal feed, construction material, or industrial raw material — the remaining 300 Mt representing an energy resource with theoretical electricity generation potential exceeding 17,000 MW if gasified at practical efficiencies. This study investigates the gasification performance of five agro-residues — rice husk, bagasse, wood chips, cotton stalk, and bamboo — in a 20 kWe downdraft fixed-bed gasifier designed and fabricated at MNNIT Allahabad, examining syngas composition (CO, H₂, CO₂, CH₄, N₂), tar content, Lower Heating Value (LHV), and Cold Gas Efficiency (CGE) as functions of Equivalence Ratio (ER=0.20-0.45) and gasification temperature (700-1000°C). The effect of a dolomite catalytic bed zone on tar cracking is evaluated, achieving 84% tar reduction at 900°C. The cleaned syngas is used to power a 15 kWe spark-ignition generator set, with engine performance (BSFC, BTE) and exhaust emissions (CO, NOx, HC, PM, CO₂) characterised across the full load range and compared against diesel baseline. The Mälardalen University collaboration contributes advanced equilibrium and kinetic modelling of the gasification reactions using the ASPEN Plus simulation platform.