STUDY OF OPTIMAL AIR FEEDING RATE ON THERMAL EFFICIENCY OF DOWNDRAFT GASIFIER

Abstract

This study aims to investigate the gasification process using a high-quality syngas production system prototype, a thermochemical process that converts solid fuel into a gaseous product through combustion inside a reactor using a limited supply of air as the oxidizing agent. Using air as the oxidant enhances product quality, resulting in fuel gas with a high heating value. Specifically, this research focuses on studying the effects of air feed rates supplied to a downdraft gasifier via a heat exchanger, comparing the resulting producer gas in terms of thermal efficiency and overall syngas quality.

In this study, a downdraft gasifier was experimentally tested, and the temperature profiles at various measurement points were recorded. The measured mass flow rate and biomass fuel consumption rate were compared across five experimental conditions. The air feeding rates supplied to the downdraft gasifier were set at 0.0104, 0.0109, 0.0115, 0.0120, and 0.0126 kg/s. For each experimental run, 22 kg of biomass fuel was used. During each test, the air mass flow rate and biomass fuel consumption rate were recorded, and syngas samples were collected and subsequently analyzed to determine their gas composition.

The experimental results showed that the best syngas obtained consisted of CO at 29.13%, H₂ at 6.72%, CO₂ at 5.58%, CH₄ at 0.80%, and N₂ at 56.32%. The corresponding heating value of the syngas was 4.69 MJ/m³. When comparing the thermal efficiency at different air feeding rates, the air feeding rate of 0.0115 kg/s yielded the highest thermal efficiency among 56.65% the experimental conditions. This result can be attributed to the optimal air-to-fuel ratio, which provided suitable conditions for the gasification reactions within the downdraft gasifier.