A study on the determination of the gasification performance of a downdraft gasifier with adjustable airflow rate

In this thesis, an experimental investigation on the gasification of pruning wastes of pellets produced using hornbeam and pine trees has been conducted in an pilot-scale downdraft fixed bed gasifier system at 4 different air feed rates. The relationship between the parameters affecting the gasification performance and the air supply rate has been investigated. During the gasification of both biomasses, the core zone temperatures varied between 650 ºC and 800 ºC. Biomass consumption rates (FCR) of hornbeam and pine pellets varied between 7,77-10,10 kg/h and 8,00-10,49 kg/h, respectively. Air velocity and biomass significantly affected FCR values. The average mass gas production rate of hornbeam pellets was 23,88 kg/h and pine pellets 24,00 kg/h. The air supply rate significantly affected the gas production rate. Average specific gas productions of hornbeam and pine pellets were 2,58 Nm3/kg and 2,48 Nm3/kg, respectively. The average lower heating value (LHV) of the synthesis gas obtained from hornbeam pellets was calculated as 5,00 MJ/Nm3, and the upper heating value (HHV) was 5,43 MJ/Nm3. The lower heating value of the synthesis gas obtained from pine pellets was 4,98 MJ/Nm3 and the upper heating value was 5,42 MJ/Nm3. Average carbon conversion rates were found to be very close to each other in both pellet samples (88,68%). Average cold gas yields were 70,0% in hornbeam pellets and 66,9% in pine pellets. It was found that there is a significant difference in cold gas yield between the two pellet samples. Average energy efficiencies of the system for gasification of hornbeam and pine pellets were 88,3% and 77;4%, respectively. The average exergy efficiency of the system was calculated as 87,7% for hornbeam pellets and 76.8% for pine pellets. Exergy efficiencies were found to be lower than energy efficiencies in both pellet samples.