Optimization of the performance ofdown-draft biomass gasifier installedat National Engineering Research &Development (NERD) Centre of Sri Lanka
Using biomass gasification to produce combustible gas is one of the promising sustainable energy options available for many countries. At present, a few small scale community based power generation systems using biomass gasifiers are in operation in Sri Lanka. However, due to the lack of proper knowledge, these systems are not being operated properly in full capacity. This stands as an obstacle for further expansion of the use of gasifier technology.The objective of this study was to identify the most influential parameters related to fuel wood gasification with a down draft gasifier in order to improve the gasification processes.A downdraft gasifier of 10kW electrical capacity was used to study the effect of equivalent ratio (Actual air fuel ratio to Stoicheometric air fuel ratio: ER) on the specific gas production, the heating value of gas produced and the cold gas efficiency using three throat diameters (125mm, 150mm and 175mm). Six trials were carried out for each throat diameter by varying the supply air flow to change the ER. The gas samples were tested for their compositions under steady state operating conditions. Using mass balances for C and N, the cold gas efficiencies, calorific values and the specific gas production rates were determined.The results showed that with all throat diameters the calorific value of gas reduced with the increase of ER. The cold gas efficiency reduced with ER in a similar trend for all three throat diameters. The specific gas production increased with ER under all throat diameters.Calorific value and specific gas production are changing inversely proportional manner. The ER to be operated is depends on the type of application of the gas produced and engine characteristics. When a large heat is required, low ER is to be used in which gas production is less. In the opposite way, when a large amount of gas is needed, higher value of ER is recommended.