Production of Producer Gas from Densified Agricultural Biomass in Downdraft Gasifier and Its Application to Small Diesel Engines

Abstract

Biomass is becoming one of the most popular renewable energy sources, especially from agricultural wastes. These wastes can be gasified and utilized in various industries. This experimental study investigated producer gas generation from densified agricultural fuels such as corncobs, rice husks, wood chips, and oil palm fronds in a 50 kWth throatless downdraft gasifier. This system produced combustible gases such as H2, CO, and CH4, which were utilized as a substitute for diesel fuel in a small diesel engine for power generation. The results showed that the gasifier performs successfully and seems to prefer pellets to briquettes. Producer gas contains 18%–20% carbon monoxide, 1%–6% hydrogen, and 0.9%–1.9% methane. Maximum gasification efficiencies of 53%–71% were achieved with biomass pellets from wood chips, corncobs, oil palm fronds, and rice husks, with producer gas calorific value of 2.94–3.85 MJ/Nm3. The average fuel consumption rate was between 6.72–14.43 kg/h, while the producer gas yield was between 2–3 Nm3/kg. The average gravimetric concentration of biomass tar in the raw product gas was found to be in the range of 23–50 g/Nm3, in which pelletized fuel appeared to show slightly lower tar than briquette fuel. The tar was primarily composed of five compounds: Benzo (a) pyrene, chrysene, pyrene, phenanthrene, 1-methylnaphthalene, and several other polycyclic aromatic compounds. The producer gas from oil palm frond briquettes and biodiesel were tested in a gas engine system in a dual fuel mode. A thermal efficiency of 22.21% was achieved with 2500 W electric load and a 72% biodiesel displacement rate, respectively.