Gasification of Fuel Cane Bagasse in a Downdraft Gasifier: Influence of Lignocellulosic Composition and Fuel Particle Size on Syngas Composition and Yield

Gasification of fuel cane bagasse briquettes and pellets was carried out in a novel 50 kW(e) downdraft autothermal gasifier to evaluate the most suitable densified form for use in downdraft gasifiers. The results showed that the calorific value of the syngas produced from the briquettes was low, ranging from 1.95 to 3.12 MJ/m(n)(3), and ballooning of the briquettes accompanied by bridging of the fuel repeatedly occurred in the pyrolysis and throat zones. In contrast, gasification of pelletized bagasse under similar operating conditions produced syngas ranging in calorific value from 4.90 to 5.94 MJ/m(n)(3), the syngas yield increased by 65%, and bridging was non-existent. Investigation of the lignocellulose composition of the bagasse found that this high-fiber cane has a high lignin/cellulose ratio with a typical lignin content of 33 +/- 4%. Scanning electron microscopy studies of the partially pyrolyzed and expanded briquettes showed that extensive porous structures had developed during pyrolysis. Because cellulose devolatilizes at a faster rate than lignin, this suggested that, during pyrolysis, the rapid production of volatile gases within the briquettes resulted in ballooning and cracking of these structures. This increase in volume coupled with the reduced mass of the briquette resulted in reduced bulk density, which restricted the capacity of the fuel bed to flow under gravity and ultimately led to bridging in the reactor, poor syngas composition, and low yield.