Volatile gases from biomass pyrolysis under conditions relevant for fluidized bed gasifiers

Artikel i vetenskaplig tidskrift, 2017

The pyrolytic volatiles released from a converting biomass particle are investigated in this work through laboratorial fluidized bed experiments simulating conditions typical of large-scale gasifiers. Two types of wood (eucalyptus and pine) and two types of pellets (forest residues and wood) with particles of 6-8 mm in diameter are fed over the hot bubbling bed at temperatures within 600-975 degrees C. The resultant major pyrolytic products (char, soot, liquids and permanent gas) are collected to verify the overall mass balance, and the composition of the permanent gas is resolved in C3H8, C2H6, C2H4, CH4, CO2, CO, and H-2. Primary pyrolysis of the parent fuel particles is essentially complete at 600 degrees C and further increase of the temperature mainly leads to a progressive change in the composition of the volatile gas mixture. Although the gas release does not attain thermodynamic equilibrium under the conditions tested, our results show that the yields of CO2 and light hydrocarbons go through maxima as temperature increases to give rise to CO and H-2 as the preferable species at high temperatures. As a whole, the gas composition evolves in such a way that the corresponding lower heating value steadily increases with temperature increase, from about 11 MJ/kg at 600 degrees C to above 17 MJ/kg at 950 degrees C. Furthermore, the yields of key gas species were found well correlated to each other (C2H4 vs. CH4, CH4 vs. CO and H-2 vs. CO), with the relation between the yields of H-2 and CO being slightly dependent on the composition of fuel.