Gas composition in a fixed bed of biofuel.

Paper in proceeding, 2006

The conditions inside and downstream of a conversion front, propagating against the air flow, have been investigated in a fixed bed of biofuel. The aim of the work is to describe temperatures and gas concentrations in the bed and to obtain data with high accuracy and with a resolution in space and time that is high enough to be useful for validation of mathematical models. To close mass balances of the main species, (C, H, O, N), O2, CO, CO2, N2, H2, H2O and hydrocarbons were measured, and samples of char and tar were analysed. For gas extraction an oil-cooled probe was used. The experimental rig was developed to achieve well-defined, one-dimensional, conditions. The measurements show the different episodes in the conversion front: initial heating by radiation, drying, release of volatiles, ignition and heat release, production of combustion products, depletion of oxygen followed by gasification reactions. During the stable devolatilisation phase a system of equations, based on concentrations measured by continuous gas analysis and mass balances, yields the content of tars, nitrogen and hydrogen (concentrations commonly not measured on-line).