Measurements of mass flux and stoichiometry of conversion gas from three different wood fuels as function of volume flux of primary air in packed-bed combustion

This paper presents the first experimental series applying a new measurement method to determine mass flux and stoichiometry of the conversion gas as well as the air factor from packed-bed combustion of biofuels. The conversion system employed in this experimental study is characterized by the following concepts: overfired, updraft, fixed horizontal grate, and batch reactor. Three types of wood fuels are studied, namely wood pellets (6 mm), wood chips (4-50 mm), and fuel wood (300 mm). The above-mentioned quantities are measured as function of six levels of standard volume flux of primary air in a range of 0.06-0.46 m(3) n/m(2) s for all the wood fuels. Altogether, 18 (3 x 6) single tests are carried out. In spite of the fact that single tests are carried out and that the course of a batch run is highly stochastic, it is possible to draw some general conclusions with respect to the particular conversion concept studied. Firstly, the course of a batch conversion of wood fuels is proven to be very dynamic. For example, the dynamic ranges for the air factor of the conversion system is 10: 1 and for the stoichiometric coefficients is CH3.1 O: CH0O0 during a batch for a constant volume flux of primary air. Secondly, despite the fact that the fuel wood was exceptionally dry, only 8 wt% water content on wet basis, the fuel wood studied displayed significantly lower time-integrated mean of mass flux of conversion gas (12-31 g/m(2) s) relative to the wood pellets (37-62 g/m(2) s) and the wood chips (50-90 g/m(2) s). Thirdly, based on the fact that the conversion gas stoichiometry is unsteady it is confirmed that the molecular composition of the conversion gas varies during batch conversion of wood fuels. (C) 2002 Elsevier Science Ltd. All rights reserved.