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 m3 n/m2 s for all the wood fuels. Altogether, 18 (3×6) 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:CH0 O0 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/m2 s) relative to the wood pellets (37–62 g/m2 s) and the wood chips (50–90 g/m2 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.