ISSN Online: 2377-424X
ISBN Print: 978-1-56700-421-2
International Heat Transfer Conference 15
Two Different Methods for Determination of Exothermic Reaction Enthalpies from Temperature Measurements in Beechwood Cylinders During Torrefaction
Resumo
Torrefaction is a process for producing "bio coal" from lignocellulosic biomass via thermal treatment in an
oxygen-free atmosphere. In order to achieve a stable and secure process, the exothermic reaction enthalpy has to be known. In this paper, two different approaches for determining the heat released in beechwood cylinders during torrefaction using temperature measurements at different radial positions are presented and compared. One approach is based on heat conduction within the cylinder, assuming quasi-stationary conditions at each point of time. The other is based on a heat balance at the cylinder's surface. The surface temperature, which cannot be measured with sheathed thermocouples, has to be known for both approaches. Therefore, it is extrapolated from the available measurement data and the impact of measurement uncertainties on this
temperature is investigated. Exothermic reaction enthalpies at different reactor temperatures ranging from
230 to 290 °C are determined with both methods. Possible sources of uncertainties through non-ideal bore
positions or imprecise temperature measurements are discussed. The highest temperatures measured in the
cylinders exceed the reactor temperature by 4 to 46K, resulting in calculated exothermic reaction enthalpies
ranging from -30 to -179 kJ/kgdry wood
Palavras-chave:
Thermochemistry, Thermophysical properties, torrefaction, biocoal, mild pyrolysis, heat of reaction, reaction enthalpy