Experimentelle und theoretische Untersuchung der Torrefizierung von Buchenholz

  • Experimental and theoretical investigation of beechwood torrefaction

Ohliger, Andreas; Kneer, Reinhold (Thesis advisor); Scherer, Viktor (Thesis advisor)

Aachen : Publikationsserver der RWTH Aachen University (2015)
Dissertation / PhD Thesis

Aachen, Techn. Hochsch., Diss., 2015

Abstract

Torrefaction is a mild pyrolysis of lignocellulosic biomass at a material temperature of about 250°C to 300°C. The objective of this process is the conversion of biomass to a solid energy carrier, which is similar to coal.In this thesis torrefaction of beechwood is investigated since this is commercially available in quite constant quality. The dependency of different product properties on the torrefaction degree is identified. These properties are heating value, energy yield, elemental composition, grindability, moisture uptake (short-term and long-term) and shrinkage of macroscopic particles. Additionally, special emphasis is placed on determination of the reaction enthalpy. Different experimental setups are used and special evaluation methods are developed. For macroscopic particles an exothermal reaction enthalpy of approximately 100 J/g is measured at a mass reduction of the dry solid of 25%.Besides the experimental work, two aspects are investigated by computer-aided calculations. Firstly, the mass and energy balance of a generic, stand-alone torrefaction process are calculated based on the experimental results. The additionally required or excess energy is quantitatively determined for several different process parameters.Secondly, a simulation program for one-dimensional calculation of torrefaction of macroscopic, cylindrical wood particles is developed. This program contains a model for the reduction of the solid mass (i.e. volatiles release rate) as well as a model for the reaction enthalpy. The latter is phenomenologically derived from the experiments. The program allows for the approximate prediction of the temperature profile as well as the resulting torrefaction degree of a beechwood specimen.