Torrefaction of Wood in a Quiescent Layer of Talc

Abstract

Biomass torrefaction can be carried out in the unsealed reactor filled with a quiescent layer of mineral filler. Mineral filler limits the oxygen access toward the biomass from the environment and favors more uniform temperature distribution inside the reactor. This paper is devoted to the experimental analysis of the torrefaction of softwoods (pine and spruce) and hardwoods (trembling aspen, maple, willow, white birch, acacia, and apple tree) in a quiescent layer of talc. It is established that pine and spruce provide the maximum mass yield independent on the regime of torrefaction. The difference in the mass yield for different wood species can be 20% if other conditions are equal. At low temperatures, torrefaction proceeds in a kinetic regime, in which the rate of chemical reactions limits the macroscopic rate of hemicellulose decomposition. At elevated temperatures of torrefaction, a diffusive regime is realized. In this regime, the mass yield mainly depends on the intensity of oxygen and water vapor diffusion through the mineral layer. We propose a simple phenomenological model to substantiate the dependence of mass yield on the height of the mineral layer. Biomass combustion characteristics are studied on the base of thermogravimetry−differential scanning calorimetry analysis. It is shown that the intensity of the biofuel combustion on the initial stage decreases with the increase in torrefaction temperature. Hydrophobicity of the biofuel is assessed via measuring the contact angle. When all the torrefaction conditions are the same, pine appears to be more hydrophobic compared to birch.

Oxidative Torrefaction of Sunflower Husk Pellets in the Kaolin Layer

“…Influence of various parameters on mass yield when using kaolin as the mineral layer was analyzed. Since the main purpose of the mineral layer is to limit the access of oxygen to biomass from the environment thereby repressing oxidation reactions and do not allow mass yield to decrease excessively [27].…”

“…Non-oxidative torrefaction is rather energy-intensive and expensive process due to the use of inert gas (nitrogen) [26], which also dilutes the gaseous products, which makes it difficult for their condensation and combustion after torrefaction [27].…”

“…In the case of oxidative torrefaction, using air as a carrier gas reduces the cost of inert gas consumption and maintenance [24,28]. Active oxygen from the air stream is burned together with volatile matters and, thus, additional thermal energy is generated, which can be useful for conversion of torrefaction into the self-sustaining thermal process [27]. Oxidative torrefaction also provides higher content of fixed carbon in biomass than non-oxidative torrefaction [29].…”

“…Due to immobility of all components in the reactor, it is possible to use biomass in the form of pellets without risk of their destruction. Depending on the changing torrefaction conditions (temperature, residence time, layer height) and type of mineral filler, properties of torrefied products can vary in a quite wide range [27]. This torrefaction technology was studied only on wood biomass [37].…”

Oxidative Torrefaction of Sunflower Husk Pellets in the Kaolin Layer

“…In the case of oxidative torrefaction, using air as a carrier gas reduces the cost of inert gas consumption and maintenance [24,28]. Active oxygen from the air stream is burned together with volatile matters and, thus, additional thermal energy is generated, which can be useful for conversion of torrefaction into the self-sustaining thermal process [27]. Oxidative torrefaction also provides higher content of fixed carbon in biomass than non-oxidative torrefaction [29].…”