Combustion and gasification characteristics of chars from raw and torrefied biomass

Abstract

Torrefaction is a mild thermal pretreatment (T<300°C) that improves biomass milling and storage properties. The impact of torrefaction on the gasification and oxidation reactivity of chars from torrefied and raw biomass was investigated. Thermogravimetric analysis was used to study the differences in O(2) and steam reactivity, between chars prepared from torrefied and raw willow, under both high- and low-heating-rate conditions. High-heating-rate chars were prepared at 900°C with a residence time of 2s. Low-heating-rate chars were prepared with a heating rate of 33°C/min, a maximum temperature of 850 or 1000°C, and a residence time of 30 min or 1h, respectively, at the maximum temperature. Pretreatment by torrefaction consistently reduced char reactivity. Torrefaction's impact was greatest for high-heating-rate chars, reducing reactivity by a factor of two to three. The effect of torrefaction on a residence time requirements for char burnout and gasification was estimated.

Is the biochar produced from sewage sludge a good quality solid fuel?

“…The range of analyzed parameters of the SS, sawdust and biochars was chosen according to the literature and they were as follows: moisture (Fisher et al 2012), lower heating value -LHV (Ratte et al 2011), higher heating value -HHV (Prins 2005), ash and volatile compounds content (Wannapeera and Worasuwannarak 2012), C, H, S content (Park et al 2012).…”

A Comprehensive Review on Biomass Torrefaction

“…The char reactivity in the oxidation process decreases after the biomass is torrefied (Fisher et al, 2012;Jones et al, 2012). The decreased reactivity of the torrefied biomass could be explained through the accumulation of ash (the mineral content of the biomass) over the char surface.…”

“…The accumulation of ash reduces the direct contact of the oxidation media with the carbon and increases the combustion time (Chan et al, 1999). Fisher et al (2012) however reported that the char reactivity depends on how the volatile is removed from the original raw biomass. Volatiles matter and porosity are two major factors affecting the char reactivity.…”

The Effect of Torrefaction Pre-Treatment on the Gasification of Biomass

“…Fisher et al (2012) found that secondary char formed during torrefaction has a lower reactivity. So, the gasification of torrefied biomass involves the reaction of less reactive secondary char while that of raw biomass generally involves reactive primary char.…”

“…However, the application of torrefied biomass in gasification remains largely unexplored. Fisher et al (2012) and Couhert et al (2009) tried to understand the kinetics of torrefied biomass char and the effect of torrefaction on the physical structure of biomass. This work examines the kinetics of steam gasification reaction for raw and torrefied biomass using a batch reactor.…”