Torrefaction - Biomass Gasification, Pyrolysis and Torrefaction - page 107

controlled by heat conduction into it and that may lead to a higher tempera-
ture in the biomass core.

4.5 DEGREE OF TORREFACTION
The torrefaction process is similar to that of roasting of coffee beans. The
higher the roasting temperature the darker is the color of the bean. The price
and taste of roasted coffee depends to some degree on the roasting tempera-
ture. Table 4.5 , for example, presents a range of roasting temperature with the
corresponding name of the coffee brand produced from it. One can thus see
how the degree of roasting varies with the torrefaction temperature. So, for
such a type of process, a gradation is indeed necessary for the quantification
of the process of torrefaction of biomass. A tentative gradation or severity of
the process (not the product) may be offered as below (Chen and Kuo, 2011):

240 Corat230 Cwhen
only hemicellulose is degraded leaving lignin and cellulose unaffected.
2. Medium torrefaction: Occurs at a temperature of 240

1. Light torrefaction: Occurs at a temperature of 200

260 C or at about

250 C, when cellulose is mildly affected.
3. Severe torrefaction: Occurs at a temperature of 260

300 Corat275 Cchar-
acterized by depolymerization of lignin, cellulose, as well as hemicellulose.

TABLE 4.5

Degree of Coffee Roasting Classified by Roasting Temperature

Roasting Temperature ( C) Name of the Coffee Product

Green unroasted coffee 75

Arabic coffee 165

Cinnamon roast 195

England roast 205

American roast 210

City roast 220

Full city 225

Vienna roast 230

French roast 240

Italian roast 245

Spanish roast 250

Immanent fire 497

Source: From wikipedia.org/wiki/Coffee_roasting .