Environmental Engineering Reference
In-Depth Information
12.9
Name five types of reactors that have been developed for biomass torrefaction.
12.10 Which of the reactor designs seem most promising for scale-up (for produc-
tion rates > 50 kt per year)?
12.11 What are the safety issues and risks involved in torrefaction processes?
12.12 What is the impact of the torrefaction temperature on the properties of the
product biomass?
12.13 What role can densification (pelletizing/briquetting) play in the torrefaction
process?
12.14 Name a few binder additives used in pelletizing of torrefied biomass. When is
it necessary to use them?
12.15 Explain the effect of the particle size on the choice of reactor used in
torrefaction.
PROBLEMS
12.1 Dry woody biomass can be represented with the molecular formula CH 1.4 O 0.6 .
A sample of this biomass is torrefied to give a product gas with the following
composition (on a mass basis): H 2 O, 51%; acetic acid (CH 3 COOH), 20%;
CO 2 , 26%; and CO, 3%.
12.2 Assuming typical values for the loss of solid mass and energy during torre-
faction, calculate the LHV of the torrefied biomass and compare it with the
LHV of the input biomass (you may use an equation based on the chemical
composition of the solid fuel). Further, plot the compositions of both the
raw biomass and products on a van Krevelen diagram.
12.3 The following scheme, depicted in Figure 12.5 (Prins et al., 2006a), uses pseu-
docomponents to model the weight loss kinetics of biomass in torrefaction.
The relations for the reaction rate coefficients (expressed in kg
kg - 1
solid s - 1 ) are as
:
follows:
V1
V2
k V1
k V2
A
B
C
k 1
k 2
FIGURE 12.5 Torrefaction reaction kinetics scheme (adapted from Prins et al., 2006a). A,
unreacted biomass; B, a moderately torrefied biomass; and C, a severely torrefied product. V1
andV2 represent amixture of volatiles released in the conversion ofA toBandB toC, respectively.
 
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