Page 59 - Biomass Gasification, Pyrolysis And Torrefaction Practical Design and Theory

38 Biomass Gasification, Pyrolysis and Torrefaction

2.3.4 Torrefier Cost
Similar to the gasifier, the capital cost of a torrefaction plant also depends on
the technology selected. Torrefier technologies fall under two broad categories:
1. Directly heated
2. Indirectly heated.

The cost of indirectly heated units could be a little higher than the cost of
directly heated units. Uslu et al. (2008) quoted a cost in the range 4.5 11.5
million euro for a 25 MWth torrefaction plant. Peng et al. (2011) gave a
comparison of capital cost of a 126,000 ton/year torrefaction unit for three
technologies as listed below:
1. Moving bed torrefier: m$10.73
2. Rotary drum: m$17.58
3. Screw torrefier: m$25.45
Commercial use of torrefaction is relatively new. So, only limited data is
available on its capital cost. These values are theoretical or biased on higher
side by the development cost. Based on capital cost (capital cost per unit
capacity) collected from some published and unpublished sources, specific
torrefier cost is plotted against capacity in Figure 2.2. In spite of large varia-
tion, one could detect an economy of scale from the figure.
It may be noted that a torrefier reactor is just one component of the total
torrefaction plant that needs additional units like dryer, cooler, mills, storage,
biomass handling, building, and others. Such units are relatively independent
of the torrefier, and could add another 50 100% to the total plant cost
(TPC) depending upon the cost of the torrefier.

30
Specific capital cost, m$. TPH 20
25

15

10

0 5
0 5 10 15 20 25 30 35
Capacity, tons/h (TPH)
FIGURE 2.2 Capital cost (per unit ton per hour capacity) of torrefier against capacity of unit.
The scatter is due to different sources with varying conditions and technologies.