Pyrolysis Processes
As discussed in Section 4.3, the logistics of biomass collection will in general limit biomass gasification facilities to a maximum of 30-40 MWth. In order to overcome this limitation in benefiting from the economies of scale, the combination of decentralized pyrolysis plant and a central bio-oil gasifier has been proposed (e. g., Henrich, Dinjus, and Meier 2002).
Figure 5-39 shows a generic bio-oil plant in which typically about 75% of the dry feedstock is recovered as bio-oil. Char (10-15 wt%) and gas (15-20 wt%) are recovered and combusted to supply the heat required for drying the feedstock and heating the reactor. The pyrolysis takes place at about 450^475 °С with a residence time of the order of magnitude of about 1 second.
Biomass pyrolysis processes are at this stage still in their infancy. There are a number of small-scale commercial and demonstration plants that have been built, the most important or representative of which are listed in Table 5-20.
The principle current use for bio-oil includes specialty chemicals, which are essential for economics at present (Freel 2002).
Various projects are in preparation for testing equipment with bio-oil feeds. Fortum have a burner-testing program with Oilon Oy. Test programs for slow-speed marine
|
Figure 5-39. Block Flow Diagram for a Bio-Oil Plant (Source: Meier 2002) |
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Table 5-20 Bio-Oil Pilot and Demonstration Plants |
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|
Company, Trade |
Plant |
||
|
Country Name |
Size |
Technology |
Comments |
|
Dynamotive, Biotherm™ |
10t/d |
Stationary |
In planning 100 t/d |
|
Canada |
fluid-bed |
UK, 200 t/d Canada |
|
|
Wellman, UK |
6t/d |
Stationary fluid-bed |
Awaiting operation permit |
|
ENSYN, Canada RTP™ ENEL, Italy |
2*45 t/d |
Circulating fluid-bed Circulating fluid-bed |
40 t/d plant operating since 1996 |
|
VTT, Finland |
0.5 t/d |
Circulating fluid-bed |
|
|
BTG, Netherlands |
4 t/d |
Rotating cone |
In planning 10 t/d |
|
Forschungszen — trum Karlsruhe, Germany |
Double screw |
Lurgi LR process |
|
|
Pyrovac, Canada |
35 t/d |
Vacuum pyrolysis |
|
|
Fortum/V apo, Forestera™ |
12 t/d |
Vacuum |
Start-up May 2002 |
|
Finland |
pyrolysis |
(Gust, Nieminen, Nyronrn 2002) |
diesel engines (e. g., Omrod) are underway, and tests are also being conducted on gas turbines. The amount of bio-oil currently available is small, however, which limits the opportunities for such testing.
Proposals for testing the gasification characteristics of bio-oil have also been made (Henrich, Dinjus, and Meier 2002). Initial pilot testing has already been completed.
The European Union has a program to develop standards for bio-oil, considering end-user requirements. A guide to analysis and characterization methods specifically adapted to bio-oil products has been published (Oasmaa and Peacocke 2002).