Biomedical Engineering Reference
In-Depth Information
11.2.5.1 Cleanup Options
For cleaning the gas of dust or particulates, there are four options: (1)
cyclone, (2) fabric or other barrier filter, (3) electrostatic filter, and (4) sol-
vent scrubber. Among organic impurities, tar is the least desirable. The three
main options for tar removal are:
Scrubbing with an organic liquid (e.g., methyl ester).
Catalytic cracking by nickel-based catalysts or olivine sand.
High-temperature cracking.
Inorganic impurities are best removed in sequence because some removal
processes produce other components that need to be removed as well. In this
sequence, first, water quenching removes char and ash particles. Next, hydro-
lysis removes COS and HCN by converting them into H
2
S and NH
3
. The
ammonia and halides can be washed with water, followed by adsorption of
H
2
S, which can be removed with the wash water. Solid or liquid adsorbents
are used to remove carbon dioxide from the product gas.
11.3 BIO-OIL PRODUCTION
Bio-oil (or biofuel) is any liquid fuel derived from a recently living organ-
ism, such as plants and their residues or animal extracts. In view of its
importance, a detailed discussion of bio-oil is presented next.
11.3.1 What Is Bio-Oil?
Bio-oil is the liquid fraction of the pyrolysis product of biomass. For exam-
ple, a fast pyrolyzer typically produces 75% bio-oil, 12% char, and 13% gas.
Bio-oil is a highly oxygenated, free-flowing, dark-brown (nearly black)
organic liquid (
Figure 11.1
) that contains a large amount of water (
25%)
that is partly the original moisture in the biomass and partly the reaction
product. The composition of bio-oil depends on the biomass it is made from
as well as on the process used.
Table 11.2
presents the composition of a typical bio-oil. It shows that
water, lignin fragments, carboxylic acids, and carbohydrates constitute its
major components. When it comes from the liquid yield of pyrolysis, bio-oil
is called pyrolysis oil. Several other terms are often used to describe bio-oil
or are associated with it, including:
B
Tar or pyroligneous tar
Biocrude
Wood liquid or liquid wood
Liquid smoke
Biofuel oil
Wood distillates
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