Environmental Engineering Reference
In-Depth Information
Particle
removal
Tar/CH
4
conversion
Inorganics
removal (Cl, S)
Water-gas
shift
Traces
removal
CO
2
removal
FIGURE 10.14
Gas cleaning and upgrading for biomass gasification in a BTL chain.
upstream the particle removal unit so that the indicated third step is also integrated in
the first cleaning step.
The following subsections deal with the different cleaning strategies with respect to
the aforementioned classes of compounds to be removed.
10.5.2 Particle Cleaning Techniques
Ash, attrited bed material and carbonaceous solids as well as fine droplets in gasifi-
cation product gas make up the particulate matter inventory to be cleaned up to certain
values needed regarding emission restriction laws and the downstream application.
Gasifiers emit such particles in a typical range of approximately 0.1
m. Major
inorganic compounds are alkaline earth metal compounds (Ca, Mg oxides), silica,
alkali species, and iron compounds. Minor inorganic species constitute, e.g., Zn,
Pb, Cu, etc. depending on the biomass source gasified. One usually discriminates
PM2.5, particles with diameters up to 2.5
-
100
μ
μ
m, and PM10, which is particulate matter
with diameters up to 10
m.
Now, gas cleaning can be carried out at low (ambient) temperature (LT), interme-
diate temperature (IT, also called warm gas cleaning, up to
μ
350
C), and high tem-
350
C). Table 10.8 summarizes available particulate matter
perature (HT, >>
cleanup equipment.
10.5.3 Tar Compound Cleanup
Tars form a challenging class of organic aromatic compounds. They have been
defined in widely differing terms. In the European tar measurement standard
(CEN/TS 15439 (CEN, 2006)) or the tar guideline (tinyurl.com/pwo46l4), tar is
defined as follows:
Generic (unspecified) term for the entity of all organic com-
pounds present in the producer gas excluding gaseous hydrocarbons (C1 through
C6). Benzene is not included in tar.
“
The primary issue is that they can condense
and deposit, thereby clogging sampling lines, fouling heat exchanger surfaces. Upon
decomposition, they can form soot, which in downstream combustion applications
leads to higher emissions of particulate matter and CO. Only gasifiers in which the
”
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