Environmental Engineering Reference
In-Depth Information
TABLE 10.8 Particulate matter cleaning equipment
Temperature
level (LT,
IT, HT)
Minimum dp
size captured
(
μ
m)
Level
of gas
cleanup
Equipment
References
Settling chamber
HT
>> 50
Low
Jacob and
Dhodapkar (1997)
Impingement
separator
HT
>10 − 20
Low
Towler and
Sinnott (2012)
Cyclone
HT/IT
>10
Moderate
Multicyclone
HT/IT
>5
Moderate
Rotating particle
separator
HT/IT
>0.1
High
Brouwers (1997)
Electrostatic filter
IT (/HT)
>2
High
Scrubber
LT
0.5 − 10
Moderate
to high
Baghouse (fabric)
filter
IT
>0.2
High
Ceramic filter
HT
>0.1
High
Heidenreich (2013)
Metal filter
HT
>0.1
High
product gas passes a hot zone of temperatures higher than approximately 1200
C
have limited tar issues due to much lower concentrations. Acceptable limits to
tar content in gasification product gas depend on the final application of this gas.
Already during combustion in gas engines and gas turbines, tars may cause serious
operational problems. In more advanced end-use applications, a virtually tar-free
gas is required. Catalyst deactivation in downstream processing of the product gas
should be avoided, and a limit of 2 gtar
m
n
−3
has been proposed before additional
catalytic reforming (Aznar et al., 1998). A literature review by Milne et al. (1998)
indicates that
m
n
−3
limiting values of less than 50
-
500 mg
are recommended
m
n
−3
m
n
−3
for compressors, 50
-
100 mg
for IC systems, and 5 mg
for direct-fired
industrial gas turbines.
Tar quantity and species composition are determined by several gasification
process parameters: type of feedstock, gasification conditions (temperature, pressure,
oxidizer-to-fuel ratio), and gasifier type. Fluidized bed gasifiers can easily produce
up to
m
n
−3
; an EF gasifier produces almost no tars as it operates at high
temperatures (>1200
C).
Strategies to decrease tar concentration levels in biomass gasification-derived
product gases can be classified into primary methods (
in situ
removal within the
gasifier) and secondary measures (downstream the gasifier). This is depicted in
Figure 10.15.
Table 10.9 presents different catalytic materials used for tar reduction. These can
be distinguished into two major classes, natural rock mineral matter and synthetic
catalytic materials.
10 gtar
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