Biomedical Engineering Reference
In-Depth Information
syngas of tar and other catalyst-poisoning elements, especially before it is
used for FTS, which uses iron- or cobalt-based catalysts. So the gas must be
cleaned of particulates and other contaminating gases. The raw syngas may
contain three principal types of impurity: (1) solid particulates (e.g., uncon-
verted char and ash), (2) inorganic impurities (e.g., halides, alkali, sulfur
compounds, and nitrogen), and (3) organic impurities (e.g., tar, aromatics,
and carbon dioxide).
The ash in the biomass appears as slag. At low temperatures, the ash
remains in the product gas as dry ash. Cleaning has two aspects: removing
undesired impurities and conditioning the gas to get the right ratio of H
2
and
CO for the intended use. The end-use determines the level of cleaning and
conditioning.
Table 11.1
presents examples of product-gas specifications for
different end uses.
TABLE 11.1
Product-Gas Specifications for Various Applications
Hydrogen for
Refinery Use
Ammonia
Production
Methanol
Synthesis
Specification
FTS
Hydrogen
content
98%
75%
71%
60%
.
Carbon
monoxide
content
10
50 ppm (v)
[CO
CO
2
]
19%
30%
,
1
,
20 ppm (v)
Carbon dioxide
content
,
10
50 ppm (v)
4
8%
Nitrogen content
,
2%
25%
Other gases
N
2
, Ar, CH
4
Ar, CH
4
N
2
, Ar, CH
4
N
2
, Ar,
CH
4
,CO
2
Balance
As low as
possible
As low as
possible
Low
H
2
/N
2
ratio
3
B
H
2
/CO ratio
0.6
2.0
H
2
/
[2CO
1.3
1.4
3CO
2
]
1
ratio
550
C
400
C
350
C
Process
temperature
350
300
200
Process pressure
50 bar
100
250 bar
50
300 bar
15
60 bar
.
Source: Adapted from Knoef (2005), p. 224.
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