Environmental Engineering Reference
In-Depth Information
4.3 THERMOCHEMICAL CONVERSION OF BIOMASS TO HYDROGEN
4.3.1 Hydrogen from Biomass via Pyrolysis
Pyrolysis of biomass is a promising route for the production of solid (char),
liquid (tar and other organics), and gaseous products as possible alternative
sources of energy. The most interesting temperature range for the production
of the pyrolysis products is between 625 and 775 K [19, 20]. Depending on
the operating conditions, the pyrolysis process can be divided into three
subclasses: conventional (slow) pyrolysis, fast pyrolysis, and flash pyrolysis.
Slow pyrolysis of biomass is associated with high charcoal continent, but the
fast pyrolysis is associated with tar at low temperature (675-775 K) and/or
gas at high temperature [21]. At present, the preferred technology is fast or
flash pyrolysis at high temperatures with very short residence time. Table 4.3
indicates the product distribution obtained from different processes of pyrol-
ysis process [22]. Although most pyrolysis processes are designed for biofuel
production, hydrogen can be produced directly through fast or flash pyrolysis
if high temperature and sufficient volatile phase residence time are allowed
as follows [23]:
Biomass Heat
+
→ +
H
CO CH
+
+
Other products
.
(4.1)
2
4
Methane and other hydrocarbon vapors can be converted into hydrogen
and carbon monoxide (CO) by steam reforming:
CH
+
H O CO
→ +
3
H
.
(4.2)
4
2
2
TABLE 4.3 Product Distribution Obtained from Different Processes of
Pyrolysis Process
Product Yield (%)
Thermal
Degradation
Residence
Time (s)
Upper
Temperature (K)
Char
Liquid
Gas
Slow pyrolysis
200
600
32-38
28-32
25-29
120
700
29-33
30-35
32-36
90
750
26-32
27-34
33-37
60
850
24-30
26-32
35-43
30
950
22-28
23-29
40-48
Fast pyrolysis
5
700
22-27
53-59
12-16
4
750
17-23
58-64
13-18
3
800
14-19
65-72
14-20
2
850
11-17
68-76
15-21
1
950
9-13
64-71
17-24
Gasification
1500
1250
8-12
4-7
81-88
Source
: Reproduced with permission from Balat [22].
Search WWH ::
Custom Search