Biohydrogen Generation and Other Methods - Hydrogen Generation, Storage, and Utilization - page 58

TABLE 4.5 Composition of Bio-Syngas from Biomass Gasification

Constituents % by Volume (Dry and Nitrogen Free)

Carbon monoxide (CO) 28-36

Hydrogen (H 2 ) 22-32

Carbon dioxide (CO 2 ) 21-30

Methane (CH 4 ) 8-11

Ethene (C 2 H 4 ) 2-4

Benzene-toluene-xylene (BTX) 0.84-0.96

Ethane (C 2 H 5 ) 0.16-0.22

Tar 0.15-0.24

Others (NH 3 ,H 2 S, HCl, dust, ash, etc.)

< 0.021

Reproduced with permission from Demirbras [36].

Steam gasification is a promising technology for thermochemical hydro-
gen production from biomass. Hydrogen is produced from the steam gasifica-
tion of legume straw and pine sawdust [41], hazelnut shell [42], paper, yellow
pine woodchips [43], mosses, algae [19], wood sawdust [44], wheat straw
[45], and waste wood [46].
Steam reforming C1-C5 hydrocarbons, nafta, gas oils, and simple aromat-
ics are commercially practiced, well-known processes. Steam reforming of
hydrocarbons, partial oxidation of heavy oil residues, selected steam reform-
ing of aromatic compounds, and gasification of coals and solid wastes to
yield a mixture of H 2 and CO, followed by water-gas shift conversion to
produce H 2 and CO 2 , are well established processes [47]. Steam reforming
and so-called dry or CO 2 reforming occur according to the following reac-
tions and are usually promoted by the use of catalysts:

C H + n H O CO ↔ + + ( n m / ) 2 H

(4.7)

n m 2 2

C H + n CO ↔ ( 2 CO n ) + ( m / ) 2 H .

(4.8)

n m 2 2

Modeling of biomass steam gasification to synthesis gas is a challenge
because of the variability (composition, structure, reactivity, and other physi-
cal properties) of the raw material and because of the severe conditions
(temperature, residence time, and heating rate) required [48]. The yield of
H 2 from steam gasification increases with increasing water-to-sample (W/S)
ratio [49] The yields of H 2 from steam gasification increase with increasing
temperature. The yield of hydrogen-rich gaseous product in the gaseous
products from the black liquor steam gasification run (W/S = 1.9) increased
from 38.0% to 50.3% with increasing temperature from 975 to 1325 K [50].
The effect of catalyst on gasification products is very important. The use
of catalysts did not affect the gas yields, but the composition of the gases