Hydrothermal Gasification of Biomass - Biomass Gasification, Pyrolysis and Torrefaction - page 328

(A)

8

7 Hydrogen

Methane
Carbon dioxide
Carbon monoxide

6

5

4

3

2

1

0

500 550 600 650 700 750 800

Temperature (°C)

180

(B)

160

140

120

Hydrogen
Carbon
Oxygen

100

80

60

40

20

0

450 500 550 600 650 700 750 800

Temperature (°C)

FIGURE 9.7 Effect of temperature on (A) gas yield and (B) gasification efficiency. Source:
From Lee et al. (2002).

100% above 700 C. Hydrogen conversion efficiency (the fraction of hydro-
gen in glucose converted into gas) also increases with temperature. It appears
strange that at 740 C, the hydrogen conversion efficiency exceeds 100%,
reaching 158%. This clearly demonstrates that the extra hydrogen comes
from the water, confirming that water is indeed a reactant in the SCWG pro-
cess as well as a reaction medium.
Hydrothermal gasification of biomass has been divided into three broad
temperature categories: high, medium, and low with their desired products
(Peterson et al., 2008). Table 9.2 shows that the first group targets production
of hydrogen at a relatively high temperature ( 500 C); the second targets

production of methane at just above the critical temperature (

.

374.29 C)
but below 500 C; and the third gasifies at subcritical temperature, using only

B