Hydrothermal Gasification of Biomass - Biomass Gasification, Pyrolysis and Torrefaction - page 347

84
82
80
78
76
74
72
70
68
66
64
62
60
58 0

R =130 - 170

R =120

R =110
R =100

R =90

R =80

R =70

R =60

R =50

R =40

R =30

T =25°C

50 100 150 200 250 300 350 400 450 500 550

Pressure (bar)

FIGURE 9.16 Equilibrium mole fraction of hydrogen in gas phase for different water to prod-
uct gas ratios, R. Source: From Ji et al. (2006).

9.7.7 Biomass Feed System
The feeding of biomass into a high-pressure ( 22 MPa) reactor is a formi-

dable challenge for an SCW gasifier. If the feed is a dilute stream of organ-
ics, the problem is not so severe, as pumps can handle light slurries.
However, if it is fibrous solid granular biomass that needs to be pumped
against high pressure, the problem is especially difficult for the reasons that
follow:

.

The irregular size and the low shape factor of biomass makes it difficult
to flow.
Pulverization is necessary for pumping the biomass, but it is very difficult
to pulverize. Pretreatment of the feedstock is necessary.
Fibrous by nature, biomass does not flow well through an augur or gear
pump, and it is difficult to make a uniform slurry for pumping through
impellers.

Most of the research work on SCWG generally used model water-soluble
biomass such as glucose, digested sewage sludge, and wastewater (Blasi,
2007), which are easy to pump. For other types of biomass, Antal et al.
(2000) used additives or emulsifiers such as corn starch gel, sodium CMC,
and xanthan to make pumpable slurries. In an industrial application, large-
scale use of emulsifiers is impractical.
A sludge pump was successfully used in a 100 kg/h pilot plant; however,
the solids had to be ground to less than 1 mm particles and pretreated before