Hydrogen-Enriched Syngas from Biomass Steam Gasification for Use in Land-Based Gas Turbine Engines - Novel Combustion Concepts for Sustainable Energy Development - page 101

builds up in the reactor during gasi cation. The volume of char increases until its

total surface area is large enough to react at a rate equal to what is being produced
by the addition of biomass feedstock.
Char gasi

cation phase: In this phase, no biomass was inserted into the fl fluidized

bed but steam still ed the solid char,

producing H 2 , CO, CO 2, and CH 4 . The limestone reacted with CO 2 , provided that
there was still unreacted CaO, and the CO 2 partial pressure was higher than the
equilibrium pressure. At 650

fl flowed through it. The steam slowly gasi

C, the equilibrium partial pressure of CO 2 is 0.8 % of
atmospheric pressure and at 700

°

C, it is 2.6 %.
CaO regeneration phase: In this phase, the temperature of the bed was increased
to promote the release of CO 2 . The temperature required to raise the equilibrium
pressure of CO 2 above atmospheric pressure is roughly 900

°

C. However, if CO 2 is
removed from the environment, lowering its partial pressure, CaO will regenerate at
lower temperatures. The dry gas stream produced in this phase consists mainly of
CO 2 and small amounts of hydrogen and carbon monoxide.
The resulting gas concentrations from gasi

°

cation using CaO are shown in
Table 4 . The maximum average hydrogen concentration seen was 69.4 %. This was
higher than any concentration seen without the use of CaO. The reason for the high
H 2 levels was the elimination of CO 2 . During the maximumH 2 concentration test, the
CO 2 concentration was 12.0 mol%, which is lower than any concentration seen
during un-catalyzed testing. The CO concentration at the maximum H 2 concentration
case was 7.5 %. This is nearly three times lower than the lowest levels seen during
un-catalyzed testing. The low carbon monoxide levels were a result of Le Chatelier

' s

principle working on the CO-shift reaction. This con rms that the CO-shift reaction

is one of the most important reactions determining the syngas composition.
The effect of CaO on hydrocarbon levels varied. All the hydrocarbon concen-
trations measured during catalytic testing were similar to levels seen at 850

° Cin

Table 4 Results from gasification with CaO
Test # 1 2 3

Reactor temperature ( ° C) 657 690 701

S/B ratio 2.9 2.9 2.1

Gas residence time (s) 2.7 2.6 2.7

Syngas component Average gas conc. (dry mol%)

Hydrogen 65.5 69.4 68.3

Methane 11.1 8.8 8.7

Carbon monoxide 10.8 7.5 9.3

Carbon dioxide 9.4 12.0 11.3

Ethylene 1.6 1.3 1.4

Ethane 0.5 0.8 0.6

Acetylene 0.1 0.1 0.1

Propylene 0.4 0.8 0.4

HHV (dry MJ/m 3 ) 15.6 14.2 14.3