Hydrogen-Enriched Syngas from Biomass Steam Gasification for Use in Land-Based Gas Turbine Engines - Novel Combustion Concepts for Sustainable Energy Development - page 100

A carbon balance was performed to determine the amount of carbon not con-
verted to syngas. At the maximum energy ef ciency case, 18 % of the carbon in the

biomass did not form usable syngas. This corresponded to any total energy loss of
9 %. There are multiple ways to increase the conversion of carbon and increase
energy ef

ciency; higher gasi cation temperatures, the addition of catalysts, and a

dual bed gasi cation system. The tar and char energy content is the least accurate

value given in the energy balance due to the indirect form of measurement. It is
necessary to note that the heat content of the outputs was 16 % larger than the
inputs. This was most likely due to the accumulation of char in the reactor bed. By
the time the measurements were taken for this analysis, a signi

cant amount of char
had probably built up in the bed and was reacting with steam adding heating content
to the syngas. To account for this in the energy flow, the difference was subtracted

from the tar and char heat content value. This gave the most accurate reporting for
steady-state gasi

fl

cation.

3.4 Gasi cation with Calcium Oxide

To further improve the energy conversion ef ciency, a catalyst was used in the

fluidized bed. This section presents the experimental findings of gasification per-
formed with a CaO reactant. The temperatures tested were between 650 and 700

C.
At lower temperatures, low char reaction rates decrease biomass utilization and
correspondingly the thermodynamic conversion ef

°

ciency. At higher temperatures,
CO 2 reaction rates with limestone decrease. A full parametric study to determine the
effect of S/B ratio or gas residence time was not performed. Test conditions were
chosen based on the gasi

er behavior observed in un-catalyzed testing. Moderate
S/B ratios of between 2 and 3 were chosen to balance hydrogen production effi- -

ciency and energy ef ciency. It was observed without a reagent, higher S/B ratios

corresponded to increasing hydrogen production ef ciency but lowered energy

ef ciency. The biomass feed rates were kept low to increase the duration of testing.

Testing times were limited by the mass of limestone in the reactor. When the
limestone becomes saturated with CO 2 , the CO 2 concentration returns to levels seen
in un-catalyzed testing. It was desired during this study to look at the behavior of
gasi er is at a quasi-steady state.

Once all of the CaO has reacted, it must be regenerated to continue testing. The
ideal way to do this is to implement a second reactor. In this case, the spent quicklime
is carried to the second reactor, regenerated, and returned to the

cation before this transition occurs, when the gasi

fl fluidized gasi cation

bed. With a single cation requires

cycling the bed. This results in three distinct phases occurring as follows:
Biomass gasi

fl fluidized bed, as the case for this study, CaO gasi

cation phase: In this phase, biomass is inserted into the fl fluidized

°

bed and gasi ed at temperatures between 650 and 700 C. CO 2 produced during

gasi cation reacts with CaO to produce CaCO 3 , removing CO 2 from the reactor.

The resulting shift in gas-phase composition creates more elemental hydrogen.
At temperatures at and below 700

° C, the reactivity of char is low. As a result, char