Hydrogen-Enriched Syngas from Biomass Steam Gasification for Use in Land-Based Gas Turbine Engines - Novel Combustion Concepts for Sustainable Energy Development - page 87

back to the gasifi- cation process, commonly referred to as indirectly heated gasifi- -

cation technology. A successful scheme to achieve the indirectly heated gasi cation

process is the dual fluidized bed (DFB) system as shown in Fig. 1 . The unreacted

char and bed material in the gasi

fl

er is carried to a combustion chamber where air is
injected. The heat produced is then transferred back into the gasi er by the bed

material. The gasi er utilizes a fl fluidized bed usually consisting of sand. When a gas

is passed through the bed of fine solids, the bed takes on the characteristics of a

liquid, allowing it to flow between the respective chambers. The continuously

circulating bed greatly increases heat transfer and interaction time between the
biomass and gasifying agent, while the sand breaks up the biomass quicker leading
to higher gas production. The bed material easily

fl

ows when aerated, and the
liquidity of the bed aids in the transfer of char to the different chambers of
the system. This approach separates the combustion reaction from the remaining
gasi

fl

cation reactions producing a product gas that has insigni cant percentage of

18 MJ/Nm 3 . N 2 and has a heating value within a range of 15

-

cation facilities that are used both in research
and power plant scenarios are listed in Table 2 (Paisley et al. 2001 ; Kappotz et al.
2009 , 2011 ; van der Meijden et al. 2007a , b ; Corella et al. 2007 ; Herguido et al.
1992 ; Xu et al. 2006 ; Wei et al. 2006 ; Matsuoka et al. 2008 ). Most comprehensive
studies of DFB gasi

A list of dual fl fluidized bed gasi

cation are more recently carried out at Vienna University of
Technology in Austria (Koppotz et al. 2009 , 2011 ) using both laboratory and pilot-
scale facilities. The key

findings from their work using the CO 2 absorption
enhanced reforming process were a signi cantly higher H 2 content (50 60 %) in the

-

producer gas as compared to the conventional dual fl fluidized bed steam gasi cation.

The high hydrogen concentrations were obtained at gasi cation temperatures of

about 700 C and using repeated cycles of carbonation and calcination.

All the systems cited above use steam as the gasi

°

cation agent in a typical DFB
system. Because of the high heat of vaporization of steam and gasi cation being

Fig. 1 Flow schematics for a dual fl fluidized bed gasification system