(567f) Chemical Looping Steam Gasification of Biomass in the Presence of Co3O4 in a Bubbling Fluidized Bed, Kinetic Modeling

Chemical
looping is a relatively new technology for the combustion and gasification of
fossil fuels. In this technique, to avoid the dilution of the product by nitrogen,
the oxygen is provided indirectly by an oxygen carrier often in the form of a
metal oxide (MeO). The effluent gas is nitrogen free and there is no
need for further separation. Chemical looping gasification consists of two
vessels (reduction and oxidation) working in parallel at 800 ^οC.
In the reduction vessel, the biomass reacts with steam and oxygen and recycled
back to the oxidation zone where it regenerates to full oxidation state by air.

Chemical
looping steam gasification of biomass takes place in four steps as shown in
Figure1. In the first step MeO releases oxygen into steam. Pyrolysis as
second step decomposes the biomass to permanent gases and char. The char reacts
with steam and oxygen and ultimately the produced gases from pyrolysis and
gasification react together.

Figure 1: Gasifier
process block diagram

A transient kinetic
model for biomass gasification is developed based on the mechanism of surface
reactions. The apparent rate constants are computed by minimizing the
differences between experimental data and theoretical results for different
temperatures (700, 750, 800 ^οC), steam content (0, 7,
10, 18%) as well as MeO/sand ratio (0, 10, 30, 50 %). Experiments
were carried out in a 7.8 cm ID by 167 cm length fluidized bed
reactor in the presence of Co₃O₄as MeO.
10 g of biomass was injected to the reactor and after completion of reaction
the fluidizing gas was switched to air to regenerate the cobalt oxide. The
product gas was sampled and analysed online with a Pfeiffer mass spectrometer.