Kinetic description derived from fluidized bed experiments for ilmenite as oxygen carrier in chemical-looping combustion
Konferensbidrag (offentliggjort, men ej förlagsutgivet), 2011
Chemical-looping combustion (CLC) is one of the most promising methods for CO2-
capture from power production as well as from industrial applications. Most work on
CLC so far has been oxygen carrier development carried out in laboratory scale units. In
parallel, process modeling and simulation are important to gain information on possible
reaction steps as well as for predicting the operation of large scale applications.
Regarding the use of solid fuels in CLC, it is assumed that some oxygen carrier
material will be lost by ash removal. Due to this fact, low cost and environmental sound
materials are preferred. Natural minerals or ores as well as industrial residues can be
promising oxygen carriers. For example the naturally occurring iron-titanium mineral
ilmenite is one of the most used oxygen carriers in tests with solid fuels.
In this work data from laboratory experiments is used to derive kinetics describing
the conversion of a natural rock ilmenite while utilizing CO and H2 as fuel gases. The
reactivity with CO and H2 is particularly important in solid fuel CLC since these are
gasification intermediates. The ilmenite was provided by Titania A/S and has been used
as oxygen carrier in former studies. The particles used whilst the experiments were
sized in the range between 125 and 180 μm.
The experimental setup consists of a tubular batch quartz glass reactor. The ilmenite
sample was placed on a porous quartz plate in the center of the reactor. The reactor
was heated to the desired temperature electrically. CO and H2 were used as fuel gases
since this are the primary gasification gases. All experiments were carried out under
fluidized bed conditions. Different fuel gas concentrations were achieved by diluting the
fuel flow with nitrogen and the bed temperature was varied from 850 to 950°C.
The fuel conversion rates were used to calculate kinetic parameters. A comparison with
published parameters is accomplished. The results for H2 and CO as fuel also allow
modeling of intermediate steps in CLC of solid fuels.