Kinetic description derived from fluidized bed experiments for ilmenite as oxygen carrier in chemical-looping combustion

Övrigt konferensbidrag, 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.