A method for determination of reaction enthalpy of oxygen carriers for chemical looping combustion – Application to ilmenite

Chemical looping combustion (CLC) is a method for combustion with inherent CO2 separation. In CLC an oxygen carrier supplies the oxygen necessary for fuel conversion. A method to determine the enthalpy of the reaction of oxygen carriers was developed. This method utilizes the fact that for many oxygen carriers the reaction enthalpy with CO is exothermic while it is endothermic with CH4. By measuring the temperature change for reduction of different mixtures of CO and CH4 it is possible to find the mixing ratio giving a thermally neutral reaction. From the known reaction enthalpies of CO and CH4 with oxygen it is then possible to deduce the reaction enthalpy of the oxygen carrier. The reaction enthalpy for a NiO based oxygen carrier is estimated to 475 ± 8 kJ (mol O2)−1. The expected value of 469 kJ (mol O2)−1 is in the error range and thus verified the method. The reaction enthalpies for three different ilmenite particles were also determined to 453 ± 12 kJ (mol O2)−1 for synthetic ilmenite and 469 ± 5 kJ (mol O2)−1 for natural ilmenite. A natural ilmenite that has previously been long term tested ended up with the reaction enthalpy 468 ± 9 kJ (mol O2)−1.