Øyvind Langørgen from SINTEF and Lei Liu from Tsinghua University presented at the public seminar of the CHEERS project on the 20th of September at Deyang, China. Covering the work done on the topic of the oxygen carrier material within work package 3, the presentation went through the selection of the oxygen carrier, its subsequent testing and validation.
The oxygen carrier is a crucial part of the chemical looping combustion technology. The oxygen carrier would transfer the oxygen from the air reactor to the fuel reactor for fuel combustion. It must also transfer the heat necessary to sustain the combustion process. These two functions ensure that this type of oxy fuel technology results in a clean stream of CO2 with very low impurities while achieving chemical looping combustion. Oxygen carriers are typically metal oxides, based on metals such as iron (Fe), manganese (Mn), calcium (Ca), or copper (Cu). These carriers can be both natural and synthetic, and to identify the correct choice many tests were conducted; first through lab scale screening tests, then through testing in CLC pilots and finally validation at the pilot scale CLC units.
Properties were prioritized when considering oxygen carriers that would best suit the CLC process. This included the capacity to transfer oxygen, fuel conversion and reaction kinetics, the lifetime of the material, and the availability and cost of the material. One of the initial materials selected was Ilmenite (FeTiO3), multiple sources were tested of this material; from Norway, Vietnam and Mozambique. This naturally occurring material was tested at different heat conditions and the Norwegian sourced (Titania) Ilmenite T2 proved to be the most effective. Despite being and appropriate candidate, initial testing at high temperatures resulted in agglomeration of the material which proved to be a barrier for achieving CLC.
As an alternative, a synthetic material Perovskite – Ca(MnxTiyFez)O3 was tested in the batch fluidized bed unit at IFPEN. The results showed partial deactivation of the material due reaction with sulphur. This alternative be was discarded as the feedstock used in the European configuration, Petcoke, has significant sulphur content.
Turning back to Ilmenite, the reason for agglomeration was evaluated. It was found that the issues lie in the delivery of the material being dry. By pretreating the material, via the addition of steam, it was noticed that agglomeration was avoided. This reduced fuel conversion and oxygen transport capacity but well within the design limits. Tests were then carried out with the material at 15 kW and 150 kW scales with various feedstocks: Petcoke, biomass and a mix of the two, showing positive results.
While the Ilmenite was being evaluated at SINTEF, Tsinghua University tested the synthetic material CMTF Perovskite. The results from 1000 cycles showed no agglomeration and short oxidation time of only 4 seconds. It also had a longer lifetime compared to the ilmenite alternative. With these benefits came a significant difference in cost; nearly 2000 USD/ton of the material whereas Ilmenite was priced well belove half.
Considering these parameters, ilmenite was chosen to be the ideal candidate for the role of oxygen carrier for the CLC process. The work package had managed to validate 3 oxygen carriers in this process. Ilmenite met the criteria for performance, cost, sulphur tolerance and availability among other parameters. 250 tons of ilmenite was shipped from Norway to Deyang, China for the pilot plant for testing of both the European and Chinese configurations.
For more information on the oxygen carrier work done on the CHEERS project, feel free to reach out.