## 2 Oxygen Carrier-Aided Combustion (OCAC)
### Procurement of Oxygen Carriers for OCAC-Experiments  
For the activities outlined in Table 1, it has been required to procure large amounts of oxygen carrier particles. The procedure has been different for different kinds of materials. The basics are explained below:  
* Rock ilmenite has been received predominantly from the company Titania A/S, which operates an open-pit mine located in Hauge in Norway. The ore is crushed to a small size on site and subject to mechanical beneficiation to enrich the ilmenite concentration to 85-90%. The facility produces about 850 kton of ilmenite concentrate per year. The process inherently produces particles low in dust in a range of different size fractions. Thus, extraction of a few dozens or hundreds of tons of particles can be done at a moderate cost. The product was sieved to provide particles at the size range required for OCAC. Once extracted from the process chain, the material was dried before transport and use. * Sand ilmenite originating from Australia has been provided by the material trading company Sibelco. Ilmenite sands can be found in placer deposits of heavy minerals occurring for example in South Africa, Australia, North America, and Asia [58]. Sand ilmenite generally stems from weathered rock deposits. The weathering causes the iron content to decrease while increasing the concentration of TiO2. Due to the natural iron oxidation and dissolution, hence also called altered ilmenite, the TiO2 content can be as high as 90 wt-%. In this case, the alteration product is called leucoxene [58]. The sand ilmenite was used as is in the OCAC experiments, without further processing. This material was found to be suitable but contains a fraction of fines which are elutriated immediately when the sand enters the boiler. * LD-slag has been provided by the Swedish-Finish steel producer SSAB, via their subsidy SSAB Merox AB. LD-slag (sometimes referred to as steel-converter slag) is produced as large chunks in the ore-based steel production. Merox handled the whole preparation chain which included crushing LD-slag from an open-air storage site, drying in a diesel-fired furnace, grinding, and sieving. Similar equipment as is normally used for crushing and grinding to produce slag products were applied. The desired particle size of 100-400 \(\upmu\)m was smaller than what is typical for slag-based products, which normally is in the size range of several mm or a few cm. Sieving was done with a horizontal shaker outfitted with a woven wire mesh sieve. This was likely not an optimal choice and sieving reportedly was very time-consuming, despite leaving <15 wt.-% material finer than 100 \(\upmu\)m in the batch. The yield from large chunks to particles in the desired size range reportedly was only about 20-25%. The process involved significant elements of trial-and-error. It seems likely that a significantly higher yield and a reduced fraction of fines could be achieved with some procedural developments. * Manganese ores have been procured from two different sources, namely Sibelco Nordic AB and Elwaleed. The Sibelco ore was provided as large heat-treated chunks. Elwaleed grade C is a low-grade ore provided as smaller chunks. Particles were produced from the ores by the company UVR-FIA GmbH in Germany. The Sibelco ore was first crushed into smaller fragments. This was apparently not needed for the Elwaleed C ore. The principal step for producing particles was multi-stage grinding, sieving, and dedusting. Final sieving reportedly was conducted by wind sifter rather than horizontal-type shake sieve. This resulted in batches principally free from fine material. The yield in the desired particle-size range 100-400 \(\upmu\)m was 40-50%. * Foundry slag from Sandvik SRP AB was used for the experiment in Lidkoping. The slag is produced at the foundry as chunks that were crushed, dried, and sieved to obtain the desired size fraction. The processing was handled by Sibelco. The material contained some elemental metal which complicated the crushing.