## 4 Discussion
Further, even though an oxygen carrying bed material can increase the overall efficiency of the plant it might be difficult to quantify how big this increase is in practice. Extensive reference operation with silica sand might be needed to evaluate this. In the same manner, positive effects in costs related to maintenance might be visible first after a couple of years of operation with the new bed material. It is not uncommon that the maintenance budget is separated from the operation budget, meaning that any potential long-term gains will be less visible for the person that is paying for the actual bed material. Apart from the technical considerations and the positive effects of decreased emissions, this study also highlights the positive environmental effects of reducing silica sand extraction. However, the idea that silica sand extraction is unsustainable is probably not widespread in the industry. It is not reflected in the sand market, since the availability of sand is high and the cost is quite low. Thus, from the view of the boiler operator, this is not a problem that needs fixing. Another reason for the quite few implementations might be simply a lack of knowledge about the advantages of using oxygen carriers or other alternative bed materials. It should be in the interest of all concerned parties to get the most value out of their activities, and utilization of by-products is a much-discussed topic for several reasons. However, to create a market for a new product, there will have to be investments into building and operating refining facilities as well as organizing transportation of the materials. There are many different forms a possible oxygen carrier market could take and some different options can be mentioned:  
* The material producer (i.e., LKAB, SSAB, or Boliden) creates a niche towards bed material production and invests in facilities in connection to existing industry. * The boiler operator installs equipment for bed material refining and buys \"raw\" material from the metallurgical industry. An alternative to this is that contractors are hired to sieve and crush bed material on-site when required. * A third party invests in building a dedicated bed material production facility, buys raw material from the steel industry, etc., and sells it to the boilers. * A combination of points 1 and 3, where a third party trades the right size fraction from the material producer, handles the logistics from producer to user, and acts as the technical competence as well as trains the operating personnel for the shift to operation with oxygen carriers. The first option has the advantage that the existing facilities and flows in e.g., a steel plant are so large that adding a facility like the one required would not be large in proportion to the main activities. There is also already to some extent infrastructure for and experience of processing by-products at the site, and this would in some cases be an adaptation of existing processes rather than building completely new facilities. In the second option, the boiler owner produces the right particle sizes from the raw material. This might be less attractive from a boiler owner's perspective as it demands large free areas and extensive logistics. Free areas are commonly not available at the boiler site, as all open space usually is covered by fuel piles during boiler operation. Further, this option also produces a byproduct where the rejected material (particles of the wrong size) is to be handled and transported away from the site. There are examples where e.g., fuel contractors bring their equipment to boiler sites to produce woodchips from round wood and when the work is carried out, they leave the site together with their equipment. In this manner, the boiler owner does not have to invest or handle the operation and maintenance of any extra equipment, nor providing the staff for it. A similar setup might be a possible solution for handling the raw material to the right size fraction.