## 3 Results
### Effect on Boiler Temperature Profile during Operation  
The temperature profile of the boiler could be expected to reveal whether LD-slag promotes combustion in the bed. Figure 4 shows the temperature at four different measuring points when the boiler was operated at a low air-to-fuel ratio (1.07), while Figure 5 shows the same temperatures when operating the boiler at a higher air to fuel ratio (1.17). The temperatures were measured with conventional thermocouples of type-K.  
Figure 4: Temperature profile over the boiler when operated with low air-to-fuel-ratio. Figure 5: Temperature profile over the boiler when operated with high air-to-fuel-ratio. Note that the cases with 10% and 30% LD-slag overlaps so well that they are difficult to distinguish. In Figures 4 and 5, T\({}_{\rm bottom}\) was 840-850 \({}^{\circ}\)C for experiments with LD-slag, and sand and 880 \({}^{\circ}\)C for experiments with LD-slag and ammonium sulphate. A reference curve for operation with sand has been included. The reference curve originates from operation with fresh silica sand with T\({}_{\rm bottom}\) at 870 \({}^{\circ}\)C in a clean boiler and thus represents a best-case scenario for conventional combustion with respect to emissions (over the course of the firing season base emission levels may increase as different parts of the boiler are subject to e.g., accumulation of ash). The fuel flow, boiler load and bed mass were comparable in all cases. The following phenomena can be observed:  
* There is always a temperature drop over the cyclone, which is to be expected since it is water-cooled. The temperature drop is reduced by the fact that final combustion is also taking place here. It is clear that the temperature drop is much more pronounced for experiments involving LD-slag compared to when only sand is used. This suggests that, with LD-slag, significantly less combustibles enter the cyclone and burn there. Considering that the concentration of incombustibles (CO, H\({}_{2}\), CH\({}_{4}\), THC) in the stack are on ppm level, this suggests that more combustion must take place inside the actual boiler body when LD-slag is used, in comparison to the sand case. * Also, from the temperature difference between the bottom of the boiler and the top of the dense bed it can be seen that more heat is generated in the dense bed when LD-slag is present for the 10% and 30% mixtures, than when only sand is used. This corroborates with the observation above. * For the case with 100% LD-slag with addition of ammonium sulphate, the picture is somewhat unclear and can be interpreted in different ways. There are reaction enthalpies for dissolution of ammonium sulphate, oxidation of ammonia and sulphation of K, which can be expected to affect the temperature in the cyclone outlet. One should also consider the unit on the y-axis and the temperature in the bottom bed, which was significantly higher than in other experiments at 880 \({}^{\circ}\)C. So as of this time insufficient information is available to explain precisely what is taking place. Even if we discard the experiments with ammonium sulphate from the analysis, it should be acknowledged that measured temperature data is good for qualitative analysis only. For example, sublime changes in boiler load could be expected to influence temperature profile. Nevertheless, Figures 4 and 5 are largely consistent with our hypotheses which is that the presence of an oxygen carrying bed material facilitates combustion in the dense part of the bed and to some extent also in the freeboard above it. The expected result would be a larger temperature increase here compared to when only sand is used. This in turn should result in less combustibles remaining to be burned in the cyclone, leading to a sharper drop in temperature here in comparison to when sand is used. The latter effect is extremely clear in Figures 4 and 5. For the same reason, the temperature drop in the cyclone should be higher for a high air-to-fuel-ratio, which was also observed.