## 3 Results
### Observations with Respect to General Operability  
Over the entire course of the experimental campaign, no issues related to general operability were encountered. All practical moments, such as handling by pressure discharge truck, pneumatic transport, filling up of the material silo and removal of bottom ash with ash screw worked flawlessly. There were no tendencies towards sintering and no agglomerations were found. This was despite the rather high temperature used, with the target temperature in the bed being 840-870 \({}^{\circ}\)C. This is near the maximum temperature for biomass combustion in a fluidized bed with silica sand as the bed material. The results of the dedicated agglomeration tests in lab reactor can be found in Table 5 below:  
It can be concluded that both practical operation of the boiler and dedicated agglomeration tests suggest that LD-slag has lower tendency towards sintering than silica sand. The slag/sand mixture eventually agglomerated in dedicated tests, but nevertheless performed adequately well with no signs of problems below 1000 \({}^{\circ}\)C.  
Figure 7: Measured concentrations of NO (mg/Nm\({}^{3}\), at 6% O\({}_{2}\)) at position kh2 in the convection path as a function of the air-to-fuel ratio. \begin{table}
\begin{tabular}{l c c c c} \hline \hline
**Sample** & **T\({}_{\text{A1}}\)** (\({}^{\circ}\)C) & **T\({}_{\text{A2}}\)** (\({}^{\circ}\)C) & **T\({}_{\text{A3}}\)** (\({}^{\circ}\)C) & **Comments** \\ \hline LD-slag (fresh) & - & - & - & Successfully reached maximum temperature without problems. \\ \hline
100\% LD-slag (extracted 2017117) & - & - & - & Successfully reached maximum temperature without problems. Some micro-agglomerations noted during cleaning of reactor. \\ \hline
30/70\% mixture LD-slag/sand (extracted 20171122) & 1010 & 1060 & 1081 & Agglomerates and increased bulk density noted during cleaning of reactor. \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Results of agglomeration tests. With respect to the generation of fly ash and bed material attrition, a simplistic but nonetheless illustrative comparison between LD-slag and silica sand have been performed. Basically, two representative 24 h periods with similar operational conditions, one for 100% LD-slag and one for 100% silica sand, were selected and compared to each other (see Table 6). In Table 6 it can be seen that 365 kg more fine material was generated over the course of 24 h when LD-slag was used as bed material, compared to when sand was used. The increase was roughly a factor of three for all measured locations. There are three potential sources for fly ash: (i) fly ash generated from the fuel; (ii) fly ash generated by attrition of bed material; and (iii) the 10-15 wt% material below 90 \(\upmu\)m present in the batch of LD-slag to begin with. Fly ash from fuel should not differ greatly between the two cases. Further, in the study covering the analysis of bed samples from the campaign [23], it is shown that fly ash samples contained the same elements as fresh LD-slag, albeit in somewhat reduced concentrations. The numbers reported in [23] support the premise that about the same amount of ash is generated from the fuel (source (i)) in both cases. Unfortunately, it is not possible to know whether the increase in fly ash generation came from attrition (source (ii)) or fine material already present in the batch due to imperfect sieving (source (iii)). A back-of-the-envelope calculation suggests that with a bed inventory of 2500 kg and a turnover of 800 kg/24h, there could be up 250-375 kg particles below 90 \(\upmu\)m in the inventory to begin with, and that another 80-120 kg added over the reference period. These numbers should be compared with the 365 kg increase in fly ash production. This clearly is in the same order of magnitude as the increase in fly ash. To summarize, operation with LD-slag did result in increased generation of fly ash.