## 3 Results
### Material Balance and Attrition Behavior  
The result from the mass balance and the rate of attrition are reported in Table 5 below.  
Because of the uncertainties pointed out in Section 4, one should be careful not to put too much weight into this very fundamental analysis. Nevertheless, the general pattern in Table 5 corresponds to what could be expected. The highest rate of attrition experienced was 0.25 wt %/h during the start-up with fresh manganese ore. In addition, for the other days when substantial amounts of fresh manganese ore were added (Day 5 and Day 16), the attrition rate was clearly above the baseline. Once the material had been in the boiler for a day or so, the attrition rate decreased. This could be expected as the attrition should be less severe after rough parts of the particles have been eroded and the smallest particles elutriated.  
Solid samples from different locations were collected over the course of operation. Some were selected and examined in a high-resolution light microscope in order to examine morphological irregularities. Pictures of four such samples can be found in Figure 9.  
It is evident that the manganese ore did undergo considerable changes over the course of the campaign. The fresh material is rough-edged, as could be expected from particles produced by crushing and grinding. Material that has been used during operation is smoother around the edges, albeit the general shapes are not substantially altered. This is consistent with the numbers in Table 5 and the general reasoning outlined above. There is also a noticeable change in colour, with fresh particles being almost black while used particles are dark brownish with rusty red also being present. The colour change is likely associated with an alteration of the chemical properties of the manganese ore, which will be subject to detailed analysis in future studies.  
It can be concluded that over the course of the experimental campaign there has been no evidence of severe attrition and no indication that manganese ore should not have sufficient physical integrity for use in CFB boilers. Based on the material balance, the expected life time of the manganese ore is \(>\)1000 h. That is an order of magnitude higher than the time silica sand typically spends in a CFB boiler for biomass.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Day**} & **Ash Added** & **Elutriated** & **In-out** & **Attrition** & **Comment** \\  & **with Fuel (kg)** & **Material (kg)** & **(kg)** & **(wt \%/h)** & **Comment** \\ \hline
1 & 105.2 & 124.5 & \(-\)19.3 & 0.05 & Ref. sand \\
2 & 141.4 & 117.6 & 23.8 & \(-\)0.05 & 10\% Mn ore \\
3 & 137.2 & 128.5 & 8.7 & \(-\)0.02 & 30\% Mn ore \\
4 & 128.3 & 119.1 & 9.2 & \(-\)0.02 & 30\% Mn ore \\
5 & 49.5 & 75.4 & \(-\)25.9 & 0.16 & 50\% Mn ore \\
8 & 93.6 & 178 & \(-\)84.4 & 0.25 & Start-up with 100\% Mn ore \\
9 & 146.1 & 199.7 & \(-\)53.6 & 0.11 & Pellets added, also 800 \({}^{\circ}\)C \\
10 & 140.0 & 159.1 & \(-\)19.1 & 0.04 & Includes gasifier operation \\
11 & 139.2 & 174.8 & \(-\)35.6 & 0.07 & Includes gasifier operation \\
12 & 117.8 & 173.4 & \(-\)55.6 & 0.12 & \\
13 & 118.6 & 145.4 & \(-\)26.8 & 0.06 & \\
14 & 127.6 & 155.8 & \(-\)28.2 & 0.06 & \\
15 & 132.9 & 189.3 & \(-\)56.4 & 0.12 & Sulfur feeding \\
16 & 141.5 & 224.8 & \(-\)83.3 & 0.17 & Regenerated bed, sulfur \\ \hline \hline \end{tabular}
\end{table}
Table 5: Mass balance and estimated rate of attrition.