# Experimental Investigation of Oxygen Carrier Aided Combustion (OCAC) with Methane and PSA Off-Gas
## 3 Results  
### Experiments with Methane  
The three materials (sand, ilmenite and C28) were examined at five different bed temperatures (600, 750, 800, 850, 900 \({}^{\circ}\)C). The results from these experiments using methane as fuel are also presented in Tables S1-S3 in the supplementary material. The vertical temperature profiles measured for the systems operated with sand, ilmenite and C28 at different bed temperatures can be seen in Figure 4. The bed heights were estimated for the three bed materials at all bed temperatures. The average bed height was 15.6 cm for sand, 15.3 cm for ilmenite and 14.6 cm for C28, based on the pressure drop measurements for experiments with methane as fuel. The estimated bed height is, therefore, between measurement points 3 and 4 for all three materials. In all gas concentration measurements with methane as fuel, \begin{table}
\begin{tabular}{c c} \hline \hline
**Compound** & **\%** \\ \hline CH\({}_{4}\) & 15 \\ H\({}_{2}\) & 25 \\ CO & 15 \\ CO\({}_{2}\) & 45 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Gas composition of PSA off-gas in vol-%. the methane concentration at the inlet was 9.07%, and the measured concentrations in the reactor are dry since steam is condensed prior to the gas analyser. In Figure 4, it can firstly be observed that the temperature profile is rather similar for all bed materials for the respective bed temperatures. The gases are rapidly heated upon entering the bed from the wind box below the distribution plate. The temperature is then rather constant in the bed (MP1-MP3) and for the most part also between MP3 and MP4, where the splash zone is considered to be located. The highest temperature is usually found just above the bed (MP4). In the freeboard (MP4-MP8), the temperature level is slowly decreased towards a value which is closer to the setpoint of the electrically heated furnace, which surrounds the reactor. The measured temperatures are overall very similar for the three bed materials although some differences can be observed in the freeboard at 700, 750 and 900 \({}^{\circ}\)C.  
Since it is expected that increased temperature results from heat release from fuel combustion, it is interesting to observe if such temperature gains can be seen for the three bed materials. It is observed that there are differences in the \(\Delta\)T between MP4 and MP5 for the three bed materials, which therefore could indicate that there are also differences in fuel conversion in this region for these materials. The temperature in the freeboard drops overall for all tested materials and bed temperatures but the drop is more significant at higher temperatures. The reason for this temperature drop is that the furnace temperature is below the temperature in the reactor where the exothermic reaction heats the inside of the reactor resulting in a heat loss to the surrounding furnace. It should also be mentioned that the operation of the ventilation system above the furnace is expected to cool the top of the freeboard to some extent. A more pronounced temperature drop, therefore, indicates that little or no fuel combustion takes place in this zone. A less pronounced temperature drop could indicate that more methane combustion takes place in the freeboard. Except for the measurements at 900 \({}^{\circ}\)C, where sand appears have a smaller temperature drop than the  
Figure 4: Measured temperatures at different measurement points (MP0–MP8) for five different bed temperatures (from 600 to 900 \({}^{\circ}\)C) for all three bed materials with methane as fuel. other two bed materials, it is difficult to observe any significant differences between the bed materials. The difficulty to see temperature differences, in general, can be traced to the fact that the convective heat transfer from the gas is lower compared to radiative heat transfer from bed materials and walls. It is also possible that conductive heat transfer from walls to the thermocouples could influence the measurements.