# Experimental Investigation of Oxygen Carrier Aided Combustion (OCAC) with Methane and PSA Off-Gas
## 3 Results
### Experiments with Off-Gas
For sand at MP1 at bed temperatures of 700 and 750 \({}^{\circ}\)C, the measured concentration of CO\({}_{2}\) indicates that almost complete fuel gas conversion takes place at the very bottom of the bed below MP1. This is, however, contradictory to the results from the results above this point, which are more in line with expectations and the rest of the results, which indicate that the result at MP1 for these two temperatures could be outliers. This is also the reason for the fact that these points are not connected with a line to the rest of the data at the respective bed temperatures. The difference in concentrations of CO and CH\({}_{4}\) is presented in Table 7. The ratio is 1 at the inlet. Figure 10: Measured unburnt carbon (CO and CH\({}_{4}\)) in relation to total measured concentration of carbon (CO, CH\({}_{4}\) and CO\({}_{2}\)) for all bed materials at different heights from the distribution plate. In Table 6, it can be observed that the ratio is generally below 1 in the bed, thus indicating higher gas conversion of CO compared to CH\({}_{4}\) in the bed, whereas the ratio is above 1 above the bed, where the ratio is especially high with sand. The ratio is higher above the bed because of significant methane conversion taking place above the bed, whereas the CO concentration is more constant over the height of the reactor. This highlights, once again, the difficulty to convert methane in the bed and motivates the focus on this compound in these experiments. Based on overall results from this study, it should be possible to use a bubbling fluidized bed, operated in OCAC configuration, to convert the targeted fuel mix of PSA off-gas and light hydrocarbons, such as methane, in the dense bed. This could be important for the implementation of the proposed process application to use an OCAC-reactor as a heat source for steam reforming, where this kind of fuel mix is intended. The NO emissions were also monitored with PSA off-gas as fuel. The results are presented in Figure 11.  
It can be observed that the NO emissions are overall low with all bed materials. The NO concentration is especially low in the bed and, in general at bed temperatures above 600\({}^{\circ}\)C. The system with C28 as a bed material results in slightly higher NO emissions \begin{table}
\begin{tabular}{c|c c c c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**Sand**} & \multicolumn{4}{c}{**Imenite**} & \multicolumn{4}{c}{**C28**} \\ \cline{2-13}  & 600 \({}^{\circ}\)C & 650 \({}^{\circ}\)C & 700 \({}^{\circ}\)C & 750 \({}^{\circ}\)C & 600 \({}^{\circ}\)C & 650 \({}^{\circ}\)C & 700 \({}^{\circ}\)C & 750 \({}^{\circ}\)C & 600 \({}^{\circ}\)C & 650 \({}^{\circ}\)C & 700 \({}^{\circ}\)C \\ \hline MP8 & 1.8 & 4.9 & 4.9 & 2.5 & 1.9 & 2.6 & 3.7 & 1.6 & 0.8 & 2.6 & 3.2 \\ MP7 & 1.3 & 5.3 & 4.2 & 2.4 & 1.5 & 2.7 & 3.5 & 2.3 & 1.1 & 2.1 & 2.7 \\ MP6 & 1.0 & 4.2 & 3.9 & 2.7 & 1.1 & 2.2 & 3.2 & 2.9 & 0.9 & 1.6 & 2.5 \\ MP5 & 0.9 & 2.1 & 2.5 & 2.6 & 0.8 & 2.1 & 2.3 & 2.2 & 0.8 & 1.2 & 2.1 \\ MP4 & 0.6 & 0.4 & 0.3 & 0.4 & 0.6 & 0.5 & 0.6 & 1.0 & 0.6 & 0.5 & 0.5 \\ MP3 & 0.5 & 0.3 & 0.2 & 0.3 & 0.5 & 0.5 & 0.5 & 0.8 & 0.6 & 0.4 & 0.4 \\ MP2 & 0.5 & 0.3 & 0.2 & 0.2 & 0.6 & 0.5 & 0.4 & 0.7 & 0.5 & 0.3 & 0.2 \\ MP1 & 0.7 & 0.5 & 2.0 & 1.6 & 0.8 & 0.7 & 0.7 & 0.9 & 0.8 & 0.6 & 0.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Measured concentration of CO (%, dry) divided by measured concentration of CH\({}_{4}\) (%, dry) at different measurement points with different bed materials and measurement points. Figure 11: Measured concentrations of NO (in ppm, dry) for all bed materials at different heights from the distribution plate with PSA off-gas as fuel. overall than the other systems, which could be connected to the previously mentioned effect that the bed material could present more oxidizing conditions than sand, for example. Combustion with low NO emissions is one of the key advantages considered when evaluating the possibility to integrate OCAC with SMR, instead of using the conventional SMR furnace with gas-fired burners.