# Experimental Investigation of Oxygen Carrier Aided Combustion (OCAC) with Methane and PSA Off-Gas
## 2 Materials and Methods
### Reactor System
At similar heights but on the opposite side of the reactor, corresponding to the same measurement points named MP1-MP8, sampling gas can be extracted. Gas sampling tubes are injected into the reactor where the ends of the tubes are located 2 cm from the inside reactor wall. The ends of the sampling tubes have porous metal cups (10 mm OD, 6 mm ID) consisting of nickel-chromium-iron-molybdenum alloy (316 L) with a porosity of approximately 150 \(\upmu\)m. The metal cups act as a filter to prevent bed material from entering the gas sampling tube. After each measurement, the sampling tubes are flushed in the opposite direction with pressurized air in order to remove possible fines from the porous surface. Jacketed tubing is used on this side to make it possible to move the tube over the cross section. In order to avoid condensation in the extracted gas stream, a hose with heating bands is attached at the end of the gas sampling tube at the vertical measurement point of interest and a temperature controller is used to keep the temperature at approximately 190 \({}^{\circ}\)C. One normal litre per minute is the required gas flow to the analysers. The sampled gases are sent to a hot filter operating at a temperature of 190 \({}^{\circ}\)C. The wet gas is then dried in a condenser followed by a cold filter before it is provided to the SICK GMS810 gas analyser. NDIR (nondispersive infrared sensors) are used to measure the concentration of CO, CO\({}_{2}\) and CH\({}_{4}\). O\({}_{2}\) is measured with a paramagnetic sensor, thermal conductivity is used to detect H\({}_{2}\) and the NO concentration is estimated with Non-Dispersive Ultra Violet Spectroscopy (NDUV). All the mentioned measurements are made online where one datapoint is retrieved every second. The analysers were calibrated at the start of each day when an experiment was carried out (at the zero point and an additional calibration point). The uncertainty in the gas concentration measurement is <0.5% for each component. Figure 2 shows the key zones of the bubbling fluidized bed and provides an indication where these zones are found in the setup used. Equal volumes of bed materials were used in the experiments. Bulk density measurements prior to the experiments were conducted to estimate the required bed inventory. The target was to have the bed height \(H_{\text{b}ed}\) between \begin{table}
\begin{tabular}{c c} \hline
**Measurement Position** & **Vertical Position (cm)** \\ \hline H\({}_{8}\) (MP8) & 79.65 \\ H\({}_{7}\) (MP7) & 63.65 \\ H\({}_{6}\) (MP6) & 47.65 \\ H\({}_{8}\) (MP5) & 31.65 \\ H\({}_{4}\) (MP4) & 15.65 \\ Targeted \(H_{\text{b}ed}\) & 13.65 to 15.65 \\ H\({}_{3}\) (MP3) & 13.65 \\ H\({}_{2}\) (MP2) & 8.88 \\ H\({}_{1}\) (MP1) & 3.65 \\ H\({}_{0}\) (MP0, in windbox) & \(-\)4.00 \\ \hline \end{tabular}
\end{table} 
Table 1: Measurement point (MP) positions in relation to the distributor plate. the third and fourth measurement points (MP3 and MP4) from the distributor plate of the reactor. This point was estimated based on the assumption that the gauge pressure at the top of the splash zone should be close to 0. Based on the pressure measurement data at MP3, the bed height was therefore estimated according to Equation (1). A constant pressure gradient is assumed between MP3 and the top of the splash zone. The air density (\(\rho_{air}\)) is assumed to be negligible compared to the particle density (\(\rho_{p}\)) and the voidage of the fixed bed (\(\epsilon_{fixed}\)) is assumed to be 0.4, whereas the voidage in the bubbling bed (\(\epsilon_{BFB}\)) is assumed to be 0.6. \[H_{bed}=H_{3}+\frac{P_{3}}{9.81\big{(}\rho_{p}-\rho_{air}\big{)}(1-\epsilon_{ BFB})} \tag{1}\]  
The particle density was determined based on the measured bed density for the bed materials used according to Equation (2).