3.1.2.1 Setup for single gas experiments
The block diagram of the facility on the single mode is presented in figure 3.2. The single gas experiments are performed using the dead-end mode (retentate closed), where the entire helium, hydrogen or nitrogen feed stream imposed by MFC6 (103 ml/min MFC calibrated for He) is forced to permeate through the membrane. The permeate pressure is imposed either using the PC associated to the vacuum pump or directly connecting this side to the ventilation where an atmospheric pressure is kept. These imposed pressures are measured/verified by PR2. The imposed feed flow leads to a pressure difference across the membrane, determined by measuring the pressure on the feed side with PR1.
ZIMT III overview and details of the main components 29
Figure 3.2: Block diagram of the experimental setup for single gas experiments. MFC - Mass Flow Controller; MFR - Mass Flow Register; PR - Pressure Register; PC - Pressure Controller. MFC6 calibrated for He (103 ml/min). MFR calibrated for He (104 ml/min).
3.1.2.2 Setup for binary mixtures gas experiments
The initial single gas apparatus was upgraded to the one presented in figure 3.3. In this configuration, the feed flow of helium is imposed with a 104 ml/min MFC calibrated for He
(MFC3 in the figure) and the feed flow of hydrogen is controlled with either a 10 or 500 ml/min MFC calibrated for H2 (MFC2 and MFC1, respectively, in the figure). Therefore, a dynamic
mixing of both species is achieved. The selected flows give rise to the concentration of each gas in the total stream. For instance, setting 50 ml/min flow for H2 and 1000 ml/min for He, a
H2/He concentration of 5% is obtained.
In this setup, the retentate line is opened. A 104 ml/min MFC calibrated for He (MFC5 in the figure) is used on the retentate side at atmospheric pressure to maintain a desired flow. As a consequence, the permeate flow is also controlled (on the permeate side a 104 ml/min MFR calibrated for He is used). The permeate pressure is maintained constant (at around 300 hPa) using the PC and the associated vacuum pump. Due to those imposed pressures, a higher pressure in feed exists, enabling the permeation/rejection of the gaseous species. The analysis of the permeate and retentate streams is then accomplished by using the QMS.
The by-pass measurements for the calibration of the QMS demonstrated that this setup provides no reliable calibrations and the steady-state measurements are reached after very long time (around two hours). The injection system by the QMS has been modified, and the resulting configuration is in figure 3.4. In this setup, the flow in the injection line of the QMS is kept constant using MFC6. Moreover, another stronger vacuum pump was introduced in the system. With the new configuration the efficiency and reliability of the QMS meauserements is improved, and the steady-state values are obtained in around 20 min.
3.1.2.3 Setup for ternary mixtures gas experiments
The schematic diagram presented in figure 3.1 presents the configuration used for the H2/H2O/He
30 Chapter 3. Experimental Setup and Comissioning of the ZIMT III Facility
Figure 3.3: Block diagram of the inital experimental setup for H2/He binary gas experiments.
MFC - Mass Flow Controller; MFR - Mass Flow Register; PR - Pressure Register; PC - Pressure Controller; QMS - Quadrupole Mass Spectrometer. MFC calibrated for H2: MFC1 (500 ml/min)
and MFC2 (10 ml/min). MFC calibrated for He: MFC3 and MFC5 (104 ml/min). MFR calibrated for He (104 ml/min).
Figure 3.4: Block diagram of the final experimental setup for H2/He binary gas experiments.
MFC - Mass Flow Controller; MFR - Mass Flow Register; PR - Pressure Register; PC - Pressure Controller; QMS - Quadrupole Mass Spectrometer. MFC calibrated for H2: MFC1 (500 ml/min)
and MFC2 (10 ml/min). MFC calibrated for He: MFC3, MFC5 (104 ml/min) and MFC6 (103 ml/min). MFR calibrated for He (104 ml/min).
system through a 10 - 200 ml/min liquid water MFC2 (MFC4 in the figure) followed by a vapor- izer with which the temperature of the steam can be set up to 200◦C. The presence of moisture in the stream requires a proper heating of the pipes all along its pathway. This was accom- plished by wrapping electrical heating cables to the pipes, while ensuring a proper insulation with fiberglass and flexible elastomeric foam. This configuration allows the dynamic mixing of helium, hydrogen and water vapour whose concentrations in the total stream are determined by the set flows.
2
The range of flows 10 - 200 ml/min comprises the minimum and maximum values that can be imposed with this MFC.
ZIMT III overview and details of the main components 31 On the permeate side, the two parallel lines containing each a MSB (MSB1 and MSB2 in the figure) for drying the carrier gas are used. In addition, two humidity sensors are placed before (HS1) and after (HS2) the MSB’s, with which relative (RH) and absolute (AH) humidity values and also temperature measurements inside the pipes can be measured. HS1 is used to obtain online measurements of the actual humidity, and HS2 is used to check the saturation of the MSB in use: if the MSB is saturated, no more H2O molecules are adsorbed and thus detected in that
sensor. It should be noted that after the MSB’s, the lines are not heated and then condensation of non-adsorbed water must be avoided. When the MSB’s are saturated, regeneration at 400
◦C with He as a sweeping gas has to be done. To perform experiments while one of the MSB is
regenerating, an additional connection before one of the MFC’s on the feed side exists where the MSB is placed. The total regeneration of each MSB lasts between three and four hours, being the first hour needed to achieve the desired temperature in the MSB.