Sweep Gas Research Articles

Dehydrogenation Coupling of Methane Using Catalyst-Loaded Proton-Conducting Perovskite Hollow Fiber Membranes.

Catalytic dehydrogenation coupling of methane (DCM) represents an effective way to convert natural gas to more useful C2 products (C2H6, C2H4). In this work, BaCe0.85Tb0.05Co0.1O3−δ (BCTCo) perovskite hollow fiber membranes were fabricated by the combined phase inversion and sintering method. SrCe0.95Yb0.05O3−δ (SCYb) perovskite oxide was loaded as a catalyst onto the inner hollow fiber membrane surface, which promoted the CH4 conversion and the C2 hydrocarbon selectivity during the DCM reaction. The introduction of steam into the methane feed gas mixture elevated the C2 selectivity and yield due to the alleviation of coke deposition. Switching N2 to air as the sweep gas further increased the C2 selectivity and yield. However, the conversion of methane was limited by both the low permeability of the membrane and the insufficient catalytic activity of the catalyst, leading to low C2 yield.

Demonstration of a high-efficiency carbon dioxide capture and methanation system with heat/material integration for power-to-gas and zero carbon dioxide emissions in flue gasses

Carbon dioxide (CO2) capture and methanation are important methods for realizing both power-to-gas and zero CO2 emissions. However, the technology needs to be improved to solve implementation barriers such as energy efficiency, compactness, economics, and CO2 source flexibility, especially for CO2 derived from fuel combustion.The present report describes the development of a high-efficiency integrated system to separate CO2 from flue gas with a high recovery rate and convert it to high-quality CH4 using in-system heat/material integration.A carbon recycling system with a throughput of 5.1-kW CH4 (LHV basis) was integrated with CO2 adsorbers using zeolite and catalytic methanation reactors. System efficiency, defined as the energy ratio of output CH4 and H2 against the sum of input H2 and power for system operation, was then evaluated using exhaust gas from a combustion furnace with a CO2 concentration of 9%. In general, a decrease in the energy required for system operations, such as gas treatment, CO2 separation, and auxiliary machines, improves efficiency. Two challenges were encountered during the study: reduction in CO2 separation energy by implementation of heat/material management using a H2 reactant as a sweep gas and the reaction heat of methanation, and a reduction in gas compression energy by conducting the methanation reaction under the lowest possible pressure. The results indicated that the CO2 conversion rate was greater than 99% under a pressure of 225 kPa-G, and the only energy consumed was by the oil pump for cooling the reactors. Due to the use of H2 sweep gas and methanation heat recovery, the CO2 recovery rate was also greater than 99%, and the additional energy consumption (1.8 GJ/t-CO2) was due to vacuum pumps. In addition, the system achieved an efficiency greater than 70% (LHV basis), while maintaining both a CO2 recovery rate and a conversion of greater than 99%. Because the energy for dehydration of the exhaust gas was the most significant portion of the total system operational energy, further improvement of the system efficiency is thought to be possible by reducing the energy required for dehydration.

Memsorb™, a novel CO2 removal device part II: in vivo performance with the Zeus IE®.

Memsorb™ (DMF Medical, Halifax, Canada) is a novel device based upon membrane oxygenator technology designed to eliminate CO2 fromexhaled gas when using a circle anesthesia circuit. Exhaled gases pass through semipermeable hollow fibers and sweep gasflowing through these fibers creates a diffusion gradient for CO2 removal. In vivo Memsorb™ performance was tested during target-controlled closed-circuit anesthesia (TCCCA) with desflurane in O2/air using a Zeus IE® anesthesia workstation(Dräger, Lübeck, Germany). Clinical care protocols for using this novel device were guided by in vitro performance results from a prior study (submitted simultaneously). After IRB approval, written informed consent was obtained from 10 ASA PS I-III patients undergoing robot-assisted radical prostatectomy. TCCCA targets were 39% inspired O2 concentration (FIO2) and 5.0% end-expired desflurane concentration (FETdes). Minute ventilation (MV) was adjusted to maintain 4.5-6.0% FETCO2. The O2/air (40% O2) sweep flow into the Memsorb™ was manually adjusted in an attempt to keep inspired CO2 concentration (FICO2) ≤ 0.8%. The following data were collected: FIO2, FETdes, FICO2, FETCO2, MV, fresh gas flow (FGF, O2 and air), sweep flow, and cumulative desflurane usage (Vdes). Vdes of the Zeus IE®-Memsorb™ combination was compared with historical Vdes observed in a previous study when soda lime (DrägerSorb 800 +) was used. Results are reported as median and inter-quartiles. A combination of manually adjusting sweep flow (26 [21,27] L/min) and MV sufficed to maintain FICO2 ≤ 0.8% and FETCO2 ≤ 6.0%, except in one patient in whom the target Zeus IE® FGF had to be increased to 0.7 L/min for 6min. FIO2 and FETdes were maintained close to their targets. Zeus IE® FGF after 5min was 0 [0,0] mL/min. Average Vdes after 50min was higher with Memsorb™ (20.3mL) compared to historical soda lime canister data (12.3mL). During target-controlled closed-circuit anesthesia in patients undergoing robot-assisted radical prostatectomy, the Memsorb™ maintained FICO2 ≤ 0.8% and FETCO2 ≤ 6.0%, and FIO2 remained close to target. Modest amounts of desflurane were lost with the use of the Memsorb™. The need for adjustments of sweep flow, minute ventilation, and occasionally Zeus IE® FGF indicates that the Memsorb™ system should preferentially be integrated into an automated closed-loop system.

Recovery of dissolved methane through a flat sheet module with PDMS, PP, and PVDF membranes

A degassing contactor using a flat sheet membrane module (FM) was operated in sweep gas mode to study the performance of several commercial polymer membranes, both dense (polydimethylsiloxane, PDMS) and microporous (polypropylene, PP, and polyvinylidenefluoride, PVDF), for the recovery of dissolved methane from water. Non-steady state experiments were conducted at different liquid (QL, 3.5–40.5 L h−1) and gas flow rates (QN2, 0.05–15.00 L h−1). In the case of PDMS, PP, and when PVDF was operated at moderate high QL (≥21 L h−1), similar methane removal efficiencies (RE) were obtained. In the case of PVDF operated at relatively low QL (3.5 L h−1), a lower RE was observed. A model for the mass transfer of methane has been selected that is adequate in predicting the experimental results. These results concluded that the mass transfer resistance was mainly located in the liquid phase. Microscopy and especially contact angle measurements were used to monitor the structural and surface stability on the membranes. The membranes were altered during the operation, especially for QL ≥ 21 L h−1, showing a decrease (PDMS and PP) or an increase (PVDF) in hydrophobicity and even cleavages (PDMS). The combination of the FM and contact angle technique has demonstrated to be very versatile and useful for monitoring the variation of the membrane properties during operation.

Sorbent-based oxygen separation with YBC114 for energy storage systems

In this work, we aimed to design, build, and evaluate an oxygen separation system to provide an inert sweep gas with low oxygen partial pressure (pO2) to redox-active thermochemical energy conversion reactors for a range of applications, including two-step redox cycles for thermochemical energy storage, water splitting, and carbon-dioxide splitting. The separation is based on an oxygen-selective sorbent, YBaCo4O7+δ (YBC114), which has excellent oxygen sorption and desorption properties demonstrated in our previous work. The oxygen separation performance of YBC114 was comprehensively studied by thermogravimetric analysis, sorption breakthrough experiments, and temperature swing sorption - desorption cycles. The results reveal that YBC114 can produce inert sweep gas with an oxygen concentration of less than 100 ppmv for at least 20 min during the thermal swing adsorption (TSA) cycle with the current sorption bed configuration, and the performance is consistent from cycle to cycle. The optimal sorption and desorption temperatures for the TSA process with YBC114 are determined to be 300 °C and 500 °C, respectively. Although challenges remain for the current separation system (e.g., high sorption temperature and slow kinetics), this study demonstrates the potential to use the oxygen-selective sorbent to produce an inert sweep gas, the feasibility of the oxygen separation concept, and guides new sorbent material development to make this application economically practical. A simple procedure is described for designing the YBC114 oxygen separation process.

Memsorb™, a novel CO2 removal device part I: in vitro performance with the Zeus IE®.

Soda lime-based CO2 absorbents are safe, but not ideal for reasons of ecology, economy, and dust formation. The Memsorb™ is a novel CO2 removal device that uses cardiopulmonary bypass oxygenator technology instead: a sweep gas passes through semipermeable hollow fibers, adding or removing gas from the circle breathing system. We studied the in vitro performance of a prototype Memsorb™ used with a Zeus IE® anesthesia machine when administering sevoflurane and desflurane in O2/air mixtures. The Zeus IE® equipped with Memsorb™ ventilated a 2L breathing bag with a CO2 inflow port in its tip. CO2 kinetics were studied by using different combinations of CO2 inflow (VCO2), Memsorb™ sweep gas flow, and Zeus IE® fresh gas flow (FGF) and ventilator settings. More specifically, it was determined under what circumstances the inspired CO2 concentration (FICO2) could be kept < 0.5%. O2 kinetics were studied by measuring the inspired O2 concentration (FIO2) resulting from different combinations of Memsorb™ sweep gas flow and O2 concentrations, and Zeus IE® FGFs and O2 concentrations. Memsorb™'s sevoflurane and desflurane waste was determined by measuring their injection rates during target-controlled closed-circuit anesthesia (TCCCA), and were compared to historical controls when using a soda lime absorbent (Draegersorb 800+) under identical conditions. With 160mL/min VCO2 and 5 L/min minute ventilation (MV), lowering the sweep gas flow at any fixed Zeus IE® FGF increased FICO2 in a non-linear manner. Sweep gas flow adjustments kept FICO2 < 0.5% over the entire Zeus IE® FGF range tested with VCO2 up to 280mL/min; tidal volume and respiratory rate affected the required sweep gas flow. At 10 L/min MV and low FGF (< 1.5 L/min), even a maximum sweep flow of 43 L/min was unable to keep FICO2 ≤ 0.5%. When the O2 concentration in the Zeus IE® FGF and the Memsorb™ sweep gas flow differed, FIO2 drifted towards the sweep gas O2 concentration, and more so as FGF was lowered; this effect was absent once FGF > minute ventilation. During sevoflurane and desflurane TCCCA, the Zeus IE® FGF remained zero while agent usage per % end-expired agent increased with increasing end-expired target agent concentrations and with a higher target FIO2. Agent waste during target-controlled delivery was higher with Memsorb™ than with the soda lime product, with the difference remaining almost constant over the FGF range studied. With a 5 L/min MV, Memsorb™ successfully removes CO2 with inflow rates up to 240mL/min if an FICO2 of 0.5% is accepted, but at 10 L/min MV and low FGF (< 1.5 L/min), even a maximum sweep flow of 43 L/min was unable to keep FICO2 ≤ 0.5%. To avoid FIO2 deviating substantially from the O2 concentration in the fresh gas, the O2 concentration in the fresh gas and sweep gas should match. Compared to the use of Ca(OH)2 based CO2 absorbent, inhaled agent waste is increased. The device is most likely to find its use integrated in closed loop systems.

Ammonia Recovery with Sweeping Gas Membrane Distillation: Energy and Removal Efficiency Analysis

Ammonia Recovery with Sweeping Gas Membrane Distillation: Energy and Removal Efficiency Analysis

Assessment on Effect of Molar Ratio of Inflow Gas on Characteristics of Biogas Dry Reforming

To improve the H2 yield and thermal efficiency for the biogas dry reforming process, this study has been conducted the experimental investigation using a membrane reactor by changing reaction temperature, differential pressure between reaction chamber and sweep chamber, and molar ratio of inflow gas with and without a sweep gas. In particular, we have focused on the effect of molar ratio of inflow gas. The concentrations of reactant and product gases were measured by gas chromatography to clarify the effects of the above operation conditions on the reaction characteristics. We have evaluated the conversion of the reacted gases (CH4 and CO2), H2 yield, H2 permeability, and thermal efficiency. As a result, the largest H2 was produced at the molar ratio of 1.5:1 irrespective of reaction temperature, and the differential pressure between reaction chamber and sweep chamber with and without a sweep gas. It was observed that the concentration of CO is larger than that of H2 irrespective of reaction temperature, differential pressure between reaction chamber and sweep chamber, and molar ratio of inflow gas with and without a sweep gas. Under the experimental conditions in this study, the H2 separation rate which is enhanced by the differential pressure and sweep gas exceeded the kinetic rate of H2 production, resulting in a low concentration of produced H2. Therefore, it is necessary to clarify the optimum conditions where the H2 separation rate matches the kinetic rate of H2 production.

The Preparation of Eco-Friendly Magnetic Adsorbent from Wild Water Hyacinth (Eichhornia crassipes): The Application for Removing Lead Ions from Industrial Wastewater

Water hyacinth ( Eichhornia crassipes) is a wild floating plant that can be found widely in pond or river areas. The plant grows fiercely and causes many harmful issues to the ecosystem around its covered area. This work provides a utilization method that converts wild water hyacinth to reliable magnetic biochar which can be used as a very effective adsorbent for the removal of lead ion Pb(II) in industrial wastewater. The mentioned magnetic biochar can be prepared via a modified pyrolysis process at 550°C with the support of cobalt sulfates as magnetite precursors and limited oxygen from the sweeping gas (the gas mixture ratio is 4 : 1 nitrogen/oxygen). The produced samples were hydrophobic biochar with high oxygen-containing functional groups that are suitable for the removal of inorganic contaminants. The impregnation of cobalt (II, III) oxides provided high magnetic separation performance and additional adsorption sites on the produced magnetic biochar. As indicated by the obtained result, the WHB-Co2M sample possesses a highly porous structure (0.126 cc/g), higher thermal stability (thermal durability reaches 900°C), relatively stable magnetic properties (14.74 emu/g), and a larger surface area (192 m2/g). These beneficial properties led to its suitability to serve as an adsorbent in removing lead ions in the contaminated effluent, recording 95% of removal efficiency and adsorption capacity of 67.815 mg/g. As indicated in the result, all prepared magnetic biochar samples were fitted to two-parameter (Langmuir models) and three-parameter (Sips model) isotherm models. Therefore, the adsorption process in this work could be carried out on both homogeneous and heterogeneous adsorbent surfaces. The adsorption kinetics of the removal process also was described by the pseudo-first-order, pseudo-second-order, and Elovich models to reveal the adsorption and desorption rate of the as-prepared magnetic biochar. This work indicates a successful waste refinery route of converting lignocellulosic biomass such as water hyacinth into value-added material for use as promising heavy metal adsorbents.

High CO2 resistance of indium-doped cobalt-free 60 wt.%Ce0.9Pr0.1O2-δ-40 wt.%Pr0.6Sr0.4Fe1-In O3-δ oxygen transport membranes

The oxygen transport membrane (OTM) has huge application prospects in gas separation and carbon neutralization based on oxygen enriched combustion. In this paper, the family 60 wt.%Ce0.9Pr0.1O2-δ-40 wt.%Pr0.6Sr0.4Fe1-xInxO3-δ (CPO-PSF1-xIxO, x = 0.01, 0.025, 0.05, 0.075, 0.1) cobalt-free dual-phase MIEC OTMs doped with indium have been successfully prepared by Pechini method. The phase structure, surface morphology, element distribution, oxygen permeability, and long-term operation stability of these OTMs are systematically explored. Among these OTMs, the champion oxygen permeable flux of CPO-PSF0.99I0.01O reaches 1.07 mL min−1·cm−2 and 0.80 mL min−1·cm−2 at 1000 °C under air/He gradient and air/CO2 gradient. Meanwhile, CPO-PSF0.99I0.01O maintains the value of 0.80 mL min−1·cm−2 steadily at 1000 °C for 100 h when pure CO2 as the sweep gas. The surface element distribution and phase structure of the OTMs after long-term oxygen permeability reaction are investigated by XRD, SEM combining with EDS, where the spent membranes retain the same structure and component as the fresh membranes, demonstrating that the In-doped OTMs have an excellent CO2 tolerance. Suitable indium substitution for iron of these OTMs not only improves the oxygen permeability, but also maintains the long-term reaction stability of the material.

Design and operation of a molten salt electrochemical cell

Molten salts such as 2LiF-BeF2 (FLiBe) have been proposed as coolants for advanced nuclear fission and fusion reactors. Critical to the design, licensing and operation of these reactors is characterization and understanding of the chemical behavior and mass transport of activation and fission products, corrosion products, and other solutes in the coolant. Electrochemical techniques are a powerful suite of tools for probing these phenomena. The design of an experimental cell for molten salt electrochemistry is described herein. As a demonstration of this design, details of the experimental methods used to conduct electrochemical experiments with molten FLiBe with addition of LiH are provided. Decommissioning of the cell is considered from the point of view of decontamination and waste generated. Main features of the cell include:•Suitable for operation up to 800 °C; suitable for operation inside and outside of a glovebox.•Enables sweep gas, gas sampling and analysis; enables addition of solid and liquid materials during operation.•Supports a variety of electrode materials and arrangements.

A New Sweeping Gas Strategy of a Reversible Solid Oxide Cell System for Efficient H2 Production and Power Generation During Dynamic Operation

A New Sweeping Gas Strategy of a Reversible Solid Oxide Cell System for Efficient H2 Production and Power Generation During Dynamic Operation

Quantification of CO2 Replacement in Methane Gas Hydrates: A Molecular Dynamics Perspective

Extraction of methane from natural gas hydrates whilst storing CO2 via gas replacement is a promising approach for reducing anthropogenic CO2 emissions during energy generation. In this study, molecular dynamic simulations were performed to identify the influence of temperature, pressure, and the initial CO2 concentration of sweep gas on the gas replacement characteristics. Simulations were performed under selected pressure and temperature conditions using five different initial CO2 concentrations. The simulation results clearly portray the replacement phenomena where methane molecules are released into the free gas layer while CO2 get enclathrated in hydrate structure. During gas replacement, minor structural changes in hydrate structure can also be observed, but they are quite insignificant as demonstrated through the alterations in Tetrahedrality order parameter. The variations of the number densities of gas and water molecules during gas replacement were used to quantify the methane recovery and CO2 storage. Based on the numerical comparisons, the replacement process is found to be strongly dependant on the temperature, yielding a higher methane recovery at higher temperatures; however, the CO2 storage capacity is found to be diminishing with increasing temperature. Having a higher initial CO2 concentration in the sweep gas may facilitate greater penetration of CO2 into the hydrate structure, eventually resulting in a higher methane recovery and improved CO2 storage.

Hydrogen permeation from F82H wall of ceramic breeder pebble bed: The effect of surface corrosion

Understanding the permeation behavior of tritium from a pebble bed breeding blanket is essential for establishing a self-sufficient fuel cycle in a nuclear fusion reactor. It is known that double corrosion layers forms on reduced activation ferritic-martensitic (RAFM) steel surface by gas release from a ceramic breeder material, however, its effect on hydrogen permeation behavior has not been elucidated. Herein, in-situ measurement of hydrogen permeation through an F82H RAFM wall of a ceramic breeder pebble bed was performed under H2-added sweep gas conditions. The corrosion layer formed on the F82H sample had a dense microstructure, which reduced hydrogen permeation flux at least by one order of magnitude. The permeation reduction factors were 20–50 at the water-coolant temperature of a blanket. A self-repairing ability is expected for the surface oxide layer as the corrosion occurs spontaneously inside a breeding blanket.

Multi-objective optimal configurations of a membrane reactor for steam methane reforming

The combination of traditional reactor and permeable membrane is beneficial to increase the production rate of the target product. How to design a high efficiency and energy saving membrane reactor is one of the key problems to be solved urgently. This paper utilizes finite-time thermodynamics and nonlinear programming to solve the optimal configurations of the membrane reactor of steam methane reforming (MR-SMR) for two optimization objectives, that is, heat exchange rate minimization and power consumption minimization. The exterior wall temperature and fixed hydrogen production rate are regarded as the control variable and constraint, respectively. The results indicate that the hydrogen production rate and heat exchange rate in MR-SMR are increased by 108.58% and 58.42%, respectively, while the power consumption is reduced by 33.44% compared with those in the traditional reactor under the same condition. Compared with the results in reference reactor (MR-SMR obtained with initial values), the heat exchange rate is reduced by 1.40% by optimizing the exterior wall temperature, and the power consumption is reduced by 5.10% by optimizing the exterior wall temperature and molar flow rate of sweep gas. The optimal distributions of exterior wall temperatures in the optimal reactors of minimum heat exchange rate and power consumption have a theoretical guiding significance for the thermal design of the membrane reactors.

A Daily, Respiratory Therapist Assessment of Readiness to Liberate From Venovenous Extracorporeal Membrane Oxygenation in Patients With Acute Respiratory Distress Syndrome.

Objectives:We assessed the effect of implementing a protocol-directed strategy to determine when patients can be liberated from venovenous extracorporeal membrane oxygenation on extracorporeal membrane oxygenation duration, time to initiation of first sweep-off trial, duration of mechanical ventilation, ICU length of stay, hospital length of stay, and survival to hospital discharge.Design:Single-center retrospective before and after study.Setting:The medical ICU at an academic medical center.Patients:One-hundred eighty patients with acute respiratory distress syndrome managed with venovenous extracorporeal membrane oxygenation at a single institution from 2013 to 2019.Interventions:In 2016, our institution implemented a daily assessment of readiness for a trial off extracorporeal membrane oxygenation sweep gas (“sweep-off trial”). When patients met prespecified criteria, the respiratory therapist performed a sweep-off trial to determine readiness for discontinuation of venovenous extracorporeal membrane oxygenation.Measurements and Main Results:Sixty-seven patients were treated before implementation of the sweep-off trial protocol, and 113 patients were treated after implementation. Patients managed using the sweep-off trial protocol had a significantly shorter extracorporeal membrane oxygenation duration (5.5 d [3–11 d] vs 11 d [7–15.5 d]; p < 0.001), time to first sweep-off trial (2.5 d [1–5 d] vs 7.0 d [5–11 d]; p < 0.001), duration of mechanical ventilation (15.0 d [9–31 d] vs 25 d [21–33 d]; p = 0.017), and ICU length of stay (18 d [10–33 d] vs 27.0 d [21–36 d]; p = 0.008). There were no observed differences in hospital length of stay or survival to hospital discharge.Conclusions:In patients with acute respiratory distress syndrome managed with venovenous extracorporeal membrane oxygenation at our institution, implementation of a daily, respiratory therapist assessment of readiness for a sweep-off trial was associated with a shorter time to first sweep-off trial and shorter duration of extracorporeal membrane oxygenation. Among survivors, the postassessment group had a reduced duration of mechanical ventilation and ICU lengths of stay. There were no observed differences in hospital length of stay or inhospital mortality.

Energy from carbon dioxide: Experimental and theoretical analysis of power generation from membrane-based sweep gas permeation

Large amounts of energy are available from gas mixture gradients at exhaust sources such as power plant flue gases. Converting energy from exhaust to useful work, may open up new opportunities for improving power plant efficiency and sustainability. In this paper, we evaluate the novel concept of using sweep gas permeation of carbon dioxide CO2 across a membrane to generate power. Using a custom laboratory bench with a commercial polydimethylsiloxane membrane, power potential of up to 6.35 W/m2 is experimentally observed from 192 g/m2/h of CO2 flux against 2 bar applied pressure difference. This power is obtained from a pure CO2 feed, and assuming ideal energy conversion at key rotating machines (compressor and turbine). When more realistic feed concentrations of 20% CO2 are supplied, and the loss of nitrogen N2 reverse flux is accounted for, power potential of 0.37 W/m2 is observed from 29 g/m2/h net flux against 1 bar applied pressure. Fundamental transport dynamics are outlined and a numerical model is validated and used to simulate possible improvements from highly permeable and selective membranes, with certain predictions approaching 40 W/m2. The model is also used to analyze the overall energy balance of the process, and it is shown that inefficiencies of the compressor and turbine impose important limitations on net power generation, unless operating conditions are carefully calibrated.

What Determines the Arterial Partial Pressure of Carbon Dioxide on Venovenous Extracorporeal Membrane Oxygenation?

Rapid reductions in P a CO 2 during extracorporeal membrane oxygenation (ECMO) are associated with poor neurologic outcomes. Understanding what factors determine P a CO 2 may allow a gradual reduction, potentially improving neurologic outcome. A simple and intuitive arithmetic expression was developed, to describe the interactions between the major factors determining P a CO 2 during venovenous ECMO. This expression was tested using a wide range of input parameters from clinically feasible scenarios. The difference between P a CO 2 predicted by the arithmetic equation and P a CO 2 predicted by a more robust and complex in-silico mathematical model, was <10 mm Hg for more than 95% of the scenarios tested. With no CO 2 in the sweep gas, P a CO 2 is proportional to metabolic CO 2 production and inversely proportional to the "total effective expired ventilation" (sum of alveolar ventilation and oxygenator ventilation). Extracorporeal blood flow has a small effect on P a CO 2 , which becomes more important at low blood flows and high recirculation fractions. With CO 2 in the sweep gas, the increase in P a CO 2 is proportional to the concentration of CO 2 administered. P a CO 2 also depends on the fraction of the total effective expired ventilation provided via the oxygenator. This relationship offers a simple intervention to control P a CO 2 using titration of CO 2 in the sweep gas.

Numerical Simulation via CFD Methods of Nitrogen Flooding in Carbonate Fractured-Vuggy Reservoirs

A reservoir-scale numerical conceptual model was established according to the actual geological characteristics of a carbonate fractured-vuggy reservoir. Considering the difference in density and viscosity of fluids under reservoir conditions, CFD (computational fluid dynamic) porous medium model was applied to simulate the process of nitrogen displacement in a fractured-vuggy reservoir after water flooding. The effects of gas injection rate, injection mode, and injector–producer location relation were studied. The results show that nitrogen flooding can yield additional oil recovery of 7–15% after water flooding. Low-speed nitrogen injection is beneficial in obtaining higher oil recovery. High speed injection can expand the sweep area, but gas channeling occurs more easily. In gas–water mixed injection mode, there is fluid disturbance in the reservoir. The gas channeling is faster in low injector–high producer mode, while the high injector–low producer mode is beneficial for increasing the gas sweep range. Nevertheless, the increment of recovery is closely related to well pattern. After nitrogen flooding, there are still a lot of remaining oil distributed in the trap area of gas cap and bottom water in the reservoir that water and gas injection can’t sweep. The establishment of the numerical conceptual model compensates for the deficiency of physical simulation research, stating that only limited parameters can be simulated during experiments, and provides theoretical bases for nitrogen flooding in fractured-vuggy reservoir.

Oxygen permeation simulation of La0.8Ca0.2Fe0.95O3−δ‐Ag hollow fiber membrane at different modes and flow configurations

AbstractMixed ionic‐electronic conducting La0.8Ca0.2Fe0.95O3−δ‐Ag (LCF‐Ag) ceramic hollow fiber membranes possess high structural stability and up to 2.24‐fold higher oxygen permeation fluxes relative to LCF hollow fibers. In this work, the oxygen permeation of LCF‐Ag hollow fiber membrane module is simulated under sweep gas and vacuum operation modes, whereas the kinetic parameters were obtained by fitting the experimental data with the simplified Tan–Li model. The good correlation obtained from the data regression confirmed the compatibility of the selected model on the LCF‐Ag hollow fiber membrane. The simulated results revealed that the countercurrent flow configuration is generally favored in sweep gas operation given its potential of complete oxygen separation under optimized conditions. For vacuum operation, the oxygen yield is practically the same for both flow configurations at a moderate vacuum setting. At a very low vacuum pressure setting, however, cocurrent flow is preferred over countercurrent flow for maximizing the oxygen yield.