Production Of Oxygen-enriched Air Research Articles

Economical Configuration of Oxygen-Enriched Air Production Process Using Polysulfone-Based Composite Membranes

Oxygen-enriched combustion technology is an emerging incineration method suitable for waste treatment. In this study, we investigated an economical modular configuration method for oxygen-enriched air production using gas separation membrane technology. Various module configurations were examined based on input pressure, gas temperature, sweep, and multistage module arrangement, and an optimal economically viable configuration was proposed. Using a polysulfone-based polymer membrane module, oxygen-enriched air with an oxygen concentration of 40–65% was produced. Even in cases of low input pressures achieved using a vacuum pump at the permeate side, oxygen-enriched air with concentrations >40% was achieved, with an approximately 20% increase in the permeation flow rate. As the permeation rate increased with increasing temperature, the oxygen recovery efficiency decreased. When the membrane area was increased, the corresponding increase in the input pressure did not result in a proportional increase in the permeation rate compared with single-module setups. Through multistage module arrangements, oxygen-enriched air with a maximum oxygen concentration of 66% was produced. By employing sweep that recirculated a portion of input air to the permeate side, the production of oxygen-enriched air was enhanced by approximately 38%. Therefore, the proposed process involving low input pressure, vacuum pumps, and sweeping was optimal for oxygen-enriched air production.

Analysis of a possible application of a new process for oxygen enriched air production

A new process for oxygen enriched air (EA) production has been applied to Claus Process. This process is simple and requires few process units. Matlab and Aspen Hysys have been used for simulations and system sizing. The results demonstrate that it could be an alternative to traditional EA processes from an economical point of view.

Production and application of O2 enriched air produced by fresh and salt water desorption in chemical plants

Oxygen enriched air intensifies oxidation processes since smaller reactors reach the same conversion of typical unit operations that employ simple air as reactant. However, the cost to produce pure oxygen or oxygen enriched air with traditional methods, i.e. cryogenic separation or membrane technologies, may be unaffordable. Here, we propose a new continuous technology for gas mixture separation, focusing on the production of oxygen enriched air as a case study. This operation is an absorption-desorption process that takes advantage of the higher oxygen solubility in water compared to nitrogen. In a pressurized solubilisation tank, water absorbs air. Subsequently, reducing pressure desorbs oxygen enriched air. PRO/II 9.3 (Simsci-Scheider Electrics) simulated, optimized, and calculated the capital and operative expenses of this technology. Moreover, we tested for the first time salt water instead of distilled water as appealing possibility for chemical plant near sea and ocean. We varied the inlet water flowrate between 5 and 15 m3/h. The optimum operative absortion unit pressure is 15–35 barg. After degassing, water may be recycled. With salt water, the extracted quantity of enriched air decreases compared with the desorption from fresh water (20% less), while the concentration of oxygen is independent from the salt concentration. The cost of enriched air at the optimum condition is 2–3.35 EUR/Nm3.

Eco design LCA of an innovative lab scale plant for the production of oxygen-enriched air. Comparison between economic and environmental assessment

Here we developed an early-stage attributional LCA of an innovative production process of oxygen-enriched air by water desorption. We compared LCA's results with a rigorous economic model, in an eco-design optimization perspective. We developed the life cycle analysis using primary data from the lab-scale plant. We used SimaPro 8.1.1.16 for the LCA analysis and the ReCiPe Endpoint V 1.12 E/A method for the interpretation of the results. The functional unit was the amount of enriched air produced by the plant in 24 h in Milano (Italy). A steady state chemical plant simulation software (PRO/II 9.3) calculated the reference flow and we input it in SimaPro with a parametric function. We considered a “cradle-to-grave” analysis. Temperature, pressure and water flowrate were varied to minimize environmental burdens and plant costs. Uncertainty analysis revealed that there is no difference between operating the degassing unit at 20 °C or 30 °C. SimaPro and PRO/II presented different optimum conditions. However, taken as a whole, we individuated the best process parameters from an eco-economic prospective. The results obtained are related to a lab-scale plant and thus no comparisons between industrial processes are possible, but the methodology we propose will improve the design of any process.

Production of oxygen-enriched air via desorption from water: Experimental data, simulations and economic assessment

Oxygen enriched air with a composition of oxygen till 35% can be produced by water desorption by simple water degassing. This work reports the simulation of a small bench-scale plant for the continuous production of oxygen-enriched air by simple water degassing. The basic thermodynamic principle involved is the higher water solubility of oxygen compared to the one of nitrogen. Different experiments were performed in a continuous small bench-scale plant changing the main operating parameters, i.e. water temperature, degasser pressure and the water flowrate in order to develop rigorous and reliable simulations with suitable software (PRO/II 9.3 by SIMSCI-Schneider Electric). The results obtained showed a good fitting between the experiments and the simulations and demonstrated the possibility for the production of enriched air using this new technology. Moreover, the calculation of the economic potentials of this new process were carried out, and the results compared to the already existing technologies.

Mixed Matrix Membranes for O₂/N₂ Separation: The Influence of Temperature.

In this work, mixed matrix membranes (MMMs) composed of small-pore zeolites with various topologies (CHA (Si/Al = 5), LTA (Si/Al = 1 and 5), and Rho (Si/Al = 5)) as dispersed phase, and the hugely permeable poly(1-trimethylsilyl-1-propyne) (PTMSP) as continuous phase, have been synthesized via solution casting, in order to obtain membranes that could be attractive for oxygen-enriched air production. The O2/N2 gas separation performance of the MMMs has been analyzed in terms of permeability, diffusivity, and solubility in the temperature range of 298–333 K. The higher the temperature of the oxygen-enriched stream, the lower the energy required for the combustion process. The effect of temperature on the gas permeability, diffusivity, and solubility of these MMMs is described in terms of the Arrhenius and Van’t Hoff relationships with acceptable accuracy. Moreover, the O2/N2 permselectivity of the MMMs increases with temperature, the O2/N2 selectivities being considerably higher than those of the pure PTMSP. In consequence, most of the MMMs prepared in this work exceeded the Robeson’s upper bound for the O2/N2 gas pair in the temperature range under study, with not much decrease in the O2 permeabilities, reaching O2/N2 selectivities of up to 8.43 and O2 permeabilities up to 4,800 Barrer at 333 K.

Unsteady state cyclic pressure-vacuum swing permeation for low pressure niche gas separation applications

A relatively higher transmembrane driving force compared to conventional steady state membrane process can be achieved in unsteady state cyclic pressure-vacuum swing permeation process, which accomplishes feed pressurization and permeate evacuation using a single pump. Moreover, a higher feed to permeate pressure ratio can be achieved and the enhanced transmembrane driving force can also be sustained over a longer period of time, which enhances gas separations. Improved separation efficiency in terms of product purity and throughput compared to the conventional steady state membrane gas separation process can be obtained for low pressure niche applications by means of pressure-vacuum swing permeation. CO2 separation for greenhouse gas emission control, oxygen-enriched air production and methane enrichment from biogas are shown as exemplary model applications to demonstrate the feasibility and effectiveness of this novel process.

Energy efficiency of oxygen enriched air production technologies: Cryogeny vs membranes

Oxygen Enriched Air (OEA) is already used for numerous chemical, medical and industrial applications (e.g. combustion enhancement for natural gas furnaces, coal gasification) and more recently attracted attention for hybrid carbon capture processes. Membrane separation has shown growing interest for OEA production, providing an alternative to conventional air separation processes such as cryogenic distillation and pressure swing adsorption. Nevertheless, based on the current polymeric materials performances, membranes are usually considered to be competitive only for medium O2 purity (25–40%) and small scale plants (10–25tons/day).Improvement in membrane materials permeability and permselectivity (O2 over N2) is often reported to be a critical issue in order to increase the attainable O2 purity and to make the process more energy efficient. Recently, several membrane materials have been reported to show performances far above the permeability/selectivity trade-off of dense polymers. In this study, the potential of current and prospective membrane materials to achieve OEA production thanks to a single stage process is analysed through a rigorous simulation approach. The two processes (membrane and cryogenic distillation) are finally critically compared in terms of energy efficiency (kWh/ton O2), depending on O2 purity and on membrane material selectivity levels.

Synthesis of silicalite-poly(furfuryl alcohol) composite membranes for oxygen enrichment from air

Silicalite-poly(furfuryl alcohol) [PFA] composite membranes were prepared by solution casting of silicalite-furfuryl alcohol [FA] suspension on a porous polysulfone substrate and subsequent in situ polymerization of FA. X-ray diffraction, nitrogen sorption, thermogravimetric analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were used to characterize silicalite nanocrystals and silicalite-PFA composite membranes. The silicalite-PFA composite membrane with 20 wt.% silicalite loading exhibits good oxygen/nitrogen selectivity (4.15) and high oxygen permeability (1,132.6 Barrers) at 50°C. Silicalite-PFA composite membranes are promising for the production of oxygen-enriched air for various applications.

Novel adsorbent hollow fibres for oxygen concentration

The research examined the development of adsorbent hollow fibres as a low pressure drop structure for the production of oxygen-enriched air. The potential benefits of using a low pressure drop flexible adsorbent structure with molecular sieving properties over a bed packed with pellets include a low attrition resistance which could extend the life of the adsorbent structure. Highly macroporous, highly adsorbent loaded (up to 90 wt%) fibres were produced. By increasing adsorbent density, the separative performance and nitrogen loading were improved. The separative performance of the adsorbent fibre was found to be slightly inferior to that of the bed of smaller 0.4–0.8 mm beads, as the diffusion path length was longer in the fibres and caused increased mass transfer resistances within the macroporous structure. The pressure drop through the fibre was found to be 40 to 70 times lower than that through an equivalent packed bed of 0.4–0.8 mm beads. This experimental feasibility study has demonstrated that the novel zeolite fibre configuration shows good potential for the production of oxygen-enriched air in a low energy, short cycle time, pressure swing process. The challenges of improving the performance of the adsorbent fibres and their operating parameters are described.

Reversible change in crystal structure of Ba(or Sr)FeO3-.DELTA. associated with oxygen sorption/desorption by pressure variation

Oxygen-enriched air has been expected to be used in several industrial processes for the purpose of less energy consumption as well as less CO 2 emission. Thus, an innovative and economical oxygen-separation method is eagerly needed for a large-scale production of oxygen-enriched air. Pressure-swing adsorption (PSA) method is considered to be effective for this purpose, if the high-performance oxygen adsorbents can be developed. It has been lately reported that La-Sr-Co-Fe-based perovskite-type oxide is a good candidate as a potential oxygen adsorbent for PSA. However, its cost is still relatively high, because the oxide is composed of relatively expensive elements of La and Co. Here, we compared the oxygen sorption behavior of the BaFeO 3-δ and SrFeO 3-δ samples which are composed of much inexpensive elements. These oxide samples were synthesized and then evaluated for oxygen sorption and desorption characteristics by the variation of oxygen partial pressure, with the simultaneous observation of change in crystal structure. As a result, it was found that the prepared BaFeO 3-δ and SrFeO 3-δ samples gave a relatively high amount of sorbed oxygen at lower (ca. 300°C) and higher (ca. 700°C) temperature, respectively. In addition, the reversible change in crystal structure associated with oxygen sorption/desorption was observed for both oxides at each best operating temperature.

Increasing the efficiency of an air separation plant by varying the cycle stage durations

A mathematical model of a plant for oxygen-enriched air production by pressure swing adsorption is proposed. The model takes into account the experimentally determined actual dependence of the longitudinal dispersion coefficient on the gas velocity and the sorbent particle size. The relationship between the plant efficiency and the duration of each of the operating cycle stages is studied using an ad hoc computer program for numerically solving the model equations. It is shown that optimization of the durations of cycle stages increases the thermodynamic efficiency of the plant to 20–22% in comparison to industrial plants.

Separation of N2 from O2 and Other Gases Using FAU-Type Zeolite Membranes.

The development of nitrogen-selective membranes is essential to realize a membrane process for the production of oxygen-enriched air. Zeolite membranes have potential for this purpose, while polymeric and carbon membranes are largely oxygen-selective. In this study, FAU-type zeolite membranes containing Na cations were prepared by hydrothermal synthesis on a porous α-alumina support tube. Permeation measurements for unary and binary systems for N2 and O2 were performed at 310 K. The membranes showed high permeation rates and high N2/O2 ideal separation factors for unary N2 and O2 gases. However, the separation factor was decreased when an N2-O2 mixture was fed. In order to further examine the permeation mechanism of the membranes, permeation rates were also determined for single-components of H2, CO2, CH4, n-C4H10, i-C4H10 and SF6, as well as for N2-H2, N2-CO2, and N2-n-C4H10 mixtures. The permeation properties can be classified based on competitive adsorptivity and diffusivity in the zeolitic pores. Ion-exchange and impregnation with Li cations were not greatly effective in increasing the N2/O2 separation factor of the membrane.

Zeolite Monoliths for Air Separation: Part 2: Oxygen Enrichment, Pressure Drop and Pressurization

Experiments have been carried out on two individual idealized steps in a pressure swing cycle in order to compare the performance of a novel adsorbent monolith with that of a packed bed of commercial pellets containing the same weight of adsorbent. The application is the production of oxygen-enriched air using 5A zeolite. For feed pressures up to 3.8 bar, maximum oxygen compositions in the constant pressure production step up to 100% and 52%were achieved for the monolith with the previous step being carried out (1) by purging the column with pure oxygen at 1 bar, and (2) by evacuating the column, respectively. For virtually all experimental conditions studied, the separative performance of the monolith was found to be somewhat inferior to that of the bed of pellets, this being due largely to the former’ s poorer film mass transfer coefficient together with the virtual independence of this coefficient on velocity. To its advantage, however, the pressure drop through the monolith was found to be 3-5 times lower than that through the equivalent packed bed and consequently the time to pressurize the monolith was found to be 3-5 times faster than for the bed of pellets. Thisexperimental feasibility study has demonstrated that the novel zeolite monolith configuration shows good potential for the production of oxygen-enriched air of low-to-medium purity, in a low energy, short cycle time, pressure swing process. The challenges associated with both improving and modelling the performance of the monolith are described.

96/05115 Performance of a hollow fibre membrane unit in oxygen-enriched air production

96/05115 Performance of a hollow fibre membrane unit in oxygen-enriched air production

Production of oxy-rich air by RPSA for combustion use

The capital and energy costs of production of oxygen enriched air by a rapid pressure swing adsorption (RPSA) process can be reduced by decoupling the air drying and the air separation duties of the process. Integration of the oxygen-RPSA process with an enhanced combustion application system allows thermal swing adsorption drying of air feed to the RPSA process. The air separation process then can be run using an ad(de)sorption pressure envelope of 2:1 atmospheres, which significantly reduces the cost and energy of operation of the air compressor.

Performance of a hollow fibre membrane unit in oxygen-enriched air production

The performance of a pilot test for biogas upgrading has been tested under different process conditions to produce oxygen-enriched air for aqueous media application. The selectivity of the polysulfone hollow fibres for N 2 O 2 permeation allows the production of an oxygen-enriched air stream in the 30–50% range and an inert gas (nitrogen between 82–98%) by operating the pilot unit at different stage-cut values in a single pass mode. Membrane area requirements for a medium size plant of 100 Nm 3 h −1 are discussed according to a simple perfect mixing model for gas permeation.

Production of oxygen enriched air by rapid pressure swing adsorption

A novel rapid pressure swing adsorption (RPSA) process is described for production of 25–50% oxygen enriched air. The embodiment consists of one or more pairs of adsorbent layers contained in a single adsorption vessel. The layers undergo simultaneous pressurization-adsorption and simultaneous depressurization-purge steps. A total cycle time of 6–20 seconds is used. The process yields a very large specific oxygen production rate and a reasonable oxygen recovery for production of 20–50 mole% oxygen enriched gas.

Feed Purge Cycles in Pressure Swing Adsorption

Abstract Three new pressure swing adsorption cycles for the production of oxygen-enriched air at very high recoveries are developed. The cycles involve a purge step using low-pressure feed gas. Local equilibrium theory is used to predict purities and recoveries for air separation with 5A zeolite. Novel methods for drying the inlet air are developed. For low product purities these processes are predicted to have very high recoveries and adsorbent productivities. A simple new method for determining the location of a curved shock wave is illustrated. Other possible applications of PSA feed purge cycles are briefly discussed.

Liquid membranes for the production of oxygen-enriched air: II. Facilitated-transport membranes

We have identified a class of facilitated-transport membranes for the production of oxygen-enriched air. The membranes consist of a transition-metal complex dissolved in a suitable solvent and immobilized within the pores of a microporous membrane. Under certain conditions, these membranes exhibited oxygen/nitrogen selectivities in excess of 20, and permeate streams with oxygen purity in the range of 80–90 mole% were achieved using a l-atm feed stream and a low-pressure permeate stream. An oxygen permeability (P o2 = 26 x 10 −9 cm 3 (STP)-cm/cm 2-sec-cmHg) about one-half that of silicone rubber was observed. Membrane life is measured in weeks.