Oxygen Production Process Research Articles

Influence Factors of Pressure Swing Adsorption for Oxygen Production by the Orthogonal Method and the Response Surface Method

Adsorption pressure is one of the important factors affecting oxygen production in the process of pressure swing adsorption oxygen production. Three important factors, namely, the adsorption period, pressure equalisation time, and outlet flow rate, determine the variation in the adsorption pressure. In this study, the effects of the adsorption period, pressure equalisation time, and outlet flow rate on oxygen concentration were investigated through orthogonal experiments and response surface analysis. The experiments verified that three factors including the adsorption period, pressure equalisation time, and outlet flow rate have optimal values in the oxygen production process. Response surface analysis showed that the adsorption period had the greatest effect on the oxygen concentration, followed by the equalisation time, and the outlet flow rate had the least effect. The optimum process conditions are an adsorption time of 7.88 s, a pressure equalisation time of 0.9 s, an outlet flow rate of 2.31 L/min, and an oxygen concentration of 96.7%.

SOFC-VPSA System for Power Generation with CO2 Separation

Solid Oxide Fuel Cell (SOFC) has attracted huge scientific attentions lately, as it is a promising power production technology that can reduce user’s dependency on electricity-grid. SOFC system can generate electricity by using liquid or gaseous fuels. Small volume and external fuel storage make SOFC technology more compatible, and it can easily be adjusted for different industry power plant scales. Moreover, SOFC operates at high temperature (700 0C), and it cogenerates high-quality heat or steam, which can be used as a heat source within the system. As maximum fuel utilization for SOFC is around 85%, a burner is required for the combustion of unconverted fuels. The burner provides additional heat to the SOFC system, at the same time, it generates more CO2.In order to meet “net zero” emission target for greenhouse gases in the year 2050, it is essential to introduce Carbon Capture and Storage (CCS) technology that can retrieve most of the produced CO2 from emission intensive activities and store it permanently in nature (e.g, sequestration and mineralization), leading to an almost carbon neutral activity. The stored CO2 can also be used in methanation process, to convert it into green methane. By integrating an existing CCS technology with SOFC, and using biofuels as energy source, SOFC system can be considered as a carbon negative technology. The most common and widely used CCS technology is Chemical Absorption (CA). The CA process presents good retrofitting options. However, corrosion and degradation are major issues.The high efficiency of SOFC system is however penalised by the fact that the flue gases contain typically a mix of CO2 and N2, which makes it difficult and expensive to separate/capture the produced CO2. There is a possibility of directly injecting pure oxygen to the burner. For industrial scale, cryogenic distillation is commonly used air separation technology for producing O2. Cryogenic distillation is an energy intensive technology, and it is not suitable for small scale O2 production. In the recent times, other technologies such as Pressure Swing Adsorption (PSA) and membrane have evolved for O2 production from air. The non-cryogenic technologies for air separation are preferred to their lower operating cost and easier integration with other processes. PSA is usually suited for medium-range production capacity, and it can produce O2 with 94 % purity. However, it is still necessary to improve performance by reducing energy consumption. The energy consumption is 3.211 MJ/kg-O2 for PSA to produce oxygen. In the oxygen production process, energy consumption accounts for more than 90% of the operating cost.This study considers integration of a SOFC system with PSA, which consists of a SOFC stack, balance of plant components for SOFC system, PSA bed and auxiliary components for PSA. The PSA produces O2 from air, that is injected to the combustion chamber (or burner). In the integrated system, the energy needed for the PSA directly comes from SOFC system. The right amount of oxygen is used to complete the oxidation of the unconverted fuel from the anodic side of SOFC, and CO2 is separated automatically after water condensation. Figure 1 shows layout of integrated system. The performance of PSA is explored for different materials, different pressure ratio and temperature, to achieve minimum energy consumption. Moreover, heat integration has been studied for SOFC system, the integrated system has waste heat available, especially at the downstream of the burner. In order to valorize the waste heat of the system, a steam cycle has been integrated for producing extra amount of electricity, to improve the overall efficiency of the system. Finally, the performance of integrated system has been optimized for maximization of electrical efficiency and minimization of exergy distraction, via multi-objective optimization.In this study, the net electricity output from SOFC-PSA system is around 9 kW. The SOFC produces 9.8 kW electricity, and about 8% electricity is consumed by the PSA for producing O2 that is required for the combustion of unconverted fuel. The integrated system has an overall efficiency of more than 55%. A steam cycle has been integrated for producing extra amount of electricity, and it produces additional 2.5 kW of electricity. Hence, the overall efficiency of the integrated system reaches above 70% with automatic CO2 separation. Figure 1

Mass and Heat Transfer of Pressure Swing Adsorption Oxygen Production Process with Small Adsorbent Particles

Rapid-cycle pressure swing adsorption (PSA) with small adsorbents particles is intended to improve mass transfer rate and productivity. However, the mass transfer mechanisms are changed with reduction of particle size during rapid-cycle adsorption process. A heat and mass transfer model of rapid-cycle PSA air separation process employing small LiLSX zeolite particles is developed and experimentally validated to numerically analyze the effects of mass transfer resistances on the characteristics of cyclic adsorption process. Multicomponent Langmuir model and linear driving force model are employed for characterizing the adsorption equilibrium and kinetic. The results of numerical analysis demonstrate that the dominant mass transfer resistance of small adsorbents particles is a combination of film resistance, axial dispersion effect and macropore diffusion resistance. The oxygen purity, recovery and productivity of the product are overestimated by ~2–4% when the effect of axial dispersion on mass transfer is ignored. As particle size decreases, the front of nitrogen-adsorbed concentration and gas temperature become sharp, which effectively improves the performance. However, the adverse effect of axial dispersion on the mass transfer becomes significant at very small particles conditions. It is nearly identical shapes of nitrogen concentration and gas temperature profiles after adsorption and desorption steps. The profiles are pushed forward near the production end with an increase in bed porosities. The optimal oxygen recovery and productivity are achieved with a particle diameter of 0.45 mm and bed porosity of 0.39 during the PSA process.

Correlation Analysis between Working Conditions and the Performance of a Small-Scale Pressure Swing Adsorption Oxygen Production Process

Correlation Analysis between Working Conditions and the Performance of a Small-Scale Pressure Swing Adsorption Oxygen Production Process

Study on PSA Oxygen producing process under plateau region: Effect of purging flow rate on oxygen concentration and recovery

The effect of purging flow rate and oxygen product concentration and recovery rate under different altitude conditions (50 m-4540 m) was studied on the PSA oxygen production platform. The results show that the higher the altitude, the less the purging flow rate consumption in PAS process. Product oxygen recovery rate at altitudes of 50 m, 2810 m, 3080 m, 3550 m, 4140 m and 4540 m is 39.6%∼42%, 42%∼47%, 43%∼46%, 43.4%∼45.5%, 42%∼46% and 48%∼52.5% respectively. At the same altitude, the oxygen recovery first increases and then decreases with the increase of purging flow rate, and there is an optimal balance between oxygen recovery and purging flow rate. This study can provide reference for the regulation of oxygen production process of PSA at high altitude.

Enhanced Electrocatalytic Activity By External Magnetic Field for Oxygen Evolution Reaction

Fossil fuel cannot be relied on anymore as an energy source. Oxygen and hydrogen from water electrolysis can be transformed into electrical energy by a fuel cell. In another way, oxygen and hydrogen can be produced by water splitting process using electrolyzer. There are two processes in water electrolysis, hydrogen evolution reaction (HER) that occur on the cathode and oxygen evolution reaction (OER) that occur on the anode. In this research, we will focus on oxygen evolution reaction.Oxygen evolution is a process of generating oxygen molecules from water by oxidizing water during electrolysis process. To optimize the reaction, a catalyst is needed to be applied to the anode. Until now, some metal oxide such as iridium oxide and ruthenium oxide show the best performance as catalysts. However, they have limited costs. Effective and low-cost catalyst is the key to optimization process.Oxygen has unpaired electrons, make it becomes paramagnetic. Magnetic field drives the direction of oxygen bubbles movement. Oxygen bubbles move towards S-pole and away from N-pole. In an electrolyzer system, the oxygen bubbles will move rotationally. This motion increases the electrolyte hydrodynamic, which serves as a stirrer. The hydrodynamic of electrolyte helps to detach oxygen bubbles in anode surface. Therefore, the internal resistance of the system decreases, and the electrocatalytic activity increases.Moreover, during OER process, oxygen spins are randomly aligned. These randomly align spins lead over potential and inefficient oxygen production process. Magnetic field helps to polarized the oxygen spins. When the oxygen spins parallelly align, the oxidation reaction is improved. Current reports on magnetic effect during OER are still rare, therefore combining magnetic nanoparticle as catalyst and external magnetic force become very interesting.Several magnetic materials such as ferrite nanoparticles and its substitutes (Mn, Co, Ni, Zn) are decorated on Ni foam as anode. Those catalysts then combined with the magnetic field by attaching a permanent neodymium magnet near the anode compartment. Pt mesh is employed as cathode and Hg/Hg2SO4 as reference electrode. Electrocatalytic activity is measured by cyclic voltammetry and chronoamperometry. OER process is done in alkaline liquid electrolyzer, and KOH is used as an electrolyte. This experiment will show the most suitable magnetic material combined with external magnet. Magnetic strength toward OER process also needs to be investigated. Further experiments will be conducted, such as detect and quantify the oxygen radical on the anode by Scanning Electrochemical Microscope (SECM), quantify the oxygen production by oxygen sensor, and detect the hydrogen peroxide formation.Finally, the magnetic field from a permanent magnet has an essential role in electrocatalytic activity of magnetic material. With magnet exposure, the current density is higher rather than without magnet. This simple approach on OER has a significant impact on further applications such as solar fuel systems and fuel cells.

FeO x Derived from an Iron-Containing Polyoxometalate Boosting the Photocatalytic Water Oxidation Activity of Ti3+-Doped TiO2.

The development of efficient and stable catalyst systems using low-cost, abundant, and nontoxic materials is the primary demand for photocatalytic water oxidation. Distinguishing the true active species in a heterogeneous catalytic system is important for construction of efficient catalytic systems. Herein, hydrothermally synthesized Ti3+ self-doped TiO2, labeled as Ti3+/TiO2, was first used as a light absorber in a powder visible light-driven photocatalytic water oxidation reaction. When an iron-containing polyoxometalate Na27[Fe11(H2O)14(OH)2(W3O10)2(α-SbW9O33)6] (Fe11) was used as a cocatalyst, an amorphous layer of active species was wrapped outside the initial Ti3+/TiO2 nanorod and the in situ formed composite was labeled as F/Ti3+/TiO2. When the composite F/Ti3+/TiO2 was tested as a photocatalytic water oxidation catalyst, dramatically improved oxygen evolution performance was achieved. The composite F/Ti3+/TiO2 showed an oxygen evolution rate of 410 μmol/g/h, which was about 11-fold higher than that of prism Ti3+/TiO2. After 24 h of illumination, an O2 yield of 36.4% was achieved. The contrast experiments, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy characterization demonstrated that FeO x is the true cocatalyst that enhanced the oxygen evolution activity of TiO2. A recycling experiment proved that the composite F/Ti3+/TiO2 has favorable stability in the oxygen production process.

Experimental study and energy saving potential analysis of a hybrid air treatment cooling system in tropical climates

A hybrid air treatment cooling system (HATCS) has been proposed to simultaneously promote energy efficiency and improve indoor air quality (IAQ). The HATCS involves a plug-and-play air treatment system. It comprises an energy-efficient oxygen production process, an ozone-based oxidation treatment unit, and an air scrubbing device. Experimental studies have been carried out to investigate the air-purification performance and the energy consumption performance. To address the issue of outdoor air pollution, the proposed HATCS has demonstrated its capability to reduce the supply of ambient polluted air and maintain an acceptable IAQ. Experimental data have demonstrated the feasibility of employing a higher chilled water supply temperature through the cooling coil due to the reduced outdoor air intake. In addition, case studies have been carried out to investigate the energy consumption performance of the proposed HATCS in a typical office building under tropical climates. Simulation results have indicated that a lower outdoor air flow rate leads to a significant reduction on total electricity consumption for cooling. For the selected cases, it is estimated that the total annual electricity consumption saving is up to 59.3 kWh/m2 by employing the air treatment system.

Thermodynamic analysis of a novel oxy-combustion supercritical carbon dioxide power cycle integrating solar-driven coal gasification

To advance the utilization of both coal resources and solar energy, a novel oxy-combustion supercritical carbon dioxide (sCO2) power cycle with solar-driven coal gasification integration was proposed and analyzed. In the proposed system, the concentrated solar energy is utilized for coal gasification to produce syngas for oxy-combustion to drive sCO2 power cycle with near-zero emission and the heat from air separation and hot syngas is recovered for coal drying, steam generation and sCO2 heating in a cascade way. Through introducing solar heat for coal gasification, the raw coal consumption is reduced and the oxygen production process can be eliminated, leading to a higher net system efficiency. The oxy-combustion power cycle can also be simplified owing to the better matching between the process waste heat and the steam generation for gasification. Detailed thermodynamic analysis showed that, the proposed system can save 28.3% of coal consumption with the net efficiency improvement of 1.6 percentage points, compared with the reference system. The solar-to-electricity efficiency can also reach as high as 23.3%.

Axial dispersion effects with small diameter adsorbent particles

Macropore diffusion is traditionally assumed to control the mass transfer rate in columns packed with zeolite particles in an oxygen production process. While numerous studies have confirmed this assumption for the particle size used in industrial size pressure swing adsorption (PSA) processes, it has not been validated for the much smaller particle size used in rapid PSA (RPSA). Smaller particles improve the mass transfer rate by increasing interfacial area per volume as well as decreasing diffusion distance. Despite this reduction, RPSA simulations often still assume a mass transfer rate solely limited by macropore diffusion. This approach fails to adequately account for the influence of other mass transfer mechanisms whose impact increases due to particle size reduction. This study experimentally demonstrates the dominant mass transfer mechanism is no longer macropore diffusion for the particle size used in RPSA for small scale oxygen production. Depending on the gas velocity, axial dispersion effects either become the limiting mechanism or equally as important as macropore diffusion. It also shows that improperly accounting for axial dispersion effects has a significant impact on the mass transfer coefficient estimation, often measured with breakthrough experiments.

Application of Nanosize Zeolite Molecular Sieves for Medical Oxygen Concentration.

The development of a portable oxygen concentrator is of prime significance for patients with respiratory problems. This paper presents a portable concentrator prototype design using the pressure/vacuum swing adsorption (PVSA) cycle with a deep evacuation step (−0.82 barg) instead of desorption with purge flow to simplify the oxygen production process. The output of the oxygen concentrator is a ~90 vol % enriched oxygen stream in a continuous adsorption and desorption cycle (cycle time ~90 s). The size of the adsorption column is 3 cm in diameter and 20 cm in length. A Li+ exchanged 13X nanosize zeolite is used as the adsorbent to selectively adsorb nitrogen from air. A dynamic model of the pressure and vacuum swing adsorption units was developed to study the pressurization and depressurization process inside the microporous area of nanosized zeolites. The describing equations were solved using COMSOL Multiphysics Chemical Engineering module. The output flow rate and oxygen concentration results from the simulation model were compared with the experimental data. Velocity and concentration profiles were obtained to study the adsorption process and optimize the operational parameters.

System analysis of pulping process coupled with supercritical water gasification of black liquor for combined hydrogen, heat and power production

Supercritical water gasification is an innovative black liquor treatment method for hydrogen production. In the present study, an integrated system of pulping and SCWG of black liquor was simulated. Combined hydrogen, power, MP and LP steam are produced for pulping process. The gas product after H2 extraction was burned with imported natural gas to supply more heat. For a reference pulp mill producing 1000 ADt pulp/day, potentially 37126 Nm3/h hydrogen can be produced. The generated MP and LP steam can fully meet the requirement of pulping process. Using air as oxidant in gas combustion is more energy-efficient than using oxygen for being free of oxygen production process. In the case of using air, 22604 kW power can be exported after balancing the consumptions and 219 kgce energy can be produced with 1t pulp production. While using oxygen, 10723 kW power needs be imported and 288 kgce energy can be consumed to produce 1t pulp. However, using air as oxidant may bring N2 and NOx in the exhaust gas, posing a challenge to the subsequent processing. Scaling-up of the system improved the energy efficiency, but the influence is very small when the capacity is above 250ADt/day.

Oxygen integration between a gasification process and oxygen production using a mass exchange heuristic

In this work we analyze different design alternatives for the integration of a gasification process with the oxygen production process, through ITM membranes. We analyze the conventional separation design compared with a novel configuration in a countercurrent arrangement with sweep gas (using the gas permeation module as a mass exchanger). To assess the oxygen transfer in the permeation modules, they are modeled with Aspen Custom Modeler V8.4 and the different design alternatives are simulated in Aspen Plus V8.6. The economic analysis carried out shows that the counter-current arrangement with a sweep stream has a Total Annualized Cost 13.5% lower than the conventional separation design.

Energy Consumption Analysis of Air Separation Process for Oxy-Fuel Combustion System

Oxy-fuel combustion is a leading potential technology to capture CO2. Because the oxygen production process is causing the largest power penalty in oxy-fuel combustion system, it is essential to cut down oxygen separation power penalty for capturing CO2 at low cost. This paper presents the energy consumption analysis results of air separation units with three different cycles offering for oxy-fuel combustion systems. The study shows that when the gaseous oxygen compression (GOXC) cycle is selected for pressuring oxygen product stream, the specific consumption of high pressure and low purity oxygen with triple column cycle is about 6.4-7.2% less than that of with dual column cycle. And when choosing triple column cycle for oxygen production, an air separation unit with pumped liquid oxygen (PLOX) cycle is a better option than with GOXC cycle because it helps to improve plant safety and to decrease energy consumption of high pressure oxygen products.

Technology of oxygen production in the membranecryogenic air separation system for a 600 MW oxy-type pulverized bed boiler

Abstract In this paper the results of the thermodynamic analysis of the oxy-combustion type pulverized bed boiler integrated with a hybrid, membrane- cryogenic oxygen separation installation are presented. For the calculations a 600 MW boiler with live steam parameters at 31.1 MPa /654.9 oC and reheated steam at 6.15 MPa/672.4 oC was chosen. In this paper the hybrid membrane-cryogenic technology as oxygen production unit for pulverized bed boiler was proposed. Such an installation consists of a membrane module and two cryogenic distillation columns. Models of these installations were built in the Aspen software. The energy intensity of the oxygen production process in the hybrid system was compared with the cryogenic technology. The analysis of the influence of membrane surface area on the energy intensity of the process of air separation as well as the influence of oxygen concentration at the inlet to the cryogenic installation on the energy intensity of a hybrid unit was performed.

Thermalhydraulic analysis and heat transfer correlation for an intermediate heat exchanger linking a SuperCritical Water-cooled Reactor and a Copper-Chlorine cycle for hydrogen co-generation

Abstract This paper presents the development of a new heat-transfer correlation for the flow of SuperCritical Water (SCW) in bare circular tubes, and its applicability to thermalhydraulic analysis for Heat eXchanger (HX) designs, linking a SuperCritical Water-cooled nuclear Reactor (SCWR) and a Copper-Chlorine (Cu–Cl) cycle-based hydrogen co-generation facility. A large set of experimental data, obtained in SCW flowing upwards in a 4-m long vertical bare tube with a 10-mm Internal Diameter (ID), was analyzed. The data were collected at pressures of about 24 MPa, inlet temperatures from 320 to 350 °C, values of mass flux ranging from 200 to 1500 kg/m2·s and heat fluxes up to 1250 kW/m2, for several combinations of wall and bulk-fluid temperatures that were below, at, or above the pseudocritical temperature. A dimensional analysis was conducted, using the Buckingham Π-theorem, to derive a general form of the empirical SCW heat-transfer correlation for the Nusselt number, which was finalized based on the experimental data obtained within the Normal Heat-Transfer (NHT) and Improved Heat-Transfer (IHT) regimes. The derived correlation showed the best fit for the experimental data within a wide range of flow conditions. This correlation has an uncertainty of about ±25% for Heat Transfer Coefficient (HTC) values and approximately ±15% for calculated wall temperatures. Subsequently, this correlation was used to calculate HTCs in support of preliminary thermalhydraulic calculations for HXs with SCW and SuperHeated Steam (SHS) as the operating fluids. The HXs are to be designed for integration into the No-Reheat or Single Reheat SCW Nuclear Power Plant (NPP) cycles and provide a link to support hydrogen production through the Cu–Cl cycle. Thermal energy will be transferred from the SCWR to an intermediate SHS loop operating at 5 MPa and delivered to the hydrolysis and oxygen-production process steps of the Cu–Cl cycle facility, which operates at temperatures of up to 530 °C. The analyzed HXs are of a double-pipe, counter-flow design. Calculations involved numerical solutions to identify HX outlet flow temperatures, required pipe lengths, number of pipes for each HX unit, mass flow rates and other relevant heat transfer parameters. Various test conditions have been assessed in support of a database to determine feasible configurations for an HX design.

Using exergy analysis to reduce power consumption in air separation units for oxy-combustion processes

Oxy-combustion is a competitive technology to capture CO2. Current air separation technologies for high volume O2 production are based on cryogenic distillation. When a double-column distillation cycle is applied to produce O2 with a purity of 95 mol%, the oxygen production process is causing the largest power penalty (6.6% points) related to CO2 capture. The actual power consumption is around 4.7 times the theoretical minimum. This paper describes a comprehensive exergy analysis of an air separation unit for producing O2 with low purity (95 mol%) and low pressure (120 kPa). The air compression process and the distillation system cause the two largest exergy losses: 38.4% and 28.2% respectively. The power consumption in the air compressor can be reduced by 19% if the isentropic efficiency increases from 0.74 to 0.9. The total power consumption is reduced by 10% when dual reboilers are applied in the lower pressure column. The exergy losses in the condenser/reboiler exchanger is responsible for only 6.3% of the total losses, thus the power saving potential by developing new heat exchangers with smaller temperature differences is limited. The plant performance in air separation units is not expected to be significantly improved unless the flowsheet structures are improved.

A hybrid process combining oxygen enriched air combustion and membrane separation for post-combustion carbon dioxide capture

For carbon dioxide capture and storage (CCS), similar to a large majority of industrial processes, the separation (i.e. capture) step dominates the costs of the technological chain. Based on a concept of minimal work of concentration, the evaluation of a tentative capture framework which combines an oxygen enrichment step before combustion and a CO 2 capture step from flue gas has been investigated through a simulation study. The performances of a cryogenic oxygen production process have been used for the upstream part, while a membrane separation process based on CO 2 selective materials has been investigated for CO 2 capture. The potentialities of this hybrid process from the energy requirement point of view are discussed. It is shown that the hybrid process can lead to a 35% decrease of the energy requirement (expressed in GJ per ton of recovered CO 2) compared to oxycombustion, providing optimal operating conditions are chosen.

Supercritical water oxidation of coal in power plants with low CO2 emissions

Abstract In this paper, the application of Super Critical Water Oxidation (SCWO) to direct combustion at low temperature of coal fine particles with pure oxygen for power generation is presented, including also a novel method for capturing and storing carbon dioxide as liquid. A detailed simulation model of a 100 MW th coal-fired SWCO plant with low CO 2 emissions characterised by a steam cooled membraned SC reactor has been developed using Aspen Plus software. According to the well-known Semenov's thermal-ignition theory, the coal particle ignition temperature in SCW conditions has been also evaluated and the results have been integrated within the Aspen Plus model. This has been tested under different operating conditions. The simulation results are presented and the effects of the main plant operating conditions, such as ignition temperature, coal particle size and combustion pressure on the plant performances are discussed. The gross and net thermodynamic efficiencies of the power plant have been estimated to be around 44% and 28%, respectively. The pure oxygen production process results the main energy penalty.

메탄 산소 확산화염에서 유속 변화에 따른 연소특성

The combustion characteristics of methane oxygen diffusion flames have been investigated to give basic information for designing industrial oxyfuel combustors. NOx reduction has become one of the most determining factors in the combustor design since the small amount of nitrogen is included from the current low cost oxygen production process. Flame lengths decreased with increasing fuel or oxygen velocity because of the enhancement of mixing effect. Correlation equation between flame length and turbulent kinetic energy was proposed. NOx concentration was reduced with increasing fuel or oxygen velocity because of the enhanced entrainment of the product gas into flame zone as well as the reduction of residence time in combustion zone.