PSA Oxygen Generator

NEWTEK Group specializes in the design, production, and sales of industrial oxygen concentrators. Industrial oxygen concentrators can be widely used in steel cutting, oxygen-enriched combustion, hospital oxygen, petrochemical industry, electric furnace steelmaking, glass production, papermaking, ozone production, and aquatic products In industries and fields such as breeding and aerospace, NEWTEK provides personalized and specialized oxygen production equipment to fully meet the gas usage requirements of different users in different industries.

 

 

 

 

PSA Oxygen Plant Types

 

Applications

 

 

Services

 

 

 

 

Experimental data

 

NEWTEK designed a small psa oxygen generator manufacturer with two adsorption beds. It simulated the influence of altitude on the small PSA oxygen generator with two adsorption beds in a low-pressure chamber. At the same time, it also investigated the impact of structural parameters and operating parameters, and established the mathematics of the oxygen production process. Model, through experimental comparison, fine-tune the model to make it consistent with reality, verify the accuracy of the model, and carry out numerical simulation and simulation research to determine the impact of relevant internal parameters and external factors on performance indicators such as the oxygen production process and oxygen production effect. According to the rules, optimal design parameters and operating parameters can be obtained under different altitudes and different working conditions, thereby improving the oxygen production efficiency and reducing the manufacturing and operating costs of the oxygen generator.

 

Compared with pressure swing absorption, PSA has a simple cycle and low product gas concentration and recovery rate, rapid pressure swing absorption, RPSA, has the advantages of short cycle and low adsorbent dosage per unit gas production. It is based on micro rapid pressure swing The small oxygen generator based on the adsorption separation principle has the advantages of simple equipment, good stability, large oxygen output, and adjustable purity. It is widely used in home health care, medical treatment, plateau oxygen supply and other fields. In order to deeply study the intrinsic characteristics of the RPSA cycle, establishing a mathematical model of the PSA process and using numerical methods to simulate the actual process has become a favorable means for the development of pressure swing adsorption devices. At the same time, numerical simulations can calculate data that are not easily obtained in experiments. , such as the amount of substances adsorbed by the gas in the tower, changes in the gas phase composition along the axial direction of the adsorption tower, etc. Our researchers are actively exploring simulations of rapid pressure swing adsorption. The theories and calculation methods involved in the pressure swing adsorption process are summarized and laid the foundation for numerical simulation based on the principle of pressure swing adsorption. The influence of lumped heat transfer and mass transfer coefficient simulation on pressure swing adsorption simulation was studied. The adsorption and desorption processes in the adsorption tower were simulated and calculated, and the adsorption kinetics, pressure drop, three transfers and one reverse process in the tower were systematically carried out. This study examines the effects of adsorbent diameter, adsorption pressure and height-to-diameter ratio on pressure swing adsorption oxygen production. Through simulation, the effects of adsorption and desorption pressure on the speed and circulation performance of the rapid pressure swing adsorption bed were studied, and the effects of different pressure equalization methods on the air separation oxygen production process of PSA and VSA (vacuum pressure swing adsorption) were explored. The dynamic mass transfer coefficient of pressure adsorption oxygen production was simulated and analyzed.

 

The above simulation is only calculated for a single adsorption tower, and auxiliary equipment, air compressors, buffer tanks and other components are not included. NEWTEK designed and built a miniature pressure swing adsorption device by simulating different altitudes in the low-pressure chamber. The shortest time sequence of the device is 9.6 s, and the device is a miniaturized device (the height of a single tower is only 339mm). On this basis, experiments were designed based on the impact of different conditions on the oxygen purity and yield of the two-tower pressure swing adsorption oxygen production process, and a complete dynamic mathematical model of the entire process was established in the Aspen Adsorption software, including the air compressor and buffer. Tank components were simulated and compared with experimental values to verify the reliability of the model. Then the model was used to compare and analyze the interrelationships of various process parameters in the process, and the influence of key parameters on the performance of the oxygen generation system was obtained.

 

1 Experimental device and process flow

1.1 Adsorption isotherm measurement device

The adsorption isotherm measurement device is shown in Fig. 1. The equilibrium adsorption capacity of N2 and O2 on the carbon molecular sieve is measured using the static volume method. The reference tank and adsorption tank are the main testing units. The principle of static volume method to determine the equilibrium adsorption capacity of pure components is based on the difference between the total amount of gas entering the system before adsorption and the amount of gas in the system after reaching adsorption equilibrium. The saturated exchange capacity is calculated through the gas PVT state equation. The reference tank is 150 ml. After filling with adsorbent, the free volume of the adsorption tank is measured by He. During the measurement of equilibrium adsorption capacity, the reference tank and adsorption tank are placed in a super constant temperature water bath. The constant temperature of the water bath is the temperature specified by the adsorption isotherm. The adsorption isotherm data measured based on the above principles and equipment are shown in Fig. 2.

1.2 Experimental device

The two-tower pressure swing adsorption experimental device is shown in Fig. 3. The tower height of the two adsorption towers is 339 mm, and the tower diameter is 68 mm. The effective filling volume of adsorbent in each adsorption tower is 1.23×10-3 m3. The raw material gas is air (the mole fractions of N2, O2, and Ar are 78%, 21%, and 1% respectively). The entire oxygen production process is controlled by a solenoid valve.

1.3 Process flow

In the pressure swing adsorption process, in order to coordinate the operations of multiple towers, a combination of PLC controllers and program-controlled valves are usually used to realize automated pressure swing adsorption operations. The pressure swing adsorption time sequence of the two towers used in the experiment is shown in Table 1. The adsorption towers perform the steps of pressure charging and adsorption AD, equalizing pressure and decreasing ED, venting PP, flushing PUR, and equalizing pressure and increasing ER. During the cycle, the adsorption stage time is 4~9 s, the venting and flushing time is 4~9 s, and the pressure equalization process time is 0.8 s. The air enters the air compressor after being purified by the filter. The compressed air is cooled by the heat exchanger and distributed by the solenoid valve to the adsorption bed for adsorption and separation. Part of the separated product gas enters the oxygen storage tank through the one-way valve. After being decompressed by the regulating valve, it is provided to the user after passing through the oxygen filter and flow meter. The other part of the product gas passes through the flushing hole to the other adsorption bed after desorption. Backflush cleaning improves the desorption effect of the adsorption bed. The desorbed nitrogen-rich gas is discharged from the muffler through the two-position four-way solenoid valve. In the pressure equalization step, the air inlets of the two towers that complete adsorption and desorption are connected to realize the pressure equalization process.

 

2 PSA oxygen production process modeling and simulation

In order to conduct in-depth research on the process of a small two-tower pressure swing adsorption oxygen generator, it is necessary to establish a mathematical model to simulate it.

The professional software Aspen Adsorption for pressure swing adsorption is used for simulation. The discrete method is the central difference method. The bed is divided into 100 nodes. In order to simplify the simulation process, the following is made: ① The gas state equation is the ideal gas state equation; ② The momentum balance equation is the Ergun equation; ③ the adsorption kinetic model is the lumped resistance linear driving force method; ④ the adsorption isotherm is the Langmuir extension type; ⑤ radial diffusion and radial concentration, temperature, and pressure changes are ignored. The mathematical model Table 2 for simulating the adsorption bed is constructed based on the above assumptions.

The adsorption bed model mainly includes mass conservation, heat conservation and momentum conservation models, which are represented by equations (1) to (6) respectively. Among them, the heat conservation is divided into a strict model of three parts: gas phase, solid phase, and tower wall and environment. It is calculated using the extended Langmuir multi-component equation, as shown in Equation (7). The gas-solid phase mass transfer equation adopts the linear driving force equation. , the diffusion coefficient is an estimated value, as shown in equation (8). The oxygen purity is calculated as shown in Equation (9). The oxygen recovery rate is calculated as shown in Equation (10). The oxygen production capacity is calculated as shown in Equation (11). The valve opening is controlled by CV, and the relationship between flow rate and valve opening is as shown in Equation (12)shown. This process uses LiLSX medical molecular sieve as the adsorbent. The relevant parameters of the adsorbent and adsorption tower are shown in Table 4. The corresponding Langmuir adsorption equation data of N2, O2, and Ar on LiLSX medical molecular sieves are obtained by fitting the measured adsorption amounts of pure gases on the adsorbent. These values are shown in Table 3. The boundary conditions of numerical simulation are shown in Table 5.

3 Results and discussion

3.1 Simulation and experimental results Table 6 shows the comparison of simulation and experimental results of two-tower pressure swing adsorption. During the simulation and experiment, the effects of altitude, adsorption time, and flushing hole diameter on the purity of product oxygen were investigated. It can be seen from the data in the table that the concentration of product oxygen in the experimental results is basically consistent with the simulation results, and the maximum relative error is 5.5%. It can be judged from this that the mathematical model established is correct. Among them, when the altitude is 3000 m, the tower height is 339 mm, the adsorption time is 7 s, and the air feed flow is 5.00 L·min-1, the purity of the product oxygen can reach 94.00%, and the yield is 41.59%. According to the oxygen purity and yield of the product gas obtained from the experiment, it can be seen that the two-tower pressure swing adsorption oxygen production process can meet the needs of normal household or military small oxygen generators.

 

 

3.2 Effect of altitude

Because the user groups of small oxygen generators vary widely across regions, it is necessary to study the oxygen purity, oxygen output and yield of the two-tower pressure swing adsorption process under different altitude conditions. The pore diameter of the flushing hole was 0.9 mm and the adsorption time was 7 s to examine the influence of altitude. The feed amounts at different altitudes and the corresponding atmospheric pressure at that altitude are shown in Figure 4. The steady-state single-cycle pressure changes in the tower at different altitudes are shown in Figure 5. The changes in experimental and simulated product gas oxygen concentration and yield with altitude are shown in Figure 6. It can be seen from the figure that as the altitude increases, the atmospheric pressure gradually decreases, and the feed amount also gradually decreases. When the adsorption time remains unchanged, the pressure of the adsorption bed adsorption decreases, the adsorption capacity of the adsorbent decreases, and the oxygen content of the product gas decreases. Purity gradually decreases. When the altitude increases from 2000 m to 5000 m, the oxygen purity of the product gas decreases by about 10%, but the yield increases by about 13%. Although the adsorption pressure in high altitude areas is low, 93% pure oxygen can still be obtained by extending the adsorption time, and the yield increases by about 14%. Under the same operating conditions, the phenomenon of "yield increases with altitude" occurs. The reasons are as follows. On the one hand, as shown in Figure 5, in an area with an altitude of 2000 m, the adsorption pressure is as high as 2.4×105 Pa, the desorption (washing) pressure is 0.9×105 Pa, and the pressure difference is 1.5×105 Pa. In an area with an altitude of 5000 m, The adsorption pressure is 1.3×105 Pa, the desorption (flushing) pressure is 0.6×105 Pa, and the pressure difference is only 0.7×105 Pa. As the altitude continues to increase, the pressure difference between the adsorption stage and the flushing stage continues to decrease, which means that the altitude The lower the area, the greater the net adsorption amount of the adsorbent in the adsorption stage of each cycle, and the greater the amount of N2 and O2 desorbed in the flushing step. Since part of the desorbed gas is directly exhausted, so in low-altitude areas The oxygen recovery rate is lower. On the other hand, by balancing the oxygen material in a single adsorption tower in a single cycle, as shown in Table 7, it can be seen that due to the smaller absolute adsorption capacity of nitrogen in high altitude areas, the gas volume required for flushing and regeneration is also reduced. , leading to an increase in oxygen yield. In addition, the oxygen production in experiments and simulations was controlled by a mass flow meter. The oxygen production in experiments at different altitudes was the same. The feed volume at high altitudes was lower, but the product gas production rate was the same as that at low altitudes, so the yield was higher. And the purity is lower.

3.3 Effect of adsorption time

The adsorption stage is the core of the pressure swing adsorption process, and the adsorption time is an important operating parameter of the adsorption process. If the adsorption time is too short, the adsorbent will not be fully utilized and the product purity will not meet the demand; if the adsorption time is too long, N2 will penetrate and the product gas quality will be reduced. Therefore, it is necessary to study the effect of adsorption time on product gas. In this set of simulations, when the altitude is 3000 m and the flushing hole diameter is 0.9 mm, the concentration distribution of N2 in the adsorption tower under different adsorption times is shown in Figure 7. When the adsorption time is greater than 7 s, the adsorption of nitrogen The leading edge is close to the top of the tower. The yield and purity of O2 under different adsorption times are shown in Figure 8. When the adsorption time is short and nitrogen has not yet penetrated, as the adsorption time increases, the adsorption pressure in the tower increases, the adsorbent adsorbs more nitrogen, and the purity of oxygen continues to increase. The adsorption front in the tower moves toward the top of the tower. The heavy component (nitrogen) increases, more oxygen is produced as product gas, and the oxygen recovery rate continues to increase. If the adsorption time is too long, when nitrogen penetrates, the product gas will be mixed with a large amount of nitrogen impurities, resulting in a significant reduction in oxygen purity of the product gas. The oxygen recovery rate will still increase, but the trend will become flat. When the adsorption time is 7 s, the purity of the product gas oxygen is 94.00%, and the yield is 41.59%.

3.4 Influence of flushing hole diameter

The flushing operation is implemented through a flushing pipe. The size of the flushing hole will affect the amount of product gas consumed for flushing. The flushing operation has a significant impact on the regeneration of the adsorbent and the product gas yield. The location of the flushing hole is shown as No. 8 in Figure 3 of the two-tower pressure swing adsorption oxygen production device. The change of the flushing gas flow rate corresponding to the flushing holes with different apertures over time is shown in Figure 9. In the figure, a positive value of the flushing gas flow rate means that the flushing gas flows from Tower A to Tower B, and a negative value of the flushing gas flow rate means that the flushing gas flows from Tower B to Tower B. Tower A. The change of pressure in the tower with time corresponding to flushing holes of different diameters is shown in Figure 10. The effect of flushing hole size on oxygen purity and yield is shown in Figure 10.

In this set of experiments, the altitude was 5000 m and the adsorption time was 9 s. When the pore diameter of the flushing hole is relatively small (<0.8 mm), as the pore size of the flushing hole increases, the product gas consumed by flushing increases (Figure 9), the adsorbent desorption and regeneration effect continues to improve, and the nitrogen adsorption capacity increases significantly. The purity of oxygen in the product gas increases significantly (Figure 11). When the pore diameter of the flushing hole increases to a certain amount (>0.8 mm), because the pore size of the flushing hole is too large, a large amount of product gas is consumed, resulting in a significant decrease in oxygen yield. Due to the excessive flushing volume, the adsorption tower in the adsorption stage The pressure decreases (Figure 10), the nitrogen adsorption amount decreases, and the oxygen purity of the product gas decreases (Figure 11). It can be seen from the simulation that when the flushing hole diameter is 0.8 mm, the purity of the product gas oxygen is 92.95%, and the yield is 48.90%. Different altitudes have different suitable flushing hole diameters, and the changing trend is: as the altitude increases, the optimal flushing hole diameter decreases.

 

Industry knowledge

 

 

PSA (Pressure Swing Adsorption) is a technology used in oxygen plants to generate high purity oxygen from compressed air. This cost-effective method utilizes zeolite molecular sieve adsorption to separate oxygen from other gases in the air. It has become a popular option for industries such as healthcare, aerospace, and metallurgy, which require a constant supply of high purity oxygen. PSA technology is also environmentally friendly, as it does not produce harmful byproducts and uses less energy compared to other oxygen generation methods. Overall, PSA technology is a reliable and efficient solution for meeting the oxygen demands of various industries.

 

The working principle of a PSA (Pressure Swing Adsorption) plant involves the separation of gases by selectively adsorbing one gas under high pressure and then desorbing it under low pressure. The plant consists of two vessels filled with a material called adsorbent which selectively adsorbs nitrogen or oxygen depending on the pressure applied. Compressed air containing a mixture of gases is introduced into one vessel while simultaneously reducing the pressure on the other vessel allowing the adsorbed gas to be released. This process is cyclically repeated to produce a continuous flow of nitrogen or oxygen gas of high purity.

 

The process of PSA oxygen manufacturing involves using special adsorbent materials to selectively adsorb nitrogen from the air, leaving behind highly concentrated oxygen. This process is eco-friendly and cost-effective, making it a popular choice for various industries.

 

PSA (Pressure Swing Adsorption) and VPSA (Vacuum Pressure Swing Adsorption) are both methods used to produce oxygen. The main difference between them is the pressure level used in the process. PSA operates at higher pressures, while VPSA operates at lower pressures.

 

PSA separates oxygen molecules from other gases in compressed air by using adsorbent materials such as zeolites. The compressed air is passed through these materials, which adsorb nitrogen and other gases, leaving behind pure oxygen. PSA plants are highly efficient and require minimal maintenance.

 

VPSA, on the other hand, uses vacuum pumps to lower the pressure of the compressed air. This causes the separation of oxygen molecules from other gases. VPSA plants are typically smaller and less expensive than PSA plants.

 

The flow rate of a PSA plant varies depending on the size and capacity of the plant. Generally, a typical PSA plant can produce hundreds to thousands of cubic meters of nitrogen or oxygen per hour. The specific flow rate required will depend on the needs of the user, whether it is for industrial or medical use. Regardless of the flow rate, PSA plants are environmentally friendly and cost-effective, making them a popular choice for many industries around the world. With advancements in technology, the flow rate of PSA plants will likely continue to improve, providing even more benefits for users.

 

Cryogenic and PSA oxygen plants are two different methods for producing oxygen. Cryogenic plants use a process of air separation where the air is cooled to extremely low temperatures, causing the different components to separate. PSA plants use a process called pressure swing adsorption, where a special molecular sieve captures the oxygen molecules from the air while the other gases are released.

Both methods have their advantages and disadvantages. Cryogenic plants are best suited for large-scale production and provide a high level of purity. PSA plants are more cost-effective for small and medium-scale production and require less maintenance. Both methods play an important role in meeting the increasing demand for oxygen in various industries and medical applications.

 

The primary expenses in an oxygen generator are attributed to the compressor and molecular sieve. Opting for a screw air compressor with low oil content (≤ 10ppm) significantly enhances oxygen system efficiency. It's advisable to choose a compressor with a rated exhaust pressure of 0.5-0.7Mpa; excessive or insufficient pressure can be counterproductive. For locations above 1000m altitude, factor in atmospheric pressure and consider a larger compressor to meet oxygen production needs efficiently.

 

PSA oxygen production typically yields oxygen purity levels of 93±3%, meeting industrial standards of 95%. For medical-grade oxygen as per the World Health Organization, the standard is 93%±3%. If a purity level of 99% or higher is necessary, the addition of a purification device is essential.

 

1、When catering to hospital beds, allocating 2-3LPM per bed suffices. For instance, with 100 beds, the requirement totals 300LPM (300*60=18,000L/hour=18Nm3/hour). It is advisable to opt for 20Nm3/hour equipment, such as our MNPO-20/93 model.

2、In the context of filling oxygen bottles, the oxygen volume in each bottle equates to water volume multiplied by filling pressure. For example, when filling 100 bottles of 40L oxygen bottles at 150 bar pressure daily, each bottle holds approximately 6 cubic meters of oxygen. Thus, for 100 bottles, you need 600 cubic meters. Calculating for 24-hour operations, 25Nm3/hour equipment is recommended.

 

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