Pressure Swing Adsorption (PSA for short) is a new typeGas adsorptionThe separation technology has the following advantages: high product purity;Generally, it can work at room temperature and low pressure, and the bed is regenerated without heating, so the product has high purity;Simple equipment, easy operation and maintenance;Continuous cycle operation can fully achieve automation.Therefore, when this new technology came out, it attracted the attention of the industrial circles of all countries, competing for development and research, developing rapidly and becoming increasingly mature.[1]
Chinese name
PSA
Foreign name
Pressure Swing Adsorption
Abbreviation
PSA
Proposed time
1960
Advantages
High product purity, easy operation and maintenance
In 1960, Skarstrom put forward PSA patent, and he took 5AZeolite molecular sieveThe adsorbent is separated from the air by a two bed PSA deviceOxygen enrichmentThe process was improved and put into industrial production in the 1960s.In the 1980s, the industrial application of PSA technology made breakthrough progress, mainly in the separation of oxygen and nitrogen, air drying and purification, and hydrogen purification.Among them, the technological progress of oxygen and nitrogen separation is to integrate new adsorbentsCarbon molecular sieveCombined with PSA, O2 and N2 in the air are separated to obtainnitrogen。
With the improvement of molecular sieve performance and quality, andPSA processThe continuous improvement ofpurityThe continuous improvement of PSA and recovery rate has promoted the economic foothold of PSA and the realization of industrialization.[2]
Development history
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PSAAir separationOxygen production was founded in the early 1960s (Skarstrom, 1960;Guerin de Montgarenil & Domine, 1964)，In the 1970s, industrial production was realized.Before that, traditional industryAir separation unitMost of them adopt cryogenic distillation method (cryogenic method for short)
Since 1980s, CaX and LiX with high adsorption and separation performanceZeolite molecular sieveThe successive development and utilization of PSA and the improvement of process flow have led to the rapid development of PSA air separation technologyAir separation unitIn contrast, PSA process has the characteristics of short startup time, convenient startup and shutdown, low energy consumption, low operation cost, high degree of automation, simple maintenance, small floor area and low civil engineering cost.When not neededHigh purity oxygenIt is more competitive than cryogenic method in oxygen production of medium and small scale (less than 100 tons/day, equivalent to 3000 Nm3/h).Widely used in electric furnace steelmaking, non-ferrous metal smeltingGlass processing, methanol production, carbon black production, chemical fertilizer gasificationchemical oxidation Process, pulp bleaching, sewage treatment, biological fermentation, aquaculture, medical and military fields (Yang, 1991;Kumar, 1996; Jee, Park, Haam & Lee,2002)。
PSA for more than 40 yearsAir separationThe research progress of oxygen generation technology is mainly shown in two aspects: the first is the research of adsorbent and its adsorption theory for air separation oxygen generation, and the second is the air separation oxygen generation processCyclic processIn the field of research (Sircar, 1994;Ruthven.Farooq&Knaebel, 1994)。Although the domestic research on this technology started early, it developed relatively slowly in a long period of time.Until the 1990s, PSAOxygen production equipmentIts advantages have been gradually recognized by Chinese people. In recent years, various process equipment have been put into production, bringing huge economic benefits to all walks of life.[2]
Temperature swing adsorption
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Adsorption separation method
Any kind of adsorption for the sameAdsorbed gas(adsorbate)adsorption equilibriumIn this case, the lower the temperature, the higher the pressure, and the greater the adsorption capacity.On the contrary, the higher the temperature and the lower the pressure, the smaller the adsorption capacity.Therefore, the adsorption and separation method of gas usually adoptsTemperature swing adsorptionOr pressure swing adsorptionCyclic process。[3]
Principle of temperature swing adsorption
If the pressure does not changenormal atmospheric temperatureOr at low temperature, and at high temperaturedesorptionMethod calledTemperature swing adsorption(TSA for short).Obviously, the adsorption and desorption of temperature swing adsorption are carried out by changing the temperature.The temperature swing adsorption operation is conducted at low temperature (normal temperature)adsorption isothermAnd the high-temperature adsorption isotherm. Because the specific heat capacity of the adsorbent is large,Thermal conductivity（thermal conductivity）Small, it takes a long time to raise and lower the temperature, and the operation is troublesome. Therefore, temperature swing adsorption is mainly used for gas purification with less adsorbate.[1][3]
pressure swing adsorption
Fig. 1 Isothermal adsorption curve
If the temperature is constant, the adsorption is carried out under pressure, and the method of decompression (vacuum pumping) or atmospheric pressure desorption is calledPSA。It can be seen that PSA is achieved byChange the pressure to absorb and desorbOf.Due to the small thermal conductivity of adsorbent, the adsorption heat anddesorptionThe adsorbent bed temperature caused by heat changes little, so it can be regarded as an isothermal process, and its working condition is approximately along thenormal atmospheric temperatureadsorption isothermCarry out adsorption at higher pressure (P2) and desorption at lower pressure (P1).Since PSA is carried out along the adsorption isothermadsorption equilibriumIt can be seen that the slope of the adsorption isotherm has a great influence on it. Under the condition of constant temperature, the relationship between pressure and adsorption capacity is shown in Figure 1. In Figure 1, PH represents the adsorption pressure, and PL represents the desorption (after decompression) pressure. At this time, the difference between the adsorption capacity corresponding to PH and PL is essentially the effective adsorption capacity, expressed in Ve.Obviously, the effective adsorption capacity of linear adsorption isotherm is larger than that of curve type (Langmuir type).
Adsorption is often carried out in a pressure environment. PSA proposes a combination of pressure and pressure reduction. It is usually an adsorption desorption system consisting of pressure adsorption and pressure reduction.Under isothermal condition, pressure adsorption and decompression desorption are combined to form adsorption operationCyclic process。The adsorption capacity of adsorbent on adsorbate increases with the increase of pressure and decreases with the decrease of pressure. At the same time, the adsorbed gas is released in the process of decompression (to normal pressure or vacuum pumping), so thatAdsorbent regenerationThe adsorbent can be regenerated without heat supply from the outside.Therefore, PSA is also calledIsothermal adsorption, also known asHeatless regeneration adsorption。[1][3]
PSA process
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adsorption process
From air compressorcompressed air, first enter the dryer for moisture removal, and then enter the PSA consisting of two adsorption towersNitrogen production unit, special use of tower fillingCarbon molecular sieveThe adsorbent selectively adsorbs Otwo、COtwoAs product gas NtwoIt will be discharged from the tower top with 99% purity.[1]
Adsorbent regeneration
During depressurization, the oxygen adsorbed by the adsorbent is desorbed and discharged through reverse venting at the tower bottom. After purging, the adsorbent can be regenerated.After regeneration, the adsorbent can be transferred to adsorption after pressure equalizing and product boosting.The two towers are used alternately to achieve the purpose of continuous separation of air for nitrogen production.[1]
PSA application
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useCarbon molecular sieveNitrogen production is mainly based on oxygen and nitrogen in carbon molecular sieveDiffusion rateDifferent, under the pressure of 0.7-1.0Mpa, that is, the diffusion rate of oxygen on the surface of carbon molecular sieve is greater than the diffusion rate of nitrogen, so that carbon molecular sieve preferentially adsorbs oxygen, while most of nitrogen is enriched in the nonabsorbent phase.The carbon molecular sieve itself hasadsorption capacity Increase and decrease the adsorption capacity of oxygen when reducing pressure.Using this featurePSASeparate oxygen and nitrogen.Thus 99.99%nitrogen。[1][4]
