The design principle of PSA

Process principle: Adsorption refers to the phenomenon and process in which, when two substances in different phases come into contact, the molecules of the substance with lower density accumulate on the surface of the substance with higher density. Substances with adsorption properties (usually porous solids with relatively high density) are called adsorbents, while the substances that are adsorbed (usually gases or liquids with relatively low density) are called adsorbates. Based on their different properties, adsorption can be divided into four main categories: chemical adsorption, active adsorption, capillary condensation, and physical adsorption. The adsorption in PSA hydrogen production units is primarily physical adsorption. Physical adsorption refers to the adsorption that occurs through molecular forces between the adsorbent and the adsorbate molecules, including van der Waals forces and electromagnetic forces. Its characteristics are: there is no chemical reaction during the adsorption process, the adsorption occurs very rapidly, the dynamic equilibrium between the various phases involved in the adsorption is established in an instant, and this type of adsorption is completely reversible. The pressure swing adsorption hydrogen purification process is possible thanks to two properties of the adsorbent in this type of physical adsorption: first, it has different adsorption capacities for various components; second, the adsorption capacity of the adsorbate on the adsorbent increases as the partial pressure of the adsorbate rises, and decreases as the adsorption temperature increases. By utilizing the first property of the adsorbent, it is possible to preferentially adsorb impurity components in hydrogen-containing sources, thereby purifying the hydrogen ； By utilizing the second property of the adsorbent, it is possible for the adsorbent to adsorb at low temperatures and high pressures, and to desorb and regenerate at high temperatures and low pressures, thereby creating a cycle of adsorption and regeneration of the adsorbent and achieving continuous separation and purification of hydrogen. The adsorbents used in industrial PSA-H2 units are all solid particles with a large specific surface area; these mainly include activated alumina, activated carbon, silica gel, molecular sieves, and some specialized adsorbents. The most important physical properties of adsorbents include pore volume, pore size distribution, surface area, and surface properties. Different adsorbents have varying adsorption capacities and capacities for adsorbing the various components in a mixed gas, due to their different pore size distributions, specific surface areas, and surface properties. It is precisely this property of adsorbents – their ability to adsorb impurity components much more effectively than hydrogen – that allows us to purify the hydrogen in mixed gases. The adsorption performance of adsorbents for various gases is primarily evaluated through experimentally determined adsorption isotherms. Excellent adsorption performance and a high adsorption capacity are the basic requirements for achieving adsorption separation. Adsorption equilibrium: Adsorption equilibrium refers to the process in which, at a certain temperature and pressure, the adsorbent comes into full contact with the adsorbate, until the distribution of the adsorbate between the two phases reaches equilibrium. During the actual adsorption process, the adsorbate molecules continuously collide with the surface of the adsorbent and are held in the adsorbed phase by the molecular forces at the surface of the adsorbent ； At the same time, the adsorbate molecules in the adsorbed phase continuously obtain energy from the adsorbent molecules or other adsorbate molecules, thereby overcoming molecular attractions and leaving the adsorbed phase ； The adsorption process reaches equilibrium when the number of molecules entering the adsorbed phase and the number of molecules leaving it are equal over a certain period of time. At certain temperatures and pressures, for the same adsorbent and adsorbate, this dynamic equilibrium adsorption capacity is a constant value. At high pressures, since a greater number of gas molecules strike the surface of the adsorbent per unit time, the higher the pressure, the greater the dynamic equilibrium adsorption capacity ； At high temperatures, due to the high kinetic energy of gas molecules, fewer molecules can be trapped by the attractive forces of the molecules on the surface of the adsorbent; therefore, the higher the temperature, the lower the equilibrium adsorption capacity. We use adsorption isotherms at different temperatures to describe this relationship, as shown in the figure below: As can be seen from B→C and A→D in the figure, at a constant pressure, the adsorption capacity gradually decreases as the temperature rises. It is this property of the adsorbent that is utilized in the temperature-programmed adsorption (TSA) process. As can be seen from B→A in the figure above, at a constant temperature, the adsorption capacity gradually increases as pressure rises ； The pressure swing adsorption process utilizes the properties of the adsorbent in the A-B region shown in the diagram to achieve adsorption and desorption. At normal temperature and high pressure (i.e., point A), the adsorbent absorbs large amounts of the impurity components in the feed gas other than hydrogen; thereafter, the partial pressure of these impurities is reduced (to point B) to enable their desorption. In practical applications, the PSA, TSA, or PSA+TSA process is generally selected based on the composition and pressure of the gas source, as well as the requirements of the product. The temperature-swapping adsorption method has a long cycle time and high investment costs, but it achieves thorough regeneration; it is typically used for the purification of trace impurities or those that are difficult to desorb ； Pressure swing adsorption features short cycle times, high utilization of the adsorbent, relatively low amounts of adsorbent required, and no need for external heat exchange equipment; it is widely used for the separation and purification of large volumes of multi-component gases. However, in the PSA process, even when the pressure in the adsorbent bed is reduced to atmospheric pressure, the adsorbed impurities cannot be completely desorbed. In such cases, two methods can be used to fully regenerate the adsorbent: one is to \"flush\" the bed with product gas in order to wash away the impurities that are difficult to desorb; the advantage of this method is that it can be carried out at atmospheric pressure without the need for any additional equipment, but the disadvantage is that it results in a loss of product gas, thereby reducing the yield of the product gas ； Another method is regeneration through vacuum pumping, which forces the more difficult-to-desorb impurities to come off under negative pressure; this is what is commonly referred to as Vacuum Pressure Swing Absorption (abbreviated as VPSA). The advantages of the VPSA process are good regeneration efficiency and high product yield, but the disadvantage is the need to add a vacuum pump. The specific process to be adopted must be determined flexibly based on the composition and flow rate of the feed gas, as well as the user’s requirements regarding recovery rate, investment, and plant footprint. For the pressure swing adsorption unit used to purify H2 in the transformed gas, since the off-gases need to be burned directly, a 10-3-4 PSA process with an improved flushing and regeneration method is employed. At its core are a total of 10 adsorption towers, with 3 towers operating simultaneously; this includes 4 consecutive processes for equalizing pressure and recovering hydrogen, along with continuous processes of reverse discharge and flushing for regeneration.

What I want is *the principles and procedures of art

It’s all confidential; check the websites of PSA’s design companies – many design institutes such as the Southwest Institute and Chengdu West China Institute also have it

Are you looking for the PSA program?

These are all confidential, big brother

By actually understanding the adsorption principle on the first floor, and combining it with the actual operations of various devices, it’s possible to get a general idea of how the program is controlled – things like the switching of valves, as well as the collection and processing of signals. ;P (Easy to say, right? ）

Hehe! Are you there? There are many people in Suzhou and Hangzhou who do this kind of work! It’s a very simple program! Just find a device and observe it for a while, and you’ll know! It’s not that easy to make PLCs these days! It’s pretty impossible to make people upload programs, right? But you can search online for the principles; the procedure is really simple!