Calculating required amount of molecular sieves for PSA?

[Voltux]

Does anyone know how to properly calculate the amount of molecular sieves needed for a pressure swing adsorption system?

I have searched application notes, books, and of course google, and while I find the basics of how they are constructed I cannot find any information on the quantity required.

My theory is that I will need enough surface area to hold the output flow rate worth of nitrogen with a minimum of 2x "safety factor". For example I want to build a 5LPM flow oxygen concentrator.

For 5LPM O2 output I would have 23.8LPM of air of which 18.8L would be N2, and 5L would be O2.

Assuming I have a 10 second cycle time I would need to hold 3.13L of N2, and with a 2x "safety factor" I would need say enough sieves to hold 6L of N2 before exhausting. I would then double that amount to get a continuous flow switching between 2 beds at approximately 50PSI input pressure.

This is however just a guess. Any input is appreciated.

 

[Achy47]

As a scientist with experience in pressure swing adsorption systems, I can offer some guidance on how to properly calculate the amount of molecular sieves needed for your system.

First, it is important to understand that the amount of molecular sieves needed will depend on the specific design and operating parameters of your system. These parameters include the desired purity of the output gas, the flow rate of the input gas, the cycle time, and the pressure and temperature conditions.

To start, you will need to determine the required purity of your output gas. This will determine the level of adsorption and desorption that needs to occur during each cycle. The higher the purity, the more adsorption and desorption will be required, which will in turn require more molecular sieves.

Next, you will need to calculate the amount of input gas that needs to be processed in a given cycle. This can be done by multiplying the flow rate of the output gas (in this case, 5LPM) by the ratio of nitrogen to oxygen in air (in this case, 18.8L of N2 for every 23.8L of air). This will give you the total volume of air that needs to be processed in each cycle.

Using your example of a 10 second cycle time, you can then calculate the amount of nitrogen that needs to be adsorbed and desorbed in each cycle. This can be done by multiplying the total volume of air by the ratio of nitrogen in air (in this case, 18.8L of N2 for every 23.8L of air). This will give you the total volume of nitrogen that needs to be processed in each cycle.

From here, you can use the adsorption capacity of your chosen molecular sieves to determine the amount of sieves needed. This will depend on the specific type and size of molecular sieves you are using. Generally, the larger the surface area of the sieves, the more nitrogen they can adsorb.

Lastly, it is important to consider the safety factor you mentioned. Adding a safety factor is a good idea, as it ensures that your system can handle unexpected variations in operating conditions. However, the exact amount of safety factor to use will depend on your specific system and its operating parameters.

In summary, to properly calculate the amount of molecular sieves needed for a pressure swing adsorption system, you will need to determine the required purity of your output gas, calculate the amount of input gas