The pressure difference before and after membrane separation is large
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Our plant uses a Prins membrane system to artificially extract natural gas from the purge gas in the methanol synthesis system. We have observed that the pressure difference across the membrane separation system for the gas that has been decarbonized using an MDEA solution is increasing continuously. Could it be that the crystallization of the MDEA solution is causing blockages in the membranes?
In my humble opinion, the crystallization of MDEA solutions leads to membrane blockage, which in turn causes the pressure difference to keep increasing; I hope experts on chemical engineering forums can provide guidance
What kind of membrane is being used? A spiral-wound membrane module or a hollow fiber membrane module? Is a filtering device installed at the membrane inlet? A large pressure difference means high pressure loss, and a decrease in flow rate is inevitably due to blockage. In our design, there is two-stage filtration at the front; the membrane becomes useless as soon as it comes into contact with water, and it also becomes ineffective when too many impurities are present. Exquisite! I have used hollow fiber membrane modules made in Germany, which are oxygen-enriching membranes. The pressure difference between the inlet and outlet is zero when passing pure oxygen. At that time, I didn’t know that holding pure oxygen would increase the pressure in the test tube. It almost exceeded the design pressure for the membrane; one membrane costs 50,000! Just thinking about it makes me sweat!
After the MDEA unit, a mechanical filter is generally installed to remove the impurities brought in by the MDEA unit; thereafter, the gas must be pre-treated again before it enters the membrane, involving gas-liquid separation, heating, and the use of an additional filter. The pressure difference across the Prison membrane is determined primarily by the air pressure of the membrane unit you choose; there are options with 5.0 MPa and 8.0 MPa pressures, and it depends mainly on the model of membrane you select. I work with membrane devices. You can get in touch and communicate.
Reply 3# chaozhan11: It is a hollow fiber type, and there is a conical filter at the inlet of the membrane separation unit.
Reply to 4# sunyong163com: Our MDEA unit does not have a mechanical filtration device behind it, but there is a cone-shaped filter at the inlet. We suspect that the separator at the outlet of the MDEA unit may not be effective enough; therefore, we plan to add another separator. We’re not sure what the effect of adding this will be. We also encountered a situation where the gas analyses of the inlet gas, permeate gas, and non-permeate gas from the membrane separation unit were basically identical for about a day, after which they gradually returned to normal; at that time we thought the membrane might be damaged.
Reply to 1# youer1986: A large pressure difference across the membrane indicates that it is blocked. Based on the poster’s description, the reason for this is as follows: After the gas phase undergoes decarburization using MDEA solution, it carries along a small amount of MDEA solution in its form of mist. When this gas phase containing MDEA enters the membrane system, the MDEA gets adsorbed by the membrane, while the water content evaporates and is carried away by the gas phase. The MDEA then forms crystals, which cause the membrane to become blocked. As the device continues to operate, the pressure difference across the membrane increases gradually, eventually leading to damage to the membrane. Therefore, it is recommended to install a demisting device in the decarburization process, and to add two filtration units before the gas phase enters the membrane system after decarburization (the first unit for coarse filtration, and the second using an ultrafiltration membrane).
Reply to 6# youer1986: Based on my experience with various systems, simply adding a gas-liquid separator is not sufficient to address the main issues. What’s more important is to install one or two mechanical filters (it’s crucial to choose the right filter elements) in order to remove impurities caused by factors such as liquid overflow in the MDEA section. Additionally, the design of the gas-liquid separator also needs to be carefully considered to achieve optimal separation results. Installing only a conical filter before the membrane separator will not be effective; at best, a conical filter can only provide rough or temporary filtration.