Seeking help with PSA problems
Thread Content
The PSA pressure swing adsorption process in our plant is divided into two stages: in the first stage, CO2 is purified to 98.5% purity and sent to the urea production unit, while the remaining gas is sent to the second stage. I would like to ask what happens to the pressure curve when one of the programmable valves in a certain section cannot be closed properly, and why. How do the purity of CO2 and the gas flow rate change? How will the CO2 content in the gas sent to the second stage change, and why?
Well, it’s displayed on the computer in the control room of your installation; you can analyze it using that computer, in conjunction with your questions, within the automatic control system
This needs to be analyzed in conjunction with one’s own processes and procedures； When the programmable valve of a certain tower cannot be closed properly, the pressure in that tower and the pressure of the equipment connected to that valve that fails to close will differ significantly from the normal pressures, and this can be analyzed by examining the pressure trends.
Create a pressure trend – it’s very clear at a glance
In daily operations, you need to pay attention to pressure trends and valve inspection alarms. Valve inspection alarms may give false positives, but generally speaking, with some experience, it is possible to discern pressure trends. Problems with control valves not closing properly usually occur with butterfly valves; such issues are less common with control valves of small diameter. In such cases, the valve either fails to close at all or closes late. When a valve fails to close, this can be easily identified from the curve. If the valve inspection alarm is accurate, the problem can be detected right away; if no alarm is given, then experience is required to identify the issue. The effects on the pressure curve when the high-pressure valve and the low-pressure valve are not closed differ. The most obvious sign of an unclosed high-pressure valve is a sudden drop in system pressure; the concentration of carbon dioxide in the intermediate product gas at the outlet also decreases, and the purity of carbon dioxide in the urea product will surely drop as well. It is necessary to inform the urea production system promptly. These issues cannot be explained in just a few words – careful observation is required in daily work. No matter how clearly I explain it, it’s better if you can experience it firsthand. In short, by carefully studying the pressure trends, many problems can be identified and a lot can be learned!
1. If the programmable valve of a certain tower cannot be closed properly, when that tower proceeds to the next stage, it will definitely have an impact on that tower as well as on other towers connected to that valve, which can be easily observed from the pressure trends displayed on the computer； It may also cause fluctuations in gas volume and variations in the quality of the product gas. 2. In such a situation, the vehicle should be stopped promptly for inspection and repair.
If the valves cannot be closed properly, one can check the computer-based trend charts; it’s necessary to observe closely during the production process. The main issue arises with high-pressure valves (the inlet and outlet valves, and in the case of VPSA, also the evacuation valve). If these valves cannot be closed properly, it causes problems and has a significant impact on production, as the pressure can drop rapidly. If other valves cannot be closed, the impact will not be significant; quick action will not result in a shutdown.
Thank you for your reply. At first, I found PSA difficult to understand, but after thinking about it more, I gradually figured it out