The regeneration issue of the adsorbent in pressure swing adsorption hydrogen production units?
Thread Content
Current situation: The adsorbents used in our plant’s pressure swing adsorption hydrogen production unit are imported, from Linde in Germany. They have been in use for over two years now. The adsorbents consist of activated carbon and molecular sieves. At present, the hydrogen production volume has decreased, mainly because it is not possible to increase the operating efficiency. The original design called for a hydrogen production rate of 50,000 units per hour, but currently only 42,000 units per hour can be produced. When the load increases, the level of CO in the produced hydrogen exceeds the specified limits. So I would like to regenerate it online, and there are several issues; I hope experts can offer some guidance: 1. \"The original design called for a hydrogen production rate of 50,000 units per hour, but currently only 42,000 units per hour can be produced. When the load increases, the CO level in the produced hydrogen exceeds the allowed limits.\" Could someone help analyze the reasons for this phenomenon? (Firstly, the adsorbent contains no water; we suspect this is due to an excessive amount of carbon dioxide being adsorbed and unable to be desorbed.) 2. Is it better to use hydrogen or nitrogen for regeneration? 3. Regeneration is best carried out using hot hydrogen or hot nitrogen; what is the appropriate regeneration temperature? What would be the effect if hot hydrogen or hot nitrogen is not used, and only cold hydrogen is used for backflow? This post was last edited by lionangelwkp on 2007-11-26 22:38]
The first reason for the phenomenon you mentioned is that the adsorbent has exceeded its designed service life and has thus become somewhat aged. The second reason is that, over time, carbon monoxide reaches saturation levels in the molecular sieve, which necessitates regeneration. Solution: It is best to use hydrogen for regeneration at a temperature of around 440 K; this allows both types of adsorbents to be regenerated simultaneously. However, care must be taken regarding safety, as hydrogen is dangerous at high temperatures. Using nitrogen for replacement yields less effective results but is safer – it’s up to you to decide. It is better to perform negative pressure regeneration first at a lower vacuum level before regenerating with hydrogen or nitrogen, as this yields better results. However, the overall performance of the regenerated adsorbent is not as good as that of a new one.
What would be the effect if hot hydrogen or hot nitrogen is not used, and only cold hydrogen is used for backflow? Could you tell me?
After being used for an extended period of time, the adsorbent will absorb moisture and other hydrocarbons, resulting in a decline in its performance. The methods for regenerating it include thermal nitrogen circulation or venting for regeneration, with the temperature controlled at around 240 degrees; this allows its activity to be restored to 90% of that of a new adsorbent
Changes in operating parameters and gas composition are also very important; if you compare the parameters before and after, you might make some new discoveries!
Generally speaking, unless there is adsorption of non-renewable components or sudden high-speed airflow scouring, the adsorbent does not age easily
If it is just cold hydrogen gas used for backflow, it is basically ineffective. Because the desorption process is an endothermic reaction. Regarding the pressurized regeneration medium and temperature, the previous speakers have already mentioned them. Of course, if your tower can withstand negative pressure, vacuum regeneration is also an option (if you suspect there is too much CO2, vacuum regeneration is an effective and safe method). After regeneration, if the tower still does not reach its original performance levels, it means that the effective adsorption capacity of the molecular sieve has decreased over time; the only solution in that case is to replace the molecular sieve. If you can take some molecular sieve from the tower and give it to me, I can help you analyze whether the adsorption capacity of the molecular sieve has decreased. I can conduct a data comparison with German new molecular sieves. My QQ is 53748807
I wonder if the designed capacity has been reached? If the regeneration is simply not effective, vacuum desorption or the use of dry nitrogen (or dry hydrogen at a temperature of 20–40 degrees; it’s important that there be no water present) can be employed. If the plant used to operate at its designed capacity but now has a lower processing capacity or output, there may be other reasons for this: 1. Internal leakage in the programmable control valve; 2. Air leakage from the valve’s packing gland or other external leaks; 3. Incomplete regeneration of the adsorbent; 4. The process pipelines and valves being too small in size (which affects the design capacity); 5. An improperly designed control program (which also affects the design capacity)
I thought about it again: actually, the original installation on the first floor also met its design specifications, and it was able to regenerate completely during operation. Because the operation of a factory does not undergo major changes over many years of operation. So the remaining reasons are either internal leakage or an expired molecular sieve. However, in the case of an internal leak, the load will not move, and the CO level in the exhaust gas from the product will also be significantly higher than that during normal production in previous years. (You can check previous analysis records.) So the last remaining reason is that the activity of the molecular sieve has decreased. In short, taking a small amount of molecular sieve and conducting an adsorption capacity analysis serves as a crucial factor for making judgments. If the molecular sieve stops working, buy it. On the first floor, if you need any help, just come to me. Don’t be polite.
Hydrogen production plant engineer 15937530156