How to Prepare Your Vessel for Unloading Molecular Sieve
8 Useful Guidelines Before Doing a Complete Molecular Sieve Change Out
You have decided to replace your molecular sieve, and now it’s time to load in what may be thousands upon thousands of pounds of molecular sieve in your vessel (of course the amount of sieve you load in depends on the size of your vessel). What can you do to prepare your vessel before unloading all of this sieve?
In order to help you with that question we have prepared eight useful guidelines that could help prepare your vessel for sieve unloading.
Note: These guidelines are to be carried out before you load the sieve into your vessel.
1) Before unloading the sieve you should regenerate your vessel by heating and cooling with process gas. Use the same operating conditions that you would normally use when regenerating your bed.
2) If process gas is not available use nitrogen or another non-toxic gas instead. Do not use any gas that contains any toxic components at hazardous levels to regenerate your vessel.
3) After heating the sieve beds, cool them with gas by de-pressurizing the bed to flare.
4) After using process gas you can start purging the vessel with inert gas at ambient temperature to flare. It is important that the gas flow rate be sufficient enough to have good distribution inside the bed.
5) It’s recommended, if you want to be very thorough in the purging process, to pressure up the bed and de-pressure to flare 2 to 3 times.
6) When outlet gas is 50% below the L. E. L. and free of toxic materials the purging process should be complete. Once purged the bed is ready to have the molecular sieve dumped inside.
7) Unloading the sieve is done from the bottom dump port (or manway) with the flow of gravity guiding the sieve to the bottom.
8) If you decide not to unload the sieve through the bottom dump port then you can unload the sieve with a vacuum hose from the top port. Bins containers or dumpsters can be used to aid you.
Here are some additional things to consider…
Never enter a vessel that contains used molecular sieve.
During the unloading process the molecular sieve may have adsorbed chemical compounds. These adsorbed chemicals may be desorbed again when the molecular sieve is exposed to open air, especially if humidity is high or the air is very moist.
These desorbed chemical compounds can create hazards if the desorbed chemical compounds are toxic. The plant manager or operator has the responsibility to know what chemicals may have be desorbed in this manner and to know what precautions may be necessary to ensure everyone’s safety.