My experience goes back too many decades to count for much.  Drums of odorant were transferred into a pressure vessel near the loading rack.  While loading a truck the rack operator would fill a sight glass to a selected point then manually sweep part of the filling fluid through the sight glass manifold.

Today I would use a coriolis meter (or perhaps a metering pump) with a ratio of odorant against the LPG flow rate.  I would also want a batch loading record stored with the bill-of-lading number.

There are several automated odorizing systems.  Emerson's Daniels division makes a danload with an odorizer, YZ makes one, there are many others.

Most state laws require a certified load reciept that indicates how much odorant was injected into the load for transportation and consumption.  The only way to do this is to have the odorant injected during loading.

If you ever want to sell un-odorized propane or butane and you have odorized it in the tanks, there goes that sale.

If you have a small leak around your tanks, then the whole area will have that plesant odor all the time (it may be a good thing too).

If you make off spec product, you cannot rerun it if the product has been odorized because of the odorant will harm equipment, be difussed into all other products, and you have no way of knowing odorant concentrations so you will have to odorize it again.

All the above and many more say to odorize at the loading rack.

Thank you for your useful answers. I see that one of the main reasons for not odorizing the storage bullets is to prevent contamination of the storaged LPG in case we want to sell un-odorized propane or butane.

In my case, we have a vapor return line from truck/raical wagons towards the storage bullets. Can these vapors of LPG/odorant contaminate the bullets? Perhaps it is necesary to clean those vapors with some kind of scrubber (i.e activated carbon adsorption)? I don't know if it is usually done so...

Regards

You will get some contamination.  I've switched to the spraybar loading system to stop the contamination and simplfy the loading, no vapor return line, just a 300 gpm 50 psi delta P vertical can pump to load with.

Unfortunately in my country spraybar loading is not that extended and client has required to use vapor return line.Any suggestion about how avoid contamination  of the bullets? Any experience?
Thank you

I've never measured the amount of mercaptan that returns, I'd guess about 2%.  The return vapors will have about 1.5 times as much ethyl mercaptan in it by weight that you odorized the truck with. so for every Kg of mercaptan in about 4 grams will go back to the tank.  

Have you ever used any kind of filter (i.e activated carbon) in the vapor return line in order to avoid any contamination with mercaptan of the supply storage vessel or the quantity that could return is considered so minimum that is usually considered as not harmful for the LPG contained?

Regards

I've never used any filters because we just isolated the vapor system for quality puposes.