I ran this by John Young, a friend who recently retired from a career at the Pepsi bottling plant in Howell, Michigan:
In the early 1950's, CO2 would probably been delivered in larger (200 gallon range) tanks and transported into the plant. These would have been delivered in box cars. The empties would also have been returned in boxcars. Remember, the bottling plants of that era were much smaller than those of today. If choosing to model a plant that has the kind of production that would require an out door storage tank, he could use a model of a horizontal LP tank, shortened a bit (you need the round ends because of the high pressure) or a vertical tank of the same design. We had one of each tank in Howell. The vertical one you are familiar with had a 50 ton capacity; the horizontal one on the other side of the plant had a 26 ton capacity. Unfortunately, I never had a reason to convert those figures to gallons or cubic feet capacity, so I don't really know how large they actually were. My guess would be that the larger one is in the 15000 gallon range, comparing them to the syrup tanks inside.
The unload method involves a two hose hook up: one hose delivers the liquid CO2 to the storage tank, the second hose returns CO2 vapor to the delivery vessel from the onsite storage tank. It both captures the gas and also balances the pressure between the two tanks making it easier to deliver.
It takes a pump to move liquid CO2, so the unload spot for the CO2 rail car will need some type of pump house. At our site, because the CO2 was delivered by truck, the trucks had a PTO driven pump under the middle of the tank.
In any case, there will be an on site storage tank. No bottling plant would have paid to use a rail car as a storage tank for CO2, CO2 is just too cheap, and the per diem rate too high to hold the tank car for a week to unload it.
The Howell plant made over 150,000 cases of pop a day and used one truck load of CO2 per day. When I entered the business in 1978, we used about a truck load a week, and we were a big operation at the time turning out about 35,000 cases a day.
One other thing to mention is to have the CO2 source be in the London, Ontario area. That has been a long time source of CO2 over many decades. There have been other sources pop up in the intervening years (such as Lima, Ohio) but even in the 1950's it would have been cheaper to ship CO2 by truck to the modeled town than to ship it by rail from Ohio.
Hopefully this answers some questions. Craig Wilson