Masud 15.

This is a bit of a backwater of a forum so you may not get many replies. Might be better to repost in Chemical process engineering.

I would have thought that the LPG vendor or tank vendor could give you this, but you will need to know surface area of your tank, minimum ambient air temperature and gas flow rate to do any calculation.

I think the answer will be quite low flow unless you're in the Middle East or somewhere it doesn't get lower than 10-15C. Also depends on how long the flow goes on for as the temperature of the liquid will fall, but if this is only for say 5 minutes you might be OK.

Also "LPG" is rather vague. You will need to know what the percent Propane/Butane is or if it's 100% Propane and get the pressure / temperature curve from the suppliers.

Why the reluctance to install a vapouriser?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

This attached image (from my own personal files) will predict the natural vaporization rate of a propane tank. Modify it for your application. Note the 50% minimum capacity is based upon the owner regularly filling the tank and is user driven.

There's more information here https://www.eng-tips.com/viewthread.cfm?qid=476218

The LPG turns out to be 70% butane so I suspect this table is rather optimistic compared to 100% propane?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

Yes you are right. This is based upon (mostly) propane. Butane has a higher boiling point, so it will bubble much slower.