Kartikeya:
Bobby is right. Your use of English is difficult to understand because of the typos, composition, and grammar mistakes.
The ONLY WAY to convey an accurate description of what you are working on is to draw a decent, detailed engineering flow diagram showing the major equipment involved and the calculated conditions (temperatures & pressures) of each flow stream. Draw a sketch for the propane unloading as well as one for the butane unloading.
I don't know if you propose to unload both liquid propane and butane at the same time into the same terminal storage tank or if you are pumping out one product at a time into the same tank - but at different times.
You don't explain the origin of the flash gas, although I am very familiar with the normal operation and can calculate the amount if given the liquid pumping rates and the conditions. What I think you mean to explain is that you would unload each product into the same terminal storage tank at different times. However, when you unload propane you are having excessive flash gas generated.
You make the mistake of calling the operation a cryogenic one. That is erroneous. Although not well defined, Cryogenics is generally described as the temperature zone below -150 oC. Your temperatures don't even come close to that.
That you will generate flash gas is fairly obvious. However, you don't explain how you plan to cool and re-liquefy the recovered, compressed flash gas that must be returned to the storage tank. Since the flash flow quantities for each product will be different, the flash gas compressor has to designed to handle each - or you employ a different compressor for each product flash gas. Which is it?
If you furnish a detailed flow diagram together with your calculations for the flash gas generation and liquefaction, our members will have an easier time of understanding your application and what you propose.