Cooling down ethylene tank 1

[vedranpetro]

Hi,
I'm trying to calculate time for cooling down tank of ethylene.
It's an atmospheric pressure tank .Temp of evaporation of ethylene at atm pressure is -103,6 deg C.Tank is now empty and at ambient temp.Tank is double-walled with an insulation between a walls.
Any tips for calculation in which can be calculated time for getting liquid ethylene in tank and amount of ethylene which will be evaporated (wasted ethylene) in that process?
Cooling capacity of refrigeration is cca 90-100 kW

 

[StoneCold]

vedranpetro
I believe the first thing you need to calculate is the thermal mass of the tank. I think you can just calculate the mass of the metal of the inner tank and its' heat capacity. I think you can ignore the insulation and the outer shell.
Once you know the heat capacity you can use the latent heat of vaporization of ethylene and the heat capacity of the gas to calculate the energy available to cool the tank. You may want to do this in stages of say 10C since as the tank heats up you will recover less and less heat from the gas as sensible heat change.

Personally I would think that dumping a truckload of liquid nitrogen into the tank and then begin loading the ethylene would be much cheaper and save a lot of your ethylene.

I always thought that you pulled vacuum on the head space in these low pressure tanks and that caused the liquid to auto refrigerate. Then you compressed the vapor then cooled it to a liquid and returned it to the tank. So these systems were closed loop, other than some non condensibles that have to be removed, probably at the high pressure liquid stage of the re-compression loop.

Were you planning on just flaring your "waste ethylene" vapor?

Regards
StoneCold

 

[vedranpetro]

StoneCold
Straight to the point, I calculated in that way.

Nitrogen is not an option,and it will create great pressure in tank in that way. Also it's more stressful for material to dump it like that,and at almost 100 deg C lower temp than ethylene.

You're right except that vacuum part.Ethylene constantly evaporates,we compressed the vapor then cooled it to a liquid and return it to the tank.

Yeah just flaring it unfortunately

tnx for answer