Dear All
I have question regarding the LPG Truck Loading terminal Vapor returned Line. I found in some terminal Reciprocating Compressor at the vapor returned line. I need to know the reason behind this.
As per my understanding LPG empty Truck has some pressure due to the vapors of LPG at ambient temperature so when the LPG is filled through the loading arms than initially LPG will be flashed due to the high temperature and low pressure. At the beginning vapor generation will be high but after some time at equilibrium point vapor will not be generated. Due to the check valve in between Loading truck and bullet, Vapor pressure shall be greater than the bullet pressure so that vapors will transfer from the truck to the bullet as long as LPG Liquid transfer to the truck. The transfer pumps shall be designed to have enough discharge head to transfer the Liquid LPG to truck.
However if we have compressor in the vapor returned in that case the LPG vapor Liquid equilibrium will not reach because all the vapors will be transferred through the compressor to the bullet. So that when the transfer pump discharge the LPG into the truck that will be vaporized due to low pressure and high ambient temperature.
Please help me why we need compressor at vapor returned line.