7 replies to this topic

[SyedAhmed]

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. 

[fallah]

Hi,

 

It might the vapor return line is more long than the vapor can return on its own pressure to the bullet. Hence one had to use a compressor in return line. A simple sketch showing the length of the lines can help. 

[SyedAhmed]

Dear Fallah 

 

Thanks for your response. Actually the return line is not too long. This is from loading area to LPG bullet. Vapors will transfer through the vapor returned line in the case of tankers vapors pressure > bullet pressure. But due to the compressor the equilibrium will not reach

[fallah]

 

Then the size of the return line may be too small...

[Bobby Strain]

Maybe you should ask the terminal operator. This doesn't seem to be your company's terminal, but you are merely looking at some drawings of a facility. What is the object of your query? If you learn more about the terminal operation in question, you can probably answer your own query. And, you don't really give us enough information to be helpful. A datasheet for the compressor may answer your question about its function.

 

Bobby

Edited by Bobby Strain, 10 November 2017 - 03:55 PM.

[SyedAhmed]

Dear Bobby

 

Thanks for your time and response. I am working on a project of LPG terminal capacity enhancement and expansion. I gone through the existing terminal P&IDs which were created in late 90's and found the compressor in the vapor returned line. The vapor is returned from LPG Tankers to the bullets. Client don't have technical information regarding the compressor requirement so I am digging out by myself.

 

I saw the below link and found very useful.

https://www.cheresou...-truck-filling/

 

In this article Post 30 March 2012 7.00 AM, Mr. S.Ahmed mentioned about the reciprocating compressor but not describe the need of compressor.

 

Regards

[Bobby Strain]

You should talk to the terminal operators. They will know what the compressor is used for.

 

Bobby

[fallah]

12345656,

 

Due to relative long distance between the storage area and shipping/truck area and limitation on the return vapor line size, using a compressor along the mentioned line to return the generated vapor to the storage is inevitable.