4 replies to this topic

[R NESAMANI]

How To Calculate The Lpg - Liquid & Vapor Volume In The Vessel At any Pressure & temp ?

Dear all,

We have a LPG vessel at 20 kg/cm2. So LPG will be 100% liquid.
When we vent the vessel, the pr. will come down, gradually the percentage of LPG-Vapor will increase in the mixture. Am i right ?

1)How to calculate the LPG - Liquid & vapor volume in the vessel at any Pressure?

2) Can we use P-V chart of LPG? so I need the P-V chart of the LPG (as per IS 4576)

Edited by R NESAMANI, 09 October 2012 - 02:18 AM.

[breizh]

http://www.quantityw...alculations.pdf

Reading this paper could help , the method is well described .

Breizh

[Art Montemayor]

R NESAMANI:

No, you are wrong. When you have an LPG vessel at 20 kg/cm², it CAN NEVER BE FILLED 100% of its volume with LPG. This is very hazardous, dangerous, and probably illegal in your country.

Liquefied Petroleum Gas (LPG) is a mixture of propane and butane (usually approximately 50%-50% by mass). This mixture, when stored as a liquid, is 100% SATURATED. This is very important information to know and should be well understood by all persons dealing with it and handling it. When you vent an LPG vessel containing the liquid phase, THE SATURATED PRESSURE DOES NOT COME DOWN – as long as there is saturated liquid in the vessel. This is assuming that you vent slowly, allowing the liquid to remain at the same saturated temperature. If you vent rapidly, the temperature within the stored liquid and vapor will decrease due to the cooling effect of the isenthalpic expansion taking place and the vapor pressure in the tank will decrease.

Whatever way you vent the LPG vapor, you will decrease the amount of liquid mass in the vessel. Even if you maintain constant temperature conditions while venting, the level of liquid volume will decrease. Therefore, the % of vapor volume in the tank will increase as you deplete the liquid content while venting. The minimum % of vapor volume in an LPG vessel is usually 20 to 15% - as dictated by local laws and regulations. I repeat: you should NEVER FILL AN LPG VESSEL 100% WITH LIQUID.

You calculate the inventory of both liquid and vapor LPG in a tank by “strapping” the tank. You calculate the volume of LPG saturated liquid by multiplying it by its liquid density at the stored temperature and the remaining volume is vapor LPG whose mass is calculated by multiplying its volume by the gas density at the saturated temperature.

You “strap” the vessel (calculate its internal volumes) by using a calculation method as I have programmed in my workbook titled “Vessel Volume” and which I have uploaded on our Forums many times in the past.

[breizh]

R Nesamani ,
let you use Google and find NFPA 58 , you will find all the answers to your query , in particular the max capacity of liquid you can store .
Hope this helps

Breizh

[R NESAMANI]

Dear Art Montemayor,

Thank you for your reply.
My purpose is we isolate the filter section of the LPG pipeline for maintenance. Filter is at 20 kg/cm2. at 30 degC.
If we connect this with low pr. line at 10 kg/cm2. Pr. of filter will come down to 10 kg/cm2.
Now the question is how much LPG has transferred from filter to low pr pipeline?
how to calculate this?