2 replies to this topic

[hirengdesai]

hi all,

recently i came across one requirement from client that he wants to compress the natural gas and wants to transport in dense phase with the requirement that the gas pressure should not fall below cricondenbar pressure. Also after compression he wants to mix some heavy hydrocarbol stream already in high pressure in the gas stream.

my question is what the dense phase actually means and what is the significance of cricondenbar pressure wrt to dense phase ? What if the pressure is higher than the cricondenbar but temp is very low ?

pl. guide.

hiren

[joerd]

Dense phase means that the natural gas mixture is somewhere between a liquid and a vapor. For a single component fluid, it would be "supercritical", no distinction can be made between two phases, and no phase transition is observed when the temperature is dropped. If you have ever seen a phase envelope (for example, there is a picture at http://www.glossary....mage.cfm?ID=611 ), you can see that there are two important points on the dew point curve: the cricondentherm - above this temperature, the fluid will be single (dense) phase no matter what the pressure is - and the cricondenbar - above this pressure, the fluid will be single (dense) phase no matter what the temperature is. As you lower the temperature, the density of the fluid (could have been gas-like) increases gradually, until at some point you may consider it more like a liquid. But no phase transition has been observed, and there is no condensation of liquid. That is (probably) why your client wants to stay above the cricondenbar.
Note that adding heavy hydrocarbons to the mixture will change the phase envelope. So you'll have to evaluate the phase envelope at the new composition, after the addition of the hydrocarbons, i.e. the pipeline composition. See for example Figure 3 in http://www.jmcampbel...603_4521864.pdf
By the way, in most gas processing plants, the requirement is to remove heavy hydrocarbons, and thus move the dewpoint curve, such that the pipeline temperature is outside the fluid's phase envelope, i.e. to the right of the cricondentherm.

[hirengdesai]

thanks a lot joerd.
hiren