How can methane solubility be calculated in NGL? Is there any process engineering simulation program (like HYSYS, Promax etc.)can be used to calculate how much CH4 can be absorbed in NGL if residue gas, which is mostly methane is used as blanket gas?
I think a EOS as Peng Robinson or Soave Redlich Kwong (extended versions if your mixture includes some little percentage of heavy or non-hdrocarbon components) should give reasonably accurate results, these models are included in almost all commercial software,
by the way I use a process library (Prode Properties) with Excel for these calc's.
NGL is not a precise term. But yes - any descent process model such as HYSYS will calculate how much C4 you can re-absorb into the NGL. The amount will of course depend on the P/T than you will have your NGL at.
Consider that a destillation tower is a contineous series of equilibrium stages. So at the bottom stage the NGL is in fact in equilibrium with C4 in the gas phase. But the amount of C4 in the gas phase is then a result of an equilibrium on the stage above in the liquid stage and so forth.
I can tell you answer without a simulator. MORE THAN ENOUGH TO MAKE THE NGL OFFSPEC. Do not ever use methane as a blanket gas on an NGL stream. Been there, done that, shut the valve, got the bonus.