In process engineering, we often have general guidelines to follow. A common example in sour natural gas processing is amine system rich loading, occurring at the bottom of the contactor…
There are ‘rules’ we follow by nature, but – how do we know how accurate they are, especially when somebody else uses a different value?
In respect to the sour natural gas processing example, most quote a value somewhere between 0.3 and 0.5 moles acid gas per mole amine. They have roots in chemistry but are practically lower due to corrosion. They are also a function of pressure.
So how can we check these values? The answer lies in solvent equilibrium charts.
Such charts are functions of acid gas partial pressure versus mole ratio of acid gas to amine liquid (rich loading) at given temperatures for a given amine weight fraction. These days, you can run your process simulation and then check the ‘general guideline’ value on the equilibrium charts using your simulation temperature, typically making sure we are no closer than 80% of equilibrium loading so that there is a reasonable driving force.
Don’t forget that CO2 affects H2S loading and vice versa so that also needs to be considered.
Of course, there are other rules in amine units as well as other chemical processes and we may need to check several values.