gas sweetening rules of thumbs

Is it going through this process as a liquid or a vapor? What is incoming feedstock temp and chemical makeup(roughly)?

Here's some rules of thumb to get you started. Start with about 20 real trays for the absorber. 30 real trays for the regenerator, feed on tray 26. Apply a stage efficiency of 30% for amine systems. Reboiler duty equivalent to 1 lb of stripping steam per gallon of amine would be typical. Circulation rate should be set to achieve about 0.25 - 0.35 moles of acid gas per mole of amine in the rich solvent. So circulation will depend on the acid gas content of your sour gas; 10 - 20 gpm/MMSCFD is in the range I'm used to seeing.

Also, depending on the simulation package you're using, simulating a perfectly clean amine may produce increased lean acid gas loadings or energy requirements to achieve lean/treated gas specification. Spiking your amine with a little bit of phosphoric acid can help to account for the impacts of impurities like heat stable amine salts on the acid gas/amine equilibrium in the bottom of the regenerator.

Homework, or a real case study?

Good luck,

Jason

Jason - good rules and valid numbers but I want to warn the original poster that rules of thumb in gas sweetening are no match for a rigorous process simulator.

Rich loading and the corresponding amine circ rate is a function of pressure, contactor temperature profiles, tray characteristics like residence time and froth height, as well as multiple other factors. You have to realize that rules of thumb can potentially throw you off track especially in cases where the spec might be tight or where you are expected to back up the numbers with real engineering. Be careful. 1 lb of steam per gallon isn't always enough.

Before you even get to rules of thumb, you'll need to make sure the gas is product being sweetened is clean and what temp/press is available. For example, if the pressure is under 200 psig, DEA won't work. If the percent acid gases are high, it may take side cooling on the absorber.

Yep, there are lots of other rules of thumb to get you going.

If you are going to be doing CO2 slipping using an activated MDEA, better have the vendor do the runs in order to get a process guarantee.

We ran DEA on refinery offgases at 9.5 barg (about 139 psig) with no problems (other than the usual amine plant problems.

goerdie87, yes it will work, but you cannot load up the amine and therfore you have to run a higher concentration of amine and a more corrosive system.

At is a paper titled

An Evaluation of General "Rules of Thumb" in Amine Sweetening Unit Design and Operation

We stuck to 0.35 mol/mol max. Seemed to work OK. Biggest problem was the ammount of reboiler duty and reboiler fouling.