GAS DEHYDRATION BY LOW TEMPERATURE SEPARATION (L.T.S) - PRINCIPLES OF GAS SWEETENING WITH AMINE SOLUTION PDF Print E-mail
Written by Norrie   
Tuesday, 16 March 2010 12:59
Article Index
GAS DEHYDRATION BY LOW TEMPERATURE SEPARATION (L.T.S)
LOW TEMPERATURE SEPARATION (L.T.S)
CHOKE KNOCK-OUT DRUM V. 3 - CLASSIFIER V. 4
NATURAL GAS SWEETENING BY AMINE SOLUTION
PRINCIPLES OF GAS SWEETENING WITH AMINE SOLUTION
GENERAL PROCESS DESCRIPTION
GAS SWEETENING EQUIPMENT AND OPERATING CONDITIONS
C. AMINE FLASH SEPARATOR
D. AMINE REGENERATION
All Pages

PRINCIPLES OF GAS SWEETENING WITH AMINE SOLUTION

For this process description 'MDEA' is the amine solution selected.

Gas sweetening with amine solution is based on the chemical reaction of weak alkaline with weak acid. The amine solution is alkaline and H2S & CO2 are acidic. The reactions involved are very complex, but the following summarises the basic processes.

The reaction in the absorber is at constant pressure and a temperature range between 80 °F to 120 °F. It is a reversible reaction.

2RNH2 + H2S >>> (RNH2)2S
amine + hydrogen sulphide >>> amine sulphide + heat

2RNH2 + CO2 + H2O >>> (RNH2)2H2CO3
amine + carbon dioxide + water >>> amine bicarbonate + heat

The Regeneration reaction in the reboiler and stripper is at a constant lower pressure and a temperature range between 240 °F and 300 °F.

(RNH3)2S + heat >>> 2RNH2 + H2S
amine sulphide >>> amine + hydrogen sulphide

(RNH3)2CO3 + heat >>> 2RNH2 + CO2 + H2O
amine carbonate >>> amine + carbon dioxide + water

The H2S is removed by a chemical reaction, that is reversible and dependent on the temperature change. The CO2 is physically absorbed.
Because of this difference in reaction, MDEA is used to selectively remove H2S while leaving most of the CO2 in the gas leaving the amine absorber.

The H2S / Amine reaction is fast, while the CO2 / Amine reaction is slow. The longer the amine solution stays in the absorber, the more CO2 will be taken in by the amine solution.

The reaction governing H2S removal from the sour gas is temperature dependent and the direction of equilibrium is shifted by temperature changes. In addition to temperature, the partial pressure of the acid gases will also influence the equilibrium of the reaction.

The amine solution used is a mixture of 50% MDEA and pure water.

The sulphide and carbonate salts that are formed as a result of the chemical reactions are dissolved in the amine solution.

Thus the rich amine solution at the bottom of the amine absorber is a mixture of water, MDEA, amine sulphide & amine carbonate.