Energy and exergical dissection of a natural gas sweetening plant using methyldiethanol amine (MDEA) solution

Demand of natural gas is increasing as it is cheaper than oil and a clean fuel. Natural gas contains impurities like water, CO2, H2S, COS, mercury & N2. Amines processes are the developed technology available today for the removal of acid gases (CO2 & H2S). N-methyldiethanolamine (MDEA) is a well-known tertiary amine and selectively used to remove mostly H2S from natural gas. Heat transfer has a huge role in many operational units of gas sweetening plant. The exergy method of analysis provides this true measure of effective energy use through its application of principles of both the first and second laws of thermodynamics. The present investigation involves development of a gas sweetening unit using process simulator ProMax®. The results showed that the unit with highest value of exergy destruction was absorber (3 MW) followed by sweet gas air cooler (2.7 MW) and flasher unit (2.2 MW). Energy and exergy efficiencies determined revealed that absorber was the most efficient process with energy and exergy efficiencies of about 94% and 98% respectively. The flasher, air coolers and pressure recovery turbine were determined to be the under performers with exergy efficiencies of 27%, 24% and 31% respectively. A further breakdown of exergy losses revealed that the chemical exergy losses are much higher than the physical exergy losses, contributing around 94% of the total exergy losses.