Amine sweetening units process

The treated gas had to meet typical pipeline gas specifications, that is, less than 4 ppm vol. H2S and less than 2.0 vol.% CO2. The add gas liberated is sent to conventional two-stage Claus units followed by a Sulfreen tail gas treating unit. Figure 10.4 illustrates the original amine sweetening units process flow-scheme. There are two identical trains, each equipped with two high-pressure absorbers and two regenerators. 

HYSYS simulation software was used as a tool to complete the simulation of the process (sample is shown in Fig.l). Fluid packages used in the simulation were Amines package which was used for Acid Gas Sweetening and CO2 Removal units, and Peng Robinson which was used for the rest of the units. When simulation was finalized, the following were collected ... 

Refinery fuel gas is collected from process units, sweetened in amine absorbers, and sent to a balance drum. Natural gas and LPG may be used to augment the fuel gas supply, and to replace it when needed. The balance drum stabilizes system pressure and ealorific content. It also provides a place for suspended liquids to separate from the gas. 

We have followed the path of the bottom cuts from the crude processing unit. We are now left with the naphtha and gas cuts from the atmospheric distillation tower. As both these cuts leave the area, they will be "sweetened in a hydrotreater or amine unit before being further processed. 

The processes are basically the same with little variation in flow scheme. The sour gas containing HaS and/or COa enters the plant through a scrubber, which removes any free liquids and/or entrained solids. The sour gas then enters the bottom of the absorber and flows upward in countercurrent contact with the descending aqueous amine solution. Sweetened gas leaves the top of the absorber and flows to a dehydration unit, where saturation water from the aqueous amine solution is removed. 

The amine unit is based on a 30% DEA solution. The feed gas is compressed to 285 psia and pretreated to remove heavy hydrocarbons. After passing through the DEA absorber, the sweet offgas is compressed to 650 psia and sent to the existing gas plant. The sour CO2 stream from the DEA stripper, at 20 psig, is compressed to 450 psia and sent to a Selexol sweetening process designed to reduce the H2S content of the CO2 product gas to less than 100 ppm. 

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