Each of the previous treating processes has advantages relative to the others for certain applications; therefore, in selection of the appropriate process, the following facts should be considered:
1. The type of acid contaminants present in the gas stream.
2. The concentrations of each contaminant and degree of removal desired.
3. The volume of gas to be treated and temperature and pressure at which the gas is available.
4. The feasibility of recovering sulfur.
5. The desirability of selectively removing one or more of the contaminants without removing the others.
6. The presence and amount of heavy hydrocarbons and aromatics in the gas.
Figures 7-11 to 7-14 can be used as screening tools to make an initial selection of potential process choices. These graphs are not meant to supplant engineering judgment. New processes are continuously being developed. Modifications to existing proprietary products will change their range of applicability and relative cost. The graphs do enable a first choice of several potential candidates that could be investigated to determine which is the most economical for a given set of conditions.
To select a process, determine flow rate, temperature, pressure, concentration of the acid gases in the inlet gas, and allowed concentration of acid gases in the outlet stream. With this information, calculate the partial pressure of the acid gas components.
Next, determine if one of the four following situations is required and use the appropriate guide:
Removal of H2S with no CO2 present (Figure 7-11)
Removal of H2S and CO2 (Figure 7-12)
Removal of CO2 with no H2S present (Figure 7-13)
Selective removal of H2S with CO2 present (Figure 7-14)