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206 Gas PuriJication

e------------ Q--;

Figure 3-7. Use of flow ratio control to control amine stripping.

increased in pference to increasing amine loadings when it is necessary to absorb more acid
gas. Although more concentrated amine solutions are more diflicdt to strip, they are preferred
as long as the regenerator reboiler has enough capacity to regenerate the solution. Figure 3-6
also shows that at constant amine acid gas loading, carbon steel corrosion increases as the tem-
perature increases. To minimize corrosion, operating and reboiler heat medium temperatures
are generally limited to maximum values. Table 3-4 summarizes various recommendations. In
most cases, it is desirable to limit the reboiler steam temperature to about 150°C (300°F).

Effect of the H#/C02 Ratio

The guidelines in API 945 (API, 1990) suggest that solutions of most amines are not cor-
rosive if the ratio of hydrogen sulfide to carbon dioxide is above about 5/95, because when
sufficient H2S is present a protective iron sulfide film is formed according to reaction 3-20:

Fe + H2S = 2H" + FeS (3-20)