Application Note: pH Control in Sour Water Stripping
Sulfur compounds such as mercaptans and hydrogen sulfide occur naturally in crude oil or are formed in certain process steps. Water and steam are extensively used in petroleum refining, and sour water is formed in the presence of hydrogen sulfide. The increased use of sour crudes obviously leads to an increase in sour water formation. Apart from H2S, sour water contains ammonia, phenols, HCN, CO2, acids, salts and many other water soluble waste compounds. After stripping, the water may be used as process water, for example in the desalter, or be treated as waste water.
After the removal of solids and hydrocarbons, the sour water is fed to the top of the stripper column. A reboiler provides heat or steam to the bottom of the stripper, or steam is injected
directly. In a counter current flow the steam liberates the dissolved gases from the sour water. Subsequently, the overhead gas flow is directed to the Sulfur Recovery Unit where elemental sulfur is produced through catalytic oxidation of H2S.
Unfortunately things are slightly more complicated than this and the use of steam alone is not enough to remove all the dissolved (sour) gases. Gas concentrations vary and both hydrogen sulfide and ammonia occur in different forms.