Hydrogen sulfide (H2S) is a common but dangerous compound that is often found in natural gas wells. When the concentration of H2S exceeds 5.7 milligrams/m3, the gas stream is referred to as Sour Gas. This gas must be treated before it can be used in pipelines or plants.
Hydrogen sulfide is particularly dangerous, as it is toxic at low levels. The gas has a characteristic “rotten egg” smell at a concentration as low as 1 ppm. However, at a 10 ppm concentration, the olfactory nerves are desensitized. At higher concentrations H2S will cause headaches and respiratory damage, and is ultimately fatal. Because of the loss of the sense of smell at such low concentrations, exposure to H2S is particularly dangerous. Many individuals have assumed that they were safe, as they could no longer smell the H2S, only to suffer severe consequences.
When the concentration of H2S at the wellhead is below 10 ppm, the gas stream can be treated easily on site. Either the Sulfatreat process or an Iron Oxide process can remove the H2S at the wellhead. Both processes use a solid absorbent that are selective to H2S. Typically, multiple beds are used, depending upon the wellhead gas flow. Over time adsorbent will lose capacity and need to be replaced with fresh media.
At higher wellhead concentrations of H2S, fixed bed adsorbent processes are not economic. An Amine Unit is a better option in this case.
An Amine Unit typically contains a countercurrent absorber where the gas and anime are contacted. The treated gas leaving the top of the absorber will be water saturated, so a TEG drying unit may be required. The rich amine solution is sent to a regenerator where the H2S is stripped and the amine recycled. The stripped H2S gas will be processed in additional units for solid sulfur recovery.
The key to selecting the proper treatment scheme is dependent upon the concentration not only of H2S, but also of carbon dioxide. Let COSTELLO help you with determining the proper treatment scheme for your natural gas.