What Is Tail Gas?
Tail Gas, or SRU Tail Gas, is the final gas stream leaving a Sulfur Recovery Unit after most of the Hydrogen Sulfide (H2S) has been removed. A typical SRU operating at design conditions can remove between 95-97% of the incoming sulfur in the feed stream. Overall recovery efficiency depends on a variety of factors.
The SRU Tail Gas contains mostly nitrogen, water vapor, the residual hydrogen sulfide and sulfur dioxide from the Claus process, and carbon dioxide. The stream also contains entrained sulfur droplets and equilibrium sulfur vapors that were not fully recovered in the SRU. Because of this, Tail Gas must be kept at tightly controlled temperatures before it makes its way to the next unit in a typical sulfur facility.
Depending on the type of processing unit, SRU Tail Gas can be further treated in a thermal oxidizer, an amine-based Tail Gas Treating unit, or a flue gas scrubber. The latter two processes can further reduce the sulfur content to reach an overall recovery efficiency of 99.9+%.