How Does a Sulfur Recovery Unit Work?
The most common SRU configuration is the Modified Claus Process. One-third of the H2S in the incoming feed is combusted to SO2 in a Thermal Reactor with temperatures usually ranging from 1800-2400°F. The remaining two-thirds of the H2S combines with the SO2 in the Thermal Reactor and 50-60% is converted to sulfur (S). Thermal Reactor effluent enters a waste heat boiler and generates up to 600 psig steam. From there, the stream enters a sulfur condenser. Condensed liquid sulfur is separated from the process vapor stream and gravity flows to a sulfur pit or tank.
In a 3-bed Claus Unit, the process vapor leaves the first condenser, is heated to about 400°F* by an exchanger, and enters a catalyst bed for further conversion of H2S and SO2 to sulfur. Effluent from the first catalytic reactor is condensed to remove sulfur from the vapor. The catalytic reaction and condensing process are repeated twice and about 95-97% of the total H2S in the unit feed streams recovered.
Process vapor leaving the final condenser is called Tail Gas and can be further processed to convert H2S to sulfur. The addition of a Tail Gas Unit can increase recovery efficiency to 99.9%.
(* Higher temperatures are required for Units designed to recover COS and CS2, a by-product of acid gas combustion in the Thermal Reactor.)