Chapter Eight: Sulfur Recovery and Pollution Control Processes

Most crude oil contain varying amounts of sulfur. Hydrotreating various distillates from these crudes generate hydrogen sulfide, which is converted to elemental sulfur to minimize atmospheric pollution. In the absence of sulfur recovery, the only option would be to burn this gas in refinery furnaces, releasing huge amounts of sulfur dioxide into the atmosphere, an option no longer acceptable due to environmental concerns.

Sulfur recovery processes recover hydrogen sulfide from various refinery gaseous streams by scrubbing with an amine solution and convert it to elemental sulfur by controlled oxidation. Stack or flue gas desulfurization removes sulfur dioxide, generated as a result of burning high-sulfur fuel oil as refinery fuel, from refinery stacks. The process consists of scrubbing stack gases with aqueous ammonia to remove sulfur dioxide, which is reduced to elemental sulfur by reaction with hydrogen sulfide.

SULFUR RECOVERY FROM ACID GAS

The sulfur recovery unit recovers elemental sulfur from the acid gas containing H ₂S by the Claus process. The chemical reaction involved is

This reaction is, in fact, a summation of the two following reactions:

The reaction of SO ₂ and H ₂S also occur in the thermal stage at 2500 F by burning one third of H ₂S to SO ₂ to obtain H ₂S/SO ₂ stoichiometric ratio of 2 to 1. At high temperature, conversion up to 70% into sulfur may be reached for the Claus reaction. In the presence of inerts (mainly CO ₂) in the feed, lower...