Natural Gas Sweetening and the Claus Process
An Overview of How Desiccants Are Involved in Sulfur Removal
Literally, in nature some naturally occurring sulfur and sulfur compound smells include skunk spray and rotting eggs. Sulfur’s reputation as a horrible smelling element has led the natural gas industry to calling any natural gas with sulfur in it, sour gas. In addition to its horrible smell sulfur can also be deadly to humans when it is potent enough, and it is also corrosive. Thus the removal of it from natural gas streams is an essential process, which is called natural gas sweetening.
In order for natural gas to be considered sour, hydrogen sulfide must exceed 5.7 milligrams per cubic meter of natural gas. Natural gas sweetening usually uses a process called amine treatment in order to remove sulfur from gas streams. Sulfur has an affinity for amine and when it passes through the tower that contains amine, the sulfur sticks to the amine and is removed from the stream. Amine treatment works similarly to glycol treatment because both use a liquid solution to remove unwanted elements and compounds from natural gas streams.
Despite my sulfur bashing earlier, and yes it does smell, it can also be useful. For example sulfur is frequently used in fertilizer, matches, and insecticides and it is used to make sulfuric acid which has many industrial applications. The sulfur that is removed from natural gas streams can be recovered using the Claus Process and sold as a separate product from natural gas.
The Claus Process has two steps: the thermal step and the catalytic step.
The thermal step is designed to turn the majority of the hydrogen sulfide removed from the gas stream into regular sulfur. This is done by oxidizing hydrogen sulfide with air at high temperatures. Approximately 60-70% of the sulfur is produced during this step.
The catalytic step is designed to take the remaining hydrogen sulfide and the newly created sulfur to make even more sulfur by heating them together over a catalyst, usually activated alumina and a specialty titania. Specialty titania helps to convert the remaining hydrogen sulfide into sulfur and activated alumina helps to protect the titania from sulfation poisoning due to oxygen breaking through.
Approximately 97% of sulfur that is removed from natural gas streams is recovered using the Claus Process. In the United States approximately 15% of all produced sulfur is extracted from natural gas streams.