Desulfurization

Definition - What does Desulfurization mean?

Desulfurization is the removal of sulfur or sulfur compounds (as from coal or flue gas), mostly from fuels. The most commonly required desulfurization process is in natural gas, but it is also required for flue gas, coal and oil.

Sulfur in crude oil, natural gas, process gas and natural gas liquids (LNG) may take many forms, including hydrogen sulfide (H2S), carbonyl sulfide (COS), sulfur oxides (SOx) and the whole family of mercaptans.

High sulfur levels in fuel, when combined with water vapor, can cause corrosive wear on valve guides and cylinder liners, which can lead to premature engine failure.

Corrosionpedia explains Desulfurization

Desulfurization is the removal of sulfur to prevent contamination. Desulfurization has variations, including:

  • Hydrodesulfurization
  • Extractive desulfurization
  • Oxidative desulfurization
  • Biodesulfurization
  • Desulfurization through alkylation, chlorinolysis and by using supercritical water

Few of these methods are viable and/or efficient for the desulfurization of heavy oil. This is mainly due to the properties of the heavy oil, such as high sulfur content, high viscosity, high boiling point, and refractory nature of the sulfur compounds.

Natural gas desulfurization is typically accomplished by adsorption. The sulfur is left behind and adsorbed into the activated carbon. Tests are performed regularly to ensure the levels of sulfur remain within acceptable levels. Flue gas desulfurization is required to reduce the amount of sulfur dioxide released into the air. It is a large factor in the formation of acid rain. A device called a scrubber is used to remove sulfur from flue gas.

In coal combustion, to generate electric power and process heat, the sulfur is emitted as SO2, which is seen as one of the main causes of acid rain. This effect has led to an interest in the three main methods of removing coal sulfur: coal cleaning, in-bed desulfurization and flue gas desulfurization. Another method of sulfur removal in coal is through flotation or flocculation.

Desulfurization of oils can be done in two main ways. The first is similar to natural gas desulfurization, which is typically only used if the oil has a relatively low (less than 50ppm) sulfur level to begin with. The second method is microbial desulfurization, which uses the Rhodococcus organism to remove sulfur compounds, reducing air pollution during the refining process.

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