What is Flue Gas Desulfurization?

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What is the Flue Gas Desulfurization Process?

Flue gas desulfurization is the process of removing sulphur compounds from the exhaust emissions of fossil-fueled power stations. This is done through the addition of absorbents, which can remove up to 95% of the sulphur dioxide from the flue gas. 

Flue gas is the emitted material produced when fossil fuels such as coal, oil, natural gas, or wood are burned for heat or power.

The 2 Types of Flue Gas Desulfurization

The flue gas desulfurization processes can be separated into two main categories: 

Once-through processes and regenerable processes. 

• Once-through is also known as non-regenerable, and is a process that utilizes the sorbent as a beneficial by-product or disposes of it as waste. 
• The regenerable processes release the sorbed sulphur dioxide to generate other products such as elemental S, H2SO4, or liquid SO2. 

How to Treat Flue Gas Desulfurization

Flue gas desulfurization is often treated in a dedicated wastewater facility rather than a plant's existing wastewater treatment system, allowing facilities to meet strict FGD wastewater discharge limits. The wastewater composition can vary from plant to plant due to factors including coal selection, scrubber chloride concentrations, the type of gypsum dewatering system, the type of FGD process used and more. 

What is Flue Gas Desulfurization Gypsum?

Flue gas desulfurization gypsum (FGDG) is an industrial byproduct generated during the flue gas desulfurization process in coal-fired power plants. Flue gas desulfurization systems have been used to limit the release of sulfur dioxide from coal-fired power plants since the late s, but in the past decade the production of FGDG has drastically decreased.

It may contain pollutants such as particulates, sulfur dioxide, mercury, and carbon dioxide, but most flue gas consists of nitrogen oxides. Untreated flue gas from power plants, industrial facilities, and other sources can significantly impact local and regional air quality.

In a typical treatment process, the gas is first sent to an electrostatic precipitator, which removes ash and other particulates by electrostatically charging them, causing them to be attracted to and deposited on plates or other collection devices.

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The gas then moves on to a denitrification unit that alters the chemical composition of nitrogen oxides, producing nitrogen gas rather than nitrogen oxides. Natural gypsum can be used in concrete production as a replacement for calcium aluminate cement (CAC),

FGDG generation has increased in the U.S. but its reuse rate has decreased.

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.

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.

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.

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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