Flue-gas desulfurization

Technologies used in fossil-fuel power plants

If you want to learn more, please visit our website SGB.

Before flue gas desulfurization was installed, the emissions from the Four Corners Generating Station in New Mexico contained a significant amount of sulfur dioxide.

Flue-gas desulfurization (FGD) is a set of technologies used to remove sulfur dioxide (SO2) from exhaust flue gases of fossil-fuel power plants, and from the emissions of other sulfur oxide emitting processes such as waste incineration, petroleum refineries, cement and lime kilns.

Methods

Since stringent environmental regulations limiting SO2 emissions have been enacted in many countries, SO2 is being removed from flue gases by a variety of methods. Common methods used:

For a typical coal-fired power station, flue-gas desulfurization (FGD) may remove 90 per cent or more of the SO2 in the flue gases.

History

Methods of removing sulfur dioxide from boiler and furnace exhaust gases have been studied for over 150 years. Early ideas for flue gas desulfurization were established in England. With the construction of large-scale power plants in England, the problems associated with large volumes of SO2 from a single site began to concern the public. The SO2 emissions problem did not receive much attention until the House of Lords upheld the claim of a landowner against the Barton Electricity Works for damages to his land resulting from SO2 emissions. This led to the imposition of SO2 controls on all such power plants. The first major FGD unit at a utility was installed at Battersea Power Station in the 1960s. These early large-scale FGD installations were suspended during World War II because their characteristic white vapor plumes would have aided location finding by enemy aircraft. After the war, the FGD plant at Battersea was recommissioned and operated until it closed in 1983. As of June 2023, there were 42 FGD units in operation, predominantly in Japan and the United States, ranging in capacity from 5 MW to 250 MW.

FGD on ships

The International Maritime Organization (IMO) has adopted guidelines on the approval, installation and use of exhaust gas scrubbers on board ships to ensure compliance with sulphur regulations. Flag States must approve such systems and can sanction the ship if they are not functioning correctly.

Sulfuric acid mist formation

Fossil fuels can contain significant amounts of sulfur. When burned, about 95 percent of the sulfur is generally converted to sulfur dioxide (SO2). However, under certain circumstances, SO2 can further oxidize into sulfur trioxide (SO3), forming liquid aerosol known as sulfuric acid mist that is very difficult to remove.

FGD chemistry

Principles

Most FGD systems employ two stages: one for fly ash removal and the other for SO2 removal. The flue gas passes first through a fly ash removal device and then into the SO2-absorber. Engineers determine site-specific methods that minimize corrosion and maintain equipment reliability.

Scrubbing with an alkali solid or solution

The typical sorbent slurries or other materials used to remove SO2 from the flue gases are alkaline like limestone slurry, which produces calcium sulfite. Additionally, some designs can further oxidize calcium sulfite to produce marketable gypsum.

Types of wet scrubbers used in FGD

Various wet scrubber designs include spray towers, venturis, and packed beds. Simple scrubbers such as spray towers are preferred due to dependability and efficiency in SO2 removal.

Venturi-rod scrubbers

A venturi scrubber accelerates the gas stream to high velocity and meets the liquid stream at the throat, aiding in the atomization of the liquid for mass transfer. These scrubbers can also remove both particulate matter and SO2 simultaneously.

For more information, please visit Desulphurization Pump solutions.

Packed bed scrubbers

A packed scrubber consists of a tower containing packing material that enhances the contact area between gas and liquid, offering high SO2 removal efficiency, though it can be prone to plugging.

Spray towers

Simplest scrubber type, consisting of spray nozzles generating droplets for surface contact. Used for circulating slurries, requiring careful management of particle loading to avoid blockage.

Scrubbing reagent

Alkaline sorbents like lime and sodium hydroxide are used. Lime is favored for its cost-effectiveness in large-scale applications, but results in a slurry that requires disposal. Caustic soda, while more expensive, forms a solution that eases operational challenges.

Gas-phase oxidation followed by reaction with ammonia

A new FGD technology includes a radiation approach where an intense beam of electrons reacts with ammonia in the flue gas. This innovative method contributes to multifunctional benefits, including the production of ammonium sulfate which serves as a fertilizer.

Facts and statistics

Flue gas desulfurization scrubbers have been effectively installed across various power plants ranging up to 1,500 MW. Approximately 85% of US FGD units are wet scrubbers, with the highest SO2 removal efficiencies achieved by wet systems.

Alternative methods of reducing sulfur dioxide emissions

An alternative to flue gas treatment includes methods of removing sulfur from fuels prior to combustion. Techniques such as hydrodesulfurization treat fuel oils before usage, while fluidized bed combustion integrates lime directly with the fuel.

The company is the world’s best Marine Dredging Pump services supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.