The Wellman–Lord process is a regenerable process to remove

sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic activ ...

from

flue gas Flue gas is the gas exiting to the atmosphere via a flue, which is a pipe or channel for conveying exhaust gases from a fireplace, oven, furnace, boiler or steam generator. Quite often, the flue gas refers to the combustion exhaust gas produced a ...

(

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

) without creating a throwaway sludge product. In this process, sulfur dioxide from flue gas is absorbed in a

sodium sulfite Sodium sulfite (sodium sulphite) is the inorganic compound with the chemical formula Na2 SO3. A white, water-soluble solid, it is used commercially as an antioxidant and preservative. A heptahydrate is also known but it is less useful because of ...

solution in water forming

sodium bisulfite Sodium bisulfite (or sodium bisulphite, sodium hydrogen sulfite) is a chemical mixture with the approximate chemical formula NaHSO3. Sodium bisulfite in fact is not a real compound, but a mixture of salts that dissolve in water to give solutions ...

; other components of flue gas are not absorbed. After lowering the temperature the bisulfite is converted to the

sodium pyrosulfite Sodium metabisulfite or sodium pyrosulfite (IUPAC spelling; Br. E. sodium metabisulphite or sodium pyrosulphite) is an inorganic compound of chemical formula Na2S2O5. The substance is sometimes referred to as disodium metabisulfite. It is used a ...

which precipitates. Upon heating, the two previously described chemical reactions are reversed, and sodium pyrosulfite is converted to a concentrated stream of sulfur dioxide and sodium sulfite. The sulfur dioxide can be used for further reactions (e.g. the production of sulfuric acid), and the sulfite is reintroduced into the process. :Na₂SO₃ + SO₂ + H₂O → 2NaHSO₃ :2NaHSO₃ → Na₂S₂O₅↓ + H₂O :Na₂S₂O₅ + H₂O → 2NaHSO₃ :2NaHSO₃ → Na₂SO₃ + SO₂ + H₂O In its initial version ( Crane Station, Maryland, 1968) the process was based on

potassium sulfite Potassium sulfite is the inorganic compound with the formula K2SO3. It is the salt of potassium cation and sulfite anion. It is a white solid that is highly soluble in water. Use Potassium sulfite is widely used for preserving food and bever ...

, but the economic prognosis was poor. Interest in the process occurred because of the worldwide shortage of sulfur in 1967 and resulting high prices; power-plant flue gas was viewed as an additional source of sulfur to relieve the shortage. the later version used sodium sulfite and was installed (as a demonstration system funded by

USEPA The Environmental Protection Agency (EPA) is an Independent agencies of the United States government, independent executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon pro ...

) at

Mitchell Station, Indiana Mitchell may refer to: People *Mitchell (surname) *Mitchell (given name) Places Australia * Mitchell, Australian Capital Territory, a light-industrial estate * Mitchell, New South Wales, a suburb of Bathurst * Mitchell, Northern Territory ...

in 1974. It was coupled with the Allied reduction (by natural gas) process to make elemental sulfur which can be shipped anywhere, for example to a

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...

plant. Additional installations of W-L were made in New Mexico. The process has been offered commercially by Davy Powergas in

Lakeland, Florida Lakeland is the most populous city in Polk County, Florida, part of the Tampa Bay Area, located along Interstate 4 east of Tampa. According to the 2020 U.S. Census Bureau release, the city had a population of 112,641. Lakeland is a principal c ...

. Because of side reactions forming thiosulfate (nonregenerable), there is a small makeup requirement in the form of

trona Trona (trisodium hydrogendicarbonate dihydrate, also sodium sesquicarbonate dihydrate, Na2CO3•2NaHCO3•3H2O) is a non- marine evaporite mineral. It is mined as the primary source of sodium carbonate in the United States, where it has replace ...

(sodium carbonate).

References

Further reading