View source for Wellman–Lord process

The '''Wellman–Lord process''' is a regenerable process to remove [[sulfur dioxide]] from [[flue gas]] ([[flue-gas desulfurization]]) without creating a throwaway sludge product.
In this process, sulfur dioxide from flue gas is absorbed in a [[sodium sulfite]] solution in water forming [[sodium bisulfite]]; other components of flue gas are not absorbed. After lowering the temperature the bisulfite is converted to the [[sodium pyrosulfite]] 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.<ref>{{cite book | chapter-url = https://books.google.com/books?id=rfSItUDqX9sC&pg=PA554 | title = Gas Purification | chapter = Sulfur Dioxide Removal | first = Arthur L. | last = Kohl |author2=Nielsen, Richard B.  | publisher = Gulf Professional Publishing | year = 1997 | isbn =  978-0-88415-220-0 | pages =554&ndash;555}}</ref><ref>{{cite book | url = https://books.google.com/books?id=f1lnQwrvOSEC&pg=PA884 | title =Environmental Engineering Dictionary| first = C. C. | last = Lee | publisher = Rowman & Littlefield | year = 2005 | isbn = 978-0-86587-848-8 | pages = 884}}</ref>
:Na<sub>2</sub>SO<sub>3</sub> + SO<sub>2</sub> + H<sub>2</sub>O → 2NaHSO<sub>3</sub>
:2NaHSO<sub>3</sub> → Na<sub>2</sub>S<sub>2</sub>O<sub>5</sub>↓ + H<sub>2</sub>O
:Na<sub>2</sub>S<sub>2</sub>O<sub>5</sub> + H<sub>2</sub>O →  2NaHSO<sub>3</sub>
:2NaHSO<sub>3</sub> → Na<sub>2</sub>SO<sub>3</sub> + SO<sub>2</sub> + H<sub>2</sub>O
In its initial version ([[Charles P. Crane Generating Station|Crane Station, Maryland]], 1968) the process was based on [[potassium sulfite]], 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]]) at [[Mitchell Station, Indiana]] 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]] plant. Additional installations of W-L were made in New Mexico. The process has been offered commercially by Davy Powergas in [[Lakeland, Florida]]. Because of side reactions forming thiosulfate (nonregenerable), there is a small makeup requirement in the form of [[trona]] (sodium carbonate).
==References==
{{Reflist}}
==Further reading==
* {{cite book | publisher = [[U.S. Environmental Protection Agency]] | title= Emissions Factors & AP 42, Compilation of Air Pollutant Emission Factors | chapter = Chapter 8.13: Sulfur recovery | chapter-url = http://www.epa.gov/ttn/chief/ap42/ch08/final/c08s13.pdf}}
* {{cite book | title = Sulfur Removal and Recovery from Industrial Processes | last1 = Osborne | first1 = W. Jeff | last2 = Earl | first2 = Christopher B. | chapter = Chapter 13: Recent Experience of the Wellman-Lord Sulfur Dioxide Recovery Process | volume = 139 | pages = 158 | year = 1975 | editor =  John B. Pfeiffer | doi = 10.1021/ba-1975-0139.ch013}}
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[[Category:Chemical processes]]
[[Category:Acid gas control]]
[[Category:Environmental engineering]]