Stone Webster Ionics process

To avoid the cost and disposal problems of once-through processes employing alkali metal compounds, a considerable amount of research and development effort has been expended on techniques for regenerating this type of absorbent. Processes used employ precipitation of insoluble compounds (double alkali), and thermal decomposition (Wellman-Lord and Elsorb). Processes under development or which have been investigated include precipitation of insoluble compounds (zinc oxide), low-temperature reduction of sulfite (citrate and potassium formate processes), high-temperature reduction (aqueous carbonate process), electro-dialysis (SOXAL), and electrolytic (Stone Webster/Ionics Process). Descriptions of some of these processes are provided in subsequent sections. 

Stone Webster/Ionics A flue-gas desulfurization process in which the sulfur dioxide is absorbed in aqueous sodium hydroxide, forming sodium sulfite and bisulfite, the sulfur dioxide is liberated by the addition of sulfuric acid, and the reagents are regenerated electrolyti-cally. Designed by Stone Webster Engineering Corporation and Ionics Incorporated and operated in a demonstration plant in Milwaukee in 1974 but not yet commercialized. 

Stone Webster Engineering Corporation and Ionics, Inc. joined forces to carry out development of this process for removing sulfur dioxide from power plant flue gases (Humphries and McRae, 1970). The process is based on the absorption of sulfur dioxide in an aqueous solution of sodium hydroxide to form sodium sulrite and bisuliite. These compounds are reacted with sulfuric acid to release sulfur dioxide, which is evolved as a pure gas, and form sodium sulfate in solution. The key to the process is in the reconversion of the inert sodium sulfate to an active absorbent for sulfur dioxide. This is accomplished in an electrolytic cell which generates both sodium hydroxide and sulfuric acid for reuse in the process. The principal chemical reactions involved in the process are... 

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