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PRECIPITATION CHEMISTRY OF MAGNESIUM SULFITE HYDRATES IN MAGNESIUM OXIDE SCRUBBING
Citation:
Lowell, P., F. Meserole, AND T. Parsons. PRECIPITATION CHEMISTRY OF MAGNESIUM SULFITE HYDRATES IN MAGNESIUM OXIDE SCRUBBING. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/7-77/109.
Description:
The report gives results of laboratory studies defining the precipitation chemistry of MgSO3 hydrates. The results apply to the design of Mg-based scrubbing processes for SO2 removal from combustion flue gas. In Mg-based scrubbing processes, MgSO3 precipitates as either trihydrate or hexahydrate. The hydrate formed depends on equipment design and operating conditions. Theoretical prediction, verified experimentally, indicated that MgSO3 trihydrate is the theromodynamically stable hydrate formed at scrubbing process conditions. MgSO3 hexahydrate is formed as a metastable solid due to kinetic phenomena. Nucleation and crystal growth rates are much faster for hexahydrate than for trihydrate. The time scales observed in kinetic experiments at scrubbing process conditions are: hexahydrate precipitation (10's of minutes), hexahydrate dissolution and trihydrate precipitation (100's of minutes), and attainment of trihydrate equilibrium (1000's of minutes). Nucleation plays a dominant role in the formation of trihydrate solids. These results indicate that Mg-based scrubbing process can be designed to precipitate a majority of either hydrate form. Important design variables include scrubbing liquor composition and temperature, seed crystal composition, slurry volume, equipment residence times, and energy inputs to the slurry that influence nucleation.