Novel Design for a Magnesium-Enhanced Lime FGD Gypsum Crystallizer Vessel

One method of gypsum production in FGD systems is the Magnesium-Enhanced Lime (MEL) external oxidation process. An air sparge grid is the sole means of agitation and solids suspension in this gas-liquid-solids system. The existing design is proven to be effective but is not optimized for agitation, oxygen transfer, or gypsum crystallization. For example, excessive amounts of air and compressor power may be used to achieve agitation than is required for oxidation. This paper presents a novel design of an external gypsum oxidizer/crystallizer, including the addition of a multi-stage mechanical agitator and baffle arrangement to optimize the oxidation and crystallization processes. A pilot scale version of this oxidizer unit has demonstrated a significant reduction in the stoichiometric oxygen requirement and a potential net energy savings of 20-30% over existing MEL FGD installation. Presented data was collected on 0.6 m (24”) diameter pilot installation of countercurrent oxidizer/crystallizer consisting of four separate mixing stages. A single full scale version of this new oxidizer design is envisioned to be about 30-feet in diameter, 50-feet tall and capable of processing absorber bleed slurry equivalent to a 700-MW unit burning 7-lb. SO2/MMBtu fuel.