Gypsum Processing for Wallboard
Gypsum is a soft sulfate mineral composed of calcium sulfate dehydrate, with the chemical formula CaSO₄·2H₂O. It is widely used in a variety of applications and is the main ingredient in many forms of wallboard, block, and plaster products.
The traditional method of gypsum processing for stucco and plaster production is in a batch or continuous type kettle. Gypsum requires size reduction and classification ahead of the kettle to provide a consistent quality product. The Raymond® roller mill has been used almost exclusively in this application and it produces excellent results
Natural gypsum (ore) should be pre-crushed to 0.75” (for 50” or 54” mills) to 1.25” (for a 66” mill). The ore usually contains 4-5% free (surface) moisture which can be removed during the grinding process. Most Raymond® roller mills used with gypsum utilize a hot gas generator, which provides the heat required reduce the free moisture content to near 0%.
A Raymond® roller mill with a straight side Raymond® Whizzer Classifier is sufficient to obtain the fineness required for nearly all stucco application. A Raymond® Turbine Classifier, in place of the Whizzer, can allow the mill to produce a much finer product or provide greater capacity at a specified fineness by narrowing the particle size distribution (PSD).
Modern wallboard production facilities use a single system to both grind and calcine gypsum. Natural gypsum can be fed directly into a Raymond® Imp™ Mill Flash Calcining (IMFC) system. High moisture feed stocks such as synthetic gypsum (FGD) can be dried in advance of the calcining and grinding system to increase capacity and consistency or it can be fed directly to the system. The flexibility of utilizing natural gypsum, synthetic gypsum of any blend of the two, make the IMFC the most flexible calcining system available.
Natural gypsum occurs in sedimentary rock formations, and is found in over 85 countries. The United States, Canada and Mexico have some of the largest reserves of high-quality gypsum in the world. Gypsum is mined in 16 states with leading producers including Colorado, Iowa, Kansas, Nevada, Oklahoma, and Texas
Synthetic gypsum is a byproduct that results from the flue gas desulfurization (FGD) or “scrubbing” process at coal-fired power plants.