BACKGROUND
The Gypsum/Wallboard Industry and related facilities utilize a very large amount of heat in various areas. Heat is needed to calcinate (i.e., thermally decompose) the CaSO₄·2H₂O (rock) to (CaSO₄)₂·H₂O (plaster of Paris,) as well as to dry and set the wall board after forming. The hot and humid process gas generated from both the calciner(s) and kiln dryer(s) are frequently vented to atmosphere, due largely to limitations of traditional heat recovery equipment. Also, the heat requirements of calciners and dryers are normally completely supplied using direct-fired heaters.

SOLUTION
The Direct Contact LLC (DCLLC) Heat Recovery System overcomes the limitations of traditional heat recovery equipment and links the heat contained in the calciner exhaust stream with a circulating “hydronic” loop. Engineered to take advantage of higher wet-bulb temperatures, the patented design of the heat recovery vessel recovers both latent and sensible heat in gas streams and routes it to processes or a hydronic loop in the form of hot water. The loop passes through heat exchangers to preheat air feeding the calciners and the dryers.

DIRECT BENEFITS
The overall energy efficiency of the Gypsum/Wallboard process increases dramatically, while waste streams from the processes are reduced. Energy savings quickly add up to offset purchase and installation costs of the DCLLC Heat Recovery System and contribute to the mill’s long-term profitability. Another benefit is that a significant amount of water condensed from the calciner exhaust is reused in the mill’s makeup water (used to rehydrate Gypsum.)

Additional benefits are realized when other hot water requirements are considered (e.g., heating of mill make-up water going to the forming process, pre-heating boiler feed-water, etc.) Similar results are realized for facilities and systems used in the manufacture of Ceiling Tiles, Fruit or Egg Cartons, and other heated processes.