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 THE CHALLENGE
The Gypsum/Wallboard Industry and related facilities utilize
a very large amount of heat in various areas. Heat is needed to calcine the
CaSO4 . 2(H2O) “rock” to CaSO4 . 1/2(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) have frequently been vented to atmosphere, due largely to the
limitations of traditional heat recovery equipment (fouling, etc.).
Separately, the heat requirements of the
calciner(s) and the dryer(s) are normally supplied using direct-fired air
heaters.
THE ANSWER
The Direct Contact Inc.(DCI) Heat Recovery System overcomes the limitations of traditional heat
recovery equipment and links the heat contained in a portion of the calciner
exhaust stream (chosen to take advantage of the higher wet bulb temperature)
with a circulating “hydronic” loop. The
patent-pending design of the heat recovery vessel recovers both the latent and
the sensible heat in the gas stream and sends it to process or the “hydronic”
loop in the form of very hot water.
This loop passes through hot water-air heaters to preheat combustion air
feeding the calciner(s) and the dryer(s)
THE DIRECT BENEFITS
The overall heat efficiency of the Gypsum/Wallboard process
increases dramatically while the waste streams emitted from the process are
reduced at the same time. Energy
savings can quickly add up to offset the initial purchase and installation cost
of the Direct Contact Inc.(DCI) Heat Recovery System and start to contribute
to the mill’s bottom line profitability.
Another consideration is that a significant amount of water is condensed
as the hot and humid calciner exhaust is cooled and reduces the mill’s overall
makeup water requirement (typically used to re-hydrate the Gypsum).
Additional benefits can be realized when other hot
water requirements are considered (e.g. heating of mill makeup water going to the
forming process, preheating of Boiler Feedwater, etc.). Similar results are anticipated for
facilities and systems used in the manufacture of Ceiling Tiles and Fruits or
Egg Cartons.
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