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Dry milling process

Clay preparation for ceramic and bricks industry starts by material granulometry calibration from the quarry agglomerated size to the natural dimension of 20 to 400 micron.

Size reduction could be obtained using two different process. Actually the most used system is the wet process, where clay is dispersed on a water media using paddles mixers. The liquid sludge, normally called “barbottina” is then pumped to a Spray Drier where it will be dried to form small grains which are directly conveyed to the line preparing the blend for pressing machines feeding. This process require a tremendous consumption of fuel to evaporate the water added to the clay on the wet process preparation as well as the naturally clay contained water.

On each ton of barbottina, 300 liters of water should be evaporated by the spray drier using about 45 cubic meters of gas.

Dry milling process consist on clay drying, evaporating only the natural water. Worldwide, clay coming from quarries has a residual humidity ranging between 12 and 25%, mainly depending on material origins and weather conditions. Drying process will reduce this range to 4% only.

Drying is made by triple run rotating drum driers. All along the drying process clay granulometry is reduced from the originals 20/50 mm down to 2/10 mm at the drum exit.

By this process 60/70 % of the infeed material is coming out from the drum drier itself, while a 30/40 % quota has dimensions below 400 micron and is collected into cyclones and sleeves filters.

The stream coming from the drum drier goes to the milling area and then to the screening line. Dust and fines coming from cyclones and filters goes directly to the screening.

In this way fuel consumption is limited to the natural water evaporation and the required electric power for milling action is reduced by about 40 %.

Rotating drum drying process has also another potential advantage, waste heat streams could be used to furthermore reduce the fuel consumption.


Macinazione a secco

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