Thermal Sand Dryers

CORECO® Rotary Process Furnaces are used for thermal reclamation of waste foundry sand containing combustible organic binders. These units are available in five standard models having capacities ranging from ½ to 5 tons per hour of waste foundry sand containing less than 2% combustible organic matter.

The reclaimed sand is generally cleaner than new sand resulting in improved casting quality. The CORECO® Thermal Sand Reclamation System also enables the user to have control over the grain fineness of the reclaimed sand.

The CORECO® Thermal Sand Reclamation System has a patented internal afterburner design that achieves air quality compliance in most applications. A cyclone dust collector and baghouse are typically provided to remove particulate from the air exhausted from the thermal sand reclamation system.

Functional Description of Thermal Sand Dryers

Waste foundry sand is fed to the input hopper (A). The screw feeder (B), which is sealed against the input end of the rotary retort (C), feeds the sand at a constant rate into the rotary retort. In the rotary retort the sand is uniformly heated to a temperature between 1,200 and 1,500° F. An annular cavity is provided between the outside surface of the rotary retort and the inside surface of the furnace shell (D). The burners (E) are fired into this cavity to heat the rotary retort from the outside (indirect heating). There is no direct flame impingement on the foundry sand.

Air is required to remove moisture from the rotary retort and to provide the oxygen required for the oxidation of the organic compounds found in the waste sand. This air enters the rotary retort through a connection provided on the screw feeder. A modulating valve controls the amount of air entering the rotary retort as required.

The hot, clean foundry sand exits the rotary retort and drops through the cooler transfer hood (G) into the rotary cooler drum (H). In the rotary cooler drum, heat from the sand is transferred to the cooling air that is flowing through the cooling drum in the opposite direction of the sand flow (counterflow). The temperature of the sand leaving the cooling drum will be approximately 30 to 50°F above ambient temperature.

The reclaimed sand is filtered through a 20-mesh screen (I) at the leaving end of the cooling drum and is collected in the  hopper of the Pneumatic Scrubber/Classifier. Metal and other rejected material greater than 20-mesh flow over the filter screen and exit the cooling drum (J), where they can be collected in a container or transferred by a conveyor.

In the Pneumatic Scrubber/Classifier, a compressed air nozzle (K) located near the bottom of the sand hopper (L) entrains the sand grains. This sand/air mixture flows through the scrubber tube (M). Turbulent airflow in the scrubber tube causes the sand grains to rub against each another which removes clay and other contaminants that are adhered to the surface of the sand grains.

After leaving the scrubber tube, the sand grains strike a series of target plates (N) within the classifier. These target plates reduce the sand velocity and spread the sand stream across the Classifier plenum (E) so that it is uniformly exposed to the classifying air stream. The larger sand grains to be reclaimed are carried toward the far wall of the Classifier and fall through the discharge gate (F) at the bottom of the Classifier. Rejected sand fines and contaminants are entrained by the upward moving airstream in the Classifier plenum. This airstream containing the sand fines and contaminants exit the top of the Classifier and is directed to a dust collection system. Adjustable vents (G) and a butterfly damper (H) are provided for adjusting the classifying air velocity and the corresponding grain fineness number.

An exhaust fan draws the dust-laden cooling air from the cooler transfer hood (G), process gases from the rotary retort exhaust hood (F), and classifying air from the classifier (O). This exhaust stream is directed through a pollution control system before being discharged to atmosphere. The pollution control system typically consists of cyclone dust collector and a baghouse dust collector.