Case Study: Coreco Model BD-40 Rotary Borings Dryer System

Aluminum Chip Dryer

EnviroAir furnished our Coreco Model BD-40 Rotary Borings Dryer System for drying and de-oiling chips from an aluminum machining operation.  The chips are created from, and used for the manufacturing of pistons in the automotive industry.  The Model BD-40 has a nominal production capacity of 1000 lbs/hr of aluminum borings with a bulk density of 25 lbs/ft³ and no more than 3% by weight of combustible organics.

Aluminum borings from the customers machining operations are fed into a chip wringer which includes a screw conveyor with feed hopper, tramp metal separator to remove solids from chips prior to entering the wringer, a continuous chip wringer with diagonal shaft and gravity discharge, a sediment settling tank, and a cutting fluid reclaiming pump.  The chip wringer ensures that the retained moisture of the chips will be between 2%-3%.  Consistant moisture content allows operators to set a constant feed rate that requires little additional operator interface.

From the chip wringer, the aluminum chips are transferred via a screw conveyor and bucket elevator to a 36 yd³ chip storage silo.  The chip storage silo includes a vibratory bin activator mounted to the discharge of the silo to ensure a consistent feed rate to the dryer in feed conveyor.  The dryer in feed conveyor is a variable speed hinged steel belt conveyor that transports the aluminum chips into the rotary borings dryer's screw feeder hopper. 

The screw at the base of the screw feeder hopper feeds the chips into the retort at a customer programmable rate.  The retort is heated from the outside by burners that are fired into the cavity between the outside of the rotary hearth and the inside of the furnace shell refractory.  Preventing direct flame impingement diminishes the possibility of surface oxidation on the aluminum chips.  Inside the retort, the aluminum chips reach a customer programmable temperature of between 700ºF and 900ºF.  At this temperature, the oil and water vaporize and are drawn out of the retort through the smoke hood.  If the temperature in the rotary hearth exceeds the set point, cooling air is automatically introduced to cool the outside of the retort.  Further, if excessive amounts of hydrocarbons or other combustibles are introduced with the borings into the retort, water sprays in the smoke hood are automatically initiated to quench the fire.

The dried aluminum chips exit the retort and enter the rotary cooling section of the dryer.  Here, the chips are cascaded through an induced draft of room temperature air and cooled to a temperature of approximately 300ºF.  A bucket elevator lifts the cooled chips onto a vibratory pan feeder where they are uniformily spread out and then fed into a double drum magnetic separator.  The magnetic separator removes contaminants with low magnetic properties and fine iron particles.

Finally, the chips travel through a vibratory screen separator.  The vibratory screen separator is designed to remove particles smaller than 20 mesh from the dried aluminum chips. 

The fumes drawn out of the smoke hood by means of an oxidizer exhaust fan are first treated in a cyclone collector to remove larger particulate from the exhaust gas.  The air is then enters a recuperator which recovers heat from the oxidizer discharge gases and uses that recovered heat to preheat the dryer exhaust air before it enters the thermal oxidizer.  The recuperator preheats the dryer exhaust air from 600ºF to 1080ºF prior to entering the thermal oxidizer.  This is done to reduce overall fuel costs.  Inside the thermal oxidizer, a burner raises the temperature of the exhaust gas from 1080ºF to 1400ºF, a temperature at which the hydrocarbon particles and gases in the exhaust stream are destroyed.  From here, the exhaust  travels out of the recuperator and into the exhaust gas cooling system. 

The exhaust gas cooling system reduces the exhaust from the thermal oxidizer to a controlled 350ºF.  At 350ºF, any acid gases that may be present in the exhaust will not condense and corrode the cooling system heat exchanger or downstream baghouse.  This control is accomplished by using a modulating bypass damper.  If, for example, the temperature leaving the cooler begins to drop below 350ºF, the bypass damper will modulate open to bypass a portion of the hot oxidizer exhaust around the heat exchanger tubes to maintain the temperature at 350ºF.

Finally, a baghouse induced draft fan draws the air from the coolers through a high temperature baghouse.  The baghouse collects the fine particulate that was able to pass through the cyclone dust collector.

 

You can read more about Chip Dryers, view our complete line of Coreco products, or contact us to discuss your specific application and requirements.