Carbon Reactivation Dryers

CORECO® Rotary Process Furnaces are used for drying and reactivating spent activated carbon media which has adsorbed moisture and organic compounds. These units are available in standard sizes having capacities ranging from 100 to 1,000 pounds per hour of activated carbon (output basis) depending upon the quality of the carbon and the constituents of the adsorbate.

The CORECO® Rotary Process Furnace has a patented internal afterburner design that achieves air quality compliance in most applications. EnviroAir can furnish a thermal oxidizer or packed bed scrubber to treat the products of combustion if hazardous or odorous gases are expected.

The rotary process furnace shown is installed at an activated carbon supplier. This unit was furnished with low NOx burners to meet the stringent Southern California emissions regulations. It was designed to process 100 pounds per hour (output basis) of spent liquid phase and vapor phase activated carbons.

Functional Description of Carbon Reactivation Dryers

Spent carbon is fed to the input screw feeder hopper (A). The input screw feeder (B), which is sealed against the input end of the rotary retort (C), feeds the carbon at a constant rate into the rotary retort. In the rotary retort, the carbon is heated to a temperature between 1,400 and 1,650°F and is mixed and cascaded multiple times until drying and reactivation are complete. The rotary retort is indirectly heated by burners (E), firing outside the rotary retort inside the furnace section (D). There is no flame impingement on the carbon or extreme temperatures that could result in oxidation and loss of the carbon material.

Air is introduced into the rotary retort to remove water vapor evaporated in the carbon reactivation process and to oxidize volatile organic compounds (VOCs) that have evaporated in the carbon reactivation process. This air enters the rotary retort through a connection on the screw feeder. A modulating valve controls the amount of air entering the rotary retort as required to maintain the setpoint oxygen concentration.  The setpoint is normally 5% to 10% Oxygen measured in the products of combustion air leaving the furnace.

Steam and high temperatures are used in the carbon reactivation process to create the micropores in the carbon. When there is inadequate moisture in the spent carbon, steam may be added to the rotary retort. This is accomplished by adding water at a controlled rate through a connection on the input screw feeder.

The hot, reactivated carbon exits the rotary retort and drops through the cooler transfer hood (G) into the rotary cooler drum (H). In the rotary cooler drum, the carbon is cascaded repeatedly. Heat from the carbon is transferred to the cooling air flowing through the cooler tube in the opposite direction of the carbon flow (counterflow). The temperature of the carbon leaving the cooling drum will be approximately 30 to 50°F above ambient temperature. Carbon fines are filtered through a screen at the leaving end of the cooling drum and are collected in the fines hopper (I).  The carbon granules or pellets flow over the fines screen and exit the cooling drum (J), where they can be collected in a container or transferred by a conveyor. An exhaust fan draws the dust-laden cooling air from the cooler transfer hood (G), along with the process gases from the rotary retort exhaust hood (F). This air and gas flow is directed through a pollution control system before being discharged to atmosphere. The pollution control system typically consists of dust collection equipment but may also include a thermal oxidizer or packed bed scrubber if hazardous or odorous gases are expected in the products of combustion from the carbon reactivation furnace.