Activated Carbon is a term used to describe material (usually organic) that has been heated at temperatures above 600°F (315°C), or first impregnated with a strong acidic or base material and then heated at temperatures above 450°F (232°C). This treatment burns or "carbonizes" the material. Carbon has a natural affinity for organic materials which bind to its surface. The activation process creates microscopic pores that increase the surface area of each particle, giving rise to activated carbon's status as a highly reliable adsorbent.

Activated carbons are made from a wide array of organic materials, ranging from coal to peach pits. Activated carbon is available in powdered (PAC), granulated (GAC), and pellet forms. The type of activated carbon chosen will likely depend on its intended application. An activated carbon with large holes is best suited at picking up heavy organic chemicals, such as benzene, while smaller pores would catch the lighter, sometimes more gaseous pollutants.1

Activated carbon has been historically used for removal of odor, color pigments and various catalytic functions. However, recent process advancements in the creation of activated carbon have led to more discoveries for its use. Activated carbon is now a key material in drinking water treatment, kidney filtering machine applications, cleaning waterborne industrial waste spills and in gold recovery.2

Characteristics and Challenges:

In powdered form, activated carbon is extremely fine, with an average particle size of only 20 microns and a bulk density of 21.5 lb/cu ft (34.4 kg/cu m). It is extremely aeratable, meaning the slightest air movement may cause the activated carbon powder to take flight and settle as dust. This dust fluidizes, or takes on the properties of a liquid. Activated carbon dust will coat nearly anything it lands on, including machinery, clothing and skin. In powder form, some activated carbons are capable of creating a dust explosion.

Another inherent difficulty with activated carbon is that it is insoluble with water and most solvents. Handlers must remain vigilant to prevent spills, and the intensive and costly dry-vacuuming cleanup that would follow.

Some grades of activated carbon can be degradable. If too severely damaged in the handling process, the material may lose its effectiveness as an adsorbent.

In activated-charcoal form, activated carbons typically carry an HMIS fire rating of 3, indicating high flammability in the presence of open flames, sparks, or heat. An activated charcoal blaze may reignite after the fire has been extinguished. Freshly prepared charcoal may heat spontaneously when exposed to air, and presence of water accelerates this.3

As previously described, powder activated carbon can aerate and tends to fluidize, This has resulted in powder activated carbon flooding a conveying line. In granular form, activated carbon may tend to interlock and resist flow in the conveying line.

If the activated carbon has been transported to the facility in bulk bags, the frames used to discharge the bags usually require additional accessories to completely empty the activated carbon from the bag. This includes features such as spring-loaded frames that will elongate and stretch the bags as they empty and lighten, making them rigid and removing any pockets of activated carbon cornered in the bags. Bag-activating devices are generally effective in agitating this material, dislodging collections of activated carbon, and promoting a better flow. Some of these bag-activating devices also serve as a dust-tight seal between the bulk bag and the receiving hopper.

As the activated carbon fills the receiving hopper, the air inside the vessel is forced out. Unless this air passes through a filter, the possibility of airborne activated carbon dust particles escaping into the surrounding atmosphere is increased. A dust collector mounted on the discharger frame will contain the activated carbon dust inside the conveyance system. This not only lowers the amount of housekeeping efforts

Carbon, Activated
necessary, but the collector can also reduce product waste if it is equipped with a reverse pulse jet which pneumatically cleans the filter media, returning the collected activated carbon back to the receiving hopper.

If the activated carbon is packaged in smaller bags, a bag-dumping station with a dust hood, and filter cartridges is likely sufficient to support the manual unloading of the material. As mentioned previously, a pneumatic pulse can be used to clean the filters and return the activated carbon back into the receiving hopper. A bag compactor connected to the bag dumping station, can allow the operator to pass the empty bags directly to a compactor, thereby reducing the volume of waste while containing dust.

The geometry of the feed hoppers is another important aspect in handling activated carbon. To prevent errors in the charging of the conveyor, there may be a need to incorporate devices such as vibrators or mechanical agitators to promote flow. Consultation with an experienced provider of activated carbon handling equipment is recommended for the correct placement of these devices.

If the activated carbon is being pneumatically conveyed into a processing system, the blower used to move activated carbon through the convey line must be sized to meet the demands of system.

If a flexible screw conveyor is being used to move the activated carbon, a round screw design is commonly used for the granular form; while the powdery form is better handled by a wider, flatter screw.

Should your application feature the loading of powdered activated carbon into bulk bags, the bag capacity will be
maximized by use of vibratory densification decks to de-aerate the activated carbon as it fills, and by the application of load cells to ensure the desired weight. Positive seals interfacing between the bulk bag and the filling equipment will ensure a dust-tight operation.

Flexicon Applications:

Flexicon's dust suppression and collection systems ensure proper containment of activated carbon throughout the conveyance process.

Two Municipal WTPs reduced dust and manual labor after installing Flexicon systems.

Consultation with a Flexicon specialist will help you decide if a flexible screw or pneumatic solution best fits your activated carbon application.

Flexicon's expert design and engineering staff will weigh each parameter and recommend the best solution for you. Upon request, Flexicon's test lab will simulate your activated carbon handling functions before the system is installed in your plant.

Flexicon's product line of advanced flow promotion conveyors, high-flow hoppers, deaeration/densification decks and a host of other components and accessories are proven performers that promote flow while reducing degradation, dusting and/or the separation of blends comprised of disparate particles.

1 Slate: How Does Activated Carbon Work? November 28,2005
2 Kuraray Chemical Company: Some Activated Carbon Examples
3 Material Safety Data Sheet, Charcoal, Activated, Powder MSDS
Sources: Where noted. All other information courtesy of Flexicon Corporation.


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