How does it work?
Carbon is manufactured by the controlled burning of Cellulose. The temperature of the burn and the amount of oxygen entering the process control the hardness, filtering power and grain size of the carbon.
Carbon filters through both its grain size and by its ability to bind up organic and inorganic materials to itself through an electrical charge on its surface. This is known as Adsorption.
Carbon filtration is used successfully in industry for filtering wastewater, for the removal of fine insoluables from water and to remove metals and chlorine compounds from domestic water. Carbon filtration is also used to control biological contamination in water.
Activated Coal carbon has a different internal structure than coconut carbon thereby allowing for more uptakes of certain contaminants.
What is activated carbon made from?
Activated carbon can be manufactured from any organic material containing carbon. Commercial carbons are made from sawdust, wood, charcoal, peat, lignite, petroleum coke, bituminous coal, and coconut shells.
Activated carbon products made from bituminous coal, coconut shell, and wood. Water Filter Corp chooses these raw materials in order to provide good activated carbon to its customers.
How is activated carbon produced?
The coal is pulverised to a very fine particle, about the size of talcum powder. The powdered coal is mixed with a binder to glue it back together and pressed into briquettes. These in turn are crushed and classified to the size of the desired end product.
This process, called reagglomeration, creates an activated carbon that is harder and less dusty than a direct activation process.
Reagglomeration also assures that the activation occurs through the granule to the core. Some direct activation processes only activate the exterior of the granule.
The sized material is heated in an oxygen void environment to avoid burning and to remove the volatile components of the coal. The carbon is activated by additional heating in a controlled environment of oxygen and steam. The activation process creates a highly porous graphitic plate structure with tremendous surface area.
How much surface area does activated carbon have?
A single pound of activated carbon has the surface area equal to 125 acres.
How much does it weigh?
Pure carbon weighs about 130 pounds per cubic foot. It is much denser than activated carbon. During the manufacturing process the structure is opened up, creating porosity (pore volume) inside the granule. The finished product has a density between 25 to 40 pounds per cubic foot.
How much void space is in carbon?
A container of carbon is roughly 20% carbon, 40% interstitial space (the volume between the carbon granules), and 40% pore volume (the volume inside the carbon granules).
Another way to visualise this is: If you had a 55 gallon drum full of dry carbon, you could add 44 gallons of water to the drum before it would overflow. Therefore, 80% of the drum volume is air.
In liquid applications, why is it important to deairiate (fully wet) the carbon?
A container of carbon is roughly 20% carbon, 40% interstitial space (the volume between the carbon granules), and 40% pore volume (the volume inside the carbon granules). If air remains in the pore volume, the fluid being treated cannot migrate to the adsorption sites. The air becomes a barrier to the carbon functioning properly.
How long does it take to fully wet the carbon?
Filling the system with the fluid you will be treating and allowing the system to sit idle for 24 hours. This time will allow the fluid to displace all of the air in the pores of the carbon.
After the system has been idle for 24 hours, the next step is to use an upflow backwash to displace any air that has been trapped in the carbon bed. This backwash will also remove most of the carbon fines in the system.
What is this pore space?
The pore space is the internal volume of the carbon granule. The pore space consists of all the cracks and crevices created when the coal is crushed and glued back together, and the volume between the graphite plates. The distance between the graphite plates determines whether the space is an adsorption pore or a transport pore.
What is an adsorption pore?
Adsorption pores are the internal volume where the graphitic plates are close together creating a higher energy. Higher energy is important to adsorption because it is the energy that holds the contaminant (the carbon adsorbs the contaminant).
The volume where the graphite plates are far apart and the cracks and crevices make up the transport pores. It is important to note that all adsorption takes place in the adsorption pores and not the transport pores.
What do you mean - an adsorption pore is a higher-energy area?
There is a natural attractive force between all things in the universe. Gravity is one of these forces. In adsorption theory, the force between the contaminate and the carbon is the adsorptive force.
It technically is a Van der Waals force. It is this attractive force that enables adsorption to occur. The forces are a function of the distance between the two objects. The closer together the objects are, the higher the attractive force is. The higher the attractive force, the higher the energy level of the pore space.
What is a transport pore?
Transport pores are the internal volume of the carbon granule where the graphitic plates are far apart or the cracks and crevices of the particle. The transport pores act as the highways for the contaminants to reach the adsorption pores where they are adsorbed.
It is important to note that no adsorption takes place in the transport pores. Transport pores are vitally important, as they allow access to the adsorption pores - especially those deeper within the carbon granule.
How does the carbon remove the contaminant?
Once the contaminant enters the carbon granule via the transport pore space, it diffuses into the carbon matrix until it enters the smaller pores where the adsorptive forces begin to take effect.
Once it reaches a higher-energy area, it can no longer migrate (or diffuse) because the adsorptive force is stronger than the diffusional force. The contaminant is adsorbed to the carbon surface by the adsorptive forces (the Van der Waals forces). In this state, the contaminant is referred to as the adsorbate.
