April 19th, 2018 | Posted in General
There are times when one’s air cleaning process may require the use of a carbon post filter. Let’s get a brief overview of carbon, how it works, and when you should consider using it.
Carbon (sometimes referred to as activated charcoal) is typically used to address Volatile Organic Compounds, or VOC’s. VOC’s include odors and other gaseous pollutants. There is also impregnated carbon that is used to increase the effectiveness of the carbon when dealing with specific gases.
The science behind carbon filtration is not complicated: carbon air filters trap gas molecules on a bed of charcoal. This process is called adsorption. By definition, adsorption means to accumulate (liquids or gases) on the surface. This process creates a film of the adsorbate (the molecules or atoms being accumulated) on the surface of the adsorbent. It differs from absorption, in which a fluid permeates or is dissolved by a liquid or solid.
Activated carbon is a form of carbon that has been processed to increase its porosity, resulting in a larger surface area for adsorption or chemical reactions. When a material adsorbs something, it attaches to it by chemical attraction. The huge surface area of activated charcoal gives it countless bonding sites. To put it into perspective, one pound of activated carbon has an approximate surface area of 100 acres.
Carbon will adsorb some of almost any vapor and has a large capacity for organic molecules, especially solvents. It will adsorb and retain a wide variety of chemicals at the same time. Carbon works well under a wide range of temperature and humidity conditions, is inert and safe to handle and use.
The first challenge with an activated carbon bed is it will adsorb a wide variety of gases. What this means is carbon is not selective regarding what it will adsorb. Carbon will adsorb nuisance gases as well as desirable gases such as air fresheners.
The second challenge with the activated carbon bed is that over time, the gaseous pollutants increasingly fill up the adsorption sites of the activated carbon. Once the bed is saturated, the filter can no longer trap pollutants. When a carbon air filter is saturated, one might notice it giving off a strange odor. The change in odor is a strong indicator that it’s time to change your carbon filter.
The top two challenges listed above makes it hard to estimate how long a carbon filter will last and it is important to determine all of the gaseous emissions in your application. One can also send a sample of the carbon for testing to determine the approximate remaining “life” of your carbon filter.
Ultimately you need to understand if what you are smelling is a particulate emission, or a gaseous emission. For some applications, general particulate filtration will address the nuisance and for other applications, activated carbon will be needed. Still, there are some applications where both, particulate filtration and carbon filtration will be required.
Please contact us if you have questions about utilizing carbon in your air filtering process. Our engineering department will review your process parameters, and make a recommendation as to what carbon option will work the best for you.