Tuesday, June 03, 2008

Activated Carbon: Mesh Size

We are often questioned about the differences between 1240 (12 by 40) mesh activated carbon and 830 (8 by 30) mesh activated carbon. The 1240 mesh activated carbon is smaller than the 830 activated carbon.

The screens or the mesh sizes are different. The 12 mesh screen has 12 openings per square inch 12 across and 12 down. The 40 mesh screen has 40 openings per square inch, 40 across and 40 down. Obviously the "holes" of the 12 mesh screen are larger than the "holes" of the 40 mesh screen. It follows that the holes on an 8 mesh screen are larger than 12 and 30 mesh holes are larger than 40 mesh holes.

Activated Carbon Particle Size Table Courtesy of Calgon Carbon Corporation

If you would like a laminated card with this guide, contact Res-Kem.

As part of the manufacturing process the activated carbon companies pass the carbon through various screens to meet the specification.
Particle Screening System Courtesy of Calgon Carbon Corporation

So if you look at 1240 mesh activated carbon, it shouldn't have particles larger than 12 mesh or smaller than 40 mesh. The 830 mesh activated carbon shouldn't have particles larger than 8 mesh or smaller than 30 mesh.

What difference does this make to the user of the activated carbon? The most commonly used activated carbons for residential POE (point of entry) systems, commercial and industrial systems are 830 and 1240 mesh. We use 1240 mesh activated carbon because it has greater surface area and provides excellent chlorine and organics removal. Because the activated carbon filter acts as a mechanical filter in addition to removing chlorine and adsorbing organics, it will accumulate particles of dirt or crud at the top of the bed. An activated carbon filter is backwashed on a regular basis to remove this and prevent pressure loss across the bed.

In instances where the water contains more turbidity or crud, an 830 mesh activated carbon may be used. Having larger particle size than the 1240 activated carbon, the filter containing 830 mesh activated carbon won't need to be backwashed as often. However, as the particle size increases from a 1240 mesh activated carbon to an 830 mesh carbon, thereby decreasing the backwash flow rate, adsorption capacity will generally decrease.

When we specify an activated carbon it's important to know the water source. If it's city water or well water from a potable source, we can assume there is little if any turbidity and use of a 1240 mesh activated carbon will work well. If an industrial plant is taking water directly from a river or lake there may be disruptions to the clarification system that may cause excess crud or turbidity. In these cases we see the use of 830 mesh activated carbon.

Here is a full glossary of activated carbon definitions.

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