Frequently asked questions about air filters

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Is an activated carbon filter enough?

For odour and volatile organic compounds (VOCs), often yes. Plain carbon captures gases such as H2S, HCl, HF and SO2 only to a lesser degree; for those you need impregnated carbon. With wet air, a lot of dust or high concentrations, carbon alone is less suitable, because the filter then fills up or clogs quickly. See Activated carbon or scrubber.

Absorption and chemisorption: what is the difference?

In absorption, a gas dissolves in a liquid, as in a scrubber. In chemisorption, the gas reacts with a substance on a solid granule and stays bound to it. That granule is activated carbon or alumina with an impregnation. Source: Informatiepunt Leefomgeving, Gaswasser and Adsorptiefilter (in Dutch).

Which filter medium suits my gas?

That follows from the substance you need to remove:

Then the air velocity, the concentration and the contact time decide the form of the filter. With a mixture of gases, one substance can saturate the medium sooner than the rest.

When does activated carbon need replacing?

Before the carbon is saturated. A full filter no longer works and can release substances again. With impregnated carbon or a chemical medium, you can measure after installation how long it will still last, its service life: after 3 to 6 months a sample goes to a laboratory, which measures how much impregnation is still active and calculates how many days the medium will last. A rising pressure drop across the filter points to clogging by dust or to carbon that is breaking up.

When do you combine two filter techniques?

When one technique cannot bring the substances below the limit value. A first stage, for example a scrubber, then removes the bulk of the load and a carbon filter captures the rest. A carbon filter is also placed as the last stage, in case an earlier stage fails.

Can I rent a filter unit for a temporary odour problem?

Yes, mobile activated carbon filter units can be in use within 2 to 3 days: Filter unit rental.

Why do electronics corrode in an MCC room?

Gases from production and chemical processes attack the metals on circuit boards. This causes faults and failures. The gases are acid gases such as H2S, SO2 and NOx, ammonia and ozone. At more than 50 % relative humidity these gases become more aggressive. You measure how corrosive the air is with copper and silver coupons that hang in the room for 30 days; the result is a class G1, G2, G3 or GX under ANSI/ISA-71.04-2013. See corrosion in switch rooms and MCC rooms.

What is molecular filtration?

Another name for filters that remove gases from the air, such as SO2, NOx, ozone and VOCs. These gases pass straight through an ordinary dust filter. On this site they are called chemical filters and activated carbon filters.

How is filter medium replaced?

The saturated medium is removed from the filter with a vacuum truck, packed in big bags, taken away and processed. Transport, paperwork and waste stream numbers are part of it. See Replacing filter medium.

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