Why Use a Panel-Type Activated Carbon Filter, and How Is Its Efficiency Tested?

Why Use a Panel-Type Activated Carbon Filter?

A panel-type activated carbon filter is made by securing activated-carbon granules or activated-carbon fiber inside a flat metal or plastic frame. Its practical value lies mainly in the following features.

Compact Structure and Broad Compatibility

The panel design is thin, generally 5–50 mm, and occupies little space. It can be installed directly in an air-conditioning system, ventilation duct, or spray-booth filter section without requiring extra room. This makes it particularly suitable where installation dimensions are restricted, such as small spray booths and local ventilation systems in cleanrooms.

Stable, Targeted Adsorption

The porous structure of activated carbon, with a porosity of more than 90% in some products, strongly adsorbs volatile organic compounds (VOCs) such as benzene and toluene from paint spraying, as well as odors and formaldehyde. The panel construction distributes airflow evenly through the carbon layer, reducing short-circuiting in which some gas exits without contacting the carbon and thereby keeping adsorption performance stable.

Different types of activated carbon—such as coal-based, wood-based, or coconut-shell carbon—can be selected for specific pollutants. Coconut-shell carbon, for example, performs particularly well in VOC adsorption.

Easy Installation and Replacement

Panel filters are commonly installed with clips or in a slide-out frame. A single person can replace one without specialized tools, reducing equipment downtime and making them well suited to rapid production-line maintenance.

Controlled Cost and a Wide Range of Uses

Compared with cylindrical, honeycomb, and other activated-carbon filter formats, panel filters generally cost less to manufacture. Their dimensions and carbon loading can be customized to the treatment requirement. They are suitable for low- to medium-concentration gaseous pollutants, including secondary VOC treatment in spray booths and indoor odor removal.

How to Test the Filtration Efficiency of a Panel-Type Activated Carbon Filter

Filtration efficiency is the key performance indicator. Gas-pollutant adsorption and, for composite panel filters that include particle media, particle capture must be evaluated separately. The principal methods are as follows.

1. Gas-Pollutant Adsorption Efficiency: The Core Indicator

This evaluates the adsorption of VOCs, odors, and other gaseous pollutants. Common standard methods include the following.

Dynamic Adsorption Method: The Most Common Test

Test setup: Place the panel filter in the airflow channel of a sealed test chamber, normally 1–10 m³ in volume. Introduce a simulated gas containing a target pollutant such as toluene or formaldehyde, and control air velocity at about 1–3 m/s to reproduce actual operating conditions.

Test procedure:

Before testing: Measure the initial pollutant concentration in the chamber using a gas chromatograph, spectrophotometer, or other suitable instrument.

During testing: Continue supplying the test gas and measure the pollutant concentration at the filter outlet at fixed intervals, such as every 10 minutes.

Efficiency calculation: Efficiency = (inlet concentration − outlet concentration) / inlet concentration × 100%.

Standard reference: Tests may refer to GB/T 14295-2019, Air Filters, or HJ/T 386-2007, Activated Carbon Adsorption Devices. A one-hour adsorption efficiency of at least 80% for the specified VOC is commonly required.

Static Adsorption Method: Supplementary Evaluation

Place the filter in a sealed container of known volume, inject a measured quantity of pollutant, and seal the container. After 24 hours, measure the remaining pollutant concentration and calculate adsorption capacity in g/m², meaning the mass of pollutant adsorbed per square meter of filter. This test evaluates saturation capacity and helps prevent efficiency loss caused by carbon saturation.

2. Particle-Capture Efficiency: For Composite Filters

Some panel activated carbon filters include nonwoven or other filter media on both sides of the carbon layer to intercept dust. Their particle efficiency is tested according to particle-filter standards.

Particle-Counting Method

Use an aerosol generator to produce particles of specified sizes, such as 0.3 μm or 1 μm talc or sodium-chloride aerosol, and pass the aerosol through the filter in a test duct.

Use laser particle counters to measure particle-number concentrations upstream and downstream of the filter.

Calculate efficiency as follows: Efficiency = (upstream particle count − downstream particle count) / upstream particle count × 100%. An efficiency of at least 50% for 0.3 μm particles is commonly required for a coarse- or medium-efficiency grade.

3. Field Spot Checks in Actual Applications

The following simple methods can provide a quick on-site assessment, such as in a spray booth.

Odor check: Compare odor intensity before and after the filter using an odor assessment or an electronic-nose detector. A clear reduction at the outlet indicates that adsorption is working.

Rapid VOC measurement: Use a portable VOC detector, such as a photoionization detector (PID), to read VOC concentrations directly at the inlet and outlet and calculate efficiency. This method is suitable for a preliminary field assessment.

Summary

Thanks to their compact construction, effective adsorption, and convenient replacement, panel-type activated carbon filters are a preferred solution for low- to medium-concentration gaseous pollutants. Their efficiency should be verified using professional methods such as dynamic adsorption testing for gases and particle counting for particulate matter. This ensures that the filter meets the environmental and purification requirements of the application—for example, a spray booth subject to a national VOC emission limit of no more than 100 mg/m³.