What is the difference between chemical filters and medium-efficiency bag filters?

In the filtration section of the air conditioning box or air handling unit, medium-efficiency bag filters and chemical filters sometimes appear at the same time. Both may have a square frame shape and may be similar in size. Some people may think: The medium-efficiency bag filter has a large area and high dust holding capacity. Can it handle gas at the same time?

This inference is not valid. The main task of medium-efficiency bag filters is to intercept particles, not to process gases. It has a large area and high dust holding capacity, which refers to the particle holding capacity and has no direct relationship with the gas processing capacity. Bag shape does not determine whether gas functionality is available. For specific division of labor logic, please refer to Discussion on the division of labor between chemical filters and primary filters .

Don't push functions by structure name

'Bag type' describes a structural form, not a function.

Medium-efficiency bag filters are usually composed of multiple filter bags. The airflow enters from the mouth of the bag and flows out from the bottom or side of the bag after passing through the filter material. This structure increases the effective filtration area and is suitable for intercepting medium-sized particles. It has a large dust holding capacity and a relatively long replacement cycle. Its evaluation index is particle filtration efficiency, such as the filtration efficiency for particles of a specific particle size.

Chemical filters deal with gaseous pollutants. Its core is the filter medium, which removes target gases by adsorption or reaction. The structure can be flat, box, V-shaped or other forms. The bag structure can also be used to fill chemical media, but at this time it is no longer a simple particle filter.

Therefore, judging whether a product can handle gas depends on its medium and performance data, not just its appearance. No matter how large the area of ​​a bag-type particle filter is, it has basically no ability to process gas molecules. Specific products can be referred to the chemical filter product range . Description of

Suitable locations may vary

The location of the two types of filters in the system is usually determined by their functions.

Medium-efficiency bag filters are commonly found in the middle section of air conditioning boxes. It is located after the primary effect and before the high efficiency. Its main function is to further reduce the particle concentration and protect the high-efficiency filtration section at the back end. Because of its large dust holding capacity, its replacement cycle is usually longer than that of primary efficiency and shorter than that of high efficiency.

The location of the chemical filter depends on the source of contamination. If the gas brought in by the fresh air is processed, it may be placed in the chemical filtration section of the fresh air unit; if the indoor circulating gas is processed, it may be placed in the return air path or FFU circulation system. If used for local protection at the equipment end, it may be integrated into the air supply unit inside the equipment.

The two may be adjacent in the system, but have different responsibilities. Medium-efficiency section tube particles, chemical section tube gas. Don't mix functions together just because they are in close proximity. involving The fresh air system of the MAU box-type chemical filter , the positional relationship between the medium-efficiency bag filter and the chemical filtration section needs to be confirmed based on the system design.

Replacement needs to review the fan and frame

In retrofit projects, it is sometimes considered to replace the medium-efficiency bag filter with a chemical filter, or vice versa.

Similar appearance does not mean the pressure drop is the same. Medium efficiency bag filters may have different resistances than chemical filters. Chemical media is usually denser than regular filter media and may have higher resistance. If the original fan capacity is insufficient, the air volume may decrease after replacing it with a chemical filter.

Maintenance and gas capabilities also vary. The replacement of medium-efficiency bag filters depends on the pressure difference, and the replacement of chemical filters depends on the gas processing capacity consumption. The maintenance basis, replacement cycle, and inspection methods of the two are different. If you only manage according to the original maintenance rhythm, the gas treatment effect may not be guaranteed.

Front-end responsibilities cannot be left out. If the medium-efficiency section originally assumed the particle protection function, after replacing it with a chemical filter, the high-efficiency filtration section at the rear end may lose protection. In this case, it is necessary to consider setting up an additional particle filtering section, or to choose a composite product that has both functions. However, the performance of the composite product also needs to be verified separately. For specific configuration, please refer to Discussion of whether chemical filters can handle both particulate matter and gases .

Project judgment example

The medium-efficiency section slot of an air-conditioning box is planned to be used for chemical filtration modification, and the original medium-efficiency bag filter is replaced with a chemical filtration section.

After the modification, it was found that the pressure difference of the rear-end high-efficiency filter increased faster. The investigation confirmed that the original medium-efficiency section assumed part of the particle pre-filtration function. After replacement, this part of the particle load directly entered the high-efficiency section, resulting in an increase in the burden on the high-efficiency filter.

Adjustment plan: Add a medium-efficiency particle filter before the chemical filtration section to restore the original particle protection function. The chemical filtration section is responsible for gas treatment, and the medium-efficiency section is responsible for particle interception, each performing its own duties. After the total system resistance was recalculated, the fan operating point was also within the acceptable range.

This case illustrates: When replacing the filter segment, you must confirm whether the original function is retained. The particle protection effect of medium-efficiency bag filters cannot be ignored just because it is changed to a chemical filtration section. involving FFU systems equipped with chemical filters also need to confirm the division of responsibilities of each layer of filters.

Key points for selection and acceptance inspection

About Aili Industrial’s filter section packages

The core of the configuration of medium-efficiency bag filters and chemical filters is to let each layer bear the load that they are good at, and then uniformly check the resistance and maintenance rhythm at the system level.

Aili Industrial has independent manufacturing capabilities in filters, motors, fans, control systems and sheet metal processing, and can provide chemical filter product series and supporting particle filtration products. For projects that require multi-stage filtration, dust load, gas composition, air volume and installation space can be combined to help check the type, sequence and maintenance methods of filters at each stage. When the filter is matched with MAU, FFU, EFU and other equipment, the resistance, interface and maintenance methods can be confirmed uniformly.

Related products:Chemical filter product series、MAU box chemical filter、FFU comes with chemical filter . Providing dust load, target gas and system conditions at the time of inquiry will help confirm the appropriate filter chain configuration. The specific selection is subject to the technical documents and test results confirmed by the project.