Is the MAU chemical filter installed before or after the surface cooler?

This issue is often discussed during the MAU design phase. Whether the chemical filter section is placed in front or behind the surface cooler seems to be just a position adjustment, but the actual impact is not only on the installation space, but also on the temperature and humidity environment of the filter section, filter material suitability, pre-filtration protection and maintenance methods.

There is no fixed answer. Both positions have their own applicable conditions. Which one to choose depends on the fresh air inlet pollution, temperature and humidity conditions, whether there is any risk of droplets, and the applicable scope of the filter material. For specific configuration logic, please refer to Discussion on why MAU needs to configure chemical filtration section .

Compare the two environments

The air conditions before and after the surface cooler are different and have different effects on the chemical filtration section.

In front of the surface cooler. The air is outdoor fresh air or air after initial or intermediate effect treatment. The temperature changes with the seasons. The relative humidity may be high but there is usually no liquid water. If the fresh air temperature is high and the humidity is high, such as in summer, the air in front of the surface cooler may be close to saturation.

After the surface cooler. After the air is cooled and dehumidified, the temperature decreases and the absolute moisture content decreases, but the relative humidity may still be high or even close to saturation. If the water removal effect of the surface cooler is not good, the air may entrain liquid droplets.

The temperature conditions are different on both sides. The temperature in front of the surface cooler is high, and some chemical reactions may be faster, but the high temperature may also accelerate the aging of the medium. The temperature after the surface cooler is low, which may be beneficial to some adsorption processes, but may be detrimental to some reactive media.

The humidity conditions are different on both sides. The relative humidity behind the surface cooler is high, and water molecules may compete with the target gas for adsorption sites, affecting the medium capacity. Some impregnation media may absorb moisture, harden, or degrade in high-humidity environments.

These differences determine the choice of filter media and how the filter sections are configured. For specific impacts, please refer to Discussion on whether to choose activated carbon or other adsorption media for chemical filters .

Address droplet risks first

The air behind the surface cooler may entrain liquid droplets, which is an important factor to consider when selecting a location.

Surface cooler drainage and water blocking effect. If the water drainage of the surface cooler is not smooth or the water baffle is not effective, the air may entrain liquid droplets. Droplets entering the chemical filtration section can cause the media to become damp, hardened, or have a reduced capacity.

Chemical filters are not a substitute for water removal structures. Chemical filtration deals with gaseous pollutants, and droplet control relies on specialized defogging or separation measures. The two have different divisions of labor and cannot be mixed. If there is a risk of droplets after the surface cooler, a defogging or water-blocking structure should be installed before the chemical filtration section.

The condition of the media after exposure to moisture needs to be evaluated. If the media has become damp, it cannot be considered recovered simply by drying it out. Some impregnation ingredients may have been lost or changed, and you need to judge whether to continue using it according to the product description and project requirements. For specific inspection methods, please refer to Discussion on how to deal with dust falling on the surface of chemical filters .

The applicable conditions of the filter material determine the choice.

The applicable conditions of the filter material are the key basis for determining which side to place it on.

Humidity sensitive media. If the performance of the selected filter material decreases in a high-humidity environment, it is recommended to place it in front of the surface cooler to avoid the high-humidity environment after the surface cooler. The air temperature before the surface cooler is higher, but the relative humidity is usually lower than after the surface cooler.

Temperature sensitive media. If the performance of the filter material decreases or its aging accelerates at high temperatures, it is recommended to place it behind a surface cooler and take advantage of the cooled air conditions. But pay attention to the humidity problem behind the surface cooler.

Comprehensive judgment is required. Some media are sensitive to both temperature and high humidity. At this time, it may be necessary to re-evaluate the filter material selection, or consider setting up pretreatment before and after the surface cooler. For specific selection methods, please refer to Discussion on why chemical filters should be selected according to target gases .

Confirm applicable conditions with supplier. The performance of the medium under different temperature and humidity conditions should be obtained from product data or supplier confirmation, rather than inferred from experience.

Guaranteed inspection and replacement

Regardless of whether it is installed before or after the surface cooler, the maintenance conditions must be confirmed during the planning stage.

Sampling point location. Sampling ports should be set up before and after the filtration section to facilitate tracking changes in outlet concentration. The sampling port should be located away from surface coolers, humidifiers and other equipment to ensure that the air before and after the filter section is collected. For specific methods, please refer to Discussion of sampling points for chemical filter performance verification .

Replace channel. The replacement cycle of the chemical filter section is different from that of the particle filter section. The replacement channel and maintenance space must be reserved during the design stage. If the filter section is blocked by other equipment, maintenance costs will increase.

Differential pressure monitoring. Pressure difference monitoring is set up before and after the filtration section to track resistance changes. However, it should be noted that the resistance change of the chemical filter does not necessarily reflect the consumption of gas processing capacity and needs to be combined with outlet concentration detection. For specific differences, please refer to Discussion on whether the chemical filter can be replaced based on the pressure difference .

System resistance accounting. Adding a chemical filtration section will increase the total system resistance. When selecting a fan, it is necessary to add up the initial resistance and final resistance of filters at all levels to confirm that the working point is acceptable. For specific methods, please refer to Discussion of how much the added resistance of the chemical filter will increase the fan's electricity consumption .

Project judgment example

A certain MAU project needs to add a chemical filtration section to the fresh air section to process the acid gas input from the outside.

The preliminary plan considers placing it behind the surface cooler and using the cooled air to extend the life of the medium. However, the inspection found that the MAU's surface cooler had a mediocre water removal effect, the relative humidity of the air behind the surface cooler was close to saturation, and there were droplets entrained in some locations.

Adjustment plan: Place the chemical filter section in front of the surface cooler to avoid high humidity environments. At the same time, medium-efficiency pre-filtration is retained before the filter section to reduce dust coverage of the media. After the system resistance was recalculated, the fan operating point was confirmed to be acceptable. After operation, check the outlet concentration to confirm that the acid gas treatment effect meets the requirements.

This case illustrates: The selection of the front and rear surface coolers should be comprehensively judged based on the risk of droplets and the applicable conditions of the filter material. involving When selecting MAU box-type chemical filters , it is recommended to provide temperature and humidity data and system conditions to the supplier for verification.

Key points for selection and acceptance inspection

About Aili Industrial’s MAU chemical filtration package

The core of the location selection of the MAU chemical filtration section is to match the inlet pollution, temperature and humidity conditions, filter material suitability and system conditions.

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 air supply equipment. For the MAU project, fresh air detection data, temperature and humidity conditions, filter section location and replacement space can be combined to assist in checking the media type and structural configuration. 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 fresh air data, temperature and humidity conditions and system requirements when inquiring will help confirm the appropriate filter section location and configuration. The specific selection is subject to the technical documents and test results confirmed by the project.