In many industrial fields, the air intake filters are cylindrical, which I often call cartridge or cylindrical filters.
While cooperating with many customers and solving the problems they encountered, I thought it was necessary to write this article to help people with the same problem.
Principle: How do the air intake cartridge filters work?
The air intake cartridge filter is like a “mask.” It has no power itself. The power comes from the negative pressure at the suction port of compressors, gas turbines, and other equipment.
Under suction negative pressure, the intake filter sucks in air from the surrounding environment. When the air enters, it will be filtered through the filter cartridge.
Some of the larger dust particles in the air settle to the bottom of the filter under gravity and inertial force. Fine dust particles are deposited on the surface of the filter material of the filter cartridge through the combined effects of Brownian diffusion and fiber interception.
After a period of dust accumulation on the filter cartridge, the resistance increases.
Backflush
When the resistance reaches the set value, the pulse backflush system starts, and the backflush gas impacts the filter cartridge from the inside of the filter cartridge. The dust on the filter cartridge is shaken off, and the resistance will decrease.
The filtered air enters the clean air chamber and is sent through the air outlet pipe to compressors, turbines, and other equipment.
Problems encountered so far for intake cartridge filters
For high-speed running machines such as compressors and turbines, particles and dust are some of the things that affect the long-term regular operation of the equipment. Expensive aerodynamic equipment is critical equipment that must operate all year round.
To ensure that they operate trouble-free and efficiently and to minimize the number of downtimes and maintenance workload, it is necessary to install air filters at the air suction intake to reduce the damage to equipment caused by dust.
According to feedback from some customers and my project experience from the actual situation, there are still many problems in the selection and use of the inlet filter cartridge, and I list them in the following:
5 issues for selecting and using air intake cartridge filters
1. No pre-filtration
Large particles(particle size ≥5um) impact the filter cartridge and airflow channel, causing surface wear. The service life of the filter cartridge is very short, and the filter cartridge is easily damaged.
2. The filter cartridge has low precision
Small dust particles (particle size <5um) form a solid scale inside the equipment. These scales affect the airflow movement, causing the equipment operating efficiency to decrease, causing the “surge curve” to drift, and sometimes destroying the “dynamics balance.”
3. The filter cartridge cannot prevent corrosive dust
Corrosive dust leads to chemical corrosion of the equipment and shortens the service life of the filter cartridge and equipment.
4. The filter cartridge has poor moisture-proof performance
The filter cartridge cannot recover in time after getting damp, and the intake filter continues to run with high resistance, which reduces the operating efficiency of the equipment and increases energy consumption.
5. Poor air permeability of the filter cartridge
Under the same precision conditions, many filter cartridges with poor air permeability will cause the resistance to rise rapidly, causing high energy consumption, short service life of the filter cartridge, and high overall operating costs.
Before we address these issues, let’s first look at what factors to consider when choosing an air intake filter cartridge.
5 factors to consider when choosing an air intake cartridge filter
The selection of the inlet filter cartridge involves many aspects, not only the filter cartridge itself but also the entire system design. Therefore, when selecting a filter cartridge, you should refer to the air volume, surrounding environment, pre-filtration, etc.
1. Conditions required for actual operation
Mainly consider the working conditions of different types of compressors and gas turbines, the expected pressure loss (pressure drop) for operation, the filtration wind speed and efficiency of the filter cartridge, the size of the target particle pollutants for filtration, dust holding capacity, dust holding type (surface filtration or deep filtration), etc. Each item here needs to be considered during design.
2. Processing air volume design
From the perspective of use effect, of course, the larger the air volume to be processed, the better. Conservative air filter designs are often seen in air compressors and gas turbine intake filters.
The intake filter matching to increase the air volume is generally designed to be 2 times larger. Sometimes, the design is even larger considering the use effect, but many users didn’t do it well.
Some owners pay more attention to the initial investment cost, so sometimes, users complain about the short service life of the filter cartridge. The reason is that the intake filter matching needs to be bigger.
3. Design of filter cartridge
The design mainly considers the installation method, filter area, filter cartridge protective net, sealing ring, filter material selection, etc. Each of these items has different requirements.
The installation method involves spatial location, maintenance, and replacement.
The filter area will affect the filtered air volume.
The filter cartridge protective fence is related to backflush and filter cartridge strength.
The sealing gasket will affect the stability of the sealing performance of the filter cartridge.
The selection of filter cartridge materials will affect the service life of the entire filter cartridge, filtration accuracy, etc.
Therefore, each choice has its detailed considerations, rather than a rigid filter cartridge that can be suitable for all working conditions.
4. Surrounding environment
The surrounding environment needs to take into account two aspects,
One is the objective climate around you. For example, changing seasons, deserts, coastal areas, cities, severe cold, and other different environments will all impact the choice of filter cartridges.
Another environment is to consider the related enterprises surrounding the use scene (such as thermal power plants, water towers, chemical plants, etc.), agricultural activities, wind direction (windward, leeward), and the height of the air intake from the ground (Local air currents due to buildings and topography), these need to be considered in design selection.
5. Multi-stage filtration
Multi-stage filtration involves pre-filtration and back-end high-efficiency filtration.
In many cases, it is challenging to complete the filtration requirements with a one-stage filter cartridge alone, such as catkins, insects, sandstorms, moisture, fog, rain, salt, snow, Smoke, and other conditions require the selective addition of pre-filtration such as climate covers, screens, inertial separators, moisture coalescers, metal protection nets, and non-woven cotton.
If the air intake requirement is H11-H13 or higher, you can add a three-stage HEPA filter. Adding multi-stage filtration can protect the filter cartridge and increase its service life. It is the most practical way of designing the current intake air filter.
A set of properly designed intake filters can complete the filtration task efficiently and save users costs.
After analyzing these factors, let’s see how to choose the filter cartridge for the air intake.
6 Expert Tips for Choosing an Air Intake Cartridge Filter
Similarly, I summarized 6 tips and wrote them in this section.
Tip1. Be aware of the Installation method
There are many ways to install the filter cartridge of the inlet filter, mainly including small hole hoisting type, vertical chuck type, vertical three-claw rotary type, and horizontal type.
The small hole hoisting type has a simple structure but is troublesome to install and maintain.
The vertical chuck type is relatively large but easy to install and maintain.
The vertical three-claw type is easy to install but requires high sealing performance.
The horizontal type is easy to install and maintain and is small in size, but there are certain dead spots in the filtration.
No matter which installation method is used, it has advantages and disadvantages. There is no best method. You can achieve the best results by choosing the most appropriate installation method.
Tip2. Understand different filter materials
Filtration materials are mainly divided into three categories: glass fiber, polyester fiber, and wood pulp fiber.
Glass fiber has outstanding advantages, such as high filtration precision, strong moisture resistance, and good air permeability. However, its low burst resistance (only 3Kpa) cannot be used as a backflush pulse filter material.
Polyester fiber has good tear resistance but poor air permeability and is rarely used for intake filtration.
The currently used air intake filter mainly uses wood pulp fiber, mixed materials of wood pulp fiber, and other fibers like nano filter materials.
Only a few companies, such as the American HV Company and the American Ahlstrom Company, can produce some of these high-efficiency filter materials.
According to different usage conditions, inlet filter materials are selected in a targeted manner:
In humid working conditions, the filter material must be hydrophobic.
Under severe operating conditions, the filter element can quickly become clogged due to sticky synthetic dust such as hydrocarbons (oil mist and soot).
The pressure recovery after the pulse cleaning process must be sufficient; in salt-corrosive working conditions, the filter material must ensure that salt cannot penetrate the host and cause corrosion.
You can consult a professional filter cartridge manufacturer for different usage environments.
Tip3. Air intake in desert working conditions
The desert weather is hot, the environment is dry, and there are often strong winds. The dust particles are of various sizes, and the dust concentration is high.
When selecting a filter cartridge, you should consider that it can filter tiny particles, has high filtration efficiency, good hydrophobicity, and can be pulsed backflushed.
My filter material recommendations are wood pulp fiber + fine fiber (layered technology or coating technology), wood pulp fiber + synthetic fiber, and nano filter material.
Tip4. Air intake in Offshore platforms
Seawater’s salt concentration is high, highly corrosive, and destructive to equipment components. Moreover, the humidity at sea is high, and there is sometimes heavy fog. In this environment, the requirements for the intake cartridge filter are very high.
I suggest choosing a filter cartridge with a medium/high-efficiency level, excellent hydrophobicity, pulse backflushing, and nano filter material.
Tip5. Air intake in coastal areas
These areas mainly have high humidity, and the moisture in the air has exceptionally high requirements on the moisture resistance of the cartridge filter. Moreover, the environment in such areas will also be salt-corrosive.
In this regard, I suggest choosing a medium-efficiency filter cartridge with good hydrophobicity and pulse backflushing. The filter material should be wood pulp + synthetic fiber with excellent hydrophobicity or nanofiltration material.
Tip6. Air intake in City
In cities, pollutant gases such as factory exhaust gas and automobile exhaust emissions are significant in amount and complex types.
Choosing a filter cartridge with high hydrocarbon dust holding capacity, good hydrophobicity, and high filtration efficiency for tiny dust particles is recommended.
The filter material can be wood pulp fiber + fine fiber (layered or spraying technology), wood pulp fiber + synthetic fiber + glass fiber, or nano filter material.
Summary
The inlet filter cartridge is a vital part of the entire filtration system; in actual use, many accidents have been caused by improper selection of inlet cartridge filters or poor quality filter cartridges. Therefore, only choosing the correct intake cartridge filter can prevent such accidents.
