1. Introduction to the principle of air inlet filter
The air inlet filter is a "mask" that has no power itself and is powered by negative pressure from the suction ports of compressors, gas turbines, and the like. Under the suction negative pressure, the inlet filter draws in the air in the surrounding environment. When the air enters the filter, it will be filtered through the filter cartridge. Some of the larger particulate dust in the air settles to the filter under the action of gravity and inertia. At the bottom, fine dust particles are deposited by the Brownian diffusion and fiber interception on the filter cartridge to deposit dust on the filter surface of the filter cartridge. After a period of ash accumulation on the filter cartridge, the resistance rises. 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, and the resistance will be decline,. The filtered gas enters the clean room and is then sent out to the compressor, steam turbine, etc. by the air outlet.
2. Status of air inlet to filter cartridge
For high-speed machines such as compressors and steam turbines, dust and dust are one of the reasons that affect the normal operation of the equipment for a long period of time. Expensive aerodynamic equipment is a key device that must operate year round. In order to ensure their unobstructed and efficient operation and minimize the number of downtimes and maintenance work, air filters should be installed at the air intake to reduce the damage of the equipment caused by dust. Although the inlet filter is very important, from the actual use, there are still many problems in the selection and use of the inlet filter cartridge, mainly reflecting the following problems:
For high-speed machines such as compressors and gas turbines, dust and dust are one of the reasons that affect the long-term operation of the equipment. Expensive aerodynamic equipment is a key device that must operate year round. In order to ensure their trouble-free, high-efficiency operation and minimize the number of downtimes and maintenance workload, air filters should be installed at the air intake to reduce the damage of the equipment caused by dust. Although the inlet filter is very important, from the actual use, there are still many problems in the selection and use of the inlet filter cartridge, mainly reflecting the following problems:
1 No pre-filtration: Large particles of dust (particle size ≥ 5um) impinge on the filter cartridge and airflow path, causing surface wear. The filter cartridge has a short service life and the filter cartridge is easily damaged.
2 The filter cartridge has low precision: small particle dust (particle size <5um) forms a solid scale inside the device. These scales affect the airflow movement, resulting in reduced equipment operating efficiency, causing the "surge curve" to drift and sometimes destroying " Dynamic balance."
3 Filter cartridges are not resistant to corrosive dust: Corrosive dust causes chemical corrosion of the equipment and shortens the service life of the filter cartridges and equipment.
4 The filter cartridge has poor moisture resistance: the filter cartridge cannot be recovered in time after being wet, and the inlet filter continues to operate with high resistance, which makes the operation efficiency of the equipment lower and the energy consumption is high.
5 Filter cartridge has poor air permeability: Under the same precision, many poorly permeable filter cartridges will increase the resistance of the inlet filter, high energy consumption, short life of the filter cartridge and high overall operating cost.
3. Selection of air inlet filter cartridge
The selection of the inlet filter cartridge actually involves many aspects, not only the cartridge itself, but also the entire system design. Therefore, when selecting the filter cartridge, you should refer to the treatment air volume, surrounding environment, pre-filtering, 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), the filtration wind speed and efficiency of the filter cartridge, the size of the target particulate pollutants, and the dust holding capacity. , dust-proof form (surface filtration or deep filtration). Every item here needs to be considered when designing.
2) Handling air volume design: From the point of view of the effect of use, of course, the larger the amount of air handled, the better. Conservative designs are often seen in the design of air compressor and gas turbine inlet filters. Increase the matching of gas volume, generally according to 2 times design, sometimes considering the use effect will be designed more, but some owners pay more attention to the initial investment cost, so sometimes users complain that the filter cartridge has a short service life, in fact, the match is done too Small reason.
3) Design of filter cartridge: The design of the filter cartridge mainly considers the installation method, filter area, filter net, seal ring and filter cartridge selection, etc. Each item has different requirements. If the installation method involves space location, maintenance and replacement, the filter area will affect the filtered air volume. The filter cartridge protection net involves the backflushing and filter cartridge strength, and the sealing ring will affect the stability of the filter cartridge. The filter cartridge is selected. It will affect the life of the entire filter cartridge, filtration accuracy and so on. Therefore, every choice has its own detailed considerations, rather than a filter cartridge that can be applied to all conditions.
4) Surrounding environment: The surrounding environment needs to consider two aspects. One is the climate that exists objectively around, such as the changing season, desert, coastal, urban, severe cold and other different environments will have an impact on filter cartridge selection. Another environment is to consider surrounding related companies (such as: thermal power plants, water towers, chemical plants, etc.), agricultural activities, wind direction (windward, leeward), the height of the air intake from the ground (local airflow due to construction and terrain) These need to be considered in the design selection.
5) Multi-stage filtration: Multi-stage filtration involves pre-filtration and high-efficiency filtration at the back end. In many cases, it is difficult to complete the filtration requirements by filtering the first stage filter. For example, catkins, insects, sand, moisture, fog, rain, salt, snow, smoke, etc. need to selectively increase the climatic hood, screen, inertial separator, moisture coalescing, metal mesh, non-woven cotton, etc. . In the case of air intake requirements of H11-H13 or higher, you can choose to add a three-stage high efficiency filter. The addition of multi-stage filtration not only protects the filter and the filter cartridge, but also improves the service life of the filter cartridge. It is the most practical way to design the inlet filter.
Efficiency and cost are opposite when designing, so a well-designed inlet filter can not only efficiently complete the filtering task, but also save the user cost.
4, the choice of air inlet filter cartridge
First of all, there are many kinds of filter cartridge installation methods from the inlet filter, mainly including small hole lifting type, vertical chuck type, vertical three-claw rotary type and horizontal type. The small hole hoisting equipment has simple structure, but the installation and maintenance are troublesome; the vertical chuck type installation and maintenance is convenient, but the relative volume is large; the vertical three-jaw type installation is convenient, but the sealing performance is high; the horizontal installation and maintenance are convenient, and the volume is small But there is a certain dead angle on the filter cartridge. No matter which type of installation has its advantages and disadvantages, no one is the best way, only the most suitable filter installation method can choose the best effect. Therefore, for inlet filtration, it is also important to choose the filter installation method.
From the material, it is mainly divided into three categories: glass fiber, polyester fiber and wood pulp fiber. Glass fiber has the advantages of high precision, strong moisture resistance and good air permeability. However, because of its low bursting resistance (only 3kPa), it can not be used as a backflushing filter material; although polyester fiber has good fracture resistance, However, it is poor in gas permeability and is rarely used in inlet filtration. The filter element for air inlet filtration currently used mainly uses wood pulp fiber, mixed material of wood pulp fiber and other fibers, nano filter material and the like.
Filter media for high-efficiency filter cartridges for air inlet filtration are not yet available for production in the country, so they are mainly concentrated in HV Corporation of the United States and Ahlstrom Corporation of the United States. According to different working conditions, the selected inlet filter element is selected: in the case of humidity, the filter element must ensure the hydrophobicity, and the filter element can be easily blocked due to the bad working condition, because of the sticky synthetic dust, such as hydrocarbons ( Oil mist and soot); the pressure recovery after the pulse cleaning procedure must be sufficient; in the case of salt corrosive conditions, the filter element must ensure that the salt does not penetrate into the host to cause corrosion. Filtering this piece at the inlet, several filter media were specially selected to suit different working conditions.
4.1 Desert area
Mainly because the weather is hot, the environment is dry, and there are often strong winds. There are many types of dust particles in the dust, and the dust concentration is large. The main characteristics that should be considered in the filter material: 1 small particles, high filtration efficiency; 2 good hydrophobic properties; 3 can be pulse backflush, filter media recommended: 1 wood pulp fiber + fine fiber (layering technology or coating Technology), filter material type RHFD/234, RHFD/234FR; 2 wood pulp fiber + synthetic fiber, filter material type RHPE80/20; 3 nanometer filter material, filter material type RHNF/123.
4.2 offshore platform
The salt concentration in seawater is high, the salt is highly corrosive, the damage to equipment components is extremely strong, and the humidity at sea is large and sometimes there is heavy fog. In this environment, the requirements for the inlet filter are very high. The main features that should be considered for the filter media: 1 choice of medium / high efficiency level; 2 excellent hydrophobic properties; 3 pulse function. The filter material of the filter cartridge is recommended: nano filter material, filter material type RHNF/123.
4.3 coastal areas
Mainly due to the high humidity, the moisture in the air requires a particularly high moisture resistance of the filter element, and the environment in this area is also salt corrosive. The main features that should be considered for the filter media: 1 select the medium effect level; 2 the hydrophobic performance is good; 3 can be pulse backflush. The filter material of the filter cartridge is recommended: 1 wood pulp + synthetic fiber RHPE80/20 with excellent hydrophobic properties; 2 nanometer filter material, filter material type RHNF/123.
4.4 city
Polluted gases such as factory exhaust gas and automobile exhaust emissions have large amounts of dust and are complex in types. The main characteristics that should be considered about the filter material: 1 high hydrocarbon hydrogen dust holding capacity; 2 good hydrophobic properties; 3 pairs of fine dust particles, high filtration efficiency. The filter material of the filter cartridge is recommended: 1 wood pulp fiber + fine fiber (layering technology or spraying technology) filter material type RHFD/234; 2 wood pulp fiber + synthetic fiber + glass fiber, filter material type RHPE80/20; nano filter material , filter material type RHNF/123.
These filters are well-suited for use in the inlet filtration of various operating conditions and the use of targeted media in different environments. This not only ensures the efficiency of the inlet filtration, but also increases the life of the filter element.
5, summary
The inlet filter cartridge is a key part of the entire filtration system. It is similar to the “mask” of compressors, air compressors and gas turbine equipment. It can only be achieved by selecting the right and suitable inlet filtration equipment, filter element and filter material. . In reality, there have been many accidents caused by improper selection of inlet filters or the selection of inferior filter elements. Therefore, only the correct understanding of the inlet filtration equipment and filter elements can effectively prevent such accidents.