Primary Medium And HEPA Filter

Introduction of primary filter
The primary filter is suitable for primary filtration of air conditioning systems and is mainly used to filter dust particles above 5μm. The primary filter has three styles: plate type, folding type and bag type. The outer frame material is paper frame, aluminum frame, galvanized iron frame, filter material is non-woven fabric, nylon mesh, activated carbon filter material, metal hole net, etc. The net has double-sided sprayed wire mesh and double-sided galvanized wire mesh.”
Primary filter features: low cost, light weight, good versatility and compact structure. Mainly used for: pre-filtration of central air conditioning and centralized ventilation system, pre-filtration of large air compressor, clean return air system, pre-filtration of local HEPA filter device, HT high temperature resistant air filter, stainless steel frame, high temperature resistance 250-300 °C Filtration efficiency.
This efficiency filter is commonly used for primary filtration of air conditioning and ventilation systems, as well as for simple air conditioning and ventilation systems that require only one stage of filtration.
G series coarse air filter is divided into eight varieties, namely: G1, G2, G3, G4, GN (nylon mesh filter), GH (metal mesh filter), GC (activated carbon filter), GT (HT high temperature resistant coarse filter).

Primary filter structure
The outer frame of the filter consists of a sturdy waterproof board that holds the folded filter media. The diagonal design of the outer frame provides a large filter area and allows the inner filter to adhere tightly to the outer frame. The filter is surrounded by special adhesive glue to the outer frame to prevent air leakage or damage due to windage pressure.3The outer frame of the disposable paper frame filter is generally divided into a general hard paper frame and a high-strength die-cut cardboard, and the filter element is pleated fiber filter material lined with a single-sided wire mesh. Beautiful appearance. Rugged construction. Generally, the cardboard frame is used to manufacture non-standard filter. It can be used in any size filter production, high strength and not suitable for deformation. High-strength touch and cardboard are used to manufacture standard-size filters, featuring high specification accuracy and low aesthetic cost. If imported surface fiber or synthetic fiber filter material, its performance indicators can meet or exceed the import filtration and production. 
The filter material is packed into a high-strength felt and cardboard in a folded form, and the windward area is increased. The dust particles in the inflowing air are effectively blocked between the pleats and the pleats by the filter material. Clean air flows evenly from the other side, so the airflow through the filter is gentle and uniform. Depending on the filter material, the particle size it blocks varies from 0.5 μm to 5 μm, and the filtration efficiency is different !

Medium filter overview
The medium filter is an F series filter in the air filter. F series medium efficiency air filter is divided into two types: bag type and F5, F6, F7, F8, F9, non-bag type including FB (plate type medium effect filter), FS (separator type) Effect filter, FV (combined medium effect filter). Note: (F5, F6, F7, F8, F9) is the filtration efficiency (colorimetric method), F5: 40~50%, F6: 60~70%, F7: 75~85%, F9: 85~95%.

Medium filters are used in industry:
Mainly used in central air conditioning ventilation system for intermediate filtration, pharmaceutical, hospital, electronics, food, and other industrial purification; can also be used as HEPA filtration front-end filtration to reduce high-efficiency load and prolong its service life; due to the large windward surface, Therefore, the large amount of air dust and low wind speed are considered to be the best medium filter structures at present.

Medium filter features
1. Capture 1-5um of particulate dust and various suspended solids.
2. Large amount of wind.
3. The resistance is small.
4. High dust holding capacity.
5. Can be used repeatedly for cleaning.
6. Type: frameless and framed.
7. Filter material: special non-woven fabric or glass fiber.
8. Efficiency: 60% to 95% @1 to 5um (colorimetric method).
9. Use the highest temperature, humidity: 80 ℃, 80%. k

HEPA filter) K& r$ S/ F7 Z5 X; U
It is mainly used to collect particulate dust and various suspended solids below 0.5um. Ultra-fine glass fiber paper is used as the filter material, and the offset paper, aluminum film and other materials are used as the split plate, and are glued with the aluminum frame aluminum alloy. Each unit is tested by the nano-flame method and has the characteristics of high filtration efficiency, low resistance and large dust holding capacity. HEPA filter can be widely used in optical air, LCD liquid crystal manufacturing, biomedical, precision instruments, beverages, PCB printing and other industries in the dust-free purification workshop air conditioning end air supply. Both HEPA and ultra-HEPA filters are used at the end of the clean room. They can be divided into: HEPA separators, HEPA separators, HEPA airflow, and ultra-HEPA filters.
There are also three HEPA filters, one is an ultra-HEPA filter that can be purified to 99.9995%. One is an antibacterial non-separator HEPA air filter, which has an antibacterial effect and prevents bacteria from entering the clean room. One is a sub-HEPA filter, which is often used for less demanding purification space before being cheap. T. p0 s! ]$ D: h” Z9 e

General principles for filter selection
1. Import and export diameter: In principle, the inlet and outlet diameter of the filter should not be less than the inlet diameter of the matched pump, which is generally consistent with the inlet pipe diameter.
2. Nominal pressure: Determine the pressure level of the filter according to the highest pressure that may occur in the filter line.
3. the choice of the number of holes: mainly consider the particle size of the impurities to be intercepted, according to the process requirements of the media process. The size of the screen that can be intercepted by various specifications of the screen can be found in the table below.
4. Filter material: The material of the filter is generally the same as the material of the connected process pipe. For different service conditions, consider the filter of cast iron, carbon steel, low alloy steel or stainless steel.
5. filter resistance loss calculation: water filter, in the general calculation of the rated flow rate, the pressure loss is 0.52 ~ 1.2kpa.* j& V8 O8 t/ p$ U& p t5 q
　　　　
HEPA asymmetric fiber filter
The most common method for mechanical filtration of sewage treatment, according to different filter media, mechanical filtration equipment is divided into two types: particulate media filtration and fiber filtration. Granular media filtration mainly uses granular filter materials such as sand and gravel as filter media, through the adsorption of particulate filter materials and The pores between the sand particles can be filtered by the solid suspension in the water body. The advantage is that it is easy to backflush. The disadvantage is that the filtration speed is slow, generally not more than 7m/h; the amount of interception is small, and the core filter layer only has the surface of the filter layer; Low precision, only 20-40μm, not suitable for rapid filtration of high turbidity sewage.
The HEPA asymmetric fiber filter system uses asymmetric fiber bundle material as the filter material, and the filter material is asymmetric fiber. On the basis of the fiber bundle filter material, a core is added to make the fiber filter material and the particulate filter material. Advantages, due to the special structure of the filter material, the porosity of the filter bed is quickly formed into a large and small gradient density, so that the filter has a fast filtration speed, a large amount of interception, and easy backwashing. Through special design, the dosing, The mixing, flocculation, filtration and other processes are carried out in a reactor, so that the equipment can effectively remove the suspended organic matter in the aquaculture water body, reduce the water body COD, ammonia nitrogen, nitrite, etc., and is particularly suitable for filtering the suspended solids in the circulating water of the holding tank.

Efficient asymmetric fiber filter range:
1. Aquaculture circulating water treatment;
2. Cooling circulating water and industrial circulating water treatment;
3. Treatment of eutrophic water bodies such as rivers, lakes, and family waterscapes;
4. Reclaimed water.7 Q! \. h1 F# L

HEPA asymmetric fiber filter mechanism:
Asymmetric fiber filter structure
The core technology of the HEPA automatic gradient density fiber filter adopts asymmetric fiber bundle material as the filter material, one end of which is a loose fiber tow, and the other end of the fiber tow is fixed in a solid body with a large specific gravity. When filtering, the specific gravity is large. The solid core plays a role in the compaction of the fiber tow. At the same time, due to the small size of the core, the uniformity of the void fraction distribution of the filter section is not greatly affected, thereby improving the fouling capacity of the filter bed. The filter bed has the advantages of high porosity, small specific surface area, high filtration rate, large interception amount and high filtration precision. When the suspended liquid in the water passes through the surface of the fiber filter, it is suspended under van der Waals gravitation and electrolysis. The adhesion of solid and fiber bundles is much greater than the adhesion to quartz sand, which is beneficial to increase the filtration speed and filtration precision.

During backwashing, due to the difference in specific gravity between the core and the filament, the tail fibers disperse and oscillate with the backwash water flow, resulting in a strong drag force; the collision between the filter materials also exacerbates the fiber’s exposure in the water. The mechanical force, the irregular shape of the filter material causes the filter material to rotate under the action of the backwash water flow and the air flow, and strengthens the mechanical shear force of the filter material during the backwashing. The combination of the above several forces results in adhesion to the fiber. The solid particles on the surface are easily detached, thereby improving the cleaning degree of the filter material, so that the asymmetric fiber filter material has the backwash function of the particulate filter material.+ l, c6 T3 Z6 f4 y

The structure of the continuous gradient density filter bed on which the density is dense:
The filter bed composed of the asymmetric fiber bundle filter material exerts resistance when the water flows through the filter layer under the compaction of the water flow. From top to bottom, the head loss is gradually reduced, the water flow speed is faster and faster, and the filter material is compacted. Increasingly high, the porosity is getting smaller and smaller, so that a continuous gradient density filter layer is automatically formed along the water flow direction to form an inverted pyramid structure. The structure is very favorable for the effective separation of suspended solids in water, that is, the particles desorbed on the filter bed are easily trapped and trapped in the filter bed of the lower narrow channel, achieving uniformity of high filtration speed and high precision filtration, and improving the filter. The amount of interception is extended to extend the filtration cycle.

HEPA filter features
1. High filtration precision: the removal rate of suspended solids in water can reach more than 95%, and it has certain removal effect on macromolecular organic matter, virus, bacteria, colloid, iron and other impurities. After good coagulation treatment of treated water, When the inlet water is 10 NTU, the effluent is below 1 NTU;
2. The filtration speed is fast: generally 40m / h, up to 60m / h, more than 3 times the ordinary sand filter;
3. Large amount of dirt: generally 15 ~ 35kg / m3, more than 4 times the ordinary sand filter;
4. The water consumption rate of backwashing is low: the water consumption of backwashing is less than 1~2% of the periodic water filtering amount;
5. Low dosage, low operating costs: due to the structure of the filter bed and the characteristics of the filter itself, the flocculant dosage is 1/2 to 1/3 of the conventional technology. The increase in cycle water production and the operating cost of tons of water will also decrease;
6. Small footprint: the same amount of water, the area is less than 1/3 of the ordinary sand filter;
7. Adjustable. Parameters such as filtration accuracy, interception capacity, and filtration resistance can be adjusted as needed;
8. The filter material is durable and has a service life of more than 20 years.” r! O4 W5 _, _3 @7 `& W) r- g.

Process of HEPA filter
The flocculating dosing device is used to add flocculating agent to the circulating water, and the raw water is pressurized by the boosting pump. After the flocculating agent is stirred by the pump impeller, the fine solid particles in the raw water are suspended and the colloidal substance is subjected to microflocculation reaction. The flocs having a volume greater than 5 microns are generated and flow through the filtration system piping into the HEPA asymmetric fiber filter, and the flocs are retained by the filter material.

The system uses gas and water combined flushing, backwashing air is provided by the fan, and backwashing water is provided directly by tap water. The system’s wastewater (HEPA automatic gradient density fiber filter backwash wastewater) is discharged into the wastewater treatment system.

HEPA filter leak detection
Commonly used instruments for HEPA filter leak detection are: dust particle counter and 5C aerosol generator.
Dust particle counter
It is used to measure the size and number of dust particles in a unit volume of air in a clean environment, and can directly detect a clean environment with a cleanliness level of tens to 300,000. Small size, light weight, high detection accuracy, simple and clear function operation, microprocessor control, can store and print measurement results, and test the clean environment is very convenient.

5C aerosol generator
The TDA-5C aerosol generator produces consistent aerosol particles of various diameter distributions. The TDA-5C aerosol generator provides sufficient challenging particles when used with an aerosol photometer such as TDA-2G or TDA-2H. Measure high efficiency filtration systems.

4. Different efficiency representations of air filters
When the dust concentration in the filtered gas is expressed by the weight concentration, the efficiency is the weighting efficiency; when the concentration is expressed, the efficiency is the efficiency efficiency; when the other physical quantity is used as the relative efficiency, the colorimetric efficiency or Turbidity efficiency, etc.
The most common representation is the counting efficiency expressed by the concentration of dust particles in the inlet and outlet airflow of the filter.

1. Under the rated air volume, according to the national standard GB/T14295-93 “air filter” and GB13554-92 “HEPA air filter”, the efficiency range of different filters is as follows:
A coarse filter, for ≥5 micron particles, filtration efficiency 80>E≥20, initial resistance ≤50Pa.
Medium filter, for ≥1 micron particles, filtration efficiency 70>E≥20, initial resistance ≤80Pa.
HEPA filter, for ≥1 micron particles, filtration efficiency 99>E≥70, initial resistance ≤100Pa.
Sub-HEPA filter, for ≥0.5 micron particles, filtration efficiency E≥95, initial resistance ≤120Pa.
HEPA filter, for ≥0.5 micron particles, filtration efficiency E≥99.99, initial resistance ≤220Pa.
Ultra-HEPA filter, for ≥0.1 micron particles, filtration efficiency E≥99.999, initial resistance ≤280Pa.

2. Since many companies now use imported filters, and their methods of expressing efficiency are different from those in China, for the sake of comparison, the conversion relationship between them is listed as follows:
According to European standards, the coarse filter is divided into four levels (G1~~G4):
G1 efficiency For particle size ≥ 5.0 μm, filtration efficiency E ≥ 20% (corresponding to US Standard C1).
G2 efficiency For particle size ≥ 5.0μm, filtration efficiency 50> E ≥ 20% (corresponding to US standard C2 ~ C4).
G3 efficiency For particle size ≥ 5.0 μm, filtration efficiency 70 > E ≥ 50% (corresponding to US standard L5).
G4 efficiency For particle size ≥ 5.0 μm, filtration efficiency 90 > E ≥ 70% (corresponding to US standard L6).

The medium filter is divided into two levels (F5~~F6):
F5 Efficiency For particle size ≥1.0μm, filtration efficiency 50>E≥30% (corresponding to US standards M9, M10).
F6 Efficiency For particle size ≥1.0μm, filtration efficiency 80>E≥50% (corresponding to US standards M11, M12).

The HEPA and medium filter is divided into three levels (F7~~F9):
F7 Efficiency For particle size ≥1.0μm, filtration efficiency 99>E≥70% (corresponding to US standard H13).
F8 Efficiency For particle size ≥1.0μm, filtration efficiency 90>E≥75% (corresponding to US standard H14).
F9 Efficiency For particle size ≥1.0μm, filtration efficiency 99>E≥90% (corresponding to US standard H15).

The sub-HEPA filter is divided into two levels (H10, H11):
H10 Efficiency For particle size ≥ 0.5μm, filtration efficiency 99> E ≥ 95% (corresponding to US standard H15).
H11 Efficiency The particle size is ≥0.5μm and the filtration efficiency is 99.9>E≥99% (corresponding to American Standard H16).

The HEPA filter is divided into two levels (H12, H13):
H12 Efficiency For particle size ≥ 0.5μm, filtration efficiency E ≥ 99.9% (corresponding to US standard H16).
H13 Efficiency For particle size ≥ 0.5μm, filtration efficiency E ≥ 99.99% (corresponding to US standard H17).

5.Primary\medium\HEPA air filter selection
The air filter should be configured according to the performance requirements of different occasions, which is determined by the choice of primary, medium and HEPA air filter. There are four main characteristics of the evaluation air filter:
1. air filtration speed
2. air filtration efficiency
3. air filter resistance
4. air filter dust holding capacity

Therefore, when selecting the initial /medium/HEPA air filter, the four performance parameters should also be selected accordingly.
①Use a filter with a large filtration area.
The larger the filtration area, the lower the filtration rate and the smaller the filter resistance. Under certain filter construction conditions, it is the nominal air volume of the filter that reflects the filtration rate. Under the same cross-sectional area, it is desirable that the larger the rated air volume is allowed, and the lower the rated air volume, the lower the efficiency and the lower the resistance. At the same time, increasing the filtration area is the most effective means of extending the life of the filter. Experience has shown that filters for the same structure, the same filter material. When the final resistance is determined, the filter area is increased by 50% and the filter life is extended by 70% to 80% [16]. However, considering the increase in the filtration area, the structure and field conditions of the filter must also be considered.　　

②Reasonable determination of filter efficiency at all levels.
When designing the air conditioner, first determine the efficiency of the last-stage filter according to actual requirements, and then select the pre-filter for protection. To properly match the efficiency of each level of filter, it is good to utilize and configure the optimal filtration particle size range of each of the coarse and medium efficiency filters. The choice of pre-filter should be determined based on factors such as the use environment, spare parts costs, operating energy consumption, maintenance costs and other factors. The lowest count filtration efficiency of air filter with different efficiency levels for different sizes of dust particles is shown in Figure 1. It usually refers to the efficiency of a new filter without static electricity. At the same time, the configuration of the comfort air conditioning filter should be different from the purification air conditioning system, and different requirements should be put on the installation and leakage prevention of the air filter.

③The resistance of the filter mainly consists of the filter material resistance and the structural resistance of the filter. The filter ash resistance increases, and the filter is scrapped when the resistance increases to a certain value. The final resistance is directly related to the service life of the filter, the range of system air volume changes, and the system energy consumption. Low-efficiency filters often use coarse fiber filter materials with a diameter greater than 10/., tm. The inter-fiber gap is large. Excessive resistance may blow up the ash on the filter, causing secondary pollution. At this time, the resistance is not Increase again, the filtration efficiency is zero. Therefore, the final resistance value of the filter below G4 should be strictly limited.

④The dust holding capacity of the filter is an indicator directly related to the service life. In the process of dust accumulation, the filter with low efficiency is more likely to show the characteristics of increasing initial efficiency and then decreasing. Most of the filters used in general comfort central air conditioning systems are disposable, they are simply not cleanable or economically not worth cleaning.