JPH07246347A - Bipolar charged filter - Google Patents

Abstract

PURPOSE: To provide an electrostatic filter apparatus and a method of filter treatment to realize a high collection efficiency by a low pressure drop filter and increase a dust load capacity substantially compared to a similar filter without bipolar charge action. CONSTITUTION: A bipolar electrostatic filter system included a negative high voltage source 4, a positive high voltage source 5, a filter 2 arranged at a downstream end of the system, and an ionizer 1 arranged at upstream end of the filter. The ionizer 1 includes a first set of ionizing wires connected to the negative high voltage source, a second set of ionizing wires connected to the positive high voltage source, and a cycle time relay to alternatingly activate the first set of ionizing wires with the negative high voltage source and the second set of ionized wires with the positive high voltage source.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the collection of particles such as dust, pollen, smoke or powder mixed in the air by using a filter, and particularly to the collection efficiency and dust of the media filter. It relates to the use of bipolar charging devices to increase load capacity.

[0002]

Filters have been used for air cleaning for many years. The collection efficiency of a filter is determined by many parameters such as fiber diameter, filter packing density, filter thickness, particle size, and air velocity.

Therefore, in order to increase the efficiency of removing particulates from the air at any operating speed, smaller fiber diameters may be employed, thicker fiber adsorption beds, higher packing densities or combinations thereof may be applied. . However, they all tend to cause a pressure drop across the filter. That is, in the filtration process using fibers (and fabrics), increasing the efficiency of the filter generally increases the pressure loss. Furthermore, such high pressure drop further restricts the air flow,
Further, further cost is required to maintain a constant flow velocity.

On the other hand, electrically charged fibers can attract airborne particles to the surface of the filter without any change in the mechanical properties of the filter, and such electrical force causes pressure through the filter. It is possible to increase its efficiency without increasing the descent. In other words, charging the filter results in higher efficiency at lower pressure drop, higher dust load capacity, higher air velocity and lower maintenance costs. Therefore, due to these advantages, research into electrical enhancement of filter performance has been done in the last few years.

That is, in recent years, it has become possible to use electric force to enhance the collection efficiency of the fabric filter. (1) By charging the fiber element, (2) in air By the charge of the particles, or (3)
By applying a constant electric field to the fibrous element, an electric field is created in the filter. As an example of a filter including such a charged fiber element, a Hansen filter and an electret filter (US Pat. No. 4,178,157) are used.
No.). That is, in the 1930s, Hansen found a remarkable improvement in the collection of submicron particles by subjecting a wool filter to powder treatment with pine or resin. This mechanism is mainly electrical. In this case, the resin particles having a diameter of about 1 micron are dispersed on the surface of the wool fiber having a diameter of 20 microns, and are negatively charged by contact or friction. This charge is then maintained by the high resistance of the resin, keeping the filter charged.

Electret filters, on the other hand, are made from fibers with separated corona charges in polypropylene. In this case, the polypropylene film is treated and charged between two opposing charging corona devices before fiberization. The electret fibers thus obtained have a rectangular cross section and become a permanently charged dielectric. Thus, the electret filter traps charged and uncharged particles by the Coulomb force and induces the particles to be bipolar. However, such electret filters tend to lose their charging effect in high humidity and high temperature environments. In addition, test results have been shown that when the surface of the fiber is coated with a deposit that shields its charge, its working effect is lost.

Therefore, a method has been studied in which particles are first charged and then they are removed by a fibrous filter.
In this case, the particles are charged by corona discharge before passing through the fibrous filter. The charged particles are then attracted by the image force to the uncharged inner surface of the filter, increasing its efficiency. However, when the charge accumulates on the surface of the fiber, it is repulsed by the Coulomb force between the same polarity charges on the fiber and particles in the air, and the particles move away from the surface of the fiber. As a result, the collection efficiency will eventually decrease.

Furthermore, the use of an externally applied electric field to enhance the filter efficiency is Iinoy.
a) and Makino. That is, by placing the fibers in a constant electric field,
The fibers are polarized and the electric field in the space around the fibers becomes non-uniform. Moreover, the uncharged particles in the non-uniform electric field are also polarized and subjected to a force towards this fiber. If the particle is electrically charged, a force is exerted on the charge of the particle by the electric field and the image force between the charged particle and the fiber. Thus, all of these increase the efficiency of the filter. The electric field applied to this filter is usually generated by placing a metal mesh screen, one of which has a high voltage and the other of which is grounded, on the upstream side and the downstream side of the filter. Furthermore, in order to obtain an improving effect with a significant difference, 15 or 20 kV
A voltage gradient of at least 1 inch / inch (5.9 to 7.9 kV / cm) is required. However, such specific specifications cannot capture conductive particles because current leakage and short-circuit phenomena occur very quickly.

On the other hand, the magnitude of the electric force in this case can be increased with a significant difference. For example, strength is 2
10 by electric field of 5 kV / inch (9.8 kV / cm)
The electric force acting on a 1-micron particle carrying 0 electrons is 3118 times the gravity acting on the same particle. Thus, the fibrous filter provided with the electrical attachment mechanism can significantly improve the efficiency as compared with the conventional fibrous filter.

[0010]

According to the present invention, a high collection efficiency can be realized by the low pressure drop filter, and further, the dust load capacity can be significantly increased as compared with the same filter without the bipolar charging action. An object of the present invention is to provide an electrostatic filter device and a filtering method that can be performed.

[0011]

SUMMARY OF THE INVENTION Embodiments of the present invention use bipolar charge media filters that provide high collection efficiency and high dust load capacity and have low pressure drop across the filter. Preferably, an ionizer comprising two arrays of ionization lines is used, with each array of ionization lines having a positive and a negative D.
It is connected to each of the C output power supply sources. In addition, the two power supplies act alternately. It should be noted that the power conversion is controlled by a repeating cycle time relay at adjustable time intervals. A media filter is also located downstream of the ionizer. The filter is a pleated bag filter or 2 inch (5 cm) or 4 inch (10 c
m) may be a panel filter or a filter of other shape, but the electric resistance of the filter material needs to be high enough to retain electric charges on the fiber surface. In the case of the present invention, a desirable filter having a high dielectric property includes a filter medium formed of a plastic material such as polypropylene or glass fiber.

[0012]

With the above arrangement, preferably only one of the ionization line arrays is powered at any given time of operation. For example, if the positive power supply is operating at a certain time, all particles in the air passing through the ionizer will be positively charged. Furthermore, as these particles pass through the media filter, most of the positively charged particles are trapped by the media filter. The charge is then retained on the fiber surface by the high resistance of the fiber material, positively charging the filter media. These positive charges continue to accumulate during the positive cycle.
The positive cycle then ends and the repetitive cycle time relay activates the negative power supply, causing the ionizer to enter the negative ionization cycle and negatively charge the particles. After that, the negatively charged particles receive a strong attractive force (Coulomb force) from the positively charged fiber surface, and the efficiency thereof is significantly improved. After that, these two types of cycles are repeated, respectively, and a permanent bipolar charging action occurs in the filter. Thus, high collection efficiency can be realized by the low pressure drop filter. Furthermore, the dust load capacity of the present invention can also be significantly increased compared to the same filter without the bipolar charging effect.

[0013]

The present invention will be described in detail based on the preferred embodiments illustrated in the accompanying drawings below.

FIG. 1 is a schematic diagram of each component used in the bipolar charging filter of the present invention.

In this case, the conventional pre-filter 3 is provided on the upstream side in order to capture large particles. It should be noted that air purifying systems are generally equipped with a prefilter to avoid premature overloading of the main filter system. However, for example, fine particles having a diameter of 5 microns or less pass through the coarse prefilter and enter the ionizer 1.

The ionizer 1 comprises two arrays of ionization lines 47 and 48, one of which is a positive output high voltage DC power supply 5 and the other of which is a negative output high voltage DC.
Each is connected to a voltage supply source 4. These two ionization line arrays 47, 48 are preferably not powered at the same time, and the repetition cycle time relay 6 is used to control the cycle time of both the positive and negative ionizations. That is, the adjustment knobs 11 and 12 are used to set the cycle times of both the positive and negative power supply sources, and these cycles can be arbitrarily continued until the power input to the relay 6 is cut off.

Alternatively, a single ionizer or ionization line array arrangement may be used with high voltage relays, which relays each array of ionization lines to a positive high voltage source 5 and The negative high voltage sources 4 are alternately connected.

Yet another embodiment uses a single ionizer or ionization line array configuration and a single high voltage power supply, the high voltage power supply having a positive high voltage and a negative high voltage. It is configured to alternately generate a voltage.

Further, a pleated bag filter 2 is arranged downstream of the ionizer 1 in order to collect particles. However, in the present invention, it is possible to use any medium filter regardless of size or shape, which is preferably formed of a high dielectric material. For example, the filter 2 may be a panel filter or a cylindrical cartridge filter. Further, the filter material may be polypropylene, polyethylene, or any other material with good dielectric properties.

Further, in the system, the fibrous bag filter 2 cannot initially carry any electric charge. However, when power is applied, either the negative power source 4 or the positive power source 5 is first excited.

For example, if the negative power supply source 4 is excited first, the negative power supply source 4 is excited to generate a high concentration (about 10 to 100 × 10 ⁶ pieces / cm ³ ).
Negative ions are generated in the ionizer 1. As a result, the particles in the air passing through the ionizer are negatively charged. After that, the negatively charged particles 7 are collected by the bag filter 2 by a mechanical collection mechanism such as inertial adhesion, blocking, diffusion, or an electric image force.

In this case, due to the high electrical resistance of the fibers, the charge accumulates on the deposited particles. As a result, the charge negatively charges the fiber. Thereafter, the negative charging process continues until the time relay 6 activates the positive power supply source 5 and shuts off the negative power supply source 4. Furthermore, as soon as this power conversion takes place, the particles passing through the ionizer 1 are positively charged. Then, the positively charged particles 8 react with the negatively charged fiber surface of the bag filter 2 due to the Coulomb force, and the reaction enhances the collection efficiency of the bag filter 2 with a significant difference. .

Tests have shown that this action increases the bag filter collection efficiency of 40% to 99%.
Further, when the positively charged particles 8 are deposited on the negatively charged bag filter 2, the entire electric charge in the bag filter 2 is neutralized at a constant rate. However, the two charge cycles can be set at different intervals, eg negative power cycle to twice the length of positive power cycle (or vice versa).
Can be set. Therefore, the amount of negative charges generated on the fiber surface is sufficiently larger than the amount of positive charges (or vice versa). In such a situation, the bug filter 2
Can always maintain a negative (or positive) charge state during its operation.

FIG. 2 is a top view of a filtration system using the bipolar charging filter of the present invention. In the figure, the pre-filter 3, the bipolar charged ionizer 1, the pleated bag filter 2, the motor 18, the blower 19 and the exhaust grill 20 are continuously shown along the air flow direction (arrow A). . Further, these components may be included in the metal cabinet 13. Also, the power supply and electrical control compartment 28 is mounted behind the access door 52, and opening the door activates the prefilter 3, ionizer 1, and bag filter 2. In this compartment 28, a power supply device 27, power indicating lights 24 and 26, a time relay 23, a main switch 25 and other necessary accessories are provided to form a complete system. In addition, the latch 30 is used to lock the access door 52 to the cabinet. Further, another access door 21 is provided for operating the blower part. It should be noted that although the blower system is shown here as being driven by belt 22, a direct drive blower can also be used. In addition, an electrical distribution box 17 is used for connecting the system with a power supply. That is, the high voltage output terminal is connected to the bipolar ionization device 1 from the power supply source by two high voltage contacts 29.
Connected through.

FIG. 3 is a front view of the same bipolar charge filter device as described above, with the access door and power supply compartment removed, showing a pre-filter 3, a bipolar ionizer 1 and a charge bag filter 2 in the cabinet. ,
The motor 18 and blower are clearly shown. The motor 18 and the blower 19 are both bolts and nuts 3.
1, 32 are attached to the cabinet.
In addition, electrical wiring 33 connects to the power supply and electrical control compartments for proper control and operation.

FIG. 4 is a top view of the bipolar ionizer. The four corner braces 35 are the ionization device 1
Used to hold the structure of. Further, the ground plate 41 is riveted to the brace 35. In addition, high voltage insulating member 36 is used to hold ionized wiring supports 39 and 40. The insulating member 36 is fixed to the brace 35 by screws 38. Thus, two arrays 47 and 48 of ionized wiring are formed.

FIG. 5 is a sectional view taken along the line AA of FIG. 4, showing one of the sets of ionized wirings 47 and 48.
In this case, the upper and lower ionized wiring supports 40, 4
6 and 39 and 54 hold the ionization wirings 47 and 48.

The ionized wires 47, 48 preferably have a diameter of about 7-10 mils (0.18-0.25 m).
It is a thin tungsten wire of m). These are cut into a certain length and wound so as to exhibit a spring action. Further, the crunch nut 44 is arranged at the end of the wiring. Also, preferably, each ionization wiring 4
One end of each of the wirings 7 and 48 is arranged in a slot formed in the upper support 40, and the wiring is extended to form a lower support 46.
Is in contact with the slot. In addition, the coiled tungsten wire is held at a position along the center line between two adjacent ground plates by the tension of the spring action.

Further, instead of the above-mentioned ionization wirings 47 and 48, another corona discharge type structure can be used. For example, instead of or in addition to ionized wiring, a corona discharge surface such as a sharp needle or spike formed on a thin metal sheet may be used.

When a high voltage is applied in such a structure, the ionization wirings 47 and 48 start corona discharge to charge the particles passing through the ionizer 1. In addition,
The two sets of ionization wirings 47 and 48 are separated and independent from each other. As described above, these wirings are connected to different power supply sources, one of which is the positive power supply source 5.
And the other one is the negative polarity power supply source 4. further,
The wires are powered at alternating timings to provide a bipolar effect.

FIG. 6 is a cross section taken along line BB of FIG.
One of the ground plates 41, the ionized wirings 47 and 48, the corner brace 35, the ionized wiring supports 39, 40 and 46,
An insulating member 36 for holding 54 and an insulating member 36 for holding the insulating member 36 on the brace 35, and an ionized wiring support 39,
A screw 38 is shown which holds 40, 46, 54 to the insulation member 36.

As shown in FIG. 5, the corner brace 35 is held at each end by end pieces 55. On the other hand, the end piece 55 is attached to the corner brace 35 by the bolt 5
6 or any other suitable means. Further, the ground plate 41 is attached to the corner brace 35 by the plate 42.

In this way, two sets of ionization wirings 47, 4 are provided.
Since 8 is connected to two different power supplies 4, 5 independently of each other, two separate ionizers as shown in FIG. 7 can also be used for the same purpose. It should be noted that such an array configuration can also be understood to be part of the present invention.

The present invention will be further described by the following experimental examples. DOP (dioctyl phthalate) by atomizer
Of droplets were generated and used in the device of the present invention. The collection efficiency of quartz microbalance (QCM) 10-stage cascade impactor (California Measure)
ent).

Fibrous bag filter (width 18 inches (46
cm) x 18 inches (46 cm) long x 12 inches (30 cm) thick placed in the test duct and its DOP
Collection efficiency was measured at an air flow rate of 1150 cfm. That is, when the DOP concentrations on the upstream side and the downstream side were measured, the collection efficiency was 40%. A bipolar charged ionizer was then installed in front of the bag filter. Also, time relay, negative power 60 seconds and positive power 3
After setting to supply in a cycle of 0 seconds, power supply was started. As a result, the output voltage and current measured in the negative power supply cycle are -11.8 kV and -1.8 m.
A was 12.2 kV and 1.9 mA in the positive power supply cycle. Then, when the ionizer was turned on, the DOP collection efficiency increased to 99%. That is, the bipolar charging action increased the efficiency with a significant difference.

Next, the effects of load capacity and pressure drop on the bipolar charging fibrous filter were investigated. A bipolar charge filter system of the type described in FIG. 2 was used for the test. Pollen was supplied to the system. Since the metal mesh prefilter cannot capture the fine powder, almost all pollen is sent to the ionizer and the bag filter.

FIGS. 8 and 9 show pressure drop curves and air flow rates in two identical bag filters, with and without operation of the bipolar charged ionizer. As shown in the figure, in the case of the bipolar charging filter, the amount of increase in pressure drop is small, the dust load capacity is large, and the flow velocity of air is high. It is believed that these apparent advantages are primarily due to the electrical deposition results.

Furthermore, the electrical force changes the form of particle deposition. That is, instead of blocking the porous portion of the fibrous filter, charged particles are deposited on top of each other to form a chain-shaped deposition pattern. Furthermore, these "dendrites" extend from the fiber surface to form minute irregularly shaped cylindrical bodies, which themselves are extremely effective collectors, and therefore the particle collection efficiency of the filter is significantly increased. To be And, since they do not block the porous part of the fiber in the same manner as when the ionizer is not used, they hardly cause an increase in pressure drop.

Further, the effect of dust loading capacity on efficiency was investigated. Place a bipolar charging filter in the test duct and add 1 pound (454 g) of pollen at 1100 cfm at a time.
It was supplied from the upstream side. At the end of each 1 lb dust load, DOP aerosol was generated to measure the DOP collection efficiency of the bipolar charge filter. In parallel with this, the same tests were carried out on another bag filter of the same type without the bipolar charged ionizer. FIG. 10 shows a comparison of DOP collection efficiency between two identical bag filters, with and without bipolar charging.

Table 1 shows the positive and negative periodic voltage, current and DOP collection efficiency up to 10 pounds (4.54 kg) of powder load for the bipolar charge filter. Each DOP efficiency in the table is the average value of 3 consecutive samples. The cycle time corresponds to 30 seconds of positive ionization processing and 60 seconds of negative ionization processing, respectively. Further, Table 2 shows the test results for the bag filter without the bipolar charged ionizer. As can be seen from these, the efficiency is kept extremely high through the load test in the case of the bipolar charge filter. On the other hand, the pressure drop is 0.25 inch (6.35 mm) of water at the beginning of the load test.
Water) value to 2.75 inches (69.9 mm water) of water at the end of the 10 pound dust load. On the other hand, the DOP efficiency in the case of the conventional bag filter without the bipolar charging effect was an extremely low value (41%) at the initial stage. Further, as the filter is loaded with powder, the pressure drop and efficiency also increase, and at the end of a 3 lb (1.36 kg) powder load, the pressure drop and efficiency are 2.5 inches (6. 35mm water) and 88%,
At the end of the fourth pound (1.82 kg) load treatment, the pressure drop is equivalent to 4.4 inches of water (1
The test was terminated because the filter burst when it reached 11.8 mm water).

[0041]

[Table 1]

[Table 2] Thus, the ability to operate at very high initial efficiencies under such harsh load conditions, maintaining high efficiencies and low pressure drops is a particular advantage of the present invention. It is then also advantageous in comparison with the electrostatic precipitator (ESP) commonly used as another air cleaning technique. That is, in this case, if an ESP having a comparable size is used to process an air flow rate of almost the same level, the ESP cannot cover the excessive load amount. That is, the corona current decreases, and a short circuit or an arcing phenomenon occurs due to cake formation in the collection cell. Thus, the ESP is approximately 1-2 pounds (454-908).
At the load level of g) the operation must be stopped for cleaning and maintenance.

Although the present invention has been described above with reference to its preferred embodiments, those skilled in the art will not particularly state in the description without departing from the spirit and scope of the present invention defined in the appended claims. Corrections to the example,
Modifications and replacements are possible.

[0043]

According to the present invention, a high collection efficiency can be realized by the low pressure drop filter. Furthermore, the dust load capacity of the present invention can also be significantly increased compared to the same filter without the bipolar charging effect.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a bipolar charging filter according to the present invention.

FIG. 2 is a top view of a bipolar charge filter device.

FIG. 3 is a front view of the bipolar charging filter shown in FIG. 2 with both the power supply compartment and the access door removed.

FIG. 4 is a top view of a preferred bipolar charged ionizer.

5 is a cross-sectional view taken along the line AA in FIG.

6 is a cross-sectional view taken along the line BB in FIG.

FIG. 7 shows an example of the use of two identical single array ionizers to achieve the bipolar charging effect.

FIG. 8 is a diagram showing a pressure drop comparison between same-type bag filters with and without the bipolar charging mechanism.

FIG. 9 is a diagram showing a comparison of air flow rates between bag filters of the same kind with and without the bipolar charging mechanism.

FIG. 10: DO between same-type bag filters with and without the bipolar charging mechanism.
It is a figure which shows P collection efficiency comparison.

[Explanation of symbols]

 1 Ionizer 2 Bag filter 3 Pre-filter 4 Negative output high voltage DC voltage supply source 5 Positive output high voltage DC power supply source 6 Repeat cycle time relay 7, 8, 9, 10 Particle 11, 12 Adjustment knob 19 Blower 47 , 48 Ionization line arrangement A Air flow direction

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location B03C 3/66

Claims (20)

[Claims] 1. A filter located at the downstream end of the system, an ionizer located upstream of the filter, a high voltage source connected to the ionizer, and a negative high voltage source for the ionizer. An electrostatic filter system comprising: a first cycle operated by a voltage and a means for converting a second cycle in which the ionizer operates by a positive high voltage back and forth. 2. The first ionization device, wherein the high-voltage supply source comprises a negative high-voltage supply source and a positive high-voltage supply source, and the ionization device is connected to the negative high-voltage supply source. 2. A filter system according to claim 1, comprising a second ionizer connected to the positive high voltage supply. 3. The filter system according to claim 2, wherein the first ionization device is a first set of ionization wiring and the second ionization device is a second set of ionization wiring. 4. The high voltage source comprises a negative high voltage source and a positive high voltage source, and the converting means directs the ionizer to the negative high voltage source and the positive high voltage source. A filter system according to claim 1, characterized in that it comprises means for alternately connecting to a voltage supply. 5. The filter system according to claim 1, wherein the high voltage source comprises a single power source capable of alternately outputting a negative high voltage and a positive high voltage. 6. The filter system according to claim 1, further comprising a pre-filter arranged upstream of the ionizer. 7. The filter system according to claim 1, wherein the filter is a pleated bag filter. 8. The filter system of claim 1, wherein the filter is a dielectric filter. 9. The filter system according to claim 1, further comprising a blower for transferring air through the ionizer and the filter. 10. A negative high voltage source, a positive high voltage source, a filter located at the downstream end of the system, and an ionizer located upstream of the filter, The ionizer comprises a first set of ionizing wires connecting to the negative high voltage source and a second set of ionizing wires connecting to the positive high voltage source, and further comprising the negative high voltage source. Bipolar electrostatics, characterized in that it comprises a first set of ionization lines having a voltage supply and a cycle time relay for alternately operating a second set of ionization lines having the positive high voltage supply. Filter system. 11. The filter system according to claim 10, further comprising a pre-filter disposed upstream of the ionizer. 12. The filter system according to claim 10, wherein the filter is a pleated bag filter. 13. The filter system of claim 10, wherein the filter is a dielectric filter. 14. The filter system according to claim 10, further comprising a blower for transferring air through the ionizer and the filter. 15. Transferring fluid to continuously filter through the ionizer and filter, operating the ionizer at a high negative voltage for a first time interval, and switching the ionizer on. Operating with a positive high voltage in a second time interval subsequent to the first time interval and repeating the cycles before and after them, the filtering method. 16. The method of claim 15, wherein the first time interval is approximately equal to the second time interval. 17. The method of claim 15, wherein the first time interval is longer than the second time interval. 18. Placing a dielectric filter downstream of the ionizer; transferring fluid to continuously filter through the ionizer and the filter; and negatively applying the high voltage to the ionizer. Operating the device to negatively charge particulate matter passing through the ionizer at a first cycle interval; and operating the ionizer at a high positive voltage to pass through the ionizer at a second cycle interval And a step of repeating the first period interval and the second period interval back and forth. 19. The method of claim 18, wherein the first periodic interval is approximately equal to the second periodic interval. 20. The method of claim 18, wherein the first periodic interval is longer than the second periodic interval.