JPS6271557A - Apparatus and method for removing contaminant from gas - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an ionization device, and in particular, a strong electrostatic field uniform in the radial and peripheral directions, through which gas is passed to ionize the gas, and to entrain the gas. The present invention relates to an electrode structure capable of generating an electrostatic field for charging particles.

Many industrial processes emit significant amounts of air pollutants such as submicron particles. This type of particulate is the most difficult to control. Since larger particles are easier to control, particulate emissions are a major source of air pollution.

Currently, there are three basic solutions to the problem of dealing with submicron-sized particles in contaminated gases.

The first solution is a common electrostatic precipitator system. There are a number of inherent difficulties in applying electrostatic precipitators to control particulates.

The second basic type of purification system is the wet scraping solution. This wet scraping solution applied to particulate control is generally of the high energy venturi type. Large amounts of water must be injected and high relative velocities must be used to capture submicron particles in the water droplets. Both of these conditions increase the pressure drop in the system, and operating costs are directly related to this pressure drop.

The third basic type is commonly referred to as a dry filter system. However, problems with this type of device include problems related to the temperature limitations of the filter element and the high cost of reducing the temperature, as well as problems associated with "sticky"
The problem is the difficulty of dealing with particulate matter such as lumps.

Efforts have been made to improve the efficiency of the various techniques described above by electrostatically precharging the contaminants upstream of the primary collection system. These efforts have generally been unsuccessful, primarily due to the lack of effective mechanisms to generate continuous and sufficiently strong electrostatic fields that affect and sufficiently charge submicron-sized particles. Met.

Ionization devices for charging particles or ionizing gas have so far been wire cylinder type, wire plate type, or needle tip type, and the electric field strength is about 10 KV/cra in the area between the electrodes. It was limited. As a result, the usefulness and effectiveness of such ionization devices has been limited.

Therefore, the purpose of the present invention is to effectively remove contaminants in the sub-micron size and larger fine particles from contaminated gas so that the gas can be released into the atmosphere without causing air pollution. An object of the present invention is to provide a method and apparatus.

Another object of the present invention is to accomplish the removal of the above contaminants in an apparatus with a competitive selling price from the outset.

Yet another object of the present invention is to accomplish the removal of the above contaminants in an apparatus with low equipment cost.

Yet another object of the present invention is to provide a method and apparatus that substantially reduces operating costs, both in terms of power consumption and maintenance, while achieving the desired removal of submicron contaminants.

These and other objects of the invention include one or more planar discharge electrodes located concentrically on a tubular outer electrode and spaced a predetermined distance from each other or from other cocona generating structures. It consists of a powerful ionization device with a flat discharge electrode similar to the one shown above. A high voltage is connected between the discharge electrode and the outer electrode to effect a corona current generating electrostatic field in the electrode gap between the discharge electrode and the outer electrode. This electrostatic field is uniform in the radial and peripheral directions and spreads out from the discharge electrode in the radial and peripheral directions so that its average strength can be very high. The ionization device is used to charge particulate matter or ionize the gas that accompanies the gas flowing in the axial direction within the external electrode through the electrostatic field of each electrode gap. The average strength of this electrostatic field in the strong ionizer of the present invention and conventional wire plate and wire cylinder ionizers can be increased as the velocity of the gas flowing through the field is increased.

Referring now to FIG. 1, contaminant-laden gas is directed through inlet duct 1 to the inlet of gas contaminant charged venturi section 2 by blower 1a.

Gases and contaminants are accelerated to high velocities reaching a maximum at the throat of the venturi. However, the principles of the present invention are also applicable to constant velocity gas flows where a venturi is not used. A strong corona discharge is maintained at the throat of the venturi by the high voltage DC power supply 3. The discharge propagates radially from a highly pressurized flat discharge electrode or disk 4 placed in the center of the throat of the venturi to the outer wall 5 of the venturi. This corona discharge is very thin in the direction of the gas flow (less than one diameter of the outer electrode 5), so that the contaminant particles remain in this electrostatic field for a short time. However, high levels of electrostatic charge are imparted to microparticles for a number of specific reasons.

By conventional convention, the term "electric field" as used herein refers to non-corona electric fields, while the term "electrostatic field" refers to corona electric fields.

Although a circular disc-shaped discharge electrode is shown and described in detail, toroidal or polygonal shapes such as oval or square may be used as long as the shape of the outer electrode corresponds to the shape of the discharge electrode. may use other shapes. Similarly, the outer edge of electrode 4 need not be smoothly curved as shown in FIG.

Other designs that may be used include, for example, an obtuse edge, a sharp edge, or an edge with a plurality of closely spaced protrusions. Electrodes with serrated edges can also be used. The term discharge electrode or internal electrode used herein includes all such shapes.

Optimum performance is obtained by centering the discharge electrode 4 concentrically within the venturi throat wall (external electrode) 5, but the device will work effectively even when positioned off-center. will be understood by those skilled in the art.

The outer electrode 5 has a radius R0 forming the transition between the inlet cone and the venturi throat (this radius of the outer electrode is shown in an axial section through the outer electrode).
. However, this external electrode need not be in the form of a venturi. This is because other structures such as cylindrical structures with straight side walls or rectangular structures may be used.

The venturi recovers the energy imparted to the gas stream by accelerating the flow at the throat of the venturi, and prevents the thin film of purifying fluid flowing along the wall of the external electrode 5 from being disrupted, as will be described later. This gives a smooth flow to the gas passing through the discharge electrode 4. The structure of the outer electrode can vary considerably, but best results are obtained with a venturi with radius R0 having a ratio of 50:1 or greater to the edge radius r of the inner electrode.

The axial position of the discharge electrode 4 within the throat of the venturi can vary within limits. Moving this electrode position upstream increases the gear R9, reduces the field strength and requires a higher voltage while reducing the velocity of the contaminated gas flow. Decreasing the velocity may enhance or reduce ionization efficiency within the ranges described below.

Although all of the above variations to the described preferred form reduce performance to some extent, many of the effects of the present invention do not require optimal operating conditions and more economical construction techniques may be acceptable. This may suggest the use of one or more variations with reduced ionization efficiency.

Accordingly, the present invention is described with respect to an ionization device for use upstream of a contaminant purification device, such as a scrubber or precipitator, to substantially increase the efficiency of the contaminant purification device. However, the ionization device also has other intermediate features. For example, an ionization device is used to generate electricity, that is, E GD (electr
o-gas-dynan+ic generation
charging of particles for n) or ionization of streams for gas phase reactions, for example the generation of oxygen atoms for oxidation reactions such as the generation of ozone to remove odors or the production of sulfur dioxide to sulfur trioxide; It may be used only in response to In these applications, a gas stream, as well as a contaminated gas stream, is directed through the ionizer at the velocities described herein, but the passage of the gas through the electric field is limited to specific radial locations. is desirable. However, if there is no adhesion of fine particles, there is no need to clean the surface of the external electrode.

Electrostatic field E maintained between the electrode 4 and the outer venturi throat wall 5. is composed of two elements: the electric field E and the space charge effect, as shown in the graph of FIG. The electric field is related to the applied voltage and the shape of the electrode. A space charge effect consisting of ions, electrons and charged particles in the interelectrode region occurs after the corona discharge is initiated. 7th
As shown, the space charge effect tends to increase the electric field in the region close to the outer henchuri throat wall and suppress the strong electric field close to the electrode 4. This effect makes the electric field uniform in the radial direction, stabilizes the corona discharge, and bridges the entire interelectrode region R3 with a high electrostatic field. This is achieved without electrode spark breakdown, keeping the velocity high in the area and the surface on the external electrode 5 clean.

To best understand the uniqueness of the electrostatic field of the present invention, a description will be given to electrostatic fields generated by two types of known electrode configurations. In the wire cylindrical electrode configuration, the wire extends along the axis of the cylinder.

The electric field between the cylinder and the wire is total (radial),
There is no component extending along the axis of the cylinder (ignoring the edge effects at the ends of the cylinder). There is no space charge when a voltage is initially applied between the wire and the cylinder. The electric field strength at each point between the wire and the cylinder is inversely proportional to the distance from the wire, so the electric field strength decreases continuously radially outward from the wire to the cylinder. When the voltage between the wire and the cylinder increases to the corona starting voltage, electrons in the air near the wire (where the electric field is maximum) are accelerated toward the cylinder (assuming the wire is at negative voltage). , collides with gas molecules and releases more electrons. The gas molecules now lose electrons and become positive ions, which accumulate near the wire due to the wire's negative potential. A space charge continues to be established by a phenomenon commonly known as the "electron avalanche process." In this electron avalanche process, high-energy electrons accelerated radially outward by an electrostatic field strike further molecules. The very high energy of the electrons causes them to separate from the nucleus of the molecule, generating yet another free electron e- and yet another positive ion. It should be emphasized that the avalanche process occurs only in the vicinity of the wire, since it is in the region near the wire that the electric field is maximum. When electrons move radially toward the cylinder, the deceleration caused by hitting molecules exceeds the acceleration caused by the electric field. This is because the electric field strength decreases as you move away from the wire. At electric fields of 30 KV/cm and above, free electrons attach to negatively charged gas molecules and form negative ions, rather than releasing more electrons through an avalanche process. For example, if the gas between the electrodes is air, it will be from 0□ to 0□-.Most of the negative electric components in air are only oxygen.Therefore, for air, negative ions are 02- ions. However, other negative ions are formed for other negative gases.Other commonly formed negative gases include SO□
It includes water vapor and CO2. 02- ions are accelerated toward the cylinder at a positive potential, and along the way they form a negative ion space charge in the interelectrode region.

Generally speaking, in the region near the wire where the electric field is greater than 30 KV/cm, the electrons accelerated by this electric field have enough kinetic energy that when they hit a molecule, they become free electrons by an avalanche process. Positive ions are formed. Upon separation from the wire, the low-energy electrons attach to oxygen molecules to form 0□-ions. Since positive ions accumulate near the wire at negative potential and 02- ions accumulate between the positive space charge and the cylinder, the strength of the electrostatic field near the wire is reduced and the electrostatic field towards the cylinder is reduced. The electric field is changed such that the strength of is increased. The reduced electrostatic field near the wire reduces the amount of free electrons and positive ions generated by the avalanche process, and the increased electrostatic field near the cylinder increases the mobility of O2- ions towards the cylinder. The result is a stabilizing or negative feedback effect, which keeps the space charge density relatively constant over time. Even if the 0□-ions increase the field strength near the cylinder, this increase is not sufficient to prevent the field strength from continuously decreasing towards the cylinder.

The electrostatic field generated by the wire cylindrical electrode configuration is relatively inefficient. This is because the relatively large area of the cylindrical wall creates a large interelectrode current to maintain a given average electric field strength.

The second conventional electric field to be considered here is a wire plate electric field in which a potential is applied between wires positioned parallel to each other between a pair of parallel plates.

In this type of electrode configuration, a gas flow is passed through an electric field along a line perpendicular to the wire and parallel to the plate. The electrostatic field generated by the wire plate electrode configuration generates a space charge similar to the wire cylindrical electrode configuration. However, since the electrostatic field near the plate is stronger directly across the wire,
Space charges formed by 02- or negative ions from other negative gases are more concentrated in this region. This is significantly different from the negative ion distribution of a wire cylindrical electrode in which the concentration of negative ions is uniformly distributed around the cylinder. The space charge amplification of the electrostatic field of the wire plate is strongest opposite the wire, and the electrostatic field strength between the wire and the plate is greatly increased toward the plate. This large electrostatic field and large local current build-up in the plates will result in sparking unless the average field strength is kept at a relatively low value. Therefore, a relatively large average electrostatic field cannot be obtained with the wire plate electrode configuration. In the wire plate electrode configuration, similar to the wire cylinder configuration, the electrostatic field does not vary along the axis of the wire (ignoring edge effects at the ends of the wire). In other words, the components of the electrostatic field extend in only two directions of the Cartesian coordinate system and give rise to a non-uniform electrostatic field.

In the electrode configuration of the present invention, a flat discharge electrode 4 located concentrically within a cylindrical external electrode 5 generates an electrostatic field with a component extending along three dimensions of the Cartesian coordinate system. do. The X and Y components (or R components in a cylindrical coordinate system) of this electrostatic field are substantially the same as the wire cylinder electric field when viewed along the axis of the cylinder. Therefore, the concentration of negative ions in the interelectrode gap in the plane that crosses the external electrode 5 is uniform with respect to the periphery of the discharge electrode 4, resulting in a uniform spatial field amplification of the electrostatic field. However, the electric field between the discharge electrode 4 and the external electric field 5, when viewed in the axial plane of the external electrode 5, is substantially the same as the electric field of a wire plate electrode configuration. The concentration of negative ions in the plane passing through the axis of the external electrode 5 is greater in the plane of the discharge electrode 4 than at points axially spaced therefrom.

The electric field strength as a function of the distance from the axis of the discharge electrode 4 varies from the electrode 4 to the outer electrode 5, as shown by the solid line in FIG.
continues to decrease towards. As shown by the dashed line in FIG. 7, the electrostatic field including the space charge amplification is substantially constant over a substantial distance from the external electrode 5 towards the discharge electrode 4, and is therefore substantially constant at D in FIG. As shown, the electrostatic field is substantially uniform within the generally wedge-shaped volume which diverges outwardly in a direction perpendicular to the gas flow. This electric field therefore has a radial dimension at the external electrode 5 equal to y to its axial dimension. The uniform space charge distribution occurring in the plane transverse to the discharge electrode 4 has the characteristics of a wire cylindrical electrostatic field in which the electric field continues to decrease as it approaches the external electrode 5. The non-uniform ion concentration occurring in the axial plane of the discharge electrode 4 has the characteristics of a wire plate type electrostatic field in which the field strength increases towards the outer electrode 5.

The electrostatic field of the present invention transforms the continuously decreasing electrostatic field of the wire cylinder into a wire plate by simulating the wire cylinder electrostatic field in one plane and the wire plate electrostatic field in a plane orthogonal thereto. radially over a substantial distance from the outer electrode 5 towards the discharge electrode 4 in a generally wedge-shaped volume which emanates outwardly in a direction perpendicular to the gas flow. Generates an electrostatic field with a substantially uniform strength. The electric field between electrodes 4 and 5 therefore has a radial dimension equal to the spacing between electrodes 4 and 5, which
, ie approximately equal to the dimension of the electric field adjacent to the external electrode 5 in a direction perpendicular to the plane passing through the electrode 4.5. The uniformity of the electrostatic field means that there is no point where the electric field becomes extremely strong (which limits the average strength of the electric field that can be applied without causing a spark) like in wire plate systems, so it can be strong without creating a spark. average electric field. This electrostatic field shape is also less prone to sparking. This is because this electrostatic field configuration provides an even smaller current per unit area of the external electrode than the wire plate configuration at a given field strength. The radial symmetry of this electrode structure produces an electric field that is constant along a circumferential path of constant radius.

The wire plate and wire cylindrical electrode structure is an elongated system that generates an electrostatic field that contacts a relatively large area, and thus generates a relatively large current. In contrast, the electrode configuration of the present invention generates current over a relatively small area such that a strong electrostatic field is maintained using minimal current (and therefore power) without creating sparks between the electrodes.

Cleaning of the outer electrode surface is required only to keep the surface relatively clean to minimize spark breakdown. If the electric field strength does not have to be at its maximum and lower voltages can be applied, or if ionization occurs in a clean gas stream, or in other situations such that no significant deposits occur on the electrode surface, Of course, cleaning or flushing is not necessary. Intermittent cleaning may also be used.

The internal electrode provides a large amount of current (ions) due to corona discharge due to the close proximity of the strong electric field to the surface of the critical state. The electrode also provides a concentrated electric field area all the way to the venturi throat wall 5.

This concentrated residual electric field is responsible for directing the space charge on this path during its migration to the throat wall and for properly amplifying the electric field. The smoothly curved, generally radial cylinder of the inner electrode extends the space charge peripherally into the throat, reducing current accumulation per unit area of the outer electrode and reducing potential spark breakdown.

Since the electrostatic field is relatively thin in the direction of the gas flow, the high velocity of the gas flow through the electrostatic field tends to diffuse the concentration of ions axially from the plane of the inner electrode. This adds further stability by extending the space charge region in the direction of gas flow and reducing the electrostatic field between the space charge region and the external electrode 5. This "velocity-enhancing" effect is maximized at gas velocities of 50 ft/s and above. Additionally, such high velocity turbulence also provides stability by mechanically disrupting the mechanisms that cause spark breakdown.

In order to preserve the corona and therefore the performance of the charge unit from contamination and degradation, the high voltage electrode 4 is isolated from the corona discharge as well as from other cage paths. As best shown in FIG. 2, probe 10 supports electrode 4 in position on external electrode 5 and provides high resistance to electrical leakage both within it and on its surface. Although not shown, the probe can be moved axially or laterally if desired. A resistance value is provided between the support structure 12 of the probe and the electrode in the upstream duct 1. The surface resistance is determined by a continuous slot around the probe just upstream of electrode 4 (0,75 mm (0,030
This improvement is achieved by providing one or more bleed gases 14 of clean air, such as 1.5 inch). Clean air provided by an external source 15 is supplied through the probe body and passes through these slots at high velocity.

This action maintains a reliable high resistance path through which surface leakage bridges the electrode 4 to short it to ground.

The probe body has a high voltage cable 16 supported by an insulated hub 18 which fixes the probe to the duct 1.
Contains. The upstream end of the probe body is contained within a sealed shroud 20 and a hollow corrugated cover 22.

The holes 23 allow air to pass axially through a plurality of spaced apart rings 26, each having a corresponding slot 24 (FIG. 3). The spacing between the rings defines a series of continuous slots 14 that bleed air as described above.

The electrode 4 also has a slot 24 that allows air to flow downstream of the electrode.
have. These rings and electrode disks are secured to the cable 16 by bolts 28 attached to the tip 30. The clean air from the tip and the downstream surface of the discharge electrode 4 prevents charged contaminants from stagnating downstream of the disk and prevents charged particles from adhering to the surface of the electrode 4. .

In order to be able to spread the electric field axially between the discharge electrode and the outer electrode 5, the discharge electrode 4 must be separated by at least one electrode gap from the other structure generating the corona current generating electrostatic field. It is important to separate by a factor of .25. In the embodiment shown in FIGS. 1-11, this is achieved by gluing one discharge electrode into the outer electrode 5. In the embodiment shown in FIGS. However, in the embodiment shown in FIGS. 12-14, a large number of discharge electrodes are used, as described below, and therefore the axial spacing conditions are similar to those shown in FIGS.
This is more precise than the embodiment of FIG.

The outer electrode 5 is kept smooth and reasonably clean over a short distance, several times the corona gap R1, as contaminants may accumulate thereon. This helps eliminate corona interference from the external electrode surface, such as depositing contaminants. This cleaning can be accomplished in a number of ways, one technique being shown in FIGS. 1 and 2. Water or a similar fluid is injected by an external pump 32 into the smooth layer on the surface of the converging conical section of the venturi wall 5. If the external electrode 5 is a venturi, the convergence angle φ of the venturi is kept at approximately 12.5° to minimize the effects of turbulence. During operation, the venturi is directed downward and the thin film of water is accelerated as it approaches the throat by both friction with the moving gas and gravity. The water injection point is located upstream of the electrode 4 at a distance approximately 1.5 times the length of the electrode gap R3. The divergence cone width downstream of the venturi is less than 3.5' to minimize effects due to flow separation.

The radius of curvature R0 of the venturi wall forming the transition between these angles must be greater than or equal to about 2 inches. The water injection is carried out through a thin (0,25 to 0,625 dragon) formed by the peripheral surface 41 of the convergent cone.
(0.025 to 0.025 inches) is accomplished by a weir arrangement that includes a continuous slot 40, and the orientation β of the nozzle relative to the sidewall of the venturi is approximately 12.5°. The action of water on the Venturi wall is approximately 75 feet/s (22.5 m/s).
) to maintain a smooth and clean surface without reducing the performance of the corona with respect to the velocity of the gas flow. Water consumption varies with venturi size and is 12.5
0.2 to 2 gpm/100 for venturi diameters of am to 125 cm (5 inches to 50 inches)
The range is 0acfm.

Inwardly facing band or deflector 4 isolated from the cooling water
2 prevents water from moving upstream along the outer electrode. Water from pump 32 is directed tangentially into the housing under pressure and exits the housing through slot 40 axially to minimize swirling of the water as it passes through the electrostatic field.

The stable and strong electrostatic field of the present invention ensures that the discharge electrode 4 is at least 1.0 mm away from other corona current-generating electrostatic fields by an electrode gap of at least 1.
A wide variety of electrode configurations can be generated as long as the separation is 25 times and the shape or periphery of the discharge electrodes matches the shape of the external electrodes 5. Variations of this electrode configuration include, for example, square or hexagonal discharge electrodes 4 in square or hexagonal outer electrodes 5, respectively, and discharge electrodes with obtuse, acute, serrated or spiky edges. An electrode 4 is included. However, for the best condition based on current experimental data, the edge radius r is designed such that the ratio of the electrode gap R3 to the radius r of the discharge electrode 4 is approximately 100:1.
It is preferable that the discharge electrode 4 has the following.

If this ratio is less than 50:1, sparking will occur at low applied voltages, resulting in low actuation currents and electric fields. When this ratio exceeds 400:1, the contribution of the electric field in the gap is reduced and the actuation current is increased to maintain a high electric field. When the external electrode 5 is in the form of a venturi, the ratio of the radius Ro (the radius of the venturi's rim in the axial cross section) to the radius r of the discharge electrode must be set to 50:1 or more. If these radii are small, sparking will be induced with a low applied voltage. The diameter of the probe 10, and therefore the total diameter of the discharge electrode disk 4, is such that the probe is approximately 1 of the cross-sectional area of the external electrode 5.
Must be set to occupy 0%. The practical minimum value for this is 5%, and the practical maximum value is 40
%. The fact that the probe occupies a small proportion of the external electrode 5 causes an increase in the surface power density of the discharge electrode. More importantly, a small value also increases the electrode gap for a constant flow capacity of the unit, thus significantly increasing the required supply voltage. Values greater than 40% increase the size of the external electrode 5 and the cost of the probe, and increase the requirement for bleed air to isolate the probe and thus the operating costs.

Generally speaking, the ratio of the electrode gap R3 to the edge radius r should be between 50:l and 400:1, and is preferably about ioo:t, with the occupied area (of the outer electrode occupied by the discharge electrode 4) percentage) should be between 5% and 40% and preferably about 10%, the discharge electrode 4 should have a shape corresponding to the shape of the external electrode 5, and the discharge electrode 4 should have a shape corresponding to the shape of the external electrode 5; Corona current generation must be spaced from all structures that generate electrostatic fields by at least 1.25 times the electrode gap. For these electrode geometries, the typical high voltage required is under standard atmospheric conditions (76 cm (29,92 inches) of mercury pressure and 2
It is such that an average electric field of about 18 to 20 KV/cm can be maintained across the electrode gap R3 at a temperature of 70'F (0°C) and zero velocity. Gas velocity is approximately i5m/5
(50 ft/s) and above, the electric field is approximately 26-28 KV/cI without sparking! can be increased to

A number of important effects occur in the strong corona region of the charging unit. The floating contaminants are charged by ion collisions in the region R3 of high ion density and by the strong applied electric field. Due to the short residence time of the particles in the corona, it is assumed that the diffusion charging mechanism makes only a small contribution to the particles here. When the particles become charged and begin to move in the strong electrostatic field of the corona, they are slightly displaced radially outward. The amount of displacement varies with particle size, so some mixing, collision, and agglomeration may occur. This is evident as a small effect when considering the presence of thermal disturbances and turbulence. However, in the case of liquid aerosol,
The effects of strong applied electrostatic fields (greater than IOKV/cm), high temperatures as well as turbulent mixing produce significant agglomeration, and this effect is evidenced downstream of the corona. This is a significant advantage when collecting fine aerosols as the particles will aggregate to a larger and larger size that is more easily collected.

The velocity of the gas through the highly charged corona region affects the charging efficiency of the system. Approximately 15m/5 (50 feet/
S) At higher speeds, the space charge region of the electric field becomes axially expanded by the gas, reducing the possibility of spark breakdown, ie a considerable degree of stability of the corona is achieved. However, under conditions of increased velocity, this advantage of increased stability reduces the residence time of contaminants in the electrostatic field, thus reducing the charge on the particulates, and when water-based cleaning is used. This begins to be offset by the disadvantage that the breakdown of the water film of the external electrode wall soil increases. Up to about 125 feet/s (37.5 m/s) there is a benefit to corona stability, but charging efficiency is reduced.

For one system tested, maximum particle charge appears to occur at 30 m/5 (100 ft/s). However, to a significant extent the gas velocity must be balanced between the capacity, electrode voltage requirements, and cleaning capacity of the venturi walls required for efficient operation of the industrial gas to be purified. .

A second method of cleaning the venturi wall is shown in FIG. In this embodiment, a perforated or porous bleed section 70 is provided adjacent to the discharge electrode 4 to create a thin film of air, rather than a thin film of water, on the wall downstream of the outer electrode 5. 5. There is an external electrode 5 downstream of this bleed section 70 by a distance several times the length of the electrode gap R1.
The walls of the chamber are coated with a material of high electrical resistivity to provide electrical isolation to particles adhering to the area.

Yet another method is to use gas flow erosion to limit the thickness of the deposit to an acceptable level.

Yet another method is to shake or shock the walls intermittently or continuously to remove contaminants before they accumulate.

Passing through the electrostatic field, suspended particulate contaminants become highly charged to a similar polarity and are transferred to the outer venturi wall 5 downstream of the corona. Only a small amount of adhesion to the wall occurs, and the adhesion represents only the particulates that were moving near the wall in their initial trajectory. The electric field applied in this region is primarily composed of space charges, and their velocity is therefore low compared to the velocity of the flow, so that most particles are retained in the flow for considerable distances. .

At least two formats are available for collecting these highly charged suspended particles.

One technique for collecting charged particulates is a conventional electrostatic precipitator. Another technique is a wet scrubber 50, described below. The gas contaminant charged section of the external electrode 5 is attached directly to the throat 52 of the Venturi scrubber 50. Generally, the design speed of the outer electrode is matched to the desired speed of the scrubber venturi, reducing the divergence cone angle of the charged section to approximately O
I am trying to set it to @. Gas entrained with charged particulates is passed through the scrubber venturi such that the particulates are collected into water droplets by collision and particulate interception is increased by electrostatic forces. Water is introduced into the Venturi scrubber in a conventional manner, such as through continuous slots 54, and is atomized by the gas flow. The water droplets are
Since the atomization process is achieved in the residual electric field region, the particles are charged with opposite polarity due to induction. Preferably, at low venturi velocities (less than about 75 ft/s), the injection point is at least a gap R1 below the discharge electrode 4 to prevent premature spark breakdown.
It should be about twice downstream.

At high Venturi velocities, ions drift downstream of the corona and this tends to invalidate the induction process by undesirably charging the droplet to the same polarity as the charged particulate. , requiring a considerable separation distance. Due to the expansion bolt 28, the induced charging field is increased in the axial direction even though the separation distance between the electrode 4 and the injection point is increased. This gives a cylindrical electric field emanating from the bolt above, downstream of the electrode 4 and on the outer wall 5.
drive ions toward

The collection efficiency of conventional venturi scrubbers is based on the inertial impingement of particulates onto water droplets. This collision is achieved by the high relative velocity of the water droplets injected at low velocity and the contaminated gas stream. Fine particles of sub-micron size do not collide with each other, but instead escape collisions by following the flow that passes around the water droplets. (One case is 1A
It is shown schematically in the figure. ) This is due to the high aerodynamic drag-to-inertia ratio. In the case of edge impact and cutoff energies, particulate repulsion and rebound are also important factors. Fine particles with low collision energy cannot penetrate water droplets due to surface tension effects.

In the present invention, fine particles that contain a high (IQKV/cm total charge) electrostatic charge and induce an electric charge on water droplets are
As shown schematically in Figure 1B, there is sufficient absorption between the charged particles and the water droplet to create a collision trajectory.

This action results in a substantial improvement in collection efficiency over basic scrubber efficiency. The improved collision effect varies with the relative velocity between the particulate and water droplet and the size of the particulate.

The photosensitivity to the particle size is slight, 0,1
Considering particulates in the micron to 10 micron size, the resulting variation is only 10 or -20%. The lower relative velocity between the charged particulate and the water droplet produces considerably improved results, since the longer the electrostatic force acts, the more effective it is. However, this lower speed also reduces the atomization efficiency of the scrubber fluid and makes the device larger, so the optimum speed range becomes apparent.

At relative speeds below about 15 m/s (50 ft/s), the atomization of the Venturi scrubber decreases rapidly and therefore the liquid requirements are substantially increased to maintain efficiency. Relative speed is 60m/5 (200ft/S)
Above this, the pressure drop across the system due to acceleration losses of water droplets becomes excessive. Therefore, the optimum improvement in collection efficiency of the gas contaminant charging unit relative to the Venturi scrubber collector is achieved with a Venturi scrubber design of approximately 125 to 150 ft/S at the throat.

The tested embodiment of the invention has a gap radius R3 of 3.75 marks (1.5 inches) and a discharge electrode edge radius r of 0.39i++++ (1/64 inch);
The peripheral radius R1 is 21.9 m (0,875 inches), the radius R2 of the outer electrode is 5.94 cm (2-3/8 inches), the conical cone angle φ is 12.5°, and the outer electrode radius R2 is 5.94 cm (2-3/8 inches). The radius R0 of the electrode (axial cross section) was 7.5 cm to 10 cI11 (3 to 4 inches).

In this example, the gas flow of the scrubber venturi is approximately 36 m/
5 (120 ft/s) and had a capacity of 750 cfm. The collection efficiency of a typical known scrubber alone of this design is approximately 81% at 0.5 micron particle size. When the gas contaminant charging unit of the present invention is activated, collection efficiency is increased to about 95% at 0.5 micron dimensions. In this state, the system weighs approximately 7.5g.
Water at pm/1000acfm, 150 watts/100
The charging unit consumes 0acfm power and the water system pressure drop is foam (4 inches).

The second example tested had a gap radius R3 of 5.3
8 cm (2,15 inch), the edge radius r of the discharge electrode is 0.39 mm (1/64 inch), the peripheral radius R1 is 21.9 mm (0,875 inch), and the radius of the outer electrode is R2 was 7.58 cm (3.03 inches), the cone angle of convergence was 15", and the venturi radius R0 was 5.0 cm (2 inches). This example shows that the scrubber venturi gas flow was approximately 45m/S (15
0 feet/s) at 1. It had a capacity of OOOacfm. A typical known scrubber-only collection efficiency of this design is about 94.5 microns at a particle size of 1.25 microns.
It is 6%. When the gaseous contaminant charging unit of the present invention is activated, collection efficiency is increased to approximately 97.5% at 1.25 micron dimensions. In this condition the system has approximately 6 gpm/l OOOacfm of water and 150
watts/1000acfm of charging unit power and the water pressure drop is 15 cm (6 inches).

Typical known corona ionization devices are generally limited to operating field strengths of 3 to 6 KV/cIll. Using an optimal electrode configuration and optimal fluid velocity through the electrodes, the ionization device of the present invention provides operating field strengths of up to I 5 KV/crn without spark breakdown.

An additional advantage of the present invention is that it advantageously utilizes only the velocity effect of axially dispersing space charge over conventional dust collection configurations to aid in reducing voltage breakdown, significantly reducing the operating field strength. It is based on the discovery that it is possible to increase

For example, FIGS. 8 and 9 illustrate a known ionization device using a single wire electrode 80 placed laterally between a venturi throat 81 of a rectangular duct 82. Insulator 83 isolates the wire from the duct in a known manner.

The wires are connected to the power source 3 as in the preferred embodiment.

Typically, single wire plate ionizers must be operated at low applied voltages such that the average electrostatic field between the electrodes does not exceed about 10 KV/am before spark breakdown occurs. The speed is approximately 3m/5 (10 feet/s)
) is kept low.

A typical example of this operation is a household electrostatic air purifier. The high speed of the present invention is about 15 m/5 (50 feet/s)
With , an average field strength of about 10 K V/crs can be obtained without spark breakdown, as the velocity sweeps excess space charge downstream of the strongest electrostatic field.

This same mechanism also allows multiple transverse wire precipitators to have transverse wires spaced axially along the duct.
Limited to low voltages even at high fluid velocities. I mean,
This is because ion displacement from one wire region is exposed to the next downstream electrostatic field region.

A large number of axially spaced lateral wires are arranged a sufficient distance to allow ions from each next upstream wire to travel to the outer electrode (duct) before entering the ionizing electrostatic field of the downstream wire. Of course, they can be used if they are axially spaced apart.

FIG. 11 shows another embodiment having a radial electrode end 80a and a linear center electrode 80b. Preferably, the duct 82 is rectangular but can be bent to match the electrodes. Air boat 24 is provided as shown in FIGS. 3-5. As for the edge radius r, all the shapes shown in FIGS. 1O'A to 100 can of course be used. This electrode shape works much like the wire plate electrode of FIGS. 8 and 9, but also provides some of the advantages of a radial shaped electrode.

Another embodiment of the dust collector shown in FIG. 12 uses multiple dust collection units 110 in parallel. The gas accompanied by fine particles passes through an annular inlet rod 114 to the inlet manifold 11.
Enter 2. The manifold 112 is partially filled with water 116, and the gas passing through the manifold 112 wraps around baffles 118, 120 and fills the water 116.
A plurality of flat, spaced apart walls 118, 120 are positioned such that the flow must flow through them. Water 116 is provided to cool the gas entering the inlet duct 114 to promote particulate formation by condensation. pipe 1
Additional cooling is provided by a preliminary quench spray with a plurality of spray nozzles 122 communicating with water inlet 124 through 26. Cooling water is circulated by a pump (not shown) at moderate pressure.

After the gases entrained with particulates have been sufficiently cooled and saturated, these gases are guided to the part of the manifold 112 below the dust collection unit 110. As best shown in FIG.
- 110 and has an annular hole 130 with a concentric cylindrical shield 132 in each dust collection unit 1.
10 such that the shield 132 extends to the lower end of the tubular outer electrode 134. Each dust collection unit 110 includes a cylindrical outer electrode 134 surrounding a flat discharge electrode 136 attached to the lower end of an elongated support electrode 138. As will be explained in detail below, fine particles in the gas passing through the hole 130 are transferred to the discharge electrode 136 and the outer electrode 13.
4 in a relatively thin radially and circumferentially uniform electrostatic field extending between them. As used herein, the term "electrostatic field" refers to an electric field that produces a corona discharge, and the term "electric field" refers to an electric field that does not produce a corona.

The term "relatively thin" shall refer to an electric field having a radial dimension that is substantially greater than its axial dimension. The charged particles are connected to the supporting electrode 138 and the external electrode 134.
is accelerated toward the external electrode 134 by a relatively low-strength electric field extending between the two. Particles adhering to the inner wall of the outer electrode 134 are collected by a thin film of water covering the inner wall of the outer electrode 134 and swept downward to the collection surface 128.
is accumulated in The liquid in the shield 132 is connected to the external electrode 134.
This liquid film is prevented from being entrained in the upper gas flow as it falls from the edge of the gas onto the collection surface 128. When the liquid from the thin liquid film covering the inner wall of the outer electrode 134 is re-entrained, the gas velocity within the outer electrode 134 is 3 m/5 (10 feet)/S).
This is a win because it destabilizes the electrostatic field when it exceeds .

External room! The upper end of 1134 projects into the exhaust fill 140 where it is surrounded by a cylindrical weir 142.

A thin film of water 144 flows over the weir 142 and external electrode 1
Water is continuously supplied via conduit 143 by a pump (not shown) so that it flows down the inner wall of 34 . A cover plate 146 extending above the weir water 144 extends to the outer electrode 134 to allow gas to flow smoothly from the outer electrode 134 to the exhaust fill 140 without disturbing the water at the top of the weir. It has a cylindrical flange 147.

The upper end of support electrode 138 extends to high voltage housing 148 where it is connected by insulator 152 and feedthrough shroud 154 to high voltage buspar 150 supported on the floor of housing 148 . This bus bar 150 has a through feed insulator 160
A high voltage conductor 156 passes through to the high voltage enclosure 148.
(FIG. 12) connects to an external high voltage power supply or transformer-rectifier arrangement (not shown). Electrode 134.13
6.138 is provided by a plurality of annular servicing covers 162 on the top surface of the housing 148.

The electrostatic field extending between each discharge electrode 136 and the outer electrode 134 is substantially the same as the electrostatic field generated in the embodiment of FIGS. 1-11. Therefore, electrode 136.1
34 forms a corona current generating electrostatic field and the characteristics of the electrostatic field will not be described repeatedly here. The large diameter of the discharge current 136 should be 0.2 to 0.5, and preferably about 0.35, of the inner diameter of the outer electrode 134.

The diameter of the support electrode 138 is 0.1 of the inner diameter of the outer electrode 134.
5 to 0.25 and preferably about 0.2 and 0.4 to 0.8 and preferably 0.5 to 0.6 of the large diameter of the discharge electrode 136. The support electrode 138 with a larger diameter is the discharge electrode 136 and the outer electrode 13.
4, which will significantly suppress the axial spread of the electrostatic field, thereby reducing the stability of the electrostatic field. Smaller support electrodes 138 tend to create excessive corona and sparks between support electrodes 138 and outer electrodes 134.

By directly securing the discharge electrode 136 to the support electrode 138, a single electrode mounting system can be used for both the charging stage of the precipitator as well as the collection stage of the precipitator.

Furthermore, by varying the diameters of the discharge electrode 136 and support electrode 138 with respect to each other and with respect to the external electrode 134, the discharge electrode 136 and the external electrode 134
The strength of the electric field extending between the support electrode 138 and the outer electrode 134 can be selected separately. The cost and complexity of the precipitator can therefore be reduced considerably compared to conventional precipitators.

To increase the efficiency of the precipitator, especially when particles of various sizes are to be removed, multiple electrode stages as shown in FIG. 14 are used. 1.25 of the discharge electrode gap
A plurality of discharge electrodes 180, 182, and 184 are fixed to the support electrode 186 at points spaced apart from each other in the axial direction. In order to prevent electric fields extending from adjacent discharge electrodes from interfering with each other and to ensure that the electric field extending from support electrode 186 has sufficient length to collect charged particulates, the distance between electrodes 180, 182, 184 is It is preferable that the distance is larger than twice the discharge electrode gap.

An interelectrode spacing smaller than 1.25 times the discharge electrode gap causes interference between adjacent electric fields, which prevents the axial spread of the electric field and reduces the stability of the corona discharge. Therefore, when the gas flows through the outer electrode 134, the particles entrained in the gas are subjected to multiple charging fields, each followed by a collecting electric field.If desired, the diameter of the discharge electrodes 180, 182, 184 is 180.182.184 and external electrode 13
The average strength of the electric field extending between each electrode 180 .
182.184 may be changed separately.

Larger particulates generally tend to collect more easily and are therefore fairly easily removed with lower strength applied electric fields. Therefore, if the size of the particulates to be collected changes, the particulates may be
It is desirable to gradually increase the diameter of the discharge electrode along the gas flow so that it is subjected to increasingly stronger electric fields as it flows through the gas flow. Therefore, the largest particle is the discharge electrode 1 with a small diameter.
80, small particles are collected just beyond the medium diameter discharge electrode 182, and the smallest particles are collected just beyond the large diameter discharge electrode 184. be done.

Large, charged particles create localized electric field anomalies, which tend to create sparks in this localized area. These large particles are transferred to a small diameter discharge electrode 18.
By removing near 2, the strength of the electric field between the large diameter discharge electrode 184 and the outer electrode 134 is increased, thereby removing a greater proportion of small particulates and increasing the overall collection efficiency of the system. I can do it.

If desired, a low field corona discharge may be created between the support electrode 138 and the outer electrode 134 by spirally wrapping a conductor, such as a wire, around the support electrode 188. This low field corona discharge is particularly useful when the external electrode is cleaned intermittently. This is because the corona current retains the particles on the inner wall of the outer electrode until the particles are removed by some suitable technique, such as by force. If the particles are constantly removed, for example by a thin film of water, it is not necessary to hold the particles on the external electrode in this way.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view of one embodiment of an apparatus employing the principles of the present invention; FIGS. 1A and 18 illustrate a conventional wet scrubber and a highly charged system according to the principles of the present invention, respectively; 2 is a partially enlarged sectional view of a portion of the apparatus shown in FIG. 1; FIG. 3 is a lateral sectional view taken along line 3-3 in FIG. 2; Figure 4 is a cross-sectional view taken along line 4-4 in Figure 2, Figure 5 is a cross-sectional view taken along line 5-5 in Figure 2, and Figure 6 is a cross-sectional view of the modified venturi wall. FIG. 7 is a diagram showing the electrostatic field between the electrodes of the present invention; FIG. 8 is an axial cross-sectional view of an ionization device of the type shown in another embodiment of the present invention; 10A to 10D are diagrams showing various edge radius configurations; FIG. 11 is a diagram showing yet another embodiment of the ionization device; Figure 13 shows another embodiment of the invention using a plurality of axially spaced discharge electrodes surrounded by a tubular external electrode; Figure 13 is a cross-sectional view of a single dust collection unit; FIG. 14 is a sectional view showing another embodiment of a dust collecting unit using discharge electrodes of various lateral dimensions. ■...Duct, 2...Gas contaminant charged venturi classification, 3...High voltage DC power supply,
4... Electrode disk (discharge electrode), 5...
...Venturi outer wall (external electrode), lO...
...probe, 12...support structure,
14... Gas bleed, 16... High voltage cable, 20... Shroud, 24...
Slot, 26...Ring, 28...
...Bolt, 40...Slot, 41.
... surface, 42 ... deflector, 110
... Dust collection unit, 112 ... Inlet manifold, 114 ... Population duct, 116 ...
...Water, 118.120...Baffle,
122... Nozzle, 128... Inclined collection surface, 130... Annular hole, 13
2... Shield, 134... External electrode, 136... Discharge electrode, 138...
Support electrode, 140...Exhaust filling part, 142.
・・・・・・Cough, 148・・・High voltage housing, 1
50...High voltage bus bar, 180.182
．． 184...Discharge electrode, 186...
Support electrode. FIG, I FIG, IA FIG, IBFTIG,
8 FIIG, 9 IQA 11OD FIG, ll

Claims (10)

[Claims] (1) An apparatus for ionizing a gas and removing contaminants from the gas, comprising: a tubular external electrode for guiding the gas; and an elongated conductive support disposed within the external electrode in substantially longitudinal alignment therewith. and at least one generally planar discharge electrode having a peripheral discharge edge portion generally corresponding to the shape of the outer electrode, the discharge electrode being disposed within the outer electrode and having a peripheral discharge edge portion substantially corresponding to the shape of the outer electrode. The space between the peripheral discharge edge portion of the electrode and the external electrode forms an electrode gap, and the discharge electrode is such that an electrostatic field generated when a high voltage is applied to these electrodes connects the discharge electrode and the external electrode. said discharge electrode is spaced apart from all corona current emitting structures by at least 1.25 times the distance of said electrode gap so as to extend axially in a substantially wedge-like configuration between said discharge electrodes; The support electrode is attached to the upstream end portion of the support electrode in electrical contact therewith, and the support electrode has an inner diameter of 0.15 times and 0.1 times the inner diameter of the outer electrode.
and between 0.4 times and 0.25 times the diameter of the discharge electrode.
．． when a predetermined potential is applied between the external electrode and the discharge and support electrode;
A corona current generating electrostatic field is generated between the discharge electrode and the outer electrode that extends in the radial and axial directions and is uniform in the radial and circumferential directions; a directional non-corona current generating electric field is generated, the non-corona current generating electric field symmetrically and axially compressing the corona current generating electric field to increase the electric field strength; high voltage application means for applying a high voltage between the external electrode and the discharge and support electrode to create the corona current generating electrostatic field of high strength extending across the electrode gap; gas moving means for moving the gas in an axially flowing state. (2) The device according to claim 1, wherein the discharge electrode occupies 5% to 40% of the area across the external electrode. (3) The apparatus according to claim 1, wherein means for collecting contaminants contained in the gas and charged by the electrostatic field are arranged downstream of the discharge electrode. 4. The apparatus of claim 3, wherein said flat discharge electrode is a substantially flat disk. (5) The high voltage applying means is capable of generating an applied average electric field strength of 8 to 12 KV per cm of the electrode gap in the electrode gap when air at a substantially standard temperature and pressure is present in the electrode gap. Claim 1: Applying a sufficient voltage between the discharge electrode and the external electrode
). (6) the at least one discharge electrode includes a plurality of generally planar discharge electrodes attached to the elongate support electrode and concentrically disposed within the outer electrode, the discharge electrodes being axially aligned with each other; a plurality of electrodes spaced apart in a direction by a distance at least 1.25 times the distance of the electrode gap so that contaminants contained in the gas passing through the outer electrode are generated between the discharge electrode and the outer electrode; repeatedly charged in a radially and axially extending and radially and circumferentially uniform corona-generating electrostatic field, and then generated between the support electrode and the outer electrode downstream of the electrostatic field. 2. The device of claim 1, wherein the device is adapted to move toward and adhere to the inner wall of the outer electrode under the influence of a radial non-corona generating electric field. (7) the diameter of the discharge electrode is gradually increasing in the direction of gas flow, such that an applied average electrostatic field of increasing strength is maintained between the discharge electrode and the external electrode, and the gas is 7. A device according to claim 6, wherein the device encounters an applied average electrostatic field of increasing strength as it moves through the electrodes. (8) The supporting electrode is arranged concentrically within the external electrode, and the discharge electrodes are each arranged concentrically with the supporting electrode in a plane substantially perpendicular to the supporting electrode. The apparatus according to claim (6). (9) A method for removing particles from a particle-containing gas comprising: a plurality of non-overlapping radially and axially extending particles having an applied average intensity between 8 KV/cm and 12 KV/cm under standard atmospheric conditions; The particles are charged by passing a gas containing the particles sequentially into an electrostatic field uniform in direction and circumference, each of the electrostatic fields being connected to a tube shaped like a tube concentrically attached to a conductive elongated support electrode and through which the gas is passed. The discharge is generated by a disk-shaped discharge electrode arranged concentrically within the external electrode of the discharge electrode, and the distance between the peripheral discharge edge of the discharge electrode and the external electrode forms an electrode gap. , the discharge electrodes are axially spaced apart from each other at the support electrode by a distance at least 1.25 times the distance of the discharge electrode gap, and the discharge electrode is attached to an upstream end of the support electrode. and
The support electrode has a diameter of 0.15 times the inner diameter of the outer electrode.
．． and has a diameter between 25 times and between 0.4 and 0.8 times the diameter of the discharge electrode, and a predetermined potential is applied between the external electrode and the discharge and support electrode. When a corona current-generating electrostatic field is generated between each of the discharge electrodes and the external electrode, extending in the radial and axial directions and uniform in the radial and circumferential directions, and a radial non-corona current generating electric field is generated between the electrodes, and the gas containing the charged particles is passed through the elongated non-corona current generating electric field downstream of the electrostatic field to remove the charged particles. A method characterized in that the particles are deflected towards the external electrode and collected. (10) The electrostatic field gradually increases in strength in the direction of the gas flow, such that larger particles are removed by the upstream electric field and finer particles are removed by the stronger downstream electric field. claim 9, which increases the stability of the downstream electric field to increase collection efficiency.
) Method described in section.