DE1557087A1 - Electrostatic device for failing - Google Patents

Description

dr. E. wiegand '2000'HAMBURGi, December 29, 1966

MONKS ΒΛΙΙΙΝΟΛΜΜΣί

DfPL.-ING. W. NIEMANN phone = 330475 «_ _ _ _ _ _

Hamburg 1557087

PATINTANWXLTC

f.22584 / 66

Donald Norman Hanson, Orinda, California (V.St.A.)

and

Charles Robert Wilke, El Cerrito, California (V.St.A.)

Electrostatic device for failure.

The invention relates to an apparatus for electrostatic precipitation and, more particularly, to an apparatus in which additional particles are fed to a stream that carries undesirable foreign particles, e.g. dust particles to accelerate the failure.

An electrostatic precipitation as a method for Purification of dust-laden air is currently carried out through the following two stages:

1. Dust particles are given an electrostatic charge, and

2. The charged particles are then transported through an imposed electric field, which causes

that the particles are driven towards a collector, e.g.

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a wall, a sieve, a filter or the like. That periodically is cleaned.

Although the collection efficiency of such precipitators can be quite high, such precipitators are in order to achieve sufficient efficiency, comparatively large and expensive.

Another disadvantage of the known precipitators is the requirement for high voltages and therefore one High voltage equipment in the collecting section. This type of equipment is expensive and carries a moment of danger.

In contrast, it is an object of the invention to provide an improved device for electrostatic precipitation to create which is extremely effective and inexpensive and which does not have high-voltage equipment in the collective level the precipitation process requires.

In the description below, embodiments of the invention are explained by way of example.

Fig. 1 is, in simplified form, a side view, partly in section, showing part of the precipitation device according to the invention.
Figure 2 is a cross-sectional view taken along line 2-2 _;

of Fig. 1.
3 is a perspective view of one of the

Collecting tubes of Figures 1 and 2. Figures 4, 5 and 6 are graphical representations,

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what the understanding of the device of the er-?

serve finding.
Fig. 7 is a cross-sectional view similar to Fig. 2;

however, shows a modified embodiment

the charger.

Fig. 8 is a cross-sectional view showing another embodiment of the invention.

and
Fig. 9 is a cross-sectional view of another

Embodiment of the invention.

In Fig. 1, a two-stage precipitation device is shown. The inlet for the polluted or those with dust loaded air is indicated on the left side of the device, and the outlet is indicated on the right side of the device. As described in detail below the first stage Io of the precipitator cleans the incoming gas flow to a large extent from its foreign particles, and the second stage 2o removes a large part of the remaining impurities by an extraordinary amount to create a clean or purified air outlet.

Each stage ίο, 2o is divided into a charging section and a collecting section. The charging sections contain conductor wires 12 and 22 which extend through the wall of the device and are insulated from them by insulators 13 , 2J. The lines are connected to a negative DC voltage source -V

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bound. Conductive probes 14 and 24 are electrically connected to the electrical conductors and extend into the adjacent ones Collector Sections.

The header sections contain a number of longitudinal passages 16 and 26, which are provided with conductive walls. The passages 16, 26 can, for example, by conductive cylindrical tubes may be formed as shown in FIG is. The pipes are packed tightly together and connected to a common point of tension, namely earth, as shown in the figures. In a modified embodiment, a larger pipe with sufficient Results are used. The passages can be provided with tubes which have different cross-sections for example square, hexagonal, square, etc. The size and shape of the tubes are not critical Feature of the invention.

Additional or complementary particles, e.g. water droplets, are introduced into the gas stream through spray nozzles 17 and 27, before the gas flow enters the charging sections. As will be described in detail below Drops of liquid or water together with foreign matter particles on the surfaces or walls of the tubes 16 and 26 precipitated, clump together, trap the solid particles and flow by gravity or some other means along the walls of the pipes to collecting troughs l8 and 28, those at the upstream ends of the devices

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Io and 2o are arranged.

Incoming foreign particles (dust or other contaminants) and the introduced additional or supplementary particles in the air stream are electrostatically charged as they pass through a suitable electrical charging part. In the device shown, the electrical charge is generated in that a voltage is applied between the probes 1K and 24 and the tubes 16 and 26 into which the probes extend. Each fine wire electrode is coupled to the negative voltage source -V and, by means of a suitable voltage difference, provides an electrical discharge for the electrostatic charge of any particles passing through it. The charging version of Fig. 2, in which the charging occurs predominantly within the tubes, enables the generation of a high space charge within each tube, while the possibility of voltage breakdown is reduced because the relatively small diameter of the tube is the field generated by the space charge limited. The additional particles from the nozzles 17 and 27 are of course also charged with the same electrostatic polarity as the foreign matter particles when they pass through the charging sections.

Fig. 3 shows in greater detail an example of one Tube 16 of the collector portion of the first stage Io, The Direction along the center line of the pipe is marked with "L" and

0 0 9 Ö 1 1/1 2 2 1

denotes the radial direction with ¹¹ R ".

As the aforesaid combination of particles passes through the charging section, they are electrostatically charged negatively (or optionally positively) to create a space charge area within tubes 16 and 26. This space charge region is shown graphically in FIG. 4, which shows the potential as a function of "R" at two longitudinal locations L ₁ and L ₂ . The electric field intensity, the oblique course of the curves, begins at zero in the center line and reaches a maximum on the wall of the pipe. Two curves are shown, curve L taken near the entry end to the tubes 16 or 26 and curve L _{2 taken} downstream of the entry points. The maximum magnitude of the electric field intensity encountered at the upstream ends of the pipes is determined by the concentration of the contaminants and the particles added and by the magnitude of the charge on each particle. The charging on a single particle is determined in principle by the field in the charging section and by the surface size of the particles. In order to achieve a selected maximum electric field strength, it is necessary to adjust the particle concentration by adding a sufficient amount of additional particles of suitable size, for example water droplets, from the inlet nozzles 17 and 27. The particles are generated by the space charge in the tubes

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exposed to an electric field. The electric field creates a force that causes the particles migrate against the walls where they are collected.

This can be better understood if one takes into account that the mutual repulsion between the particles or Particles causes a large. Percentage of them is deposited on the walls of the pipes. The extent of the abseiling or precipitation or the efficiency of this repelling effect is, as mentioned above, proportional to the total electric field strength, which in turn is caused by a particle concentration and a charge on the single particle is determined. The liquid particles such as water that are collected flow along the walls of the tubes down and are in the Troughs 18 and 28 collected. Of course, when the water flows down along the walls of the pipes, see the pollution particles.

In a typical exemplary embodiment, FIG. 5 shows the effect of the initial particle concentration or -accumulation in expressions of the grain sizes per cube foot in Percentage of particles not precipitated. Both axes are "logarithmic, and the parameters, e.g. as a charge and particle diameter, are given oversized in the example. From the curve it can be seen that the efficiency drops rapidly at lower initial particle concentrations.

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The curves of FIGS. 4, 5 and 6 were derived simultaneously from the solution of the Poisson ¹ equation and the equation of particle continuity for a cylindrical tube through which a gas charged with particles flowed in laminar flow. In the case of turbulent flow, the precipitation is even more effective. The solution of the equation requires finite difference quantities for the solution of the two coupled partial differential equations. This is done in a simple manner using a computer.

The reduction in particle concentration as a function of the distance "L" along the tube is shown in FIG shown. The slope of the curve shows the extent of the precipitation. It can be seen that the extent of precipitation is very high near the entrance of the tube and low near the downstream end of the tube Value leveled down. This is of course a result of the much higher electric fields when entering the pipe. on this way most of the particle precipitation (contamination and additions) occurs at the initial one upstream part of the pipe and relatively little is achieved towards the downstream end. This behavior arises logically because when the initial particles precipitate and settle on the walls of the pipe or lay down the surfaces, the size of the space charge is reduced. Since this space charge in turn determines the extent of the

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Precipitation determines when the particles precipitate, the driving force for the precipitation / and the disappears ■ The speed or the extent decreases towards zero. Fig. 6 also shows that the part of the pipe that the Entry end is closer, the most effective part is. A single stage with long pipes is therefore less effective than two or more stages with shorter tubes.

The particle size is still a factor in the efficiency the precipitation, however, is not critical to the practice of the invention. The speed of a single particle that moves against the surface of the wall of one of the pipes is loaded by the charge on the particle which is determined mainly by its surface size "and its mobility, which is mobility inversely proportional to the entrainment (flow resistance) "which is related to the diameter of the particle. Da however, the charge is proportional to the surface area or the square of the diameter, the larger the particles will be turned out lighter, as the increased size of the charge does more than just compensate for the increased resistance. Purely smaller particles with a reduced amount of electrostatic charge on them will become the Flow resistance not reduced enough to compensate for its reduced charge. However, the AufIa- " still large enough to have sufficient precipitation efficiency to maintain, and since the particle

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- Io -

size is reduced to about a micron, the charge-to-resistance ratio for the precipitation will turn cheaper. As a result, precipitation is extremely successful over the entire range of particle sizes available.

Other factors may be important in determining the desired particle size of the additional particles introduced be. For example, if water droplets are introduced and if the water droplets are too small «it may be unnecessary be difficult to collect. Conversely, if the water droplets are too large, they may have a tendency to to precipitate against the pipe walls faster than the smaller dust particles. In the latter circumstances the efficiency of the precipitation is reduced, since the rapid precipitation of the water droplets is a result resulting decrease in the electric field intensity, which in turn causes a decrease in the rate of precipitation or the precipitate size of the undesired particles.

By using water droplets in addition to creating a sufficient electric field, to cause rapid precipitation, the water continues to capture and wash away the dust particles deposited on the walls, preventing watches from re-entering or taking them back with you. Since the air flow through the header sections 16 and 26 with a gentle

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know speed moves, there is a tendency that the deposited material is shifted in its position and along the surface by the action of this air flow is dragged along. The liquid film causes precipitated material to be trapped and quickly The collected dust particles run off to the collecting troughs 18 and 28. Furthermore, the conductivity of the water prevents the particles from being charged against the wall, which would result in a reduction in the electric field intensity at this point. Of the Main factor in preventing charge build-up

that the walls of the collecting pipes consists in / they are connected to earth, which functions as an electron drain to to discharge deposited negatively charged particles. The exit from the first stage Io of the precipitator exhibits a combination of additional parts added by the nozzle 17, water droplets and pollution particles that were initially contained in the polluted incoming air. For purposes of illustration, assume that the pollution particles and the supplied water drops are the same size and shape. These two types of particles are present in a proportion which is the original proportion of in the upstream end the device introduced water droplets in comparison to the initial concentration of contaminated particles

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is equal to. Thus, for example, if an equal number of water droplets are added to the foreign matter particles present, the same ratio would exist at the exit end of the first device. If the collection efficiency or the precipitation efficiency is 96 % , which means that only 4 % of the total particles remain uncollected, then 2 % of them would be water droplets and 2 % foreign matter or dust particles.

If the remaining foreign matter particles are present in such an amount that they are for the particular The range in which the precipitator is used may be a single stage or a precipitator make adequate cleaning. In situations, however, in which the foreign particles particularly are harmful and of which even very small amounts are undesirable, a few allow additional amounts Precipitation stages almost all of the elimination of these particles. This is done, for example, through stage 2o and, As discussed above, the amount of foreign matter particles remaining in the exit of the stage 2o is determined by determines the initial ratio of water droplets and foreign matter particles at the entrance to the stage. If therefore again it is believed that a precipitation efficiency of

96 % is present at stage 2o by adding enough water droplets to bring the particle concentration to the same level as at the point of entry of the first

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Bringing stage Io, the amount of contaminant particles precipitated in the two stages is 99.84 % of the initial foreign matter particles.

Even higher collection efficiencies can be achieved by adding further stages can be obtained. It can be seen, however, that the process achieved efficiencies of such Height ensures that several steps would only be necessary in exceptional situations. The collecting zones 16 and 26 need not to be electrically isolated nor is there a risk of high potentials as the whole is electrostatic Charging of both the water and dust particles occurs in the vicinity of the charging electrodes 14 and 24, which are separated from the headers.

Depending on the particular application of the precipitation devices the additionally added particles, which in the preferred embodiment form water droplets be other than liquid substances that serve as humectants, e.g. oil for carbon particles or in another embodiment even solid particles. In the latter case, the solid particles would deliver the correct repulsion space charge field » Any re-entry of precipitated particles on the pipe walls could be prevented by a layer of liquid, which the pipe walls continuously washed down.

In the above-mentioned case in which, for example

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Oil used as a humectant for a carbon foreign particle and it is undesirable to have any harmful oil droplets in the exit of the precipitator remain, a second stage of precipitation can be used in which water droplets that are not harmful if they are released into the atmosphere, mixed with the oil droplets left over from the first stage of precipitation, to reduce the amount of oil droplets in the exit gas stream from the second stage. This system could still be used if additional solid particles were initially introduced into the first precipitation stage will.

The following example shows the operation of a single pipe in an apparatus of the type shown in FIG Kind of again.

Pipe length 9o cm

Pipe diameter 2.54 cm

mean air speed 90 cm / sec Inlet particle concentration 4.4 χ Io 'particles (including water droplets per ecm marriages and dust)

Particle diameter from both

Dust as well as sprayed 1 micron

In the exemplary embodiment explained above, there was a charge of 26 l electron charges per particle used.

The portion of particles that are in the first stage of precipitation

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precipitated is 96.35 % · When using the. second precipitation stage and the addition of sufficient additional water droplets through the nozzle 27 to again build up a particle concentration equal to the initial particle concentration, the total precipitation efficiency achieved is 99 * 87 % of the original dust particles.

The electrostatic charging device shown in Figures 2 and 3 with the electrodes 14 or 24, the placed in close proximity to the opening of each tube can be changed as desired. Like for example As shown in Figure 7, they can be a single corona wire for a group of multiple pipes. At this point, vertical corona wires 30 and 3I are provided, which are shown in FIG Combination with grounded cylindrical rods 32a, 32b and 32e provide an electrostatic charging field.

Another method of charging the added Water droplets can be sprayed out of a nozzle (Fig. 8), which with respect to earth on a suitable negative potential is maintained. These charged atomized particles can be used to the normal corona charging in stages behind the first Completely eliminate stage. In a modified embodiment, individual nozzles can be assigned to each manifold be.

The dust particles can still be charged by partial evaporation of charged water droplets.

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When the drops are reduced in size, the charge escapes from them, which with the surrounding ones Dust particles collide and charge them. Such a method of charging the dust particles can be most effective be used in high temperature streams, with the evaporation of the charged atomized particles causing the gas stream cools and at the same time charges the foreign matter particles. Such a device as shown in Fig. 8 can be used for this double charging.

In some cases, the initial dust concentration of foreign particles may in itself be sufficient to an electric field intensity to successfully precipitate a large part of the particles in the first stage Io enable. If possible, water droplets can only be added through nozzle 27 at the beginning of stage 2o, in turn to create a sufficient concentration of particles and an electric field intensity to precipitate almost all of the remaining dust particles or foreign matter particles.

Fig. 9 shows a modified embodiment of a precipitation device, which is directed vertically and directly can be placed in a chimney to collect combustion products. Headers 16 are like the nozzle 17 'arranged vertically. The runoff of water droplets from the pipe walls is collected through a trough 35, the one passage of the polluted incoming air

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allows, but intercepts the water droplets.

This embodiment can be used in conjunction with a non-volatile liquid to provide particle removal and significant heat recovery from the hot gas stream in a device. The atomized liquid becomes hot and is circulated through a heat exchanger 36 before it is cleaned by a filter device 37 and returned to the spray or atomizer nozzle. The main liquid is circulated by pump 38 > through heat exchanger 36 and back to trough 35. The remainder of the liquid would be pumped through filter 37 by pump 39 to atomizing nozzle 17 *. Droplets of non-volatile liquid remaining in the gas> could be removed in a second stage in which water jets are used.

In summary, the present invention provides an improved electrostatic precipitator which is extremely effective and relatively low in cost. Electrical insulation problems are reduced, since the collector devices do not have high potential electrodes. It enables comfortable accumulation the dust particles as the droplets of water or other liquid used for precipitation continue the purpose of entrainment of these particles and their subsequent removal through the liquid drain into the

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Serve receiving trough. The simple shape of the precipitator allows convenient gas flow through it and therefore allows it to be in the conduit or chimney of a pollutant-producing source can be arranged directly with very little changes. Furthermore, the fact that one or two or at most a few steps create a highly effective precipitator that only takes up a very small amount of space is required.

The device of the invention can be used for removal of the most varied Types and impurities to be precipitated from gas streams are used. The invention is particular useful for sterilizing or purifying air through essentially complete precipitation of microorganisms .

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Claims (1)

Claims. 1. Electrostatic device for precipitation to remove foreign particles from a gas stream, characterized by combining means for introducing additional particles into the gas stream with means for electrostatic charging of both the foreign matter particles as well as the additional particles with an electrical charge of predetermined polarity and conductive with the earth connected surface parts to at least partially To limit gas flow and which are arranged downstream of the charging device and close to the charged particles create a space charge region of the conductive device in which at least a portion of the foreign matter particles and the additional particles move against the surface under the influence of the electric field and get struck down on it. 2. Electrostatic device according to claim 1, characterized in that the additional particles are a Contain dampening agent, which removes the foreign matter particles collected on the surface. J-. Electrostatic device according to claim 1, there being characterized in that the additional particles are water droplets. k. Electrostatic device according to claim 1, characterized in that the device for charging the 009811/1221 - 2ο - Particle forms part of a first stage and at this point no additional particles in the first stage are introduced, and a second stage is planned, which receives the gas stream from the first stage and this stage means for introducing additional particles into Contains the gas flow, as well as a device for electrostatic Charging both the foreign matter particles and the additional particles with an electrical charge of a predetermined polarity, as well as conductive ones connected to the earth Surface parts that limit at least part of the gas flow and this downstream of the charging device are arranged, and the charged particles close to the conductive device a space charging area create in which at least a part of the foreign matter particles and the additional particles are under the influence of the electric field move against the surface and be deposited on it. 5. Electrostatic precipitation device according to claim 1, characterized in that the device for charging the particle forms part of a first stage and includes a second stage which contains the gas stream from the first Stage can accommodate, and this second stage has means for introducing additional particles into the gas stream, and a device for electrostatically charging the additional particles with an electrical charge predetermined polarity and conductive surface parts 009811/1221 le are connected to the earth and at least partially limit the gas flow and are located downstream of the charging device, and the charged particles create near the conductive device a space charge area in which at least a portion of the particles and the additional particles move under the influence of the electric field against the surface and are deposited on it will. 6. Electrostatic precipitation device according to claim 5, characterized in that both the foreign matter particles as well as the additional particles of the second stage electrostatically with an electrical charge predetermined Polarity are charged and the charged particles near the conductive device have a space charge area create where at least some of the particles and the extra Particles move against the surface under the influence of the electric field and are deposited on it will. 7. Electrostatic precipitation device according to claim 6, characterized in that the additional and the complementary Particles are of the same type. 8. Electrostatic precipitator according to claim 6, characterized in that the additional particles of one type and the additional particles of one other type. 9. Electrostatic precipitator according to claim 009811/1221 6, characterized in that the additional particles Contain a wetting agent that can take away foreign particles that are deposited on the surface and in which the complementary particles contain water droplets. 10. Electrostatic precipitator according to claim 9, characterized in that additional particles are harmful. 11. Electrostatic precipitator according to claim 1, characterized in that the additional particles are introduced into a zone and the conductive surfaces are formed by longitudinal passages, the conductive walls located downstream of the electrostatic charging device to form a second zone and the electrostatically charged particles within the passage (passages) form a space charge area form in order to generate an electric field between the space charging area and the walls, which causes the particles to move against the walls of the passages under the influence of the electric field and be struck down on them. 12. Electrostatic precipitation device according to claim 11, characterized in that the additional particles Contain water droplets and that the longitudinal passages are inclined, whereby the water droplets deposited on the walls flow downwards and depressed strangers 009811/1221 Take with you fabric particles. I ?. Electrostatic precipitator according to claim 11, characterized in that the additional particles contain droplets of a non-evaporable liquid and the gas flow is above the ambient temperature, whereby the particles are heated and this heat is at least partially given off to the liquid and heat exchangers for recovering the heat are provided. l4. Electrostatic device according to claim 1, characterized characterized in that the additional particles are liquid and the gas stream is at a temperature which is sufficient to vaporize at least part of the liquid, and the charging device means for charging having only the additional liquid particles, and the evaporation of the charged liquid particles an escape of the charge from ihne.n and a Allows colliding with surrounding foreign matter particles, thereby charging the foreign matter particles. 009811/1221