DE2914340A1 - METHOD AND EQUIPMENT FOR REMOVING PARTICLES FROM A GAS STREAM - Google Patents

Description

DR. BERG DIPL.-ING. STAPF DIPL.-ING. SCHWABE DR. DR. SANDMAIR

FATfcNTAMWALTE

P.O. Box 860245 -8000 Munich 86 2914340

Λ0

Attorney's file: 29,970

Γ S, Aurii 1379

Monsanto Company

St. Louis, Missouri / USA

Method and apparatus for removing particles from a

Gas flow

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• (019) 9IM72 "hhtmatiK Uakkoatm: Hypo-Btek Munich 4410123t »

911273 BERGSTAPFPATENT MUeclnn (BLZ 70020011) Swiil Codt: HYPO OE MM

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Attorney's file: 29 970 ο η ι / ο / λ

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description

The invention relates to a device and a method for Removing particles from a gas stream, particularly insoluble, solid particles having a submicron particle size (i.e. with a size or diameter between 50 and 2000 Å) with the help of a fiber bed collecting device which the trapped insoluble solid particles can be removed during operation without taking out the fiber bed and must be cleaned by customer service.

Industrial exhaust gases and gas streams often contain undesirable ones solid particles which have to be separated from the gas stream with regard to environmental and process requirements. Particles with a particle size of three or more microns can be used in many ways with high efficiency Separating or separating devices are easily recovered. Smaller particles and especially those of submicron size and especially those with a size of less than about 0.2 μm are more difficult to achieve with a high degree of efficiency separate and separate.

In general, so-called fiber filters are used for particle separation and separation. tt separation or separation devices used, which can be divided into three groups; borrowing those with high submicron efficiency, those

at high speed and so-called atomization collection -

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facility (spray catcher).

With fiber bed separators working with high efficiency Usually fibers from 5 to 20 μm, e.g. glass fibers which are packed in a bed void fraction of 85 to 98% are used to produce submicron particles with a Efficiency of 95 to 98%, but usually at low gas flow rates (i.e. bed velocities) separated by up to about 0.15 m / s. At bed speeds Above this value, the pressure drop through the fiber bed increases considerably, whereupon the energy requirements also increase. Liquid particles such as spray, etc. flow efficiently from the fiber bed during operation. Easily soluble solid particles can be removed from such fiber beds during operation in that the fiber bed with a liquid is sprinkled in which the solid particles are easily dissolved. Gas flows that have a noticeable charge of insoluble solid particles, in particular with a size of over 1μΐη, can even with a sprinkling in with high Efficiency working fiber bed separator can be treated without gradually insoluble particles in the Build up the fiber bed until the fiber bed either becomes clogged or the pressure drop through the fiber bed due to the clogging has risen in an unacceptable manner, so that the fiber bed is then taken out for cleaning or replacement by customer service must become.

Fiber bed separators operating at high speed

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tings are used in such applications * where high Gas flow rates (e.g. bed velocities of 1.5 to 3 m / s) and a less effective separation of submicron particles can be allowed. At this Type of filter bed separating device are usually fibers with a diameter of 25 to 50 μm in the case of a bed cavity part used from 85 to 98%. For a given bed void fraction, the top fibers have one at high speed working fiber bed (compared to one with high efficiency working fiber bed) a considerably smaller fiber surface per unit volume of the fiber bed and consequently a more open one Fiber network. Consequently, this type of bed relies more on an inertial entrapment or impact mechanism of particle separation and consequently has poorer efficiency in ■ separating submicron particles. An elimination of insoluble, solid particles from such fiber beds by sprinkling or rinsing is for lower particle loads and possible for particles up to 2 µm in size; but here, too, there is again a gradual increase in the pressure drop and finally to clogging due to the difficulty of removing larger particles, which is present in most applications. after a few days or weeks of operation for removal, cleaning or replacement, contact customer service is required.

Finally, fiber beds with so-called spray or atomization devices are used in such applications,

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where high gas volumes are to be processed and only large particles with a size of 3 μm or larger have to be separated. A spray or mist collector typically uses fibers of an average diameter from 100 to 300 pm with a bed void ratio of 90 to 98%. These fiber beds have the lowest fiber area per unit volume of all fiber bed separating devices listed here for a given bed void fraction. she are mostly based entirely on the inertial impaction or pinch separation mechanism. As a result, the spray or atomization collection mechanism has the poorest efficiency to pick up submicron particles to separate. However, even large (e.g. five-inch) insoluble, solid particles can be sprinkled with or out Fiber beds are rinsed with spray collecting devices.

In the invention, fiber beds with spray or atomization traps for separating particles, and especially insoluble, solid particles from gas streams at high bed velocities of about 1.8 m / s or more with a high efficiency of at least 90% separation or separation of submicron particles and in the case of a liquid sprinkling of the fiber bed in order to remove the trapped solid particles in order to enable long-term, continuous and continuous operation without the fiber bed having to be removed by customer service as a result of clogging for cleaning or replacement. ..

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As used herein, "insoluble solid particles" includes on solid particles that do not dissolve in water or any other such liquid, which is used as a sprinkling liquid can be chosen ^ or which one such have a low rate of solubility in the liquid that their solubility cannot be effectively used can to remove them from the fiber bed.

As is well known, the collection efficiency of most separation devices, to remove particles from gases, electrostatically increased and improved. Even so, none is electrostatic improved fiber bed separator is known in which the difficulty is due to a gradual increase the pressure drop through the fiber bed due to clogging is avoided, due to which it will eventually become necessary is that the fiber bed is serviced by the customer for cleaning or replacement is taken out.

U.S. Patents 3,874,858 and 3,958,958 teach one device and a method for removing particles from a gas stream is described, wherein a (tightly) packed wet cleaning device is used after an electrical charge is first applied to the particles in an electrostatic field. the charged particles are in the densely packed wet cleaning device, which is kept electrically neutral, by a "Attraction" mechanism between charged particles and the electrically neutral wet cleaning device. In one such, described in the two patents

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On the catch and sainmel mechanism, it is necessary that the Gas stream flows at a velocity that is low enough in terms of attractive forces to keep the particle velocity and to overcome the viscous flow resistance of the gas on the particles. In the publications there is a upper limit of about 3m / s specified for the bed speed / however, the test results cited there show that, for example, at 1.2 and 2.1 m / s, the collection and collection efficiency was well below 90% in terms of submicron particles. Furthermore, the facility itself is very large and demanding a large packing depth in the direction of the gas flow, e.g. in the examples given 60 and 120 cm.

In US Pat. No. 4,029,482, particles are removed by means of a dry fiber bed after an electrical charge has first been applied to the particles in an electrostatic field, with at least initially high efficiency in separating submicron particles. The charged particles are in the dry fiber bed, which has a (high) electrical resistance (ie is non-conductive) _; separated by a "space charge" mechanism whereby the charged particles which are captured and collected in the dry, non-conductive fiber bed create a significant electrical charge density in the fiber bed, thereby deflecting gas-borne charged particles out of the direction of gas flow around the Increase the collection efficiency of the fiber bed. - | g _

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In US Pat. No. 4,029,482, a "space charge" mechanism is between ■ nism and the well-known "Bildkraff" mechanisms, which seem to be the same as the one in the OS-PS "Attraction Mechanism" mentioned in US Pat. No. 3,874,858 4,029,482 is mentioned that the "Bildkraff" mechanisms on low gas flow rate (i.e. bed velocity) are limited and provide little improvement in submicron particle collection efficiency; this are, as noted, those in U.S. Patents 3,874,858 and US Pat

3,958,958 cited disadvantages.

Although these disadvantages are overcome in U.S. Patent 4,029,482, this has only been achieved at the expense of another major disadvantage, namely, the disadvantage that the fiber bed cannot be cleaned while it is in operation, to a low pressure drop maintain. The separator in US-PS

4,029,482 operates so that trapped particles are in the dry fiber bed be built up or rocked to create the required space charge. At a constant bed speed the pressure drop through the fiber bed increases as the fiber bed becomes progressively more clogged, up to a certain level Time the fiber bed must be removed for overhaul and cleaning. In addition, U.S. Patent 4,029 482 it can be seen that a maximum value of the collection efficiency of this separation device at bed speeds of only about 0.9 m / s, while the collection efficiency is at higher bed speeds drops sharply. _ 17 »

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Of great importance for the invention are the tests given in US Pat. No. 4,029,482 with fiber beds which are made with Water spray, and with conductive fiber beds, both of which, however, adversely affected the collection efficiency. U.S. Patent 4,029,482 has attributed this drop in efficiency to the fact that such wet fiber beds or conductive Fiber beds work with the "Bildkraff" mechanism and not with the "space charge" mechanism. State of the art Thus, it can be seen that using the "image force" or "attraction force containment" mechanisms, low bed velocities are observed must be applied and only a modest degree of efficiency in terms of separation of submicron particles is achieved. Furthermore, it can be seen from the prior art that these disadvantages are overcome by employing the so-called "space charge" mechanism can be overcome, but a new disadvantage must be accepted, namely the fiber bed can not be kept clean of trapped, insoluble particles, so that the pressure drop in the during operation Fiber bed gradually increases until the fiber bed must finally be removed for maintenance and cleaned.

The invention is intended to provide a method and a device for removal of particles from a gas stream by placing a fiber bed trap with a low pressure drop in the fiber bed is used. Furthermore, the invention is intended to provide a method and an apparatus for removing particles, and in particular of insoluble, solid particles, from a gas stream with the help of a fiber bed \: - create a collection device, out

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which trapped, insoluble, solid particles during operation can be removed without the customer having to use the Paserbett must be removed for maintenance.

In addition, the invention provides a method and a device in which even submicron particles can be separated from the gas stream with a high collection efficiency. Further The invention provides a method and an apparatus in which a fiber bed can be used to with a high efficiency of separating insoluble, submicron solid particles, with the trapped, insoluble, solid particles removed during operation without interruption to an unacceptable increase in pressure drop to forestall in the fiber bed during long periods of operation. Finally, according to the invention, a A method and apparatus can be provided in which there is a continuous, on-going useful life of a fiber bed separation direction for insoluble solid particles is no longer limited by how quickly the fiber bed becomes clogged.

Here, in the method according to the invention, in which a particle containing gas flow is first passed through an electrostatic or ionization field to produce a positive! or negative To apply charge to the particles, and then passed through a fiber bed, simultaneously the fiber bed with a The liquid is sprinkled at such a flow rate that at least a sufficient part of the fiber bed is

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contains sufficient liquid so as to remove the electrical charge from the fiber bed and the charged particles trapped therein to atomize through the liquid or to dissipate to earth, without a significant space charge on the fibers and the particles captured in the fiber bed is created. A liquid can be used here, which is either self-conducting or which becomes conductive during operation due to the suspended and / or dissolved particles.

In particular, to carry out the above-mentioned procedure described device according to the invention comprises a housing with inlet and outlet sides, a particle loading section in the housing with an electrostatic or ionizing field generating device, a fiber bed that is between disposed in the particle loading section and the outlet, sprinkler means; around a flow of liquid through to provide the fiber bed at a flow rate such that at least a sufficient portion of the fiber bed is sufficient Liquid contains in order to continuously transfer the charge from the fiber bed and the charged particles trapped therein to deliver the liquid to an electrical ground potential without creating any significant space charge in the fiber bed will.

Although the method and apparatus according to the invention are suitable for any liquid or solid particles to separate from gas streams at a high bed velocity and with a high collection efficiency even for submicron cells,

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are the method and the device according to the invention in particular applicable to insoluble, solid particles with high efficiency and at high bed speeds of about Dissolve 1.8 to 4.6 m / s or more from gases.

The fiber bed used in the device and the method according to the invention is a bed of fibers with an average diameter of about 50 to 1000 μm and in particular about 100 to 500 μm, which are packed with a bed void fraction of at least 90%. Preferably, fibers having an average diameter of about 100 to 250 used to in a bed void fraction of about 95 to 98%. For example, fibers with an average diameter of 200 μm, which are packed in a bed void fraction of 95%, create a fiber surface area of approximately 1013 m ^a / m ³ .

Although the charge is derived from the fiber bed, so that no significant charge develops on the fibers of the fiber bed or may remain on the trapped particles, space charge effects in the gas phase in the fiber bed are in particular present with larger fiber diameters and larger particles. In the preferred embodiment in which fibers used with an average diameter of 100 to 250 μπι however, the image force collecting mechanism is maximized and the space charge collecting mechanism is reduced to a minimum. In a less preferred embodiment for fibers with an average diameter from 500 to ΙΟΟΟμπι is the space charge collection mechanism (in the

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Gas phase) brought to a maximum value, and the image forces mechanism is reduced to a minimum.

The fibers used preferably have a relatively uniform distribution of the fiber diameter within. + 30% the selected average fiber diameter. As long as "however, the average fiber diameter in the broad is the range specified in the previous paragraph, a large range of fiber diameter distribution can also be permitted, provided that no more than about 10% of the fibers have a diameter of less than 40 μm.

The bed void fraction, expressed as a percentage void volume fraction is expressed by the following equation

defined: _nn

v% " * - P * ¹⁰ ° ^D f

where V% is the percentage void fraction, D »is the density of the fiber material and D is the packing density of the fiber bed. For example, if glass fibers with a specific gravity of, for example, 2.55 are used, the density of the fiber material (D-) is 2.55g / cm ³ . A bed of glass fibers with an average diameter of 200μπι, which _{are packed with a packing density (D f} ) of 0.11g / cm ³ , have a bed void fraction (V%) of 95.6%.

As can be seen from the foregoing, the fiber beds used in the invention are quite loose packed, open network of relatively coarse fibers.

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With a void fraction of about 96%, the distance between the fibers is usually about five times the fiber diameter. Although insoluble, solid particles can easily be flushed out of such a fiber bed, such have hitherto been found Fiber beds are not suitable for submicron lichen with a remove acceptable efficiency from gas streams. Rather, their use has been limited to applications where either there are not enough submicron particles of interest or where there is a significant amount of submicron particles, but does not need to be removed, or by means of known or subsequently arranged means for removing Submicron is removed.

The invention is not restricted to the fiber material used. In a preferred embodiment, glass fibers and fibers made of other dielectric materials are used; the sprinkling liquid and / or the particles it contains create sufficient conductivity to to derive electrical potential from the captured, charged particles, so that there is no disruptive space charge on the fibers and can form on the particles trapped in the fiber bed. Such dielectric fiber materials include, for example Synthetic fibers, such as polyester, polyvinyl chloride, Polyethylene terephthalate, fluorocarbon polymers such as Teflon, Nylon; Polyalkylenes such as polyethylene and polypropylene, mineral or slag wool, asbestos, etc. _ 23 -

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However, if necessary, conductive fiber materials can also be used because they are practical of the invention so that the fiber bed itself becomes conductive without relying solely on the irrigation liquid / particles to leave. In this embodiment it is sprinkling or watering the fiber bed is still necessary in order to constantly moisten and rinse the trapped particles in order to remove the To prevent or minimize the tendency of dry particles to be drawn back into the gas stream. Corresponding conductive fiber materials are, for example, metals such as stainless steel, titanium, copper, brass etc. or a wire mesh with a corresponding fiber diameter, such as carbon or graphite fibers.

The distribution of the fibers in the fiber bed can be arbitrary and arbitrary, but in order to achieve the best results, the fibers are at least partially aligned parallel to the vertical plane that runs transversely to the direction of gas flow, and are oriented less or substantially arbitrarily across the front of that plane. This is in FIG. 5 shown schematically.

This oriented fiber bed can be quantified by saturating (or filling in) a cubic volume of a trial or test fiber bed (as shown in Figure 5) with water with the cube positioned so that the more oriented plane is vertical and the residual water saturation in the fiber bed is measured after a drain

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has ceased due to gravity, whereupon the search bed is rotated so that its surface, which would normally be the downstream surface, is now in the ground or base position, and the test for residual saturation is then repeated. The desaturation of the cubic fiber bed in which the more oriented plane is arranged vertically should be at least 15% smaller than the desaturation when the other plane is oriented vertically. Any build-up of water at the bottom of the fiber bed due to capillary and surface tension should be corrected by such tests relating to the residual tension, or alternatively a sufficiently large fiber bed, e.g. about 25 cm in each direction, can be used so that such a build-up with respect to the residual saturation becomes negligible.

In general, a fiber bed depth is sufficient in the direction of the gas flow from about 5 to 15 cm for an effective separation of even submicron particles from the gas flow from deeper fiber beds only create a marginally improved containment effect, however at the expense of a proportionally greater pressure drop. If necessary, the fiber bed can then be a series of fiber beds shallower depth, for example from about 2.5 to 5 cm, the fibers in each case are in contact with the fiber and / or to a small extent A distance of, for example, about 0.5 to a few centimeters are arranged from one another.

The invention is also not limited to such devices or

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driving restricted, in which an electrostatic or ionizing DC voltage field generated.by which the electrical charge is applied to the particles. Such facilities and methods are well known and usually have one or more discharge electrodes of one polarity in connection with one or more grounded electrodes, the charging electrodes being connected to a DC voltage source of up to 35 00OV or more are connected.

However, the strength of the electrostatic or ionizing field must be sufficient to apply the required electrical charge to the particles, and for best results such a field should extend across the entire cross-sectional area of the housing in the particle loading zone. For example, yields a direct current of about 6 to 20 mA at 25 00OV a corona power of 150 to 500W, which is appropriate to process about 19.8 to 28,3m ³ / min gas.

Corresponding devices for sprinkling or washing out the fiber bed in order to remove particles therefrom are known and do not represent a limitation of the invention. It is only necessary that the sprinkler or irrigation device can irrigate at least the upstream part of the fiber bed in the bed depth where the essential Part of the particle is captured. Preferably, however, the entire fiber bed is sprinkled and watered.

Thus, the fiber bed can be filled with liquid from a liquid

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Distributor are sprinkled, which is arranged above or in the upper part of the fiber bed. Various liquid distribution devices can be used here in order to distribute the liquid on the upper side of a fiber bed, for example perforated distribution plates, etc., can be used. Advantageously, deflection or baffle surfaces can also be used
be placed at the top of the fiber bed in order to prevent the gas flow from surrounding the fiber bed
Bypasses liquid distributor head or a corresponding distributor device.

As an alternative to or in connection with such a fiber bed sprinkling device arranged above it, the
Sprinkling liquid can be sprayed onto the upstream surface of the fiber bed, the viscous resistance of the flowing gas at least partially transferring the liquid over the
Depth of the fiber bed takes away before the liquid due
gravity drains from the bottom of the fiber bed. Such a viscous gas phase flow swider stood acting on the liquid increases with increasing velocity of the gas in the bed. At higher bed speeds, e.g.
3 _r 3 m / s entrainment of the liquid as well as of droplets in the gas leaving the fiber bed becomes a difficulty, but one which can be eliminated by a number of means or at least substantially reduced by either
entrainment at high speeds is prevented or entrained droplets are separated again in subsequent separation devices. - 27 -

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The speed of liquid flow required in the fiber bed depends on the particular application. The minimum flow rate is necessary to prevent space charge from developing in the fiber bed, which is a function of the fiber bed dimensions, the nature of the fibers with respect to conductivity, and the conductivity of the liquid particles with respect to the fiber bed. In addition, however, the flow rate of the liquid must be sufficient to wash the solid particles out of the void portion of the fiber bed and depends on the fiber diameter, the speed of the gas to be processed in the bed and the charge of solid particles in the gas stream per unit volume of the fiber bed . For example, water flow rates of about 3.8 to 38 l / min / m ^{3 have been found} to be sufficient for fiberglass beds to remove boiler dust with charges of about 200 to 100 mg / m ^{3 of} gas at bed speeds of about 1.8 to 3.7 m / s to separate.

In a preferred embodiment of the invention, the grounded electrodes of the device generating the electrostatic field are sprinkled with a liquid in order to wash away particles that have been caught from the grounded electrodes. Corresponding sprinkling and irrigation devices, methods and the corresponding flow velocities of the liquids are known for electrostatic precipitating devices. The liquid used may be water or any other liquid prescribed or usable in the particular application. For example, if

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Can solid the particles caught are a mixture of insoluble matter and resinous, fatty or solid particles, which are soluble in a certain solvent or a corresponding solution, then advantageously the solvent or the solution is used to dissolve the soluble matter as well as to wash away the insoluble matter. When the gas flow unpleasant smelling substances or gaseous components such as sulfur dioxide, nitrogen oxide etc. as well as substances to be removed Contains particles, a liquid is advantageously used, which either with the odorous substance or the gaseous component reacts or absorbs it. Consequently, in various embodiments, the liquids aqueous solutions of cleaning agents, ammonium hydroxide or other alkali, sulfuric acid, acidic or basic salts, etc., non-aqueous liquids such as diethanolamine or their be aqueous solutions, etc. Others known in gas processing liquids used can also be used. If conductive fibers are used, non-conductive ones can be used Liquid-particle systems are used. When particle-laden Gas is processed, an electrostatic charge, preferably a negative charge, is applied to the particles, when they pass through the electrostatic field. In the case of negatively charged particles, there can be electrostatic fields with a higher voltage per centimeter of electrode gap before flashover occurs. In a before The preferred embodiment is, in particular when very dirty gases with a high dust load are to be processed, which Electrostatic field generating device with sprinkled

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or irrigated, grounded electrodes, a substantial part of the charged particles on the grounded electrodes to collect. The grounded electrodes mainly attract and trap the larger particles, whichever they are due to because of their greater mass, they will accept a higher charge. Although some submicron particles will be trapped on the grounded electrode can, they are mainly captured on the fiber bed. The trapped particles are held by the grounded electrodes removed by a conventional measure, such as by knocking or by means of forced air, but in particular in that the grounded electrodes are constantly sprinkled with a liquid, or that at least that is collected nen particles are intermittently washed away before they or their agglomerates are blown away by the air stream and to the Fiber bed to be worn. In this way, up to 50 to 95% of the dust contained in the gas flow can be removed, before it reaches the fiber bed, and the dust load which must be removed by the fiber bed can be reduced.

The remaining charged particles, or essentially all, if not the grounded electrodes as a containment and collection device are used, are entrained in the gas stream to the fiber bed and separated in this from the gas stream, while the fiber bed is sprinkled with a liquid in order to wash away the trapped and collected solid particles and to derive the electrical charge from the charged particles in order to prevent a significant space charge in the Developed fiber bed. - 30 -

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Much of the particles are in the upstream one third of the depth (in the direction of the gas flow) of the fiber bed, while gradually smaller amounts, especially larger particles are caught over the remaining depth of the bed. The fiber bed sprinkling system is preferably designed to carry the majority of the liquid with the aid of this upstream portion of the fiber bed of the viscous gas-phase flow resistance to be imparted to the liquid, which is a function of the velocity of the gas is in the bed, which takes the liquid deeper into the bed before the liquid is at the bottom due to gravity of the fiber bed flows off.

In a preferred embodiment, the sprinkling system is designed so that with regard to the gas phase resistance the liquid at least 50% of the irrigation liquid used in the fiber bed through the upstream one a third of the depth of the fiber bed flows. This can be achieved by sprinkling the fiber bed from above or that a liquid is uniform over the upstream lying surface of the fiber bed (especially at high bed speeds) is sprayed, or it can be done by combining of the two possibilities can be achieved. With this measure, the requirements regarding the sprinkling liquid be reduced to a minimum. Another means of meeting the irrigation requirements To minimize it is to use fiber beds which are tall and narrow, as far as aerodynamic ones are

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Allow ratios of the fiber bed design.

Depending on the application, it may or may not be desirable to add the liquid used to the fiber bed irrigation device _; a sprinkler system with either grounded electrodes or both. In view of the maintenance and cost, particularly of expensive liquids, recirculation and recirculation / when it is feasible is quite desirable. In the simplest case, only the undissolved, solid particles need to be separated from the liquid by a conventional device before it is fed back again. In many cases, however, the liquid used can contain soluble particles, absorbed gases or reaction products which prevent it from being fed back and recirculated, if the liquid used is not at least treated beforehand by regenerating it and removing imperfect constituents.

For example, if the device and method according to the invention are used to scrub obscure gases together with particles from an exhaust gas stream and to clean it, at least a partial regeneration of the liquid is necessary before it is returned to the irrigation system. An example of such a cleaning process to remove sulfur dioxide from gas streams in order to scrub out sodium or ammonia or an alkanolamine is described in US Pat. No. 3,873,673. In addition to the above

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The device and the method according to the invention can be used in a wide range of industrial applications and environmental applications used to be liquid or to remove solid (soluble or insoluble) particles or mixtures thereof. In a preferred embodiment, the However, the invention is particularly designed for applications that require the separation of insoluble, solids from gases and particularly where separation of submicron insoluble particles with high efficiency is required will. Examples of such insoluble particles for which the invention is suitable are fly ash, boiler dust, Combustion dust and smoke, carbon, silica dust, pigment dust residues, Hüttenrauch et al.

The device and the method according to the invention are particularly suitable for the preparation of gas flows at high Velocities in the fiber bed. The overall collection efficiencies from 98 to 99.9% at at least 85% and preferably from 90 to 95% efficiency with respect to submicron particles in the The range from 0.2 to 0.9 μm can be achieved at bed speeds of 1.8 to 3.3 m / s and even at around 4.6 m / s and more can be obtained by preventing or re-entrainment Removal is provided. Despite these high bed velocities, the invention provides high collection efficiency with minimal pressure drop in a more compact device than, for example, that packaged in U.S. Patents 3,874,858 or 3 958 958 described bed cleaning device- Dasich die

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energy required for the smaller fans compared to the Keeping the energy roughly in equilibrium, which is required for the device generating the electric field, results in energy savings compared to other high-efficiency separating devices, such as fiber bed separating devices, whereby the use of the invention becomes advantageous in those applications where there are no insoluble solid particles are present, such as in the case of ammonium nitrate and urea prilling towers, for smoke, powered by charcoal Roasting stems etc.

The invention thus provides a method and a device for removing particles from gas streams with a high Auffangbzw. Collection efficiency even with submicron particles. Here, the device according to the invention has a grounded Fiber bed with fibers with an average diameter of 50 to ΙΟΟΟμπι, which with a bed void fraction of at least 90% are packed, an electrostatic or ionizing field generating device. the upstream with respect to of the fiber bed is arranged to apply an electrical charge to the particles, and a sprinkler on in order to irrigate the fiber bed and, if necessary, the grounded electrodes of the electrostatic device, as well as to be collected Flush particles out of the fiber bed and, if necessary, away from the grounded electrodes. The inventive The method is particularly applicable for separating any particles and is particularly advantageous for removing insoluble, solid Separate particles from gas streams at high bed velocities of 1.8 to 4.6 m / s or more. The preferred fiber bed

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has glass fibers with a diameter of 100 to 5 (preferably from 100 to 250 μΐη. Will be used during operation Particles are introduced into the electrostatic device and the charged particles are captured in the fiber bed and collected, with the electric charge passing over the irrigation liquid-Z-particle mixture is derived, so that there is no significant space charge effect on the fibers of the Fiber bed can develop and entrainment of particles is avoided.

The invention is described below on the basis of preferred embodiments Forms with reference to the accompanying drawings explained in detail. Show it:

Fig. 1 is a sectional side view of an embodiment of the invention;

1A shows a sectional view from above of the device of FIG. 1 generating the electrostatic field.

Figures 2 and 2A are top and end views, respectively, of a Portion of a preferred, practically usable device for generating the electrostatic field;

Figure 3 is a side sectional view of the upper part of the fiber bed with a preferred embodiment of a

Sprinkling liquid distribution from above;

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4 is a side sectional view of an inclined fiber bed, according to one embodiment of the invention; and

Figure 5 is a schematic representation of the plane of alignment of the fiber in a preferred fiber bed embodiment the invention.

In the embodiment according to the FIGS. 1 and 1A, the inventive Device a housing 2 with a gas inlet side 4 and an outlet side 6. Inside the housing is close to the inlet side a device generating an electrostatic field is arranged, which has a number of high-voltage discharge electrodes 8, which emit a high voltage with a not shown DC voltage source are connected, and a number of grounded electrodes 10 has. The discharge electrodes * 8 can either have positive or negative polarity, but are preferably negative as shown in Figures 2 and 2A. The grounded electrodes 10 have opposite polarity to the discharge electrodes, for example they are positive, as shown in Figures 2 and 2A.

Downstream in the housing (in the direction of the gas flow) of the device generating the electrostatic field, a fiber bed 12 with a sprinkling device 14 provided above it, in order to keep the sprinkling liquid in the Distribute fiber bed. Apart from the irrigation liquid supply, the circumference (edges) of the fiber bed should be in the housing by means of a frame, not shown, with the aid

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of sealing or other conventional edge sealing devices be appropriately sealed to prevent gas leakage at the edges of the fiber bed. By means of a Sprayer 16 will spray the irrigation liquid uniformly at least across the top of the downstream sprayed lying surface of the fiber bed. In most cases, the sprinkler installed above it creates 14 a sufficient irrigation of the fiber bed so that a additional use of the spray device 16 is not required. However, under certain circumstances, the use of both the sprinkling device 14 arranged above and the spraying device 16 can be advantageous. With others Applications especially with a light dirt load in the Gas or in the case of fiber beds with a depth of only 5 to 7.6 cm in the direction of the gas flow or at a sufficiently high gas flow rate In the bed, when using the spray devices 16, the liquid can be sufficiently deep into the Penetrate fiber bed, so that the use of sprinkling devices 14 arranged above it is not necessary. During operation, gas containing dirty particles 18 is introduced on the inlet side 4 and flows through the electrostatic Field between the discharge electrodes 8 and the grounded electrodes 10, the particles e.g. are negatively charged as shown in the drawings. Charged particles 20 flow downstream and are in the Fiber bed 12 collected, which is electrically grounded. The particles trapped and collected in the fiber bed are by sprinkling with a liquid either from the above

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909843/0766

arranged sprinkling device 14 or the spraying device 16 or flushed out by a liquid from both devices. The liquid and the particles contained therein flow off on the underside of the fiber bed 12 and are out removed from the facility.

In a preferred embodiment of the invention, the used Liquid can be treated by removing solid particles and any other contaminants then fed back into the sprinkler system. In the simplified, In the flow profile shown in Fig. 1, the used liquid flows from the fiber bed in a series of lines 22 or into a container (not shown), then into one or more lines 22, into a collecting line 24 and from there into a liquid treatment device 26. This device can be a single or multi-stage clarification device or a settling device. container or other system to separate solid particles from the liquid. On the other hand, the liquid treatment device any other fluid treatment or regeneration system and method to be used Liquid for renewed circulation in the sprinkler system at least partially in its original condition bring back. From the liquid processing device 26 all or part of the liquid can be used together with fresh Liquid, if necessary, back to the sprinkling device 14 or the spraying device 16 or be directed to both. _ 38 -

909843/0768

29U34Q

In the preferred embodiment, also shown in FIG For example, the grounded electrodes 10 can be used as collecting or collecting devices for part of the charged particles In this case the grounded electrodes are also sprinkled with liquid to avoid the trapped To wash away particles. Conventional devices and methods can be used for such irrigation, for example a sprayer 28 disposed upstream of the grounded electrodes 10. Such a one Spray means 28 may, for example, be a number of pipes emanating from a manifold (not shown) each of which has a number of nozzles and which are each upstream of a discharge electrode 8 in the direction of flow are arranged; the nozzles are oriented so that the liquid hits the surfaces of the grounded electrodes is sprayed facing the charge electrode.

The liquid and particles produced by the grounded electrodes run off, are diverted from the underside by means of conventional devices, which are not shown, but are only indicated schematically by a line 30. If a return and a recirculation of the used Liquid is desired, it can be prepared separately, especially if this liquid is not the same as the is liquid used in the fiber bed. However, if both liquids are the same, that of the grounded electrodes Drained liquid can also be processed in the liquid preparation device 26. At different Embodiments can only use fresh liquid for sprinkling the

9 098 4 3/0 7 66 - 39 -

29H34Q

grounded electrodes are used and a feedback can only be applied to the fiber bed irrigation system, or it Treated liquid can be used to sprinkle the grounded electrodes.

In the preferred embodiment shown in Figures 2 and 2A, the electrostatic field generating means a number of rods 8A are used as discharge electrodes, each of which has a number of needle-shaped projections 8B which protrude parallel to the direction of gas flow both upstream and downstream from the rods. Like on As best seen in the end view of Figure 2, is the distance between those defined by the rod 8A (the solid circles with a point in the middle) needle-shaped projections 8B protruding upstream are essentially of the same size. In a similar way Thus, the distance between the needle-shaped protruding downstream from the rod 8A (the dashed circles) is Parts 8B are also essentially the same, but the downstream row of needles is upstream with respect to the row of needles aligned needles offset by half the distance. In this way, the corona discharge overlaps between each needle tip and the grounded electrode, as indicated by the slightly parabolic lines in Figures 2 and Fig. 2A is shown to thereby ensure that all of the particles are exposed in the electrostatic field.

In another preferred embodiment in which the grounded electrodes 10 are used as particle collection and collection devices, they are flat or somewhat convex plates that

909843/0766 - 40 -

% 29H34Q

are at least 12cm wide in the gas flow direction, respectively 12 to 25 cm wide. These broad, grounded electrodes result in a longer dwell time for the particles in the electrostatic field, which helps capture them at the grounded electrodes.

Although in the drawings only a series of discharge electrodes and grounded electrodes in the electrostatic field section of the device shown can of course also have two or more such rows as a function of the necessities of a given application one after the other in the gas flow direction.

In Fig. 3 both an embodiment is arranged above Sprinkling device 14 and a possibility shown, a high proportion of the sprinkling liquid allocate upstream portion of the fiber bed. One Liquid distribution line 15 is provided with a number of delivery pipes or outlets 15A. By appropriate arrangement of the pipes or outlets 15a along the length of the manifold 15, the liquid can, if necessary, in different Quantities are distributed along the depth of the fiber bed. The liquid is drawn from the pipes or outlets 15A released via a perforated plate 32 and then flows through the holes into the fiber bed 12. Advantageously, is a series of baffles 34 are provided to restrict the liquid to a series of chambers, in the present case Case three chambers a, b and c are shown, and in order to

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"- **" 29U340

prevent gas from bypassing it. As shown, there are three tubes or outlets 15A in chamber a, two in chamber b and one into chamber c. Due to the pressure drop along the manifold 15, at least 50% of the Liquid discharged into the chamber a, which is about the upstream lying one third of the depth of the fiber bed served and covered. With regard to the gas-phase viscous flow resistance Chamber c can be operated dry on the liquid in the fiber bed, i.e. none flows into it Liquid, especially at high Geasgeschwindigke iten in the fiber bed. "Fiber bed

In the embodiment shown in FIG. 4, there is a fiber bed 12 inclined at an angle, so that the sprinkling liquid that flows through the fiber bed both due to the Gravity and the viscous gas phase resistance drains downward through the fiber bed, as shown by the arrows is, flows downward essentially along the planes which run parallel to the respective surface of the fiber bed. This acts under the influence of the viscous gas phase flow resistance contrary to what otherwise individual parts of the liquid deeper into the fiber bed and at very high speeds away from the downstream surface of the fiber bed and entrainment. The corresponding angle of inclination of the fiber bed can be easily understood by the person skilled in the art with the help of the vector decomposition of the gas phase drag force and the force of gravity on the liquid at a given gas velocity in the bed and a certain flow velocity of the liquid can be calculated. At this

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909843/0786

291434Q

Embodiment can in terms of depth towards the gas flow and / or at higher flow velocities, e.g. from 3.6 to 4.6 m / s or more, narrower fiber beds are used with less fluid being entrained from the downstream surface of the fiber bed.

The invention is illustrated with the aid of the following table, using the device described in FIGS. 1 / 1A and 2 / 2A. In each test run, the fiber bed is a vertical, 5 to 10.1 cm deep bed of irregularly arranged, chemically resistant glass fibers with an average diameter of about 200μπι and a packing density of about 0.11g / cm ³ , resulting in a bed void fraction of about 95.6% calculated. In each case the height and width of the fiber bed were each 30.5 cm. The fibers are partially oriented in the fiber bed so that their unsaturation in the vertical direction is about 0.4 grams of water per gram of fiber and their unsaturation when rotated 90 degrees so that their surface is downstream (in the direction of gas flow) in the lower layer is about 1.55g of water per gram of fiber.

A number of runs were included, with Fly ash has been used in various air charges. On each of Runs 1 through 16, the fiber bed only became used as a collection and collection device, with water as Irrigation fluid from a manifold above the fiber bed

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909843/0786

"**" 29H340

was used and the grounded electrodes were not sprinkled. For comparison purposes, some of these runs were made with the electrostatic switched off. Field carried out, which is labeled "none" in the "coronal output" column. In test run 17, both Both the fiber bed and the grounded electrodes were used as collection and collection devices and both were filled with water sprinkled.

909843/0766

O CD OO -P-

Run.
No. Bedding
dizzy
speed (m / s) Fiber bed
depth (cm) ötauü-
load
(mg / m ^3. ), '.'. H ₂ U / LurT-- '
relationship
. (. 1 / 1.QQOACM) corona
power
. (W). . . ,. Middle
diameter
.Inlet. . Particles
he (μπι)
. . .Exit total
catching
Efficiency 1 3.0 5 76.3 . 12.9 no . 1.55 ' 0.75 77.0% 2 3.0 5 105.1 . 12.9 no . 1.45 0.64 82.0% 3 3.0 5 .111.4 . 12.7 . 126 1.50 0.92 89.3% 4th 3.0 . 5. .1.1.1. , .4. . \ 12.7 .1.26. . . .1.,. 5O. . 0.71 91.9% 5 3.3 5 170.1 23.4 no . 1.75 0.56 91.4% 6th 3.3 5. . 1.70.1 .23.4. . . . .1.26. . .1, 75 0.45 95.3% 7th 2.5 5 207.1 30.4 no 1.74 0.60 90.4% 8th 2.5 5 207.1. 30.4 . 1.26. 1.74 0.56 96.6% 9 3.3 5 163.2 11.7 no 1.75 '0.55 92.6% 10 3.3 5. 163.2. . 11.7 . . .1.26. . . . 1.75 0.40 96.4% 11 1.8 10.1 294.9 21.7 no 1.60 0.56 92.7% 12th 1.8 10.1 294.9. 21.7 .... . /.1.26. . . . . .1.60. . 0.47 98.4% 13th 3.3 5 844.1 23.4 » . 143 3.2 0.43 99.2% 14th 3.3 5 837.1 23.4 . 120 3.0 0.45 98.9% 15th 1.8 . 5 028.7 43.4 . 105 2.35 0.56 99.0% 16. .1,8. ·. ·. .-. ·. '753' 'Q'. . '.'. , \: '. 43> 4'. ' 122 . .2, .5.Q 0.55. 99.2% 17th 3.0 5 926.4 Fiber bed 3.2
Electrode Ί, 9 110 2.00. 1.15 90.2

cn I

Run.
No. Auffanc
0.2 ' jeffect
0.4 2%, id after <
0.6 '' Size
0.8 (in ¹ μπι)
1.0 2.0 8th% 3.0 3% . 1 - 29 0 37.2% 46.3% 90 9 96, 3 2 - 42, 2 63.5 64.0 93, 7th 98 8th 3 - 76 5. ". · 90.1 86.6 93, 5. 95 4th 4th - 79 4th 85.0. \ 6.7.,. 9. . . 96, 9 98., 4th 5 - 72, 7th 74.3 62.9 97 6th 99 3 6th - 89 4th 90.7 94.9 98 9 99 2 7th - 66 1 71.2 90.0 96, 9 99 6th 8th - 88 2 91.5 .96.4 98 3 99 4th 9 - 70 6th 77.7 90.7 98 4th 99 8th 10 - 85 1 91.0 96.4 99 3 99 3 11 63.4 73, 5 85.3 86.1 96, 7th 99 9 12th 89.7 94, 9 96.9 97.5 99 9 99 9 13th - 93, 8th 97.0 98.3 99 8th 99 9 14th - 9O ₁ 5 97.7 97.5 99 9 99 9 15th - 96, ¹ T '' 97.9 97.2 99 7th 99 9 16 • 95, 3 90.4 98.7 99 6th 99 0 17th 85 86.9 90.2 92, 94, .71.0% 73.9 86.4 89.2 90.4 96.5 87.5 96.1 90.6 95.5 90.8 90.4 99.4 98.4 98.4 90.7 90.2

GO Q

291434Q

When reviewing the data listed in the table, it should be noted that the test runs 1 to 10 and 13 to 16 used fiber bed was only 5 cm deep in the gas flow direction and even had such a narrow fiber bed the practical application of the invention still a noteworthy improvement with regard to the collection efficiency in particular of submicron particles creates. In the test runs 1 to 12, a two-stage arranged one behind the other was used Wire-plate arrangement where the electrostatic field is generated Device used (as shown in Figures 1 and 1A) is. Runs 13 through 16 were three-stage such an arrangement is used, thereby allowing a longer residence time for the particles in the electrostatic field, resulting in an average efficiency factor Submicron particles of over 95% even with those shown high dust loads.

That used in runs IT and 12, 10.1 cm deep fiber bed, which is an economically feasible depth, gives a submicron particle collection efficiency of over 96%, even if only the two-stage, sequentially arranged wire-plate arrangement of the electrostatic field generating device is used.

In run 17, a single stage of the needle and plate assembly illustrated in Figures 2 and 2A is that of the electrostatic Field generating device was used, whereby the earthed electrodes, i.e. the plates, were sprinkled with water.

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90984370766

The results presented are below the desired, but are with the object of the invention in view of the Consistent fact that the required coronal power for the needle-plate assembly of the used electrostatic Device is about 500 to 600 W, while in this test run only a coronal power of 118 watts was obtained. The collection efficiencies of at least 95% for submicron particles and even higher efficiencies with larger particles can be extrapolated from this data at corona powers of 500 to 600W.

End of description

903843/0766

Blank page

Claims (28)

Claims fly method for removing particles from a gas stream, wherein the gas first flows sequentially through an electrostatic field to place a positive and negative charge on the particles to be applied, and then flows through a sprinkled, packed collecting and collecting device in the form of a fiber bed, mark where the charged particles are then collected rejects that submicron particles from the gas stream with high efficiency at high velocities in the Fiber bed are separated while at the same time the trapped solid particles are removed from the packed fiber bed, without the gas flow being interrupted, the gas flow containing the charged particles through a bed of fibers with an average fiber diameter of 50 to 1,000 µm is conducted, wherein the fiber bed has a void fraction of 90 to 98%, which at the same time the fiber bed with a liquid is sprinkled which has a flow rate such that at least a sufficient part of the fiber bed has sufficient liquid contains to dissipate the electrical charge from the fiber bed and the trapped particles contained therein, and which flows at least in such an amount that there is no significant space charge in the fibers and on those in the fiber bed trapped particles can develop, and the trapped Bank account): Hjrpo-Buk MOnchm 4410122150 (BLZ 70020011) Swift Code: HYPO DE MM Bayer Verehubuk Manchen 4S3100 (BLZ 70020270) RoMGheck Manchen 65343-808 (BLZ 70010080) 909843/0766 ORIGINAL INSPECTED »(019) 918272 TeUtnnum: 9I827J BERCSTAPF PATENT Some 98 «274 TELEX: 9 * 3310 0524560 BERG d " ² " 29H340 solid particles from the paserbed without a substantial residue removed so that the electrical charge is diverted to earth potential, and that the liquid and that contained therein Particles flow out of the fiber bed. 2. The method according to claim 1, characterized in that it rejects, that the irrigation is continuous and continuous. 3. The method according to claim 2, characterized in that it rejects, that after the liquid and the solid particles contained therein have drained from the fiber bed, the solid particles at least partially separated from the liquid and the liquid is fed back again to sprinkle the fiber bed. 4. The method according to claim 1, characterized in that it rejects, that the sprinkling liquid is distributed in the fiber bed so that at least 50% of the liquid taking into account the viscous flow resistance of the gas phase in the upstream lying one third of the depth of the fiber bed is distributed in the gas flow direction. 5. The method according to claim 4, characterized in that the sprinkling is continuous. 6. The method according to claim 5, characterized thereby, that after the liquid and the solid particles contained therein have drained from the fiber bed, the solid particles at least partially separated from the liquid and the liquid to the 909843/0788 Sprinkling'des fiber bed is passed back again. 7. The method according to claim 1, characterized in that ic h- n e t that a number of grounded electrodes in the first electrostatic Field is provided and that the grounded electrodes are cleaned at least intermittently to avoid trapped Remove particles. 8. The method according to claim 7, characterized in that the grounded electrodes are cleaned by sprinkling with a liquid. 9. The method according to claim 8, characterized in that it rejects, that the irrigation of the grounded electrodes is continuous. 10. The method according to claim 9, characterized in that that the sprinkling of the fiber bed is also continuous. 11. The method according to claim 10, characterized in that it rejects, that the same liquid is used both for sprinkling the fiber bed and the grounded electrodes, that suspended particles are at least partially separated from the drained liquid, and that the liquid at least is fed back for sprinkling the fiber bed and / or the grounded electrodes. 9 09 8A3 / Ü76B 29U340 12. The method according to claim 1, characterized in that that the fibers of the fiber bed are at least partially aligned parallel to the vertical plane that transversely. to the direction of gas flow and that fewer fibers are oriented transversely to the face of that plane. 13. Device for removing solid particles from a gas stream, with a housing with inlet and outlet sides, with a particle charging section in the housing close to the inlet side and with a number of high-voltage discharge electrodes, .which are connected to a DC voltage source, wherein at least one grounded electrode is disposed in a corresponding location with respect to the high voltage electrodes to create a substantially uniform electrostatic field therebetween, with a packed bed charged particle collector disposed in the housing downstream of the particle loading section and having means for sprinkling the packed bed collecting and collecting means with a liquid, characterized in that submicron particles are separated from the gas stream with a high efficiency at high velocities in the bed, while at the same time the trapped solid particles are separated from the Bed are removed without interrupting the gas flow therethrough, a) the packed bed (12) having fibers with an average fiber diameter of 50 to 1000 µm, whereby the fiber bed has a void fraction of 90 to 98% , and 909843/0768 ~ ⁵ ~ 29U340 b) the sprinkling device a device (14) for a has such a liquid flow that at least a sufficient Part of the fiber bed (12) contains sufficient liquid to dissipate the electrical charge from the fiber bed (12), without a significant space charge developing in the fiber bed, and the charged, solid particles from the fiber bed (12) can be removed without substantial residue. 14. Device according to claim 13, characterized by a line arrangement (222,24) j to feed liquid and solid particles contained therein from the underside of the fiber bed to a liquid treatment (26), where the liquid is at least partially separated from the solid particles, and by a conduit arrangement for returning at least a portion of the treated liquid to the fiber bed irrigation device (14). 15. Device according to claim 14, thereby g e ke η η ζ e i c hn e t, that the fiber bed sprinkler (14) is designed and arranged so that at least 50% of the liquid in the one third of the depth of the upstream Fiber bed (12) in the direction of gas flow from the inlet (4) is distributed to the outlet side (6). 16. Device according to claim 15, characterized by a line arrangement (22,24). around liquid and in it contained solid particles from the lower part of the fiber bed (12 * 909843/0768 - ⁶ - 29U340 to be fed to a liquid treatment device (26). In which the liquid is at least partially separated from the solid particles, and by a conduit arrangement to at least part of the treated liquid to the fiber bed area. redirecting device (14). 17. Device according to claim 13, marked by ic h net a device (28). to at least partially remove captured particles from at least one grounded electrode (10) and to clean them thereby. 18. Device according to claim 17, characterized in that that the means for cleaning the trapped particles from at least one grounded electrode is a sprinkling device (28). 19. Device according to claim 18, characterized through a conduit arrangement (22,24,30) to remove liquid and the solid particles contained therein from the lower part of the Fiber bed (12) and from the lower part of the electrostatic field generating device (8,10) to a liquid treatment device (26) in which the liquid is at least partially separated from the solid particles, and by a conduit arrangement to at least a portion of the treated liquid of at least the fiber bed sprinkler (16) to feed again. 909843/0766 29H34Q 20. Device according to claim 19, characterized by a line arrangement to a part of the processed Liquid to the sprinkler (28) of the grounded Lead back electrode. 21. Device according to claim 13, characterized in that e t that each of the high voltage electrodes (8) has a number of needles (8B) from the front and the back of a they supporting rod (8a) protrude parallel to the gas flow direction and which needles (8B) in a substantially the same way large spacing from one another along the length of the rod (8A) with the needles (8B) on the back of the rod (8A) with respect to the needles (8B) on the front of the rod (8A) are essentially offset by half the distance. 22. Device according to claim 21, characterized in that that at least one grounded electrode (8) has a number of grounded plates, which in the gas flow direction of the inlet (4) to the outlet side (6) are at least 12 cm wide. 23. Device according to claim 22, characterized through a conduit arrangement (22,24) to remove liquid and solid particles contained therein from the lower part of the fiber bed (12) to a liquid treatment device (26) to convey to the liquid from the solid particles. separate, and through a conduit arrangement to at least one Part of the treated liquid to the fiber bed sprinkler 909843/6768 ~ ^Ö ~ 29U340 device (16) to return. 24. Device according to claim 21, characterized in that the fiber bed sprinkling device (14) is designed and arranged so that at least 50% of the liquid in the upstream one third of the depth of the fiber bed (12) in the gas flow direction from the inlet (4) is distributed to the outlet side (6). 25. Device according to claim 24, marked rejects through a conduit arrangement (22,24) to remove liquid and solid particles contained therein from the lower part of the fiber bed (12) a liquid treatment device (26) to pass the liquid at least partially from the solid particles to separate, and through a line arrangement to at least a part of the treated liquid to the fiber bed sprinkler (14). 26. Device according to claim 21, characterized by a sprinkling device in order to wash away trapped solid particles intermittently with the aid of a liquid from at least one grounded electrode (8) in the device (8, 10) generating the electrostatic field. 27. Device according to claim 26, characterized by a line arrangement (22,24,30) to remove liquid and solid particles contained therein from the lower part of the fiber ■ - 9 - 909843/0768 29U340 betts (14) and the lower part of the electrostatic field to convey the generating device (8,10) to a liquid treatment device in which the liquid is at least partially separated from the solid particles, and by a line arrangement to at least part of the treated liquid to at least the fiber bed sprinkler (14). 28. Device according to claim 27, denotes marked through a conduit arrangement to convey a portion of the treated liquid to the sprinkler (28) of the earthed Return electrode (8). 909843/0768