GB1600232A

GB1600232A - Dust precipitator

Info

Publication number: GB1600232A
Application number: GB24135/78A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1977-06-02
Filing date: 1978-05-30
Publication date: 1981-10-14
Also published as: AU3671678A; NL7806055A; IN148737B; DK244978A; FR2392723A1; SE7806075L; FI771757A; NO781843L; FR2392723B3; IT7849682A0; DE2823971A1; FI56776B; DD136801A1; JPS542578A; ES470409A1; IT1105309B; CA1098052A; FI56776C; AT361584B; ATA389578A

Description

(54) DUST PRECIPITATOR (71) I, ARVI ARTAMA, a citizen of Finland, of Laukontori 4 C 30, SF-33200 Tampere 20, Finland, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to an electrostatic dust precipitator of the type comprising several pairs of electrodes, past which a medium to be cleaned may be caused to flow, one electrode of each pair being connectable to one pole of a voltage supply, and the other electrode of each pair being connectable to the other pole of the voltage supply so that an electrostatic field can be created.

Electrostatic dust precipitators are used to remove impurities in the air, to clean and separate gases and to remove particles found in gases. According to the main principles found in precipitators of known types the medium to be cleaned, e.g. air, is caused to flow through a space provided with discharge electrodes and collector plates. Between the discharge electrodes and the collector plates a voltage is applied, high enough to produce a corona discharge from the discharge electrodes and to create an electrostatic field between the said electrodes and the collector plates at the same time. There is preferably a negative voltage at the discharge electrodes to produce a negative corona and ionization.

During the corona discharge both positive and negative ions are produced, and the positive ions remain at the discharge electrode because of its negative charge, while the negative ions move towards the collector plates along the lines of force of the electrostatic field. The negative ions will encounter the particles to be removed from the medium, charge them and carry them on to the collector plates. The medium thus cleaned is then exhausted from the other end of the precipitator.

The collector plates are cleaned at regular intervals to remove the dust deposited on the collector plates. This cleaning is generally carried out by means of powerful water sprays. Sometimes vibrating devices are used for better effect. The difficulty in cleaning the collector plates is a major defect of this type of dust precipitator. Dust particles will adhere very strongly to the collector plates.

The collector plate cleaning arrangements become very complicated and expensive and therefore precipitators of this type can be used only as large units in connection with major air conditioning and dust removing installations.

Dry electrostatic precipitators have proved rather ineffective, the degree of cleaning of the medium obtained being rather poor.

Moreover, they may constitute fire and explosion hazards, because in certain circumstances the dust deposited on the collector plates may catch fire, and in dusty environments, the fire may easily spread widely.

Therefore they neither can nor are allowed to be used in industry, for example. Removal of dust deposits from these precipitators may prove very difficult.

There are also known wet electrostatic precipitators of a type in which a water spray of finely divided droplets is provided in the space through which the air is caused to flow.

These droplets are ionized by the discharge electrodes and the ions will then encounter the dust particles found in the air and carry them on to the collector plates. The construction of this kind of precipitator is very complicated and its maintenance is also difficult, thus causing high costs to be incurred in its use.

An objective of the present invention is to provide an effective and constructionally simple electrostatic dust precipitator, particularly suited to room air-conditioning as well as industrial dust precipitation.

Further objectives are to provide an electrostatic dust precipitator which uses less energy in service than known types of precipitator, which has continuous flushing away of collected dust particles and the maintenance of which is simplified compared with precipitators of known types.

According to the invention, there is provided an electrostatic dust precipitator, comprising several pairs of electrodes, past which a medium to be cleaned can be caused to flow, ijne electrode of each pair being con nectable to one pole of a voltage supply and the other electrode of each pair being connectable to the other pole of the voltage supply so that an electrostatic field can be created, characterised in that the electrodes are arranged adjacent to each other in sequence in the flow direction of the medium to produce several electrostatic fields adjacent to each other in sequence in the said direction, the electrodes which are connectable to the one pole of the voltage supply being substantially of string form, and the electrodes connectable to the other pole being substantially of plate form, said electrodes when connected to said voltage supply producing non-homogeneous electrostatic fields, without the generation of corona discharge, by application of a voltage at a predetermined value which will not cause any corona discharge effect, said electrostatic fields causing separation of the positive and negative charges of the particles from one another, and the particles being converted into electric dipoles so that the particles move towards the string electrodes, and that means are provided to supply each of the string electrodes with a liquid stream to flush away the particles hitting it.

A precipitator according to the invention is of simple construction, effective and reliable in service and easy to maintain. The amount of energy required by it in service is also quite small.

Some embodiments of the invention are illustrated in the following description with reference to the accompanying drawings, in which: Figure 1 is a schematic presentation of the basic principle of operation of a precipitator according to the invention; Figure 2 shows in section a precipitator according to the invention, viewed from one side and depicted for the most part schematically; Figure 3 depicts in front view the positive electrode of one electrode pair of a precipitator according to the invention, on larger scale, viewed in part section on the line B-B of Figure 2; Figure 4 depicts the same in side view; Figure 5 depicts a section on line A-A of Figure 2, a negative electrode bing visible; Figure 6 depicts, as an enlarged detail view, an advantageous mode of construction of the negative electrode;; Figure 7 shows partly in section a side view of another embodiment of the dust precipitator according to the invention; Figure 8 is a front view of the precipitator of Figure 7; Figure 9 is a front yiew of an electrode element of the precipitator of Figure 7; Figure 10 is a side view of the element of Figure 9 partly in section; Figure 11 is a front view of another embodiment of an electrode element of the precipitator of Figure 7; and Figure 12 is a side view of the element of Figure 11 partly in section.

The principle of an electrostatic dust precipitator according to the invention is illustrated in Figure 1, in which A and B are electrodes shown in cross-section. A is a negative plate electrode and B a positive string or rod electrode. A relatively high voltage of some kilovolts is connected across the electrodes, which creates an electrostatic field between the electrodes. When a particle C is carried by a stream of air into this field, it is converted into an electric dipole and begins to move towards the region where the field strength is highest, in this case towards string electrode B. Since in a precipitator according to this invention, the string electrode is provided with a jet or thin stream of liquid, the particle is carried away by it. In a dust precipitator according to this invention the air is therefore not ionized to charge with electricity the particle to be removed.No electric discharge is produced.

A precipitator (Figures 2 to 6) according to this invention consists of a boxlike frame 1, most suitably of square or rectangular shape.

The top 2 of the boxlike frame is open and may be fitted with an openable lid for inspection and maintenance. Both ends are also open. The opening at the front part 3 is provided with an air filter 4, in itself of known construction, and a fan 6 which causes air to flow through the precipitator, is fitted in the back part 5. Of course, it is possible to provide the openings with suitable grilles or lattices which, without preventing the flow of air, protect the parts inside and are openable to facilitate maintenance. The boxlike frame is most suitably made of appropriate plastics material to minimise problems of electrical insulation.

The bottom of the boxlike frame comprises a basin 7 for holding liquids, and legs 8 are provided under the frame.

Positive and negative electrodes 10 and 11 are arranged alternately in succession in a space 9 between the front and back parts 3 and 5. Each of the positive electrodes 10 (Figures 3 and 4) consists of a frame 12, with a trough 13 or the like, for liquid, at the top of it. The bottom of the trough 13 is provided with small flow openings 14 placed closed to each other; thin strings 15 pass through the openings; the top ends of the strings are fastened to a bar 16 running along the middle of the trough and the lower ends of the strings are fastened to the bottom part of the frame. The purpose of the strings is to act as guides for the flow of liquid. Water or some other liquid runs along these strings.

Oil is appropriate on account of its insulation being easier. In this instance the guide string has to be of some conductive material such as metal. In the middle of the electrode frame there is an overflow pipe 17 for preventing the trough from being excessively filled. The troughs of individual electrodes are furthermore connected to each other by means of a connecting pipe 18, which keeps the fluid in all the troughs at the same level. The inside surface of the boxlike frame of the precipitator may be provided with guides into which the electrodes are pushed so that they take their correct positions. Intermediate plates 19 separate the positive electrodes from each other and support the negative electrodes 11.

The positive electrodes are, however, electrically connected with each other, e.g. by means of the connecting pipe 18, which may be electrically conductive. The lower ends of the electrodes 10 reach below the liquid level in the basin 7. The precipitator is provided with a pump 20 for pumping liquid from the basin 7 to the troughs 13, when the precipitator is working; from the troughs 13 the liquid flows continuously down along the strings 15.

The bottom of the basin is provided with a filter, the purpose of which is to collect impurities from the liquid in the basin. The filter is, of course, of a changeable or cleanable type.

Each of the negative electrodes 11 consists of a wire-net plate (Figures 5 and 6) or a finemesh honeycomb plate so as to allow the air stream to pass through it. The electrodes 11 may also be solid plates without any holes, provided that the air flow is parallel to them.

The electrodes 11 may also be coated with some electrically insulating material to prevent electric discharge between the electrodes. Most conveniently they are fitted into guides that are formed on the inside walls of the boxlike frame; the guides are provided with stops to prevent the negative electrodes from reaching down to the surface of the liquid in basin 7. The basin is provided with transverse partitions directly below the electrodes; however, the partitions do not divide the basin into totally separate sections.

To operate the precipitator, poles 22 of a voltage supply higher than 4 kV are connected to the electrodes and the pump and the fan are started. As voltage builds up in the electrodes and the flow of the air to be cleaned passes through the precipitator, the opposite electric charges of minute dust and other particles in the air separate and the particles become electric dipoles, as already stated above. The particles now move to the string electrodes provided with the liquid streams, the streams then carrying the particles away and the air becoming thus effectively cleaned. The poles of the voltage supply can be reversed, or one of the electrodes in each pair, e.g. that provided with the liquid streams, can be earthed. In spite of this, the direction of movement of the particles in this field remains the same, i.e.

towards the string electrodes.

Ordinary water from the mains is suitable for use in the precipitator, wherever it contains a sufficient quantity of salts to make the water electrically conductive. Of course other liquids may also be used. If the flowing liquid is an insulating substance, the guide strings must be bf some conductive material.

In the Figures 7 to 12 preferred embodiments of the invention are shown. The precipitator has a casing 30 of box-like form, and preferably of plastics material. In the front wall 31 of the casing, there is an opening 32 through which the air to be cleaned is conducted into the precipitator. In the opening 32 a fan 33 is mounted, which blows the air through a space 34 within the casing and electrode elements to create the electrostatic field are mounted within this space. The air is exhausted through another opening 35 in the opposite end of the casing.

On the bottom of the precipitator there is provided a basin 36 receiving the flushing water together with dust particles, flowing down from the electrode elements. A pump 37 with a driving motor and filter is mounted within the basin. The filter prevents the dust particles from coming back on to the electrode elements along with the water which is pumped back into channels at the upper parts of the elements through a hose 38. Only a pump of low power is needed for this purpose, because the amount of water required is quite small. The precipitator is also provided with a voltage source, e.g. a voltage transformer 39, which transforms the mains voltage into an operating voltage of about 4 kV.

Each of the electrodes (Figures 9 to 12) of this embodiment comprises a rectangular frame 40 preferably made of plastics material. The frame 40 consists of vertically arranged members 41 at the opposite sides of the frame. At the top and bottom, troughs 42 are attached. The trough at the top is open upwards thus forming a channel to receive flushing water for the electrodes. Support plates 43 are attached at upper and lower parts of the frame to make the construction more rigid. At the bottom of the trough 42 at the top of the frame, a plurality of flow openings 44 is formed, evenly spaced and close to one another. Through these openings pass thin strings or wires, preferably of metal, to form the electrodes 45. The openings 44 are of greater diameter than the diameter of the springs thus allowing the water to flow downwards through the holes and along the strings towards the basin 36.In addition to the string electrodes a plate electrode 46 is also mounted on the frame 40. The plate electrodes 46 are preferably made of wire-net plate as in the first embodiment and may also be coated with insulating material as before.

The troughs 42 at the tops of the electrode frames act as channels for the flushing liquid as in the first embodiment. In this embodiment the adjacent troughs are not connected with each other by means of overflow tubes, but an overflow lip is formed at the middle part of one side of the trough by bending the edge partially outwards and downwards.

When the electrode frames are mounted in the casing, the first frame is set on its place and then the following frame rests against the side of the trough of the first frame which is not provided with an overflow lip, and so on for the rest of the frames. When water flows through the hose 38 into the trough of the first electrode element at the right in Figure 7, the excess water will flow over the overflow lip into the trough of the following frame and so on, so that all the frames receive flushing water for the electrodes.

From the last frame at the left (in Figure 7) the excess water flows into a channel 48 and then into the basin 36.

The side parts of the troughs 42 at the bottoms of the frames are bent in the same way as those of the troughs at the tops. Thus the frames will support each other by means of this feature. This construction is also very useful in that the frames can be mounted in position no matter which end is downwards or upwards. The walls of the casing can be provided with suitable rests or guides, supporting the frames in their places.

According to a further embodiment (Figures 11 and 12) the plate electrode in the frame of the element may also consist of a plurality of metal sheet strips 49 which are connected together and mounted between the said string electrodes.

The electrode elements according to the described embodiments are particularly advantageous in being easy to clean and maintain.

Construction of the electrostatic dust precipitator using these types of electrode elements may be very simple and economical.

Various sizes of dust precipitators can be manufactured by means of only a few sizes of elements.

The connection of the elements to the poles of the voltage source can be easily achieved.

WHAT I CLAIM IS: 1. An electrostatic dust precipitator, comprising several pairs of electrodes, past which a medium to be cleaned can be caused to flow, one electrode of each pair being connectable to one pole of a voltage supply and the other electrode of each pair being connectable to the other pole of the voltage supply so that an electrostatic field can be created, charaterised iii that the electrodes are arranged adjacent to each other in sequence in the flow direction of the medium to produce several electrostatic fields adjacent to each other in sequence in the said direction, the electrodes which are connectable to the one pole of the voltage supply being substantially of string form, and the electrodes connectable to the other pole being substantially of plate form, said electrodes when connected to said voltage supply producing non-homogeneous electrostatic fields, without the generation of corona discharge, by application of a voltage at a predetermined value which will not cause any corona discharge effect, said electrostatic fields causing separation of the positive and negative charges of the particles from one another, and the particles being converted into electric dipoles so that the particles move towards the string electrodes, and that means are provided to supply each of the string electrodes with a liquid stream to flush away the particles hitting it.

2. An electrostatic dust precipitator in accordance with claim 1, characterised in that each electrode of string form comprises at least one string fastened to an electrode frame and adapted to guide a liquid stream.

3. An electrostatic dust precipitator in accordance with claim 2, characterised in that each electrode of string form comprises a plurality of strings arranged adjacent to each other in a said frame.

4. An electrostatic dust precipitator in accordance with claim 3, characterised in that a top part of each electrode frame comprises a receptacle for liquid, the bottom of the receptacle being provided with holes through which the strings pass to a lower part of the frame and from which the liquid runs along the strings.

5. An electrostatic dust precipitator in accordance with claim 4, characterised in that the receptacle comprises a trough.

6. An electrostatic dust precipitator in accordance with claim 5, characterised in that the electrodes are arranged within a boxlike casing, the ends of the casing being provided with openings for flow of the medium to be cleaned and the bottom of the casing being provided with a basin for liquid, and a pump being provided to circulate the liquid via the troughs and strings.

7. An electrostatic dust precipitator in accordance with claim 6, characterised in that a filter is provided in the basin to clean the liquid.

8. An electrostatic dust precipitator in accordance with claim 6, characterised in that each trough is provided with an overflow.

9. An electrostatic dust precipitator in accordance with claim 6, characterised in that a connection is provided between individual troughs.

10. An electrostatic dust precipitator in accordance with claim 6, characterised in that a filter is provided in one end opening of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. frames act as channels for the flushing liquid as in the first embodiment. In this embodiment the adjacent troughs are not connected with each other by means of overflow tubes, but an overflow lip is formed at the middle part of one side of the trough by bending the edge partially outwards and downwards. When the electrode frames are mounted in the casing, the first frame is set on its place and then the following frame rests against the side of the trough of the first frame which is not provided with an overflow lip, and so on for the rest of the frames. When water flows through the hose 38 into the trough of the first electrode element at the right in Figure 7, the excess water will flow over the overflow lip into the trough of the following frame and so on, so that all the frames receive flushing water for the electrodes. From the last frame at the left (in Figure 7) the excess water flows into a channel 48 and then into the basin 36. The side parts of the troughs 42 at the bottoms of the frames are bent in the same way as those of the troughs at the tops. Thus the frames will support each other by means of this feature. This construction is also very useful in that the frames can be mounted in position no matter which end is downwards or upwards. The walls of the casing can be provided with suitable rests or guides, supporting the frames in their places. According to a further embodiment (Figures 11 and 12) the plate electrode in the frame of the element may also consist of a plurality of metal sheet strips 49 which are connected together and mounted between the said string electrodes. The electrode elements according to the described embodiments are particularly advantageous in being easy to clean and maintain. Construction of the electrostatic dust precipitator using these types of electrode elements may be very simple and economical. Various sizes of dust precipitators can be manufactured by means of only a few sizes of elements. The connection of the elements to the poles of the voltage source can be easily achieved. WHAT I CLAIM IS:

1. An electrostatic dust precipitator, comprising several pairs of electrodes, past which a medium to be cleaned can be caused to flow, one electrode of each pair being connectable to one pole of a voltage supply and the other electrode of each pair being connectable to the other pole of the voltage supply so that an electrostatic field can be created, charaterised iii that the electrodes are arranged adjacent to each other in sequence in the flow direction of the medium to produce several electrostatic fields adjacent to each other in sequence in the said direction, the electrodes which are connectable to the one pole of the voltage supply being substantially of string form, and the electrodes connectable to the other pole being substantially of plate form, said electrodes when connected to said voltage supply producing non-homogeneous electrostatic fields, without the generation of corona discharge, by application of a voltage at a predetermined value which will not cause any corona discharge effect, said electrostatic fields causing separation of the positive and negative charges of the particles from one another, and the particles being converted into electric dipoles so that the particles move towards the string electrodes, and that means are provided to supply each of the string electrodes with a liquid stream to flush away the particles hitting it.

the casing, and a fan is provided in the other end opening thereof.

11. An electrostatic dust precipitator in accordance with any one of claims 1 to 8, characterised in that the electrodes of plate form comprise sheets of mesh.

12. An electrostatic dust precipitator in accordance with any one of claims 1 to 8, characterised in that the electrodes of plate form comprise metal plates without any holes.

13. An electrostatic dust precipitator in accordance with claims 1 to 8, characterised in that the electrodes of plate form are coated with an electrically insulating substance to prevent discharges of electrcity.

14. An electrostatic dust precipitator in accordance with any one of claims 2 to 6 characterised in that a pair of electrodes is mounted in each frame.

15. An electrostatic dust precipitator in accordance with claim 14 when dependent on claim 5, characterised in that a part of the side edge of each trough is formed into an overflow lip over which excess liquid may flow into the trough of an adjacent electrode frame.

16. An electrostatic dust precipitator in accordance with claim 14, characterised in that the electrode of plate form comprises strips of sheet material and the electrode of string form comprises a plurality of strings, the strips of sheet material being situated between the strings.

17. An electrostatic dust precipitator in accordance with claim 14 when dependent on claim 3, characterised in that the electrode of plate form comprises a sheet of mesh mounted in a plane parallel to a plane containing the strings of the electrode of string form.

18. An electrostatic dust precipitator in accordance with claim 14 when dependent on claim 5, characterised in that a lower part of each frame comprises an inverted trough similar to that at the top part of the frame.

19. An electrostatic dust precipitator substantially as described herein with reference to Figures 1 to 5, Figure 6, Figures 7 to 10 or Figures 11 and 12 of the accompanying drawings.

20. A method of cleaning a medium, wherein the medium is caused to flow through an electrostatic dust precipitator in accordance with any preceding claim, characterised in that non-homogeneous electrostatic fields are produced by the application of a voltage to the electrodes of the precipitator at a predetermined value which will not cause any corona discharge, said electrostatic fields causing separation of the positive and negative charges of the particles from one another, the particles being converted into electric dipoles and moving towards the string electrodes, and that each of the string electrodes is supplied with a liquid stream, the stream flushing away the particles hitting the string electrodes.

21. A method of cleaning a medium, in accordance with claim 20, and substantially as described herein.