WO2000010236A1

WO2000010236A1 - Dust suppressor

Info

Publication number: WO2000010236A1
Application number: PCT/FI1999/000675
Authority: WO
Inventors: Juha Oranen; Pekka Lahtinen
Original assignee: Roxon Oy
Priority date: 1998-08-17
Filing date: 1999-08-16
Publication date: 2000-02-24
Also published as: AU5293199A; ZA994934B; FI108972B; FI981766A; AR021202A4; FI981766A0; PE20000675Z; DE29980204U1

Abstract

The invention relates to a dust suppressor comprising corona electrodes (7) to which a high voltage is supplied. The voltage supply means comprise an intermediate voltage unit (2) and a voltage multiplier (6). The intermediate voltage unit (2) produces an intermediate voltage which the voltage multiplier (6) raises sufficiently high. The voltage multiplier (6) is arranged in conjunction with the corona electrodes (7), and the intermediate voltage unit (2) and the voltage multiplier (6) are placed at a distance from each other and connected by an intermediate voltage cable (5).

Description

DUST SUPPRESSOR

The invention relates to a dust suppressor comprising corona electrodes, voltage supply means for supplying high voltage to the corona electrodes, and a control unit for controlling the operation of the dust suppressor. It is often necessary to install at least some kind of dust removal system in conjunction with mass material conveyors, for example mine ore conveyors. Dust is typically removed in a dust suppressor equipment based on ionization of dust particles, a high voltage being supplied to the corona electrodes. The wall and other steel structures of the housing of the dust sup- presor, and the material to be conveyed provide a grounded surface, whereby an electric field is generated between the electrodes and the grounded surface. When the voltage at an electrode is sufficiently high, the electric field near the electrode exceeds the electric disruptive strength of the air, resulting in ionization of the air. A partial electric discharge on the surface of an elec- trode is called a corona discharge. In a negative corona discharge, free electrons are emitted from the electrode and drift away from the electrode under the influence of the electric field. Between the electrode and the grounded surface is an electric field and electric current starts to flow under the influence of free charge carriers. As negative ions and free electrons pass towards the grounded surface under the influence of the electric field, they collide with dust particles in the air, the collisions causing the dust particles to become charged. Dust particles accumulate by two different mechanisms. First of all, the majority of the accumulation takes place under the influence of an external electric field, whereby charged dust particles drift towards the grounded sur- face and adhere thereto. The second mechanism by which particles accumulate is what is known as accumulation caused by state charge.

The voltage required by a corona electrode is typically produced by a high-voltage unit comprising a high-voltage supply and a voltage multiplier in the same casing. A high-voltage unit produces the voltage required by co- rona electrodes and said voltage is supplied to a distributing unit and from the distributing unit further to each dust suppression unit. The high-voltage unit is controlled by a manually adjustable variac transformer which adjusts the magnitude of the voltage supplied to the high-voltage unit. High-voltage units are extremely large and heavy. Furthermore, the high-voltage cables required are thick and expensive and have to be installed over quite long distances. Distributing units are also large and expensive. It is also cumbersome and difficult to adjust the system since an individual dust suppression unit cannot be adjusted separately, but all units are adjusted simultaneously. Solutions using such an arrangement are disclosed for example in SU publications 1208265 and 1574828. In another known solution the voltage required by corona electrodes is produced by an equipment comprising a high-voltage unit having a high-frequency unit, a transformer and a multiplier. The operation of the high- voltage unit is controlled by a separate control unit. Said structure enables the high-voltage unit to be made smaller than in the above solution, and conse- quently a separate high-voltage unit can be installed for each dust suppression unit. However, the high-voltage unit is still quite large and hence requires quite a large, bulky and expensive enclosure, particularly if the unit is to be placed near the dust suppression unit. On the other hand, if the unit is not placed near the dust suppression unit, expensive high-voltage cabling has to be used.

It is the object of the present invention to provide a dust suppression equipment avoiding the above drawbacks.

The dust suppression equipment of the invention is characterized by the voltage supply means comprising an intermediate voltage unit and a voltage multiplier, the voltage multiplier and the intermediate voltage unit being placed at a distance from each other, the voltage multiplier being arranged in conjunction with the corona electrodes, and the intermediate voltage unit and the voltage multiplier being connected to each other by an intermediate voltage cable. It is an essential idea of the invention that the equipment comprises an intermediate voltage unit for producing the intermediate voltage, and a voltage multiplier for producing the final high voltage, and the intermediate voltage unit and the voltage multiplier are arranged at a distance from each other and connected by an intermediate voltage cable. It is an advantage of the invention that substantially only the voltage multiplier is placed in conjunction with the corona electrode, and the intermediate voltage unit is placed at a distance from the dust suppression unit, whereby difficult dusty conditions have to be taken into account only in the encapsulation of the voltage multiplier, and the rest of the equipment required for producing high voltage can be located in surroundings having substantially easier external conditions. In this case high voltage does not have to be car- ried over long distances along an expensive high voltage cable, but the voltage is carried by an intermediate voltage along an intermediate voltage cable. The resultant equipment is small and inexpensive to manufacture. Each dust suppression unit can be separately adjusted and the control unit serves to monitor different error situations and to adjust the equipment accurately.

The invention will be described in the attached drawing, in which Figure 1 is a block diagram of an equipment of the invention, Figure 2 is a schematic side view and partial cross section of a dust suppression unit of the invention, and Figure 3 is a block diagram of a second equipment of the invention.

Figure 1 is a block diagram of an equipment of the invention. A voltage supply 1 is used to supply operating voltage to an intermediate voltage unit 2. The intermediate voltage unit 2 is composed of a high-frequency unit 3 and a voltage transformer 4. The high-frequency unit 3 and the voltage transformer 4 can be installed on the same circuit board, resulting in a small equipment which is easy to manufacture. In the high-frequency unit 3 the frequency of the electric current is raised high, to about 15 kHz, for example. The magnitude of the voltage is then raised with the voltage transformer 4 to a maximum of some kVs. After the intermediate voltage unit 2, the maximum voltage can be 10 kV, for example. A voltage varying between 0 and 24 V, for example, can be supplied to the intermediate voltage unit 2, and the intermediate voltage unit 2 produces a voltage varying between 0 and 2 kV, for example. The intermediate voltage produced by the intermediate voltage unit 2 is carried by an intermediate voltage cable 5 to a voltage multiplier 6. In this case the voltage multiplier 6 and the intermediate voltage unit 2 are located at a distance from each other. The voltage multiplier 6 produces the final voltage which may vary between 0 and 60 kV, for example, and which is supplied to corona electrodes 7. In dust suppression, the voltage of the corona electrodes 7 has to exceed 40 kV in order for the equipment to be able to suppress dust in conjunction with a mass material processing device. The operation of the different parts of the equipment is monitored and controlled by a control unit 8. The voltage supply 1 and the control unit 8 can be interconnected by a series bus, for example. The control unit 8 measures the voltage and current of the voltage supply 1 and sets the voltage and current to a suitable level in view of the operation of the equipment. Furthermore, error information is obtained to the control unit 8 from the supply voltage source 1. The control unit 8 switches the high-frequency unit 3 on and off, and overcurrent, overheat alarms and current measurement can be supplied from the high-frequency unit 3 to the control unit 8. An overheat alarm, for example, can be supplied from the voltage transformer 4 to the control unit 8. Current and voltage measure- ments, for example, can be supplied from the voltage multiplier 6 to the control unit 8. The control unit 8 can be connected to the rest of the data system by a series port, for example.

Figure 2 shows the equipment of the invention arranged in conjunction with a conveyor 9. Instead of a conveyor 9, the dust suppression equip- ment can be placed in conjunction with some other mass material processing device, such as a feeder, screen or crusher. The dust suppression equipment can also be placed for example in a storehouse, silo or mass material receiving station. The conveyor 9 conveys material, for example mine ore, in the direction of arrow A. The conveyer 9 is provided with a dust suppression housing 10. The dust suppression housing 10 comprises the corona electrodes 7 in a manner known per se. Since the intermediate voltage unit 2 and the voltage multiplier 6 are connected by the intermediate voltage cable 5, they can be placed at a distance from each other, whereby, in addition to the electrodes 7, only the voltage multiplier 6 has to be placed in conjunction with the dust suppression housing 10. The voltage multiplier 6 is placed in conjunction with the corona electrodes 7 within an insulator. The intermediate voltage unit 2 can be placed in less demanding environmental conditions. In any event, not a very high voltage has to be carried in the intermediate voltage cable 5, and the intermediate voltage cable 5 can be dimensioned for a maximum voltage of 10 kV, for example.

Figure 3 shows a block diagram of a second equipment of the invention. In the solution of Figure 3, the intermediate voltage unit 2 is used to produce a high-frequency intermediate voltage which varies between 0 and 30 V, for example, and which is supplied with the intermediate voltage cable 5 to a unit which is composed of the voltage transformer 4 and the voltage multiplier 6 and which supplies the required voltage of over 40 kV to the corona electrodes 7. In this case the permissible voltage in the intermediate voltage cable 5 does not have to be very high. Since a power of about 100 W is sufficient for the equipment, the current in the intermediate voltage cable 5 does not have to exceed 10 A in the solution of Figure 3, whereby dissipation and heating of the intermediate voltage cable 5 do not cause problems. The volt- age transformer 4 and the voltage multiplier 6 can be arranged within the same insulator, for example cast into the same resin case.

The drawing and the related specification are only intended to illustrate the inventive idea. The details of the invention may vary within the scope of the claims.

Claims

1. A dust suppressor to be arranged in conjunction with a mass material processing device, the dust suppressor comprising corona electrodes (7), voltage supply means for supplying high voltage to the corona electrodes (7), and a control unit (8) for controlling the operation of the dust suppressor, characterized by the voltage supply means comprising an intermediate voltage unit (2) and a voltage multiplier (6), the voltage multiplier (6) and the intermediate voltage unit (2) being placed at a distance from each other, the voltage multiplier (6) being arranged in conjunction with the corona elec- trodes (7), and the intermediate voltage unit (2) and the voltage multiplier (6) being connected to each other by an intermediate voltage cable (5).

2. A dust suppressor as claimed in claim 1, characterized by the intermediate voltage unit (2) comprising a high-frequency unit (3) and a voltage transformer (4).

3. A dust suppressor as claimed in claim 2, characterized by the high-frequency unit (3) and the voltage transformer (4) being installed on the same circuit board.

4. A dust suppressor as claimed in claim 1, characterized by the dust suppressor comprising a voltage transformer (4) arranged in con- junction with the voltage multiplier (6).

5. A dust suppressor as claimed in any one of the preceding claims, characterized by the voltage multiplier (6) being arranged within an insulator.

6. A dust suppressor as claimed in any one of the preceding claims, characterized in that in dust suppression the voltage of the corona electrodes (7) exceeds 40 kV.