GB2274794A

GB2274794A - Dust separator

Info

Publication number: GB2274794A
Application number: GB9402055A
Authority: GB
Inventors: Henry Jack Porter
Original assignee: Individual
Current assignee: Individual
Priority date: 1993-02-05
Filing date: 1994-02-03
Publication date: 1994-08-10
Anticipated expiration: 2014-02-03
Also published as: GB2274794B; GB9302292D0; GB9402055D0

Abstract

A dust separator comprises an upper chamber 12 held above a lower inlet chamber 10 by struts 14. A duct 15, with a central column 16 and a plurality of radial vanes 17, connects the two chambers. Air laden with dust particles passes into the lower chamber 10 through an inlet pipe 11, is drawn up through the duct 15 to the upper chamber 12 by the bent-over ends 18 of the vanes 17, or by a separate fan, and passes out through an outlet pipe 13. The duct 15 is rotated by an electric motor 26, so that as the air passes up through the duct, suspended particles are centrifugally thrown outwards and deposited on the inside of the duct. The ends of the duct are sealed by seals (eg of plush) 32, 33. The pressure in the separator may be kept below atmospheric to prevent leakage. The lower chamber has a dust collector 31. Sensors may sense the accumulation of dust therein, or (by sensing imbalance) in the duct 15. Two separators may be operated alternately. <IMAGE>

Description

Dust Sepa retor The present invention relates to dust separators.

There are many situations in which the separation of dust from air is required (using the term air" to include other gases as well). There are four major techniques available for dust separation: precipitation, filtering, electrostatic separation, and the cyclone technique.

Precipitation essentially involves settling under the influence of gravity.

The particle-leden air stream is suddenly expanded, causing a drop in flow velocity and consequent deposition by gravity of the heavier particles into a separator. This technique has obvious limitations.

Filtering involves passing the particle-laden air stream through e fibrous or other labyrinthine filter medium, which captures entrained particles. This can achieve substantially complete removal of particulate contaminants from the air stream. However, it suffers from progressive deterioration of the free passage of the air due to blockage, giving a high back pressure on the air stream.

Further, the suspended particles so removed are not easily recovered, should they be required, and eventually the filter has to be removed and replaced.

Electrostatic separation involves passing the particle-laden air stream through an electrostatic discharge which applies a high electrostatic charge to the particles, which then become deposited on collectors by electrostatic attraction. This tends to be most effective with small particles.

Cyclone separation involves injecting the dust-laden air stream tangentially into a rotary path around the inside of e chamber the upper part of which is in the form of a vertical cylinder and the lower part of which is in the form of a cone. The suspended particles are centrifugally carried towards the wall of the chamber and sink, under gravity, to the apex of the chamber, whence they can be removed, while the air is removed from an outlet at the centre of the top of the chamber. This requires relatively large particles to work well.

These techniques all have their attendant advantages and disadvantages. In particular, the only technique which gives substantially complete separation of suspended particles is filtering.

Of course, two different techniques can be applied one after the other, but that obviously doubles the cost and complexity.

The general object of the present invention is to provide a further dust separation technique for removing particulate matter from an air stream without using filters of the labyrinthine type discussed above.

Accordingly the present invention provides a dust separator comprising a duct assembly through which the air is passed, the duct containing a plurality of radial plates, so as to achieve centrifugal deposition of suspended particulate matter. A further important feature is that the duct is preferably mounted .

vertically, with the air stream passing up through it, and a collector for deposited matter is provided below the duct.

Deposited matter will be free to fall when the rotation of duct is stopped and the centrifugal force disappears. However, e vibrator is preferably mounted to vibrate the duct to assist in the dislodging of deposited matter. If the separator is used intermittently, clearance of collected matter may be performed when it is not in use; otherwise, a pair of separators may be provided and operated alternately, so that each may be cleared while the other is operating.

The present separator may be used to separate a wide variety of types of particulate matter, such as coal dust in mine ventilation, fly ash from coal burning, oxides and carbonates from oil burning, fibres from textile factory ventilation, radioactive particles from nuclear processes, sand end detritus from industrial processes, and many others.

The agglomerated particles, which will be substantially intact and unadulterated, are collected in a pit or collector below the duct, and can readily be removed. They can then be either re-used or disposed of as waste, as desired.

In suitable circumstances, the present separator can achieve substantially complete separation of suspended particulate matter. It can be incorporated in an air conditioning plant in which the air is largely recirculated (so saving on heating costs), or for servicing a clean room in the medical, chemical or scientific industries.

An air separator embodying the invention will now be described, by way of example, with reference to the drawings, in which: Fig. 1 is a general sectional view of the separator; and Fig. 2 is a perspective view of the top of the rotatable duct of the separator.

Referring to Fig. 1, the separator comprises a lower chamber 10, an upper chamber 12 held in position above the inlet chamber by a set of struts 14, and a vertical rotatable duct 15 connecting the two chambers together. Air laden with suspended particulate matter passes into the lower chamber 10 through an inlet pipe 11, up through the duct 15 (which, as will be explained below, effects the removal of the dust) to the upper chamber 12, and out (in the clean condition) from that chamber through an outlet pipe 13. The chambers are large enough to permit the air stream passing through the separator to change direction with a minimum of frictional resistance.

The duct 15 has, as shown more clearly in Fig. 2, a central column 16 and a plurality of radial vanes 17. Each of these vanes extends along the length of the duct, and is attached along one side to the central column 16 and along the opposite side to the outer wall of the duct. These vanes thus divide the crosssection of the duct into a plurality of sectors.

The duct 15 is mounted on a pair of stub shafts 20 and 21. (A single shaft passing through the duct may of course be used instead.) Stub shaft 20 is mounted in a thrust bearing 22 which is supported in the inlet chamber 10 by struts 24; stub shaft 21 is mounted in a plain bearing 23 which is supported in the outlet chamber 12 by struts 25. An electric motor 26 is coupled by a coupling 27 to the stub shaft 23. This motor may either be contained within the chamber 12 as shown, or mounted outside and above this chamber. The duct is preferably balanced statically and dynamically.

In operation, the duct 15 is rotated at a suitable speed by the motor 26, and the air to be separated passes up through the duct. As the air passes through the duct, it is carried round with the duct as the duct rotates. Suspended particles in the air therefore experience a centrifugal force, and are thrown outwards. These particles will therefore follow a helico-spiral path, circling with the duct 15, rising gradually with the air passing up it, and also moving outwards under the influence of the centrifugal force. These particles will therefore move outward until they reach the inside of the outer wall of the duct, where they will become deposited and accumulate as long as rotation continues.

The various parameters (eg the size and rotational speed of the duct 15) must be chosen to give the required degree of separation for the particular characteristics of the contaminated air flow (eg the flow rate and the size and mass of the particles carried therein). Depending on circumstances, the separator may be designed to give either a desired degree of separation or substantially complete separation. (In an experiment, a separator with a duct 300 mm long and 150 mm diameter, and rotating at 70 rps, produced substantially total separation of air contaminated with household flour.) .; .

The speed of the duct 15 must be fast enough for centrifugal force to carry the contaminating particles to its outer wall. The centrifugal force will be least close to the axis of the duct, so that while particles entering the duct near its outer regions will experience a large force and so become deposited rapidly, particles entering it near its axis will take longer to reach its outer regions. To reduce this effect, the duct may be include a central column 16, as shown, ensuring that all particles start at at least a certain minimum distance from its axis.

The air flow rate should not be so great that the particles emerge from the top of the duct before reaching the outer wall, or are dislodged from the outer wall once they have reached it.

The air will thus have been effectively separated from of particulate contamination by the time it emerges from the top of the duct into the upper chamber 12, the solid content being deposited on the inner wall of the spinning duct.

The separated air stream leaves this chamber through the outlet pipe 13, whence it can for example be vented to a chimney or re-used.

Seals 32 and 33 are provided where the rotatable duct 15 enters the top and bottom chambers. These seals may for example consist of plush, or of rings of openweave spun fibreglass, making light contact with the cylindrical outer surface of the duct 15. If the pressure inside the separator is arranged to be slightly below atmospheric (ie a suck at the outlet rather than a blow at the inlet), any slight leakage around the seals will result only in a very slight inefficiency, with no escape of contaminated air.

Alternatively, the duct 15 may be enclosed in a closed chamber (a "duct chamber") between the bottom and top chambers 10 and 12, so that no leakage can occur. The seal 32, preventing leakage of contaminated air into the duct chamber, will still be important, but the seal 33 will be of lesser importance.

The air flow through the separator may be produced either by the separator itself or by some external fan. The disadvantage of generating the air flow by the separator itself is that some passage of contaminating particles may occur through the separator during starting and stopping; however, this can be minimized by providing an external valve or gate, so that the flow path is closed l during starting and stopping.

A fan can be attached to the shaft of the motor 26 in the upper chamber 12, located between the top of the duct 15 and the outlet pipe 13 (for this, the chamber 12 must of course be appropriately modified). However, the duct 15 can itself be modified to produce an air flow.

As so far described, the duct has strictly longitudinal divider plates 17 extending between its top and bottom ends. To provide a fan effect, these plates are extended to project slightly beyond the top end of the duct 15, and the extending portions are bent over at an angle, as shown at 18 (Fig. 2).

These extensions may be of uniform width as shown, or may narrow towards the axis of the duct. When the duct is rotated in the appropriate direction relative to the bend of the extensions 18, as shown in Fig. 2, these extensions will give an impetus to the emerging air stream and so cause a flow of air through the separator.

The deposit on the inside of the duct 15 will remain in position and gradually build up, and will therefore have to be cleared in due course. The lower end of the stub shaft 20 and bearing 22 therefore has an agitator or vibrator 30 attached to it. To clear the deposit in the duct 15, the separator is stopped from operating. The motor 26 is stopped, so that the duct ceases to rotate, and the vibrator is energized to vibrate the duct 15; the vibrator may be air or elec trically operated. The deposit in the duct is thereby dislodged. This operation can be automated if desired, to occur at eg regular intervals.

The divider plates are preferably free of bolt heads, stiffeners or other protuberances, both to avoid impeding the free flow of the air being separated and to enhance the detachment of the deposit when the duct is #being cleared.

The divider plates and the inside of the outer wall of the duct may be coated with a suitable coating, such as nylon or PTFE, again enhancing the shedding of deposit therefrom.

The separator is less suitable for wet dust, which will tend to adhere more strongly to the walls of the duct, so that more forcible means may be required to dislodge it.

The collector 31 is detachably connected to the chamber 10 to allow it to be removed and emptied. The' separator will normally be operated through a considerable number of cycles of clearing deposit from the duct 15 before the collector 30 becomes sufficiently full to need emptying. The lower chamber 10 has the deposit collection container 31 located on its floor or in a pit below it, so the dislodged deposit falls down out of the duct and through the chamber 10 into the collector 31.

Sensors may be provided for sensing the build-up of deposit on the walls of the duct 15 and/or the accumulation of deposit in the collector 31, to give warning of when deposit clearance and/or collector emptying is required. Various sensing techniques can be used, eg sensing the increase of mass in the duct 15 and the collector 31.

The motor 26 may be located below the duct 15 rather than above it as shown in Fig. 1. To protect the motor from dust falling during cleaning, an inclined plate may be provided in the chamber 10, separating the motor from the air flow path, with a bearing mounted in it through which the motor is coupled to the duct. A dust collection pit or chamber is preferably located at the lower edge of the inclined plate. This arrangement allows the upper chamber 12 to be provided with an access lid through which the duct 15 can easily be reached and withdrawn from the its normal position for cleaning.

If the separator is used intermittently, clearance of collected matter and collector emptying may be performed when it is not in use, either in response to an indication that such clearance or emptying is required or on a regular basis.

If, however, substantially continuous operation for extended periods is required, then it may be desirable to provide two separators connected in parallel. Only one will be operating at any given time, so that the other can be emptied; when the one operating requires clearance or emptying, the other will be started up to allow such clearance or emptying.

It may be convenient to have several separators in parallel. In this case, they would all normally be operating, and any one could be briefly closed down for clearance when desired without seriously affecting the performance of the system.

If desired, a badly contaminated air stream may be subjected to a preliminary coarse separation by some other technique before being passed to the present separator.

It will be seen that the present separator provides an air separation system with virtually no impedance of free passage of the air stream, low maintenance, and no consumable components. Further, the present system is highly compact compared with most conventional systems of comparable performance.

Claims

1 A dust separator comprising a duct assembly through which the air is passed, the duct containing a plurality of radial plates, so as to achieve centrifugal deposition of suspended particulate matter.

2 A dust separator according to any previous claim wherein the duct is sealed at its ends by seals of plush or rings of openweave spun fibreglass making light contact with the cylindrical outer surface of the duct.

3 A dust separator according to any previous claim wherein the pressure inside the separator is arranged to be slightly below atmospheric.

4 A dust separator according to any previous claim wherein the duct extends between end chambers and is enclosed in a closed chamber between the end chambers so that no leakage can occur.

5 A dust separator according to any previous claim wherein the duct has strictly longitudinal divider plates extending between its ends.

6 A dust separator according to any previous claim wherein the air flow through the separator is produced by the separator.

7 A dust separator according to claims 5 and 6 wherein the duct plates are extended to project slightly beyond the top end of the duct, and the extending portions are bent over at an angle.

8 A dust separator according to any of claims 1 to 5 wherein the air flow through the separator is produced by an external fan.

9 A dust separator according to any previous claim including an external valve or gate, so that the flow path can be closed during starting and stopping.

10 A dust separator according to any previous claim wherein the duct is mounted vertically, with the air stream passing up through it, and a collector for deposited matter is provided below the duct.

11 A dust separator according to claim 10 including a vibrator mounted to vibrate the duct to assist in the dislodging of deposited matter.

12 A dust separator according to any previous claim wherein the lower end chamber has a deposit collection container located on its floor or in a pit below it.

13 A dust separator according to any previous claim wherein the duct is mounted vertically.

14 A dust separator according to claim 13 wherein the duct is driven by a motor mounted in the lower end chamber, and the upper end chamber has access means through which the duct can be withdrawn.

15 A dust separator according to any previous claim wherein sensors are provided for sensing the build-up of deposit on the walls of the duct and/or the accumulation of deposit in the collector, to give warning of when deposit clearance and/or collector emptying is required.

16 A dust separator according to claim 14 wherein the sensors sense the increase of mass in the duct or the collector.

17 A pair of dust separators according to any previous claim including means for operating them alternately, so that each may be cleared while the other is operating.

18 Any novel and inventive feature or combination of features specifically disclosed herein within the meaning of Article 4H of the International Convention (Paris Convention).