WO1999059698A1 - Arrangement for separating solid particles from gases - Google Patents

Abstract

The invention relates to an arrangement for separating solid particles, particularly light fibre-like or plate-like and/or plate-like or ribbon-like pieces, from gases, the arrangement comprising means for supplying a mixture of gases and solid particles into a container part (12) and second means by which the gases are arranged to be led out of the container part. To achieve a simple solution with low operating costs, one or more substantially horizontal partition plates (2), made of a material separating particles and enabling gases to flow through, are arranged above the container part, and the arrangement comprises one or more blow nozzles (3) that are arranged to remove the particles separated from the gas and adhered to the partition plates (2).

Description

ARRANGEMENT FOR SEPARATING SOLID PARTICLES FROM GASES

The invention relates to an arrangement for separating solid particles, particularly light fibre-like or plate-like particles and/or plate-like or ribbonlike pieces, from gases, the arrangement comprising means for supplying a mixture of gases and solid particles into a container part and second means by which the gases are arranged to be led out of the container part.

In various fields of industry, such as in paper industry, printing industry, textile and weaving industry, leather industry, and so on, relatively large particles, e.g. measuring up to 0.1 to 3 mm, are produced in connection with the manufacturing process, which particles are often aspirated with air through dust collecting ducts to be separated in various dust separators, for instance, for reuse or incineration or simply for waste treatment. Major scrap pieces produced in conjunction with manufacturing are often shredded with various devices to facilitate handling and transport. Trims produced in paper making can be mentioned as examples of these major scrap pieces.

However, paper, textile and like waste material can also be transported pneumatically, unshredded, whereby a mixture containing large pieces, in addition to dust, e.g. ribbons measuring tens of metres, standard-size paper sheets, etc, must be separated from air. To separate this kind of a mixture from the air is practically impossible with known separators, except with two separators coupled in series, of which the first provides separation of large pieces and the second one provides separation of particles. In this case, both the price of the equipment and the pressure loss are considerable.

Separating large particles from a gas flow is in general fairly easy, for instance, in a settling chamber, or in so-called cyclone separators utilizing centrifugal power. However, this requires that particle density is so high and/or the shape of the particles is so regular that the so-called settling rate of particles in static air is high, generally exceeding 10 cm/s. The particles concerned here are, however, irregular in shape, in general plate-like or fibre-like, and their density is low, so an average settling rate is relatively low. The worst thing is, however, that the settling rate of particles of the same size varies greatly, and for the same particle it may vary greatly at different times. Therefore, separating particles of this kind is difficult, for instance, in a cyclone separator. Moreover, pressure loss in cyclones, and as a consequence, energy consumption is relatively high. Perhaps the worst thing is, however, that these particles are difficult to remove from the cyclone, even though they could be separated in so-called high-efficiency cyclones. Blockages in the discharge pipes of the cyclones and service interruptions resulting therefrom are common and costly. An arrangement of this kind is known, for instance, from Finnish Patent 71 175, wherein the use of two nested cyclones, coupled in princi- pie in series, is disclosed for light particles. This solution naturally further increases costs and power consumption.

Attempts have been made to solve the problem in a variety of ways. For instance in textile industry so-called rotating cleaning drums are common in cleaning exhaust air, an example of which is disclosed in German Patent Publication 3 212 892 A1. Dusty air is supplied through the outer surface of a cylindrical drum into the drum and is exhausted via an exhaust duct in the axial direction. The outer surface of the drum is formed of or covered with a wire netting, filtering material, perforated plate or such like, to which the particles adhere and form a layer on the surface of the drum, which layer is mechani- cally scraped off in a given part of the drum. Structures having a rotating plate instead of the drum are also known. These equipments are expensive and large. Moreover, sealing of large devices and ducts relating thereto is difficult and costly. Wearing of seals and scraping devices causes considerable operating costs. Leaks easily give rise to problems. It is particularly difficult to re- move the separated material from the device, which must be carried out either manually or by means of expensive special devices. Since no better solution has been found, these devices are commonly used in textile industry.

Textile industry also employs so-called roller filters, particularly, when the dust content of the air to be cleaned is low or moderate. The filter consists of two rollers with a relatively long straight portion of a filter mat between them through which the air to be cleaned flows, whereby the particles adhere to the filter mat. When sufficiently dust is accumulated on the surface of the mat, the operating mechanism of one roller starts rolling the fouled mat onto that roller and clean mat unwinds from the other roller in replacement. Generally, starting is currently performed automatically by a differential pressure switch. These devices are relatively expensive and their pressure loss and thus the energy consumption are considerable. If the particle content of air is high, operating costs are high, since the filter mat cannot be cleaned and reused. Hence the use of these devices is currently restricted to cleaning re- turn air in ventilation, and they are not in general used for cleaning exhaust air of a manufacturing process. One possible solution is a so-called tubular dust collector, which is disclosed in US Patent 4 878 926, for instance. Particles are separated in long filtering tubes in the shape of vertical cylinders, and the air to be cleaned flows through the outer surface thereof. The upper ends of the tubes are attached to a partition plate having openings to match the tubes, through which openings the cleaned air flows into a plenum chamber and therefrom into discharge ductwork. When dust is accumulated on the outer surfaces of the tubes, they are cleaned mechanically, by compressed-air blow or so-called reverse air blow. For instance, the above-mentioned US Patent discloses a reverse air blow device comprising a centrally pivoted, rotating blow nozzle positioned above the round partition plate, through which nozzle air is blown through the tubes in a direction which is opposite to that of a working flow. The air detaches the dust, accumulated on the outer surfaces of the filtering tubes, which falls into a collecting funnel below. Solutions, in which the air to be cleaned flows onto the inner surface of the tubes, are also known.

The above-described apparatuses are very expensive and their pressure loss and hence the energy consumption are high. For instance, the above US Patent widely describes problems and difficulties arising from arranging air blow into a rotating nozzle. Another, greater difficulty is that plate- like particles in particular block the filtering tubes quickly, so they should be cleaned very often. Cleaning is very time-consuming, because when the particles come off the surface of the filtering tube, they also get detached from each other, and as a consequence the particles descend very slowly between the tubes and easily drift with the reverse air to adjacent, cleaned tubes. Therefore, the tubular filters are mainly used for separating fine-grained heavy dust whose particles additionally tend to agglomerate into larger particles that fall down quickly from the tubes. They are hardly ever used to filter the air containing large plate-like or fibre-like particles because of the costs, energy consumption and a plurality of technical problems that are hard to solve. Corresponding problems also appear in cleaning fluids. A device for removing suspended matter from a fluid is known from Finnish Patent 59 340. The equipment comprises a container which is divided into three compartments by means of two horizontal filtering partition plates. The fluid to be cleaned flows into the uppermost and lowermost compartments, wherefrom it passes through the filtering partition plates into the compartment in the middle, wherefrom the cleaned fluid is discharged. In general, the middlemost com- partment is pressurized. When sludge accumulates on the filtering surfaces, it is removed by means of a specific moving vacuum box and is supplied to the discharge manifold. The overpressure of the container provides the necessary driving force, in the solution of said Finnish patent, the discharge manifold comprises a rotating hollow shaft, which extends vertically throughout the container and against which the vacuum boxes are attached with perpendicular pipes.

To apply the above-described principle to the cleaning of gases is completely impossible. The size of the equipment is the first restricting thing. Generally, fluid flows to be treated are inferior to gas flows, which is shown by the commonly used measuring units for the flow: for fluids l/s or l/min, for gases m³/s or m³/h. The equipment in accordance with said Finnish patent, applied to gas flows, would be several metres high, the rotating hollow shaft would be tens of centimetres in diameter, and so on. It can only be imagined, how costly this equipment would be and what technical problems would arise from mounting in bearings the shaft, which is several metres long and tens of centimetres in diameter, sealing the shaft and the vacuum boxes, and so on. Another serious drawback is the blockage of the aspirating tubes. Dust conveyor tubes have to be designed in quite a specific way: for instance, the ra- dius of curvature of a 90-degree bent tube generally has to be ten times the diameter, the angle between the axes of the interconnecting tubes is allowed to be 15 degrees at most and the connecting has to be designed in quite a specific way, and so on. To design functioning dust conveyor tubes according to the solution of said Finnish patent is completely impossible. However, the most crucial thing is that conveying particles by means of air requires large quantities of air. The mass ratio of air and particles is called the mixing ratio, whose maximum value cannot be exceeded. Generally, particles are supplied to the separators discussed here by so-called pneumatic transport, the mixing ratio being at the maximum value or close thereto. To aspirate the separated particles from the separator using the principle of said Finnish patent would require an air flow which equals to the air flow by which the particles are supplied to the separator, in other words, nothing would be achieved with the equipment using the principle of said Finnish patent. Said patent publication does not suggest either that the equipment could be applied to separate parti- cles from gases. The object of the invention is to provide an arrangement by which the drawbacks of prior art could be eliminated. This is achieved with an arrangement according to the invention, which is characterized in that one or more substantially horizontal partition plates extending throughout the cross section of the container, fully or mainly made of a material separating particles and enabling gases to flow through, are arranged above the container part, and that the arrangement comprises one or more blow nozzles that are arranged to remove the particles separated from the gas and adhered to the partition plates. An advantage of the invention is primarily that the operating costs and/or energy consumption of the arrangement are substantially lower than those of the prior art equipments. The structure of the arrangement according to the invention is simple and consequently it is reliable in use. In addition, operation of the arrangement can be adjusted to any material to be treated and to any dust content, so the same standard equipment is applicable to many uses. It is easy to arrange the collected dust to be removed from the separator, in some applications it can be automated to the extent that the particles are directly supplied for reuse.

In the following, the invention will be described in greater detail by means of preferred embodiments with reference to the accompanying drawing, wherein

Figure 1 is a schematic view of a first embodiment of the arrangement of the invention,

Figure 2 is a schematic view of a second embodiment of the ar- rangement of the invention,

Figure 3 is a schematic view of a third embodiment of the arrangement of the invention.

The basic idea of the invention can advantageously be described by means of the example of Figure 1. A mixture of gases and particles to be cleaned is supplied, for instance, to a vertically positioned, cylindrical, large- diameter container part, i.e. separator 12, as a vertical flow directed downwards in the axial direction of the cylinder, whereby the separator serves as a settling chamber. If the mixture is supplied horizontally to the outer circumference of the separator 12, the separator acts as a cyclone utilizing centrifugal power. In the upper part of the separator, a surface plate comprising a wire netting, perforated plate, filter mat or the like, i.e. a separating partition plate 2, is placed horizontally, through which plate the gas to be cleaned, e.g. air, flows into a chamber 11 of the upper part, whereby particles adhere to the separating partition plate. Said partition plate can form an entire chamber 11 wall or part thereof. In the example of Figure 1 , the partition plate 2 is rotatable in structure. The air passes from the chamber 11 into discharge ducts. In the embodiment of Figure 1 the entire separator has partial vacuum. In the upper part of the separator, a connection to the ambient space is arranged by means of a nozzle 3 in such a way that the nozzle 3 opening is close to the partition plate 2. As a result of the partial vacuum in the separator, ambient air flows from the nozzle 3 into the separator, and consequently an air jet from the nozzle 3 blows the particles adhering to the partition plate downwards. Either the partition plate or the nozzle is rotated, whereby the entire partition plate can be cleaned. Separated particles are collected from the lower part of the separator. In the embodiment of Figure 1 , the mixture to be cleaned flows into the separator, i.e. into the container part 12 through a supply pipe and the flow is turned downwards at the separator's 12 axis by means of a bent pipe 8. In some cases it is advantageous to arrange an expansion part in the shape of a low-gradient cone to follow the bent pipe 8, which expansion part may enhance the operation of the separator as a settling chamber. Also, a conical reducing part can be used, if an intention is to improve the separating capacity by blowing the particle-containing air powerfully against a liquid surface. For instance a water nozzle or nozzles can be arranged in the outflow opening 9 of the dust-containing air, by which nozzles the particles can be wetted, whereby their weight increases and they separate more readily. First the mixture of air and particles flows downwards in the separator 12, but the flow then turns to flow at a low rate up the external walls of the separator 12. The majority of the particles fall down onto the bottom 10 of the separator, wherefrom they are discharged through a discharge opening 7. The upward air flow passes through the partition plate 2, whereby the particles still contained in the air adhere to the partition plate 2 and the cleaned air passes into the chamber 11 formed by the partition plate 2 and the upper part of the separator, wherefrom it flows into a discharge duct 6. Depending on the type of dust, desired separation capacity, allowed pressure loss, i.e. energy consumption, and so on, the partition plate can be manufactured of a wire net- ting, perforated plate, filter mat or some such material known per se or combinations thereof. In the example of Figure 1 , a drive motor 4 rotates the partition plate 2 with the intermediary of actuators 5 and a shaft 13. All applications known per se are naturally within the scope of the invention. The separating partition plate can be attached directly to the gearbox shaft, for instance, to which gearbox the motor 4 is directly connected.

As appears from the above description, the arrangement in accordance with the invention is simple and inexpensive to manufacture as compared with known equipments, and moreover, the energy consumption is moderate. By modifying the proportion of the diameters of the inflow pipe and the separator and the air admission rate into the separator, the same basic structure can be used for providing a separator that is suitable for a variety of dust types and dust contents. Correspondingly, it is possible to vary the rate of rotation and the material of the separating partition plate or of the nozzle, as well as the area and shape of the nozzle opening in connection with ambient air in order to provide a suitable cleaning system for various dust types and dust contents. A dust collecting equipment of the desired type can be selected from the equipments known per se to be positioned in the lower part of the separator. Separated dust can even be fed directly for reuse in a manner described later on in the text. The operation of the separator can readily be en- hanced by arranging dust wetting either on a transversal surface of the entire separator, or for instance, in an inflow opening or in a nozzle opening in connection with ambient air or at some other suitable point.

In some cases, for instance, because of the separator's large size, enhancement of the separating capacity or for some such reason, it is advan- tageous to divide the flow passing through the supply pipe 1 into two or more partial flows, which are applied into two or more separators connected side by side, whereafter the flows are reunited.

Figure 2 illustrates a solution of another kind. The cross-section of the separator is a rectangle. Air is supplied through the supply pipe 1 into a settling space divided by a partition plate 15 inside a container part, i.e. a separator 12, where the air flow turns downwards. After the lower edge of the partition plate 15 the air flow turns upwards in the separator and the particles fall into a funnel 14, wherefrom they are discharged with a scraper conveyor 16 constituted by the bottom of the funnel. Instead of the scraper conveyor, a screw conveyor or conveyors, a rotating disc feeder, a lock feeder or feeders, compressed-air nozzles or water nozzles or other feeding devices known per se can be used, naturally. Below the funnel 14, there can be a storage container or storage containers, an interchangeable platform or any other device known per se. It is also possible to let the waste fall directly into a manufacturing process, in paper making into a pulper. In the arrangement of Figure 2, the separator further has a partition wall 16, with a rotatable or fixed partition plate 2 in the opening thereof. Particularly, if the separator is large, it is often advantageous to provide the partition wall 16 with more than one separating partition plates 2, each of which having a separate cleaning nozzle 3. The partition plate or plates 2 can natu- rally have more than one cleaning nozzle 3 and actuators 4, 5, 13 each.

Figure 3 illustrates a third embodiment of the arrangement in accordance with the invention. The container part, i.e. the separator 12 is here in the shape of a truncated cone and the air passes tangentially from two supply pipes 1 and 1' into the separator, wherein centrifugal power is thus utilized. Naturally, supply pipes may be more than two. Likewise, the separator can be in the shape of a cylinder or a combination of a cylinder and a cone.

The arrangement of Figure 3 can also be used when the separator is pressurized. For this purpose, the discharge pipe 6 is provided with a branch 17, wherefrom a blower 8 aspirates cleaned air and blows it through a duct 19 to a cleaning nozzle 3. This solution is particularly advantageous also when it is not wanted to mix ambient air with the air to be cleaned. Naturally, it is also possible that the blower 18 takes in air from the upper part of the separator, outdoors or elsewhere.

The arrangement of Figure 3 is most advantageous when the air to be cleaned is aspirated from more than one points.

The above-described embodiments are not intended to restrict the invention in any way but the invention can be modified quite freely within the scope of the claims. It is thus to be understood that the arrangement of the invention or any details thereof need not necessarily be exactly as shown in the figures, but that other kinds of solutions are also possible. All applications achieved by combining the embodiments, as well as replacement of the devices known per se described in the examples by other known devices or addition of such devices thereto are naturally within the scope of the invention. For instance, separating partition plates can be more than one also in the flow direction of air in such a way that the first partition plate is a wire netting which separates the largest particles and the second partition plate is a filter mat for separating minor particles. Cleaning and/or descending of the separated material can be enhanced with vibrators, air or water nozzles or any other device or equipment known per se, either when the separator is operating or when the separator is out of service for cleaning. Operating can be controlled in a vari- ety of ways known per se, for instance, by controlling the air flow of the nozzle 3 with a pressure sensing device and a damper or with any other device known per se and/or by controlling the rotation rate of the separating partition plate 2 and/or the nozzle 3. Cleaning can also be cyclic, in which case starting is effected by means of a clock, a differential pressure switch or any other de- vice known per se.

Claims

1. An arrangement for separating solid particles, particularly light fibre-like or plate-like particles and/or plate-like or ribbon-like pieces, from gases, the arrangement comprising means for supplying a mixture of gases and solid particles into a container part (12) and second means by which the gases are arranged to be led out of the container part, characterized in that one or more substantially horizontal partition plates (2) extending throughout the cross section of the container, fully or mainly made of a material separating particles and enabling gases to flow through, are arranged above the container part (12), and that the arrangement comprises one or more blow nozzles (3) that are arranged to remove the particles separated from the gas and adhered to the partition plates (2).

2. An arrangement as claimed in claim 1, characterized in that the partition plates (2) are fixed in structure.

3. An arrangement as claimed in claim 1, characterized in that the partition plates (2) are rotatable in structure.

4. An arrangement as claimed in claim 1, characterized in that the blow nozzles (3) are fixed nozzles.

5. An arrangement as claimed in claim 1, characterized in that the blow nozzles (3) are movable nozzles.

6. An arrangement as claimed in claim 1, characterized in that the mixture of gases and solid particles is arranged to be fed into the container part (12) in such a way that in the container part the mixture flows substantially vertically downwards.

7. An arrangement as claimed in claim 1, characterized in that the cross section of the container part (12) is substantially round, and that the mixture of gases and solid particles is arranged to be fed into the container part (12) substantially horizontally in a tangential direction thereof.

8. An arrangement as claimed in claims 6 and 7, character- i z e d in that the mixture of gases and solid particles is arranged to be fed into the container part (12) through more than one supply openings (1 , 1').

9. An arrangement as claimed in any one of preceding claims 1 to 8, characterized in that an equipment (16) for discharging or storing the particles is arranged below the container part (12).

10. An arrangement as claimed in claim 1, 4 or 5, characterize d in that the blow nozzles (3) are arranged to operate for air that does not flow through the separator.

11. An arrangement as claimed in claim 1, 4 or 5, character- i z e d in that the blow nozzles (3) are arranged to operate with air from which solid particles have been removed.