WO2003033158A1

WO2003033158A1 - Dust separator

Info

Publication number: WO2003033158A1
Application number: PCT/SE2002/001837
Authority: WO
Inventors: Willy FURÅSEN; Ola Antonsson
Original assignee: Rapid Granulator Ab
Priority date: 2001-10-19
Filing date: 2002-10-09
Publication date: 2003-04-24
Also published as: DE60235033D1; EP1444044B1; SE0103501D0; ATE454218T1; EP1444044A1; WO2003033164A1

Abstract

An apparatus for preventing the spread of small particles into the ambient surroundings in the granulation of plastics includes a cyclone. In the cyclone (3), there is disposed a dust separator (11) with a separator chamber (18) with a deflector device (19). The separator chamber (18) is disposed between the lower outlet (12) of the cyclone for the particles and an inlet conduit (13) for air. In the separator chamber (18), air flows through a curtain of falling particles where fine dust is entrained upwards by the air, while larger particles depart to a subjacent discharge sluice (10) for the granulate. The cyclone (3) has a conduit (16) which extends far down in the conical section (17) of the cyclone so that dust separated in the dust separator chamber (18) may depart via the conduit (16).

Description

SEPARATION

TECHNICAL FIELD

The present invention relates to an apparatus for preventing the spread into the ambient surroundings of dust and small particles which, together with larger particles, are produced in a granulator mill, the apparatus comprising a dust separator which is intended to be placed between an outlet for larger particles from a cyclone and a discharge sluice for large particles.

BACKGROUND ART

In the granulation of plastics waste in a granulator mill, a main fraction of plastics particles is produced where the individual particles are of relatively large size, often of the order of magnitude of one or a few mm. In addition, smaller particles or pure dust are also produced where the individual particle may be of extremely small size. The dust particles or the smaller particles often adhere to the larger particles as a result of purely mechanical forces, but also as a result of electrostatic bondings.

Conventionally, the granulate is conveyed with dust admixed therein from the granulator mill via a conduit to a cyclone where the granulate is separated from the air current carrying the granulate. Because of the slight mass of the small particles, their separation from the air current will be defective in the cyclone, for which reason a certain fraction of the particles departs with the exhaust air flow from the cyclone.

Those dust particles and otherwise smaller particles which adhere to the granulate particles accompany them in the separation and, as a result, wind up among the granulate. If this latter is handled without specific safety measures, the dust particles will be separated from the granulate and spread into the ambient surroundings, which may give considerable pollution problems. A fan is often placed between the granulator mill and the cyclone for positively advancing the air current which passes the cyclone and which entrains the granulate and dust particles with it. This implies that the cyclone is under excess pressure in relation to the ambient surroundings and also to components placed downstream of the cyclone. The smallest leakage in the system entails that dust constantly flows out into the ambient surroundings which, in particular in clean environments, is totally unacceptable. PROBLEM STRUCTURE

The present invention has for its object to realise a dust separator which eliminates the problems inherent in prior art technology. In particular, the present invention has for its object to realise an environment in connection with the granulation of plastics waste where the pollution problems as a result of the spread of dust are in principle solved. The present invention also has for its object to attain a solution which offers an extremely high separation effect and which is simple and economical in manufacture and operation.

SOLUTION

The objects forming the basis of the present invention will be attained in respect of the dust separator if this is characterised in that a separator chamber of larger cross sectional area than the outlet of the cyclone for larger particles is disposed therebeneath, that a deflector device is disposed in the separator chamber to be impinged upon by falling, larger particles and dust carried thereby, and that an inlet for air is provided beneath the deflector device, whereby there is created an air current through the flow of falling, larger particles and dust.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

The present invention will now be described in greater detail hereinbelow, with reference to the accompanying Drawings. In the accompanying Drawings:

Fig. 1 schematically illustrates a plant for separating granulate and dust from an airborne flow from a granulator mill; and

Fig. 2 shows, on a larger scale, those components which are employed for separating the granulate and the dust.

DESCRIPTION OF PREFERRED EMBODIMENT

In Fig. 1, reference numeral 1 relates to an arrow which represents a conduit from the outlet side of a granulator mill (not shown) to the inlet 2 to a cyclone 3. In its upper regions, the cyclone is somewhat unconventional, as will be apparent below, but has a centrally located outlet 4 on the upper end of the cyclone. To the outlet 4, there is connected a conduit 5 which runs to the inlet side of a filter 6 whose downstream side is connected via a conduit 9 to a fan 7 with an outlet 8.

It will be apparent from the foregoing that the fan is placed at the terminal end of the series of components employed for separating, on the one hand, granulate and, on the other hand, for separating dust which is produced in the granulator mill not shown on the Drawings. It should also be observed that the air current which the fan 7 generates not only flows through the cyclone 3 but also through the granulator mill so that at least certain parts of its interior are under a partial vacuum in relation to the ambient surroundings. The same conditions naturally apply also to the cyclone 3, the conduits 5 and 9, as well as the filter 6 and the intake side of the fan 7. In that, in this manner, the system is kept under partial vacuum, dust can hardly - regardless of particle size - escape into the ambient surroundings since, in the event of leakages, air would flow into the system and thereby entrain with it any possible dust.

Beneath the cyclone 3, there is provided a conventional discharge sluice 10 whose purpose is to discharge such granulate as was separated in the cyclone without allowing any air flow either into or out from the cyclone 3. This discharged granulate is then transferred to a receptacle container located beneath the discharge sluice 10 or is conveyed further for re-use with the aid of an air current flowing in a conduit system.

Since the granulate which departs from the discharge sluice 10 can be handled under atmospheric pressure and, for example, be poured or blown via a conduit to the infeed of an injection moulding machine, it will readily be perceived that even minor quantities of dust in the granulate would cause major pollution problems in the ambient surroundings. For this reason, it is vitally important that the granulate which departs from the discharge sluice 10 is dust-free as far as this is humanly possible. It will be apparent from Fig. 1 that there is disposed, beneath the outlet 12 of the cyclone 3 for larger particles or granulate, a dust separator 11 which in turn is placed over an inlet conduit 13 to the discharge sluice 10.

As was mentioned above, in the cyclone larger particles and granulate are separated from the air current which enters in via the conduit 1 in the upper region of the cyclone 3. In the lower region of the cyclone at the outlet 12, the granulate or large particles are no longer airborne, but these fall down under the action of gravity in order, in due course, to arrive in the discharge sluice 10. The dust separator 11 is disposed to separate, from the flow of downwardly falling large particles or granulate, dust particles which may possibly float freely in the air, but also separate such dust particles as adhere to the downwardly falling granulate particles. These released small particles and dust particles are conveyed upwards through the central region of the cyclone and depart via the outlet 4 of the cyclone, the conduit 5 and to the filter 6 where the dust and small particles are separated and accumulated. A relatively dust-free current of air then passes from the downstream side of the filter, through the conduit 9, through the fan 7 and out via the outlet 8.

In order to realise an air current through the lower region of the cyclone 3 and upwards through the central region of the cyclone and out to the outlet 4, there is provided, beneath the dust separator 11, an inlet 14 via which air from the ambient surroundings can be sucked in under the action of the fan 7. The air volume sucked in via the inlet 14 carries the dust and small particles released in the dust separator 11 upwards through the cyclone and to its outlet 4.

As was intimated above and as is apparent from Fig. 2, the cyclone is, at least as regards its upper regions, somewhat unconventional in design. In a conventional manner however, it has a tangentially directed inlet 2 which discharges in an annular flow space between a cylindrical outer wall 15 and a cylindrical inner wall 16. The cylindrical inner wall 16 has a downwardly directed opening which discharges in the conical section 17 of the cyclone 3. Upwardly, the space inside the inner wall 16 discharges in the outlet 4 of the cyclone.

That which distinguishes the present cyclone from conventional cyclones is the fact that the cylindrical inner wall 16 extends considerably further down in the cyclone than was previously the case. Thus, the inner wall extends down into the conical region 17 of the cyclone so far that the radial distance between the inner wall 16 and the conical section 17 is considerably smaller than the radial distance between the inner wall 16 and the cylindrical outer wall 15, or, if this were to be absent, the corresponding radial distance at the height level of the inlet 2. Preferably, this radial distance at the lower end of the inner wall 16 is of the order of magnitude of 0.25 to 0.5 of the radial distance at the upper region of the inner wall 16. Further, there is disposed, inside the inner wall 16, one or more plates 23 whose purpose is to prevent or reduce rotation of the flow which takes place with the major direction upwards inside the inner wall. In one embodiment, use is made of one such plate 23 which is placed in an axial diametric plane to the inner wall 16. The plate 23 has a lower edge which, in the vertical direction, is located at the lower end of the inner wall 16 and an upper edge which is located a distance up which approximately corresponds to the diameter of the inner wall 16, which is approximately twice as large as the diameter of the lower outlet 12 of the cyclone.

As will be apparent from Fig. 2, the dust separator 11 has a separator chamber 18 which is approximately in the form of two frustoconical shells which are turned to face with their large ends towards one another. Possibly, as is the case in Fig. 2, a small cylindrical band may be placed between both of the large ends. In accordance with that disclosed above, the separator chamber is rotation-symmetrical and is coaxial with the cyclone 3 and its outlet 12.

The separator chamber has a largest diameter in the central region in the vertical direction and this diameter is greater than the diameter of the outlet 12 of the cyclone 3, but is also greater than the diameter of the inlet conduit 13 to the discharge sluice 10.

Interiorly in the separator chamber 18, there is disposed a deflector device 19 which may also be considered as being composed of two conical shells which are turned to face with their large ends towards one another. The diameter of the deflector device 19 is equal to or greater than the inner diameter in the outlet 12 of the cyclone 3. The deflector device 19 is placed concentrically in the separator chamber 18 and thereby also concentric in relation to the outlet 12 of the cyclone and the inlet 13 of the discharge sluice.

The inlet conduit 14 to the inlet 13 of the discharge sluice has its centre line placed in a diametric plane to the inlet 13 and has a downwardly angled portion 20 located most proximal the inlet and discharging in the inlet 13. For regulating the air current which passes in through the inlet 14, there is provided a regulator valve 21 which controls the volume flow of air sucked in through the inlet 14.

The dust separator functions in the following manner. Via the inlet 2 a mixture of air, granulate and small particles and dust flows into the cyclone 3. The air and these particles begin to rotate with increasing speed of rotation the further down in the conical region of the cyclone the come. Gradually as the larger particles impinge on the wall of the conical region, the rotation speed is retarded and the particles chute or slide along the inner surfaces of the cyclone down to the outlet 12 whence they fall under the action of gravity down into the separator chamber 18 where they strike the deflector device 19. At least the greater proportion of the falling granulate particles chute along the upper side of the deflector device 19 and depart therefrom at the peripheral edge 22 of the deflector device in order subsequently (once again under the action of gravity) to fall down and possibly strike the lower wall of the separator chamber 18 under the deflector device 19. As a result, there will be formed a curtain-like flow of granulate and larger particles from the peripheral edge and possibly the region diametrically outside this edge down to the lower wall of the separator chamber 18 and the inlet 13 to the discharge sluice 10. The air which is sucked in via the inlet 14 passes in a direction upwards and is forced to pass straight through the falling flow of granulate and large particles. Initially, the flow takes place at least partly radially outwards under the deflector device 19, past its periphery 22 and then at least partly radially inwards over the deflector device. This implies that the air current passes twice through the curtain of falling granulate, once under the deflector device 19 and once over it. As a result, the air volume sucked in via the inlet 14 will entrain with it both loose dust particles in the flow of granulate particles, but will also tear loose small particles ands dust particles adhering to the granulate particles, these small particles and dust particles being borne upwards by the air current centrally through the cyclone 3 and out through the outlet 4 of the cyclone. The granulate which in due course arrives in the discharge sluice 10 is as good as completely free of dust and small particles.

As a result of the downward drawing of the inner wall 16 far down into the conical section 17 of the cyclone, the distance in the vertical direction which the dust-carrying air current must pass in an upward direction will be considerably shorter than it would have been in a conventional cyclone. Further, the plate 23 may be expected to reduce the turbulence or rotation in the upwardly flowing air current in the central regions of the cyclone.

According to the present invention, it is possible further to amplify the dust separating effect by employing two separator chambers 18 with deflector devices 19 placed therein above one another. Between the separator chambers, there is a short conduit section dimensioned analogous with the outlet 12 and the inlet conduit 13. The above-described dust separating process can, to some degree, be controlled by a regulation of the air flow entering via the valve 21.

In the foregoing, the separator chamber 18 has been described as composed of two frustoconical shells. However, it also falls within the scope of the present invention that the separator chamber 18 is approximately spherical or approximately discus-shaped.

Further regulation possibilities reside in an adaptation of the peripheral diameter (at 22) of the deflector device 19 in relation to the inner diameter in the separator chamber 18 at its central seen in the vertical direction.

Alternative embodiments of the deflector device 19 are also conceivable and, thus, this may conceivably be composed of approximately spherical hemispheres or be generally approximately discus-shaped.

Claims

WHAT IS CLAIMED IS:

1. A dust separator disposed to be placed between an outlet (12) from a cyclone (3) intended for larger particles and a discharge sluice (10) for larger particles, characterised in that a separator chamber (18) of larger cross sectional area than the outlet (12) of the cyclone (3) for larger particles is disposed therebeneath, that a deflector device (19) is disposed in the separator chamber to be impinged upon by falling larger particles and by dust carried thereby, and that an inlet (14) for air is disposed beneath the deflector device, whereby there is created an air current through the flow of falling larger particles and dust.

2. The dust separator as claimed in Claim 1, characterised in that the deflector device (19) is dimensioned and placed in the vertical direction so as to realise a passage of the air current through the falling larger particles and dust carried thereby, both under and over the deflector device.

3. The dust separator as claimed in Claim 1 or 2, characterised in that the separator chamber (18) has the approximate configuration of two frustoconical shells which are united with one another at their large ends and which, with their small ends, are united on the one hand with the outlet (12) of the cyclone (3) for larger particles, and, on the other hand, with an inlet conduit (13) to the discharge sluice (10).

4. The dust separator as claimed in Claim 3, characterised in that the inlet (14) for air has a regulator valve (21) and is connected to the inlet conduit (13) of the discharge sluice (10).

5. The dust separator as claimed in Claim 3 or 4, characterised in that the inlet (14) lies in a longitudinal diametric plane to the inlet conduit (13) and that it is slightly angled downwards.

6. The dust separator as claimed in any of Claims 1 to 5, characterised in that the deflector device (19) is approximately in the form of two cones united at their large ends.

7. The dust separator as claimed in any of Claims 1 to 6, characterised in that the deflector device (19) has the same or larger diameter (22) than the outlet (12) of the cyclone (3) for larger particles.

8. The dust separator as claimed in any of Claims 1 to 7, characterised in that the deflector device (19) has the same or larger diameter than the inlet conduit (13) of the discharge sluice (10).

9. The dust separator as claimed in any of Claims 4 to 8, characterised in that the outlet (12) of the cyclone (3) for larger particles, the separator chamber (18), the deflector device (19) and the inlet conduit (13) of the discharge sluice (10) are all substantially coaxial with a vertical axis.