GB2183502A - Inertial separator - Google Patents

Abstract

A separator for pneumatically conveyed solids comprising a generally horizontal inlet (14) at the upper end of a downwardly curved duct (16) which terminates in a solids outlet at the bottom, having a rotary outlet airlock (22, 24). A radially inward wall of the duct comprises a perforated screen on the other side of which is an outlet duct (18) for air. The solids are inertially separated from the airflow and tend to flow against the radially outward wall (20) of the duct, away from the screen. <IMAGE>

Description

SPECIFICATION Inertial Separator This invention relates to pneumatic conveying systems typically used for conveying andlor drying products such as tobacco in its various forms, wood shavings, sawdust, paper and cardboard scrap. At the termination or discharge of such a conveyor, it is necessary to separate the conveyed product from the conveying air or gas stream.

A number of different types of such separators have been proposed previously, some of which involve passing the flow to be separated over a screen behind which suction is applied, whilst others use a cyclone principle which has the disadvantage that the material being separated can remain within the separator for an undesirably long time, which can cause it to be mechanically degraded also also undesirably dried.

One well known type of separator is shown in U.S.

patent No. 3,727,755, and includes a suction drum (212) having an air permeable surface, and the stream of cut tobacco is directed to move almost tangentially beneath the drum, as it is delivered from the end of the conveyor 13. The movement of air through the surface of the drum causes relatively iight particles of tobacco from the stream to move upward and collect on the surface of the drum whilst the relatively heavy stem and foreign matter falls down into a collecting bin.

In this type of arrangement, the air inlet comprises a grating consisting of louvres (104) below the suction drum, and the gas turbulence caused by the presence of the grafting lifts some of the product being treated which then has to pass across the face of the grating in order to exit into the collecting bin.

Consequently the grating tends to become blocked.

An alternative type of arrangement is shown in GB patent No. 1,575,175, in which the pneumatically conveyed stream of product to be treated passes into the inlet 10, through a separation zone 14 in which it is directed towards a screen which is flat and slightly angled downwards. On leaving the screen, the material falls into an expansion chamber immediately above an air-lock exit and the gas passes through the screen to the exhaust exit. Since the screen is angled downwardly relative to the product flow, so that the product is in effect scrubbing the screen, blockage of the screen is effectively prevented. However, because the tobacco impacts against the screen, it can become degraded, and accordingly the present invention seeks to provide a separator which reduces the possibility of damage to the product, and also does not suffer from screen blockage.

Accordingly the present invention comprises a separator for pneumatically conveyed particulate material comprising a first curved duct defining a path which is substantilly horizontal at the inlet and then curves downwardly to terminate in a product outlet; the radially inward side of the duct being defined by a correspondingly curved screen having an air outlet on the other side.

Since the inlet is at the top of the apparatus, rather than at the bottom as in the above mentioned U.S. patent No. 3,727,755 the screen does not tend to become blocked by the incoming material, and since this material is directed away from the screen as it enters the apparatus, it is not degraded by impacting against the screen itself.

One embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a vertical cross-section through an inertial separator according to the invention; Figure 2 is an end elevation, seen in the direction Z of Figure land Figure 3 is a partial horizontal cross-section through the device of Figure 1 taken on the iine w-w.

Referring first to Figure 1, the apparatus comprises a generally curved duct assembiy 10 which is mounted on a discharge air lock device 12, to be described in more detail below.

A pneumatically conveyed stream of tobacco enters the upper end of the curved duct via the inlet 14, and as can be seen from Figure 1, the duct then branches into a radially outward portion 16, and a radially inward portion 18. A curved screen 2 is interposed at the junction of the branch, so that the product entering the inlet 14 is prevented from passing into the exhaust plenum 3. As can be easily appreciated from a consideration of this layout, the stream of tobacco will tend to move outwardly, owing to its inertia, so as to flow round the inside of the outer wall 20 of the duct.

Since air flow out of the base of the device is effectively prevented by an air lock mechanism in the discharge section (to be described in more detail below), the conveying air, and any very light fractions to be separated, whose inertia is of course less, pass through the screen 2 and into the other branch of the duct 18 to the exhaust plenum 3. As will be seen from the drawing, a vane 4 is positioned in the plenum, to optimise the air distribution through the screen.

The base 12 of the device incorporates a rotary air lock of a well known type, comprising a cyiindrical housing 22, with an axially mounted set of radial vanes 24. These are equipped with resilient sealing blades 26 at their ends, and the vane assembly is rotated by means of a chain drive 30 powered by an electric motor 28. An adjustable tensioning device 32 (illustrated diagrammatically by dashed lines in Figure 1) may be incorporated to adjust the tension of the chain 34. In use, the air lock is driven at a suitable speed to enable the flow of tobacco to pass through it to a discharge port 36 in the base of the device, whilst effectively preventing the passage of air through the discharge port.

It will be clearly appreciated from a consideration of the layout of the device, that it avoids two significant problems of the prior art devices, namely the tendency to degrade the product to be separated, and the tendency to screen blockage, since the inertia of the product flow is employed to carry it away from the screen, so that it abuts against a smooth surface rather than a grating type of surface. In addition, since there is no recirculation of gas flow, in contrast to the cyclone type of separator, the time of residence of the product in the apparatus is kept to a minimum, avoiding over drying of the product.

Claims (6)

1 . A separator for pneumatically conveyed particulate material comprising a first curved duct defining a path which is substantially horizontal at the inlet and then curves downwardly to terminate in a product outlet; the radially inward side of the duct being defined by a correspondingly curved screen having an air outlet on the other side.

2. A separator according to claim 3 in which the air outlet comprises a second duct which is also curved and extends alongside and radially inwardly of the first duct, the said screen forming a common wall for the said ducts.

3. A separator according to claim 4 in which the second duct terminates in an outlet which is substantially horizontal so that the air leaves the duct in a direction opposite to the inlet direction.

4. A separator for pneumatically conveyed particulate material, comprising an inlet into which the stream of material is directed tangentially against a downwardly extending, smooth concave surface which terminates in a product discharge duct; and a generally coextensive convex perforated screen, facing the said concave surface, with an air outlet behind the said screen, the arrangement being such that the inertia of the material entering the inlet causes it to move outwardly aiong the concave surface, whilst the air is exhausted through the screen.

5. A separator according to any preceding claim in which said product outlet includes a rotary airlock.

6. An inertial separator substantially as herein described with reference to the accompanying drawings.