WO1991019683A1

WO1991019683A1 - Device for conveying powder to a pipe

Info

Publication number: WO1991019683A1
Application number: PCT/SE1991/000412
Authority: WO
Inventors: Lars Saltin
Original assignee: AGA AB
Current assignee: Linde Sverige AB
Priority date: 1990-06-15
Filing date: 1991-06-11
Publication date: 1991-12-26
Anticipated expiration: 1992-12-15
Also published as: SE9002142D0; SE9002142L

Abstract

The present invention relates to a device for delivering powdered solids to and through a central passageway (15) in an oxygen burner (16), for melting the material subsequent to its exit from the central passageway (15) of the burner (16). The device includes a screw pump (1) whose outfeed end is connected to the central passageway (15) of the burner (16). The invention is characterized in that the screw pump (1) has a hollow shaft (3) whose infeed end can be connected to a gas source (7), and in that the pump (1) is connectable to the central passageway (15) of the burner (16) through the intermediary of a bridging piece (11).

Description

DEVICE FOR CONVEYING POWDER TO A PIPE

The present invention relates to a device for delivering powdered solids to and through a central passageway in an oxygen burner, for melting the material subsequent to its exit from the central passageway of said burner, said device including a screw pump whose outfeed end is connected to said central passageway.

It is desirable in many instances, for example in the destruction of mineral wool scrap, to return the scrapped material to a process for the manufacture of fresh material. In the case of mineral wool, the wool is first finely ground and then delivered to and transported through the central passageway of an oxygen burner. When exiting from the central passageway, the material is melted by the hot burner flame and can then be admixed with fresh starting material, for delivery to a spinning machine in which new mineral wool is produced.

According to one method, the finely ground mineral-wool scrap is delivered to the central passageway of the oxygen burner with the aid of a gas, the gaseous medium used to transport the finely ground mineral wool normally being air. The amount of gas supplied to the system in relation to the amount Of mineral-wool scrap present is often excessive, which radically changes the operating conditions of the burner in a negative sense. Another drawback with this method is that the amount of solid material delivered to the burner varies with time.

The object of the present invention is to provide a device for delivering a constant quantity of powdered solids to the central passageway of an oxygen burner without using an excessive quantity of transporting gas to this end.

This object is achieved with a device of the kind described in the preamble, which is characterized in that the screw pump has a hollow shaft whose infeed end can be con¬ nected to a gas source; and in that the connection end of the pump can be connected to the central passageway of the burner through the intermediary of a bridging piece which tapers conically in a direction away from the pump. Preferred embodiments of the invention are set forth in the dependent Claims.

A non-limiting embodiment of the invention will now be described with reference to the accompanying drawing, in which

Figure 1 is a schematic, sectional view taken along the longitudinal axis of the inventive device, which comprises a screw pump and a bridging piece which is connected to the central passageway of an oxygen burner;

Figure 2 is a schematic sectional view of an insert intended for use as an exit orifice for gas leaving the hollow shaft in the screw pump; and

Figure 3 is a schematic cross-sectional view of a preferred embodiment of the helix profile of the screw pump.

Figure 1 is a sectional view of a screw pump 1 having a cylindrical housing 2, taken through the pump shaft 3, which has a throughpassing passageway or channel 5. The hollow shaft 3, together with a helix profile 4, forms the feed screw of the pump 1 and extends through the rear defining wall 6 of the pump 1 in an essentially gas-tight fashion and opens into a gas pressure chamber 7, also in a gas-tight fashion. The hollow shaft 3 is rotated by a motor 8, through the intermediary of power transmission means 9. The motor 8 is a variable speed motor and is capable of rotating the shaft 3 at a preferred speed of 50-500 revolutions per minute. Mounted on the rear end of the pump is an infeed funnel or hopper 17.

Mounted on the front end of the pump housing 2 is a flange 10 which is connected with a bridging piece 11 having flanges 12, 13 mounted on respective ends thereof. The bridging piece 11 preferably has the form of a truncated cone and its base end carries the flange 12, which is connected to the outfeed end of the pump 1. The front flange 13 of the bridging piece is connected to the infeed end of the central passageway 15 of the oxygen burner 16, via a flange 14 at the infeed end of the passageway 15. The oxygen burner 16 is provided with oxygen and fuel connections. Figure 2 illustrates an insert 18 which is intended for insertion into the downstream end of the hollow shaft 3. The insert 18 forms an outfeed opening 19 in the form of a laval nozzle. This outfeed opening enables gas exiting from the hollow shaft 3 to flow at greater speed. As will be under¬ stood, the hollow shaft 3 may also be manufactured with an outfeed opening in the form of a laval nozzle. The outfeed opening of the insert 18 as well as the outfeed opening of the hollow shaft 3 for gas can be in the form of a Lavel nozzle.

Figure 3 illustrates in section an embodiment of the helix profile 4, which is shown in larger scale. The profile has a triangular cross-sectional shape and defines a channel 24 which extends through the whole of the profile and which is defined by the hollow shaft 3 and the walls 20, 21 of the profile. The channel 24 can be divided into sections. The wall 21 is directed in the forward direction of the screw pump or press and contains a number of openings 23. The channel 24 connects through openings 23 with the gas pas- sageway in the hollow shaft 3. As will be understood, the hollow profile 4 can have cross-sectional shapes other than triangular.

In use, the finely ground material is fed to the infeed hopper 17 of the device and falls gravitationally into the cylindrical housing 2. The feed screw, driven by the motor 8, then advances the material towards the outfeed end of the pump and into the bridging piece 11. Gas under pressure, for instance a pressure of 6 bars, is passed through the hollow shaft 3 in order to prevent the powdered solids from fas- tening in the bridging piece 11, particularly when the bridging piece 11 tapers conically in the flow direction. This gas fluidizes the powdered material and imparts a greater translation velocity thereto. This is necessary when using a conical bridging piece 8. According to one preferred embodiment, gas is also passed through the exit openings in the helical profile in the flow direction of said material, in order to prevent packing of the material between the turns of the helix profile. The amount of gas that passes through the profiled openings can be adjusted by varying the size and the number of said openings.

Claims

1. A device for delivering solid powdered material to and through a central passageway (15) in an oxygen burner (16) for melting the material subsequent to its exit from said central passageway (15) , said device including a screw pump (1) whose outfeed end is connected to the central passageway (15) of said burner (16) , characterized in that the screw pump (1) has a hollow shaft (3) whose infeed end can be connected to a gas source (7) ; and in that the pump (1) is connectable to the central passageway (15) of the burner (16) through the intermediary of a bridging piece (11) .

2. A device according to Claim 1, characterized in that the bridging piece (11) tapers conically in the flow direction; and in that half the cone angle is smaller than 10°, prefer- ably smaller than 5°.

3. A device according to Claim 1 or 2, characterized in that the helix profile (4) of the pump (1) feed screw is provided with at least one radially extending channel (25) communicat¬ ing with a passageway (5) of the hollow shaft (3) , said channel (25) being provided with at least one exit orifice (23) in the flow direction in order to fluidize the trans¬ ported material.

4. A device according to Claim 3, characterized in that the ends of the helix profile (4) passageway (25) are closed and in that the passageway (25) extends along the whole of the profile (4) and is provided with a plurality of exit orifices (23) in the axial direction of the screw pump (1) towards the burner (16) .

5. A device according to one or more of Claims 1-5, charac- terized in that the exit orifice of the hollow shaft (3) has the form of a laval nozzle.

6. A device according to one or more of Claims 1-4, charac¬ terized by an insert (18) mounted in the exit end of the hollow shaft (3) , thereby to form an exit opening in the form of a laval nozzle (19) .