GB2268976A

GB2268976A - Flow accelerating device for a pipe duct.

Info

Publication number: GB2268976A
Application number: GB9313748A
Authority: GB
Inventors: Erwin Schulze
Original assignee: Individual
Current assignee: Individual
Priority date: 1992-07-21
Filing date: 1993-07-02
Publication date: 1994-01-26
Also published as: BE1006420A3; DE4223924A1; FR2693995A1; GB9313748D0

Abstract

A device for the acceleration of the flow of particulate material, for example flue or coal dust, conveyed in a pipe duct (5) by a gaseous medium comprises a cylindrical body (2), which incorporates an injector (6) for the blowing-in of an auxiliary fluid medium in flow direction (arrow x). The injector (6) consists of a tube which extends through the wall of the body and then in the flow direction (x) in the body. The body (2) is connected into the pipe duct (5) by way of an entry diffuser (3) and an exit member (4) of reducing cross-section defined by a convexly then concavely curved wall portion. <IMAGE>

Description

2268976 -1- FLOW ACCELERATING DEVICE FOR A PIPE DUCT The present invention

relates to a flow accelerating device for a pipe duct for conveying a gaseous medium with entrained particulate material, for example flue dust or coal dust.

Flue dust arises in power stations from the combustion of coal and is conveyed through pipe ducts from the boiler to deposits. The conveying of the flue dust in the pipe ducts is effected by air.

Depending on the length of the pipe duct, the air must be blown into the duct with a relatively high initial pressure to compensate for the duct losses, so that the flue dust will actually issue at the end of the duct. It has, however, proved that continuous conveying of flue dust in a longer duct is not possible even at high air pressures. Rather, even shortly after the start of the duct, deposits form at the base of the duct, in front of which depositsa correspondingly high pressure builds up. This has the consequence that the deposits are carried away on reaching of a certain pressure, but come to rest again at once at another place. This conveying of deposits becomes even more problematic if the flue dust has a certain degree of moisture. The moisture has the effect that the deposits bake together into a compact mass which may be able to be detached only with the use of hammer blows onto the outside of the duct or by heating with blowtorches.

There is therefore a need for a flow accelerating device to assist with continuous conveying of flowable materials, especially of flue dust through longer pipe ducts, with the use of relatively small quantities of energy such as compressed air.

According to the present invention there is provided a flow accelerating device for a pipe duct for conveying a gaseous medium with entrained particulate material, comprising a substantially cylindrical hollow body defining a flow path therethrough and an injector extending in body to inject an auxiliary fluid medium into the flow path in a given flow direction thereof.

Preferably, the injector comprises a tube which extends through the wall of the body and extends in flow direction in the body. The part of the tube extending in flow direction, which part can be bent over at about a right angle, preferably extends in about the longitudinal centre line of the body.

As seen in flow direction, a pressure can build up in front of the injector opening, whilst a suction force can arise behind the opening. Both cause an acceleration of the material to be conveyed.

The suction effect behind the injector opening can be increased at the entry of the body if the transition from the pipe duct to the body has the form of a diffuser, i.e. an en.largemient- in cross-section is present in flow direction. At the exit side, i.e. downstream of the injector opening as seen in flow direction, the body preferably adjoins a connecting member reducing in cross-section. Due to the reduction in the cross-section, the pressure building up in front of the injector opening is further increased by virtue of nozzle effect, which leads to an acceleration of the conveyed material. In particular, the wall of the connecting member can be an arcuately curved part, the curvature of which is directed towards the longitudinal centre line as seen in flow direction so that the 3 connecting member has a bulging shape ahead of the pipe duct. Thi s shape of the connecting member prevents deposits from forming in the region of the member. The reason for this is that a pressure builds up in the region of the curved part of the member and leads to a pressure cushion, which in turn causes the solid substance particles, such as flue dust, to avoid the wall region when flowing through the member. In order that eddy formations do not arise between the body and the curved part of the connecting member, the transition is formed to be progressive, i.e. without any edges which would induce turbulence in the flow.

In order to obtain a uniform distribution of conveyed material in the body, the body is preferably provided with means for the splitting-up of the conveyed material, for example a sieve. The sieve can, for example, have the form of an elongate sinusoidal curve, wherein the sieve, seen in flow direction, is preferably arranged to extend obliquely in the body. Due to such a sinusoidal construction of the sieve and the sloping arrangement in the body, it is possible to achieve a sieve area equal to about 1.5 times the cross-sectional area of the body. It has proved that a particularly fine distribution of the conveyed material is achieved with such a cross-sectional ratio between the sieve and the body, with the consequence that the conveyed material is blown continuously into the connecting member at the end of the body. The portion of the injector tube extending along the axis of the body can extend through the sieve to about the connecting member. This means that no pressure is built up in front of the sieve by the injector and the conveyed material can be sucked through the sieve by the suction effect produced by the injector.

An embodiment, of the present invention will now be more particularly described by way of example with reference to the accompanying drawing, the single figure of which is a schematic sectional view of a device embodying the invention.

Referring now to the drawing there is shown a device 1 for the acceleration of flow of a particulate material conveyed by a gaseous medium, for example coal dust conveyed by air, in a pipe duct 5, the device comprising a cylindrical body 2, a conical connecting member 3 constructed as diffuser at an entry end of the body and a bulging connecting member 4 at an exit end of the body. The connecting members 3 and 4 are each connected to the pipe duct 5, which has a smaller crosssection than the body 2. An injector 6, which has the form of a tube bent over at a right angle with a horizontal portion 6a extending along the longitudinal axis 7 of the body 2, is led radially through the wall of the body 2 and connected externally thereof to a source of an auxiliary fluid medium, such as compressed air, to be blown or drawn into the device 1. The injector tube projects up to about the transition of the body 2 to the connecting member 4, an outlet opening 6b of the tube being disposed in this region.

A sieve 8, which has the form of an elongate sinusoidal curve, is also disposed in the body 2. The sieve 8 is arranged in the body to extend at an angle as seen in flow direction (arrow x). The sieve 8 has a bore 8a through which the horizontal portion 6a of the injector 6 extends.

The bulging form of the connecting member 4, defined by a convexly curved wall portion adjoining the body 2 and a concavely curved wall portion smoothly adjoining the convexly curved wall portion, as denoted by the curve sections 4a, has the effect that a pressure air cushion builds up in this region and prevents conveyed solid material particles from laying themselves against the wall of the member 4, whereby wear of the wall is avoided.

In use, solid material particles entrained in a gaseous medium are transported through the pipe duct, with intermediately connected flow accelerating device 1, and an auxiliary gaseous medium is injected into the device by way of the injector 6. A pressure builds up in front of the injector outlet opening and a suction force arises behind the opening, which leads to an acceleration of the conveyed material. The combination of pressure and suction effects and consequent flow acceleration reduces or avoids formation of deposits of the solid material.

S

Claims

1 A flow accelerating device for a pipe duct for conveying a gaseous medium with entrained particulate material, comprising a substantially cylindrical hollow body defining a flow path therethrough and an injector extending in body to inject an auxiliary fluid medium into the flow path in a given flow direction thereof.

2. A device as claimed in claim 1, wherein the injector comprises a tube extending through the wall of the body and at least in part in said flow direction.

3. A device as claimed in claim 2, wherein the tube comprises a first portion extending from the wall to the region of the axis of the body and a second portion extending from the first portion substantially along said axis.

4. A device as claimed in any one of the preceding claims, comprising flow influencing means to influence distribution of the entrained material in a flow of the gaseous medium through the body.

5. A device as claimed in claim 4, the flow influencing means comprising a sieve.

6. A device as claimed in claim 5, wherein the sieve has the form of an elongate substantially sinusoidal curve and extends in the body at an angle to said flow direction.

7 - 7. A device as claimed in any one of the preceding claims, comprising a diffuser arranged at an entry end of the body for connection thereof to such pipe duct.

8. A device as claimed in any one of the preceding claims, comprising a connecting member of reducing cross-section arranged at an exit end of the body for connection thereof to such pipe duct.

9. A device as claimed in claim 8, wherein the wall of the connecting member has an inwardly curved length portion in said flow direction.

10. A device as claimed in claim 9, wherein the wall has a convexly curved length portion adjoining the body and a concavely curved length portion adjoining the convexly curved portion.

11. A device as claimed in claim 5 when appended to claim 3, comprising a connecting member of reducing cross-section arranged at an exit end of the body for connection thereof to such pipe duct, the second portion of the tube extending through the sieve and into the region of the connecting member.

12. A flow accelerating device substantially as hereinbefore described with reference to the accompanying drawings.

13. Duct means for conveying a gaseous medium with entrained particulate material, comprising a pipe duct and a device as claimed in any one of the preceding claims connected into the duct.