WO2001098668A1

WO2001098668A1 - Guiding arrangement for a large blower unit

Info

Publication number: WO2001098668A1
Application number: PCT/DK2000/000329
Authority: WO
Inventors: Henrik Bagger
Original assignee: Howden Power AS
Current assignee: Howden Power AS
Priority date: 2000-06-21
Filing date: 2000-06-21
Publication date: 2001-12-27
Anticipated expiration: 2002-12-21

Abstract

A guiding arrangement for a large blower unit of the type which at the suction side of the impeller is connected to an inlet suction box (3) that impart to the inlet airflow a change of flow direction of between 45° and essentially 90°, whereby a tubular body (4) is passed through the suction box (3), where an essentially wedge shaped guide body (5) is confined by substantially level sheet members (6, 7), which are parallel with the flowdirection of inlet air at introduction into the suction box (3) and at a frontwall (8) of the sution box (3) facing away from the impeller are connected substantially tangentially to the tubular body (4), while in the axial direction of the impeller they converge to a pointed wedge shape, to thereby provide a reduced flow resistance for the inlet airflow in a suction box.

Description

Guiding arrangement for a large blower unit

The present invention relates to a guiding arrangement for a large blower unit of the type which at the suction side of the impeller is connected to an inlet suction box that impart the inlet airflow a change of flow direction of between 45° and essentially 90°, where the driving shaft of the impeller is supported in a tubular body, which is passed through the suction box.

In blowerunits it is often necessary, owing to shortage of space, cost of making conduits, etc. to connect an air or gas conduit to the suction inlet of a blower in a direction which is perpendicular to the axis of the blower. If the conduit is connected to the suction inlet by means of a pipe bend, the bulk of the air will flow along the outer wall of the bend, whereby the impeller is loaded asymmetrically. In this case the blower will not achieve the required pressure and volume flow, and its efficiency will be lowered significantly. In large blowers for power stations and fluidized bed systems, tunnels and the like, the power of the motor to drive the impeller may be 700 k or even more, so the efficiency of the blowerunit is of critical importance.

Therefor inlet suction boxes for blowerunits have been developed, which shall give the inlet airflow an change in flow direction of between 45° and essentially 90° with increased efficiency compared to an ordinary bend. A preferred assembly of blowerunits is constructed with a tubular body housing a through-going driving shaft for the impeller, control parts, inlet for sealing air, instruments, bearings or other parts for ensuring the desired machine function. The tubular body is also preferred because it gives good accessi- bility in connection with maintenance and repair, but on the other hand the tubular body represents a flow obstruction in the suction box.

An example of a suction box for a blower unit emerges among others from US patent no. 4,540,338, which relates to a suction box with carefully chosen dimensions to achieve a suction box with reduced power loss due to flow resistance. The document does not mention anything about special guiding arrangements. To minimize the flow related unfavourable effect of the tubular body in the suction box there has for a number of years been manufactured suction boxes, where the tubular body is equipped with a guiding arrangement on the downstream face, which guiding arrangement is a guide body of essentially snow plough shape, which from a wide end at the intersection of the tubular body with a front wall of the suction box facing away from the impeller is connected substantially tangentially to the tubular body, while they in the direction of the impeller axis converges to a pointed wedge shape, the guiding arrangement being confined by curved sheetmem- bers .

Furthermore there are known suction boxes equipped with rotatable guide vanes to achieve an adjustable blower unit without considerably increased flow resistance, which emerges from US patent no. 4,167,368. The impeller of this blower unit is driven by a shaft through the suction box from a driving assembly placed on the opposite side thereof, the shaft bearings being placed outside the suction box, so that the shaft gives rise to a relatively small flow resistance and no special guiding arrangement is required around the shaft .

An object for the present invention is to provide a guiding arrangement for a blower unit, which guiding arrangement causes a reduced flow resistance for the inlet airflow in a suction box.

The guiding arrangement according to the invention is characterized in that a essentially wedge shaped guide body is confined by substantially plane sheet members, which is parallel with the flowdirection of inlet air at introduction into the suction box and at a front wall of the suction box facing away from the impeller is connected substantially tangentially to the tubular body, while they in the axial direction of the impeller converges to a pointed wedge shape . This design is cost saving to manufacture compared to the plough shaped body and gives a minimized pressure loss in the suction box by virtue of the fluidic improved design of the guiding arrangement .

According to a preferred embodiment the guiding arrangement ' is characterized in that the guide body at its end facing the impeller is connected to a guide vane or baffle plate in conventional guiding arrange- ment with stationary or adjustable guide vanes or baffle plates on the suction side of the impeller. These additional guiding vanes or baffle plates can further improve the flow into the impeller and in case of adjustable vanes, the flow can be optimized to the actual flow velocity of the incoming flow.

The invention will in the following be descriped in detail with reference to the associate drawing, where

Fig. 1 is an end view of a large blower unit in partial cross section.

Fig. 2 is an inclined perspective view of the suction box with a guiding arrangement according to the invention

Fig. 3 is a side view of the suction box in Fig. 2. Referring to Fig. 1, the blower unit 1 for a large blower includes a suction box 3 with an inlet for air, an impeller 2 and a diffusor . The impeller 2 is driven by a motor 10 connected to the impeller 2 by a shaft 11 through the suction box 3. A tubular body 4 through the suction box 3 contains the shaft 11, main bearings 12 and any other equipment. A fluid e.g. air to a power station or exhaust from a power station is drawn in by the impeller 2 into the suction box 3 in the direction shown by the arrow A, and the suction box

3 imparts a change of flow direction from the inlet to the impeller 2. The impeller 2 with blades is rotated by the shaft 11 connected to the motor 10, while the blades in turn provides an increase in pressure in the fluid. As mentioned the shaft 11 passes through the suction box 3 in a tubular body 4, which also may hold main bearings 12 for the shaft 11, conduits for sealing air, and equipment necessary or useful for the function, monitoring or control of the blower. This means that the dimensions of the tubular body 4 is usually rather large, e.g. for a impeller 2 with a diameter at the blade tip of 3200 mm, the diameter of the tubular body 4 may be 1600 mm.

The tubular body 4 gives rise to flow resistance because of separation of the flow past the tubular body

4 and/or generation of different kinds of vortices, such as the von Kar an vortex trail, depending on the flow velocity. To countervail this flow resistance of the tubular body 4 different kinds of guiding arrange- ments have been proposed.

In Fig. 2 and 3 is depicted a suction box 3 with a guiding arrangement according to the invention. For illustration purpose, the suction box 3 is drawn as a transparent body with normally hidden lines shown by dashed lines, and the guiding arrangement shown by dashed lines in bold. Air will be drawn in through the rectangular inlet of the suction box 3 and imparted a change of flow direction towards the annular outlet of the suction box 3 and the subsequent impeller 2. The suction box 3 has an inclined frontwall 8 facing away from the impeller 2 and a rounded part remote from the inlet of the suction box 3. Part of the air will flow around the tubular body 4 and may .result in stationary vortices and dramatically reduced efficiency if there was no guiding arrangement on the side facing away from the inlet or downstream of the tubular body 4. The guiding arrangement according to the invention includes an essentially wedge shaped guide body 5 confined by two plane walls 6, 7 e.g. of sheet metal, which are parallel with the flowdirection of inlet air at introduction into the suction box 3 and at a front wall 8 of the^' suction box 3 facing away from the impeller 2 are connected substantially tangentially to the tubular body 4, while they in the axial direction of the impeller 2 converges to a pointed wedge shape.

Claims

P A T E N T C L A I M S

1. A guiding arrangement for a large blower unit

(1) of the type which at the suction side of the impeller (2) is connected to an inlet suction box (3) that impart to the inlet airflow a change of flow direction of between 45° and essentially 90°, whereby a tubular body (4) is passed through the suction box (3), c h a r a c t e r i z e d in that an essentially wedge shaped guide body (5) is confined by substantially level sheet members (6,7), which are parallel with the flowdirection of inlet air at introduction into the suction box (3) and at a frontwall (8) of the suction box (3) facing away from the impeller (2) are connected substantially tangentially to the tubular body (4) , while in the axial direction of the impeller (2) they converge to a pointed wedge shape.

2. A guiding arrangement according to claim 1 , c h a r a c t e r i z e d in that at its end facing the impeller (2) the guide body (5) is connected to a guide vane or baffle plate in a conventional guiding arrangement with stationary or adjustable guide vanes or baffle plates on the suction side of the impeller

(2) .