WO1995015439A1

WO1995015439A1 - A device in a vacuum pump

Info

Publication number: WO1995015439A1
Application number: PCT/SE1994/001125
Authority: WO
Inventors: Rolf Ekholm; Ulf Jansson
Original assignee: Kvaerner Pulping Technologies Ab
Priority date: 1993-12-01
Filing date: 1994-11-24
Publication date: 1995-06-08
Also published as: AU1206995A; SE9303987L; SE502127C2; SE9303987D0

Abstract

A device in a vacuum pump (23) of the liquid-ring type, serving a pulp pump and having a cylindrical vacuum chamber (25) and an impeller (26) eccentrically journalled in the vacuum chamber to rotate therein together with a liquid ring (29). According to the invention a channel (50) is arranged in the cylindrical wall (30) of the vacuum chamber, said channel having a first section (51) that is located within a converging pressure space (33) of the vacuum chamber and is in open communication therewith, and a second section (52) that is located within a diverging suction space (34) of the vacuum chamber and is in open communication therewith. A valve means (53) is arranged in the pump housing (24) between the channel sections (51, 52) in order, in a first position, to close the connection between them and thus the connection between the pressure and suction spaces and, in a second position, to open said connections, whereby pressure equalisation is achieved and the vacuum function ceases temporarily.

Description

A device in a vacuum pump

The present invention relates to a device in a vacuum pump serving a pump for pumping pulp, said vacuum pump being of the liquid-ring type and comprising a pump housing with a cylindrical vacuum chamber; an impeller eccentrically journalled in the vacuum chamber to rotate therein together with a liquid ring; a gas inlet channel from said pulp pump to the vacuum chamber; and a gas outlet channel from the vacuum chamber, said impeller dividing the vacuum chamber into a diverging suction space containing the inlet of the gas inlet channel, and a converging pressure space containing the outlet of the gas outlet channel.

The outlet channel from a vacuum pump built into a pulp pump to be driven by the same drive shaft must be closed during certain operating conditions, viz. when the pressure of the pulp in the inlet part of the pulp pump becomes so high that there is a risk of pulp being forced into the vacuum pump and on out into the waste water system. To prevent this, the outlet channel from the vacuum pump is closed by a valve. However, this measure gives rise to new problems. When the outlet channel is closed a strong pressure increase occurs in the vacuum chamber since the impeller is arranged eccentrically in the vacuum chamber. This pressure increase causes considerable loss of energy and cavitation inside the vacuum pump.

The object of the present invention is to provide a device that will limit the energy loss to a minimum and eliminate the risk of cavitation.

This is achieved according to the invention in that a channel is arranged in the cylindrical wall of the vacuum chamber, said channel having a first section that is located within the converging pressure space and is in open communication therewith, and a second section that is located within the diverging suction space and is in open communication therewith, and that a valve means is arranged in the pump housing at the transition between the first and second channel sections in order, in a first position, to close the connection between the first and second channel sections and thus the connection between said pressure and suction spaces and, in a second position, to open said connections, whereby pressure equalisation is achieved between the pressure and suction spaces and the vacuum function ceases temporarily.

The invention will be described in more detail in the following, by way of an example, with reference to the accompanying drawings.

Figure 1 is a longitudinal section of a pulp pump with a built-in vacuum pump, which is provided with a device according to the present invention and which has an operating position with vacuum function.

Figure 2 is a cross-section along the line II-II in Figure 1.

Figure 3 shows the vacuum pump according to Figure 1 in inoperative position, i.e. without vacuum function.

Figure 4 is a cross-section along the line IV-IV in Figure 3.

With reference to Figure 1 this shows a pump for pumping pulp, in particular paper pulp of medium consistency, i.e. about 6-15% dry solids content. The pulp pump comprises a main housing 1 with inlet 2 and outlet 3 for the pulp. The outlet 3 is substantially perpendicular to the inlet 2. The pulp pump has a shaft 4 rotatable about an axis of rotation 5 and driven by a motor 6. The inlet 2 is concentric in relation to the axis of rotation 5. The housing 1 has a cylindrical part 7 extending from the inlet 2 and, in relation to the cylindrical part 7, a radially enlarged part 8 provided with said outlet 3 for the pulp. A wall member closes the pulp pump at the end facing away from the pulp inlet 2, said wall member comprising a partition wall 9 and an end wall 10 through which wall parts 9, 10 said shaft 4 extends. Sealings 11 provide sufficient seal between the shaft 4 and the end wall 10 of the housing. The pulp pump comprises an impeller 12 of radial wheel type, disposed on the shaft 4 to rotate in the radially enlarged part 8 of the housing. The impeller 12 is provided with a plurality of front blades 13 with their side edges facing the pulp inlet 2, and a plurality of rear blades 14 with their side edges facing the partition wall 9. Furthermore, the pulp pump has a fluidizing rotor 15 disposed on the impeller 12. The rotor comprises a plurality of blades 16 attached to the impeller 12 and extending spaced from and parallel to the axis of rotation 5 and the cylindrical inner side 17 of the part 7 of the housing. The pulp pump may be mounted horizontally or vertically in an opening in the bottom of a container (not shown) containing pulp of medium consistency. During their rapid rotation the rotor blades 16 agitate the pulp at such high speed and create such turbulence in the pulp that this is fluidized to pumpable state. The gas present in the fiber suspension to a greater or smaller extent will be collected in front of the impeller 12 during the fluidizing process, thereby forming a gas bubble. The gas is removed from the pulp pump via a gas channel comprising a plurality of small axial holes 20 in the impeller 12, the inner part 21 of the space between the impeller 12 and partition wall 9, and an annular passage 35 in the partition wall 9. The pulp pump is also equipped with a vacuum pump 23 of the liquid-ring type, comprising a pump housing 24 with a cylindrical vacuum chamber 25 and an impeller 26 rotating therein and having a plurality of blades 27 which, between them, define pockets 28. The vacuum chamber 25 is defined by the partition wall 9 and end wall 10. The impeller 26 of the vacuum pump is disposed on the shaft 4 to rotate together with the pulp impeller 12 and rotor 15 about the axis of rotation 5. In order to obtain a suction and pressure effect the vacuum chamber 25 and impeller 26 are arranged eccentrically in relation to each other so that the impeller 26 divides the vacuum chamber 25 into a diverging suction space 34 and a converging pressure space 33 (see Figure 2). The vacuum chamber 25 contains a liquid ring 29, which thus normally has the same eccentricity in relation to the impeller 26 as the vacuum chamber 25 since the liquid ring 29 slides along the cylindrical wall 30 of the vacuum chamber. The radial size of the liquid ring 29 is adjusted so that its inner, eccentric surface in circumferential direction lies within the length of the blades 27. Liquid to control the size of the liquid ring 29 is supplied through a conduit (not shown). Since the liquid ring 29 and impeller 26 are eccentric in relation to each other, said blade pockets 28 will become gradually enlarged within the suction space 34 and gradually reduced within the pressure space 33, seen in the direction of rotation of the impeller 26. Maximum pressure is achieved at the transition 32 between the converging pressure space 33 and the diverging suction space 34.

Said passage 35 in the partition wall 9 is arc-shaped circumferentially and opens into the vacuum chamber 25 to form a gas inlet, shown in broken lines in Figure 2, since it is located to the left of the shown section II-II. The vacuum chamber 25 communicates with a gas outlet channel 36 for removal of the gas withdrawn from the centre of the pulp pump. The gas outlet channel 36 extends through the end wall 10 and comprises an arc- -shaped gas outlet 37 from the vacuum chamber 25. The gas outlet 37 is thus arranged on the inner side of the end wall 10 and is displaced substantially 180° circumferentially in relation to the gas inlet 35. The gas inlet 35 and gas outlet 37 are located close to the hub 38 of the impeller 26, the gas inlet 35 increasing and the gas outlet 37 decreasing circumferentially in the direction of rotation of the impeller. The radially outermost edge of the arc-shaped gas outlet 37 determines the size of the liquid ring. Excess liquid will consequently be forced out through the gas outlet 37. The gas outlet channel 36 is provided with a valve 42 enabling the channel 36 to be closed during certain operating conditions.

When the level of the pulp is low in the pulp tower to which the pump is connected, the pressure at the inlet 2 of the pump is correspondingly lower (atmospheric pressure and lower), so that large and varying amounts of air in the pulp are separated in the pump and disturb pumping. The pressure at the centre of the impeller 12 is below atmospheric pressure and the air is drawn out with the aid of the vacuum pump 23. Since the amounts of air separated out vary at different times, the pressure will also vary. In order to maintain constant pressure, therefore, additional air is supplied via a channel (not shown) that is provided with a pressure sensitive valve set at a predetermined partial vacuum, e.g. -0.4 bar. The built-in vacuum pump is dimensioned for a capacity enabling it to evacuate the largest quantities of air that may be separated out of the pulp at low pressure.

The pump housing 24 has a special channel or groove 50 located in immediate conjunction with the vacuum chamber 25 and radially outside this. The channel 50 is open radially inwardly and extends around a main part of the vacuum chamber 25 so that it encloses a sector angle of from about 180° up to 360°. The channel 50 has a first section 51, located within the region of the converging space 33 of the vacuum chamber 25, and a second section 52 located within the region of the diverging space 34 of the vacuum chamber 25. A valve means 53 is arranged in the pump housing in connection with the channel 50, in order to close or open the connection between the first and second channel sections 51, 52, and thus between the pressure space 33 and the suction space 34 of the vacuum chamber 25. For this purpose the valve means 53 is controlled by a certain suitable operating parameter of the vacuum pump or pulp pump, or by the operating position of one of their construction elements. In the open position the deplacement of the liquid ring 29 is redistributed in relation to the impeller 26, and an equalisation occurs between the converging and diverging pressure and suction spaces 33, 34 so that the vacuum function of the vacuum pump ceases. The valve means 53 is arranged radially outside said transition 32 between the converging and diverging pressure and suction spaces 33, 34 where the pressure is greatest. The two channel sections 51, 52 separated by the valve means 53 are suitably identical in shape, with continuously decreasing cross-sectional area in their directions away from the valve. In the embodiment shown, the valve means 53 comprises a radially directed piston 54 and piston rod 55 which, in closed position, seals against the side walls of the channel and with its free, domed end surface 56, coincides with the surface of the cylindrical wall 30 of the vacuum chamber 25. The piston rod 55 extends through a cylindrical aperture 57 opening into a wider pressure chamber 58 for the piston 54, channels 59, 60 being arranged in the pump housing 24 and connected to the pressure chamber 58 on each side of the piston 54 for the supply and removal, respectively, of pressure medium, depending on whether the piston rod 55 is to be moved to or from closed position.

In the embodiment shown the valve means 53 is controlled by the setting of the valve 42 in the outlet channel 36, which in turn is controlled by the pressure situation in the inlet 2 of the pulp pump. The valve 42 is normally set in open position and the valve means 53 in closed position. When the inlet pressure of the pulp exceeds a certain increased value, at which there is a risk of pulp being pressed into the vacuum pump 23 via the holes 20, space part 21 and gas inlet 35, and on out into the waste water system via the outlet channel 36, the valve 42 is influenced to close the outlet channel 36. At the same time, or in near connection to the time when the outlet channel 36 is closed, the valve means 53 is influenced to move to open position, thereby placing the channel sections 51, 52 in direct communication with each other so that the pressure and suction spaces 33, 34 will also communicate with each other via the channel 50 thus opened and the pressure is immediately equalised. The deplacement of the liquid ring is redistributed so that the centre of the enclosed volume of air will coincide with the centre of the impeller 26 as illustrated in Figure 4. The vacuum function has thus ceased. When the inlet pressure on the pulp has dropped after a longer or shorter time to the level when gas is collected at the centre of the pulp pump, the valve 42 will again open the outlet channel 36, while at the same time the valve 53 closes the channel 50 and the vacuum function is restored.

The invention is not limited to the embodiments described above, but may be varied in many ways within the scope of the claims. The valve means 53 may be designed and arranged differently from that shown and described. It may comprise a pivotably journalled valve body, for instance, with a through-passage running transversely to its pivot axis so that the valve body can close or open the connection between the channel sections 51, 52 by turning, depending on whether the vacuum function shall be maintained or not. Furthermore, the valve means 53 can be controlled in many ways other than that described, such as with the aid of the pressure that is measured in the pulp pump, the position of the outlet valve on the pulp pump, etc.

Claims

C L A I S

1. A device in a vacuum pump (23) serving a pump for pumping pulp, said vacuum pump (23) being of the liquid- -ring type and comprising a pump housing (24) with a cylindrical vacuum chamber (25); an impeller (26) eccentrically journalled in the vacuum chamber (25) to rotate therein together with a liquid ring (29); a gas inlet channel (20, 21, 35) from said pulp pump to the vacuum chamber (25); and a gas outlet channel (36) from the vacuum chamber (25), said impeller (26) dividing the vacuum chamber (25) into a diverging suction space (34) containing the inlet (35) of the gas inlet channel, and a converging pressure space (33) containing the outlet (37) of the gas outlet channel, characterized in that a channel (50) is arranged in the cylindrical wall (30) of the vacuum chamber, said channel (50) having a first section (51) that is located within the converging pressure space (33) and is in open communication therewith, and a second section (52) that is located within the diverging suction space (34) and is in open communication therewith, and that a valve means (53) is arranged in the pump housing (24) at the transition between the first and second channel sections (51, 52) in order, in a first position, to close the connection between the first and second channel sections (51, 52) and thus the connection between said pressure and suction spaces (33, 34) and, in a second position, to open said connections, whereby pressure equalisation is achieved between the pressure and suction spaces (33, 34) and the vacuum function ceases temporarily.

2. A device as claimed in claim 1, characterized in that the valve means (53) is controlled by a suitable operating parameter of the vacuum pump or pulp pump, or by the operating position of a suitable functional construction element (42) of the vacuum pump or pulp pump.

3. A device as claimed in claim 1 or 2, characterized in that the valve means (53) is arranged to open and close said connections depending on whether a valve (42) in said gas outlet channel (36) is in closed or open position, respectively.

4. A device as claimed in any of claims 1-3, characterized in that the two channel sections (51, 52) are identical in shape, their cross-sectional area decreasing continuously in the direction away from the valve means (53) .

5. A device as claimed in any of claims 1-4, characterized in that the channel encloses a sector angle of between 180° and 360°.

6. A device as claimed in claim 4 or 5, characterized in that the cross-sectional area of the channel sections (51, 52) is 0 at the end facing away from the valve means (53).

7. A device as claimed in any of claims 1-6, characterized in that the impellers (26, 12) of the vacuum pump (23) and pulp pump are arranged on the same shaft (4) to be co-driven.

8. A device as claimed in any of claims 1-7, characterized in that the valve means (53) comprises a piston rod (55) and a piston (54), preferably directed radially in relation to the vacuum chamber (25).