Pulp pump

BACKGROUND OF THE INVENTION

The present invention relates to a centrifugal pump for pulp suspensions of lignocellulosic material. More particularly, the present invention relates to a pump where gas, such as air, can be separated from the pulp in the pump.

The presence of gas, which follows along with the pulp, causes problems during pumping by centrifugal pumps. The gas in the pulp forms into bubbles, which accumulate in front of the impeller and thereby deteriorate the capacity of the pump. This problem can be remedied by evacuating the gas from the space in front of the impeller, for example by means of vacuum pumps of the liquid ring type. The pumps are often a separate vacuum pump, the suction pipe of which is connected to the sealing space of the pulp pump. They can also be designed as a separate vacuum impeller in the form of a liquid ring impeller located on the shaft of the pulp pump so that a common drive for both impellers is obtained.

In those cases when a separate vacuum pump is used, the pulp pump becomes relatively complicated and expensive, because more components are required in the system. When a separate liquid ring impeller of a conventional type is placed on the same shaft as the pulp pump, the capacity of the liquid ring impeller is restricted for space reasons.

SUMMARY OF THE INVENTION

In accordance with the present invention, these and other problems in the prior art have been eliminated by the discovery of apparatus for pumping a pulp suspension including entrained gas comprising a housing including an inlet for the pulp suspension and an outlet for the pulp suspension, a rotary shaft, an impeller mounted for rotation on the rotary shaft within the housing, the impeller having a front face and a rear face and including a central hub, a wheel disk surrounding the central hub, a plurality of pump blades extending radially from the central hub along the wheel disk, the wheel disk including at least one opening for the discharge of the entrained gas therethrough, a vacuum pump disposed at the rear face of the impeller, the vacuum pump including a vacuum pump housing, a plurality of vacuum pump blades mounted for rotation within the vacuum pump housing, the vacuum pump housing including an outer wall eccentrically disposed with respect to the plurality of vacuum pump blades and a rear vacuum pump wall including a suction port for receiving the entrained gas, the vacuum pump housing being mounted adjacent to the central hub to provide a gap therebetween, an exhaust port for exhausting the exhaust gas therefrom, the vacuum pump housing being axially adjustably mounted whereby the gap between the central hub and the vacuum pump housing can be altered by axial adjustment of the vacuum pump housing, a gas passage disposed radially outside the outer wall of the vacuum pump housing for connecting the at least one opening in the wheel disk with the suction port, and a gas evacuation chamber connected to the exhaust port for evacuation of the entrained gas therefrom. In accordance with a preferred embodiment of the apparatus of the present invention, the apparatus includes a liquid inlet connected to the gas passage for the supply of liquid thereto.

In accordance with another embodiment of the apparatus of the present invention, the apparatus includes a passageway disposed outside the outer wall of the vacuum pump housing for connection of a separate vacuum pump to the gas passage.

The present invention suggests that these problems can be eliminated by the fact that the vacuum impeller is designed to be integrated into the impeller of the pulp pump. The construction is compact and simple, and the capacity of the vacuum pump can be easily controlled. Moreover, the arrangement is formed so that it can easily be combined with a separate vacuum pump so that both pumps can be used in parallel. Alternatively, the separate vacuum pump can be connected at an operation drop-out of the integrated vacuum pump according to the present invention in order thereby to ensure the accessibility for the centrifugal pump.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in greater detail in the following detailed description, with reference to the accompanying Figures illustrating an embodiment of the present invention, in which:

FIG. 1

is a side, elevational, sectional view of a centrifugal pump according to the present invention; and

FIG. 2

is a front, elevational, sectional view, taken along line A—A in FIG.

1

.

DETAILED DESCRIPTION

Referring to the Figures, the centrifugal pump shown in

FIG. 1

comprises a pump housing

10

with an inlet

11

and an outlet

12

for the pulp suspension. Such pumps are used at relatively high pulp concentrations, for example from about 8 to 12%. On a rotary shaft

13

in the pump housing

10

an impeller

14

with pump blades

15

is located, which pump blades

15

extend from a hub

16

outward along a wheel disk

17

. On the rear side of the wheel disk

17

rear blades

18

are located. The wheel disk

17

is formed with openings

19

for the discharge of gas collected in front of the impeller. The openings are preferably designed as slits extending from the hub

16

outward.

Behind the wheel disk

17

the hub

16

is provided with vacuum pump blades

20

, which are surrounded by a vacuum pump housing

21

. The vacuum pump housing

21

comprises a cylindrical outer wall

22

and a rear wall

23

. The cylindrical wall

22

is eccentric in relation to the vacuum pump blades

20

so that a liquid ring pump is formed. In the rear wall

23

a suction port

24

and an exhaust port

25

for gas are, respectively, located. The ports,

24

and

25

, are spaced from each other in the circumferential direction, counted for gas suction into the vacuum pump housing and gas exhaust out of the vacuum pump housing, respectively. This effect is brought about by the rotation of the vacuum pump blades and the variations in volume in the circumferential direction of the vacuum pump housing as a consequence of the eccentric location of the wall

22

. The exhaust port

25

communicates with a chamber

26

behind the rear wall

23

for gas evacuation through a gas outlet

27

. In a sealing housing

28

in the pump housing

10

outside the outer wall

22

a gas passage

29

is located for communication between the openings

19

in the wheel disk

17

and suction port

24

.

The vacuum pump housing

21

is axially adjustable in the sealing housing

28

by an adjustment means

30

for setting a gap

31

between the hub

16

of the wheel disk and the outer wall

22

.

An inlet

32

for liquid is connected to the sealing housing

28

for the supply of liquid in the gas passage

29

. The liquid thus supplied is utilized both as drive liquid for the liquid ring in the vacuum pump as well as flush liquid in the passage

29

and in the sealing housing

28

for external flushing of the shaft sealing

34

.

An additional connection opening

33

in the sealing housing

28

to the gas passage

29

can preferably be provided for rendering it possible to connect a separate vacuum pump (not shown).

During the pumping of a pulp suspension from the inlet

11

to the outlet

12

gas enclosed in the pulp will be collected in front of the impeller

14

. The vacuum pump integrated in the hub

16

will then suck in the gas through the openings

19

in the wheel disk

17

and from there through the gas passage

29

into the vacuum pump through the suction port

24

. By the pumping effect brought about by the vacuum pump blades

20

together with the rotating liquid ring in the vacuum pump housing

21

eccentric with respect to the hub

16

, the gas is pumped through the exhaust port

25

and evacuated through the gas outlet

27

.

By adjusting the gap

31

the capacity of the vacuum pump can be controlled. By increasing the gap width the liquid leakage through the gap will increase, whereby the capacity of the vacuum pump is reduced, and vice versa.

In the case when a separate vacuum pump is connected to the connection

33

, this vacuum pump can serve in parallel with the integrated vacuum pump according to the present invention or be connected at an operational drop-out of the integrated vacuum pump. The operation of the centrifugal pump is thereby ensured.

Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.