Pulp pump

Abstract

Centrifugal pumps for pumping a pulp suspension and conducting gas away from the pulp suspension are disclosed including a pump housing having an inlet and an outlet, a rotary shaft, an impeller mounted on the rotary shaft within the pump housing, the impeller including a hub and pump blades extending outwardly from the hub, a wheel disk adjacent to the impeller so that the pump blades extend outwardly along the wheel disk, a vacuum impeller within the pump housing behind the wheel disk and including a vacuum pump housing, vacuum impeller blades, a seal for sealing the vacuum pump housing to the rotary shaft, the vacuum pump housing including a suction port for drawing gas into the vacuum pump housing and an exhaust port for expelling gas therefrom.

Description

FIELD 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.

Gas following along with the pulp creates problems during pumping of pulp by centrifugal pumps. The gas in the pulp forms bubbles, which are accumulated in front of the impeller and thereby deteriorate the capacity of the pump. This problem can be overcome by evacuating the gas from the space in front of the impeller, for example by means of vacuum pumps such as the liquid-ring pump type. Such a pump can be a separate vacuum pump, the suction pipe of which is connected to the sealing space of the pulp pump, or it can be formed with a separate vacuum impeller in the form of a liquid-ring impeller, which is mounted on the shaft of the pulp pump, so that for both impellers a common operation is obtained.

In cases where a separate vacuum pump is used, the pulp pump becomes relatively complicated and expensive, because the system comprises more components compared to a pulp pump, where the vacuum impeller is mounted on the shaft of the pulp pump.

Swedish patent specification No. 502,127 and European patent specification No. 298,949 describe embodiments of pulp pumps where the vacuum impeller is mounted on the shaft of the pulp pump. During, for example, control of the capacity of the vacuum pump by adjustable throttling or resetting the eccentricity of the vacuum pump housing, as shown in Swedish patent specification No. 502,127, several movable parts are required in the pump housing. This requires more or less extreme designs, with the concurrent risk of faulty functioning. The maintenance will also thus be more complicated and expensive. In cases when the vacuum pump is controlled by means of additional air, as shown in European patent specification No. 298,949, a great amount of air is supplied to a pump system, with the intention being that air should be removed therefrom.

The present invention implies that the aforesaid problems can be eliminated. The manufacture and maintenance costs for the pulp pump, for example, can be reduced. The need of liquid for the operation is decreased, and control and sealing of the vacuum pump can be carried out more simply. The need of air to be added to the pump can also be reduced substantially.

SUMMARY OF THE INVENTION

In accordance with the present invention, these and other objects have been realized by the invention of a centrifugal pump for pumping a pulp suspension and conducting gas away from the pulp suspension, the centrifugal pump comprising a pump housing including an inlet for the pulp suspension and an outlet for the pumped pulp suspension, a rotary shaft, an impeller mounted on the rotary shaft within the pump housing, the impeller including a hub, and a plurality of pump blades extending outwardly from the hub, a wheel disk adjacent to the impeller whereby the pump blades extend outwardly along the wheel disk, a vacuum impeller disposed within the pump housing behind the wheel disk, the vacuum impeller including a vacuum pump housing, a plurality of vacuum impeller blades disposed within the vacuum pump housing, and a seal for sealing the vacuum pump housing to the rotary shaft, the vacuum pump housing including a suction port for drawing gas into the vacuum pump housing and an exhaust port for expelling gas from the vacuum pump housing. In a preferred embodiment, the centrifugal pump includes a channel connecting the suction port with the exhaust port, and a valve disposed within the channel for controlling the vacuum in the vacuum pump housing.

In accordance with another embodiment of the centrifugal pump of the present invention, the vacuum pump housing includes a first side adjacent to the impeller and a second side distal from the impeller, the suction port and the exhaust port being disposed on the first side of the vacuum pump housing, the seal being disposed on the second side of the vacuum pump housing and including a sealed housing and a liquid inlet connected to the sealed housing, the sealed housing communicating with the vacuum pump housing to supply the liquid to the vacuum pump housing.

In accordance with the present invention, the pulp pump is formed so that the suction port and exhaust port of the vacuum pump housing are in controllable connection with each other.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG. 1 is a side, elevational, cross-sectional view of a centrifugal pump according to the present invention; and

FIG. 2 is a side, elevational, schematic view of the coupling between gas inlet and gas outlet to and from the vacuum pump in accordance with the present invention.

DETAILED DESCRIPTION

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 concentration, for example from about 6% to 18%. On a rotary shaft 13 in the pump housing 10 an impeller 14 is mounted, the pump blades 15 of which extend from a hub 16 outward along a wheel disk 17. On the rear side of the wheel disk 17 back blades 18 are located. The wheel disk 17 is further formed with openings 19 for the discharge of gas collected in front of the impeller.

Behind the impeller 14 a vacuum impeller with vacuum impeller blades 20 is located, which impeller is surrounded by a vacuum pump housing 21. This vacuum pump housing 21 comprises an outer cylindrical wall 22, a rear wall 23 and a front wall 24. The cylindrical wall 22 is eccentric in relation to the vacuum impeller blades 20, so that a liquid ring pump is formed. In the front wall 24 a suction port 25 for gas and an exhaust port 26 for gas are located. These ports, 25 and 26, are placed at a distance from each other in the circumferential direction disposed for gas suction into the vacuum pump housing and gas exhaust from the vacuum pump housing, respectively. This effect is brought about in a manner which is known by the rotation of the vacuum impeller blades and the volume variation in the circumferential direction of the vacuum pump housing as a consequence of the eccentric position of the cylindrical wall 22.

The exhaust port 26 communicates with a chamber 27 for gas evacuation through a gas outlet 28. On the rear side of the impeller 14 between the wheel disk 17 and front wall 24 of the vacuum pump housing a gas passage 29 for communication between the openings 19 in the wheel disk 17 and suction port 25 is located.

Behind the rear wall 23 a sealing housing 30 with a shaft sealing 31 for the vacuum pump and pulp pump is located. The sealing is intended for the flow-through of liquid, which is supplied by a liquid inlet 32. The sealing housing 30 also communicates with the vacuum pump housing 21 for the supply of liquid from the sealing to the vacuum pump.

By using a common liquid inlet 32 for the sealing 31 and vacuum pump housing 21, the liquid amount can be restricted without problems. Only one liquid connection is required. The pressure difference arising between the sealing housing 30 and vacuum pump housing implies a barrier for flow in the opposite direction, i.e. only clean water will be found in the surrounding of the sealing.

The suction port 25 and exhaust port 26 of the vacuum pump housing are in controllable connection with each other, for example by means of an overflow channel 35 with a device 36 for vacuum control. By means of this control device 36 the connection between the suction and exhaust side can be controlled without the use of air addition from the outside in order to prevent the pulp suspension from being sucked into the vacuum pump, if the pressure would be much too low. Instead of air addition from the outside a portion of the air is thus used which already has been sucked out of the pulp pump for the control. This implies a pump system with less air flows. At the same time the design is simpler and easier to control. The control device 36 can be a valve in the overflow channel 35, for example of the on/off type, a throttle valve or the like. The control device can be controlled by signals from the system in a suitable way which is known per se.

The present invention, of course, is not restricted to the embodiment shown, but can be varied within the scope of the claims with reference to the description and Figures.

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.

Claims

1-3. (canceled).

4. A centrifugal pump for pumping a pulp suspension and conducting gas away from said pulp suspension, said centrifugal pump comprising a pump housing including an inlet for said pulp suspension and an outlet for said pumped pulp suspension, a rotary shaft, an impeller mounted on said rotary shaft within said pump housing, said impeller including a hub, and a plurality of pump blades extending outwardly from said hub, a wheel disk adjacent to said impeller whereby said pump blades extend outwardly along said wheel disk, a vacuum impeller disposed within said pump housing behind said wheel disk, said vacuum impeller including a vacuum pump housing, a plurality of vacuum impeller blades disposed within said vacuum pump housing, and a seal for sealing said vacuum pump housing to said rotary shaft, said vacuum pump housing including a suction port for drawing gas into said vacuum pump housing and an exhaust port for expelling gas from said vacuum pump housing.

5. The centrifugal pump of claim 4 including a channel connecting said suction port with said exhaust port, and a valve disposed within said channel for controlling the vacuum in said vacuum pump housing.

6. The centrifugal pump of claim 4 wherein said vacuum pump housing includes a first side adjacent to said impeller and a second side distal from said impeller, said suction port and said exhaust port being disposed on said first side of said vacuum pump housing, said seal being disposed on said second side of said vacuum pump housing and including a sealed housing and a liquid inlet connected to said sealed housing, said sealed housing communicating with said vacuum pump housing to supply said liquid to said vacuum pump housing.