Technical field

[001] The present invention relates to a centrifugal pump for pumping a multiphase suspension containing liquid, solid material and gas according to the preamble of claim 1. More specifically, the present invention relates to a centrifugal pump for pumping a multiphase suspension containing liquid, solid material and gas, the pump comprising:

- a pump housing having a suspension inlet and a suspension outlet and a flow channel between the inlet and the outlet,

- a shaft mounted by bearings for rotation about its center axis A-A,

- an impeller which is rotatable by the shaft, in alignment with the inlet and arranged to be rotated about the axis A-A in the flow channel,

- gas collecting openings for gas removal arranged in the flow channel.

[002] The present invention relates also to a gas removal device for use in a centrifugal pump.

Background art

[003] A prior art document EP 0298693A2 discloses a centrifugal pump that is shown generally by reference numeral 10 in Fig. 1. The pump comprises a main housing 11 including a suspension (e.g. pulp) inlet 12 and a suspension outlet 13 generally transverse to the inlet 12. A shaft 14 is mounted by bearings or the like (not shown) for rotation about axis A-A, generally in alignment with the inlet 12. The shaft 14 is hollow having a plurality of elongated slots 15, 16 therein, the slots 15, 16 being generally, although typically not exactly, parallel to the axis A- A, and allowing communication between the interior and the exterior of the hollow shaft 14. In the figured embodiment, gas in the pulp will collect at shaft 14, pass through openings 15 into shaft 14, and then will pass out through slots 16 and be discharged with the pulp out through the outlet 13. [004] An object of the invention is to provide a centrifugal pump capable of pumping multiphase suspension containing liquid, solid material and gas where the gas can be efficiently separated and the pump can be operated with high net efficiency and low net positive suction head so that the performance is considerably improved compared to the prior art solutions.

[005] An object of the invention is also to reduce axial bearing load of the shaft caused by gas removal in some of the prior art solutions.

[006] An object of the invention is also to provide a gas removal arrangement that can be easily to cleaned or remove possible gloggings.

[007] An object of the invention is also to provide a centrifugal pump capable of pumping multiphase suspension containing liquid, solid material and gas where the gas removal arrangement of the pump can be easily configured to various operating conditions in terms of suspension type, gas content, consistency and pressure.

Disclosure of the Invention

[008] Objects of the invention can be met substantially as is disclosed in the independent claims and in the other claims describing more details of different embodiments of the invention.

[009] According to an embodiment of the invention it is provided a centrifugal pump for pumping a multiphase suspension containing liquid, solid material and gas, the pump comprising:

- a pump housing having a suspension inlet and a suspension outlet and a flow channel between the inlet and the outlet,

- a shaft mounted by bearings for rotation about its center axis A-A,

- an impeller which is rotatable by the shaft, in alignment with the inlet and arranged to be rotated about the axis A-A in the flow channel,

- gas collecting openings for gas removal arranged in the flow channel, the inlet end of the flow channel is provided with a number of static vanes comprising the gas collecting openings connected to gas channels configured through the vanes, the vanes are extending radially from an inner wall of the flow channel toward the center of the flow channel, the vanes are located upstream of the impeller.

[0010] A centrifugal pump having this gas removal arrangement provides an efficient way to remove gas from the multiphase suspension at the beginning of the flow channel so that the gas does not enter the impeller of the pump and deteriorate the efficiency. As the vanes are located upstream of the impeller, a distance from the impeller to the vane depends on several factors such as relative amount of gas, flow speed, pressure, rotational speed and other flow characteristics. The distance may be in a range from very short i.e. a close proximity of less than 0.1 *D (where the D stands for the diameter of the inlet) to a distance of inlet diameter (1*D) or above, such as 2 to 3*D. The efficiency performance of the centrifugal pump according to the invention is considerably improved. This arrangement also reduces axial load for the shaft bearings because in some prior art configurations the impeller is provided with gas removal openings leading to the back side of the impeller. This causes a pressure difference between the front side and the back side of the impeller thus creating equal axial load to the impeller and further to the shaft bearings.

[0011] According to an embodiment of the invention it is provided a gas removal device for use in a centrifugal pump. The gas removal device comprises a tubular element having a first axial end and a second axial end and a flow channel between the ends, the gas removal device is configured to be coupled to an inlet of a centrifugal pump, the gas removal device comprises static vanes extending radially from an inner wall of the flow channel toward the center of the flow channel, and the vanes are provided with gas collecting openings, the gas removal device is configured to be located axially upstream of an impeller of the centrifugal pump. According to an embodiment the vanes are extending radially from a tubular element that is configured to the inlet end of the flow channel. This gas removal device can be installed or attached practically to any centrifugal pump being capable of pumping multiphase suspensions provided that the tubular element comprises an annular ring or flange being attachable to the pump housing.

[0012] According to an embodiment of the invention the gas collecting openings are connected to gas channels configured through the vane(s) for leading the gas away from the flow channel. There may be just one opening and gas channel or multiple gas openings and gas channels or multiple gas openings connected to one gas channel. The gas collecting openings are connected to a system for collecting the gas, such as a network of pipes or conduits. The system for collecting gas provides a pressure difference between the gas in the suspension and outside of the pump. The gas is led away due to the pressure difference that may be a natural pressure difference between the inlet channel and an outer side of the pump housing or assisted pressure difference by providing a vacuum system to generate a sufficient pressure difference through the gas channel.

[0013] According to an embodiment of the invention the vanes have an annular, elliptical, triangular or wing shaped outer cross section in the flow direction of the suspension. One aspect in designing the shape of the vanes is that the solid material should not accumulate on a leading edge of the vane. The gas collecting openings are suitably provided at a trailing edge of the vane to reduce the risk of accumulation of solid material and also because the fluid pressure is low by the trailing edge it improves the effect of gas removal. For the same reasons the gas collecting openings may also be provided at a backside of the vane, in respect to the flow direction when in use. For similar reasons it is also possible that the gas collecting openings are provided at the vane end facing radially towards the center axis A-A.

[0014] Still according to an embodiment of the invention the gas collecting openings and following gas channels may be kept clean of any solid matter residuals so that an amount of the multiphase suspension, most suitable liquid, such as dilution water, is pressed in counter current direction to the gas channels and further to gas collecting openings. If a high pressure or impact for the liquid is utilized, possible cloggings are pressed back to the flow channel.

[0015] An embodiment of the invention is a pump that designed for multiphase suspension having a consistency of cellulosic fibers of 0,1 to 18 weight % (wt%) or other multiphase suspension having a consistency of 0,1 to 20 wt%.

[0016] The exemplary embodiments of the invention presented in this patent application are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" is used in this patent application as an open limitation that does not exclude the existence of also unrecited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims.

Brief Description of Drawings

[0017] In the following, the invention will be described with reference to the accompanying exemplary, schematic drawings, in which

Figure 1 illustrates a prior art centrifugal pump according EP0298693A2,

Figure 2 illustrates a cross sectional overview of a centrifugal pump according to an embodiment of the invention.

Figure 3 illustrates a cross sectional overview of a centrifugal pump according to another embodiment of the invention.

Figure 4 illustrates an overview of a centrifugal pump according to an embodiment of the invention.

Figure 5A and Figure 5B illustrates an embodiment of the gas removal device of the invention.

Figure 6 illustrates some embodiments of possible cross sections of static vanes utilized in the invention.

Detailed Description of Drawings

[0018] Figure 1 depicts schematically an embodiment of prior art document EP 0298693A2. It discloses a centrifugal pump that is shown generally by reference numeral 10. The pump comprises a main housing 11 including a suspension (e.g. pulp) inlet 12 and a suspension outlet 13 generally transverse to the inlet 12. A shaft 14 is mounted by bearings or the like (not shown) for rotation about axis A- A, generally in alignment with the inlet 12. The shaft 14 is hollow having a plurality of elongated slots 15, 16 therein, the slots 15, 16 being generally, although typically not exactly, parallel to the axis A-A, and allowing communication between the interior and the exterior of the hollow shaft 14. In the figured embodiment, gas in the pulp will collect at shaft 14, pass through openings 15 into shaft 14, and then will pass out through slots 16 and be discharged with the pulp out through the outlet 13.

[0019] In Fig. 2 it is presented a cross sectional overview of centrifugal pump according to an embodiment of the invention. It is presented a centrifugal pump 10 for pumping a multiphase suspension containing liquid, solid material and gas, the pump comprising:

- a pump housing 11 having a suspension inlet 12 and a suspension outlet 13 and a flow channel 110 between the inlet 12 and the outlet 13,

- a shaft 14 mounted by bearings for rotation about its center axis A-A,

- an impeller 18 which is rotatable by the shaft 14, in alignment with the inlet 12 and arranged to be rotated about the axis A-A in the flow channel 110,

- gas collecting openings 20 for gas removal arranged in the flow channel 110,

- the inlet end 120 of the flow channel 110 is provided with a number of static vanes 2 comprising gas collecting openings 20, the vanes 2 are extending radially from an inner wall 111 of the flow channel 110 toward the center of the flow channel 110, the vanes 2 are located upstream of the impeller 18.

The gas collecting openings 20 are connected to gas channels 21 configured through the vane 2. According to the embodiment the gas collecting openings are provided at a trailing edge of the vane, as shown also in Fig. 2. This trailing edge position is advantageous in several reasons, the effect is to prevent clogging and it is also optimal for gas removal due to the pressure changes at this area. The vanes 2 may also be configured so that the gas collecting openings are provided at the vane end facing radially towards the center axis A-A. Suitably the number of vanes 2 is 1 to 6, preferably 2 to 4 vanes. The vanes 2 are attached to the pump housing 11 at the inlet end 120 of the flow channel 110.

[0020] In Fig. 3 it is presented a cross sectional overview of centrifugal pump according to another embodiment of the invention. It is presented a centrifugal pump 10 for pumping a multiphase suspension containing liquid, solid material and gas, the pump comprising:

- a pump housing 11 having a suspension inlet 12 and a suspension outlet 13 and a flow channel 110 between the inlet 12 and the outlet 13,

- a shaft 14 mounted by bearings for rotation about its center axis A-A,

- an impeller 18 which is rotatable by the shaft 14, in alignment with the inlet 12 and arranged to be rotated about the axis A-A in the flow channel 110,

- gas collecting openings 20 for gas removal arranged in the flow channel 110,

- the inlet end 120 of the flow channel 110 is provided with a number of static vanes 2 comprising gas collecting openings 20, the vanes 2 are extending radially from an inner wall 111 of the flow channel 110 toward the center of the flow channel 110, the vanes 2 are located upstream of the impeller 18.

The embodiment shown in Fig. 3 is otherwise similar to the embodiment of Fig. 2 but the embodiment of Fig. 3 comprises also a rotatable inducer 4 is arranged in flow direction upstream of the vanes 2. The inducer 4 and the impeller 18 are rotatable by the common shaft 14 as shown in Fig. 3 or by separate shafts or rotating means (not shown in Figures). In the embodiment of Fig 3 having a common shaft 14 for both impeller 18 and the inducer 4 the vanes 2 may optionally be provided with a gas collecting opening 20 at the vane 2 end so that there is provided a clearance between the vane 2 end and the shaft 14 for a gas bubble layer to enter to the clearance and further to the gas collecting opening 20. As in a rotating flow of multiphase suspension the gas phase has a tendency for find its way to the center of the stream, this location for gas collecting openings is very effective. The function of the inducer 4 is to feed the multiphase suspension toward the flow channel 110 and the impeller 18.

[0021] In Fig. 4 it is presented an embodiment of the invention, a centrifugal pump 10 for pumping a multiphase suspension containing liquid, solid material and gas, the pump comprising:

- a pump housing 11 having a suspension inlet 12 and a suspension outlet 13 and a flow channel 110 between the inlet 12 and the outlet 13,

- a shaft 14 mounted by bearings for rotation about its center axis,

- an impeller which is rotatable by the shaft 14, in alignment with the inlet 12 and arranged to be rotated about the axis in the flow channel 110,

- gas collecting openings for gas removal arranged in the flow channel 110, - the inlet end 120 of the flow channel 110 is provided with a number of static vanes 2 comprising gas collecting openings, the vanes 2 are extending radially from an inner wall 111 of the flow channel 110 toward the center of the flow channel 110, the vanes 2 are located upstream of the impeller but downstreams of the inducer 4. The Fig. 4 shows an embodiment where the vanes 2 are extending radially from a tubular element 23 is configured to the inlet end 120 of the flow channel 110. The tubular element 23 comprises an annular ring or flange being attachable to the pump housing 11.

[0022] In Fig. 5A and Fig. 5B it is presented an embodiment of a gas removal device for use in a centrifugal pump. The gas removal device comprises a tubular element 23 having a first axial end and a second axial end and a flow channel 110 between the ends, the gas removal device is configured to be coupled to an inlet of a centrifugal pump, the gas removal device comprises static vanes 2 extending radially from an inner wall 111 of the flow channel 110 toward the center of the flow channel 110, and the vanes 2 are provided with gas collecting openings 20, the gas collecting openings 20 are connected via gas channels 21 to a system for collecting the gas 3, the gas removal device is configured to be located axially upstream of an impeller of the centrifugal pump.

[0023] In Fig. 6 it is presented some possible embodiments for the vane 2 cross sections. The vanes 2 may have an annular, elliptical, triangular or wing shaped outer cross section in the flow direction of the suspension. The selection of the shape is highly dependent on the properties of the multiphase suspension, different suspensions require different shape. From this cross sectional view one can note some embodiments how the gas collecting openings 20 may be connected to gas channels 21 configured through the vane 2. In these embodiments the gas collecting openings 20 are provided at a trailing edge of the vane. Also other possibilities are available, but these on figures have been noted to function properly and being very little prone to cloggings. One other possibility is that the gas collecting openings are provided at a backside B of the vane 2, in respect to the flow direction F when in use. In Fig. 6 this backside is illustrated in accordance with the annular shaped vane 2 and with the elliptical vane 2. The flow direction F is indicated with an arrow and backside B is a surface area of the vane 3 that is located opposite to the flow side and between two parallel lines, both being tangent to the vane and parallel to the flow direction.

[0024] While the invention has been described herein by way of examples in connection with what are, at present, considered to be the most preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is intended to cover various combinations or modifications of its features, and several other applications included within the scope of the invention, as defined in the appended claims. The details mentioned in connection with any embodiment above may be used in connection with another embodiment when such combination is technically feasible.

Part list

10 pump

11 pump housing

110 flow channel

111 inner wall

12 inlet

120 inlet end

13 outlet

14 shaft

15 slot

16 slot

18 impeller

2 vane

20 gas collecting opening

21 gas channels

23 tubular element

3 system for collecting the gas, vacuum system

4 inducer

A-A center axis

B backside

F flow direction