Patent Description:
wherein 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 and the gas collecting openings are provided at a trailing edge of the vane or at a backside of the vane, in respect to the flow direction when in use.

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

A prior art document <CIT> discloses a centrifugal pump that is shown generally by reference numeral <NUM> in <FIG>. The pump comprises a main housing <NUM> including a suspension (e.g. pulp) inlet <NUM> and a suspension outlet <NUM> generally transverse to the inlet <NUM>. A shaft <NUM> is mounted by bearings or the like (not shown) for rotation about axis A-A, generally in alignment with the inlet <NUM>. The shaft <NUM> is hollow having a plurality of elongated slots <NUM>, <NUM> therein, the slots <NUM>, <NUM> 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 <NUM>. In the figured embodiment, gas in the pulp will collect at shaft <NUM>, pass through openings <NUM> into shaft <NUM>, and then will pass out through slots <NUM> and be discharged with the pulp out through the outlet <NUM>.

A prior art document <CIT> discloses a centrifugal pump in which the pumped liquid may comprise gas and solids, 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, an impeller which is rotatable by the shaft, in alignment with the inlet and arranged to be rotated about the axis in the flow channel, gas collecting openings for gas removal arranged in the flow channel, 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.

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.

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.

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

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.

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.

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:.

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 gas collecting openings are provided at a trailing edge of the vane or at a backside of the vane, in respect to the flow direction when in use, 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.

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 <NUM>*D (where the D stands for the diameter of the inlet) to a distance of inlet diameter (<NUM>*D) or above, such as <NUM> to <NUM>*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.

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 collecting openings are provided at a trailing edge of the vane or at a backside of the vane, in respect to the flow direction when in use, 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.

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.

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.

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.

An embodiment of the invention is a pump that designed for multiphase suspension having a consistency of cellulosic fibers of <NUM>,<NUM> to <NUM> weight % (wt%) or other multiphase suspension having a consistency of <NUM>,<NUM> to <NUM> wt%.

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 novel features which are considered as characteristic of the invention are set forth in the appended claims.

<FIG> depicts schematically an embodiment of prior art document <CIT>. It discloses a centrifugal pump that is shown generally by reference numeral <NUM>. The pump comprises a main housing <NUM> including a suspension (e.g. pulp) inlet <NUM> and a suspension outlet <NUM> generally transverse to the inlet <NUM>. A shaft <NUM> is mounted by bearings or the like (not shown) for rotation about axis A-A, generally in alignment with the inlet <NUM>. The shaft <NUM> is hollow having a plurality of elongated slots <NUM>, <NUM> therein, the slots <NUM>, <NUM> 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 <NUM>. In the figured embodiment, gas in the pulp will collect at shaft <NUM>, pass through openings <NUM> into shaft <NUM>, and then will pass out through slots <NUM> and be discharged with the pulp out through the outlet <NUM>.

In <FIG> it is presented a cross sectional overview of centrifugal pump according to an embodiment of the invention. It is presented a centrifugal pump <NUM> for pumping a multiphase suspension containing liquid, solid material and gas, the pump comprising:.

The gas collecting openings <NUM> are connected to gas channels <NUM> configured through the vane <NUM>. According to the embodiment the gas collecting openings are provided at a trailing edge of the vane, as shown also in <FIG>. 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 <NUM> 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 <NUM> is <NUM> to <NUM>, preferably <NUM> to <NUM> vanes. The vanes <NUM> are attached to the pump housing <NUM> at the inlet end <NUM> of the flow channel <NUM>.

In <FIG> it is presented a cross sectional overview of centrifugal pump according to another embodiment of the invention. It is presented a centrifugal pump <NUM> for pumping a multiphase suspension containing liquid, solid material and gas, the pump comprising:.

The embodiment shown in <FIG> is otherwise similar to the embodiment of <FIG> but the embodiment of <FIG> comprises also a rotatable inducer <NUM> is arranged in flow direction upstream of the vanes <NUM>. The inducer <NUM> and the impeller <NUM> are rotatable by the common shaft <NUM> as shown in <FIG> or by separate shafts or rotating means (not shown in Figures). In the embodiment of <FIG> having a common shaft <NUM> for both impeller <NUM> and the inducer <NUM> the vanes <NUM> may optionally be provided with a gas collecting opening <NUM> at the vane <NUM> end so that there is provided a clearance between the vane <NUM> end and the shaft <NUM> for a gas bubble layer to enter to the clearance and further to the gas collecting opening <NUM>. 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 <NUM> is to feed the multiphase suspension toward the flow channel <NUM> and the impeller <NUM>.

In <FIG> it is presented an embodiment of the invention, a centrifugal pump <NUM> for pumping a multiphase suspension containing liquid, solid material and gas, the pump comprising:.

In <FIG> it is presented an embodiment of a gas removal device for use in a centrifugal pump. The gas removal device comprises a tubular element <NUM> having a first axial end and a second axial end and a flow channel <NUM> 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 <NUM> extending radially from an inner wall <NUM> of the flow channel <NUM> toward the center of the flow channel <NUM>, and the vanes <NUM> are provided with gas collecting openings <NUM>, the gas collecting openings <NUM> are connected via gas channels <NUM> to a system for collecting the gas <NUM>, the gas removal device is configured to be located axially upstream of an impeller of the centrifugal pump.

In <FIG> it is presented some possible embodiments for the vane <NUM> cross sections. The vanes <NUM> 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 <NUM> may be connected to gas channels <NUM> configured through the vane <NUM>. In these embodiments the gas collecting openings <NUM> 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 <NUM>, in respect to the flow direction F when in use. In <FIG> this backside is illustrated in accordance with the annular shaped vane <NUM> and with the elliptical vane <NUM>. The flow direction F is indicated with an arrow and backside B is a surface area of the vane <NUM> 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.

Claim 1:
A centrifugal pump (<NUM>) for pumping a multiphase suspension containing liquid, solid material and gas, the pump comprising:
- a pump housing (<NUM>) having a suspension inlet (<NUM>) and a suspension outlet (<NUM>) and a flow channel (<NUM>) between the inlet (<NUM>) and the outlet (<NUM>),
- a shaft (<NUM>) mounted by bearings for rotation about its center axis (A-A),
- an impeller (<NUM>) which is rotatable by the shaft (<NUM>), in alignment with the inlet (<NUM>) and arranged to be rotated about the axis (A-A) in the flow channel (<NUM>),
- gas collecting openings (<NUM>) for gas removal arranged in the flow channel (<NUM>),
wherein the inlet end (<NUM>) of the flow channel (<NUM>) is provided with a number of static vanes (<NUM>) comprising the gas collecting openings (<NUM>) connected to gas channels (<NUM>) configured through the vanes (<NUM>), and wherein the vanes (<NUM>) are extending radially from an inner wall (<NUM>) of the flow channel (<NUM>) toward the center of the flow channel (<NUM>), the vanes (<NUM>) are located upstream of the impeller (<NUM>), characterized in that the gas collecting openings (<NUM>) are provided at a trailing edge of the vane (<NUM>) or at a backside of the vane (<NUM>), in respect to the flow direction (F) when in use.