METHOD FOR CONTROLLING OF A PUMP UNIT AND A PUMP UNIT FOR PUMPING LIQUID OR SUSPENSION

Abstract

A method for controlling a pump unit for pumping liquid or suspension includes controlling a pump unit based on a determination of a combination of an inducer and a centrifugal pump at least on parameters of a total volumetric flow rate and pressure difference over the pump unit, and controlling the pump unit based on a rheology of a fluid to be pumped so that necessary fluidization parameters of the fluid are predetermined to enable operation of the pump unit, and the rotation speed of the inducer rotor or an output power of the inducer rotor is controlled to a desired volumetric flow rate.

Claims

1. A method for controlling a pump unit for pumping liquid or suspension, the pump unit comprising a centrifugal pump and an inducer in a proximity upstream of an inlet (210) of the centrifugal pump, the centrifugal pump comprising a pump housing forming a flow channel inside the pump housing and an impeller configured to be rotated in the flow channel around a central axis by a shaft, the inducer comprising an inducer rotor having a sleeve-shaped rotor body, the inducer rotor is configured to be rotated around the central axis in the flow channel, the rotor body including a number of blades extending inwards from the rotor body, the inducer rotor being is separate to the impeller and a rotation speed of the inducer rotor is independently controlled in relation to a rotation speed of the impeller, the inducer comprising an electric motor that is an annular motor encircling and connected to the inducer rotor, the method comprising: controlling of the pump unit based on a determination of a combination of the inducer and the centrifugal pump at least on parameters of a total volumetric flow rate and pressure difference over the pump unit, and controlling the pump unit based on a rheology of a fluid to be pumped so that necessary fluidization parameters of the fluid are predetermined to enable operation of the pump unit, and the rotation speed of the inducer rotor or an output power of the inducer rotor is controlled to a desired volumetric flow rate.

2. The method according to claim 1, wherein the pump unit is controlled based on the rheology of the fluid to be pumped so that a calculated Power numberReynolds numbercurve is used as a reference curve to control the rotation speed of the inducer rotor or an output power to operate the pump unit at a desired operational window.

3. The method according to claim 1, wherein the pump unit is controlled so that the output power of the inducer rotor is less than an output power of the centrifugal pump.

4. The method according to claim 1, wherein, wherein the rotation speed of the inducer rotor is controlled based on detected cavitation at the centrifugal pump, and a head generated by the inducer is increased or decreased to maintain a margin to an outbreak of cavitation of the impeller.

5. The method according to any of claim 1 to 3, wherein an NPSHaB (Net Positive Suction Head Available at the inlet of the impeller) is measured, calculated or otherwise determined, and the rotation speed of the inducer rotor or a head of the inducer is driven along a predetermined NPSHr (NPSH required) curve for a given operation condition.

6. The method according to claim 1, wherein the rotation speed of the inducer rotor or the output power of the inducer rotor is controlled based on required gas separation for given-a fluid to be pumped, the required gas separation determinable based on gas detection or predetermination to determine a gas content in the fluid.

7. A pump unit for pumping liquid or suspension, the pump unit comprises: the centrifugal pump comprising the inducer in the proximity upstream of the inlet of the centrifugal pump: the centrifugal pump comprising the a pump housing forming the flow channel inside the pump housing and the impeller configured to be rotated in the flow channel around the central axis by a shaft, the inducer comprising the inducer rotor having the sleeve-shaped rotor body, the inducer rotor is configured to be rotated around the central axis in the flow channel, the rotor body includes the number of blades extending inwards from the rotor body, the inducer rotor is separate to the impeller and the rotation speed of the inducer rotor is independently controllable in relation to the rotation speed of the impeller, the inducer comprising the electric motor that is the annular motor encircling and being connected to the inducer rotor, the pump unit connected to a controller configured to execute the method of claim 1 such that the pump unit is controlled based on the rheology of the fluid to be pumped so that necessary fluidization parameters of the fluid are predetermined to enable operation of the pump unit, and the rotation speed of the inducer rotor or the output power of the inducer rotor is controlled to the desired volumetric flow rate.

8. The pump unit according to claim 7, wherein the inducer rotor and impeller are drivable by separate electric motors electrically connected to the controller.

9. The pump unit-according to claim 7, wherein the inducer rotor is rotatable to an opposite or to a same direction as the impeller.

10. The pump unit according to 7, wherein the inducer-comprises an inlet, an inducer housing to enclose a stator, an annular motor and the inducer rotor, the inducer housing being connected to the pump housing via a flange attachment at a distance from 0.01 up to 10 times a diameter of the flow channel.

11. The pump unit according to 7, wherein guide vanes are disposed between the inducer and the impeller, the guide vanes having a fixed or adjustable pitch.

12. The pump unit according to claim 11, wherein the guide vanes-comprise conduits for gas removal from the liquid.

13. A pump unit according to 7, wherein the rotation speed of the inducer rotor is variably or independently controllable in relation to the rotation speed of the impeller.

14. The pump unit of claim 7, further comprising at least one sensor of the following sensors to monitor the centrifugal pump or to determine NPSHaA (Net Positive Suction Head Available at the inlet of the inducer) or NPSHaB values: a pressure sensor, an acoustic sensor for cavitation monitoring, a vibration monitoring sensor, an on-line consistency sensor, an on-line gas content meter, or a thermometer.

15. The pump unit of claim 7, further comprising a device configured to monitor the centrifugal pump calculations using software of variable speed drive.

16. A controller for controlling the pump unit according to claim 14, the controller comprising executable instructions to control the rotation speed of the inducer rotor or the output power of the inducer rotor based on a sensor signal of the at least one sensor such that the pump unit is controlled based on the rheology of the fluid to be pumped so that the necessary fluidization parameters of the fluid are predetermined to enable operation of the pump unit, and the rotation speed of the inducer rotor or the output power of the inducer rotor is controlled to a desired volumetric flow rate.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0040] In the following, the disclosure will be described with reference to the accompanying exemplary, schematic drawings, in which

[0041] FIG. 1A illustrates a pump unit according to an embodiment of the disclosure,

[0042] FIG. 1B illustrates a 3D overview of the pump unit of FIG. 1A,

[0043] FIG. 2 illustrates a pump unit according to another embodiment of the disclosure connected to a control system,

[0044] FIGS. 3A and 3B illustrates different curves of the effect of the inducer,

[0045] FIGS. 3C and 3D illustrates still different curves about the effect of inducer.

[0046] FIG. 4 illustrates an embodiment of the pump unit having guide vanes between the inducer and the centrifugal pump,

[0047] FIG. 5 illustrates an embodiment of a power number/Reynolds number curve, and

[0048] FIG. 6 illustrates an embodiment of a target QH-curve.

DETAILED DESCRIPTION

[0049] FIG. 1A depicts schematically a pump unit 1 for pumping liquid or suspension, the pump unit 1 comprises a centrifugal pump 2 and an inducer 3 in a proximity upstream of an inlet 210 of the centrifugal pump 2: [0050] the centrifugal pump 2 comprises a pump housing 21 forming a flow channel 20 inside the pump housing 21 and an impeller 22 configured to be rotated in the flow channel 20 around a central axis 200 by a shaft 23, [0051] the inducer 3 comprises an inducer rotor 32 having sleeve-shaped rotor body 321, the inducer rotor 32 is configured to be rotated around the central axis 200 in the flow channel 20, the rotor body 321 is provided with a number of blades 323 extending inwards from the rotor body 321, [0052] the inducer rotor 32 is separate to the impeller 22 and rotation speed of the inducer rotor 32 is independently controllable in relation to the rotation speed of the impeller 22, the inducer 3 comprises an electric motor 35 that is an annular motor that encircles and is connected to the inducer rotor 32. As regarding to the present method, the inducer rotor 32 is separate to the impeller 22 and rotation speed of the inducer rotor 32 is independently controlled in relation to the rotation speed of the impeller 22, the inducer 3 comprises an electric motor 35 that is an annular motor that encircles and is connected to the inducer rotor 32, [0053] controlling of the pump unit 1 is determined as a combination of the inducer 3 and centrifugal pump 2 at least on parameters of total volumetric flow rate and pressure difference over the pump unit 1.

[0054] According to the embodiment shown in FIG. 1A the inducer 3 comprises an inlet 310, an inducer housing 31 for enclosing a stator 351, annular motor 352 and rotor 32, the inducer housing 31 being connected to the pump housing 21 via a flange 211 attachment at a distance from 0.01 up to 10 times the diameter of the flow channel 20. This distance can be for example the distance L between the inducer blades 323 and the impeller 22, while the diameter of the flow channel 20 is measured at the inducer 3. This enables to achieve a compact pump unit where the inducer rotor and impeller are at a sufficiently close distance to each other and easy to assembly. The inducer creates a flow field that begins at an inducer/pump unit inlet 310 and continues to the flow channel and if the distance between the inducer rotor and impeller is relatively long, the flow field has equalized before the impeller and then the situation would be the same as just having two pumps in series, not having the desired effect as the inducer normally does.

[0055] In FIG. 1B it is presented a general outside 3D-overview of the present pump unit 1. The FIG. 1B illustrates an embodiment of centrifugal pump 2, comprising a pump housing 21 forming a flow channel 20 inside the pump housing 21 and an inducer 3 comprising an inducer rotor 32 configured to be rotated in the flow channel 20 by a shaft 23, the rotor 32 is provided with blades 323.

[0056] According to an embodiment shown in FIG. 2, the inducer rotor 32 and impeller 22 are drivable by separate electric motors 25, 35 electrically connected to a common control unit 5. Preferably the pump unit 1 is controlled so that an output power of the inducer 3 is less than an output power of the centrifugal pump 2. There are several operational principles that can be applied in the control of the pump unit. For example, the inducer rotor 32 rotation speed can is controlled based on detected cavitation at the centrifugal pump 2, the head generated by the inducer 3 is increased or decreased to maintain a margin to an outbreak of cavitation of the impeller 22. In FIG. 2 it is also illustrated some possible sensors 4, 4A, 4B to monitor the centrifugal pump or to determine NPSHaA or NPSHaB values: pressure sensor, acoustic sensor for cavitation monitoring, vibration monitoring sensor, on-line consistency sensor, on-line gas content meter, thermometer. The pump unit 1 can comprise means to monitor the centrifugal pump: calculations using software of variable speed drive. A control unit 5 can comprise executable instructions to control the inducer rotor 32 rotation speed/output power based on sensor signal.

[0057] Also, in FIG. 2 it is illustrated how the pump unit 1 is controlled based on a surface level on pump unit 1 suction side wherein a NPSHaA at an inlet 310 before the inducer/pump unit 1 is measured by a sensor 4A, calculated or otherwise determined, and if necessary, the output power of the inducer 3 is increased or decreased to affect a NPSHaB, measured at sensor 4B at the flow channel 20 before the impeller 22, so that during operation of the pump unit 1 the NPSHaB is greater than a NPSHr of the centrifugal pump 2.

[0058] In the following the method of the present disclosure is explained in more detail with reference to accompanying graphs in FIGS. 3A, 3B, 3C and 3D illustrates pumping curves in different situations. FIG. 3A presents NPSH (y-axis) in a function of volumetric flow rate Q (x-axis) for a centrifugal pump. There are three horizontal levels (dashed lines, NPSHa 1, NPSHa 2, etc.) describing different surface level generated suction heads and the three curves illustrates the required NPSHr of the centrifugal pump at different rotational speeds n1, n2 and n3 of the impeller, depending on the volumetric flow rate Q. This means that on higher Q the required NPSHr of the centrifugal pump can be more than the available NPSHa 1, 2 etc. This would mean that the centrifugal pump would begin to cavi-tate. At FIG. 3B it is shown the effect of the inducer by dependency of head (or NPSH) and volumetric flow rate Q with different rotational speeds n1, n2, n3 of the inducer rotor. As can be seen on FIG. 3B, the head H decreases as the volumetric flow rate Q has increased. However, as one can note in FIG. 3A, with higher Q the NPSH difference between the required NPSHr of centrifugal pump and available NPSHa 2 increases as is illustrated with arrow dan inducer rotated at n1, n2 or n3 can generate the missing d of NPSH even at higher Q as shown in FIG. 3B. Thus, it would make it possible to achieve such high Q with the pump unit without cavitation. This means that by increasing the rotational speed of the inducer rotor, it can compensate a significant amount of NPSH that would otherwise be needed to be arranged at a plant for example by increasing surface level in a suction vessel. The present disclosure having independently controllable inducer and centrifugal pump it enables optimal and effective performance of the pump unit on wide range of operational conditions.

[0059] FIGS. 3C and 3D illustrates how the inducer rotor 32 rotation speed/output power is controlled based on required gas separation or fluidization for given fluid to be pumped, the required gas separation can be determined based on gas detection, predetermination or other means to determine the gas content in the fluid. The curves c1, c2 and c3 presents different materials to be pumped, the difference can be in consistency or in respect to gas content. The power needed by the inducer depends on the needed fluidization or gas removal in order to create a required volumetric flow rate Q.

[0060] For practical example in one studied pump unit 1, if the inducer rotor is driven in a speed 1100-1780 rpm for Q=200 l/s, it would fluidize the material enough and reduce the flow resistance so that the centrifugal pump can be driven at 1780 rpm to create the requested head.

[0061] In FIG. 4 it is illustrated an embodiment where between the inducer 3, or the inducer rotor 32 and the impeller 22 (not shown in FIG. 4) it is provided guide vanes 24 having fixed or adjustable pitch. These guide vanes can be of conventional type just for controlling the swirl in the flow channel 20 or these can be such that the guide vanes 24 comprise conduits 241 for gas removal from the liquid.

[0062] In FIG. 5 it is illustrated an embodiment of the present method, the pump unit 1 is controlled based on a rheology of the fluid to be pumped so that necessary fluidization parameters of the fluid are predetermined to enable operation of the pump unit, and the inducer rotor rotation speed/output power is controlled to a desired volumetric flow rate. An energy dissipation of the inducer is proportional to both the fluid viscosity and shear rate, It can be assumed that fluidization occurs when a local shear stress equal to the yield stress of the fluid to be pumped, such as pulp suspension. Thus, the fluidization involves rupture of the fibrous network on a local scale. For viscous fluids, inducer can be characterized by a power numberReynolds number relationship following equation Re=D.sup.2N/, where Re is Reynolds number, D is the diameter of the inducer rotor, N is rotation speed, p is density and p is apparent viscosity of the fluid. Power number N.sub.p indicates nominal power delivered to fluid in certain inducer geometry N.sub.p=P/(D.sup.5N.sup.3). In FIG. 5 it is presented such Power number/Reynolds number curve for two different configurations, illustrated as configurations A and C. According to an embodiment, this calculated Power numberReynolds numbercurve is used as a reference curve for controlling the inducer rotor rotation speed/output power to operate the pump unit at a desired operational window.

[0063] In FIG. 6 it is illustrated a target QH-curve, volumetric flow rate Q on the horizontal axis and head on the vertical axis. If a measured head Hm at a given Q is below the curve point head target Ht then the difference between the Ht and Hm is H, the inducer speed is increased to meet the target/reference curve. As the necessary fluidization parameters of the fluid are predetermined to enable operation of the pump unit1, and the inducer rotor 32 rotation speed/output power is controlled to a desired volumetric flow rate as illustrated in FIG. 6.

[0064] While the disclosure 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 disclosure 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 disclosure, as defined in the appended claims. The details mentioned in connection with any embodiment above can be used in connection with another embodiment when such combination is technically feasible.