Progressive cavity pump with torque limiting coupling

Abstract

A progressive cavity pump for transporting an explosive emulsion, comprising: a pump body having a stator; a drive shaft rotatable by a motor; a rotor operatively connected to the drive shaft; and a torque limiting coupling operatively connected to the drive shaft. The torque limiting coupling activates in response to the determined torque exceeding a threshold value to disengage the rotor from the motor. A system for transporting an explosive emulsion including the progressive cavity pump and method are also provided.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a progressive cavity pump. The present disclosure has been developed primarily for use as a progressive cavity pump and system for transporting explosive emulsions and will be described hereinafter by reference to this application. However, it will be appreciated that the present disclosure may also be implemented for any type of progressive cavity pump, regardless of its application.BACKGROUND

[0002] The following discussion of the prior art is intended to present the present disclosure in an appropriate technical context and allow its advantages to be properly appreciated. Unless clearly indicated to the contrary, however, reference to any prior art in this specification should not be construed as an express or implied admission that such art is widely known or forms part of common general knowledge in the field.

[0003] Ammonium nitrate (AN) emulsion facilities use progressive cavity pumps in production processes (using one or more production pumps) and loadout processes (using loadout pumps). In both processes, the pumps are at risk of failure in a ‘no-flow’ or ‘deadhead’ scenario; i.e. there is an insufficient flow of the emulsion or a loss of pressure in the pump. This can result in the pump cavitating, generating heat via friction. The inability for the system to dissipate the heat via product flow may create a hotspot that could result in AN decomposition.

[0004] The plant is protected from this situation by using three layers of protection. The primary layer is a pressure sensor trip, the secondary layer is a temperature sensor trip and the tertiary (and final) layer is a burst disc rupture. Currently, the third and final layer of protection tends to be activated before the primary and secondary layers can respond. While this arrangement validates the effectiveness of a burst disc to protect against a catastrophic event, it creates a loss of containment event that must be reported in compliance with work and safety requirements. This results in downtime for the system, maintenance and labour to replace the burst disc, and administrative costs with reporting the loss of containment event.

[0005] It is an object of the present disclosure to overcome or substantially ameliorate one or more of the disadvantages of prior art, or at least to provide a useful alternative. It is an object of the disclosure in at least one preferred embodiment to provide a more convenient mechanism for preventing pump failure that minimises downtime, maintenance and labour, and avoids reportable loss of containment events and associated administrative costs.SUMMARY OF THE DISCLOSURE

[0006] The present disclosure provides a progressive cavity pump for transporting an explosive emulsion, comprising:

[0007] a pump body having a stator;

[0008] a drive shaft rotatable by a motor;

[0009] a rotor operatively connected to the drive shaft; and

[0010] a torque limiting coupling operatively connected to the drive shaft;

[0011] wherein the torque limiting coupling activates in response to the determined torque exceeding a threshold value to disengage the rotor from the motor.

[0012] In one or more embodiments, the torque limiting coupling is operatively connected to the drive shaft and the torque limiting coupling disengages the drive shaft from the motor.

[0013] In one or more embodiments, the rotor comprises a rotor shaft and the drive shaft is connected to the rotor shaft. In one or more embodiments, wherein the motor comprises a motor shaft operatively connected to the drive shaft.

[0014] In one or more embodiments, the torque limiting coupling is located or interconnected between the motor shaft and the drive shaft. In one or more embodiments, the torque limiting coupling disengages the drive shaft from the motor shaft

[0015] In one or more embodiments, the torque limiting coupling is located or interconnected between the rotor shaft and the drive shaft. In one or more embodiments, the torque limiting coupling disengages the rotor shaft from the drive shaft.

[0016] In one or more embodiments, the torque limiting coupling may be located anywhere between the motor and the pump body.

[0017] In one or more embodiments, the torque limiting coupling comprises a friction plate slip-clutch type, a shear pin type, ball detent type or a pawl and spring type of torque limiting coupling.

[0018] In one or more embodiments, a first torque limiting coupling is located between the rotor shaft and the drive shaft and a second torque limiting coupling is connected to the drive shaft. In one or more embodiments, the first torque limiting coupling and / or the second torque limiting coupling comprises a friction plate slip-clutch type, a shear pin type, ball detent type or a pawl and spring type of torque limiting coupling

[0019] In one or more embodiments, a sensor is provided for determining the torque on the drive shaft. In one or more embodiments, the sensor detects the torque on the rotor shaft. In one or more embodiments, the sensor detects the torque on the motor shaft. In one or more embodiments, the sensor detects the torque on the drive shaft directly.

[0020] A system for transporting an explosive emulsion, comprising:

[0021] a feed line for feeding the explosive emulsion to a progressive cavity pump according to the first aspect;

[0022] a discharge line fluidly connected to the progressive cavity pump;

[0023] a motor operatively connected to the drive shaft to rotate the rotor via the drive shaft; and

[0024] wherein the torque limiting coupling activates in response to a torque on the drive shaft exceeding a threshold value to disengage the rotor from the motor.

[0025] A method of transporting an explosive emulsion, comprising:

[0026] feeding the explosive emulsion through a progressive cavity pump according to the first aspect;

[0027] detecting the torque on the drive shaft; and

[0028] in response to a torque on the drive shaft exceeding a threshold value, activating the torque limiting coupling to disengage the rotor from the motor.

[0029] In one or more embodiments, the method comprises connecting the torque limiting coupling to the drive shaft and activating the torque limiting coupling comprises disengaging the drive shaft from the rotor.

[0030] In one or more embodiments, the rotor comprises a rotor shaft and the drive shaft is operatively connected to the rotor shaft, the method comprising interconnecting the torque limiting coupling between the rotor shaft and the drive shaft and activating the torque limiting coupling comprises disengaging the rotor shaft from the drive shaft.

[0031] In one or more embodiments, the motor comprises a motor shaft operatively connected to the drive shaft, the method comprising interconnecting the torque limiting coupling between the motor shaft and the drive shaft and activating the torque limiting coupling comprises disengaging the motor shaft from the drive shaft.

[0032] In one or more embodiments, the method comprises determining the torque on the drive shaft. In one or more embodiments, the method comprises detecting the torque on the rotor shaft. In one or more embodiments, the method comprises detecting the torque on the drive shaft directly.

[0033] Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to”.

[0034] Furthermore, as used herein and unless otherwise specified, the use of the ordinal adjectives “first”, “second”, “third”, etc., to describe a common object, merely indicate that different instances of like objects are being referred to, and are not intended to imply that the objects so described must be in a given sequence, either temporally, spatially, in ranking, or in any other manner.BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Preferred embodiments of the disclosure will now be described, by way of example only, with reference to the accompanying drawings in which:

[0036] FIG. 1 is a schematic drawing of a prior art system utilising a progressive cavity pump and its associated pump controls;

[0037] FIG. 2 is a graph showing the increase torque where there is a loss of pressure in the progressive cavity pump;

[0038] FIG. 3 is a side view of a progressive cavity pump according to one embodiment of the present disclosure;

[0039] FIG. 4 is a perspective view of a torque limiting coupling used in the progressive cavity pump of FIG. 3;

[0040] FIG. 5 is a front end view of the torque limiting coupling of FIG. 4;

[0041] FIG. 6 is a cross-sectional view of the torque limiting coupling of FIG. 4;

[0042] FIG. 7 is a rear end view of the torque limiting coupling of FIG. 4;

[0043] FIG. 8 is a rear perspective view of the torque limiting coupling of FIG. 4;

[0044] FIG. 9 is another cross-sectional view of the torque limiting coupling of FIG. 4;

[0045] FIG. 10 is a partial sectional view of the torque limiting coupling of FIG. 4;

[0046] FIG. 11 is a front view of an insert for the torque limiting coupling of FIG. 4; and

[0047] FIG. 12 is a front view of a segment of the insert of FIG. 11.DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

[0048] The present disclosure will now be described with reference to the following exemplary embodiments which should be considered in all respects as illustrative and non-restrictive. Although the disclosure has been described with reference to specific exemplary embodiments, it will be appreciated by those skilled in the art that the disclosure may be embodied in many other forms. Some of the figures may have been simplified by the omission of selected elements for the purpose of more clearly showing other elements. Such omissions of elements in some figures are not necessarily indicative of the presence or absence of particular elements in any of the exemplary embodiments, except as may be explicitly delineated in the corresponding written description. None of the drawings is necessarily to scale. In the Figures, corresponding features within the same embodiment or common to different embodiments have been given the same reference numerals.

[0049] Referring to FIG. 1, a prior art system 1 for transporting an explosive emulsion have a progressive cavity pump 10 operated by a motor 20 driven by a variable speed drive (VSD) 30. The cavity pump 10 comprises a helically shaped rotor 33 and a stator (not shown). A feed line 40 transports the explosive emulsion to a hopper 50 and then to the progressive cavity pump 10 via a connecting line 60. Another line 70 is downstream of the progressive cavity pump 10 to continue transportation of the explosive emulsion in the system 1. A temperature sensor 80 and a pressure sensor 90 are provided downstream of the progressive cavity pump 10 and are in fluid communication with the line 70. The temperature sensor 80 detects the temperature of the emulsion and communicates with the VSD 30 to stop the motor 20 if the temperature exceeds a threshold temperature value. Similarly, the pressure sensor 90 detects the pressure within the line 70 and communicates with the VSD 30 to stop the motor 20 if the pressure exceeds a threshold pressure value.

[0050] A burst disc 100 further downstream from the temperature and pressure sensors 80, 80 is in fluid communication with the line 70. The rupture disc 100 has a membrane that is designed to rupture or break when the pressure exceeds a threshold pressure value. Once ruptured, the burst disc 100 releases the pressure in the line 70 by permitting escape of the emulsion. This stops operation of the progressive cavity pump 10 and the system 1, leading to downtime as the burst disc 100 is replaced. This also results in the need to report the loss of containment of the emulsion in compliance with work safety regulations.

[0051] In this system 1, when a “deadhead” scenario occurs (an insufficient flow of the emulsion or a loss of pressure in the progressive cavity pump 10), cavitation can occur within the pump, generating heat from friction between the non-lubricated parts of the pump no longer submerged in the emulsion. The increase in temperature and pressure would usually trigger the temperature sensor 80 or pressure sensor 90 to stop the motor 20. However, it has been found that the burst disc 100 tends to respond more quickly to the pressure change and ruptures prematurely to stop the motor 20. While the burst disc 100 is effective in preventing AN decomposition, it forces more downtime of the system 1, more maintenance in replacing the burst disc and creates additional administrative work in reporting the loss of containment, compared to either the temperature or pressure sensor 80, 90 activating to stop the motor 20.

[0052] Referring to FIG. 2, testing of the burst disc 100 was performed and it observed in the recorded data that the motor amps increase at 120 as the discharge pressure of the cavity pump 10 increase at 130 in a “dead head” scenario. Accordingly, the inventors have taken advantage of this direct correlation between the rise in torque in the motor 20 and the rise in discharge pressure to propose the embodiments of the present disclosure as a technical solution to premature activation of the burst disc 100. This technical solution essentially involves disengaging the motor from the rotor when the absorbed torque is increased above the normal operating torque range using a torque limiting coupling.

[0053] Referring the FIG. 3, one embodiment provides a progressive cavity pump 200 comprising a feed inlet 210 and a pump body 220 having a stator (not shown). A rotor 230 is operatively connected to a drive shaft 240 rotatable by a motor 250. In some embodiments, the drive shaft 240 is directly connected to the motor 250, but in this embodiment the motor has a driving or motor shaft (not shown) operatively connected to the drive shaft 240. In this embodiment, the rotor 230 has a rotor shaft 260 that is operatively connected to the drive shaft 240. A torque limiting coupling 270 is operatively connected to the drive shaft 240 and activates in response to the determined torque exceeding a threshold value to disengage the rotor 230 from the motor 250.

[0054] The torque limiting coupling 270 in this embodiment may be connected in two possible locations. Firstly, the torque limiting coupling 270 may be located between the motor shaft and the drive shaft 240, as shown by arrow 300 in FIG. 3. That is, the torque limiting coupling 270 interconnects the motor shaft and the drive shaft 240. Alternatively, the torque limiting coupling 270 is located between the rotor shaft 260 and the drive shaft 240, as shown by arrow 310 in FIG. 3. That is, the torque limiting coupling 270 interconnects the rotor shaft 260 and the drive shaft 240. In either case, the torque limiting coupling 270 activates to disengage the rotor 230 from the motor 250. However, in other embodiments, the torque limiting coupling may be located anywhere between the motor 250 and the pump body 220.

[0055] The torque limiting coupling 270 can take a variety of forms, including a friction plate slip-clutch type limiting coupling, a shear pin type limiting coupling, ball detent type limiting coupling or a pawl and spring type of torque limiting coupling.

[0056] Referring to FIGS. 4 to 12, one embodiment of the torque limiting coupling is shown, taking the form of a ball detent type limiting coupling 400 comprising two clamping body portions or “hubs”410 and 420, each with integrally formed engagement formations 430 and 440, respectively. These engagement formations 430 and 440, often called “jaws”, extend axially from their respective hubs 410 and 420 parallel to the longitudinal axes of the hubs, and are preferably concave in shape.

[0057] The hubs 410 and 420 also have respective bores 450 and 460 for receiving a shafts of the cavity pump 10 for mounting the coupling 400. They also have laterally extending bores 470 and 475 for receiving fasteners, such as screws, to securely tighten the hubs 410 and 420 to the shafts of the cavity pump 10. The shafts of the cavity pump 10 are either the motor shaft 250 and drive shaft 240 or the drive shaft 240 and the rotor shaft 260.

[0058] An insert 480, preferably made of elastomer, is placed between the jaws 430 and 440 to transmit torque between the hubs 410 and 420 with little or no backlash or vibration. This reduces shaft misalignment during disengagement of the torque limiting coupling 400. The insert 480 may comprise of individual segments 482, as best shown in FIG. 12.

[0059] The hub 420 also comprises a plurality of balls 500 located in detents 510, as best shown in FIG. 9. The balls 500 are held in place with a biasing mechanism, which in this embodiment takes the form of an actuation ring 520 and one or more springs (not shown). The actuation ring 520 is forced by the spring(s) against the balls 500 in the detents 510. Hence, torque from the drive shaft 240 is passed to the hub 420, which in turn transmits the torque to the hub 410 via the balls 500. Thus, the coupling 400 rotates with the motor shaft, the drive shaft 240 and rotor 230. When the torque on the drive shaft 240 exceeds a threshold amount, the biasing force of the springs is overcome and the actuation ring 520 is released, permitting the balls 500 to be dislodged or displaced from their respective detents 510. This action disengages the hubs 410 and 420 from each other, resulting in disengagement of the drive shaft 240 from the motor shaft, or the rotor shaft 260 from the drive shaft 240. In either case, the rotor 230 is disengaged from the motor 250. Consequently, the coupling 400 prevents the transmission of excessive torque to the rotor 230, and thus undesirable cavitation and heat that may prematurely trigger operation of the burst disc 100.

[0060] In operation, when a “deadhead” scenario occurs, the discharge pressure of the pump 10 increases, rapidly followed by an increase in the torque of the motor 250, as shown in FIG. 2. The torque limiting coupling 270 or 400 responds to this increase in motor torque by disengaging the motor 250 from the rotor 230. Where the torque limiting coupling 270 is located between the motor shaft and the drive shaft 240, it disengages the motor shaft from the drive shaft, preventing the drive shaft from rotating the rotor 230. Where torque limiting coupling 270 or 400 is located between the rotor shaft 260 and drive shaft 240, it disconnects the rotor shaft from the drive shaft, also preventing rotation of the rotor 230.

[0061] The disengagement of the drive (motor) and driven equipment (rotor) has the advantages of preventing the addition of torque in the deadhead scenario; reduces the risk of premature activation of the final layer of protection (burst disc rupture); reduces reportable loss of containment events; and provides an independent layer of protection against catastrophic failure of the progressive cavity pump 10.

[0062] In other embodiments, it is possible to provide more than one torque limiting coupling 270 or 400. In this case, a first torque limiting coupling is located between the rotor shaft 260 and the drive shaft 240 and a second torque limiting coupling is located between the motor shaft and the drive shaft 240.

[0063] In further embodiments, a sensor may be provided for determining the torque on the transmission shaft 240. This may be achieved by the sensor detecting the torque on the rotor shaft 260, motor shaft or the drive shaft 240 directly.

[0064] It will further be appreciated that any of the features in the preferred embodiments of the present disclosure can be combined together and are not necessarily applied in isolation from each other. For example, the torque limiting coupling 270 or 400 may be used in conjunction with the temperature sensor 80, pressure sensor 90, the burst disc 100 or any combination of these devices. Similar combinations of two or more features from the above described embodiments or embodiments of the present disclosure can be readily made by one skilled in the art.

[0065] By providing a torque limiting coupling to disengage the rotor of a progressive cavity pump from the motor, the embodiments of the present disclosure ensure that the burst disc 100 does not prematurely rupture in a deadhead scenario during operation of the pump. Consequently, there is less downtime for the pump and system, less maintenance work as the burst disc does not need to be replaced and less administrative work in reporting loss of containment events caused by the premature rupturing of the burst disc. Furthermore, torque limiting coupling can be readily retrofitted to existing progressive cavity pumps and systems for transporting explosive emulsions. In all these respects, the present disclosure represents a practical and commercially significant improvement over the prior art.

Claims

1. A progressive cavity pump for transporting an explosive emulsion, comprising:a pump body having a stator;a drive shaft rotatable by a motor;a rotor operatively connected to the drive shaft;a torque limiting coupling operatively connected to the drive shaft; andwherein the torque limiting coupling activates in response to a torque on the drive shaft exceeding a threshold value to disengage the rotor from the motor.

2. The progressive cavity pump of claim 1, wherein the torque limiting coupling is operatively connected to the drive shaft and the torque limiting coupling disengages the drive shaft from the motor.

3. The progressive cavity pump of claim 1, wherein the rotor comprises a rotor shaft and the drive shaft is connected to the rotor shaft.

4. The progressive cavity pump of claim 1, wherein the motor comprises a motor shaft operatively connected to the drive shaft.

5. The progressive cavity pump of claim 4, wherein the torque limiting coupling is located between the drive shaft and the motor shaft and the torque limiting coupling disengages the drive shaft from the motor shaft.

6. The progressive cavity pump of claim 2, wherein the torque limiting coupling is located between the rotor shaft and the drive shaft and the torque limiting coupling disengages the rotor shaft from the drive shaft.

7. The progressive cavity pump of claim 1, wherein the torque limiting coupling comprises a friction plate slip-clutch type, a shear pin type, ball detent type or a pawl and spring type of torque limiting coupling.

8. The progressive cavity pump of claim 1, wherein the rotor comprises a rotor shaft and the drive shaft is connected to the rotor shaft; the motor comprises a motor shaft operatively connected to the drive shaft; a first torque limiting coupling is located between the rotor shaft and the drive shaft and a second torque limiting coupling is located between the motor shaft and the drive shaft.

9. The progressive cavity pump of claim 8, wherein the first torque limiting coupling comprises a friction plate slip-clutch type, a shear pin type, ball detent type or a pawl and spring type of torque limiting coupling.

10. The progressive cavity pump of claim 8, wherein the second torque limiting coupling comprises a friction plate slip-clutch type, a shear pin type, ball detent type or a pawl and spring type of torque limiting coupling.

11. The progressive cavity pump of claim 1, wherein a sensor is provided for determining the torque on the drive shaft.

12. The progressive cavity pump of claim 11, wherein the sensor detects the torque on the rotor shaft, the torque on the motor shaft or the torque on the drive shaft directly.

13. A system for transporting an explosive emulsion, comprising:a feed line for feeding the explosive emulsion to a progressive cavity pump according to any one of the preceding claims;a discharge line fluidly connected to the progressive cavity pump;a motor operatively connected to the drive shaft to rotate the rotor via the drive shaft; andwherein the torque limiting coupling activates in response to a torque on the drive shaft exceeding a threshold value to disengage the rotor from the motor.

14. A method of transporting an explosive emulsion, comprising:feeding the explosive emulsion through a progressive cavity pump according to claim 1;detecting the torque on the drive shaft; andin response to a torque on the drive shaft exceeding a threshold value, activating the torque limiting coupling to disengage the rotor from the motor.

15. The method of claim 14, comprising connecting the torque limiting coupling to the drive shaft and activating the torque limiting coupling comprises disengaging the drive shaft from the motor.

16. The method of claim 15, wherein the rotor comprises a rotor shaft and the drive shaft is operatively connected to the rotor shaft, the method comprising interconnecting the torque limiting coupling between the rotor shaft and the drive shaft and activating the torque limiting coupling comprises disengaging the rotor shaft from the drive shaft.

17. The method of claim 15, wherein the motor comprises a motor shaft operatively connected to the drive shaft, the method comprising interconnecting the torque limiting coupling between the motor shaft and the drive shaft and activating the torque limiting coupling comprises disengaging the motor shaft from the drive shaft.

18. The method of claim 16, comprising determining the torque on the drive shaft.

19. The method of claim 18, comprising detecting the torque on the rotor shaft, the torque on the motor shaft or the torque on the drive shaft directly.

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