A PUMP WITH RACKS AND PINION

Abstract

A pump, in particular a heavy-duty pump for pumping liquid or mixtures of liquids and particulate material, such as mud, proppant and concrete, said pump having at least one electric motor (15) coupled to a gear assembly (17), said gear assembly (17) in turn being coupled to at least one pinion (13, 14). The at least one pinion (13, 14) is meshing with two racks (9, 10) that are arranged in parallel on the same side of said pinion (13, 14) and said piston rod is arranged between the two racks (5, 6). The piston rod is operatively coupled to the set of racks (5, 6). The piston rod has at least one piston, or alternatively being coupled to a combined piston rod and piston (5, 6). The piston is received within a pump cylinder (1, 2) chamber.

Description

TECHNICAL FIELD

The present invention relates to a pump. In particular a heavy-duty pump for mixtures of liquids and particulate material, such as mud, proppant and cement.

BACKGROUND ART

Heavy-duty pumps play an important role in many industries. In for instance, the oil and gas exploration industry, heavy-duty pumps are used for pumping mud into the borehole, for injection or fracking. The pumps are required to deliver a very high pressure and high flow. Piston pumps have been found to be very suitable for delivering on these requirements.

Until a few years ago most piston pumps for the oil and gas industry where short stroke. However, with the development of stronger and more reliable electric motors, long stroke pumps have been introduced.

Some of the prior art pumps are shown in:

U.S. Pat. No. 6,749,408 shows a piston pump having an electric drive gear assembly that moves a toothed piston rod within two opposing cylinders. The drive gear assembly housing and the cylinders are fluidly connected. A total of four electric motors are required to drive each piston rod.

U.S. Pat. No. 7,556,480 shows a piston pump with an electrically driven gear assembly comprising two main gears that through shaft pins interact with guides extending in a transverse direction to the piston rods.

CA 2382668 shows a hydraulically driven double acting piston pump. Several pump units are set up to be driven out of phase to reduce pressure pulsations.

US 2016363116 A1 shows a pump system comprising a piston pump with a long stroke length, driven by an electrical motor. The piston is connected to a toothed rack via a piston rod.

US 2012230841 A1 and US 2007286750A1 show a piston pump driven by an electrical motor, where the piston pump having at least one pinion in mesh with two toothed racks positioned in parallel on the same side as said pinion, and that the piston rod is positioned between the two toothed racks and that the piston rods are connected to both said toothed racks.

Other piston pumps are known from US 2019/0120218, WO 2009/097338 and WO 98/36192.

SUMMARY OF INVENTION

The present invention provides a new and reliable pump with a high capacity and capability of even flow from the pump. The pump, in particular a heavy-duty pump for pumping liquid or mixtures of liquids and particulate material, such as mud, proppant and cement, has at least one electric motor coupled to a gear assembly, said gear assembly in turn being coupled via at least one pinion to at least one toothed rack that in turn is coupled to at least one piston rod, said piston rod having at least one piston, or alternatively being coupled to a combined piston rod and piston, said piston being received within a pump cylinder chamber, wherein said at least one pinion is meshing with two racks that are arranged in parallel on the same side of said pinion and said piston rod is arranged between said two racks, said piston rod being operatively coupled to said set of racks.

In a further embodiment, the two racks are interconnected by a coupling assembly, said coupling assembly being coupled to said at least one piston rod. This ensures that the two racks can act on the same set of piston rods.

In a still further embodiment, said coupling assembly comprises a link that is rotatably attached to said interconnected piston rods and rotatably attached to said racks. The link will even out any small differences between the racks and ensure smooth movement and less wear.

In a preferred embodiment the link is arranged coinciding with the longitudinal axis of the piston rods. This ensures an optimal point of attack for the pump drive.

In a further preferred embodiment, said racks have a guide rail on the opposite side of the rack from said toothing to ensure that the racks maintain a rectilinear motion.

In a still further preferred embodiment said set of racks is coupled to two oppositely acting and interconnected piston rods to create a simple way of obtaining a double acting pump unit.

In a yet further preferred embodiment, said cylinders of said piston rods are connected to a drive housing, said drive housing surrounding said at least one pinion, said racks and exposed parts of said piston rods. This provides a simple and lightweight solution.

In a still further embodiment, said drive housing comprises a central part extending between said cylinders and extension housings attached to said central part and surrounding said racks along their travelling path outside said central part. This further simplifies the construction and provides easy maintenance.

In a preferred arrangement of the pump unit, at least two pump cylinder chambers are arranged side by side and are coupled to a respective valve block, said valve blocks being coupled to a common header. This provides for an even more even flow of fluid out of the pump.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be described in more detail, referring to embodiments shown the accompanying figures, in which:

FIG. 1 shows an embodiment of the pump unit of the invention in isometric view, with pump housing removed,

FIG. 2 shows the pump of FIG. 1 in a similar view but with the pump unit in another position,

FIG. 3 shows the pump unit of FIG. 1 in a similar view but with the pump in yet another position,

FIG. 4 shows the pump of FIG. 1 in an isometric view with the pump housing in place,

FIG. 5a shows the pump unit of FIG. 4 in a planar view,

FIG. 5b shows the pump unit of FIG. 4 in a side elevation longitudinal partial section,

FIG. 6 shows a detail of the pump unit in a cross section,

FIG. 7 shows a detail of the pump unit in a different cross section than FIG. 6,

FIG. 8 shows a detail of a longitudinal section of a part of the pump drive,

FIG. 9 shows an isometric view of a pump comprising five pump units according to the invention,

FIG. 10 shows a planar view of the pump in FIG. 9,

FIG. 11 shows a pressure diagram for a pump unit having two independently working cylinders,

FIG. 12 shows a similar diagram as in FIG. 11 but with five pump units, as shown in FIG. 9,

FIG. 13 shows circle diagram representing a cycle of a pump cylinder,

FIG. 14 shows schematically a setup for controlling motors actuating the pump units of the pump in FIG. 9,

FIG. 15 shows a diagram illustrating an algorithm to control the position and speed of the pump,

FIG. 16 shows a diagram illustrating an algorithm to determine the relative angular position between the motors of the pump, and

FIG. 17 shows a diagram illustrating an algorithm for adjustment of the motors based on pressure measurements.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIGS. 1-17, an embodiment of the pump of the invention will now be explained.

FIG. 1 shows an embodiment of the pump of the invention. The pump has in this simplest embodiment two cylinders 1, 2. Within each cylinder 1, 2 is a piston 5, 6 (in the embodiments described, the piston and piston rod are constituted by the same element) (see FIG. 5b), which will be described later.

Two toothed racks 9, 10 are coupled to the pair of cylinders 1, 2. These will also be described in more detail below.

A set of pinions 13, 14 are meshing with the racks 9, 10. The pinions 13, 14 are (indirectly) coupled to a motor 15. The two pinions may be separate but interconnected parts, or they may be integral on the same part. The motor is preferably an electric motor, but it may also be a hydraulic motor or driven by other known means. The motor 15 is via a gear assembly 17 mounted on a drive housing 19, which has been removed in FIG. 1 but is shown in FIG. 4.

At the ends of each cylinder 1, 2, distal of the motor 15, there is a respective valve block 20, 21. The valve blocks 20, 21 are coupled to a header pipe (not shown here but will be explained in connection with a further embodiment of the invention).

The racks 9, 10 extend in parallel with a distance therebetween. They are interconnected by coupling arrangement 3. The pistons 5, 6 are arranged in the gap between the racks 9, 10 and extend in opposite directions from the coupling assembly 3 and are connected by a coupling piece 3b (see FIG. 8).

While FIG. 1 shows the pump in a mid-position of the stroke within the cylinders 1, 2, FIG. 2 shows the pump of FIG. 1 in an extreme position at one side, which means that one piston is at its most distal position and the other piston is at its most proximal position.

FIG. 3 shows the pump in an extreme position at the opposite side.

Thus, in operation the two racks 9, 10 being driven by the same motor 15, will move in synchronicity alternatingly to each side. This means that as the piston 5 is in its pressure stroke, the piston 6 will be in its suction stroke, and vice versa. This will provide an almost constant flow out of the headers coupled to the valve blocks 20, 21 at either end of the pump, as will be explained later.

It is possible to arrange additional racks meshing with the pinions 13, 14 on the opposite side of these from the racks 9, 10, these additional racks moving additional pistons in additional cylinders, i.e. an assembly being mirror image of the one shown. Those pistons would then move in opposite directions to the pistons shown in the figures.

The pistons 5, 6 are in this embodiment rams where the piston is formed at the outer end of the piston rod and the piston rod and piston may have the same cross-section where there is no division between the piston and piston rod. It is, however, conceivable also to use other types of pistons and rods, where the piston has a greater diameter than the piston rod.

FIG. 2, 3 also show mounting brackets 25, 26 that fix the cylinders 1,2 relative to the drive housing 19. The coupling arrangement 3 between the racks 9, 10 and the pistons 5, 6 is also shown. This coupling arrangement is better shown in FIG. 7 and will be explained in detail below.

FIG. 4 shows the pump with the drive housing 19 in place. The motor 15, gear assembly 17 and pinions 13, 14 are connected to the housing as one unit through mounting flanges with bearings 7, 8 (se FIG. 1).

In addition to a housing part surrounding the pinions 13, 14 and the gap between the cylinders 1, 2, where the pistons 5, 6 extend outside the cylinders 1, 2, the housing also has extensions 19a, b, c and d to accommodate the travel of the racks 9, 10. These extensions also keep any oil inside the housing and dirt from entering the housing. They are also a safety measure to prevent injury to any persons being close to the pump during operation.

FIG. 5a shows the pump in planer view seen from the top of the motor 15. It is clear from this view that the whole pump unit is a very slim unit.

FIG. 5b show the pump unit as seen in an elevation longitudinal section view from the opposite side of the side visible in FIGS. 1-4. This view shows the pistons 5, 6, the racks 9, 10 and the coupling arrangement 3.

FIG. 6 shows a cross-section through the pinions 13, 14 and the racks 9, 10. As can be seen from this view, each of the racks 9, 10 have a rail 16, 18 fix to the opposite side of the rack having the toothing formed thereon. These rails 16, 18 both stiffen the racks 9, 10 and form surfaces against which guides (not shown) may act.

FIG. 7 shows a similar cross-section as FIG. 6, but here the pump is in a position where the coupling arrangement 3 of the racks 9, 10 and pistons 5, 6 is shown. The coupling arrangement 3 comprises a link 3a, which is coupled to the pistons 5, 6 and the racks 9, 10.

FIG. 8 shows a detail of FIG. 5b where the link 3a is clearly shown. The link 3a is coupled to a connecting piece 3b interconnecting the two pistons 5, 6 by a journal 3c about which the link 3a may rotate. The link is connected to each of the racks 9, 10 through a respective journal 3d, 3e at a respective outer end. The link 3a is rotatable about these journals.

The coupling mechanism allows the racks 9, 10 to move longitudinally with respect to one another. The movement is however restricted by the pinions 13, 14, which are fixedly connected to one another. The freedom of movement ensures that any misalignments between the toothing of the pinions or the racks may be self-adjusted by a slight relative longitudinal movement of the racks 9-10.

FIG. 9 shows another embodiment of the invention. Here five pump units A, B, C, D, E have been arranged in a side-by-side configuration. Each of the pump units may be identical to the pump unit explained above and shown in FIGS. 1-8. However, to reduce the necessary width for the arrangement, the motors 15 have been staggered by arranging every second motor displaced somewhat to respective ends of the pump unit. This means that the pump units can be placed closed together without the motors 15 interfering.

The valve blocks 20, 21 of each pump units are connected to headers 22, 23. The headers 22, 23 are shown better in FIG. 10. As can be seen here, the valve blocks 20, 21 are coupled to both headers 22, 23. One header 23 is acting as an inlet header and the other header 22 is acting as a pressure header. The valve blocks 20, 21 will automatically open to the right header depending on the pressure in the valve block. A feeder pump (not shown) may be present on the inlet side to provide a slight pressure, such as 5 bar in the inlet header 23. The pressure in the pressure header can be as high as 1000 bar.

FIG. 11 shows a pressure diagram for a double acting pump with interconnected piston rods and opposing cylinders C1, C2, each with a piston P1 and P2, such as the pump unit shown in FIGS. 1-8. The upper graph 31 of the diagram shows the pressure caused by piston P1. The arrows 32, 33 show the direction of movement of the piston. As can be seen from the diagram the pressure in the cylinder C1 increases as the piston P1 moves towards the block at the distal end of the cylinder C1. The pressure increases rapidly as the piston P1 starts to move, as shown by the ramp 34, then the pressure reaches a plateau, as denoted by 35, after which it is rapidly ramped down, as denoted by 36, when the piston P1 reaches the end of the stroke.

After the pressure stroke 34, 35, 36, the piston returns and goes through a fill stroke 37. During the fill stroke 37, a low-pressure high-volume charging pump fills the cylinder. During the fill stroke the exit valve (not shown) of the valve block 20, 21 is closed and an inlet valve is opened. These valves can be one-way valves.

The second piston P2 in the second cylinder C2 works the same way as the first piston P1 in the first cylinder C1, except that the stroke is phase shifted by 180°. Consequently, the second piston P2 performs a pressure stroke when the first piston P1 performs a fill stroke, and vice versa, as shown by the second graph 38 of the diagram in FIG. 11.

The combined pressure graph of both pistons P1 and P2 and cylinders C1 and C2 is shown by the third graph 39 in FIG. 11. This is representative of the pressure of the flow out of the pump when the flow from the two cylinders C1, C2 have been joined. Ideally the transition between the pressures created by the first piston P1 and the second piston P2 should be as smooth as possible. This optimal transition is shown at point 40 in the graph.

Points 41-44 show non-optimal transitions. At 41 the combined pressure has a drop at the turning point of the stroke of the two pistons P1, P2. At 42 the pressure drop occurs slightly before the turning point of the two pistons. At 43 there is a peak in the pressure at the turning point, and at 44 the peak in the pressure occurs slightly before the turning point.

All of the above non-optimal transitions may create problems downstream of the pump due to pressure pulses travelling through the fluid. The pressure pulses can cause valves to flutter and disturb instruments. Furthermore, as described above, pressure pulses are negative to well formations, may disturb instruments and actuators that rely on pressure pulse communication.

FIG. 12 shows a similar diagram to FIG. 11, but for a pump arrangement with five pumps, such as the embodiment described in FIGS. 9 and 10, where each piston rod is double acting and has oppositely acting pistons P1, P2. Each pair of piston rods is actuated by a separate motor, denoted M1-M5 in FIG. 12.

The motors M1-M5 drive their piston rods with an approximately 72 degrees phase shift. This would ideally result in an even flow from the pump, as the flow and pressure caused by each piston, when combined, sums up to a constant value. However, as can be seen from FIG. 11, the flow is not necessarily even at the transition between strokes of different pumps.

FIG. 13 shows a circle representing one cycle of the pump where each piston has made one pressure stroke and one fill stroke. The phase angle from 1 to 2, 2 to 3, 3 to 4, 4 to 5 and 5 to 1 represents the phase shift between one piston rod and the next piston rod. This phase angle is nominally 72 degrees. However, to compensate for non-optimal transitions, the piston rods are allowed to alter their phase shift relative to the other piston rods within a certain angle (denoted by a hatched area in FIG. 13).

Moreover, the stroke length can also be changed to compensate for non-optimal transitions. The nominal stroke length is denoted by the radius of the circle in FIG. 13.

In a given case, the stroke of pump number five can be shifted both in angle and stroke to the actual stroke and angle shown by the point 45 in FIG. 13.

To be able to detect non-optimal transitions, both with regard to unintended phase shifts, dips and peaks in the pressure, as shown in FIG. 16 by 41-44, the pump has pressure sensors located in the valve blocks 20, 21.

FIG. 14 shows a flow chart of the setup for controlling the motors actuating the pump units of the embodiment shown in FIGS. 9 and 10. The motors are denoted MOTOR 1-MOTOR 5. The motors are controlled by a respective variable frequency drive, denoted VFD 1-VFD 5. The VFDs are connected to a pump controller 46 through a network 47. The pump controller 46 is in turn controlled by a main processor 48, and a human interface 49 to provide commands to the main processor 48. The human interface 49 may conveniently be a display and keyboard.

Encoders, denoted ENCODER 1-ENCODER 5 provides input to the pump processor 46. The input includes angular position of motor. In addition, there may be sensors (not shown) that measures the pressure in each cylinder and the pressure in the header 23. Based on the position data of the motor, the speed and acceleration of the motor is calculated. The flow out of the header 23 may be calculated based on the pressure measurements, but may also be direct flow measurements.

The algorithms for controlling the phase shift and stroke of the piston rods 5, 6 will now be described, referring to FIGS. 14-17. In the following adjacent motors or adjacent cylinders is understood to mean two motors that are closest to one another in angular distance or cylinders that are closest to one another in angular distance. For a pump with more than two cylinders, this means that two adjacent cylinders will overlap in their pressure strokes.

The algorithm illustrated in FIG. 15 aims to control the position and speed of the pump by adjusting the rotational speed of the motors.

At the start-up of the pump, the initial angular position of each motor is determined, as denoted by 51. A part of this determination is to set the difference in angular position between the motors, such as 72 degrees for a five-motor pump. In a four-motor pump the angular difference is set to 90 degrees and in a six-motor pump the angular difference is set to 60 degrees. The set motor position for each motor is denoted setpoint.

The encoders ENCODER 1-ENCODER 5 provides the instantaneous angular position of the motors M1-M5 with a high sampling frequency. The positions of the motors are directly correlated to the positions of the associated pistons of the pump. From the sampled position data, the speed of each motor is calculated by the pump processor 46 from the position data delivered by the encoders, as denoted by 50. The instantaneous position for each motor is compared with the setpoint for the motor at 52. If the instantaneous position is equal (see 53) to the setpoint the motor speed is kept at the current speed. If the instantaneous position is behind the setpoint (see 54), the speed of the motor is increased (see 55), and if the instantaneous position is forward of the setpoint (see 56), the speed of the motor is decreased (see 57). This process is continuously repeated to keep the motors and hence the pistons at the predetermined angular distance.

FIG. 16 illustrates the algorithm for determining the relative angular position between the motors. The input to this algorithm is the instantaneous angular position of each motor M1-Mn (where n is the number of motors in the pump arrangement), as denoted by 58. The angular position of each motor is compared with the angular position of the first motor M1. If the angular position of the n'th motor Mn satisfies the equation Pos₁=Pos_n+360/n, where Pos₁ is the angular position of M1 and Pos_n is the angular position of Mn, the angular position difference is correct (see 59). If the n'th motor has a smaller angular difference (see 60), the speed of this motor is increased and if it is larger (see 61), the speed of the motor is decreased.

The algorithm in FIG. 17 illustrates adjustment of the motors based on pressure measurements. The pressure sensors input the pressure of each cylinder 1-n as illustrated by 62. The pressures of two adjacent cylinders, when they both are in the pressure stroke, are compared. If the pressures are within a predetermined differential pressure, such as +/−5%, the difference is considered acceptable. If it is outside this range, the speed of the trailing motor is adjusted to increase or decrease the pressure.

Even if the adjustment of the pressure stroke of one piston also has direct influence on the suction stroke of the piston coupled to this piston, this really does not matter. A fluttering suction stroke influences only on the suction side of the pump, and here the pressures are low.

Claims

1. A pump, in particular a heavy-duty pump for pumping liquid or mixtures of liquids and particulate material, such as mud, proppant and concrete, the pump having at least one electric motor coupled to a gear assembly, the gear assembly in turn being coupled via at least one pinion to at least one toothed rack that in turn is coupled to at least one piston rod, the piston rod having at least one piston, or alternatively being coupled to a combined piston rod and piston, the piston being received within a pump cylinder chamber, wherein each of the two pinions are driving one of the racks the pinions meshing with two racks that are arranged in parallel on the same side of the pinion and the piston rod being arranged between the two racks, the piston rod being operatively coupled to the set of racks.

2. The pump of claim 1, wherein the two racks are interconnected by a coupling assembly, the coupling assembly being coupled to the at least one piston.

3. The pump of claim 2, wherein the coupling assembly comprises a link that is rotatably attached to the interconnected piston rods and rotatably attached to the racks.

4. The pump of claim 3, wherein the link is arranged coinciding with the longitudinal axis of the piston rods.

5. The pump of claim 1, wherein the racks have a guide rail on the opposite side of the rack from the toothing.

6. The pump of claim 1, wherein the set of racks is coupled to two oppositely acting and interconnected piston rods.

7. The pump of claim 6, wherein that the cylinders of the piston rods are connected to a drive housing, the drive housing surrounding the at least one pinion, the racks and exposed parts of the piston rods.

8. The pump of claim 7, wherein the drive housing comprising a central part extending between the cylinders and extension housings attached to the central part, the extension housings surrounding the racks along their travelling path outside the central part.

9. The pump of claim 1, wherein at least two pump cylinder chambers are arranged side by side and are coupled to a respective valve block, the valve blocks being coupled to a common header.

10. The pump of claim 9, wherein the pistons arranged in the at least two pump cylinder chambers are driven by separate electric motors, at least one pressure sensor being arranged in the header, the sensor being coupled to a processor that controls the rotation of the electric motors, each motor having an encoder detecting the angular position of the motor, the encoder being coupled to the processor, the processor being set up to adjust the speed and hence the angular position of the motors when the difference in pressure in the header is greater than a predetermined tolerance.

11. The pump of claim 10, wherein each of the motors are operating at least two oppositely arranged and interconnected piston rods, the piston rods each having a piston that is received within a respective one of two oppositely arranged pump cylinder chambers, the cylinder chambers together with adjacent cylinder chambers forming a set of first cylinder chambers on a first side of the pump and a set of second cylinder chambers on a second side of the pump, the set of first cylinder chambers being coupled to a first common header and the set of second cylinder chambers being coupled to a second common header.

12. The pump of claim 10, wherein the processor is set up to drive the motors at an initial angular separation equal to 360° divided by the number of motors.

13. The pump of claim 10, wherein the processor is configured to adjust the angular separation of the motors to obtain an even flow out of the header.