Patent Application
20120210865
This invention relates to flow control devices, and more particularly to flow control devices in reciprocating pumps used for example in, but not limited to, mud-pumping and frac-pumping applications in the oil-and-gas industry.
Reciprocating pumps are commonly used in applications where high volumes of fluid need to be pumped at high pressures. Highest efficiency reciprocating pumps are commonly driven by a crank mechanism. Since any given crank mechanism provides for a constant stroke of the plunger, two methods are typically used for controlling volumetric flow of these pumps:
Both methods have limitations. Changing the liners and plungers is labour-intensive and requires skilled labour, and the pump must be taken out of service during changing, resulting in “down time” of the pump. Controlling the speed may be practical within a limited range if a diesel or gas engine is being used as a prime mover. However, if an electric motor is used as a prime mover, very expensive and inefficient speed controls need to be used, such as VFD or DC controllers.
In order to achieve an appropriate match between pumping requirements and capabilities of the engines used as prime movers, expensive, multispeed transmissions are often used, especially in frac-pump applications where they are often 6, 7 or even 8-speed units. Mud-pumping applications often use 2-speed transmissions. Furthermore, shifting between speeds can result in momentary interruptions in fluid flow.
There is a need for improved apparatus and methods for controlling the volumetric flow of fluid discharged from reciprocating pumps.
In one aspect of the invention, a reciprocating pump is provided. The reciprocating pump includes: a first sleeve defining a first compression chamber; a first plunger receivable in the first sleeve; a second sleeve defining a second compression chamber, the second compression chamber in fluid communication with the first compression chamber; a second plunger receivable in the second sleeve; at least one outlet and at least one inlet in fluid communication with both the first and second compression chambers; a first crankshaft coupled to the first plunger, the first crankshaft drivingly coupled to a prime mover; a second crankshaft coupled to the second plunger, the second and first crankshafts coupled to each other through a differential and rotatable about a common crankshaft axis; a differential housing for housing the differential, the differential housing rotatable about the common crankshaft axis; rotation means for rotating the differential housing; whereby rotation of the differential housing effects a phase shift between strokes of the first and second plungers to modulate effective flow of fluid out of the outlet.
In drawings which show non-limiting embodiments of the invention:
It will be appreciated that numerous specific details are set forth in order to provide a thorough understanding of the exemplary embodiment described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein may be practiced without these specific details. In other instances, well-known methods, procedures and components have not been described in detail so as not to obscure the embodiment described herein. Furthermore, this description is not to be considered as limiting the scope of the embodiment described herein in any way, but rather as merely describing the implementation of the embodiment described herein.
The invention provides apparatus and methods for active stroke control for controlling fluid flow of multi-throw reciprocating pumps. Fluid flow is controlled by canceling out at least a portion of a discharge stroke of one plunger with a suction stroke of another plunger. Controlling the degree to which the discharge stroke is cancelled out is used to control the actual volume of fluid being pumped.
Some embodiments provide pumps with an even number of throws (2, 4, 6, etc.) while other embodiments provide pumps with any number of throws. Those skilled in the art will understand that:
The term “pair” of plungers as used in this specification refers to two plungers each connected to their respective crankshafts, for example by means of cross-heads and connecting rods, and the crankshafts connected to each other by means of a differential gear arrangement in any known manner such that the phase of stroke may be varied between the two plungers. Compression chambers of the pair of plungers may be connected in any manner that provides minimal restriction to the flow of fluid between the compression chambers.
The description will describe apparatus and methods for controlling a two-plunger pump as an example.
Respective compression chambers of the pump (shown above the two pistons/plungers in
The crankshaft of the pump is divided into a primary crankshaft and a secondary crankshaft. Each of the primary crankshaft and secondary crankshaft actuate one connecting rod and one piston (i.e., a plunger). The primary and secondary crankshafts are coupled by means of a differential, such as a differential gear assembly. The differential gear assembly is housed in a differential housing. As shown in
The differential housing is supported in differential housing bearings in such a manner that it may be rotated in a controlled manner around an axis common with the crankshaft, i.e., the crankshaft axis. The rotation means (not shown) used to control such movement may be one of any number of mechanisms known to those of ordinary skill in the art. For example, rotation means may include a worm gear coupled to the differential housing and driven by a motor or the like.
The two throws of the crankshaft are in phase in
The differential housing may be rotated away from the in phase position, around the crankshaft axis, and then held in a new angular position to effect a “phase shift” between the two plungers. The phase shift will be equal to twice the angle of the rotation of the housing. For example, to achieve a 50 degree phase shift, the differential housing must be rotated by 25 degrees.
Since the path of a stroke of the plunger resembles a sinusoid, once the phase-shift occurs, the plungers will “follow” each other along the sinusoid. Accordingly, there will be instances where one plunger is moving “up” (i.e., in the discharge stroke) while the other one is moving “down” (i.e., in the suction stroke). During these instances, at least a portion of the fluid will be flowing between the two compression chambers through the fluid passage rather than out the discharge valves, thus reducing the effective discharge flow of the pump.
Increasing the phase shift will increase the flow between the compression chambers to reduce the effective flow of the pump.
Because phase shifting merely requires rotation of the differential housing about the crankshaft axis, simple and uninterrupted flow control is achieved. Once a desired effective flow is achieved, the differential housing may for example be locked in that angular position until further adjustment is required.
As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.
| Number | Date | Country | |
|---|---|---|---|
| 61376606 | Aug 2010 | US |
