Multi-Plunger Pump Drive With Planetary Gearing Against Cavitation
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Solution Overview
Problem
Hydraulic fracturing pumps often suffer damage due to operating at speeds above the critical speed, causing cavitation and damage accumulation, as diesel-powered transmissions provide excessive gear speeds that accelerate fluid too quickly, leading to vacuum bubble formation and implosion.
Innovation Solution
Implementing a system with multiple electric or hydraulic motors driving a planetary gear train, allowing for precise control of pump speeds to maintain operation at or below critical speeds, using variable frequency drives and speed reduction gearboxes to achieve desired pump rates without exceeding critical plunger speeds, and utilizing odd numbers of plungers and longer stroke lengths to minimize cavitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If diesel-powered transmissions with high gear speeds are used to increase pump rate, then productivity is improved, but pump reliability deteriorates due to cavitation and damage accumulation from operating above critical speed
Solution Approach 1:
The pump system is divided into multiple independent plungers (e.g., quintuplex with five plungers) that operate in parallel. This segmentation allows the total pump rate to be maintained through multiple units operating at lower, safer speeds rather than a single unit operating at high speed, thereby resolving the contradiction between productivity and reliability.
Solution Approach 2:
The invention changes the operational parameters by limiting pump speed to at or below the critical speed (e.g., maintaining plunger speed at or below 120 rpm for an 8-inch stroke pump). By adjusting the number of plungers and their individual stroke lengths, the system achieves the required pump rate without exceeding the critical speed threshold, thus preventing cavitation while maintaining productivity.
2Productivity
If transmission speed is increased to compensate for offline pumps, then productivity is maintained, but harmful factors increase due to vacuum bubble formation and implosion
Solution Approach 1:
The system proactively prevents cavitation by designing the pump configuration (number of plungers, stroke length, and speed limits) to operate below the critical speed threshold where vacuum bubble formation occurs. This preliminary anti-action approach addresses the harmful effect before it can manifest, allowing the system to maintain productivity without generating cavitation damage.
3Reliability
If pump speed is reduced to stay below critical speed, then reliability is improved, but productivity deteriorates due to lower pump rate
Solution Approach 1:
Multiple plunger units are merged into a single pump system (e.g., quintuplex pump with five plungers). Each plunger operates at a reduced, safe speed below the critical threshold, but their combined output maintains the required total pump rate. This merging allows the system to achieve both reliability (through low-speed operation) and productivity (through combined output of multiple plungers).
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach prevents pump cavitation and damage, extends the life of pump fluid ends, and maintains efficient fluid transfer by ensuring pumps operate within safe speed limits, even when compensating for offline pumps, while allowing for slight overspeed as a safety margin.
Implementation Method 1
a planetary gear train having a plurality of input pinion gears in rotational contact with each of the plurality of motors
Implementation Method 2
use of variable frequency drives and speed reduction gearboxes to achieve desired pump rates without exceeding critical plunger speeds
Implementation Method 3
the formation of vacuum bubbles as a result of fluid being accelerated too fast through the pump. A heightened speed of operation creates low pressure within the pumps, creating vacuum bubbles. As the pump plungers retract, the vacuum bubbles implode, causing damage (cavitation) to the pump and engine systems.
Data Source
AI summary
A hydraulic fracturing system for fracturing a subterranean formation is described according to various embodiments. In an embodiment, the system can include a multi-plunger hydraulic fracturing pump fluidly connected to a well associated with the subterranean formation, the multi-plunger pump configured to pump fluid into a wellbore associated with the well at a high pressure so that the fluid passes from the wellbore into the subterranean formation and fractures the subterranean formation. In an embodiment, a plurality of motors can be positioned to power the multi-plunger pump, and a planetary gear train can have a plurality of pinion gears in rotational contact with each of the plurality of motors. In an embodiment, a gear ratio of the planetary gear train and a speed at which the plurality of motors operates can be selected so as to limit a maximum pump speed associated with the multi-plunger pump.