Cryogenic Pump NPSH Protection via Buffer Storage
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Solution Overview
Problem
Cryogenic liquid pumping installations face challenges with managing vaporization gases, leading to pressure rises and potential losses of Net Positive Suction Head (NPSH), particularly when handling low molar mass fluids like hydrogen, which are difficult to maintain in liquid form and prone to cavitation, resulting in inefficient energy use and economic imbalance.
Innovation Solution
A device with a buffer cryogenic storage system, separate pipes for connecting the buffer storage to the reservoir, and a liquefaction member, including heaters and valves controlled by a data acquisition and processing unit, to manage gas vaporization and maintain pressure within the reservoir, allowing for bi-directional flow and efficient liquefaction of gases, thereby minimizing gas returns to the tank and optimizing pump operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If gas is returned to the tank in gaseous phase, then tank pressure rises and temperature increases, but this causes losses of NPSH at the pump inlet and potential cavitation
Solution Approach 1:
The gas return system is segmented into two separate lines: a first line returning gas to the upper part of the tank, and a second line returning gas to the lower part of the tank. This segmentation allows selective routing of gas flows to different tank zones, enabling control over tank pressure distribution and preventing NPSH losses at the pump inlet by avoiding excessive pressure buildup in the liquid phase.
Solution Approach 2:
The invention introduces an intermediary buffer volume (the buffer at the lower part of the tank) that temporarily receives and stabilizes returned gas before it mixes with the bulk liquid. This buffer acts as a mediator that absorbs pressure fluctuations and prevents direct transmission of pressure rises to the pump inlet, thereby maintaining adequate NPSH margin.
2Use of energy by moving object
If liquid hydrogen is pumped, then energy efficiency is improved compared to gas compression, but difficulty is increased in maintaining liquid form due to low density and volatility
Solution Approach 1:
The system actively manages temperature and pressure parameters to maintain liquid hydrogen in pumpable state. By controlling the thermal state through insulated tank design and managing heat inputs, the system keeps the liquid hydrogen below its boiling point while maintaining sufficient pressure for pumping, thus preserving the energy-efficient liquid pumping mode despite hydrogen's volatility.
Solution Approach 2:
The invention converts the harmful effect of heat input and vaporization into a beneficial thermal management mechanism. The vaporization gases returned to the tank serve as a cooling mechanism through evaporation, helping to maintain the cryogenic temperature required for liquid hydrogen stability, thus turning the volatility problem into a self-cooling benefit.
3Duration of action of stationary object
If pump is stopped and lines are hot, then vacuum tank vaporizes liquid due to heat input, but this raises pressure in the tank requiring degassing
Solution Approach 1:
The system performs preliminary cooling of the pump and lines before stopping the pump, and maintains insulation on all cryogenic lines. This preliminary action reduces the thermal mass and heat input potential when the pump stops, thereby minimizing vaporization gas generation during standby periods and reducing the frequency and volume of required degassing operations.
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
The solution effectively controls pressure in the tank, reduces gas losses, and maintains sufficient NPSH to prevent cavitation, optimizing energy efficiency and reducing the need for additional compressor stations, while maintaining functionality across varying liquid levels.
Implementation Method 1
The pump is supplied with liquid from a reservoir via a suction line and maintained at a low temperature during operation
Implementation Method 2
the degassing outlet of the pump is connected to the lower part of the tank (liquid phase). The hotter gas or liquid is returned to the liquid phase where it is re-liquefied or cooled
Implementation Method 3
a pump for drawing off and compressing cryogenic liquid from an insulated tank under vacuum
Implementation Method 4
the pumped liquid can be vaporized in a vaporizer
Implementation Method 5
an insulated tank under vacuum
Data Source
Figure 1
AI summary
A fluid supply device comprising a reservoir (2) for storing gaseous fuel at a cryogenic temperature in the form of a liquid-gas mixture, a cryogenic pump (3), the pump (3) comprising a suction inlet (4) connected to the lower part of the reservoir (2) via a suction line (5), a first high-pressure outlet (6) for supplying pressurized fluid to a user, and a second degassing outlet (7) connected to the upper part of the reservoir (2) via a return line (9), the device (1) being characterized in that it comprises a cryogenic buffer storage (8), a first line (10) connecting the lower part of the buffer storage (8) to the reservoir (2), and a second line (11) connecting the upper part of the reservoir (2) to the buffer storage (8), and in that the device comprises a gas liquefaction device (12) in the buffer storage (8).