Cryogenic Pressure Tank Hydrogen Withdrawal Control
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Solution Overview
Problem
Cryogenic pressure tanks used in light motor vehicles face challenges with long downtimes, where heat input causes pressure increases, leading to hydrogen liquefaction and difficulties in determining remaining storage capacity due to phase segregation and low tank pressure, potentially preventing vehicle operation despite sufficient hydrogen.
Innovation Solution
A method for operating cryogenic pressure tanks involves planning a desired pressure curve for hydrogen removal from supercritical initial conditions to a minimum pressure, with controlled heat supply regulation to maintain pressure within a safe range, preventing liquefaction and ensuring accurate capacity determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If hydrogen is rapidly withdrawn from a nearly full cryogenic pressure tank to reduce pressure quickly, then the buffer until maximum permissible pressure is extended, but the thermodynamic state approaches the two-phase boundary causing hydrogen liquefaction and insufficient tank pressure
Solution Approach 1:
The patent applies preliminary action by providing heat to the hydrogen before rapid withdrawal begins. The control unit activates heating elements or opens heating valves in advance to raise the hydrogen temperature, which increases the buffer to the two-phase boundary. This preliminary thermal preparation ensures that even during rapid withdrawal, the hydrogen remains in the gaseous phase and maintains sufficient pressure throughout the process.
2Productivity
If hydrogen is rapidly withdrawn to achieve maximum downtime buffer, then pressure reduction speed is improved, but temperature measurement accuracy near the two-phase boundary deteriorates making capacity determination impossible
Solution Approach 1:
The patent implements feedback control by continuously monitoring temperature and pressure values and using these measurements to control the heating process. The control unit adjusts heating power or valve openings based on real-time feedback from sensors, maintaining the hydrogen state within a safe operating window away from the two-phase boundary. This closed-loop control ensures both rapid withdrawal and accurate measurement capabilities are maintained.
3Productivity
If the tank is emptied quickly to maximize productivity, then withdrawal time is reduced, but heat supply becomes insufficient leading to phase separation and operational failure
Solution Approach 1:
The system applies preliminary action by activating heating elements or opening heating valves before the rapid withdrawal phase begins. This advance thermal preparation ensures that the hydrogen is pre-heated to a temperature where the buffer to the two-phase boundary is maximized. During the subsequent rapid emptying, this thermal head start maintains sufficient heat supply adequacy even at high withdrawal rates.
Solution Approach 2:
The patent employs dynamic control by continuously adjusting heating power or valve openings based on real-time temperature and pressure measurements. The control unit modifies the heating rate dynamically throughout the withdrawal process, intensifying heat supply when the hydrogen approaches critical thresholds and reducing it when safe margins are maintained. This dynamic adaptation enables both high productivity and adequate heat supply.
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 reduces the risk of hydrogen liquefaction, maintains sufficient tank pressure during emptying, and allows precise determination of remaining hydrogen, preventing operational issues and the need for expensive sensors.
Implementation Method 1
controlling a heat supply to the cryogenic pressure tank during at least 70% of the complete removal process
Implementation Method 2
the thermodynamic state of the hydrogen stored in the cryogenic pressure tank approaching or even reaching the two-phase boundary, beyond which at least a portion of the stored hydrogen transitions into the liquid phase
Data Source
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AI summary
A method (300) is provided for operating a cryogenic pressure tank (16) in which cryogenic hydrogen is stored at a supercritical initial pressure and density, for supplying a consumer (14) with hydrogen withdrawn from the cryogenic pressure tank (16). The method (300) comprises planning (306) a desired pressure profile over a process for the complete withdrawal of the hydrogen stored in the cryogenic pressure tank (16) at the initial pressure and density to a predetermined minimum density at a predetermined minimum pressure of the hydrogen in the empty state of the cryogenic pressure tank (16), such that a pressure decrease of the hydrogen in the cryogenic pressure tank (16) towards the minimum pressure extends over the entire process for complete withdrawal.Furthermore, the method (300) includes controlling (308) the supply of heat to the cryogenic pressure tank (16) during at least 70% of the process for complete removal such that the pressure profile of the hydrogen in the cryogenic pressure tank (16) does not deviate by more than 10% from the desired pressure profile.