Vacuum Pump Control for Liquefied Gas Tank Membrane Integrity
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Solution Overview
Problem
Sealed and thermally insulating tanks with membranes used for liquefied gas storage are prone to pressure differences that can cause the primary sealing membrane to tear, especially when the tank is under subcooled conditions, leading to potential depressurization and damage.
Innovation Solution
A method involving a pumping device connected to a thermally insulating barrier, which uses vacuum pumps to maintain a negative relative pressure within the barrier, controlled by measuring and adjusting pressures based on temperature and setpoint pressures determined by relationships with liquid-vapor equilibrium curves, ensuring the pressure inside the tank remains above the barrier pressure to prevent membrane damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the tank is placed under subcooled conditions to reduce natural evaporation and enable long-term storage, then the temperature of the liquefied gas is reduced below its liquid-vapor equilibrium temperature, but the vapor phase heats up and stratifies inside the vessel, creating temperature gradients of the order of 100°C
Solution Approach 1:
The patent implements a dynamic control system that continuously monitors temperature and pressure conditions and adjusts the vacuum pump operation accordingly. The control module modifies the setpoint pressure Pc1 as a function of measured temperature T using an increasing monotonic function f1(T), allowing the system to adapt to changing thermal conditions and maintain membrane integrity despite temperature gradients
Solution Approach 2:
The system employs feedback control by measuring the actual temperature T of the liquid phase and using this information to determine the appropriate setpoint pressure Pc1 through the relationship Pc1 = f1(T). This closed-loop control ensures that the pressure in the thermally insulating barrier is continuously adjusted to match the current thermal state of the tank, preventing membrane damage under varying subcooled conditions
2Reliability
If the vacuum pump maintains a negative relative pressure in the thermally insulating barrier to protect the sealing membrane, then the pressure difference presses the membrane against the barrier preventing tearing, but energy expenditure increases
Solution Approach 1:
The patent applies partial action by maintaining only the minimum necessary negative pressure in the thermally insulating barrier required to protect the sealing membrane. The setpoint pressure Pc1 is determined as an increasing monotonic function of temperature, ensuring that the pressure differential is sufficient to press the membrane against the barrier under all operating conditions without applying excessive vacuum that would waste energy
Solution Approach 2:
The system dynamically changes the pressure parameter in the thermally insulating barrier based on temperature conditions. By using the relationship Pc1 = f1(T) where f1 is an increasing monotonic function, the setpoint pressure is adjusted according to the actual temperature T, optimizing the balance between membrane protection and energy consumption across different operating conditions
3Reliability
If the pressure inside the primary thermally insulating barrier is maintained lower than the vessel interior pressure to prevent membrane tearing, then the membrane is pressed against the barrier, but the system becomes sensitive to pressure differences that could cause overpressure tearing
Solution Approach 1:
The patent implements preliminary action by pre-establishing the pressure relationship between the thermally insulating barrier and the vessel interior before any harmful pressure differences can occur. The vacuum pump proactively maintains the barrier pressure below the vessel pressure, creating a safety margin that prevents membrane tearing from overpressure conditions before they can develop
Solution Approach 2:
The system provides beforehand cushioning by maintaining a controlled pressure differential that acts as a protective buffer for the sealing membrane. The negative pressure in the barrier creates a cushioning effect that absorbs and mitigates pressure fluctuations in the vessel, protecting the membrane from sudden overpressure events that could cause tearing
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
Effectively protects the sealing membrane by maintaining pressures that prevent tearing, even under subcooled conditions, while minimizing energy expenditure and ensuring the tank's integrity during temperature gradients and movements.
Implementation Method 1
maintain a pressure inside the primary thermally insulating barrier which is lower than that prevailing inside the vessel so that the pressure difference on either side of the primary sealing membrane tends to press it against the secondary thermally insulating barrier
Implementation Method 2
the liquefied gas is mainly stored in the tank in a subcooled thermodynamic state, that is to say at a temperature which is lower than the liquid-vapor equilibrium temperature of the gas in question
Implementation Method 3
determining a setpoint pressure Pc1 by means of a relationship Pc1 = f1(T); f1 being an increasing monotonic function and T being a variable representative of a measured temperature of the liquid phase
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The invention relates to a device for operating a pumping device associated with a sealed and thermally insulated tank (2); said tank (2) containing a liquefied gas (8) having a liquid phase and a vapour phase and having a multilayer structure comprising a sealing membrane (7) in contact with the liquefied gas (8) and a thermally insulating barrier (6) arranged between the sealing membrane (7) and a bearing structure (4), said thermally insulating barrier (6) comprising solid matter and a gaseous phase; said pumping device comprising a vacuum pump (16) connected to the thermally insulating barrier (6) so as to place the gaseous phase under a negative relative pressure; said method planning to control the vacuum pump (16) on the basis of a reference pressure Pc1 and of a measurement of the pressure Pi of the gaseous phase of the thermally insulating barrier (6); said method further comprising: - measuring the temperature T of the liquid phase of the liquefied gas (8); and - determining the reference pressure Pc1 by means of a relationship Pc1 = f1(T); f1 being an increasing monotonous function.