Liquid gas vs. Compressed gas
With renewables the storage of gases like hydrogen and liquified natural gas (LNG) is getting more and more interesting in mobile applicationis.
In principle there are two possibilities to store gas at higher density to reduce the volume. (speaking about realtively ideal gases like Nitrogen, Oxigen, Hydrogen, Helium)
One can compress gas to increase it´s density(typical max 150l and 300bar)
it´s easy to understand that the increase in pressure relates to an increase of the forces of the surrounding vessel walls (Force is equal pressure per exposed surface area). So the forces on the vessels walls limit the total pressure a vessel can withstand at a given exposed surface area. If the storage volume at a given pressure should be increased the walls thickness get at some point to senseless values to withstand the tension (surface area goes with 2 potency in the equation….) so for small volume storage it will work, with increasing storage volume you either have to multiply the number of round vessels (or their length) or you have to go “liquid gas storage”
One can liquify gas to it´s maximum density:
The liquid storage of gas bellow / at it´s boiling point has the advantage that it works at ambient pressure (or slightly above) so the storage volume is not limited by increased forces on the walls (not considering gravity) and maximum density is reached. The disadvantage of liquified gas at it´s boiling point is that it´s energy and cost intensive to cool it down. The effect of getting into the liquid phase is strongly gas dependent, the more ideal the gas is (Nitrogen < Oxigen < Hydrogen < Helium), the higher the energy effort (“costs”), the lower boiling point and the temperature it needs to be stored. To keep the liquid cool and not to waste gas & money by “boil of” proper vacuum insulation and control is a must….Another advantage of liquid gas is that you can also use the evaporation enthalpy of the liquified gas to cool other systems down (transfer heat) and to use some the cold gas e.g. to run adsorber to maintain Insulation Vacuum (a Cryo Pump itself)
Liquid Gas Storage
The advantage of storing gases in liquid phase is that it works at ambient pressure (or slightly above, for relatively ideal gases like Nitrogen, Oxygen, Hydrogen, Helium). The storage volume is not limited by increased forces on the walls (not considering gravity). The disadvantage of liquefied gas is that it´s energy and cost intensive to cool it down. The effect of when and how changing into the liquid phase is strongly gas dependent, the more ideal the gas (Hydrogen, Helium),
- the higher the energy effort (“costs”),
- the lower the boiling point
- the lower the temperature that it needs to be stored
- the greater the need to keep the liquid cool and not to waste gas & money by “boil off”
proper vacuum insulation and control is a must….
Liquid Gas Transport
Liquid Gas can be transported different ways, but in general the use of the SRG Technology makes sense to control the Insulation Vacuum quality. These vessels are extremely stressed, by construction they are optimized to have minimum conduction (contact to outside), should carry maximum volume and are used in mobile applications, translating to an unpredictable and harsh environment….
Stress is caused by
- Vibrations
- regular warm up and cool down (empty/full vessel)
- environmental factors (hot sun to freezing temperatures)
- form factor: long linear dimensions
- possible accidents (maybe not reported to management…)
These impacts can cause micro-cracks, leakage, and in worst case undetected leakage causing a fill up of the adsorber and an uncontrolled expansion of the gas going back to ambient temperatures and to overpressure….in best case the result may be just a loss of expensive liquefied gases (boil off). SRG sensors can be used for
- Vacuum Insulated Pipes VIP / Vacuum Jacketed Pipes VJP
- Cryogenic Trailers
- Static Cryogenic Containers / Tanks
- ISO Containers / Tanks
Long distance transportation by truck
The SRG Technology can be used to regularly measure the quality of the insulation vacuum without breaking the vacuum and with no additional electronics required on the truck. Is the technology suitable as vibrations may impact the sensor ball? It should, as the ball is hard stainless steel used for bearings. Otherwise, it is fixed with a magnet and protected by a mechanical housing during storage…
Medium distances by transfer lines.
The SRG Technology can be used to measure regularly the quality of the insulation vacuum w/o breaking the vacuum, even in areas where there is no easy access otherwise. (Alternatively one would have to move a High Vacuum pumping system around and perhaps several meters above ground level. Horizontal alignment of the Sensor tube is needed.
Short and medium distances by moveable tanks.
The SRG Technology can be used as a cost-effective way to regularly measure the quality of the insulation vacuum without breaking the vacuum. Especially as the smaller size tanks are moved through buildings, doors, hit walls…the one welding at the top of the vessel tends to absorb the forces that occur…
Liquid Gas Control
To control and measure the liquid gas flow, a variety of components are needed (such as shut off valves, control valves, measurement equipment, etc.). Commonly a proper insulation vacuum is needed to avoid condensation at the ambient side of the component and to limit the heat transfer into the cold area of the system.
As the contact area to the liquid (cold) gas is limited, the use of adsorbers is not always possible, and the need to secure a (very) leak tight system at manufacturing is a must.
The SRG Technology can be used to measure the insulation vacuum properties accurately and reproducibly during pump down, out-gassing phase and after closing the “plug”.
Liquid Gas Generation
A complex system based on the original Linde process needs proper insulation to increase its efficiency and to avoid the waste of energy, see a summary of the applications above.
| Features | Benefits |
| No need to open the sealed vacuum chamber | Ideal for monitoring sealed vacuum systems Easy to connect to port |
| No electrical feedthroughs | Chamber remains sealed |
| Electromagnetic/Mechanical measurement | Does not affect pressure or gas composition Insensitive to vacuum process and temperature conditions |
| All-metal Sensor (in metal or glass tube) | Contactless measurement provides long-term stability High accuracy direct vacuum measurement No component to fail or replace Cost effective Sensor concept Glass sensor tube maybe removed and be disposed of before shipment |
| Removeable Sensor head/readout | Electronics remain protected Measurement and mounting on demand One head for multiple sensors Heads are universal, fit all sensors |
| High intrinsic accuracy/reproducibility | No adjustments: Sufficient accuracy for most applications Long term stability for years |
| No electronics remain after measurement | Corrosion and “outdoor” weather resistant |
| One-button operation | No special training or specialist needed |
| Protection cap and magnet for storage | No breakage risk or damage of the ball's surface |
| Remote PC control | User friendly |
| Serviceable sensor | Quick and easy to clean and reassemble |
| Single connection to multiple units via RS-485 interface | Simultaneously monitors multiple vacuum chambers |