Refrigeration – Storage of solidified or liquified gas – Cryogen stored in both phases
Reexamination Certificate
2000-10-23
2002-06-18
Doerrler, William (Department: 3744)
Refrigeration
Storage of solidified or liquified gas
Cryogen stored in both phases
Reexamination Certificate
active
06405541
ABSTRACT:
The object of the invention relates to a method for producing slush from liquefied gas, by which solid crystals are formed and mixed or are mixed with the liquefied gas to produce slush. The invention also relates to a device for producing slush from liquefied gas.
Hydrogen (H
2
) is suitable as fuel due to its light molecular weight and its high degree of combustion heat for highly energetic rocket propellant combinations as fuel. Liquid hydrogen (LH
2
) belongs to the cryogenic fuels and requires that the tanks be appropriately heat-insulated if applied in a motive power unit. Special safety measures must be taken when handling hydrogen. The danger of explosion by hydrogen is greater than in the case of other fuels because of its high diffusion velocity. Even small sparks (e.g. by static charge) is sufficient to cause a fire or an explosion.
Due to the requirements for space transport systems to be constructed to save weight and space, gas liquefaction and further compression of the liquid hydrogen at a low temperature was considered for storage of the driving gas, hydrogen. It was finally proposed to apply slush—with hydrogen crystals mixed with liquid hydrogen, having a crystal content of 40-60% by weight. Slush has a number of favourable characteristics, like high density, high cold content and flows well. Due to these characteristics the slush of liquefied gases is extremely suitable as a cryogenic refrigerating agent not only for space missions but also for terrestrial application.
Methods have already been developed by which hydrogen slush can be produced. The freezing-thawing technology and the Auger methods which have been described in different ways in literature also belong to these methods.
In the freezing-thawing technology, liquid hydrogen which is cooled down to triple point level, is vaporized by creating a vacuum, by which hydrogen crystals are formed on the surface of the liquid hydrogen. The vacuum pressure undergoes cyclic changes to values slightly above and slightly below the triple point pressure, by which a movable matrix of hydrogen crystals forms at a pressure which is below the triple point pressure. Hydrogen condenses on the crystals at a pressure that is slightly above the triple point pressure and the solid particles sink into the liquid. A certain advantage of this method is the relative simplicity of the required technical equipment. However, since the slush production is achieved at underpressure when this method is applied, there is a certain safety risk because an unintentional suction of air, thus the formation of an explosive hydrogen-oxygen mixture should be expected. The production quantity is also limited, perhaps due to the cooling process of the liquid hydrogen which is either achieved by the vaporization of a given quantity of liquid hydrogen via indirect cooling by means of injecting cold helium or by means of a gaseous mixture of helium-neon. The required large quantities of at least some tons per day could not be achieved according to this method up to now because of the commercial expenses involved. To improve the quality of the hydrogen slush also necessitates an aging process of one to two days.
In the case of the second indicated method for producing hydrogen slush, the Auger method, a hollow cylinder filled with helium gas and placed in liquid hydrogen is cooled down to a temperature below the freezing point of the hydrogen. The design enables the formation of solid hydrogen on the inner walls of the cylinder, which is constantly scraped off by means of a swiveling spiral. At the bottom part of the device, the hydrogen crystals which are formed by that method mixes with the liquid hydrogen to slush.
This procedure has the advantage over the freezing-thawing method that the safety risk involved is not given in this case because there is no underpressure. However, it was only possible to apply this method up to now only for the production of quantities for the laboratory. A device which is appropriate for the industrial production of slush according to this method would hardly be able to be realized because of the required mechanical efforts and the costs involved. The slush produced according to this method must also undergo an aging process of one to two days in the long run.
The aim of the invention is now to develop a method for producing slush from liquefied gases, especially for producing hydrogen slush, by which the application of underpressure can be avoided and by which even larger quantities of slush can be produced. Apart from that it should also be possible to improve the quality of the forming slush so that, for instance, the duration of the aging process of the slush can be reduced and the flowing quality of the forming slush in the lines, valves, etc. can be improved. The aim of the invention is also to develop a device which is appropriate for the application of this method, safe to operate and to produce slush according to the industrial standards, with which the aims indicated can also be achieved with as little mechanical effort as possible.
The invention solves these tasks by solid crystals being formed from liquid particles which are released or admitted under pressure to a gas atmosphere, which has a temperature which is below freezing point of the liquid particles.
The method according to the invention thus ensures freezing or crystalizing of the particles in a relatively short space of time. Therefore, the forming solid particles have more of a round shape and there is a good quality of slush at increasing density. Due to the round shape either no or a slight aging process is necessary in order to ensure a high density of the slush and good flowing. No underpressure is required for producing the slush so that safety risk is reduced extremely in case hydrogen slush is produced.
According to another feature of the invention, the liquid particles are formed in a special and simple way by atomization of the liquefied gas.
For this process only an appropriate atomizing device device is required which can be mounted in a simple manner and consists of at least a nozzle or a centrifugal and mixing chamber or similar.
The atomization process can be effected in a simple manner at least partly by gas being supplied to the atomizing device under pressure which preferably is according to the gaseous phase of the supplied liquefied gas.
Therefore the liquefied gas supplied to the atomizing device can be cooled down before and/or during the atomizing process by means of a gaseous cooling medium. Additional cooling-down shortens the period of crystalization.
The method can be designed in such a way that either additionally or alternatively to atomization and by applying a supplied gas which is pressurized, atomization can be effected at least partly when the liquefied gas discharges into the cold gas atmosphere.
In order to ensure atomization which is as optimum as possible, i.e. bursting of the liquid jet discharging from the atomizing device, the pressure in the cold gas atmosphere is set at a rate which is below the corresponding critical pressure at the discharge aperture of the atomizing device.
In order to minimize the safety risk, the pressure in the cold gas atmosphere where crystalization occurs is set in such a way so that it corresponds at least to the ambient air pressure, it will particularly be at a value that is slightly above the ambient air pressure.
The inventive method has the special advantage that the forming slush can be continuously drained off essentially during the production of new slush. For this process it is favourable if draining-off of the slush is controlled by constant measurement of its density, which ensures the same quality of the drained slush.
The inventive method is especially suitable for producing hydrogen slush which has become more important as cryogenic fuel.
In this case helium gas is suitable as a cooling medium which is to be supplied to the atomizing device.
There is an advantage when a helium gas atmosphere, which can be made available at a corresponding low temperature,
Clark Hill PLC
Doerrler William
Drake Malik N.
MI Developments Austria AG & CO KG
LandOfFree
Method and device for the production of slush from liquefied... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and device for the production of slush from liquefied..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and device for the production of slush from liquefied... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2916898