DE2822587A1 - Protection of Dewar flasks from overpressure - using dip pipe down into body of flask with one or more bursting discs leading out to atmos. via relief valve - Google Patents

Abstract

Protection for dewar flask against internal explosion should the neck become blocked with solid air or ice involves a dip pipe leading down into the flask. This has one or more bursting discs on it. The pipe leads to a release valve behind which is a further bursting disc. In this way the vessel is protected from blockage which prevents pressure escape. Used for storage of liq. gases e.g. He. Gives safe release of pressure even if neck freezes up.

Description

Mainauweg 9 “ \ _m

7750 Constance 19

Protective device to prevent overpressure in dewars.

The invention relates to a protective device for dewars, which protects them from explosion even if the neck or even parts of the inner container are blocked by a plug of solid air or ice.

The safety valves on both the fixed and the movable head can then no longer respond if the entire Neck inside and outside of the safety tube is frozen by air condensed into it. Even less so than the plug can also extend deep into the inner vessel. Since recently some Deware explosions have become known it seems to be the order of the day to construct a protective device that provides adequate protection offers and yet does not give up any of the essential advantages of previous lightweight construction technology.

Liquid helium of 4.2 K is stored in dewars. A dewar consists of 2 thin-walled kettles placed one inside the other, whereby the inner and outer are connected by a thin-walled neck because of its poor heat conduction stainless steel is used as the material. The space between the boilers is also used for better insulation evacuated. Copper shields are soldered to the neck, which are cooled by the escaping gas and thus the radiation Reduce. There is also super insulation between the shields surrounding the inner body for better insulation arranged. The neck protrudes outward over the outer cup and is flanged at its outer end. The outer part of the neck is called the fixed head. On the fixed head there is C at least with good dewars) at least a non-lockable pressure relief valve.

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The movable head is attached to the fixed head with the help of a Leybold small flange. The movable head consists essentially of the safety neck, the shut-off valve and an overpressure valve. The safety neck is a tube that about 2/3 of the way down into the neck, with a certain distance between the neck and the safety neck. A lifter can now be inserted into the dewar through the shut-off valve to remove helium. There are usually two further valves on the fixed head. One is a lockable pressure relief valve (35g / cm - gas ballast) the other is the exhaust valve. If recovery is available, the dewar is attached to the return gas line via the exhaust valve, otherwise it is attached to the gas ballast valve. The usual safety argumentation is something like this: If air enters the safety neck through the open valve on the movable head, gas that develops between the safety neck and neck can still escape through the exhaust valve, but solid air that has entered through the open exhaust valve closes the space between the safety neck and neck then the overpressure developing in the inner container can escape via the overpressure valve in the movable head. This reasoning is no longer valid if the outer neck and inner neck are clogged. This can occur, for example, due to defective valves, human error, stuck siphon etc .. One liter of liquid helium results in approx. 750 liters of gas at room temperature. You can easily calculate the pressure in a 100-liter dewar that is created by the inward flow of heat that cannot be prevented. Since the wall thickness of the dewars cannot be increased in order to absorb the resulting pressure, this is where the problem arises.

The aim of the invention is to create a protective device which is still safe even when the neck is completely blocked offers ^ without having to increase the wall thickness or prohibitively increase the heat flow inwards.

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To solve the problem, a relatively thin-walled tube made of stainless steel is used, which extends to the bottom of the inner kettle is enough. At its upper end it leads into the open and at its end is also through a rupture disc locked. This ensures that nobody can mistakenly manipulate anything on this security part can. Because the lower part of the tube (1) is immersed in liquid helium, the gas in the tube becomes (Air) condenses in the lower part of the tube (1). This means that no heat can be transported via gas convection. Burst pressure approx. 1 bar overpressure.

Inside the pipe space there should now be a non-return valve in front of the outer bursting disc (3) that is briefly opens below the external burst pressure. This prevents air from flowing back into the dewar in the event of an action.

It makes sense to have a paint powder chamber behind the bursting disc Or the like. Arranged, which signals danger in the event of an action and initiates accompanying measures leaves.

In the lower part of the pipe (1) there can be additional bursting disks (7,8,9,10,11) are staggered in height. These guarantee that one will break through safely. Usually, however, they will all break. Through the top one however, only gas will escape, so that no liquid He gets into the pipe to the outside.

In the event that the dewar has a wide neck approx. 2 "in diameter, the tube (1) between the neck and Safety neck can be guided up into the fixed head.

However, if the neck is relatively narrow, the tube (1) should be guided through the shields into the outer space. It must be gas-tight on the inner container as well as on the outer container be welded. In both cases, the

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but be within the crown (12).

An advantage of the invention is that the protection devices are not made at the expense of a large thermal leak got to. The inner container would have to be made of material that, for example, can withstand the pressures occurring in the If a blockage could take up, then a sensible helium storage would no longer be possible.

Another advantage is the extensive security against technical and human error. The device also protects against explosion for a long time, if necessary until all liquid helium is gasified and in the end only gas from 1 bar is in the Dewar. Dewars that have triggered the protective device must be withdrawn from use immediately will. They can only be used again after a protective device has been installed and the identification color has been removed will.

Another advantage is that most of the dewars on the market come with the protective device can be easily retrofitted. This refutes the fear that has been voiced lately that everyone is at the time Dewars currently in use taken out of circulation and for safety's sake. "- with new explosion-proof 6r £ et: zt would have to be.

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An embodiment of the invention is shown in the drawing and is described in more detail below.

It shows

FIG. 1 :

Structure and mode of operation of a dewar with a built-in protective device that also protects the dewar, if the neck or even parts of the inner container are blocked by a plug of solid air or ice.

The outer container (20) is connected to the inner container (19) connected by the neck (18). Shields (23) shield the inner container from excessive heat radiation. The pressure relief valve (14) is located on the fixed head (21) and the exhaust valve (T5). In addition, the protective tube (1) penetrates the fixed head. The removable head (22) emerges with the safety neck (17) up to approx. 2/3 in the neck. The passage valve (16) is usually designed as a ball valve to allow the jack to pass through. There is also a pressure relief valve on the movable head (2 2) (13). Defects in the pressure relief valve on the fixed or movable head can cause the dreaded total plug. It can also be caused by human error (valves (15), (16)).

The protective tube (1) dips at its lower end to the bottom of the inner container. It's locked here through the bursting disc (3) As soon as there is liquid helium in the dewar, all gas is inside the protective tube (1) Pumped into the lower area so that there is a vacuum in the upper part of the protective tube. Through this heat transport by convection is prevented. The check valve (4) prevents the ingress of Air in the dewar. When the rupture disc (2) bursts, it hurls what is in the dye chamber (5) Color powder in the upper, open part of the dewar, which is limited by the crown (12), so that everyone can immediately recognizes the danger and initiates accompanying relief measures

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can guide in order to possibly save the contents of the dewar C helium is very expensive). But even if nobody notices the damage, there is no longer any danger, because the He ^ lium then slowly gasses out. The color signals Furthermore, the protective tube must always be replaced before the dewar is put into operation.

The bursting disks (7), (8), (9), (10), (11) should be in If possible, the effect of bursting is that gas and no liquid helium flows out. On the other hand, they offer additional Safety, because one of the many rupture discs will respond safely.

Β098Λ8 / Ο172

Claims (6)

1J protection device for dewars, the same even then Protects against explosion if the neck or even parts of the inner container are solidified by a plug Air or ice are blocked. characterized, that the inner container is connected to the atmosphere via a pipe (1) which has bursting disks at its limits (-2, 3) carries. 2. Device according to claim characterized in that that there is a check valve in front of the rupture disc "(4} is located. 3. Device according to claim 1 or characterized in, that behind the bursting disc (2) there is a powder chamber (5) located, in turn, through a thin Slide (6) is complete. 4. Device according to one of claims 1 to, characterized in that that at the lower part of the tube (1) further bursting disks (7,8,9,10,11,) are arranged staggered in height. 5. Device according to one of claims 1 to, characterized in that ,. 9 0 9 8 A 8/0 1 7 2. \ ^ ^e That the tube (1) opens into the fixed head between the neck and the safety neck. 6. Device according to one of claims 1 to 4, characterized that the tube (1) outside the neck (18) to the outside to be led. 909848/0172