DD141944A5 - DRUCKGASBEHAELTER - Google Patents

Abstract

The invention relates to a particular embodiment of a container for receiving liquefied petroleum gases such as butane, propane, · ethylene oxide, hydrazine, Venylazetat and the like. The invention achieves a considerable reduction in the risk of danger and thus high explosion safety. The essence of the invention is that the container is at least partially filled with an expending metal mesh and on the outside has an inturceszierenden coating. ~ Fig.2A

Description

Compressed gas containers

Field of application of the invention; ,

The present invention relates to containers which are primarily for receiving liquefied petroleum trineugens, such as butane, propane, ethylene oxide, hydrazine, vinyl acetate and the like. The invention is concerned with a container construction which, upon intensive heating of the container, e.g. In the 3? all of a fire, either completely prevents an explosion of the tank or significantly delays the time to an explosion of the tank.

In recent years, it has been found that it is possible to protect containers containing flammable gas / air or vapor / air mixtures from fire explosion by filling the container interior with expanded aluminum foil. Such containers, e.g. Gasoline tanks for vehicles typically contain sufficient oxygen to aid combustion

and allow the Flaium Front to achieve detonation speeds; the expanded foil prevents the explosive ignition of gas or vapor mixtures by dissipating the heat from the combustion site so rapidly that the flame front can not spread.

Liquefied petroleum gas tanks are always under atmospheric pressure to keep the gas in the liquid phase, in which case it is not possible for air to enter the tank and form an explosive mixture. However, there have been a number of serious incidents in which such containers, such as railroad tank cars, have been exposed to fire and the resulting explosions have assumed alarming proportions, such as fireballs having a. Diameter of 60 m or more have been generated. Such explosions are known as "boiling liquid / expanding vapor explosion and investigations of these explosions have shown that they are the result of a particular sequence of events." First, there is a triggering accident, ZoB, the derailment of a train of liquefied gas vessels, and then breakage A fire causes the fire to escape from the liquid gas or the contents of other wagons, which in turn causes the exterior of one or more liquefied gas containers to heat Up as the temperature rises, the liquid phase boils and the pressure in the tank rises until the normally existing pressure relief valve The gas stream flowing out of the safety valve is ignited and the ignited gas flow from a leak or from the pressure relief valve of one container to another container

Continued heating of the pressurized container above the internal liquid level, the usually made of steel wall of the container is brought to a temperature at which its tensile strength is reduced so that it breaks. When the break occurs, the container pressure drops rapidly and the liquid vaporizes very rapidly and expands to a large cloud of gas which is ignited by the fire and gives a destructive ball of fire. On the same side, the ball is very often driven many hundreds of meters high by the burning gas expelled from the crushed container. If, for some reason, the pressure relief valve does not open, or is below the level of the liquid as a result of the container overturning, bursting of the container as a simple pressure fracture may occur earlier but with the same destructive consequences. This also applies to containers without pressure relief valves

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According to the present invention, a container, in particular a pressure vessel for liquefied petroleum gas is at least partially provided with a filling of an expanded metal network or grids and has on the outside an intumescent or swellable coating.

Small containers, such as gas cylinders for portable ovens, may have an expanded foil filling over their entire interior if it is more convenient to equip the container in this way. Larger containers may be partially filled to provide the same effective protection against explosion. The partial filling is cheaper, takes less hem and weighs less.

Depending on the thermal conductivity of the expanded metal present inside the container, it is possible to simply line the inside of the container with the expanded metal grid and keep the central part of the container free of fill.This reduces the volume occupied by the expanded metal and, if necessary, allows to use a thicker material .;

In particular, the intumescent coating should be "very impact and abrasion resistant when used on mobile or portable containers."

Intumescent paints and paints are well known and used especially in buildings to burn wood materials and overheat. To delay steel structures. The intumescent coatings foam and char, forming a heat-insulating layer. Such a coating system may comprise only a single layer or a plurality of layers, including underlays and cover layers, depending on the particular container protection O demanded

Intumescent coatings normally contain a carbonating agent, a foaming agent, a catalyst and a resinous binder. The carbonating agent is a chemical mixture which, by reaction with the catalyst, releases a large amount of carbonaceous material. forms carbonized material. This foamable carbon produces the non-flammable protective layer that is characteristic of intumescent coatings. A typical carbonylating agent is di- or ^ tripentaerythritol. The foaming agent or the "blowing agent" sets at its

temperature decomposition releases non-combustible gas. Suitable foaming agents are chlorinated paraffin and crystalline melamine. The catalyst is a material that contains a high percentage of phosphorus and decomposes to phosphoric acid under heat and at a temperature below the decomposition temperature of the carbonator. Common materials are ammonium polyphosphate and melamine phosphate. Suitable binders are chlorinated rubber and vinyltoluene / acrylate binder.

Intumescence involves a number of processes that can take place simultaneously: decomposition of the catalyst; Reacting the resulting acid with the carbonylating agent to form a carbonaceous material; Softening the binder to form a skin that prevents escape of the incombustible gas released from the foaming agent; Foaming the carbon material to form a honeycomb blanket which provides highly effective insulation.

It has been initially believed that applying an intumescent coating to a container already containing an expanded metal grid may reduce the time to explosion in a fire because the isolation obtained could prevent heat dissipation from a cooler part of the container wall.

However, it has been found that the heat is transferred to the LPG, where the energy is used to convert the liquid to gas, and limiting the heat flowing into the vessel wall is therefore of great importance.

Since the insulating effect of the coating before intumescence is small, in use, "heat transfer through the vessel wall to vaporize the liquid will not hinder normal operation by the coating.

Of course, the containers to be protected for the proposed purpose may vary in size, and so on. from underground storage tanks to gas containers for camping ovens and aerosol cans, "Freon, which is normally used as a propellant in aerosol cans, has been attacked in many countries for various reasons, and it has been proposed to replace Preon with, for example, butane. However, of course, the danger of explosion of such a container poses a serious problem that does not exist in the non-combustible 3 'reon.

The requirement for large-scale storage facilities for LPG has led to an even greater number of potential risks where aerosol bottling plants are present ».

It is believed that the mechanism for preventing an explosion of containers in accordance with the present invention during a first time involves, first, a delay in the rate at which the heat reaches the outside of the container, e.g. due to the presence of the intumescent coating, and second, rapid dissipation of heat from the container wall through the expanded metal to the liquid, which absorbs a great deal of heat energy by evaporation.

When the container has a pressure relief valve, it also vaporizes some liquid gas as it is opened, consuming large amounts of heat energy that passes through the walls of the container and through the expanded metal grid into the liquid. Since the wall of the container is insulated on the outside by the foamed intumescent coating, the temperature of the container wall is greatly lowered compared to its previous temperature. The container walls are thereby prevented from assuming a temperature at which they undergo a remarkable weakening, and the internal pressure present in the container therefore can not burst the container wall. The cooling effect also increases the time between the closing and opening of the pressure relief valve, thus reducing the amount of escaping gas.

With unstable gases, such as ethylene oxide, which may be explosive as a 100% gas without additional oxygen and which is spontaneously flammable at relatively low temperatures, possibly as a result of decomposition, the expanded metal may prevent at any point of the liquefied gas , that this assumes a self-igniting temperature. Ethylene oxide is particularly dangerous because after it reaches a temperature of $ 60 ° C, explosive decomposition occurs, which continues even if the temperature source is removed. The decomposition may continue with other phenomena without becoming apparent until autoignition is achieved. It will be understood that the expanded metal, due to its inherent ability to dissipate heat very rapidly, prevents the decomposition temperature from being reached, thus substantially reducing the risk.

An expanded aluminum grid with a weight of 25 g / l has up to 500 times greater thermal conductivity than petroleum gas, and therefore transfers heat from the vessel wall 500 times faster than would be the case if only the gas were present. However, since the gas is in contact with it at all points on the surface of the container wall, except where expanded metal is in contact with the container wall, most of the heat is likely to be conducted from the wall into the gas and then directly into the gas Tests have shown that the expanded metal grid can be in contact with the wall of the container at relatively few points This is significant because in portable containers, the expanded metal is in some places, eg due to vibrations, from the wall of the container Container, which would pose a serious problem if the expanded metal the main conductor for the wall heat would be.

Various tests have been carried out to determine the degree of protection afforded by containers according to the invention, and Fig. 5 shows a test arrangement for these purposes.

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The tests were carried out on dome-shaped, valveless camping gas cartridges of standard steel containing 200 g of liquid butane. The test stand is simple and has a protective steel plate A, through which a gas burner B protrudes and to which a clamp C for the gas container D is attached. The flame E from the gas burner is directed at the top and at the side wall of the container, u.zw.

at a point that is above the liquid sphere.

A first test was performed on a cartridge as it is normally delivered, i. without protective layer. To. 31 see the domed floor F of the vessel reversed its vault and the vessel burst after 2 min and 26 sec. The bursting of the container was not due to a weakening of the container wall, but simply to the very high pressure created by the expanding gas.

A second container with a complete filling of an expanded aluminum alloy grid of 0.04 ran thickness was tested and the time to reversal of the bottom curvature of this container was 54 seconds and bursting occurred only after 4 minutes and 4 minutes 18 see.

Two more tests were then carried out. First of all, a container which contained the interior of the sieved, exoanced aluminum grid, but which was provided with a 15 mm thick insulating coating (the coating is manufactured by Sigma Coatings B-VV in Holland and is known as "Firescreen"). known). The bottom of the container reversed its curvature only after 23 minutes and 51 seconds, and the container did not burst.

The fourth container tested was substantially the same as the third, but had another intumescent protective layer of 7,000 μm in thickness. A reversal of the bottom curvature occurred after 33 min and there was just no bursting of the container.

From the above information it appears that, by means of a construction according to the invention, a considerable reduction in the danger of bursting can be achieved.

• Another series of tests was carried out with a burner with a "better flame, which generated greater heat, and at the same time at an ambient temperature that was much lower, in the order of 10 to 15 ° C, which meant a larger one There was an explosion after 45 seconds for an unprotected cartridge, which was split at the side, and for a cartridge filled with foil only, an explosion occurred after 50 seconds , A third cartridge with a film filling and a 15 ¹ ^ thick fire barrier coating ( "Fire Screen") and a 700 micron thick outer layer in the bottom region exploded · after 26 min and 45 see under the high internal pressure. A bursting of the container side due to weakening of Be. The wall of the container did not occur, but the blasting away of the bottom was rather like a pressure relief effect, which occurs in the presence of a pressure relief valve. It is understood that up to jed.och _v Druckbersten a considerable delay was achieved "

Examples of containers according to the invention are explained in more detail below with reference to the drawings. Show it:

Fig. 2A and 2B schematically in a vertical and in

a horizontal section of a portable liquefied gas tank, as it is for ovens in caravans and the like. is used;

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Fig. 3A is a schematic cross-sectional view of a container used for railway vehicles;

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Fig. 3B schematically in cross section another container for rail vehicles, and

Fig. JC is a longitudinal section of the container of Fig. JB.

The container of known type shown in Figs. 2A and 2B comprises an elongated cylindrical wall 1 provided with domed ends 2 and 3, with a cylindrically shaped base 4 fixed to the lower end 3 and having a lower flange 5, with which the container can stand safely on the ground. The upper end of the container has a gas outlet 6 to which is attached a valve unit 7 having a manually operable valve and a pressure relief valve. These elements of the container are standard elements. In its interior, the container additionally comprises a helically wound coil 8 of an expanded aluminum alloy foil, which occupies only between 1 and 2% of the interior of the container, but extends through the container so as to absorb the heat from the container walls can conduct the liquefied gas in the container, u.zw. no matter what orientation the container has. The expanded aluminum alloy grid has a thickness of 0.04 mm and a web width of 1.78 mm. In the longitudinal direction of the grating, i. along the length of the rhombic openings created during the expansion process in the grid, each opening has a length of 15 mm. The width of each opening is about 8, A- mm in the expanded state. When such a grid is wound into a coil, it has a density of about 0.03 g / cm.

On the outside of the container, an intumescent coating 9 is provided, which can be applied either in the form of a single layer or in the form of several layers, as in the experiments described above.

Fig. 3A shows a cross section through a much larger container, which is normally mounted on a railway vehicle. Per container also has a generally cylindrical wall 11 and domförinige ends 12 and 13 which are formed into a hemispherical shape in this example, as ~ $ 0 .. FIG. In contrast to the portable container shown in Figs. 2A and 2B, the container for the rail vehicle having the cylinder main axis is substantially horizontal and has a pressure relief valve (not shown). On the outside, the container has a single layer or multiple layers of an intumescent coating 14, as in the previous example, whereas in its interior it has only a partial filling of expanded metal lattice 15, the lattice being in the form of large coils 16 which is supported separately in an annular array by an expanded metal grid which extends radially in the form of sheets 17 and by a pair of substantially semi-cylindrical expanded metal grid sheets 18.

Figures 3B and 3C show an alternative embodiment to that shown in Figure 3A. In this example, the expanded metal grid is provided in the form of several layers 19 and forms a ring on the wall of the container, wherein it is on the inside by a cylinder 20 of an expanded metal mesh with

larger overall dimensions is supported, which is stiffened in the interior by crossbars 21.

It is understood that the arrangement of the expanded metal grid inside a container can be changed from case to case and depending on the size of the container.

Claims (10)

Invention claim: 1. container, characterized in that it is at least partially filled with an expanded metal mesh and on the outside of an intumescent coating on v / eist. 2. container according to item Ί, characterized in that it is a pressure vessel for liquefied petroleum gases. J. container according to item 1 or 2, characterized in that it is filled over its entire Innenrauia with an expanded metal grid. 4. Container according to item 1 or 2, characterized in that the filling of an expanded metal grid forms a lining of the container. 5. A container according to any one of items 1 to 4, characterized in that the expanded metal grid is formed from an expanded aluminum foil. 6. Container according to one of the items 1 to 5? characterized in that it is a gas cylinder. 7. Container according to one of the items 1 to 6, characterized in that it is a rail or road. transport tank is. , 8. Container according to one of the items 1 to 5i, characterized in that it is a fixed mounted Storage tank is. 9. Container according to one of the items 1 to 5> characterized. characterized in that it is an aerosol can. 10. Container according to one of the items 1 to 9, characterized in that the intuineszierende coating formed by a single layer. 11. Container according to one of the items 1 to 9> characterized characterized in that the intumescent coating comprises a plurality of layers. For this .... ^. Ropes zeldmungen