WO1993008103A1

WO1993008103A1 - Apparatus for flame- and explosion-proofing an inflammable and explosive liquid in a tank, and for cleaning the tank when empty

Info

Publication number: WO1993008103A1
Application number: PCT/NL1992/000185
Authority: WO
Inventors: Aldo Indovino
Original assignee: Noya N.V.
Priority date: 1991-10-18
Filing date: 1992-10-16
Publication date: 1993-04-29
Also published as: AU2929192A; EP0607358A1; KR100229701B1; DE69202155D1; CH685240A5; JPH07503924A; EP0607358B1

Abstract

The apparatus comprises a container (2) for a flame retardant substance, and a device (5) for delivering the flame retardant substance in gaseous phase into a tank (1) to maintain a permanent non-flammable atmosphere therein. The main advantage of the apparatus is that an atmosphere largely made up of a flame retarding agent is maintained within the tank (1) to eliminate any danger of fire or explosion. The apparatus further comprises devices for supplying (27) and injecting (28) a liquid cleaning agent into the container (2). Given that the flame retardant substance also acts as a cleaning agent, the devices for delivering the flame retardant substance form part of a circuit having common pumping, suction, compression and purging devices. The flame retarding and cleaning agent is a halogenated gas.

Description

INSTALLATION FOR MAKING A FLAMMABLE AND EXPLOSIVE LIQUID NON-FLAMMABLE AND NON-EXPLOSIVE WHEN CONTAINED IN A TANK AND FOR WASHING THE TANK WHEN IT IS EMPTY.

The invention relates to an installation for making non-flammable and non-explosive permanently a flammable and explosive liquid when it is contained in a reser¬ see.

All tanks that contain or have contained flammable liquids are exposed to the risk of fire and explosion.

The volume of the tank not occupied by the liquid is filled with a mixture of air and vapor in a percentage which varies according to the nature of the liquid, the ambient temperature and that of the liquid, the pressure which prevails in the volume. unoccupied tank, depending on whether it is open, closed, closed and pressurized. If the liquid contained in the tank consists of a mixture, the majority of the compounds in the vapor will be the compounds of the mixture which are the most volatile, ie those which are generally the most flammable.

When the vapors of the flammable liquid and the air are mixed, there is a minimum quantity and a maximum quantity of vapor, relative to the air, which delimit a range of values of the air-vapor mixture, known as the range of flammability, and the limit values are called lower limit and upper limit of flammability.

These values are characteristic of each flammable liquid, and vary as a function of temperature and pressure.

When the vapor mixture ignites, it gives up energy to the liquid and all of its surroundings. This energy can propagate at a very high speed which can lead to the explosion of the tank. Indeed, high amounts of liquid vaporize very quickly,

REPLACEMENT SHEET representing a danger to the entire environment of the reservoir. To avoid this, several techniques have been developed.

Some of these methods are based on the principle of controlling and minimizing the combustion energy so that its propagation speed is very low, this in order to eliminate the danger of overpressure and explosion of the tank. This can be done in accordance with what is described in UK patent 1,584,955, by dividing the volume of the reservoir into as many smaller cells and therefore with a more limited energy content, by means of a mass. filling which has a high absorption of the heat produced.

Other methods are based on the principle of making the mixture of vapor contained in the tank non-flammable and non-explosive, which we will call ignifuga¬ tion.

In what follows, the term flame retardant is considered to be an action to make it non-flammable and non-explosive and the term flame retardant means an agent intended to make it non-flammable and non-explosive.

In particular, fireproofing can be achieved in several ways: either by ensuring that the volume of the unoccupied reservoir of liquid is oversaturated with vapor and therefore beyond the upper flammability limit, by means of devices various which cause, for example, the air to bubble through the liquid when the tank is sampled, or by making so that the atmosphere inside the tank also contains a percentage of substance not suitable for combustion such as as nitrogen, exhaust gases from internal combustion engines, carbon dioxide, or substances with high extinction characteristics such as halogen gases for example, in which cases these substances are used in a percentage of the order of 10% to 20%, depending on the volume occupied in the tank by steam. These fireproofing operations are also made necessary when it is necessary to intervene for operations of handling and repairing of the tanks, to avoid the danger that certain accidental causes may cause disastrous explosions.

It is normal practice to periodically wash the tanks, both to change the nature of the liquid contained, and to remove the materials that are inevitably present in the liquid and that settle on the bottom of the tank.

The washing operation requires fireproofing of the tank beforehand, to avoid any danger and to make the interior of the tank accessible to operators under safe conditions.

The present invention aims to provide a permanent fireproofing installation which not only has all the performance provided by the most advanced fireproofing systems currently known, but also provides other advantages, in particular that of guaranteeing protection against environment surrounding the tank in the event of rupture of the latter, sufficient to avoid explosions in the first moments of the spill outside the liquid contained, and in most cases, to also avoid fire . An improved form of this installation also has the advantage of allowing the tank having contained the combustible liquid to be washed.

The subject of the invention is an installation according to claim 1.

The accompanying drawings show schematically and by way of example, an embodiment of the installation according to the invention, which can also be used for fireproofing the flammable and explosive contents of a tank and for washing such a tank.

RElVβPLACEMi r T SHEET To facilitate understanding, there is shown in Figure 1, only the parts of the installation used for fireproofing, while it has been shown in Figure 2 only the parts of the installation used for cleaning.

The installation as shown in FIG. 1 comprises a tank 1 containing the liquid fuel to be protected by flame retardancy, a container 2 containing the flame retardant, a pump 3 intended for transferring the flame retardant agent from the container 2 to the zone situated above the liquid ^' of the reservoir 1, by passing it through a unidirectional solenoid valve 4 and through gasifiers 5, by means of a supply line 6 and a valve 29.

The reservoir 1 is provided with a liquid sampling tube 7 which can be closed by a valve 8. The end of the sampling tube 7 is a short distance from the bottom. The valve 8 is actuated either manually or by means of a known level detector not shown, which prevents the escape of the flame retardant, by preventing the exit of the liquid when the level of the latter is below a level of guard previously fixed.

An inlet pipe 9 allows the introduction of the combustible liquid into the tank 1, by means of a valve 10. In this way, only the liquid which comes to supply the tank 1 at a pressure higher than that existing in tank 1 can enter the latter.

As the combustible liquid is added, the pressure increases in the tank 1, which has the effect of compressing the flame retardant gas due to the reduction in the volume available for it, due to the liquid introduced into the tank 1, which causes the arrival of combustible liquid in the tank 1 to decrease. To continue the introduction of the liquid, it is necessary to reduce the pressure of the flame retardant gas. To this end, part of this gas is sucked in by means of a pipe 11 opening into the upper part of the tank. The gas thus sucked in is compressed by a compressor 12 until it liquefies. A purification device 13, comprising a series of baffle separators and filters, is used to separate the impurities and the fraction of the combustible liquid which has condensed in this compression phase, from the flame retardant, so that only l the pure and liquid flame retardant is introduced into the container 2. The products other than the flame retardant are recovered via the line 14.

A 'pressure gauge 15 controls, by a known automatic mechanism, the operation of the compressor 12 and the pump 3, so as to maintain in the tank 1 an atmosphere of flame-retardant gas at a pressure previously fixed. The value of this limit pressure is chosen as a function of thermodynamic considerations, the nature of the combustible liquid and the flame retardant chosen, as well as the amplitude of the thermal variations to which the tank is subjected. This pressure will be called "operating pressure".

In addition to the normal pressurization means (pump 3 and valve 4), a reservoir 16 of compressed nitrogen is provided which, by means of a pressure reducer 17, keeps inside the container 2 containing the flame retardant. , a pressure such that it causes, during a stop of operation of the pump 3, an influx of flame retardant agent into the tank 1, by means of an additional line 18 and a non-return valve 19, which guarantees the presence of flame retardant gas in the tank 1 at a pressure close to the "working pressure". A non-return valve 20 then prevents the flame-retardant agent from reaching the purification device 13 and the pipe 11.

The tank 1, containing the flammable and explosive liquid is, in most cases, the object of phenomena complexes such as the sedimentation of the solid particles contained in the liquid, the separation of the drops of liquids initially retained in emulsion (water, acid, etc.), the deposition of the particles on the bottom deriving from the oxidation of the walls of the container or any varnishes or paints from the latter or the accumulation of heavier fractions of the liquid at the bottom of the tank, often in conjunction with temperature variations.

It is therefore necessary to periodically remove from the bottom the deposits which have accumulated and which by their nature and their viscosity, are not easily eradicable, particularly if one wants to change the nature of the liquid to be stored in the tank 1, or to carry out handling or repair operations, when said materials are more easily flammable and can give rise to explosive mixtures with air.

The embodiment which has just been described makes it possible to carry out the washing and cleaning of the tank 1 under conditions ensuring the non-flammable and non-explo¬ sive nature of the gases contained in the tank 1. Figure 2 shows only the parts of the installation necessary for washing.

In Figure 2, we see the tank 1 having contained the combustible liquid, the container 2 containing the washing agent which here is the same as the flame retardant, the pump 3 intended to transfer the washing agent from the container 2 to tank 1, passing it through a unidirectional solenoid valve 4 and through the in ectors

28, by means of a supply line 27 and the valve

29. The injectors 28 are arranged to inject the washing agent in the liquid state on the walls of the tank 1 and on its upper part, with sufficient energy supplied by the pump 3, in a manner which guarantee

FIRE weaves an effective wash, combining the mechanical action with the solvent properties of the washing liquid used.

The deposits, which have become much more fluid thanks to the solvent properties of the washing liquid, are discharged into a bottom discharge 21 through a valve 22 in a retention tank 23 which includes a heating element 24 allowing the washing liquid to evaporate. . These vapors of the washing liquid are brought, by means of a pipe 25 provided with a non-return valve 26, to the compressor 12 which will liquefy said vapors, thus allowing their purification by means of a purification device 13 comprising a group of baffle separators and filters. This makes it possible to recover almost entirely the washing liquid used. The other products are recovered via line 14.

The washing cycle is determined from time to time depending on the nature of the liquid which was contained in the reservoir 1; The amount of washing liquid introduced into the tank 1 and the time of this introduction will vary depending on the consistency of the deposits. By providing two or more washing cycles depending on the case, it will be possible to achieve complete cleanliness of the reservoir 1, and storage of the deposits in the retention tank 23.

In the example described, the container 2 for the storage of the flame retardant and washing agent is preferably a tank capable of withstanding the pressure.

The tank 1 and the container 2 are preferably part of the load-bearing structures of a ship.

The transfer of the flame retardant and washing substance is carried out by means of a single pumping means 3, switchable by means of a valve (29), in order to be able to carry out the two functions of fireproofing and washing as desired.

The suction of the evaporating flame retardant and washing gases, and of compression of these gases, is carried out by means of a single suction and compression means 13, co mutable by means of a valve provided to optionally provide the two fireproofing and washing functions.

The separation of impurities from the flame retardant and washing agent is carried out by means of a single purification unit 13.

The flame retardant and washing agent is preferably halogen gas.

In a variant of the embodiment described and shown, the installation could be provided only to make the flammable and explosive liquid contained in a tank non-flammable and non-explosive. In this case, this variant would only include the parts shown in Figure 1.

The numerous advantages of the installation described are enumerated below.

If a wall of a tank that is not part of the installation breaks due to a shock due to physical causes such as a collision between the means which carries the flammable liquid and a fixed or mobile obstacle for example, or chemical such as an explosion, for example, the liquid contained in the tank leaves, vaporizes in large quantities, and mixes with the surrounding air. The vapor is then in ideal conditions to be able to ignite because it is in the field of flammability described in the introduction. A primer such as a hot spot or a spark due to friction between metallic parts is sufficient for the combustion phenomenon to initiate and gives rise to an incan¬ descending sphere of ignited vapors which propagates and spreads with great rapidity.

If the ruptured tank is the flame retardant tank 1 of the installation of the present invention, the flame retardant gas which constitutes almost all of the atmosphere contained in tank 1, leaves with the liquid; the drop in pressure in the reservoir 1 when it ruptures is immediately signaled by the pressure gauge 15. Since there is a connection 6 between the container 1 and the container 2 in which the flame-retardant agent is contained, the agent flame retardant conti¬ naked out of the opening in large quantities thanks to the nitrogen pressure provided by the devices 16, 17 and 19, and this even if, as a result of the collision the pump 3 stops working. Outside, there is then a mixture of two gases, that of the flammable liquid and that of the flame retardant, much more volatile under the same conditions. In this way, the explosion is prevented and, in most cases, the fire too. In the worst case it will be an easy to control combustion.

In addition, thanks to this installation, a loss of liquid or gas is immediately signaled by the internal pressure drop of the reservoir 1 revealed by the pressure gauge 15.

Another advantage of this installation is that, since the atmosphere of the tank consists of an inert and flame-retardant gas, the air never enters the tank 1 and the problems of corrosion by oxidation of the walls of the tank are reduced .

Another advantage of this installation is that, after the tank 1 has been washed, the tank can be handled in an inert atmosphere.

Another advantage of this installation is that it makes it possible to carry out washing operations immediately after having emptied the tank, without having to resort to an external installation. It is a considerable advantage if the tank 1 described is a load tank of a tank vessel intended for the transport of flammable liquids such as crude oil, for example, in which case, washing can be done during navigation. , during the return journey between the port of destination of the crude oil and the port of loading.

REPLACEMENT SHEET Another advantage of this installation is that the washing deposits can be piled up in a suitable container, which can also be fireproofed if necessary.

Another advantage of this installation is that the quantity of flame retardant and washing agent does not vary, unless an inevitable loss occurs. It therefore constitutes a fixed load which does not influence the stability of the means on which the installation is arranged.

Another advantage of this installation is that it makes it possible to have a flame retardant agent tank with a compression pump and pipes, which can be used, under emergency conditions, for purposes other than those for which they were expected.

Another advantage of this installation is that, if there are several tanks to be protected, it is possible to have a simple fireproofing and washing installation, the tanks of which are interconnected with one another, obviously maintaining the overall quantity. of flame retardant identical to that necessary which derives from the sum of the quantities of flame retardant that it takes for each container.

REPLACEMENT SHEET

Claims

1. Installation for making non-flammable and non-explo¬ sive, permanently, a flammable and explosive liquid contained in at least one tank (1), characterized in that it comprises:

- at least one container (2) for the storage of at least one flame-retardant substance in the form of gas liquefied by compression;

- Means for the supply (6) and the transformation into the gas phase (5) of said flame-retardant substance inside the tank (1) of fuel to be protected from a fire or an explosion in the area occupied by the fuel vapors;

- a pressure gauge (15) for controlling the pressure inside said tank (1) and controlling a valve (4) located on said supply means (6);

- A pump (3) for the transfer of said flame retardant substance, from the container (2) containing the flame retardant substance to the reservoir (1) to be protected;

- auxiliary means (16) for supplying the pressure independently of said pump (3), comprising a compressed nitrogen tank (16) with a corresponding pressure reducer (17) and a valve (19) ;

- Means (11) for the suction in the tank (1) of gases from the upper zone of this tank occupied by the vapors, so as to maintain a constant pressure in this tank during the addition of combustible liquid inside;

- Means (12) for compressing the gases of the flame retardant aspirated from the fuel vapor zone to obtain liquefaction;

- Means (13) for the purification of said liquefied flame-retardant agent.

F

2. Installation according to claim 1, characterized in that the container (2) for the storage of the flame retardant is a tank capable of withstanding the internal pressure.

3. Installation according to claim 1 or 2, caracté¬ ized in that said tank (1) and said container (2) are part of the load-bearing structures of a ship.

4. Installation according to claim 1, characterized in that, to allow washing of the tank (1) having contained the combustible liquid, the container (2) containing at least one flame retardant and the pump (3) ensuring the transfer of the flame retardant in the tank to be protected, ensure the washing of the tank to be protected, because this flame retardant also has the quality of a washing agent, in that it includes means for supplying (27) and injecting (28) in the liquid state the washing agent into the container (2), in that it comprises means (21, 23) for the accumulation of deposits deriving from said washing, in this that it comprises means for heating (23) of said deposits in order to evaporate the washing agent; the means (12) for the compression of the evaporating flame retardant and washing agent gases ensuring its liquefaction during washing; and in that it comprises means (13) for the separation of impurities from said flame retardant and liquefied washing agent.

5. Installation according to claims 1 and 4, characterized in that the transfer of the flame retardant and washing agent is carried out by means of a single pumping means (3) switchable by means of a valve (29) to be able choose one of the two fireproofing and washing functions.

6. Installation according to claims 1 and 4, charac¬ terized in that the suction of the gases of the flame retardant and washing agent evaporated, and the compression of these gases, are carried out by means of a single means d 'suction (11) and compression (12) switchable by means of a valve pre¬ view to ensure choice of each of the two functions of ignition and washing.

7. Installation according to claims 1 and 4, charac¬ terized in that the means for the separation of impure¬ tes of the washing agent, are a single set of purification (13).

8. Installation according to any one of claims 1 to 7, characterized in that the flame retardant and washing agent is halogen gas.

REPLACEMENT SHEET