IL37503A - Dispersal of flammable materials - Google Patents

Description

DISPERSAL OF FLAMMABLE MATERIALS D'j? ,,71 D ' Tain TI T 'S THE PRESENT INVENTION relates to a method and apparatus for the safe dispersal of potentially dangerous concentrations of flammable vapours which are heavier than air.

In the processing, handling or storage of flammable fluids it is clearly desirable to prevent accidental release of the fluid into the atmosphere. Equipment which is to contain the flammable material is designed specially to prevent such accidental release and operation of the equipment is also laid down with this object in view. However, on occasion leakage and spillage of flammable material may occur despite the precautions taken to prevent the accidental release. When release occurs a cloud of heavy vapour may be formed which is capable of travelling considerable distances over the ground in flammable concentrations and which may be ignited by a source of ignition some hundreds of feet from the point of release. This hazard is most apparent in the case of lique ied gases , but it applies equally well to materials which are liquid under ambient conditions, when they are processed or handled at elevated temperaturesΊ The invention is particularly applicable to flammable fluids which are processed, handled or stored at a temperature above their atmospheric boilin point. In designing plant for these purposes it is the aim to arrange the plant equipment so that there is a sufficient distance between potential sources of leakage or spillage and fixed sources of ignition to allow any escape of flammable vapour to disperse safely before the cloud of vapour Baches a source of ignition.

Nevertheless there are circumstances in which a particular plant area may contain a relatively large number of potential sources of leakage or spillage , or in which the provision of an adequate safe distance between the source of a leakage or spillage and a source of ignition is impracticable. The chances of a fire and explosion resulting from an accidental release of fluid may then be unacceptably high. We have now devised a method and equipment for the safe dispersal of concentrations of flammable, heavier than air vapours in such circumstances.

Accordingly, the present invention is a method for dispersing flammable, heavier than air vapour which comprises restraining the horizontal advance of the vapour and, by means of turbulent steam jets, entraining the vapour together with sufficient air to reduce the concentration of vapour below its lower flammability limit .

Flammable vapours which can be dispersed by the method of the present invention, include gases, for example ethylene, and the vapours of liquefied gases, for example liquefied petroleum gas (LPG) , and of liquids, for example petrol.

Although the method will disperse a moving cloud of vapour which has a narrow front , it is preferred to promote spreading of the cloud to a wide front , for example while restraining the horizontal advance of the vapour, since. the entrainment together with air in the steam jets is then made easier.

The present invention also comprises equipment for dispersing a cloud of flammable vapour which comprises a solid barrier at ground level and a steam jet -system associated with the solid barrier to disperse the vapour cloud by entrainment of the vapour with air.

The solid barrier is preferably a firewall which may be made of solid brick but which may also be made of other materials which allow easy building and dismantling of the wall, for example , precast concrete panels and ribbed aluminium sheeting panels. Conveniently the wall is vertical bu it may also be Inclined awa from the vertical, for exam le , a bund wall, provided that it retards advance of the va pour .

Spacing of the solid barrier from the potential source of leakage or spillage may be governed by the proximity of sources of ignition but if possible, it is desirable to allow the cloud, of vapour to broade i s. front before meeting the wall.

Where ci cums ances allow, a suitable spacing of the solid barrier from the potential source of leaka e or spillage is 9 to 1¾ metres, preferably 11 to 3 metres. This spacing in particular is suitable where ethylene is the vapour to be dispersed.

The steam jet system is preferably a pipe, or pipes , perforated with substantially circular holes and supplied with steam under pressure.

The perforated pipe, or pipes, may be positioned on top of the solid barrier or, relative to the source of leakage or spillage, behind or in front of the solid barrier provided always that the relative positioning of solid barrier and the pipe allows substantially no vapour to evade the steam jet system. A preferred arrangement is to position the pipe level with and adjacent to the top of a vertical wall. The pipe may rest on top of the solid barrier or may be level with or below the level of the top of the barrier.

The length of the perforated pipe is preferably at least as great as the distance between the potential source of escape and the solid barrier on which it is placed. Preferably the pipe is long enough to surround the potential source of escape.

Preferably the jets in the perforated pipe are directed upwards so that in operation, vapour reaching the solid barrier and steam jet system is entrained in the jets of steam together with a much larger quantity of air. It is preferred for the steam to issue at at least sonic velocity from the holes 37503/2 ≠' in the perforated pipe or pipes.

To allay spark discharge of static electricity generated by the steam passing through the holes in the perforated pipe it is desirable to ensure that the steelwork of the steam jet system and all other steelwork and electrically conducting material in the vicinity of the steam jets is earthed.

Conveniently, vapour detectors are provided between the potential source of leakage or spillage and the solid barrier to detect and give warning of the presence of flammable vapour. Preferably, the detectors also provide an audible and/or visible signal which, optionally, actuates the steam jet system so that dispersal of the vapour commences as soon as possible after its presence is detected.

The method and apparatus of this invention considerably reduce the risk of fire and explosion attributable to escaping flammable vapours by safely dispersing the vapours relatively quickly. The safe dispersal is achieved either at the point of entrainment of the vapour with the steam.jets or at a relatively short distance beyond that point.

One embodiment of the invention will now be described with reference to the accompanying drawing which is a diagrammatic view in perspective.

The equipment comprises a wall 1 made of precast concrete panels and 1.5 metre high, spaced about 12 metres from a potential source of escape of ethylene from an defines plant 2. A perforated pipe 3 having 1/4 inch diameter holes 4 spaced 6 inches apart was mounted level with the top of the wall 1 to provide a steam curtain 30 metres long. The jets to detect and give warning of the presence of flammabl vapour.

A vapour escape of ethylene at a rate of 7.2 kg/s . was found to require a distance of 88 metres from the escape point for safe dispersal using natural air movement at a wind speed of 2.2 metres/ second.

A similar escape in the same air condi ions was safely dispersed in 28 metres from the escape point using the wall and steam curtain hereinbe ore described. The initial velocity of the steam jets was of the order of 25 metres/second and. the height of the steam curtain formed was 2k metres.

Claims (1)

V H.22810 : G.B. ' 1. A me thod for dispersing flammable eavier- than-air vapotir which comprises restraining the horizontal advance of the vapour and, by means of turbulent steinn jets, entraining the vapour together with sufficieiit air to reduce th^ concentration of vapour below i ts lower flammability limit. 2. Equi ment for dispersing a cloud of lammable, heavier-than-air vapour which comprises a solid barrier at ground level and a steam jet system associated with the solid barrier to disperse the vapour c loud by entrainment of the vapour with air. 2 3. Equipment as claimed in claim Jf wherein the solid barrier is a firewall. k . Equipment as claimed in claim 2 or 3 wherein the solid barrier is made of solid brick, precast concrete panels or ribbed aluminium sheetin panels. 5- Equipment as claimed in claim 2, 3 or k wherein the barrier is vertical. 6. Equipment as claimed in any one of claims: 2 to 5 wherein the spacing of the solid barrier from the potential source of flammable vapour is 9 to 1 metres. 7· Equipment as claimed in claim 6 wherein the spacin is 11 to 13 metres. 8. Equipment as claimed in any one of claims ,2 to 7 wherein the steam jet system is a pipe or pipes perforated with substantially circular holes. H . 2281 0 : G . 9 . Equipment as claimed in claim 8 wherein the perforated pipe or pipes are positioned on top of the solid barrier. 1 0 . Equipment as claimed in claim 8 or 9 wherein the Length of perforated pipe is at least as great as the distance between the potential source of flammable vapour and the solid barrier on which it is placed. 1 1. Equipment as claimed in any one of claims 2 to 1 0 wherein the steam jets are directed upwards. 1 2 . Equipment as claimed in any one of claims 2 to 1 1 wherein vapour detectors are positioned between the potential source of flammable vapour and the solid barrier. 1 3 . Equipment as claimed in claim 2 wherein the vapour detectors upon detection of flammable vapour actuate the steam jet system.

1. . Equipment for dispersing a cloud of flammable vapour substantially as described with reference to the accompanying drawing.