WO2018108965A1

WO2018108965A1 - Flame arrester block for protection devices against the propagation of flames

Info

Publication number: WO2018108965A1
Application number: PCT/EP2017/082518
Authority: WO
Inventors: Federico LA MONTAGNA
Original assignee: F.N.C. - Fabbrica Nazionale Cilindri S.P.A.
Priority date: 2016-12-14
Filing date: 2017-12-13
Publication date: 2018-06-21
Also published as: IT201600126375A1; EP3554649A1

Abstract

Flame arrester block (230) for protection devices against flames propagation, comprising: at least one first plate (305) having an external perimeter and at least one aperture in a region inside the external perimeter; a second, closing plate (405) stacked on the at least one first plate (305) along a stacking direction (X), and, between the at least one first plate (305) and the second plate (405), at least one gap transversal to the packing direction (X). The at least one first plate (305) comprises a portion (325), located between the external perimeter and the at least one aperture, having reduced thermal conductivity, lower compared to the thermal conductivity of the material forming the remaining portion of the first plate (305).

Description

FLAME ARRESTER BLOCK FOR PROTECTION DEVICES AGAINST THE

PROPAGATION OF FLAMES

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DESCRIPTION

Technological background of the invention

Technical Field of the invention

The solution proposed in this document relates to devices for the protection against the propagation of flames in the presence of explosions and / or detonations caused by any source of ignition. Such protection devices are also known as flame arresters (or flame arrestors) or flame traps or deflagration arresters. In particular, the present invention relates to a flame arrester block (or filter) for use in such protection devices.

Brief overview of the state of the art

Flame arresters are devices whose purpose is to extinguish, prevent, interrupt the propagation of flames, for example in the presence of deflagration or detonation, generated by any cause of ignition.

Flame arresters are used as protection devices in various application fields, for example in the petrochemical, chemical, pharmaceutical fields, and, more generally, wherever in the presence of potentially explosive atmospheres. In particular, flame arresters are typically used, still for the purpose of interrupting the propagation of flames, as end-of-line protection devices or as in-line protection devices, and they can also be combined with other protection devices, such as overpressure valves (relief valves or vent valves), underpressure valves or vacuum valves, breathing valves.

A flame arrester is a device that, while stopping the propagation of flames, allows the passage of fluids (liquid or gases).

The operating principle on which flame arresters are based is the extinction of the combustion ("fire quenching" or "combustion quenching") due to the transfer of heat from the flame to a body of thermally conductive solid material at a lower temperature. This transfer of heat is made more efficient by forming, in the body of solid material, several narrow passages, through which the flame is forced to pass.

One type of commonly used flame arrester is called "Crimped Metal Ribbon" or CMR. A CMR flame arrester includes one or more flame arrester elements, each composed of layers of smooth and corrugated thin metal sheets alternated to each other, for example arranged in a generally coaxial way with a central mandrel to form a multilayer cylindrical body, the whole assembly being enclosed within an outer jacket. The spaces created between the corrugations of the corrugated metal sheets and the adjacent smooth metal sheets define a plurality of passages or channels for the fluid. Such passages, for example of approximately triangular section, extend generally parallel to the axis of the cylindrical body (or with a limited angle of inclination relative to the axis of the cylindrical body).

A CMR flame arrester is for example described in WO 94/00197.

A typical process for manufacturing a CMR flame arrester element calls for taking, from respective reels, two smooth metal sheets, creating a ripple on one of the two metal sheets by means of a toothed wheel, and then wrapping like a spiral the two metal sheets on the central mandrel.

Typically, in CMR flame arresters, one or more flame arrester elements are arranged in axial succession, with interposed spacing elements to generate turbulence in order to increase the heat exchange efficiency and thus ensure the stopping of the flame without having to increase the number of flame arrester elements.

WO 2015/091747, in the name of the present Applicant, discusses that, despite their common use, CMR flame arresters show a number of drawbacks.

For example, they can be easily damaged during handling, in particular during maintenance operations. The damage can cause the alteration of the size of the passages for fluids, which may result in the extremely dangerous inability to stop the propagation of the flame, or the misalignment of the metal sheets, which can result in increased pressure drops.

Also, since the size of the passages or channels for fluids are extremely limited, such passages can easily be clogged by deposits, which makes a periodic maintenance of the flame arresters essential.

Moreover, CMR flame arresters involve a significant pressure drop. The pressure drop depends on the internal construction of the CMR flame arrester, i.e. on the number of flame arrester elements, on the cell size of the elements ("gap" or height of the passages or channels for the fluid), the height of the elements, on the inclination of the passages or channels of the elements and on the thickness of the metal sheets that compose the elements. This pressure drop is a function of the flow rate, the fluid type and its physical condition, and increases greatly when the flame arrester element becomes dirty, with the consequent obstruction of the passages or channels. The dirtying can be very high in the case of fluids containing impurities and sticky fluids. Another drawback of CMR flame arresters is their relative complexity of construction, given the rather large number of different parts of which they are composed (central mandrel, smooth metal sheets, undulated metal sheets, external jacket), which require specific processes for their manufacture using dedicated automatic or semi-automatic machines that make the assembling rather complex. All this makes CMR flame arresters quite expensive. Another consequence of the complexity of construction of CMR flame arresters is that they, once assembled, cannot be completely disassembled for cleaning, because it would be virtually impossible to reassemble them and ensure the initial security. For their clearing, it is necessary to resort to the use of solvents or high pressure steam (the only way to penetrate into the interstices of the CMR flame arrester), and the operations are therefore complex, lengthy and sometimes not entirely effective.

Furthermore, it is critical to obtain high accuracy and repeatability of the production, and a robustness of the flame arrester element against flexion and deformation. It is not easy to obtain a low ovalization of the flame arrester elements (determined by the spiral winding of the metal sheets on the central mandrel).

Still in WO 2015/091747 there is described a flame arrester block for protection devices against the propagation of flames, different from the CMR flame arrester element, and comprising: at least one first plate having an outer perimeter and at least one opening in a region internal to the outer perimeter, and a second, closure plate stacked on said at least one first plate along a stacking direction and spaced apart from the at least one first plate so as to define, between said at least one first plate and said second plate, a gap transverse to said stacking direction.

Summary of the Invention

According to the solution proposed in the present document, there is provided a flame arrester block of filter for use in protection devices against the propagation of flames, whether they are a consequence of explosions or detonations. In particular, the solution proposed herein relates to a flame arrester block of the type described in WO 2015/091747, with improved features.

The flame arrester block according to the solution proposed herein comprises:

- at least one first plate having an outer perimeter and at least one opening in a region internal to the outer perimeter;

- a second, closure plate stacked on said at least one first plate along a stacking direction, and

- at least one gap, transverse to said stacking direction, between said at least one first plate and said second plate.

Said at least one first plate comprises a portion, located between the external perimeter and the at least one aperture, having reduced thermal conductivity, lower compared to the thermal conductivity of the material forming the remaining portion of the first plate.

Said at least one first plate is preferably flat or essentially flat.

Said second, closing plate is preferably flat or essentially flat.

In exemplary embodiments, said portion of the at least one first plate having reduced thermal conductivity may comprise at least one interruption of the material forming the first plate.

In exemplary embodiments, said interruption of material may comprise at least one slot passing through the first plate in the direction of the thickness thereof (i.e. in the stacking direction).

In exemplary embodiments, said portion of the at least one first plate having reduced thermal conductivity may comprise a portion of the first plate in a material having a thermal conductivity lower than that of the material forming the remaining portion of the first plate.

In exemplary embodiments, said at least one first plate may comprise a plurality of first plates stacked over each other along said stacking direction and mutually spaced apart by means of respective spacers for defining, between adjacent pairs of first plates of said plurality, a plurality of said gaps.

In exemplary embodiments, the second plate may be spaced apart from the at least one first plate by means of at least one spacer.

In exemplary embodiments, said at least one spacer may comprise washers which are separated parts, separated from the at least one first plate and from the second plate.

In exemplary embodiments, said at least one spacer may comprise thickened portions of the material of the at least one first plate and/or of the second plate, deep drawn parts of the at least one first plate and/or of the second plate.

In exemplary embodiments, said at least one first plate and said second plate are tightened to form a pack.

In exemplary embodiments, said first plate may have the shape of a quadrangular frame, particularly a square or rectangular or rhomboidal frame, an ellipsoidal frame, a star-shaped frame, a frame with lobes, a quadrangular frame or an annulus-shaped frame, and preferably said second plate may have a shape correspondent to the shape of the first plate, particularly disc-shaped or quadrangular.

The flame arrester block or filter according to the solution proposed herein is simple to manufacture (being composed of few component parts, each of which is of simple construction or even already commercially available), and easy to assemble and install, and therefore is inexpensive.

In addition, the flame arrester block according to the solution proposed herein is simple to maintain, because it is easy to disassemble and reassemble, and moreover the cleaning can also be performed with normal abrasive systems and without the need to resort to the use of solvents or high pressure steam.

Another significant advantage of the flame arrester block according to the present invention is its modularity: in fact, by increasing the number of stacked (and mutually spaced apart) plates, pressure drops can be reduced substantially at will, without compromising the performance in terms of the ability to stop the propagation of flames.

A very important advantage of the flame arrester block according to the solution proposed herein is that it reduces the transmission of heat from the outer periphery of the flame arrester block toward the interior thereof: this has the advantageous consequence that, even in conditions of persistent flames outside the flame arrester block, the temperature at the interior of the flame arrester block does not rise at dangerous levels.

The present document also proposes a protection device against fires and/or explosions, comprising at least one flame arrester block according to the solution disclosed in the foregoing, and wherein said protection device comprises at least one among: an end-of-line protection device, an in-line protection device, an overpressure valve, an underpressure valve, a breather valve, for the protection against the propagation of flames in presence of deflagrations or detonations.

The protection device may be used in a reservoir or tank of a plant, particularly a petrochemical plant or a chemical plant or a pharmaceutical plant or the like, wherein the reservoir is intended to contain a flammable liquid exhaling flammable vapors. The reservoir may be provided with a vent duct for venting the flammable vapors which develop internally to the reservoir (105). The protection device may be mounted to the vent duct.

The protection device may equip a pipeline for transporting flammable fluids in a plant, particularly a petrochemical plant or a chemical plant or a pharmaceutical plant or the like.

In the present document a solution is also proposed for a flame arrester block comprising:

Said at least one first plate, and possibly said second plate, comprise drawn or deep-drawn parts forming spacers for obtaining said at least one gap.

Brief description of the appended drawings

These and other features and advantages of the present invention will be made apparent by the following detailed description of possible exemplifying and not restrictive embodiments of the present invention, description that will be carried out referring to the accompanying drawings. In the drawings:

- Figure 1 schematizes a possible application to an end-of-line protection device of a flame arrester block according to an embodiment of the solution proposed in the present document;

- Figure 2 shows, partly in section, an embodiment of the end-of-line protection device of Figure 1;

- Figure 3 shows, in plan view, a plate of the flame arrester block of the protection device of Figure 2;

- Figure 4 shows, enlarged, a detail of Figure 2, and

- Figures 5 and 6 show, respectively, in plan view and in section along a diametral plane, an embodiment of spacers between plates of the flame arrester block.

Detailed description of exemplary embodiments of the invention

With reference to the drawings, Figure 1 shows schematically a possible application of a flame arrester block or flame arrester filter according to an embodiment of the solution proposed in the present document.

Reference 105 indicates a reservoir, for example a tank of a petrochemical plant (or a chemical plant, a pharmaceutical plant, etc.). The tank 105 is intended to contain a flammable liquid 110, for example oil (petroleum) or a liquid derived from petroleum refining, exhaling flammable vapors 115.

The tank 105 is provided with a vent duct 125 for venting the flammable vapors 115 which develop internally to the tank 105. At the end of the vent duct 125 an end-of-line protection device 130 is mounted, provided with a flame arrester block or filter to stop the potential propagation of flames along the vent duct 125 and within the reservoir 105 in the presence of deflagrations that trigger the combustion of the flammable vapors 115, for example explosions triggered by an electrical discharge, for example due to atmospheric events such as lightning 135 from storm clouds. The end-of-line protection device 130 may be provided with a rain cover 140.

Figure 2 shows, partly in section, an exemplary embodiment of the end-of-line protection device 130 of Figure 1, comprising a flame arrester block according to an embodiment of the solution proposed herein.

The end-of-line protection device 130 of the exemplary embodiment of Figure 2 comprises a hollow body 205 comprising a first end flange 210 for mounting, for example, to the vent duct 125 shown in Figure 1. The hollow body 205 comprises, starting from the first end flange 210, a first portion 215, for example substantially cylindrical, followed by a second portion 220, for example conical, terminating in a second end flange 225.

On the second end flange 225 there is mounted a flame arrester block or filter 230 according to an embodiment of the solution proposed herein. In the example considered, above the flame arrester block 230 the rain cover 235 is mounted (however, as explained below, thanks to the structure of the flame arrester block according to the present invention, the provision of rain cover 235 is optional and not essential).

The flame arrester block 230 comprises one, two or more, preferably a plurality of first plates 305, each having an outer perimeter and at least one opening in a region internal to the outer perimeter, for example of the type shown (in plan view) in Figure 3 and indicated 305 therein. Preferably, the first plates 305 are flat or essentially flat plates. The first plates 305 are for example flat or essentially flat metal sheets, preferably made of carbon steel or stainless steel or special steel. The first plates 305 have for example the shape of a circular crown (annulus), having an outer perimeter 315 and an opening 320 formed in a region internal to the outer perimeter 315, and they are stacked along the longitudinal axis X of the end-of-line protection device 130 corresponding to the axis of the inner hole of the hollow body 205. Preferably, the annulus-shaped first plates 305 are of equal diameter, both internal and external. For example, the inner diameter of the annulus-shaped first plates 305 may correspond to the inner diameter of the second end flange 225. The outer diameter of the annulus-shaped first plates 305 may correspond to the outer diameter of the second end flange 225.

At the top (according to the orientation of Figure 2), the flame arrester block 230 is closed by a second, closure plate, better visible in the enlargement of "detail A" of Figure 2 shown in Figure 4 and indicated as 405 therein. The second, closure plate 405 is for example shaped as a disc (i.e., a circle) and has diameter preferably equal to the outer diameter of the annulus-shaped first plates 305. Also the disc-shaped second, closure plate 405 is preferably a flat or essentially fiat plate. The disc-shaped second, closure plate 405 may be a flat or essentially flat metal sheet, preferably made of carbon steel or stainless steel or special steel.

The first plates 305 and/or the second, closure plate 405 can be produced starting from fiat metal (e.g., carbon steel or stainless steel or special steel) sheets, by laser cut and/or water jet cut and/or plasma cut.

As better visible in Figure 4, the first plates 305 and the second, closure plate 405 are clamped, tightened to form a pack. The first plate 305 at the bottom of the stack or pack of first plates 305 rests on the second end flange 225. Pairs of consecutive first plates 305 of the stack or pack of first plates 305 are kept suitably spaced apart from each other by means of spacers 410, for example being separated parts from the first plates 305. The spacers 410 are for example washers. The second, closure plate 405 can rest on the first plate 305 at the top of the stack or pack of first plates 305 (as in the example shown in the figure) or it can be spaced apart from the first plate 305 at the top of the stack by means of spacers similar to the spacers 410, for example being separated parts from the first plates 305 and from the second plate 405. For clamping in a pack the stacked first plates 305 and second, closure plate 405 with interposed the respective spacers 410, bolts or tie rods 415 may be used (as in the example shown), inserted in through holes formed in circumferential succession and in corresponding positions in the vicinity of the outer perimeter of the first plates 305, and in corresponding through holes formed (still in circumferential succession) in the vicinity of the outer perimeter of the second, closure plate 405, and of the second end flange 225.

Above the second, closure plate 405, the rain cover 235 can be mounted, being a substantially cap-shaped element with a diameter preferably greater than the diameter of the flame arrester block 230, that is, preferably greater than the outer diameter of the first plates 305. For the assembly of the rain cover 235 (when provided) it is advantageous to exploit the same tie-rods 415 already used for clamping into a pack the first and second plates 305, 405 and the spacers 410 that form the flame arrester block 230. As mentioned above, the provision of the rain cover 235 is however not essential, since the closure plate 405 already performs rain cover functions, preventing the penetration of raindrops within the hollow body 205. Possibly, the size in plan view (e.g., the diameter) of the second, closure plate 405 can be increased with respect of the size in plan view (e.g. the outer diameter) of the first plates 305. The flame arrester block 230 thus formed gives rise to an inner passage 417 (central in the shown example) for the fluids (vapors or gases) coming for example from the tank 105, which inner passage 417 is defined by the apertures formed in the region internal to the outer perimeter of the first plates 305. The inner passage 417 extends along the X axis (i.e., along the direction of stacking of the first plates 305 and the second plate 405), it is closed at the top by the second plate 405, and a plurality of radial passages departs from the inner passage 417. Said radial passages are transverse, for example substantially orthogonal to the X axis, and are defined by the interspaces (gaps), created by the spacers 410, between the various pairs of first plates 305 adjacent to each other (and possibly by the interspace between the first plate 305 of the top of the stack and the second, closure plate 405).

The thickness of the spacers 410, and thus the distance between two first plates 305 (and, possibly, between the first plate 305 at the top of the stack and the second, closure plate 405), that is, the height (along the direction X) of the gaps, are designed such that a possible flame 420 that generates outside the flame arrester block 230 does not propagate inside the hollow body 205 thanks to the action of extinction ("quenching") determined by the transfer of heat from the flame 420 to the first plates 305 and the second plate 405 of the flame arrester block 230.

Advantageously, even in the presence of persistent flames 420 (so-called "endurance burning"), i.e. flames that are not extinguished after a short time but remain for an indefinite time, it is not necessary to provide systems for opening the rain cover 235 (if provided) to dissipate the generated heat: as shown schematically in Figure 4, the flame 420 is not localized at the top of the flame arrester block 230 (which instead happens in the CMR flame arrestors), and then the flame is not localized in the area covered by the rain cover 235 (what would prevent the dissipation of the heat), but rather the flame is localized all around the flame arrester block 230.

According to an embodiment of the solution proposed in the present document, the first plates 305 (all of them, or at least some of the first plates 405 in the stack) are made in such a way to have a portion, located between their outer perimeter and the at least one aperture in the region internal to the outer perimeter, having reduced thermal conductivity, lower compared to the thermal conductivity of the material (e.g., carbon steel or stainless steel or special steel, as mentioned in the foregoing) of which the first plates 305 themselves are made.

For example, as visible in Figure 3, such portion having a reduced thermal conductivity is formed by one or more slots 325 formed in a portion of the first plates 305 which is intermediate between the outer perimeter 315 and the opening 320. In the example here considered, the slots 325 have the same depth as the thickness of the first plates 305, i.e. the slots 325 perforate, pierce the first plates 305 from side to side, however nothing prevents from making slots having minor depth. Still in the example here considered, the slots 325 are a circumferential succession of slots having the shape of a sector of an annulus (sector of circular crown), mutually separated by portions 330 of the material (e.g., steel) of which the first plates 305 are made. The slots 325 form a portion with reduced thermal conductivity because the air gap which originates from the slots 325 has a thermal conductivity lower than the thermal conductivity which would be exhibited by portion of full material. The slots 325 can for example be removed, excised, cut out material portions of the material forming the first plates 305, formed by laser cut and/or water jet cut and/or plasma cut of the flat metal sheet from which the first plates 305 are obtained.

The provision, in the first plates 305, of the aforesaid portion with reduced thermal conductivity allows to reduce the heat transmission from the outer region of the first plates 305, close to their outer perimeter, towards the inner region of the same. This is important since in case of a considerable heating of the outer peripheral portion of the first plates 305 caused by the flame 420, the inner part of the first plates 305, with which the flammable vapors 115 exhaling from the fluid contained in the tank 105 come into contact, does not reach such temperatures as to ignite the vapors themselves. The robustness of a protection device, such as for example the end-of-line device 130, to such operating conditions is also one of the homologation tests that a protection device must overcome. In particular, in the "endurance burning" tests, a continuous flow of certain fluids (belonging to different hazard classes depending on the application for which the protection device is intended) is made to flow through the protection device, and a flame is ignited outside the protective device (such as the flame 420 in Figure 4). The flow of gas, and consequently the flame, is maintained for a certain period of time, typically 2 hours, and by means of temperature sensors it is verified that the protection device reaches and maintains a condition of thermal equilibrium, with the temperature inside of the protection device which rises up to reach and maintain a certain temperature, lower than that which would cause the flame to propagate inside the protection device itself. Once this time has elapsed, the flow of gas is interrupted and, consequently, the flame 420 is extinguished due to lack of fuel, but the loss of the gas flow (to which the flame arrester block gave off part of the heat) can cause an increase of the temperature of the inner part of the flame arrester block, to the point of triggering a flame in the part upstream of the protection device. Thanks to the provision, in the first plates 305, of the aforesaid portion with reduced thermal conductivity, the heat transmitted by the outer region of the first plates 305, close to their external perimeter, towards the inner region thereof, and consequently the temperature at the interior of the protection device rises less, even after the flow of fluid has stopped. The constructive parameters that determine the composition of the flame arrester block 230 are few and simple, and are summarized in the following: the thickness first plates 305, the distance between the adjacent first plates 305 in the stack (possibly, the distance between the first plate 305 at the top of the stack and the second, closure plate 405), the width of the first plates 305, the outer diameter of the first plates 305, the number of first plates 305 stacked to form the pack, the material of the first plates 305.

The choice of the values of such constructive parameters depends on the fluid of the specific application of interest and the operating conditions of the fluid itself in the considered application (for example, pressure and temperature in the tank 105).

In particular, the distance between the first plates 305 adjacent in the stack (and possibly between the first plate 305 at the top of the stack and the second, closure plate 405) may be of the order of magnitude of the value of the parameter known as MESG ("Maximum Experimental Safe Gap") related to the particular fluid of interest for the specific application from time to time considered. The MESG parameter is defined in ISO 16852, which is the reference standard for the test of flame arresters. For example, the reference standard establishes that the value of the MESG for class IIA fluids (e.g. propane) is 0.9 mm, the value of the MESG for class IIB3 fluids (for example ethylene) is of 0.65 mm, and the value of the MESG for class IIC fluids (e.g. hydrogen) is 0.5 mm. Given the specific fluid of the application of interest, the distance between the adjacent first plates 305 in the stack (and possibly between the first plate 305 at the top of the stack and the second, closure plate 405) is advantageously chosen so as to be less than or at most equal to the value of the MESG established by the standard for that fluid.

The number of first plates 305 to be stacked to form the flame arrester block 230 depends instead on the maximum acceptable pressure drop. By increasing the number of first plates 305 in the stack the pressure drop decreases.

For example, using annulus-shaped first plates 305 like those shown in the drawings, having an inner diameter of 200 mm for a class IIA fluid, about 60 first plates 305 spaced apart by about 0.9 mm can be provided, if it is desired to have full flow, that is, without reduction of the flow section of the gas. By doubling the number of first plates 305, the pressure drop is halved.

The flame arrester block 230 described above, in addition to being applicable to an end-of- line protection device 130, can be applied to other protection devices, for example for the protection of tanks 105 intended to contain flammable liquids 110, such as oil (petroleum) or its derivates, and which give off flammable vapors 115. For example, one or more flame arrester blocks 230 can be mounted on overpressure / depression (vacuum) valves (valve protection devices designed to prevent tank deformation caused by an excessive increase/decrease in the pressure inside the tanks, for example as a consequence of filling/emptying of the tanks with the liquids they are designed to contain), breathing valves (valve protection devices that combine the functions of overpressure valves and vacuum valves), mono-or bi-directional protection devices (protection devices used for example in pipelines of petrochemical, chemical, pharmaceutical plants, etc., and more generally whenever there are flammable fluids - vapors or gases, to allow the flow of the fluid but to prevent the transmission - propagation - of a possible flame from one part of the pipeline to another part of the pipeline, which flame may, for example, occur in the presence of a deflagration or detonation within the conduit).

Various modifications may be made to the embodiments of flame arrester block 230 described above.

For example, the spacers 410, rather than being separated parts from the first plates 305 (and from the second plate 405), can be formed in one piece with the first plates 305 (and possibly with the second plate 405), providing a thickening of the material of the first plates 305 (and possibly of the second plate 405), and / or an appropriate deformation / drawing of the first plates 305 (and possibly of the second plate 405), so as to form a sort of suitably protruding bosses, for example in correspondence with the holes 310. For example, as shown in Figures 5 and 6, bosses 505 protruding from a face of the first plates 305 (and possibly of the second plate 405) may be formed, or protruding from both faces of the first plates 305. The bosses 505 may for example be formed at the holes 310; for example, as shown in Figures 5 and 6, it is possible to provide pairs of bosses 505 in correspondence with each hole 310, for example on opposite sides of the hole 310 itself. Other arrangements of the bosses 505 are also possible. It is emphasized that there is nothing preventing the application of the bosses 505 also to the plates of a flame arrester block of the type described in WO 2015/091747 (therefore not necessarily in combination with the solution proposed in this document).

The first plates 305, the second plate 405 and / or the spacers 410 can be made so as to define, once stacked, generally transverse interspaces, even not strictly orthogonal to the X axis. In particular, the first plates 305 do not necessarily have a flat surface.

Moreover, the first plates 305 may have shapes different from an annulus (circular crown shape), for example they may have ellipsoidal, square, rectangular, rhomboidal, star-shaped or lobed shapes. More generally, the first plates 305 may be plates of any shape in plan, having an outer perimeter and at least one opening in the region inside the perimeter. As an alternative to (or in combination with) grooves 325, multiple holes (through holes or not) may be provided in the material of the first plates 305. As a further alternative, the first plates 305 may be made in such a way as to have a portion, for example an intermediate band between the external perimeter 315 and the opening 320, made of a material having a low thermal conductivity with respect to the remaining material, for example a refractory material.

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Claims

1. Flame arrester block (230) for protection devices against flames propagation, comprising:

- at least one first plate (305) having an external perimeter and at least one aperture in a region inside said external perimeter;

- a second, closing plate (405) stacked on said at least one first plate (305) along a stacking direction (X), and

between said at least one first plate (305) and said second plate (405), at least one gap transversal to said packing direction (X),

characterized in that

said at least one first plate (305) comprises a portion (325), located between the external perimeter and the at least one aperture, having reduced thermal conductivity, lower compared to the thermal conductivity of the material forming the remaining portion of the first plate (305).

2. Flame arrester block according to claim 1 , wherein said at least one first plate (305) is flat or essentially flat.

3. Flame arrester block according to claim 1 or 2, wherein said second, closing plate (405) is flat or essentially flat.

4. Flame arrester block according to any one of the preceding claims, wherein said portion (325) of the at least one first plate (305) having reduced thermal conductivity comprises at least one interruption of the material forming the first plate (305).

5. Flame arrester block according to claim 4, wherein said interruption of material comprises at least one slot passing through the first plate (305).

6. Flame arrester block according to any one of claims 1 to 3, wherein said portion (325) of the at least one first plate (305) having reduced thermal conductivity comprises a portion of the first plate in a material having a thermal conductivity lower than that of the material forming the remaining portion of the first plate (305).

7. Flame arrester block according to any one of the preceding claims, wherein said at least one first plate (305) comprises a plurality of first plates (305) stacked over each other along said stacking direction (X) and mutually spaced apart by means of respective spacers (315;505) for defining, between adjacent pairs of first plates (305) of said plurality, a plurality of said gaps.

8. Flame arrester block according to any one of the preceding claims, wherein the second plate (405) is spaced apart from the at least one first plate (305) by means of at least one spacer.

9. Flame arrester block according to claim 7 or 8 when depending on claim 2 or 3, wherein said spacers comprise washers (410) which are separated parts, separated from the at least one first plate (305) and from the second plate (405).

10. Flame arrester block according to claims 7 or 8, wherein said spacers comprise thickened portions of the material of the at least one first plate (305) and/or of the second plate (310), deep drawn parts (505) of the at least one first plate (305) and/or of the second plate.

11. Flame arrester block according to any one of the preceding claims, wherein said at least one first plate (305) and said second plate (405) are tightened to form a pack.

12. Flame arrester block according to any one of the preceding claims, wherein said first plate (305) has the shape of a quadrangular frame, particularly a square or rectangular or rhomboidal frame, an ellipsoidal frame, a star-shaped frame, a frame with lobes, a quadrangular frame or an annulus-shaped frame, and preferably said second plate (405) has a shape correspondent to the shape of the first plate, particularly disc-shaped or quadrangular.

13. Protection device against fires and/or explosions, comprising at least one flame arrester block according to any one of the preceding claims, wherein said protection device comprises at least one among: an end-of-line protection device, an in-line protection device, a pressure valve, a depression valve, a breather valve, for the protection against the propagation of flames in presence of deflagrations or detonations.

14. A reservoir or tank (105) of a plant, particularly a petrochemical plant or a chemical plant or a pharmaceutical plant or the like, the reservoir (105) being intended to contain a flammable liquid (110) exhaling flammable vapors (115), the reservoir (105) being provided with a vent duct (125) for venting the flammable vapors (115) which develop internally to the reservoir (105), and, mounted to the vent duct (125) an end-of-line protection device (130) according to claim 13.

15. A pipeline for transporting flammable fluids in a plant, particularly a petrochemical plant or a chemical plant or a pharmaceutical plant or the like, the pipeline being equipped with a protection device according to claim 13.