Technological background of the invention
Technical Field of the invention
[0001] The present invention relates to devices for protection against the propagation of
flames in the presence of explosions and / or detonations caused by any source of
ignition. These protection devices are also known as flame arresters or flame arrestors.
In particular, the present invention relates to the arrangements of flame arrester
blocks for use in such protection devices.
Brief overview of the state of the art
[0002] Flame arresters are devices whose purpose is to extinguish the flame propagation,
for example in the presence of deflagration or detonation, generated by any cause
of ignition.
[0003] Flame arresters are used as protection devices in various application areas, for
example in the petrochemical, chemical, pharmaceutical fields, and, more generally,
wherever in the presence of potentially explosive atmospheres.
[0004] A flame arrester is a device that, while stopping the propagation of flames, allows
the passage of fluids (liquid or gaseous).
[0005] The operating principle on which the 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.
[0006] One type of flame arrester commonly used 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, for example the whole 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).
[0007] A CMR flame arrester is for example described in
WO 94/00197.
[0008] 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.
[0009] 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.
Summary of the Invention
[0010] The Applicant has observed that in spite of their common use, the CMR flame arresters
have some drawbacks.
[0011] 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.
[0012] 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.
[0013] Moreover, the 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.
[0014] 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.
[0015] 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).
[0016] The Applicant has faced the problem to solve these and other drawbacks of the prior
Many of these problems are solved by the stacked parallel plate design of the flame
arrestors such as the ones known from
EP 1 586 350 A1 and
CH 234 193. According to the present invention, there is provided a protection device against
flames and/ or explosions comprising an in-line protection device for the protection
against the spread of flames in the presence of deflagration or detonation, comprising
two flame arrester blocks, where each flame arrester block includes:
- 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.
[0017] The two flame arrester blocks are arranged one opposed to the other with facing second,
closing plates and contained in a jacket, for allowing a bidirectional flow of fluid
and a bidirectional protection against propagation of flames.
[0018] Preferably, the second plate of each flame arrester block is spaced apart from the
first plate by at least one spacer.
[0019] Said at least one first plate may comprise a plurality of first plates stacked one
on the other along said stacking direction, and mutually spaced apart by respective
spacers to define, between adjacent pairs of first plates of said plurality of first
plates, a plurality of interspaces or gaps.
[0020] Said first plate may be in the form of a quadrangular frame, particularly, square-shaped
or rectangular or rhomboidal, elliptical, star-shaped, quadrangular with lobes or
annular-shaped (i.e., having the shape of an annulus).
[0021] Said second plate is preferably of a shape corresponding to the shape of the first
plate, in particular the second plate may be disc-shaped or square-shaped.
[0022] Said at least one spacer may be a washer.
[0023] Said at least one spacer may also be a thickened portion of the material of the first
plate and / or the second plate.
[0024] Said at least one first plate and said second plate are preferably clamped, tightened
to form a pack.
[0025] The flame arrester block that is part of a protection device according to the present
invention is simple to manufacture (being composed of few component parts, each of
which is of simple construction or even already commercially available), assembly
and installation, and therefore is inexpensive.
[0026] In addition, the flame arrester that is part of a protection device according to
the present invention is simple to maintain, because it is easy to disassemble and
reassemble it, 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.
[0027] Another significant advantage of the flame arrester block that is part of a protection
device 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.
Brief description of the appended drawings
[0028] 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 of a flame arrester block;
- Figure 2 shows, partly in section, an exemplary end-of-line protection device with a flame
arrester block;
- Figure 3A shows, in section, a detail of the flame arrester block of Figure 2;
- Figure 3B shows, in section, a detail of an alternative embodiment of the end-of-line protection
device of Figure 2, with two nested flame arrester blocks;
- Figures 4 and 5 show, respectively, in plan view from below and in section along the plane indicated
by V-V in Figure 4, a part of the flame arrester block of Figure 2;
- Figure 6 shows, enlarged, a detail of Figure 5;
- Figure 7 shows the application of flame arrester blocks on a breathing valve for a tank of,
for example, petroleum or its derivatives;
- Figure 8 shows in section an embodiment of an in-line protection device with flame arrester
blocks according to an embodiment of the present invention;
- Figure 9 shows in section another embodiment of an in-line protection device with flame arrester
blocks according to an embodiment of the present invention, and
- Figure 10 shows in section another embodiment of an in-line protection device with flame arrester
blocks according to an embodiment of the present invention.
Detailed description of exemplary embodiments of the invention
[0029] With reference to the drawings,
Figure 1 shows schematically a possible application of a flame arrester block. 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 or a liquid derived from petroleum refining, exhaling vapor
115.
[0030] The tank
105 is provided with a vent duct
125 for venting of flammable vapors
115 which develop internally. At the end of the vent duct
125 an end-of-line protection device
130 is mounted, provided with a flame arrester block 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 is preferably provided with a rain cover
140.
[0031] Figure 2 shows, partly in section, the end-of-line protection device
130 of
Figure 1. In
Figure 3A there is shown, in section, a detail of the flam arrester block which equips the
end-of-line protection device
130 of
Figure 2, while
Figures 4,
5 and
6 show the flame arrester block respectively in bottom plan view, in section along
the plane indicated
V-V in
Figure 4, and in a detail.
[0032] The end-of-line protection device
130 of the example shown on
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 includes, 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.
[0033] On the second end flange
225 there is mounted a flame arrester block
230. In the example considered, above the flame arrester block
230 a 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 not essential).
[0034] The flame arrester block
230 includes a plurality of plates
305, for example metal sheets, preferably made of carbon steel or stainless steel or
special steel, for example having the shape of a circular crown (annulus), 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 plates
305 are of equal diameter, both internal and external. For example, the inner diameter
of the annulus-shaped plates
305 may correspond to the inner diameter of the second end flange
225. The outer diameter of the annulus-shaped plates
305 may correspond to the outer diameter of the second end flange
225.
[0035] At the top (according to the orientation of
Figure 2), the flame arrester block
230 is closed by a closure plate
310 in the shape of a disc (i.e., a circle) of diameter preferably equal to the outer
diameter of the annulus-shaped plates
305. Also the disc-shaped plate
310 may be a metal sheet, preferably made of carbon steel or stainless steel or special
steel.
[0036] The annulus-shaped plates
305 and the disc-shaped closure plate
310 are clamped, tightened to form a pack, being kept suitably spaced apart by spacers
315, such as washers. For clamping the annulus-shaped plates
305 and the disc-shaped closure plate
310 with interposed the respective spacers
315 in a pack, bolts or tie rods
320,
405 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 perimeter of the
disc-shaped closure plate
310, in the vicinity of the outer perimeter of the annulus-shaped plates
305, and advantageously on the second end flange
225.
[0037] Above the disc-shaped closure plate
310, 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 annulus-shaped plates
305. For the assembly of the rain cover
235 (when provided) it is advantageous to exploit the same tie-rods
320 already used for clamping into a pack the plates
305,
310 and the spacers
315 that form the flame arrester block
230. As mentioned above, the provision of the rain cover
235 is however not essential, since the closing plate
310 already performs rain cover functions, preventing the penetration of raindrops within
the hollow body
205.
[0038] The flame arrester block
230 thus formed gives rise to a plurality of radial passages for fluid (vapor or gas),
said passages being transverse, for example substantially orthogonal to the
X axis, and being defined by the interspaces (gaps), created by the spacers
315, between the various pairs of annulus-shaped plates
305 adjacent to each other and by the interspace between the last annulus-shaped plate
305 of the stack and the disc-shaped closure plate
310.
[0039] The thickness of the spacers
315, and then the distance between two adjacent annulus-shaped plates
305, or between the last annulus-shaped plate
305 of the stack and the disc-shaped closure plate
310, are designed such that a possible flame
330 that generates outside the flame arrester block
230 does not propagate inside the hollow body
205 by the action of extinction ("quenching") determined by the transfer of heat from
the flame to the plates
305,
310 of the flame arrester block
230.
[0040] 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 s of the annulus-shaped
plates
305, the distance
d between the adjacent annulus-shaped plates
305 in the stack, and the distance
d between the last annulus-shaped plate
305 of the stack and the disc-shaped closure plate
310, the width (indicated with
L in
Figure 6) of the circular crown formed by each plate
305, the outer diameter
D of the annulus-shaped plates
305, the number of annulus-shaped plates
305 stacked to form the pack, the material of the annulus-shaped plates
305.
[0041] The choice of the values of these constructive parameters depends on the fluid of
the specific application of interest and on the operating conditions of the fluid
in the considered application (for example, pressure and temperature inside the tank
105).
[0042] In particular, the distance between the adjacent annulus-shaped plates
305 and between the last annulus-shaped plate
305 of the stack and the disc-shaped closure plate
310 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 annulus-shaped plates
305 and between the last annulus-shaped plate
305 of the stack and the disc-shaped closure plate
310 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.
[0043] The number of annulus-shaped 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 plates 305 in the stack the pressure drop decreases.
[0044] For example, using annulus-shaped plates
305 having an inner diameter of 200 mm for a class IIA fluid, about 60 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 plates
305, the pressure drop is halved.
[0045] Advantageously, even in the presence of persistent flames
330 (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 to dissipate the generated heat: as shown schematically in
Figure 3A, the flame
330 is not localized at the top of the flame arrester block
230 (which instead happens in the CMR flame arrestors), and then in the area covered
by the rain cover
235, what prevents the dissipation of the heat, but all around the flame arrester block.
[0046] Optionally, one or more CMR flame arrester elements (not shown in the drawings) may
be associated with the flame arrester block
230, by placing the CMR flame arrester elements in series with, preferably upstream,
the flame arrester block
230, for example inside the hollow body
205, e.g. in a position corresponding to the second end flange
225.
[0047] It is also possible to provide two (or, possibly, more) flame arrester blocks
230 arranged concentrically, coaxially (along the
X axis), with one flame arrester block
230 of smaller external diameter
D arranged in a nested way inside another flame arrester block
230 of greater external diameter
D. The two flame arrester blocks
230, preferably not in thermal contact with one another, results in series from the viewpoint
of the fluid path. An example of such an arrangement is visible in
Figure 3B, wherein the outer flame arrester block is denoted
230-e, whereas the inner flame arrester block is denoted
230-i.
[0048] 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 against fire and explosion, for example
for the protection of tanks
105 intended to contain flammable liquids
110, such as oil or its derivates, and which give off flammable vapors
115.
[0049] For example, as shown in
Figure 7, one or more flame arrester blocks
230 can be mounted on a breathing valve
705. Breathing valves are known valve protection devices designed to prevent the deformation
of the tank caused by an increase or a decrease of the tank internal pressure, for
example resulting from the filling or emptying of the tanks with the liquid that they
are intended to contain.
[0050] With reference to
Figure 7, the breathing valve
705 includes a vacuum (underpressure) valve
710 and an overpressure (relief) valve
715 coupled together and in fluid communication. The vacuum valve
710 is activated to compensate (with air from the outside environment) a depression (underpressure)
in the tank to which the breathing valve
705 is applied. The overpressure valve
715 is activated to compensate (by means of vent into the atmosphere) an overpressure
in the tank to which the breathing valve
705 is applied.
[0051] The breathing valve
705 comprises a first valve hollow body
720 for the vacuum valve
710 and a second valve hollow body
725 for the overpressure valve
715, the first and the second valve bodies
720 and
725 being coupled to each other and in fluid communication (in other embodiments, the
first and the second valve bodies
720 and
725 may be a single body). The first valve body
720 includes a flange
730 for the attachment to the tank (or to a flanged pipe in fluid communication with
the interior of the tank), a first opening
735 to put the interior of the first valve body
720 in communication with the atmosphere, and a second opening
737 for fluid communication with the second valve body
725. In the first valve body
720 a first shutter
740 is housed, to selectively open or close the opening
735, said first shutter
740 operating by simple weight force (or by reaction of a spring). The second valve body
725 includes a first opening
745 for fluid communication with the first valve body
720 and a second opening
750 to put the inside of the second valve body
720 in communication with the atmosphere. Inside the second valve body
725 a second shutter
755 is housed, to selectively open or close the second opening
750, said second shutter
755 operating, as the first shutter
740, by simple weight force (or by reaction of a spring).
[0052] Associated with the first opening
735 of the first valve body
720 and the second opening
750 of the second valve body
725 there are a first and a second flame arrester blocks
230-1 and
230-2 of the type described above in relation to
Figures 2-6.
[0053] Above the second flame arrester block
230-2 there is mounted a rain cover
765 (although, as described above, the provision of the rain cover is not essential,
since the closure plate
310 of the second flame arrester blocks performs itself the functions of shelter against
the penetration of raindrops).
[0054] The breathing valve
705 is, thanks to the provision of the two flame arrester blocks
230-1 and
230-2 provided at the openings to the atmosphere of the valve itself, protected against
the propagation of flames that develop in the atmosphere.
[0055] In addition to an end-of-line protection device and to a breathing valve, such as
the end-of-line protection device
130 and the breathing valve
705 described above, the flame arrester block
230 may be associated with other protection devices, such as for example overpressure
valves, underpressure valves and in-line protection devices, such as that shown by
way of embodiment according to the invention in
Figure 8 and indicated therein with reference
805.
[0056] The in-line protection according to the invention
805 is used for example in pipes of petrochemical, chemical, pharmaceutical plants, etc.,
and more generally whenever in the presence of a flammable fluid (vapor or gas), to
allow the flow of fluid but preventing the transmission (propagation) of a possible
flame from a portion of the pipeline to another portion of the pipeline. The flame
may arise for example in the presence of a deflagration or detonation within the pipeline.
In particular, the in-line protection device
805 shown in the figure is bidirectional, to prevent the propagation of flames from both
sides.
[0057] The in-line protection device
805 comprises two junctions having flanged ends
810 and
815 for the attachment to a first and a second portion of a pipeline to be protected
(not shown in the figure). In its central part, the in-line protection device
805 has a pair of flame arrester blocks
230-3 and
230-4 of the type described above in relation to
Figures 2 - 6 opposed to each other, that is, with the respective closing plates
310- 3 and
310-4 facing one another. The two flame arrester blocks
230-3 and
230-4 are accommodated within a jacket
820 of the in-line protection device
805. The arrows in the figure schematize a possible fluid path (the opposite path is
also possible).
[0058] Figures 9 and
10 show other possible embodiments of bidirectional in-line protection devices according
to the invention
905 and
1005, respectively.
[0059] The in-line protection device
905 comprises two junctions having flanged ends
910 and
915 for the attachment to a first and a second portion of a pipeline to be protected
(not shown in the figure). In the central part thereof, the in-line protection device
905 has a pair of flame arrester blocks
230-3 and
230-4 of the type described above in relation to
Figures 2 - 6 opposed to each other, having a common closing plate
310, and forming an assembly. The two flame arrester blocks
230-3 and
230-4 are surrounded by a jacket
920 having a lateral (e.g., cylindrical) wall
920-1 and two end walls
920-2, the end walls
920-2 being attached (e.g., soldered) to a respective one of the junctions
910 and
915. The jacket
920 is tightened between a pair of rings
925 by means of tie-rods
930, preferably arranged in circumferential sequence. Screws
935 secure each one of the rings
925 to a respective one of the end walls
920-2 of the jacket
920. This in-line protection device
905 can be dismounted directly in-situ (i.e., without the need of removing the protection
device from the pipeline), and also enables the in-situ inspection and cleaning of
the flame arrester blocks
230-3,
230-4. The protection device
905 can be opened by loosening the tie-rods
930. In order to gain access to the flame arrester blocks
230-3,
230-4, the screws
935 are unscrewed, so as to make the jacket
920 free to move along the
X axis uncovering the flame arrester blocks
230-3,
230-4. The assembly of the two flame arrester blocks
230-3,
230-4 is held within annular grooves formed in the end walls
920-2 of the jacket
920 (with sufficiently low tolerance in order to avoid the propagation of flames) but
is free to move along the
X axis.
[0060] The in-line protection device
1005 comprises two junctions having flanged ends
1010 and
1015 for the attachment to a first and a second portion of a pipeline to be protected
(not shown in the figure). In the central part thereof, the in-line protection device
1005 has a pair of flame arrester blocks
230-5 and
230-6 of the type described above in relation to
Figures 2 - 6, arranged opposed to each other, with facing closing plates
310-5 and
310-6. The two flame arrester blocks
230-5 and
230-6 are surrounded by a jacket
1020 having a lateral (e.g., cylindrical) wall
1020-1 and two end walls
1020-2, and which is tightened between a pair of rings
1025 by means of tie-rods
1030, preferably arranged in circumferential sequence. Each of the two flame arrester
blocks
230-5 and
230-6 is mounted to a respective one of the jacket end walls
1020-2 by means of tie-rods
1035. Also this in-line protection device
1005 can be dismounted directly in-situ (i.e., without the need of removing the protection
device from the pipeline), by lateral extraction of the jacket
1020 (with the flame arrester blocks
230-5 and
230-6 contained therein) after having loosened the tie-rods
1030. Once the jacket
1020 has been extracted, access to the flame arrester blocks
230-5 and
230-6 can be gained by pulling out the end walls
1020-2 of the jacket
1020.
[0061] Also in the protection devices of
Figures 7 to
10 (as well as in other protection devices like overpressure valves and underpressure
valves) it is optionally possible to associate (in series) one or more CMR flame arrester
elements with the flame arrester block
230, and/or to provide two (or, possibly, more) flame arrester blocks
230 arranged concentrically, coaxially (along the
X axis), with one flame arrester block
230 of smaller external diameter
D arranged inside another flame arrester block
230 of greater external diameter
D.
[0062] Various modifications may be made to the embodiments of flame arrester block
230,
230-1,
230-2,
230-3 and
230-4 described above.
[0063] For example, the spacers
315, rather than being separate parts distinct from the plates
305 and
310, may be formed in a single piece with the plates
305 and / or with the plate
310, providing a thickening of the material thereof, for example in correspondence of
the holes
405.
[0064] The plates
305 and
310 and / or the spacers
315 may be made so as to define, once stacked, generically transverse interspaces, even
if not strictly orthogonal to the
X axis. In particular, the plates
305 do not necessarily have flat surface.
[0065] Furthermore, the annulus-shaped plates
305 may have different shapes, for example elliptical, square, rectangular, diamond-shaped,
star-shaped, lobed. More generally, the plates
305 may be plates of any shape in plan view and having an outer perimeter and at least
one opening in the inner region inside the perimeter.