Device for venting a flammable gas and unit comprising such a device

Abstract

The invention relates to a device (1) for venting a gas flow for a unit for producing and / or transferring a flammable gas such as hydrogen, the device (1) comprising: - a main duct (2) that is vertical in the position of use having a lower end (21) intended to be fluidly connected to the unit; and - a U-shaped secondary duct (4) connected to an upper end (22) of the main duct (2), the secondary duct (4) comprising a first straight portion (41) connected to the upper end (22) of the main duct (2) so as to form a first bend (6) directed downwards, and a second straight portion (42) connected to the first straight portion (41) via a second bend (43) directed upwards, the second straight portion (42) bearing a vent opening (44) located above the second bend (43), characterised in that the first bend (6) and the second bend (43) define an upper point (PH) and a lower point (PB), respectively, which are spaced apart from one another by at least 50 cm, and in that the first straight portion (41) of the secondary duct (4) has a height and a diameter defined according to a height / diameter ratio that is at least equal to 5, preferably at least equal to 10.

Description

Device for venting a flammable gas and unit comprising such a device.

[0001] The invention relates to a device for venting a gas flow for a unit for producing and / or transferring a flammable gas such as hydrogen.

[0002] “Venting” means the release of gas into the atmosphere, in an area far from a heat or energy source, and inaccessible to operators. The gas to be vented will subsequently be referred to as “gas to be released” or “flammable gas”.

[0003] The venting device comprises a main conduit which is vertical in the use position and has a lower end intended to be fluidically connected to the unit for producing and / or transferring a flammable gas. The venting device also comprises at least one U-shaped secondary conduit connected to an upper end of the main conduit.

[0004] In particular, the secondary conduit comprises a first rectilinear portion connected to the upper end of the main conduit so as to form a first downward-facing elbow, and a second rectilinear portion connected to the first rectilinear portion via a second upward-facing elbow.

[0005] The second straight portion of the secondary duct has a vent opening located above the second elbow.

[0006] The venting of a flammable gas from a gas production or transfer unit is carried out in particular when the pressure of this gas within the production or transfer unit reaches a certain threshold which must not be exceeded. In a known manner, this venting is controlled by a regulating valve or a relief valve arranged between the production and / or transfer unit and the venting device.

[0007] When the control valve or relief valve is in the open position, a flow of gas to be discharged is forced back through the vent opening of the venting device. As long as the control valve or relief valve remains open and the pressure of the gas flow to be discharged remains above atmospheric pressure, ambient air cannot flow back through the vent opening.

[0008] After the control valve or relief valve is closed, the pressure of the gas to be discharged, located downstream of this valve or relief valve, decreases. The air then rushes rapidly through the vent opening, counter-current to the gas to be discharged, creating a risk of forming an explosive mixture with the gas to be discharged.

[0009] In view of such a risk, the venting device described above is designed to slow the progression of air introduced through the vent opening, and thus limit the risk of formation of an explosive mixture with the gas to be released.

[0010] Indeed, the second bend of the secondary duct is designed to trap the air introduced counter-currently through the vent opening. Then, due to its density being higher than that of the gas to be discharged (typically hydrogen), the air thus trapped at the second bend rises very slowly by diffusion through the gas to be discharged located upstream of the second bend. The gas to be discharged is said to form a gas lock.

[0011] It should be noted that a purge of the venting device may be provided by means of an inert gas, called a purge gas, such as nitrogen or helium. The purge gas is injected from the lower end of the main duct in order to force the gas to be discharged back through the vent opening and to further reduce the entry of air through the vent opening. Furthermore, in the event of a leak in the control valve or relief valve, a leak of the gas to be discharged may be observed, which tends to rise from the lower end of the main duct.

[0012] The venting device described above is also designed to operate in such a scenario by preventing the formation of an explosive mixture between the vent gas leaking through the control valve or relief valve and the ambient air which tends to rush counter-currently through the vent opening. In this scenario, the inert gas forms a gas slug separating the vent gas and the ambient air.

[0013] If the device described above makes it possible to slow down the diffusion of air through the gas to be discharged, the risk of acceleration of this diffusion remains present, particularly in the case of natural convection of the air (surrounding the vent opening), or in the case of convection of the gas to be discharged (convection induced for example by heating the ducts).

[0014] Such convections promote movements of air molecules and / or gas to be released, and can lead to an explosive mixture between the gas to be released and the air.

[0015] Therefore, it appears necessary to develop a venting device capable of further slowing down the natural convection acting on the air surrounding the vent opening, or acting on the gas to be discharged located downstream of the control valve or relief valve. Similarly, it appears necessary to develop a venting device capable of minimizing the risk of formation of an explosive mixture between the air and the gas to be discharged.

[0016] To this end, according to a first, the invention, moreover in accordance with the generic definition given in the preamble above, is essentially characterized in that the first elbow and the second elbow respectively define a high point PH and a low point PB which are at least 50 cm apart from each other, and in that the first rectilinear portion of the secondary conduit has a height and a diameter which are defined according to a height / diameter ratio at least equal to 5.

[0017] Thus, by providing such a distance between the high point and the low point and such a ratio between the height and the diameter of the first straight portion of the secondary duct, the invention further reduces the diffusion speed of the air in the gas to be discharged.

[0018] Other embodiments of the device include the following features:- the main duct and the secondary duct are connected by a fitting forming the first elbow;- the main duct and / or the secondary duct are each formed from an assembly of pipe elements welded together;- the vent opening is located above the high point;- the vent opening is located at one end of the second straight portion of the secondary duct;- the vent opening faces upwards;- the secondary duct includes a discharge orifice located at the low point;- the discharge orifice is closable by means of a plug;- the vent opening has a diameter of between 25 mm and 250 mm;- the device includes a plurality of secondary ducts regularly distributed around the main duct;- the secondary conduits are connected to the main conduit by means of a star connector and a plurality of elbow connectors fixed to the star connector.;

[0019] According to a second aspect, the invention relates to a unit for storing and / or producing and / or transferring a flammable gas such as hydrogen, said unit comprising a venting device according to any one of the embodiments described above, and a flammable gas collector connected to the lower end of the main conduit of the device.

[0020] Advantageously, the storage unit comprises a source of a sweep gas for discharging the flammable gas through the vent opening of the device and reducing the entry of air through said vent opening.

[0021] Other features and advantages will become apparent upon reading the description below, made with reference to the following figures:

[0022] is a sectional view illustrating a venting device according to a first embodiment of the invention.

[0023] is a sectional view illustrating a venting device according to a second embodiment of the invention.

[0024] As illustrated above, the invention relates to a device 1 for venting a gas flow for a unit for producing and / or transferring a flammable gas such as hydrogen.

[0025] The device 1 comprises a main conduit 2 and a secondary conduit 4 which extends in a general U shape.

[0026] The main conduit 2 and the secondary conduit 4 form a continuous wall delimiting a continuous channel intended for the flow of the gas to be discharged.

[0027] Furthermore, the main conduit 2 and the secondary conduit 4 may be formed from the same piping element, manufactured for example by extrusion or 3D printing; or from separate piping elements which are assembled directly (by welding or other assembly technique) or by means of a fitting.

[0028] By “connection” is meant a mechanical part distinct from the piping elements which respectively form the main conduit 2 and the secondary conduit 4. Such a mechanical part extends between one end of the main conduit 2 and one end of the secondary conduit 4 so that the two conduits 2, 4 are not fitted into each other.

[0029] The main conduit 2 is intended to be arranged vertically in the position of use. To do this, the main conduit 2 has a lower end 21 intended to be fluidically connected to the production and / or transfer unit. The main conduit 2 also has an upper end 22 which is connected to the secondary conduit 4.

[0030] The secondary conduit 4 has a first rectilinear portion 41 which is connected to the upper end 22 of the main conduit 2 so as to form a first elbow 6 facing downwards. The secondary conduit 4 also has a second rectilinear portion 42 which is connected to the first portion 41 via an elbow 43 facing upwards.

[0031] Thus, the first elbow 6, the first rectilinear portion 41, the second elbow 43 and the second rectilinear portion 42 of the secondary conduit 4 are arranged in this order starting from the main conduit 2.

[0032] It should be noted that the second rectilinear portion 42 of the secondary duct 4 has a vent opening 44 through which the gas to be discharged is discharged into the atmosphere. The vent opening 44 is located above the second elbow 43.

[0033] According to the invention, the first elbow 6 and the second elbow 43 respectively define a high point PH and a low point PB which are distant from each other by at least 50 cm and preferably by at least one value between 50 cm and 150 cm, for example 100 cm. In addition, the first rectilinear portion 41 of the secondary conduit 4 has a height and a diameter which are defined according to a height / diameter ratio at least equal to 5.

[0034] Advantageously, the main conduit 2 has a diameter greater than a diameter of the secondary conduit 4. In particular, the diameter of the main conduit 2 is between 2.5 cm and 60 cm. The diameter of the secondary conduit 4 is between 1.3 cm and 36 cm.

[0035] Advantageously, the main conduit 2 has a height (measured from the ground) of between 10 m and 35 m.

[0036] Advantageously, the first rectilinear portion 41 of the secondary conduit 4 can be connected to the main conduit 2 by means of an angular connection or a C-shaped connection. Such a connection forms the first elbow 6.

[0037] Alternatively, the first straight portion 41 of the secondary conduit 4 may be connected to the main conduit 2 directly without the presence of a connector. To do this, the upper end 21 of the main conduit 2 may be beveled. Similarly, the proximal end of the first straight portion 41 of the secondary conduit 4 may be beveled. The two respective beveled ends of the main conduit 2 and of the first straight portion 41 of the secondary conduit 4 may then be assembled by welding or any other assembly technique to form the first elbow 6.

[0038] According to this variant, the first elbow 6 is angular. In other words, the first elbow 6 defines an acute angle (for example 45°).

[0039] Advantageously, the vent opening 44 has a diameter of between 2.5 cm and 25 cm.

[0040] Advantageously, the vent opening 44 can be formed at a free end of the second straight portion 42 of the secondary duct 4. The vent opening 44 then has an axis which merges with a main axis of the second rectilinear portion 42 of the secondary duct 4. The free end of the second rectilinear portion 42 is said to be open.

[0041] Alternatively, the vent opening 44 may be formed through a side wall of the second rectilinear portion 42 of the secondary duct 4, at a certain distance from the free end of this second rectilinear portion 42. According to this variant, the vent opening 44 has an axis which forms a certain angle with the main axis of the second rectilinear portion 42 of the secondary duct 4. The free end of the second rectilinear portion 42 of the secondary duct 4 is closed.

[0042] When the vent opening 44 is formed at the free end of the second straight portion 42, it can be turned upwards. In this orientation, the vent opening 44 can be exposed to precipitation (rain, snow, etc.).

[0043] In order to allow the evacuation of any precipitation introduced through the upwardly facing vent opening 44, the second elbow 43 is provided with a discharge orifice. This orifice can be closed by means of a plug.

[0044] It should be noted that regardless of its positioning or orientation, the vent opening 44 may be equipped with a grid intended to prevent the introduction of debris or the formation of birds' nests in the device 1.

[0045] Advantageously, according to the embodiment illustrated in , the vent opening 44 is located above the first elbow 6. Such positioning of the vent opening 44 makes it possible to protect the venting device 1 in the event of an explosion which could occur at the vent opening 44.

[0046] In a variant illustrated in , the vent opening 42 is located below the first elbow 6, in an intermediate position between the first elbow 6 and the second elbow 41.

[0047] Advantageously, the venting device 1 may comprise a plurality of secondary conduits 4. These secondary conduits 4 may be regularly distributed around the main conduit 2.

[0048] In the example illustrated, the venting device 1 comprises two secondary conduits 4 which extend “in buffalo horns”, on either side of the main conduit 2. These secondary conduits 4 are connected to the main conduit 2 by means of a first T-shaped connector and two elbow connectors.

[0049] In particular, the T-connection has a vertical branch which is fitted or nested in the main conduit 2. The T-connection also has a horizontal (or transverse) branch which has ends each intended to receive an elbow connection. The secondary conduits 4 are fitted or nested respectively in the elbow connections.

[0050] The performance of the venting device according to the invention was evaluated during tests for venting gaseous hydrogen from a production or transfer unit. For these tests, the distance between the high point PH and the low point PB was set at 1 m with a diameter of the secondary conduit 4 equal to 10 cm.

[0051] The venting tests were carried out with the valve (located between the production unit and the venting device) in the closed position, and the venting device filled with hydrogen. Furthermore, these tests were carried out in the presence or absence of a sweep gas (nitrogen) and considering different ambient temperatures.

[0052] After closing the valve located between the production unit and the venting device, the air (consisting of oxygen) quickly enters the latter, then reaches the low point PB before slowly migrating towards the high point PH.

[0053] In a first venting test without sweep gas, the molecular diffusion of oxygen in hydrogen is 0.8 cm2 / s for an ambient temperature equal to 300K. This gives a characteristic time of 3.5 hours to travel 1 m. At lower ambient temperatures, the diffusion of oxygen through hydrogen is even slower, and the characteristic time even longer.

[0054] In a scenario with nitrogen flushing of the venting device, the molecular diffusion of oxygen through nitrogen is 0.2 cm2 / s for an ambient temperature equal to 300K. This gives a characteristic time to travel 1 m of 14h.

[0055] These tests show that the minimum distance between the high point PH and the low point PB as well as the height / diameter ratio of the first portion 41 of the secondary conduit 4, as defined in the invention, lead to a reduction in the diffusion speed of oxygen through the hydrogen or through a sweeping gas, compared with a venting device which does not have these dimensional characteristics.

Claims

Device (1) for venting a gas flow for a unit for producing and / or transferring a flammable gas such as hydrogen, the device (1) comprising:- a main conduit (2) vertical in the position of use and having a lower end (21) intended to be fluidically connected to said unit, and- a U-shaped secondary conduit (4) connected to an upper end (22) of the main conduit (2), the secondary conduit (4) comprising a first rectilinear portion (41) connected to the upper end (22) of the main conduit (2) so as to form a first bend (6) facing downwards, and a second rectilinear portion (42) connected to the first rectilinear portion (41) via a second bend (43) facing upwards, the second rectilinear portion (42) carrying a vent opening (44) located above the second bend (43),characterized in that the first elbow (6) and the second elbow (43) respectively define a high point (PH) and a low point (PB) which are at least 50 cm apart from each other, and in that the first rectilinear portion (41) of the secondary conduit (4) has a height and a diameter defined according to a height / diameter ratio at least equal to 5, preferably at least equal to 10., Device (1) according to the preceding claim, characterized in that the main conduit (2) and the secondary conduit (4) are connected by a connector forming the first elbow (6). Device (1) according to the preceding claim, characterized in that the main conduit (2) and / or the secondary conduit (4) are each formed from an assembly of pipe elements welded together. Device (1) according to any one of the preceding claims, characterized in that the vent opening (44) is located above the high point (PH). Device (1) according to any one of the preceding claims, characterized in that the vent opening (44) is located at one end of the second rectilinear portion (42) of the secondary conduit (4), the vent opening (44) facing upwards. Device (1) according to the preceding claim, characterized in that the secondary conduit (4) comprises an evacuation orifice located at the level of the low point (PB). Device (1) according to the preceding claim, characterized in that the discharge orifice can be closed by means of a plug. Device (1) according to any one of the preceding claims, characterized in that the vent opening (44) has a diameter of between 25mm and 250mm. Device (1) according to any one of the preceding claims, characterized in that it comprises a plurality of secondary conduits (4) regularly distributed around the main conduit (2), the secondary conduits (4) being connected to the main conduit (2) by means of a star connector and a plurality of elbow connectors fixed to the star connector. Unit for storing and / or producing and / or transferring a flammable gas such as hydrogen, said unit comprising a venting device (1) according to any one of claims 1 to 9, and a flammable gas collector connected to the lower end (21) of the main conduit (2) of the device (1). A storage unit according to the preceding claim, comprising a source of a sweep gas for discharging the flammable gas through the vent opening (44) of the device (1) and for reducing the entry of air through the vent opening (44).

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