The present invention relates to bellows safety valves used on cryogenic fluids.
A bellows valve comprises a circuit for fluid conveyed through a valve body, a sealing member that can move between a rest position and an active position, taken from an open position and a closed position of said circuit, and a resilient annular bellows system for connection between said sealing member and said body, sealing off said circuit.
Bellows valves are safety devices which, by their design, make it possible to accommodate a high back-pressure at exhaust thereof. To do so, it is essential for the body of the valve, called the bonnet, to be in pressure balance with the outside. The balancing function is provided by the vent of the bonnet, and therefore it is essential for this vent not to be obstructed, as indicated in the API 520 standard.
Because of the abovementioned constraints, the use of bellows safety valves in cryogenics is not recommended, or even sometimes prohibited because of the risk of the valve being blocked by the accidental presence of ice 9 in the bellows 5 (
The presence of ice 9 (
The presence of water may occur through two effects:
The low temperature may be due to various causes:
To overcome the aforementioned problems, it is possible to make use of another valve technology, namely control valves, but the cost of these is substantially higher.
The invention described below makes it possible at very low cost to use the technology of bellows valves in cryogenics by overcoming the aforementioned drawbacks.
As described above, it is the conjunction of two events that make it dangerous to use bellows valves in cryogenics, namely:
Since the temperature is a parameter on which they may be little influence, the solution consists in permanently having an atmosphere free of any moisture in the cavity formed by the bonnet of the valve (which cavity is in contact via orifices with the inside of the bellows).
According to one subject of the invention, what is provided is a valve of the type comprising a circuit for fluid conveyed through a valve body, a sealing member that can move between a rest position and an active position, taken from an open position and a closed position of said circuit, and a resilient annular bellows system for connection between said sealing member and said body sealing off said circuit, the fluid circuit being open to the outside of the valve through a vent formed in the body, and the vent being provided with means preventing the ingress of wet gas into the body, characterized in that a tube is connected to the vent, this tube being connected to a source of pressurized dry gas.
According to other optional aspects, the valve comprises:
According to another aspect of the invention, what is provided is the use of a valve as described above at a temperature below 0° C., or even below −50° C.
According to another aspect of the invention, what is provided is a gas separation unit operating by distillation at a temperature below 0° C. in an enclosure, the walls of which are scavenged by a dry gas, the unit including a valve as described above, the fluid being a gas intended for or coming from the distillation and the tube being connected to a wall of the enclosure so that the dry scavenging gas penetrates the tube.
The unit is optionally provided with bellows rupture detection means.
The unit may be a gas separation unit operating by distillation at a temperature below 0° C. that includes a valve as described above, the fluid being a gas intended for or coming from the distillation.
The invention will be described in greater detail with reference to the figures that illustrate the four families of solutions according to the invention:
For all the figures, the basic structure of the bellows valve, illustrated in
In
In
In
A filter element 33 will be installed on the end of the dip tube 35 so as to prevent any entry of perlite.
A T-piece 35 equipped with a plug 29 may also be installed so as to carry out measurements for detecting any rupture of the bellows 5.
Number | Date | Country | Kind |
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0952977 | May 2009 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FR2010/050816 | 4/29/2010 | WO | 00 | 11/4/2011 |