Patent Application
20110297273
The present invention relates to methods for filling a container or tank with a cryogenic liquid such as liquid nitrogen, from a primary container or storage unit, said filling operation exploiting a difference in pressure and gravity between the storage unit and the tank.
The invention is particularly concerned with filling tanks present in trucks used to transport and distribute heat-sensitive products, such as pharmaceuticals and food products.
One of the techniques employed in this type of truck (called indirect injection) uses one (or more) heat exchangers (for example simple coils), conveying a cryogenic fluid, the chamber also being equipped with an air flow system (fans) making said air contact the cold walls of the heat exchanger, thereby serving to cool the air inside the cold chamber of the truck, the cryogenic fluid supplied to the heat exchanger or exchangers originating from a tank of cryogenic fluid conventionally located under the truck.
One of the problems arising here stems from the fact that during the filling operation, a non-negligible portion of the cryogenic liquid is converted to the gas phase in the tank. Thus, to preserve the requisite pressure difference between the storage unit and the tank, the gas must be discharged from the tank via a gas outlet.
The valves controlling, on the one hand, the cryogenic liquid feed to the tank and, on the other hand, the gas outlet of the tank, must be open while the tank is being filled, and closed at the end of the filling operation. The end of the filling operation may be recognized automatically by suitable means or else manually by the operator.
As will be understood, it is necessary to have, between the storage unit and the tank, elements for controlling the flow rate and the opening/closure (valves) of the channel for supplying the tank with cryogenic liquid. Thus, in the following description, all of these elements (their type, assembly, operation) are comprehensively referred to as “filling station”.
At present, this filling operation is generally managed by one of the following procedures:
a) In a first approach, the filling station comprises a single manual valve. A hose for transferring liquid nitrogen connects the filling station (that is to say, the manual valve) with the tank. The gas created during injection is discharged from the tank to the exterior in an uncontrolled manner. The operator decides to terminate the filling operation when he visually detects liquid particles in the gases discharged from the tank. After stopping the filling operation, the operator purges the hose.
The drawbacks of this solution, which is basically empirical, can be summarized as follows:
In fact, in the case of such a manual filling operation, the gas outlet line of the tank is opened or closed using a manual valve present on the tank. Said valve allows for complete opening/closure. During the filling operation, the manual valve is open, the gas is discharged and the tank is then at atmospheric pressure.
If we consider an application of the use of liquid nitrogen from the tank, requiring a minimum pressure of 2 to 2.5 bar, it is clear that this manual procedure is unable to deliver said minimum pressure. It would therefore be necessary to wait for the heat intake to raise the pressure in the tank, and in practice it is necessary to install a pressurizing system (vaporizer).
b) Another type of approach has been proposed, in which the filling operation is stopped when the tank is full, for example by adding elements to the tank such as a solenoid valve or a temperature probe, and by transmitting data by electrical cable from these elements to the station:
It is therefore clear that a novel technical solution must be proposed, one that provides better ergonomics (automating all or part of the operations), limiting the risks of error indicated above, and serving, whenever necessary, to reach the minimum pressure for subsequent use of the tank concerned, without the need to employ a pressurizing system.
As shown in greater detail below, the present invention proposes a novel filling procedure, whose essential feature is the fact that the gas discharged from the tank is not “lost” but, on the contrary, recovered and controlled, by the fact that a gas discharge channel from the tank connects the tank to the filling station, where this gas discharged from the tank is treated in terms of process control.
In brief:
The present invention accordingly relates to a method for filling a tank with a cryogenic liquid from a storage unit, during which filling operation part of the cryogenic liquid is converted to the gas phase in the tank, and in which, during the filling, at least part of the gas thus formed is discharged, which method comprises providing a filling station through which there passes a first channel, which connects the storage unit to the tank and allows the transfer of cryogenic liquid from the storage unit to the tank, and where there terminates a second channel which connects a gas outlet of the tank to the filling station and makes it possible to transfer the gases to be discharged to the filling station, where said gases will be discharged to the exterior, the station comprising means for detecting the presence of cryogenic liquid in the gas transferred to the station, and the detection data being transmitted to a data acquisition and processing unit, inside or outside the station, suitable for automatically stopping the filling operation when the tank is considered to be full.
As clearly appears to a person skilled in the art, this “full tank” concept must be understood as relating to the position of the gas return tube in the tank. In practice, filling “to the brim” is never permitted, and a free space (for example 5% of the tank volume) is always left, which is necessary for movement and vaporization of the liquid. The tank is accordingly considered to be “full” when it is filled for example to 95% and, because of the filling dynamics, liquid will escape toward the station upon approaching the 95% level, which, according to the invention, will cause the filling to stop. A person skilled in the art is therefore familiar with these “full tank” concepts.
According to one of the embodiments of the invention, said detecting means consist of a temperature probe located on said second channel, indicating an abnormally high drop in temperature in the gas transferred to the station.
As will be clearly apparent to a person skilled in the art, and in order to illustrate this question of a temperature drop, the drop in temperature recorded by the station in the gas return line will obviously vary according to the situations and conditions. For illustration, if we consider the example of a liquid nitrogen tank at 2-2.5 bar, the temperature of the cold gas is close to about −150° C., and when liquid touches the temperature probe, the temperature measured by the probe drops to about −180° C.
In practice, in the early moments of filling, the gas is “warm” (ambient temperature) and its temperature will steadily fall as the filling proceeds, until reaching about −150° C.
Therefore, when the tank is “full”, for example to the 95% level, liquid will leave the tank and flow toward the probe of the station, initially in what can be described as “small jets”, and these preliminary small jets cause the temperature to drop to about −160/−165° C., triggering the automatic interruption of the filling operation.
According to the invention, the second channel, connecting a gas outlet of the tank to the filling station, is equipped with a back pressure regulator, said back pressure regulator being set to an upstream pressure setpoint serving to reach a minimum pressure in the tank, which is necessary for a subsequent use of the tank concerned, without the need to employ a pressurizing system.
The invention may also adopt one or more of the following technical features:
A/ the connections between the storage unit and the tank on the one hand, and between the gas outlet of the tank and the station on the other hand, are made by a system of two male/female double couplers:
B/ said second double coupler “tank side” is in fluid connection with the upper part of the tank.
C/ a purge line is provided, equipped with a solenoid valve, said purge line being connected in its upstream portion to said first channel connecting the storage unit to the tank, and to which the second channel which transfers the gases to be discharged to the filling station is advantageously connected, thereby allowing the discharge of the gases discharged from the tank via this line to the exterior (it should be understood that the purge lines of the liquid line, and the discharge to the exterior of the gases transferred to the station, could also be two separate and independent lines in the station).
D/ According to one of the embodiments of the invention, at least a portion of said first channel connecting the storage unit to the tank is purged after the filling is stopped, by the fact that after a predefined time t1 the portion of first channel to be purged is purged by opening a solenoid valve located on a purge line which is connected in its upstream portion to said first channel connecting the storage unit to the tank.
E/ According to one of the embodiments of the invention, the flexible portion of the first channel connecting the storage unit to the first double coupler is purged, using one of the following techniques:
F/ the tank is present on a truck used to transport and distribute heat-sensitive products, such as pharmaceuticals and food products.
According to optional but advantageous embodiments of the invention, the invention may have one or more of the following features:
And according to one possible embodiment of the invention, the detection of the absence of the double coupler on the fastening element (parking plate, for example) may be used to authorize the start of the filling and therefore refuse said start when the coupler is still on its plate.
Other features and advantages will appear from the following description, of exemplary embodiments of the invention, provided in particular with reference to the appended drawings in which:
With reference to
For better legibility, the two connections of the two double couplers have been separated in space (reference 4) in this figure, but as will be clearly apparent to a person skilled in the art, these two double couplers must be understood as a storage-unit-side first double coupler, for example a male double “connector”, and a tank-side second double coupler, for example a female “housing”, i.e. double channel for accepting the opposite, male, double connector.
The double couplers have been positioned outside the area symbolizing the station, but this is a subsidiary point, for definition; these double couplers can be considered as being optionally part of the station, without really modifying the scope of the present invention.
In the liquid-nitrogen first channel, the presence of a solenoid valve 10 and a pressure sensor 12 can be recognized.
In the gas-return second channel, the presence can be recognized of a solenoid valve 20 and a back pressure regulator 21 (whose role has been broadly explained above), as well as the presence of a temperature sensor 23 (whose essential role has also been explained above in the present description) and a pressure sensor 22.
It should be noted that for reasons of legibility, the figure does not show the second parallel line, for transferring cryogenic liquid from the storage unit to the tank, for filling the tanks whose maximum service pressure is reduced, said second line comprising a calibrated orifice for limiting the maximum pressure acceptable to the tank, but it has already been stated above that this possibility is feasible and advantageous.
As we have shown, the temperature probe 23, installed on the gas return line in the filling station, serves to detect—via an abnormally high drop in temperature of this gas return line—the presence of liquid nitrogen in the gas return line, indicating a complete filling of the tank. Said detection data is sent to the data acquisition and processing unit present in the station (not shown to avoid cluttering the figure), which unit orders the filling to be stopped (closure of the valve 10, and closure of the valve 20 to prevent a loss of pressure in the tank and its inadvertent degassing).
When the operator uncouples the “storage unit side” double coupler (which can also be called the “station side” double coupler), the two (liquid line and gas line) valve flaps of the coupler are closed and liquid is confined between the valve flap of the liquid line and the solenoid valve 10 on the liquid line. To carry out the purge, the valve 31 on the purge line 30 must be opened and therefore controlled. For illustration, two events can be used to order the opening of this valve 31:
Another eventuality (in very specific cases however) is that before the lapse of the time delay t1, another filling operation must be carried out (for example to fill a second tank present under the truck in the case of high nitrogen requirements): in such a case, it will obviously be useless and superfluous to initiate the intermediate purge, and it is simpler for the operator to disconnect the double coupler of the first tank and reconnect said double coupler to the second tank, and then press a “start” button to start said second filling, the purge only being carried out after the second filling has been stopped.
Obviously, this description of two sequential filling operations of two tanks would also apply to cases, which are admittedly even more infrequent, of more than two tanks and hence more than two sequential filling operations to be carried out, but the principle thereof is nevertheless quite clear from the above description.
Thanks to the presence of the back pressure regulator 21, the outgoing gas is returned to, and controlled in, the filling station, thereby serving to preserve a minimum pressure in the tank (for example 2 bar), which is very useful in certain subsequent applications requiring a minimum pressure, and not simply atmospheric pressure, and according to the invention the solenoid valve 20 can be controlled according to the pressure required in the tank.
As will be understood, the manual filling operations according to the prior art do not allow such control, because in the case of such a manual filling operation, the gas outlet of the tank is opened or closed by means of a manual valve on the tank. Said valve allows complete opening/closure. During the filling operation, the manual valve is opened, the gas is discharged and the tank is thus again under atmospheric pressure, which does not serve to deliver the minimum pressure required by certain subsequent uses (for example 2 to 2.5 bar for the “direct injection” technique in refrigerated truck transport).
According to this prior manual procedure, it is then necessary to wait for heat inputs to raise the pressure in the tank, or to have a pressurizing system (vaporizer).
For illustration, an example is provided below of an automatic filling procedure of a tank according to the invention.
1) Connection by the operator of the double coupler of the filling station to the tank-side double coupler to be filled. The tank cavity is now connected via the hoses with the filling station and its control elements (valve, pressure sensor, temperature sensor, etc.).
2) Recognition of the tank to be filled and consideration of its maximum acceptable pressure.
3) The operator presses a button so as to initiate the filling operation.
4) The pressure in the hoses is checked so as to check the proper connection of the tank (via sensor 12).
5) If the hoses are properly connected: opening of the valve 10 on the liquid nitrogen line.
6) During the filling operation, the liquid pressure (12) is monitored as an indicator of the pressure in the tank and the valve 10 on the liquid nitrogen line is closed in case of excessive pressure: the sensor 12 serves to ensure that the pressure in the tank does not exceed a safe pressure, and therefore causes the closure of the valve 10 as required.
7) During filling: opening/closing cycles of the valve 20 on the gas return line to control the pressure in the tank and thereby also increase the filling rate.
As a first exemplary application, a tank A may need a working pressure of 2.5 bar, while in a second exemplary application a tank B needs 1 bar only.
The back pressure regulator 21 and the solenoid valve 20 on the gas return line provide a maximum flow rate for the gas outlet while preserving the minimum pressure required.
8) The detection of an abnormally low temperature on the gas return line (as already explained above) indicates the presence of liquid nitrogen in the gas return line and the complete filling of the tank. The valve 10 is consequently closed, and also the valve 20, and the operator is informed of the end of filling by any suitable (acoustic, visual) signal.
It is clear that in precise and exceptional cases, particularly a safety situation, the signal in question may allow the operator to avoid relying on the automatic stopping of the filling operation by the station, and instead to order the filling operation to be stopped himself, for example by pressing an appropriate button, but it is clear that above all, the merit of the present invention resides in the fact that the discharged gases are not lost, but are returned to a process control station, thereby serving to limit human actions, which are such sources of errors and malfunctions.
9) After a predefined time t1 (for example 2 minutes), the liquid nitrogen transfer hose is purged by opening the solenoid valve 31 connecting the liquid nitrogen line to the gas outlet of the station. The purge can also be initiated when the presence of the “station” double coupler is detected on the parking plate of the station.
As will have been understood, the fact of performing this dual “filling/gas return” operation by a male double coupler on a female double coupler is optional, certainly highly advantageous but still optional, and it is also possible, without departing from the scope of the present invention, to connect two well-separated channels (and couplers) issuing from the station to two well-separated couplers on the tank or in fluid communication with said tank.
As already mentioned, the data acquisition and processing unit is preferably located within the station, for obvious reasons of convenience of wiring, but, without departing from the scope of the invention, the unit could equally well be located outside the station, and the required cables would then be drawn between the unit and the station.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0951073 | Feb 2009 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR2010/050237 | 2/11/2010 | WO | 00 | 8/19/2011 |
