The present invention relates to the field of processes for filling a downstream tank with a cryogenic liquid, such as liquid nitrogen, from an upstream storage tank.
It more particularly relates to processes enabling rapid filling.
Such filling operations are used, for example, to fill the tanks of trucks used to transport and distribute heat-sensitive products such as pharmaceutical products or foodstuffs.
Conventionally, the cryogenic fluid, for example liquid nitrogen, is stored in a high-capacity upstream storage tank connected downstream to equipment that consumes this fluid, such as the tank of a truck, the upstream storage tank containing, under a storage pressure higher than atmospheric pressure, the cryogenic fluid in liquid phase at the bottom of the tank and in gas phase at the top of the tank, this storage tank being designed to, on the one hand, supply the downstream consuming equipment with liquid extracted from the bottom of the storage tank, and on the other hand, to be supplied from the exterior with fluid.
Most commonly, storage tanks called “low-pressure storage tanks” are used, i.e. the maximum pressure reached at the top of the tank is in general lower than about 4 bar absolute and conventionally the pressure at the top of the storage tank is 1.5 bar relative.
To rapidly transfer the fluid between this upstream storage tank and such a downstream point, for example a tank to be filled, conventionally a cryogenic pump is used to increase the upstream pressure during transfer to the downstream cryogenic tank (see
However, it is known that using such cryogenic pumps may entail drawbacks in terms of cost, maintenance, and specific operational constraints such as the pump requiring cooling before use. This is because cryogenic pumps comprise moving parts that require specific maintenance.
Another solution has been suggested, which consists in using an intermediate transfer tank that is pressurized before the ultimate filling of the downstream tank. This solution involves the use of an additional tank, thus entailing a volume constraint and an operating mode that is greatly dependent on the downstream process (pressurization before use and managing filling when it is empty, etc.).
Another solution has been suggested, which consists in maintaining the upstream cryogenic storage tank at the transfer pressure, but it is known, because of the characteristic behavior of cryogenic fluids, that under these conditions the fluid will tend to gravitate toward its equilibrium temperature at the pressure in the storage tank, which will produce a diphasic fluid during transfer and therefore reduce the flow rate because there will be gas in the flow (by way of illustration, 1% of diphasic fluid by weight in nitrogen implies a ratio of the mass of gas to the total mass equivalent to a void rate, i.e. the volume occupied by the gas/total volume, of 50%).
One of the objectives of the present invention is thus to provide a novel approach to rapid filling, solving the technical problems described above.
As will be seen in more detail below, the present invention provides a new filling process, the essential features of which may be summarized as follows:
The present invention thus relates to a process for filling at least one downstream tank with a cryogenic liquid from an upstream storage tank, which upstream storage tank contains, under a storage pressure higher than atmospheric pressure, the cryogenic fluid in liquid phase at the bottom of the storage tank and in gas phase at the top of the storage tank, said upstream storage tank being designed to supply the downstream tank with liquid extracted from the bottom of the storage tank, and to be supplied from the exterior with fluid, noteworthy in that a pressure difference is created and maintained between the upstream storage tank and the downstream tank, by establishing, in the gas phase in the upstream storage tank, a pressure that is higher than the equilibrium pressure in the storage tank.
According to one embodiment of the invention, the gas phase in the upstream storage tank is brought to and maintained at a pressure equal to:
Pg=ΔP+P1−pgh
where:
Other features and advantages of the present invention will become more clearly apparent from the following description, given by way of completely nonlimiting illustration, and with regard to the appended drawings, in which:
For its part,
By way of example, the transfer pressure of the cryogenic fluid is set to the nominal desired value, for example 5 bar relative for a given downstream application using liquid nitrogen, the temperature of the fluid is moreover controlled relative to a reference value under given conditions, for example −187° C., which corresponds to an equilibrium pressure of 1.5 bar relative. If after a period of use, the temperature difference with respect to the setpoint value is greater than the allowed hysteresis, a new pressure setpoint is delivered to the controller in order to reduce the pressure of the associated gaseous atmosphere and therefore limit heating of the fluid in the storage tank during idle periods during the transfers. The system resets to the pressure setting with regard to operational reuse of the rapid transfer installation. The control device thus enables parameterized control of pressure, temperature and time data in order to optimize the overall consumption of the installation.
The table of experimental results below will allow the advantages of such conditions, according to the invention, to be better understood.
This table indicates the filling times obtained for the transfer of 410 liters of liquid nitrogen from upstream to downstream, for various operating conditions:
For each set of operational conditions, the table gives the filling time and the average flow rate achieved.
Thus, by way of example, for a delta of 3 bar (Pupstream=5 bar and Pdownstream=2 bar) with the temperature of the liquid regulated to −187° C., the 410 liters of a downstream tank were filled in 3.7 minutes, with an average flow rate of 110.8 1/min.
The following teachings may be deduced from this table:
Number | Date | Country | Kind |
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1053199 | Apr 2010 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/FR11/50075 | 1/17/2011 | WO | 00 | 10/25/2012 |