Refrigeration – Cryogenic treatment of gas or gas mixture – Liquefaction
Reexamination Certificate
1999-03-02
2001-01-09
Capossela, Ronald (Department: 3744)
Refrigeration
Cryogenic treatment of gas or gas mixture
Liquefaction
C062S923000
Reexamination Certificate
active
06170290
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a refrigeration process, using a thermal cycle of a fluid having a low boiling point, especially helium, in which:
the fluid is compressed in the gaseous state to a pressure called the high pressure,
the compressed fluid is precooled on passing through a precooling first stage,
the compressed and precooled fluid is cooled and liquefied, at least partially, on passing through a cooling and liquefying second stage where the fluid is expanded to a pressure called the low pressure,
at least some of the cooled and expanded fluid is collected in a tank for storing the fluid in a two-phase state,
some of the gas phase is sent back via a warming line from the tank successively through the second and first stages, this gas phase being warmed on passing through these stages by heat exchange with the compressed fluid passing through them,
at least some of the cooled and expanded fluid forming a first force of refrigeration.
The invention applies in particular to the cooling of superconducting components of particle accelerators, using helium.
The pressures involved here are absolute pressures.
BACKGROUND OF THE INVENTION
The cooling of the superconducting elements requires the use of fluids at very low temperatures, generally below 5 K, these fluids forming sources of refrigeration placed in heat-exchange relationship with the components.
A fluid having a low boiling point, such as helium, allows such temperatures to be reached inside the storage tank where it is in a liquid/vapour equilibrium state.
Thus, it is possible, for example, to use the liquid phase contained in this tank as the source of refrigeration, by evaporating the liquid phase and optionally warming the gas thus produced.
This vaporization may take place inside the actual tank, the cold source then being isothermal and the corresponding refrigeration plant operating in a so-called refrigerating mode.
The vaporization may also take place outside the tank, after drawing off the liquid phase contained in the latter, the corresponding refrigeration plant then operating in a so-called liquefying mode. In this mode of operation, the gas thus produced is also used as the source of refrigeration, by warming it.
Finally, these two modes of operation may be combined in a mixed mode of operation, in which two sources of refrigeration are provided, namely a first source outside the storage tank and an isothermal second source actually inside this tank.
The production of refrigerating power at the required temperatures entails a high operating cost which corresponds to the compression requirements of the fluid used.
OBJECT OF THE INVENTION
The object of the invention is to solve these problems by providing, in particular, a refrigeration process which can be used for all the modes of operation described above, making it possible to optimize the overall compression power budget and therefore to reduce the operating costs of the plants.
SUMMARY OF THE INVENTION
For this purpose, the subject of the invention is a refrigeration process, using a thermal cycle of a fluid having a low boiling point, especially helium, in which:
the fluid is compressed in the gaseous state to a pressure called the high pressure,
the compressed fluid is precooled on passing through a precooling first stage,
the compressed and precooled fluid is cooled and liquefied, at least partially, on passing through a cooling and liquefying second stage where the fluid is expanded to a pressure called the low pressure,
at least some of the cooled and expanded fluid is collected in a tank for storing the fluid in a two-phase state,
some of the gas phase is sent back via a warming line from the tank successively through the second and first stages, this gas phase being warmed on passing through these stages by heat exchange with the compressed fluid passing through them,
at least some of the cooled and expanded fluid forming a first force of refrigeration,
characterized in that the precooled fluid is divided into at least two separate streams which are expanded in parallel in the second stage, namely a first stream intended to supply, at least partly, the first source of refrigeration and at least a second stream, one of these streams being at least partially liquefied separately on passing through the second stage.
Depending on the particular embodiments, the process may comprise one or more of the following characteristics, taken alone or in any technically possible combination:
the first stream is at least partially liquefied on passing through the second stage in order to feed the storage tank;
at least a second stream is liquefied, at least partially and separately, in the second stage, in order also to feed the storage tank with fluid;
the liquid phase contained in the tank is used to form the first source of refrigeration;
some of the liquid phase is drawn off from the storage tank in order to form the first source of refrigeration outside the said tank;
the liquid phase contained in the storage tank is used as an isothermal second source of refrigeration inside this tank;
the first source of refrigeration is a gas, especially a supercritical gas, which is produced from the first stream, and the storage tank is fed from a second stream at least partially liquefied in the second stage;
the gas is cooled downstream of the second stage, by heat exchange with the liquid phase stored in the tank, in order to form the first source of refrigeration;
the liquid phase contained in the storage tank is used as an isothermal second source of refrigeration inside this tank;
the first stream is furthermore cooled, in at least part of the second stage, by countercurrent heat exchange using another of the expanded streams;
the other stream, cooled and expanded into a gas phase in the second stage, is sent back directly to the warming line in order to cool the first stream in the second stage,
the other stream, expanded and cooled into at least one gas phase, is sent back to the storage tank, the gas phase being sent back via the warming line in order to cool the first stream in the second stage.
The subject of the invention is also a plant for implementing a process as defined above, characterized in that it comprises means for compressing the fluid, a precooling first stage, a cooling and expansion second stage, a tank for storing the fluid in a two-phase state, a line for cooling the compressed fluid, which, at least partly, passes through the two stages and connects the compression means to the tank, a line for warming the gas phase of the tank, which passes through the two stages and communicates with the said tank, in that the cooling line is divided in the second stage into at least two separate pipes, each provided with its own expansion, means, belonging to the second stage, a first of these pipes, the pipe corresponding to a first stream, being intended to supply, at least partly, a first source of refrigeration, and in that expansion means of one of the pipes comprise means of at least partial liquefaction.
Depending on particular embodiments, the plant may comprise one or more of the following characteristics, taken alone or in any technically possible combination:
the expansion means of the first pipe comprise means of at least partial liquefaction and this first pipe emerges in the storage tank in order to feed it with fluid;
the expansion means of at least one second pipe, corresponding to a second stream, comprise means of at least partial liquefaction and this second pipe also emerges in the storage tank in order to feed it with fluid;
the plant comprises means for bringing the liquid phase of the storage tank into heat-exchange relationship with the outside, in order to use this liquid phase as the first source of refrigeration;
the plant comprises means for drawing off the liquid phase from the storage tank in order to form the first source of refrigeration outside the tank;
the plant comprises means for bringing the liquid phase contained in the storage tank into heat-exchange relationship with the outside
Capossela Ronald
L'Air Liquide, Societe Anonyme pour l'Etude et l'
Young & Thompson
LandOfFree
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