Patent Application
20140238070
The present invention concerns a refrigeration installation and method.
The invention concerns in particular a low-temperature refrigeration installation and method wherein a gas with a low molar mass (for example hydrogen or helium) is used as a refrigerating fluid in order to attain very low refrigeration temperatures (for example 4.5 K for helium). Obtaining refrigeration at temperatures of 30 K and lower generally requires the use of a refrigerant such as helium. The helium is compressed at a hot end of the loop or circuit, and then cooled and expanded in the cold part of the loop (cold box). The major part of the refrigerant is heated by exchange and recycled in the compression stage. In some applications, part of the working gas may be liquefied.
The compression of the helium liquefaction/refrigeration cycles generally uses one or more stages of compression machines (compressors) with lubricated screws followed by an oil-separation system.
If it is necessary to have several refrigerators, each refrigerator is connected to its own compression station. According to the rates required, each compression level may be divided into several compressors in parallel. The primary oil-management and cooling systems may be common to several compressors or be dedicated to each one.
After the compression and oil separation thereof the low molecular mass gas is cooled and expanded in cryogenic expansion turbines of a cold box in order to attain the required temperature level. The cold not used by the user of the refrigerator/liquefier is then transmitted to the working fluid at high pressure in order to cool it in the heat exchangers. The working gas at low and medium pressure of the circuit returns to the intake of the compressors.
For large refrigeration systems, for example greater than 20 kW, equivalent to 4.5 K, it is necessary to use several separate refrigerators in parallel connected to the same application to be cooled. The fluctuating thermal loads of the application to be cooled cause fluctuations in output on the compressors of the compression station. The costs of the compression station (equipment, integration and installation) are relatively high compared with the total cost of the installation.
The refrigeration cycles (which generate the cold) are conventionally “closed” at each refrigerator. That is to say the cycle output of working fluid that enters the cold box stems mainly from this same cold box. On the other hand, these cycle outputs are “open” or combined at the application to be cooled (the working fluid output supplied by the refrigerators is shared for the application to be cooled and then returns to each refrigerator through a respective distribution system).
One aim of the invention is to propose a refrigeration method and installation of an application by means of several refrigerators/liquefiers disposed in parallel that solve all or some of the above problems. In particular, one aim of the invention may be to propose a refrigeration method and installation that are less expensive and/or more compact and/or more effective and/or more flexible in use than the known systems.
To this end, the refrigeration installation of the same application by means comprises several refrigerators/liquefiers disposed in parallel, the refrigerators/liquefiers in parallel using a working gas of the same nature having a low molar mass, that is to say having a mean total molar mass of less than 10 g/mol such as pure gaseous helium, each refrigerator/liquefier comprising a station for compressing the working gas, a cold box intended to cool the working gas at the output from the compression station, the working gas cooled by each of the respective cold boxes of the refrigerators/liquefiers being put in thermal exchange with the application with a view to supplying cold to the latter, wherein a single compression station compresses the working gas for each of the respective separate cold boxes of the refrigerator/liquefiers disposed in parallel, the single compression station comprising only compression machines of the lubricated-screw type and systems for removing oil from the working fluid output from the compression machines, so that the compression machines and the oil-removal systems are shared by the refrigerators/liquefiers disposed in parallel.
Moreover, embodiments of the invention may comprise one or more of the following features:
Another aim of the invention is to propose a refrigeration installation for the same application by means of a single refrigerator/liquefier or several refrigerators/liquefiers disposed in parallel, the refrigerator(s)/liquefier(s) using a working gas of the same nature having a low molar mass, that is to say having a mean total molar mass of less than 10 g/mol such as pure gaseous helium, each refrigerator/liquefier comprising a station for compressing the working gas, a cold box intended to cool the working gas discharged from the compression station, the working gas cooled by each of the respective cold boxes of the refrigerators/liquefiers being put in heat exchange with the application with a view to supplying cold to the latter, wherein a single compression station provides the compression of the working gas for each of the cold boxes of the refrigerator(s)/liquefier(s), the compression station comprising only compression machines of the lubricated-screw type and systems for removing oil from the working fluid discharged from the compression machines, and in that the compression station comprises a plurality of compression machines defining several pressure levels for the working fluid, the passage from one pressure level to the following higher pressure level is achieved via one or more compression machines in series or via several compression machines disposed in parallel, the compression station comprising at least two compression machines defining at least two increasing pressure levels above the pressure level of the fluid at the inlet of the compression station, two main compression machines being disposed in series and defining at their respective fluid outlets pressure levels respectively said to be “low” and “high”, another secondary compression machine being supplied at its inlet with fluid issuing from the cold boxes at a so-called “medium” pressure level intermediate between the low and high pressure levels, this secondary compression machine defining at its fluid outlet also a “high” pressure level.
According to other possible particularities
The invention also concerns a method for refrigerating the same application by means of a refrigeration and/or liquefaction installation comprising several refrigerators/liquefiers disposed in parallel, the refrigerators/liquefiers in parallel using a working gas of the same nature having a low molar mass, that is to say having a mean total molar mass of less than 10 g/mol such as pure gaseous helium, each refrigerator/liquefier comprising a station for compressing the working gas, a respective cold box intended to cool the working gas discharged from the compression station, the working gas cooled by the respective cold boxes of the refrigerators/liquefiers being put in heat exchange with the application with a view to supplying cold to it, wherein a single compression station compresses the working gas for each separate cold box of the refrigerators/liquefiers disposed in parallel, the single compression station comprising solely compression machines of the lubricated-screw type and systems for removing oil from the working fluid discharged from the compression machines, so that the compression machines and the oil-removal systems are shared by the refrigerators/liquefiers disposed in parallel.
According to other possible particularities:
The invention may also concern any alternative device or method comprising any combination of the above or following features.
Other particularities and advantages will emerge from a reading of the following description given with reference to the figures, wherein:
The refrigeration installation shown schematically in
The refrigerators/liquefiers (L/R) disposed in parallel use a working gas of the same nature having a low molar moss, that is to say having a mean total molar mass of less than 10 g/mol such as pure gaseous helium for example.
Each refrigerator/liquefier (L/R) uses a station 2 for compressing the working gas and a cold box 3 intended to cool the working gas output from the compression station 2. The working gas cooled by each of the respective cold boxes 3 of the refrigerators/liquefiers (L, R) is put in heat exchange, via a distribution circuit 11, with the application 1 with a view to supplying cold to the latter.
According to an advantageous particularity, a single compression station 2 compresses the working gas for each of the separate respective cold boxes 3 of the refrigerators/liquefiers L/R disposed in parallel.
The compression 2 station 2 may where applicable be connected to a so-called “hot” buffer 12 for storing working fluid. According to another advantageous particularity, the single compression station 2 comprises compression machines solely of the lubricated-screw type and systems for removing oil from the working fluid at the discharge from the compression machines. In this way, the compression machines (lubricated-screw compressors) and the oil-removal systems are shared by the refrigerators/liquefiers disposed in parallel.
This configuration makes it possible to limit the number of machines and items of equipment necessary for compressing the working fluid.
This also makes it possible to concentrate the variations in load over a limited number of compressors with suitable regulation means (for example frequency variators, regulator valves, etc.).
In addition, this also where applicable makes it possible to group the compression stations by type of compressor or by function (refrigeration cycle and/or customer supply) rather than by refrigeration cycles.
The architecture also where applicable makes it possible to provide several fluid cycle pressures per function or per compression station.
At the inlet of the compression station 2, the fluid issuing from one or more cold boxes 3 arrives at a so-called “very low” pressure (VLP). This very low level pressure depends on the application 1 and this very low pressure level may not be present for some applications (that is to say the first pressure level in the compression station is said to be “low”, that is to say included in the range mentioned below). A first compression machine EC1 provides a pressure rise in the working fluid to a so-called “low” pressure LP that is higher than the very low pressure VLP. At the discharge from this first compression machine EC1, the fluid may be de-oiled in an oil-removal member 4 and then cooled in a heat exchanger 5. The discharge of the first compression machine EC1 is then connected to the inlet of a second compression machine EC2, which compresses the fluid from the basic pressure LP to a high pressure HP. The inlet of this second compression machine EC2 also receives the fluid at this low pressure level LP issuing from the cold boxes 3. As before, at the discharge from this second compression machine EC2, the fluid may be de-oiled in an oil-removal member 4 and then cooled in a heat exchanger 5. Before returning to the cold boxes 3, the fluid may undergo a last more selective oil removal in a final oil-removal system 14. A third compression machine EC3 is disposed in the compression station 2. This third compression machine EC3 is supplied at its inlet with fluid from the boxes 3 at a so-called “medium” pressure MP intermediate between the low LP and high HP levels. This third compression machine EC3 also defines at its fluid outlet a “high” pressure level HP for the working fluid. At the discharge from this second compression machine EC2, the fluid may be de-oiled in an oil-removal member 4 and then cooled in a heat exchanger 5. The high-pressure working fluid is injected upstream of the final oil-removal system 14 (a pipe is connected to the outlet of the second compression machine EC2.
This solution therefore combines several lubricated-screw compression machines between the low pressure LP and high pressure HP and in addition has a compression level between the intermediate pressure MP and the same high pressure HP.
This configuration has the advantage of reducing the size of the primary oil-management systems 4 (oil-removal system 4 before the final oil removal 14) in particular on the part of the cycle between the low pressure LP and the high pressure HP. This architecture also makes it possible simultaneously to preserve flexibility on the variations in flow rate and pressure possible in this part of the circuit (in particular between the medium pressure MP and the high pressure HP).
On the other hand this solution is less flexible with regard to the possibility of varying the flow rate of working fluid in the low pressure LP since the combined compression machines are interdependent and the fluctuations are more difficult to control.
Each of the compression stages implemented by a compression machine may of course be replaced by two (or more) compressors disposed in parallel. This is because, depending on the flow rates of working fluid necessary, each compression level may be divided into several compressors disposed in parallel. In this case, the primary oil management (oil removal) and cooling systems may be common to several compressors or be dedicated to each one.
According to the very low pressure level VLP and the compression ratio of the first compression machine EC1, the outlet of the first compression machine EC1 may also be connected to the inlet of the third compression machine EC3 at a so-called “medium” pressure level MP. The rest of the architecture remaining similar.
The variant in
As before, the second EC2 and fourth EC4 compression machines in parallel may each have at their outlet a dedicated oil-removal system 4 and a dedicated heat exchanger 5. In a variant these oil-removal systems 4 and heat exchanger 5 may be common and therefore shared.
As before, according to the working fluid flow rates required, each compression level may be divided into several machines (compressors) disposed in parallel.
As before also, this solution combines several compressors between the low pressure LP and the high pressure HP and in addition provides a compression level between the intermediate pressure MP and the same high pressure HP.
In the case of
The latter compression machines EC12 may be equipped with speed variators in order to react to variations in low-pressure fluid flow rate. The recirculation of fluid between the low pressures LP and medium pressure MP is also possible in order to react to variations in load.
The compressor or compressors EC2 combined between the low pressure LP and the high pressure HP may function with a constant flow rate and independently of the fluctuations in load (application 1) and working cycle. The fluctuations in flow rates and pressures are absorbed by the group of compressors EC1, EC3, EC12 between the very low input pressure VLP as far as the higher levels (LP->MP->HP).
The variant in
In this configuration of
As before, part of the flow of fluid at low pressure LP is compressed directly to a high pressure HP2. In this configuration in
This architecture also makes it possible to optimise the sizes and efficiencies of the various types of compressor of the various compression stages.
The variations in flow rate and pressure of the fluid on the circuits resulting respectively in the two high pressure levels HP1 and HP2 can therefore also be managed more independently.
The circuit comprising a compression stage between the medium pressure MP and high pressure HP1 in general supplies the majority of the pressure-reduction turbines of the cycle of the cold boxes 3 that are the refrigeration source of the system. A variation of this cycle therefore permits a direct variation of the refrigeration capacity of the refrigerators/liquefiers L/R.
On the other hand, the high-pressure fluid circuit HP2 issuing from the second compression machine EC2 may be used preferentially for supplying an application 1 and/or an expansion circuit of a cooling of the Joule-Thompson type at the cold end of the cycle.
The invention may in particular apply to any refrigeration/liquefaction unit with a high liquefaction or refrigeration capacity using helium or a rare gas.
By way of non-limitative example (circuit with three compression stages but defining four pressure levels), the respective pressure levels very low VLP, low LP, medium MP and high HP of the compression stages as well as the corresponding compression ratios and flow rates of the working gas may be included in the following ranges.
The architectures of the compression stations in the examples illustrated may advantageously apply also to an installation using a single liquefier/refrigerator (rather than several in parallel).
| Number | Date | Country | Kind |
|---|---|---|---|
| FR 1 158 478 | Sep 2011 | FR | national |
| FR 1 160 744 | Nov 2011 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR2012/051896 | 8/14/2012 | WO | 00 | 3/21/2014 |
