Patent Grant
10753659
This application is a 371 of International PCT Application PCT/FR2015/051492 filed Jun. 5, 2015, which claims priority to French Patent Application No. 1457100 filed Jul. 23, 2014, the entire contents of which are incorporated herein by reference.
The present invention relates to a method for adjusting a cryogenic refrigeration apparatus and to a corresponding apparatus.
The invention relates more particularly to a method for adjusting a cryogenic refrigeration apparatus comprising several refrigerators/liquefiers arranged in parallel to cool one and the same application, each refrigerator/liquefier comprising a working circuit for a working gas equipped with at least one valve for controlling the flow of working gas, the refrigerator/liquefiers in parallel using a working gas of the same kind such as pure gaseous helium, each refrigerators/liquefier comprising a working gas compression station, a cold box intended to cool a flow of working gas leaving the compression station to a cryogenic temperature at least close to its liquefaction temperature, said flows of working gas cooled by each of the respective cold boxes of the refrigerators/liquefiers being mixed and then placed in a heat exchange relationship with the application in order to give up frigories thereto, the cold working gas having exchanged heat with the application then being divided into several return flows distributed respectively through the respective compression stations.
The invention relates to what is referred to as “large-scale” refrigeration apparatuses employing several refrigerators/liquefiers in parallel in order to cool one and the same user application
A “refrigerator/liquefier” denotes a device which subjects a working gas (for example helium) to a thermodynamic cycle of work (compression/expansion) that brings the working fluid to a cryogenic temperature (for example a few degrees K in the case of helium) and where appropriate liquefies this working gas.
One nonlimiting example of such an apparatus is described in application no. FR2980564A1.
The refrigeration cycles (which generate cold) are said to be “closed” at the level of each refrigerator. What that means to say is that the flow of working gas that enters the cold box of a refrigerator/liquefier reemerges for the most part from this same cold box. By contrast, the flow of working gas is said to be “open” at the level of the application that is to be cooled, which means to say that the gas from the various refrigerators/liquefiers is mixed therein. The flow of working gas supplied by the refrigerators/liquefiers is therefore pooled for cooling the application then returned separately to each refrigerator by a distribution system.
Adjustment of the refrigerators of such an apparatus generally involves manually positioning the control valves of the working circuit (from and to the application that is to be cooled).
Suitable adjustment becomes more difficult when the apparatus comprises a great many interfaces and when the thermal loads that need to be cooled vary over time. This is because static adjustment of the valves may be unsuitable if the flow rate and/or pressure of the system vary.
The fluctuating thermal loads of the application indeed generate fluctuations in the flow rate through the compressors.
If this is not corrected, certain refrigerators/liquefiers will recuperate more working gas and cold than others. Thus, certain refrigerators/liquefiers may diverge from their nominal operating point. Certain components of these refrigerators/liquefiers may therefore be used at their limit (compressors, turbines, etc.) whereas the other refrigerators/liquefiers will be underutilized. The overall cold power of the apparatus and the efficiency thereof will therefore be reduced.
Providing systems for control and adjusting the independent flows for each refrigerator/liquefier may lead to a system which overall is unstable in which the loads and flow rates will be distributed inconsistently between the refrigerators/liquefiers. In addition, the specific features of helium (a density that varies greatly as a function of temperature) lead to a phenomenon in which the imbalances between the refrigerators are amplified.
The distribution of helium flow rates between the refrigerators is performed generally via a common helium feed pressure and the resistance (pressure drop) of the circuit returning to the source of pressure (compressors).
When one refrigerator/liquefier receives in relative terms more cold gas coming from the application, the mean temperature of the return circuit drops and the pressure drop of the circuit is therefore reduced. Specifically, the density of the gas may change more rapidly than the speed of the gas through the circuit. This drop in pressure drop in a circuit leads to a relative increase in the flow rate of cold gas accepted into the circuit concerned and therefore leads to divergence within the apparatus.
It is an object of the present invention to alleviate all or some of the disadvantages mentioned hereinabove of the prior art.
To this end, the method according to the invention, in other respects in accordance with the generic definition given thereof in the above preamble, is essentially characterized in that it comprises a step of simultaneous measurement, for each of the refrigerators/liquefiers, of the instantaneous value of at least one and the same operating parameter from: a flow rate of what is referred to as a “return” flow of working gas returning to the compression station, a flow rate of what is referred to as an “outbound” flow of working gas circulating through the cold box having left the compression station, a differential in temperature of the working gas between, on the one hand, the outbound flow of working gas and, on the other hand, the return flow of working gas, both flows being situated in the cold box in one and the same temperature range, the method comprising a step of real-time calculation of the dynamic mean value of the at least one operating parameter for all the refrigerators/liquefiers, the apparatus performing real-time control of the at least one working gas flow control valve of at least one refrigerator/liquefier as a function of the difference between the instantaneous values of the parameter with respect to said dynamic mean value, so as to cause said instantaneous values of said operating parameter of the various refrigerators/liquefiers to converge toward this dynamic mean value.
This particular feature allows the apparatus to be adjusted dynamically in order to react automatically to the variations in refrigerator parameters (temperature, pressure, flow rate, level, etc.).
This adjustment makes it possible to get as close as possible to the predetermined optimum operation (calculated beforehand) in which the various refrigerators/liquefiers operate identically (same flow rates/pressure/temperature of the working gas in the circuit).
In order to meet this requirement, the method compares one of the dynamic parameters indicative of the operation of a refrigerator and compares it against the mean of this same parameter across all the other refrigerators. The control action of the method uses this difference in value of the parameter to modify the set point of the regulators existing on each refrigerator having an impact on the parameter. That then also modifies the mean of the parameters and therefore the set point is also updated. This is a control system which may be qualified as being “in cascade” with a set point that is “dynamic” that causes each parameter to converge toward the mean of this parameter across the various refrigerators.
Moreover, embodiments of the invention may comprise one or several of the following features:
The invention may also relate to any alternative device or method comprising any combination of the features above or below.
The invention may also relate to a cryogenic refrigeration apparatus comprising several refrigerators/liquefiers arranged in parallel to cool one and the same application, each refrigerators/liquefier comprising a working circuit for a working gas equipped with at least one valve for controlling the flow of working gas, the refrigerators/liquefiers in parallel using a working gas of the same kind such as pure gaseous helium, each refrigerator/liquefier comprising a working gas compression station, a cold box intended to cool a flow of working gas leaving the compression station to a cryogenic temperature at least close to its liquefaction temperature, said flows of working gas cooled by each of the respective cold boxes of the refrigerators/liquefiers being mixed and then placed in a heat exchange relationship with the application in order to give up frigories thereto, the cold working gas having exchanged heat with the application then being divided into several return flows distributed respectively through the respective compression stations, the apparatus comprising electronic control logic connected to simultaneous measurement means, for measuring, for each of the refrigerators/liquefiers, the instantaneous value of at least one and the same operating parameter from: a flow rate of what is referred to as a “return” flow of working gas returning to the compression station, a flow rate of what is referred to as an “outbound” flow of working gas circulating through the cold box after having left the cold box, a differential in temperature of the working gas between, on the one hand, an outbound flow of working gas within the cold box and, on the other hand, the return flow of working gas in the cold box, the electronic logic being configured for real-time calculation of the dynamic mean value of the at least one operating parameter for all the refrigerators/liquefiers, and to perform real-time control of the at least one control valve controlling the flow of working gas from at least one refrigerator/liquefier according to the difference between the instantaneous values of the parameter compared with said dynamic mean value in order to cause said instantaneous values of said operating parameter of the various refrigerators/liquefiers to converge toward this dynamic mean value.
The invention also relates to any alternative device or method comprising any combination of the features above or below.
Further specifics and advantages will become apparent from reading the following description, given with reference to the figures in which:
Each refrigerator/liquefier comprises its own station 2 for compressing the working gas and its own cold box 3 intended to cool the flow 30 of working gas leaving the compression station 2 to a cryogenic temperature at least close to its liquefaction temperature.
The flows 30 of working gas cooled by each of the respective cold boxes 3 of the refrigerators/liquefiers L, R are mixed and then placed in a heat exchange relationship with the application 1 in order to give up frigories thereto. The cold working gas having exchanged heat with the application 1 is then split into several return flows 31 distributed respectively across the compression stations 2.
The parallel refrigerators/liquefiers L/R use a working gas of the same nature such as pure gaseous helium.
The apparatus 100 preferably comprises electronic control logic 50 comprising for example a microprocessor (a computer and/or controller). The electronic logic 50 is connected to measurement members for simultaneous measurement, for each of the refrigerators/liquefiers L/R, of the instantaneous value of at least one and the same operating parameter regarding the working gas in the working cycle of each of the refrigerators/liquefiers L/R. For the sake of simplicity,
The at least one operating parameter measured for each refrigerator/liquefier L/R preferably comprises at least one out of: a flow rate of the return flow of working gas returning to the compression station (after exchanging heat with the application or a return flow of working gas returning directly to the compression station without passing via the application 1 or certain parts of the cold box 3), a flow rate of the flow of cooled working gas at the outlet of the cold box (after having left the compression station), a differential in temperature of the working gas between, on the one hand, the flow of working gas in the cold box (heading toward the application) and, on the other hand, the return flow of working gas returning to the compression station (from the application).
The electronic logic 50 is configured (for example programmed) to perform real-time calculation of the dynamic mean value of the at least one operating parameter for all the refrigerators/liquefiers L/R and for performing real-time control of the at least one working-gas flow control valve of at least one refrigerator/liquefier L/R as a function of the difference between the instantaneous values of the parameter with respect to said dynamic mean value. More specifically, the electronic logic is configured to cause said instantaneous values of said operating parameter of the various refrigerators/liquefiers R/L to converge toward this dynamic mean value.
What that means to say is that each refrigerator/liquefier L/R is controlled in its working cycle as a function of an operating mean of the whole set of refrigerators/liquefiers L/R, so as to cause all the refrigerators/liquefiers L/R to converge toward this mean.
This adjustment may be implemented via controllers of the “proportional integral” (PI) type for controlling the working-gas circuits.
For preference, the apparatus performs real-time control of the at least one working-gas flow control valve of at least one refrigerator/liquefier (L/R) as a function of the difference between the instantaneous values of the parameter with respect to said dynamic mean value, so as to cause said instantaneous values of said operating parameter of the various refrigerators/liquefiers R/L to converge toward this dynamic mean value.
Various examples of the control of the apparatus will be described with reference to
As partially illustrated in
Each compression station 2 comprises a bypass circuit 14 for selectively bypassing the low-pressure compressor 12 and which is equipped with a variable-opening controlled bypass valve 4.
The apparatus comprises, for each of the refrigerators/liquefiers L/R, a sensor 13 for measuring the operating parameter consisting of the instantaneous value of the flow rate Q of the return flow 31 of working gas returning to the compression station 2. This measurement sensor 3 is, for example, situated within the cold box 3, upstream of one or more exchangers 26 which both cool toward the working gas toward the application and heat the working gas returning toward the compression station 2.
The electronic logic 50 may perform real-time calculation of the dynamic mean value of this operating parameter for all the refrigerators/liquefiers L/R. The electronic logic 50 performs real-time control of the opening/closing of each bypass valve 14 as a function of the difference between the instantaneous values of the operating parameter of the refrigerator/liquefier concerned so as to cause said instantaneous values of said operating parameter of the various refrigerators/liquefiers R/L to converge toward this dynamic mean value.
For example, the opening/closing of each bypass valve 14 is controlled according to a pressure set point CP according to a formula of the type CP=A−B·ΔQ, where A is a predetermined pressure value, B is a predetermined coefficient (dimensions=pressure/flow rate) and ΔQ is the differential (dimensions=flow rate) between, on the one hand, the dynamic mean value of the flow rate of the three coolers and, on the other hand, the instantaneous flow rate of the refrigerator/liquefier concerned.
In addition, each refrigerator/liquefier L/R may comprise a sensor 15 for measuring the temperature differential DT=T31−T32 of the working gas between the return flow 31 (returning to the compression station) and the “outbound” flow 32 (toward the application 1) which are situated in the cold box (3) in a part of the circuit that has one and the same determined temperature range.
The expression “one and the same temperature range in the cold box” means points on the working circuit at which the outbound flow 32 (toward the application that is to be cooled 1) and return flow 31 (toward the compression station 2) are situated at the same level with respect to the cooling exchangers of the cold box 3 (for example, the two measurement points are situated in legs of the circuit which are situated between two same cooling exchangers). What that means to say is that the two points on the circuit have relatively similar temperatures, for example differing by just a few degrees Kelvin (typically between 0.1 and 4° K. of difference).
The outbound flow 32 is, for example, the flow of working gas leaving a cooling exchanger of the cold box (for example at the outlet of the first heat exchanger which cools the working gas after it has passed through the compression station 2). The return flow 31 in the same temperature range is the part of the working circuit in which the working gas returns toward the compression station 2 before entering this same heat exchanger. According to one advantageous feature, the control of each bypass valve 14 may be corrected as a function of the discrepancy between said temperature differential DT=T31−T32 for the refrigerator/liquefier L/R concerned with respect to the mean of said temperature differential DT=T31−T32 calculated for all of the refrigerators/liquefiers L/R. This temperature differential DT=T31−T32 is indicative of the imbalance in the flow rates of working gas between the return flow 31 (toward the compression station) and the outbound flow 32 (toward the application 1).
For example, the opening of each bypass valve 14 may be increased when the temperature differential DT=T31−T32 for the refrigerator/liquefier L/R concerned increases (in terms of absolute value) with respect to the mean of said temperature differential. This control will have the effect of reducing the imbalance in the flow rates of the working gas between the return flow 31 (toward the compression station) and the outbound flow 32 (toward the application 1).
As illustrated schematically in
In addition, each refrigerator/liquefier L/R may comprise a measurement sensor 16 for measuring the operating parameter consisting of the instantaneous value of the flow rate of the flow 30 of gas at the outlet of the compression station 2.
As previously, the electronic logic 50 may be configured to perform real-time calculation of the dynamic mean of this operating parameter for all the refrigerators/liquefiers L/R. The electronic logic 50 may perform real-time control of the opening/closing of each outlet valve 11 according to the difference between the instantaneous values of the operating parameter of the refrigerator/liquefier concerned so as to cause said instantaneous values of said operating parameter of the various refrigerators/liquefiers R/L to converge toward this dynamic mean value.
For example, the opening/closing of each outlet valve 11 is controlled according to a pressure set point CP according to a formula of the type CP=C+D·ΔQ, where B is a predetermined pressure value, C is a predetermined coefficient (dimensions=pressure/flow rate) and ΔQ is the differential (dimensions=flow rate) between, on the one hand, the dynamic mean value of this flow rate for the three coolers and, on the other hand, this instantaneous flow rate for the refrigerator/liquefier concerned.
As illustrated in
Each main pipe 19 comprises a variable-opening controlled downstream valve 5 situated downstream of the cooling exchanger 20. Each apparatus comprises a sensor 24 of the operating parameter consisting of the instantaneous value of the flow rate of the flow of working gas in said main pipe 23 downstream of the flow cooling exchanger 20.
The electronic logic 50 may be configured to perform real-time calculation of the dynamic mean value of this operating parameter for all the refrigerators/liquefiers L/R and to perform real-time control of the opening/closing of each downstream valve 5 as a function of the difference between the instantaneous values of this operating parameter of the refrigerator/liquefier concerned so as to cause said instantaneous values of said operating parameter of the various refrigerators/liquefiers R/L to converge toward this dynamic mean value.
For example, the secondary pipe 23 is equipped with a variable-opening distribution valve 25, the opening of which is increased in the event of increased production of liquefied working gas in the cold box 3. In addition, control of each downstream valve 5 may be corrected according to the degree of opening of the distribution valve 25 so as to reduce the opening of the downstream valve 5 when the opening of the distribution valve 25 increases, and vice versa.
As illustrated in
As depicted, the bypass pipe 27 is connected to several portions of the working circuit in a heat exchange relationship with the exchangers 26 via respective controlled bypass valves 6, 7, 8 (valves with variable opening).
Each refrigerator/liquefier may comprise a measurement sensor 28 for measuring the operating parameter consisting of the instantaneous value of the flow rate of the flow of gas in said bypass pipe 27. The electronic logic 50 may comprise a step of real-time calculation of the dynamic mean value of this operating parameter for all the refrigerators/liquefiers L/R and for the real-time control of the opening/closing of at least one of the bypass valves 6, 7, 8 as a function of the difference between the instantaneous values and the dynamic mean value of this operating parameter of the refrigerator/liquefier concerned, so as to cause said instantaneous values of said operating parameter of the various refrigerators/liquefiers R/L to converge toward this dynamic mean value.
For example, the opening/closing of the bypass valve 7 is controlled according to a pressure set point CP according to a formula of the type CP=G+H·ΔQ, where G is a predetermined pressure value, G is a predetermined coefficient (dimensions=pressure/flow rate) and ΔQ is the differential (dimensions=flow rate) between, on the one hand, the dynamic mean value of this flow rate for the three coolers and, on the other hand, this instantaneous flow rate for the refrigerator/liquefier concerned. The other bypass valves 6, 8 allow adjustment of the temperature of the circuit for the refrigerator/liquefier concerned. As illustrated in
Each cold box 3 comprises a measurement sensor 130 for measuring the operating parameter consisting of the instantaneous value of the flow rate of the flow of gas in said hot leg 129.
The electronic logic 50 may be configured to perform real-time calculation of the dynamic mean value of this operating parameter for all the refrigerators/liquefiers and to perform real-time control of the opening/closing of the valve 9 of the hot leg 129 as a function of the difference between the instantaneous values and the dynamic mean value of this operating parameter of the refrigerator/liquefier concerned, so as to cause said instantaneous values of said operating parameter of the various refrigerators/liquefiers to converge toward this dynamic mean value.
For example, the opening/closing of each valve 9 of the hot leg is controlled according to a pressure set point CP according to a formula of the type CP=I+J·ΔQ, where I is a predetermined pressure value, J is a predetermined coefficient (dimensions=pressure/flow rate) and ΔQ is the differential (dimensions=flow rate) between, on the one hand, the dynamic mean value of this flow rate for the three coolers and, on the other hand, this instantaneous flow rate for the refrigerator/liquefier concerned.
Similarly, each cold leg 229 comprises a variable-opening controlled regulating valve 10 and a measurement sensor 131 for measuring the operating parameter consisting of the instantaneous value of the flow rate of the flow of gas in said leg 229. The electronic logic 50 may be configured to perform real-time calculation of the dynamic mean value of this operating parameter for all the refrigerators/liquefiers and to perform real-time control of the opening/closing of the valve 10 of the cold leg 229 as a function of the difference between the instantaneous values and the dynamic mean value of this operating parameter of the refrigerator/liquefier concerned, so as to cause said instantaneous values of said operating parameter of the various refrigerators/liquefiers R/L to converge toward this dynamic mean value.
As before, the opening/closing of each valve 10 of the cold leg may be controlled according to a pressure set point CP according to a formula of the type CP=K+L·ΔQ, where K is a predetermined pressure value, L is a predetermined coefficient (dimensions=pressure/flow rate) and ΔQ is the differential (dimensions=flow rate) between, on the one hand, the dynamic mean value of this flow rate for the three coolers and, on the other hand, this instantaneous flow rate for the refrigerator/liquefier concerned.
It will be understood that many additional changes in the details, materials, steps and arrangement of parts, which have been herein described in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims. Thus, the present invention is not intended to be limited to the specific embodiments in the examples given above.
| Number | Date | Country | Kind |
|---|---|---|---|
| 14 57100 | Jul 2014 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2015/051492 | 6/5/2015 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2016/012677 | 1/28/2016 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 3167113 | Kleiss | Jan 1965 | A |
| 20140238070 | Bernhardt et al. | Aug 2014 | A1 |
| Number | Date | Country |
|---|---|---|
| 2 954 973 | Jul 2011 | FR |
| WO 2013 041789 | Mar 2013 | WO |
| Entry |
|---|
| Butkevitch et al., Parallel Operation of Cryogenic Units with a Single Steady-State Operated Device, ICEC 14 Proceedings, ICEC Supplement, Cryogenics, 1992, pp. 130-133, vol. 32. |
| French Search Report and Written Opinion for FR 1 457 100 dated Mar. 20, 2015. |
| International Search Report and Written Opinion for PCT/FR2015/051492 dated Aug. 28, 2015. |
| International Search Report and Written Opinion for PCT/FR2015/051492 dated Aug. 28, 2015 (English machine translation). |
| Number | Date | Country | |
|---|---|---|---|
| 20170219265 A1 | Aug 2017 | US |
