Refrigeration device and method

Abstract

The refrigeration device comprises a working circuit (10) of a working fluid forming a cycle comprising mechanisms (2, 3) for compression, cooling, expansion and heating, an electric motor (11) rotatingly drives a shaft (15) supporting a compressor wheel (2), an electronic control device (12) configured to receive a signal (13) requesting a defined cooling power (P) and to control the rotational speed (V) of the motor (11) accordingly, the electronic control device (12) configured to limit the maximum operating speed (Vmf) of the motor (11) to a value equal to or less than its maximum design speed (Vmc), in nominal operation the electronic control device (12) fixes the maximum operating speed (Vmf) of the motor to a rotational speed that provides a cooling capacity (P) and adjusts the rotational speed (V) of the motor according to the demand for cooling capacity without exceeding the maximum operating speed (Vmf).

Description

[Technical field]

[0001] The present invention relates to a refrigeration device and method.

[0002] The present invention relates more particularly to a refrigeration device for refrigeration at low temperatures, in particular at very low temperatures, i.e. temperatures including -100 degrees Celsius to -273 degrees Celsius, the refrigeration device comprising a working circuit forming a loop and containing a working fluid, the working circuit forming a cycle comprising in series a compression mechanism for compressing the working fluid, a cooling mechanism for cooling the working fluid, an expansion mechanism for expanding the working fluid, and a heating mechanism for heating the working fluid, the device comprising a cooling heat exchanger intended to extract heat from at least one element by providing a predetermined refrigeration capacity through heat exchange with the working fluid circulating in the working circuit after it has been expanded in the expansion mechanism ... The compression mechanism includes at least one electric motor driving rotation of a shaft supporting at least one compressor impeller at a rotational speed controlled between a minimum speed and a maximum design speed determined by characteristics of the motor, the apparatus being of a type having variable refrigeration capacity controlled by adjusting the rotational speed of the motor, the apparatus including an electronic control device configured to control the refrigeration capacity delivered by the refrigeration apparatus by controlling the rotational speed of the motor, the electronic control device configured to receive a demand signal requesting a predetermined cooling capacity to be delivered and to control the rotational speed of the motor accordingly to meet the demand for said cooling capacity.

[0003] The present invention is particularly concerned with managing the load on a cryogenic machine based on control set points provided by client systems / cooled operators while automatically keeping the system safe.

[0004] The invention is particularly concerned with the autonomous management of the motor's speed, especially in the case of insufficient operating conditions (insufficient flow rate for cooling, the temperature of the fluid to be cooled is already too low, etc.). For this type of device, the cooling capacity provided depends on the motor's speed. The higher the motor's speed, the higher the cooling capacity the machine delivers to the client fluid. When the machine operates nominally (cooling the client fluid), the temperature of the working fluid is determined by the temperature of the client fluid. The internal regulation control point of the machine is based on the temperature of the working fluid. This means that the speed controller adjusts the speed of the motor to maintain this temperature of the working fluid at this setpoint. If this measured temperature of the working fluid exceeds the setpoint, the motor is accelerated. In contrast, if this measured temperature of the working fluid is lower than the setpoint, the motor is decelerated. This control setpoint is generally lower than the setpoint temperature of the client fluid to be cooled. The speed controller calls for an acceleration of the motor speed, but achieves an increase in the cooling capacity provided, without having an effect on the temperature of the working fluid. [Background technology]

[0005] For such applications, it is a known practice to employ PID control type regulation, where one parameter (motor speed) is adjusted to maintain a measured value (the cooling capacity of the machine) at a particular set point (operating point provided by the client).

[0006] The regulation of such devices relies on the quality of the measurement of the parameters. If one of the sensors in the cooling capacity measurement chain is lost, it is no longer possible to accurately regulate the load of the machine. Moreover, in known systems, the reaction of the regulation is insufficient, since the system takes a certain time to reach the set value. Excessively rapid adjustment of the "PID" control type leads to a high risk of load fluctuations. Summary of the Invention [Problem to be solved by the invention]

[0007] SUMMARY OF THE PRESENT EMBODIMENT An object of the present invention is to overcome all or part of the above-mentioned disadvantages of the prior art. [Means for solving the problem]

[0008] To this end, the device according to the invention, which further corresponds to its general definition given in the preamble above, is essentially characterized in that the electronic control device is configured to limit the maximum operating speed of the motor to a value equal to or lower than the maximum design speed, and in nominal operation, i.e. when the device is delivering a given cooling capacity, the electronic control device is configured to set the maximum operating speed of the motor to a rotational speed which delivers the given cooling capacity and to manage the rotational speed of the motor as a function of the demand for cooling capacity without exceeding said maximum operating speed.

[0009] The controller limits the motor speed to a maximum value. The invention therefore consists in regulating the delivered capacity by modifying the maximum speed that can be requested by the speed controller. The regulation remains active, based on the target temperature that the working fluid achieves. Thus, since the maximum speed of the motor or motors is managed, it becomes possible to regulate the cooling capacity delivered by the machine to the client fluid to be cooled.

[0010] Furthermore, embodiments of the invention may include one or more of the following features. - An electronic control unit is a speed control unit that includes a microprocessor and / or a computer. - the device comprises at least one temperature sensor, for example at the inlet and / or outlet of the expansion mechanism, for detecting the temperature of the working fluid of the working circuit, and the electronic control device is configured to receive the measured values ​​from the at least one temperature sensor. The electronic control device is configured to control the rotational speed of the motor in order to achieve a target temperature value at the at least one temperature sensor. The electronic control device is configured to calculate the value of the motor rotational speed as a function of the demand for cooling capacity using a formula obtained as a regression function of the actual measured values ​​of the performance of the device. the regression function is a polynomial function of the cooling capacity of order 2 or higher, said function and in particular the coefficients of the polynomial function being calculated from actual measurements of the performance of the device. - the compression mechanism comprises one or more compressor impellers, if applicable, arranged in series and / or in parallel in the working circuit and forming one or more compression stages for the working fluid, the one or more compressor impellers being rotationally driven by one or more motors, and the expansion mechanism comprises one or more turbines, if applicable, positioned in series and / or in parallel in the working circuit and forming one or more expansion stages for the working fluid, at least one of the turbines being mounted on the same shaft of the motor that drives the rotation of the at least one compressor impeller. the device comprises several motors, the electronic control device being adapted to control the rotational speed of all or some of the motors in order to meet said demand for cooling capacity; A cooling heat exchanger intended to extract heat from at least one element comprises a fluid circuit for cooling the element consisting of a fluid flow.

[0011] The invention also relates to a method of refrigeration for freezing an element such as a fluid flow to a low temperature, i.e. a temperature including between -100 degrees Celsius and -273 degrees Celsius, using a refrigeration device according to any one of the above or below characteristics, the method including regulating the cooling capacity delivered by the device by controlling the maximum operating speed of the motor.

[0012] According to one possible particular feature, the method includes receiving a demand signal requesting a predetermined cooling capacity to be delivered by the apparatus, determining a predetermined rotational speed of the motor to satisfy said demand for capacity, setting a maximum operating speed to a predetermined rotational speed value, and maintaining the rotational speed of the motor at said maximum operating speed.

[0013] The invention may also relate to any alternative device or method comprising any combination of the above or below features within the scope of the claims.

[0014] Further particular features and advantages will become apparent from the following description, which is provided with reference to the drawings. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 shows, diagrammatically and partially, a first example of the structure and operation of a refrigeration device according to the invention. [Diagram 2] FIG. 2 shows, diagrammatically and partially, a second example of the construction and operation of a refrigeration device according to the invention. [Diagram 3] FIG. 3 shows, diagrammatically and partially, a third example of the construction and operation of a refrigeration device according to the invention. [Figure 4] FIG. 4 shows, diagrammatically and partially, an example of the variation of the cooling capacity produced by the device as a function of the rotational speed of the motor. [Diagram 5] FIG. 5 shows, in a schematic and partial manner, an example of the control of the adjustment of the rotational speed of the motor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] A refrigeration device 1 for cryogenic refrigeration, ie operating at low temperatures including, for example, -100 degrees Celsius to -273 degrees Celsius, comprises a working circuit 10 forming a loop and containing a working fluid.

[0017] The working circuit 10 forms a cycle having, in series, compression mechanisms 2, 3 for compressing the working fluid, cooling mechanisms 6, 16 for cooling the working fluid, an expansion mechanism 7 for expanding the working fluid, and heating mechanisms 6, 8 for heating the working fluid.

[0018] The device 1 comprises a cooling heat exchanger 8 intended to extract heat from at least one element 25 or a user by providing a given refrigeration power P through heat exchange with a working fluid circulating in a working circuit 10 after the working fluid has been expanded in an expansion mechanism 7. The cooling heat exchanger 8 intended to extract heat from at least one element 25 comprises, for example, a fluid circuit for cooling the element 25 consisting of a flow of the fluid to be cooled.

[0019] The compression mechanism 2, 3 comprises at least one electric motor 11 driving the rotation of a shaft 15 carrying at least one compressor impeller 2, at a rotational speed controlled between a minimum speed and a maximum design speed Vmc of the motor, which speed is determined, for example, by the design and manufacturing characteristics of the motor 11.

[0020] As shown in the various examples, the compression mechanisms 2, 3 may comprise one or more compressor impellers 2, where applicable, arranged in series and / or parallel in the working circuit 10 to form one or more compression stages for the working fluid. The one or more compressor impellers 2 may be rotationally driven by one or more motors 11. Meanwhile, the expansion mechanism 7 may comprise one or more turbines 7 (and / or expansion valves), where applicable, positioned in series and / or parallel in the working circuit 10 to form one or more expansion stages for the working fluid.

[0021] At least one of the turbines 7 may be mounted on the same shaft 15 of the motor 11 that drives the rotation of at least one compressor impeller 2 .

[0022] The refrigeration device is of the type having a variable refrigeration capacity P which is controlled by adjusting the rotation speed V of the motor 11 .

[0023] For example, this speed may be determined on the basis of a characteristic curve giving the cooling capacity P as a function of the rotational speed of the motor, as shown diagrammatically in Figure 4. It should be noted that the curve shown as an example is a parabolic function, but this is entirely non-limiting.

[0024] For example, the electronic control device 12 may be configured to calculate the value of the rotational speed V of the motor as a function of the demand for cooling capacity, using an equation in which said speed is given by a polynomial function of degree 2 or higher of the cooling capacity P, said equation being predefined (determined or calculated) based on measured actual values ​​of the performance of the device 1.

[0025] For example, these actual values ​​can be measured on an apparatus and coefficients (formulas) can be defined for the entire range of the same apparatus (or for each machine in each case).

[0026] As shown, the device 1 comprises an electronic control device 12 configured to control the refrigeration capacity P provided by the refrigeration device 1 by controlling the rotation speed V of one or more motors 11. This means that when there are several motors, the electronic control device 12 may be configured to control the rotation speed V of all or some of the motors 11 in order to meet said demand for cooling capacity.

[0027] The electronic control device 12 is, for example, a speed control device that includes a microprocessor and / or a computer. The electronic control device 12 may be integrated in the device 1 or may be at least partially separate from the device 1.

[0028] The electronic control device 12 is configured in particular to receive a demand signal 13 requesting a certain cooling capacity P to be delivered and to control the rotational speed V of the motor 11 accordingly to meet the demand for cooling capacity.

[0029] According to one advantageous particular feature, the electronic control device 12 is configured to limit the maximum operating speed Vmf of the motor 11 to a value equal to or less than the maximum design speed Vmc. Moreover, in nominal operation, i.e. when the device 1 is delivering a given cooling capacity, the electronic control device 12 is configured to set the maximum operating speed Vmf of the motor to a rotational speed that delivers a given cooling capacity P and to manage the rotational speed V of the motor as a function of the demand for cooling capacity without exceeding said maximum operating speed Vmf (for example Vmf is a percentage of Vmc, see FIG. 5).

[0030] What that means is that during operation, the speed of the motor can vary as a function of the demand for cooling capacity P.

[0031] The maximum operating speed Vmf of the motor can be set, for example, at the start of operation of the device 1 (at the start of operation of the installation), and is the actual speed that allows the delivery of the nominal capacity requested by the client or user 25. "Nominal operation" is, for example, the operation of the device when it is delivering 100% of its nominal capacity.

[0032] This allows the set cooling capacity delivered to be achieved more quickly compared to known PID control type adjustments. This solution also results in a higher responsiveness in reaching the control setpoints (pressure, temperature, etc.) in the application being cooled.

[0033] This allows the operation to be independent of the actual measured value of the cooling power delivered, thereby avoiding possible errors in the adjustment in case of anomalous measurements (e.g. sensor drift).

[0034] For example, the device 1 includes at least one temperature sensor 9, 19 for detecting the temperature of the working fluid in the working circuit 10, for example at the inlet and / or outlet of the expansion mechanism 7, and the electronic control device 12 is configured to receive measurements 14 from the at least one temperature sensor 9, 19.

[0035] For example, the electronic control device 12 is configured to control the rotational speed V of the motor 11 in order to achieve a target temperature value at at least one temperature sensor 9, 19 of the actuation circuit.

[0036] The target temperature may be constant and equal to the low temperature requested by the client application to be cooled.

[0037] The regulation system may be autonomous with regard to temperature management (controller 12 remains active since only the maximum speed is regulated). If a problem occurs with the flow rate of the fluid 25 to be cooled (if the pump stops working or if some other problem occurs), controller 12 could adjust the rotational speed of the motor so that the working fluid does not fall below its set temperature.

[0038] The maximum operating speed Vmf of the motor is preferably limited to a value strictly lower than the maximum design speed Vmc of the motor.

[0039] In other applications, the maximum operating speed Vmf of the motors can be equal to the maximum design speed Vmc of the motors. In these applications (e.g., biomethane liquefaction), the temperature of the client fluid to be cooled (e.g., at the outlet of the cooling heat exchanger) is used as a control parameter to adjust the speed of one or more motors. The measured temperature leads to a correction of the target temperature setpoint, which in turn leads to a change in the speed setpoint of one or more motors (e.g., as a percentage (%) of the maximum operating speed of the motors).

Claims

1. A refrigeration device for refrigeration at low temperatures, in particular cryogenic temperatures, i.e. temperatures between -100 degrees Celsius and -273 degrees Celsius, comprising a working circuit (10) forming a loop and containing a working fluid, said working circuit (10) forming a cycle comprising in series a compression mechanism (2, 3) for compressing said working fluid, a cooling mechanism (6, 16) for cooling said working fluid, an expansion mechanism (7) for expanding said working fluid, and a heating mechanism (6, 8) for heating said working fluid, said device (1) being adapted to circulate said working fluid in said working circuit (10) and to circulate said working fluid in said working circuit (10). The compressor (2, 3) comprises at least one compressor element (25) including at least one electric motor (11) for driving the rotation of a shaft (15) carrying at least one compressor impeller (2) at a rotation speed controlled between a minimum speed and a maximum design speed (Vmc) determined by the characteristics of the motor (11). The device (1) is of a type having a variable refrigeration capacity (P) controlled by adjusting the rotation speed (V) of the motor (11), the device (1) comprises an electronic control device (12) configured to control the refrigeration capacity (P) delivered by the refrigeration device (1) by controlling the rotation speed (V) of the motor (11), the electronic control device (12) receiving a request signal (13) requesting that the predetermined cooling capacity (P) be delivered and, in response, In a refrigeration system configured to control the rotational speed (V) of the motor (11) to meet the cooling capacity requirement, the electronic control device (12) is configured to limit the maximum operating speed (Vmf) of the motor (11) to a value equal to or less than the maximum design speed (Vmc); and in nominal operation, i.e. when the system (1) is delivering the predetermined cooling capacity, the electronic control device (12) sets the maximum operating speed (Vmf) of the motor to the rotational speed that delivers the predetermined cooling capacity (P);and adapted to adjust the rotational speed (V) of the motor as a function of the demand for cooling capacity without exceeding the maximum operating speed (Vmf).

2. 2. The device according to claim 1, characterized in that the electronic control device (12) is a speed control device equipped with a microprocessor and / or a computer.

3. The device according to claim 1 or 2, characterized in that, for example, at the inlet and / or outlet of the expansion mechanism (7) is provided with at least one temperature sensor (9, 19) for detecting the temperature of the working fluid of the working circuit (10), and the electronic control device (12) is configured to receive measurement values ​​(14) from the at least one temperature sensor (9, 19).

4. 4. The device according to claim 3, characterized in that the electronic control device (12) is configured to control the rotational speed (V) of the motor (11) in order to achieve a target temperature value at the at least one temperature sensor (9, 19).

5. 5. The device according to claim 1, wherein the electronic control device (12) is configured to calculate the value of the rotational speed (V) of the motor as a function of the demand for cooling capacity, using an equation obtained as a regression function of the actual measured values ​​of the performance of the device (1).

6. 6. The device according to claim 5, characterized in that the regression function is a polynomial function of the cooling capacity of two or more orders, the equation and, in particular, the coefficients of the polynomial function being calculated from actual measurements of the performance of the device (1).

7. 7. The apparatus according to any one of claims 1 to 6, characterized in that the compression mechanism (2, 3) comprises one or more compressor impellers (2), if applicable, arranged in series and / or in parallel in the working circuit (10) and forming one or more compression stages for the working fluid, the one or more compressor impellers (2) being driven in rotation by one or more motors (11), and the expansion mechanism (7) comprises one or more turbines (7), if applicable, positioned in series and / or in parallel in the working circuit (10) and forming one or more expansion stages for the working fluid, at least one of the turbines (7) being mounted on the same shaft (15) of a motor (11) that drives the rotation of at least one compressor impeller (2).

8. 8. The device according to claim 7, characterized in that it comprises several motors (11), the electronic control device (12) being configured to control the rotational speed (V) of all or some of the motors (11) in order to meet the demand for cooling capacity.

9. 9. Apparatus according to any one of the preceding claims, characterized in that the cooling heat exchanger (8) intended to extract heat from at least one element (25) comprises a fluid circuit for cooling the element (25) consisting of a fluid flow.

10. A refrigeration method for freezing an element (25), such as a fluid flow, to low temperatures, i.e. temperatures between -100 degrees Celsius and -273 degrees Celsius, using a refrigeration device according to any one of claims 1 to 9, comprising regulating the cooling capacity delivered by the device (1) by controlling the maximum operating speed (Vmf) of the motor (1).

11. 11. The method according to claim 10, characterized in that it comprises the steps of receiving a demand signal (13) requesting a given cooling capacity (P) to be delivered by the device (1), determining a given rotational speed (V) of the motor to meet said demand for capacity, setting the maximum operating speed (Vmf) to said given rotational speed value, and maintaining the rotational speed (V) of the motor at said maximum operating speed (Vmf).

Images