Refrigeration device and method

Abstract

Refrigeration device comprising a working circuit (10) of working fluid forming a cycle comprising a mechanism (2, 3) for compression, cooling, expansion and heating, an electric motor (11) driving in rotation a shaft (15) which carries a compressor wheel (2), an electronic controller (12) configured to receive a signal (13) demanding a defined cooling power (P) and, in response, to control the speed of rotation (V) of the motor (11), the electronic controller (12) being configured to limit the maximum operating speed (Vmf) of the motor (11) to a value less than or equal to its maximum design speed (Vmc), in nominal operation, the electronic controller (12) fixing the maximum operating speed (Vmf) of the motor at the speed of rotation that supplies the cold power (P), and regulating the speed of rotation (V) of the motor in accordance with the demand for cold power, without exceeding the maximum operating speed (Vmf).

Description

Refrigeration device and method

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

[0002] The invention relates more particularly to a low-temperature refrigeration device, in particular cryogenic, i.e. at a temperature between minus 100 degrees centigrade and minus 273 degrees centigrade, comprising a working circuit forming a loop and containing a working fluid, the working circuit forming a cycle comprising in series: a working fluid compression mechanism, a working fluid cooling mechanism, a working fluid expansion mechanism and a working fluid heating mechanism, the device comprising a cooling exchanger intended to extract heat from at least one member by providing it with a determined refrigeration power by heat exchange with the working fluid circulating in the working circuit after its expansion in the expansion mechanism,the compression mechanism comprising at least one electric motor rotating a shaft carrying at least one compressor wheel at a controlled rotation speed between a minimum speed and a maximum design speed determined by the characteristics of the motor, the device being of the type with variable refrigeration power controlled by regulating the rotation speed of the motor, the device comprising an electronic controller configured to control the refrigeration power supplied by the refrigeration device by controlling the rotation speed of the motor, the electronic controller being configured to receive a signal requesting determined cooling power to be delivered and, in response, to control the rotation speed of the motor to provide said cooling power request.,

[0003] The invention relates in particular to managing the load of a cryogenic machine from a set point coming from a customer system / operator to be cooled, while leaving the system self-secured.

[0004] The invention relates in particular to managing the speed of an autonomous motor in the event of poor operating conditions (insufficient flow rate to be cooled, temperature of the fluid to be cooled already too cold, etc.). For this type of device, the cooling power supplied is a function of the speed of the motors. The higher the speed of the motor, the more cooling power the machine will deliver to the customer fluid. When the machine is in nominal operation (cooling of the customer fluid), the temperature of the working fluid is imposed by the temperature of the customer fluid. The internal regulation point of the machine is based on the temperature of the working fluid. That is to say, the speed controller will adjust 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 accelerates.On the contrary, if this measured temperature of the working fluid is below the setpoint, the motor decelerates. This setpoint is generally colder than the setpoint temperature of the customer fluid to be cooled. The speed controller will request an acceleration of the motor speed, without having any effect on the temperature of the working fluid but will increase the cooling power supplied.

[0005] For these applications, it is known to use PID type regulation, with a regulated parameter (motor speed) to maintain a measurement (cold power of the machine) at a certain setpoint (operating point coming from the customer).

[0006] The regulation of such a device depends on the quality of the parameter measurement. If one of the sensors on the cold power measurement chain is lost, it is no longer possible to correctly regulate the machine load. In addition, in known systems, the reactivity of the regulation is low because the system takes a certain time to reach the setpoint. If the "PID" type adjustment is too fast, there is a significant risk of load oscillation.

[0007] An aim of the present invention is to overcome all or part of the drawbacks of the prior art noted above.

[0008] To this end, the device according to the invention, moreover in accordance with the generic definition given in the preamble above, is essentially characterized in that the electronic controller is configured to limit the maximum operating speed of the engine to a value less than or equal to the maximum design speed, in nominal operation, that is to say when the device provides the determined cold power, the electronic controller being configured to set the maximum operating speed of the engine to the rotation speed providing the determined cold power and to regulate the rotation speed of the engine as a function of the cold power demand without exceeding said maximum operating speed.

[0009] The controller will limit the motor speed up to the maximum value. The invention therefore consists of regulating the power delivered by modifying the maximum speed that can be requested by the speed controller. The regulation on the target temperature of the working fluid to be reached remains active. Thanks to the management of the maximum speed of the motor(s), it is thus possible to regulate the cooling power delivered by the machine to the customer fluid to be cooled.

[0010] Furthermore, embodiments of the invention may comprise one or more of the following features:the electronic controller is a speed controller comprising a microprocessor and / or a computer,the device comprises at least one temperature sensor of the working fluid in the working circuit, for example at an inlet and / or at an outlet of the expansion mechanism, the electronic controller being configured to receive the measurement of the at least one temperature sensor,the electronic controller is configured to control the rotational speed of the engine to reach a target temperature value at the at least one temperature sensor,the electronic controller is configured to calculate the rotational speed value of the engine as a function of the cold power demand via a formula obtained by a regression function of the actual performance measurements of the device,the regression function is a polynomial function of degree greater than or equal to two of the cold power, said formula and in particular the coefficients of the polynomial function being calculated from actual performance measurements of the device, the compression mechanism comprises one or more compressor wheels arranged where appropriate in series and / or in parallel in the working circuit forming one or more compression stages for the working fluid, the compressor wheel(s) being driven in rotation by one or more motors, the expansion mechanism comprising one or more turbines arranged where appropriate in series and / or in parallel in the working circuit forming one or more expansion stages for the working fluid, at least one of the turbines being mounted on the same shaft of a motor driving at least one compressor wheel in rotation, the device comprises several motors,the electronic controller being configured to control the rotation speed of all or part of the motors to provide said cold power demand, the cooling exchanger intended to extract heat from at least one member comprises a fluid circulation passage for cooling a member consisting of a fluid flow.,

[0011] The invention also relates to a method for refrigerating at low temperature, i.e. at a temperature between minus 100 degrees centigrade and minus 273 degrees centigrade, a member such as a fluid flow using a refrigeration device conforming to any one of the characteristics above or below, comprising regulation of the cooling power delivered by the device by controlling the maximum operating speed of the motor.

[0012] According to a possible feature, the method comprises a step of receiving a determined cold power demand signal to be delivered by the device, a step of determining a determined rotation speed of the engine to provide said power demand, a step of setting the maximum operating speed to the value of the determined rotation speed and a step of maintaining the rotation speed of the engine 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] Other features and advantages will appear on reading the description below, made with reference to the figures in which:

[0015] represents, schematically and partially, a first example of structure and operation of a refrigeration device according to the invention,

[0016] schematically and partially represents a second example of structure and operation of a refrigeration device according to the invention,

[0017] schematically and partially represents a third example of structure and operation of a refrigeration device according to the invention,

[0018] schematically and partially represents an example of variation in the cold power produced by such a device as a function of the engine rotation speed,

[0019] schematically and partially represents an example of control of the regulation of the rotation speed of the motor.

[0020] The cryogenic refrigeration device 1, i.e. operating at a low temperature of, for example, between minus 100 degrees centigrade and minus 273 degrees centigrade, comprises a working circuit 10 forming a loop and containing a working fluid.

[0021] The working circuit 10 forms a cycle comprising in series: a mechanism 2, 3 for compressing the working fluid, a mechanism 6, 16 for cooling the working fluid, a mechanism 7 for expanding the working fluid and a mechanism 6, 8 for heating the working fluid.

[0022] The device 1 comprises a cooling exchanger 8 intended to extract heat from at least one member 25 or user by providing it with a cooling power P determined by heat exchange with the working fluid circulating in the working circuit 10 after its expansion in the expansion mechanism 7. The cooling exchanger 8 intended to extract heat from at least one member 25 comprises for example a fluid circulation passage for cooling a member 25 consisting for example of a flow of fluid to be cooled.

[0023] The compression mechanism 2, 3 comprises at least one electric motor 11 rotating a shaft 15 carrying at least one compressor wheel 2 at a controlled rotation speed between a minimum speed and a maximum design speed Vmc of the motor which is determined for example by the design and manufacturing characteristics of the motor 11.

[0024] As illustrated in the various examples, the compression mechanism 2, 3 may comprise one or more compressor wheels 2 arranged, where appropriate, in series and / or in parallel in the working circuit 10 and forming one or more compression stages for the working fluid. The compressor wheel(s) 2 may be driven in rotation by one or more motors 11. The expansion mechanism 7 may comprise one or more turbines 7 (and / or expansion valve(s)) arranged, where appropriate, in series and / or in parallel in the working circuit 10, forming one or more expansion stages for the working fluid.

[0025] At least one of the turbines 7 can be mounted on the same shaft 15 of an engine 11 rotating at least one compressor wheel 2.

[0026] The refrigeration device is of the variable refrigeration power P type controlled by regulating the rotation speed V of the motor 11.

[0027] For example, and as shown diagrammatically in the figure, this speed can be determined from a characteristic curve giving the cold power P as a function of the engine rotation speed. Note that the curve shown as an example is a parabolic function, however this is in no way limiting.

[0028] For example, the electronic controller 12 can be configured to calculate the value of rotation speed V of the motor as a function of the cold power demand via a formula in which said speed is given by a polynomial function of degree greater than or equal to two of the cold power P, said formula being predefined (established or calculated) from actual measured performance measurements of the device 1.

[0029] For example, these actual values ​​are measured on one device and the coefficients (the formula) can be defined for a whole range of identical devices (or each time for each machine).

[0030] As illustrated, the device 1 comprises an electronic controller 12 configured to control the refrigeration power P supplied by the refrigeration device 1 by controlling the rotation speed V of the motor(s) 11. That is to say, when there are several motors, the electronic controller 12 can be configured to control the rotation speed V of all or some of the motors 11 to provide said cold power demand.

[0031] The electronic controller 12 is, for example, a speed controller comprising a microprocessor and / or a computer. It may be integrated into the device 1 or at least partly remote.

[0032] The electronic controller 12 is in particular configured to receive a signal 13 requesting the determined cold power P to be delivered and, in response, to control the rotation speed V of the motor 11 to provide said cold power request.

[0033] According to an advantageous feature, the electronic controller 12 is configured to limit the maximum operating speed Vmf of the motor 11 to a value less than or equal to the maximum design speed Vmc. In addition, in nominal operation, that is to say when the device 1 provides the determined cold power, the electronic controller 12 is configured to set the maximum operating speed Vmf of the motor to the rotation speed providing the determined cold power P and to regulate the rotation speed V of the motor as a function of the cold power demand without exceeding said maximum operating speed Vmf. (for example Vmf is a percentage of Vmc Cf.).

[0034] That is to say, during operation, the engine speed can be varied according to the cold power P required.

[0035] The maximum operating speed Vmf of the motor can be set for example at the start of device 1 (at the start of the installation), it is the actual speed which makes it possible to deliver the nominal power requested by the customer or user 25. By "nominal operation" we mean for example the operation of the device when it supplies 100% of the nominal power.

[0036] This allows the cooling power setpoint to be quickly reached compared to a known PID type control. This solution also allows greater responsiveness to reach the setpoint at the level of the application to be cooled (pressure, temperature, etc.).

[0037] This can make the operation independent of the actual measurements of the cold power supplied. This avoids a possible regulation error in the event of an incorrect measurement (sensor drift, for example).

[0038] For example, the device 1 comprises at least one temperature sensor 9, 19 of the working fluid in the working circuit 10, for example at an inlet and / or at an outlet of the expansion mechanism 7 and the electronic controller 12 is configured to receive the measurement 14 from the at least one temperature sensor 9, 19.

[0039] For example, the electronic controller 12 is configured to control the rotation speed V of the motor 11 to reach a target temperature value at the level of the at least one temperature sensor 9, 19 in the working circuit.

[0040] The temperature target can be constant and equal to the cold temperature requested by the customer application to be cooled.

[0041] The regulation system can be autonomous with regard to temperature management (the controller 12 remains active because only the maximum speed is regulated). In the event of a problem with the flow rate of the fluid to be cooled 25 (stoppage of a pump or other), the controller 12 can adjust the rotation speed of the motor so as not to fall below the temperature setpoint of the working fluid.

[0042] The maximum operating speed of the motor Vmf is preferably limited to a value strictly lower than the maximum design speed of the motor Vmc.

[0043] In other applications, it is possible that the maximum operating speed of the Vmf motor is equal to the maximum design speed of the Vmc motor. In these applications (in the liquefaction of biomethane for example), the temperature of the customer fluid to be cooled (for example at the outlet of the cooling exchanger) is taken as a control parameter for regulating the speed of the motor(s). The measured temperature leads to a correction of the target temperature setpoint which then leads to a variation of the speed setpoint of the motor(s) (for example as a percentage % of the maximum operating speed of the motor.

Claims

Low-temperature refrigeration device, particularly cryogenic, i.e., at a temperature between -100 degrees Celsius and -273 degrees Celsius, comprising a working circuit (10) forming a loop and containing a working fluid, the working circuit (10) forming a cycle comprising in series: a working fluid compression mechanism (2, 3), a working fluid cooling mechanism (6, 16), a working fluid expansion mechanism (7), and a working fluid heating mechanism (6, 8), the device (1) comprising a cooling exchanger (8) for extracting heat from at least one component (25) by supplying it with a cooling power (P) determined by heat exchange with the working fluid circulating in the working circuit (10) after its expansion in the expansion mechanism (7), the mechanism (2,3) compression comprising at least one electric motor (11) driving in rotation a shaft (15) carrying at least one compressor wheel (2) at a controlled rotational speed between a minimum speed and a maximum design speed (Vmc) determined by the characteristics of the motor (11), the device (1) being of the type with variable refrigeration power (P) controlled by regulating the rotational speed (V) of the motor (11), the device (1) comprising an electronic controller (12) configured to control the refrigeration power (P) supplied by the refrigeration device (1) by driving the rotational speed (V) of the motor (11), the electronic controller (12) being configured to receive a signal (13) of demand for a determined cooling power (P) to be delivered and, in response, to drive the rotational speed (V) of the motor (11) to supply said cooling power demand,characterized in that the electronic controller (12) is configured to limit the maximum operating speed (Vmf) of the motor (11) to a value less than or equal to the maximum design speed (Vmc) and in that, in nominal operation, i.e. when the device (1) supplies the determined cooling power, the electronic controller (12) is configured to set the maximum operating speed (Vmf) of the motor to the rotational speed supplying the determined cooling power (P) and to regulate the rotational speed (V) of the motor according to the cooling power demand without exceeding said maximum operating speed (Vmf). Device according to claim 1, characterized in that the electronic controller (12) is a speed controller comprising a microprocessor and / or a computer. Device according to claim 1 or 2, characterized in that it comprises at least one working fluid temperature sensor (9, 19) in the working circuit (10), for example at an inlet and / or outlet of the expansion mechanism (7), the electronic controller (12) being configured to receive the measurement (14) from at least one temperature sensor (9, 19). Device according to claim 3, characterized in that the electronic controller (12) is configured to drive the rotational speed (V) of the motor (11) to reach a target temperature value at the level of at least one temperature sensor (9, 19). Device according to any one of claims 1 to 4, characterized in that the electronic controller (12) is configured to calculate the speed value (V) of rotation of the motor as a function of the cold power demand via a formula obtained by a regression function of the actual performance measurements of the device (1). Device according to claim 5, characterized in that the regression function is a polynomial function of degree greater than or equal to two of the cooling power, said formula and in particular the coefficients of the polynomial function being calculated from actual performance measurements of the device (1). Device according to any one of claims 1 to 6, characterized in that the compression mechanism (2, 3) comprises one or more compressor wheels (2) arranged optionally in series and / or in parallel in the working circuit (10) forming one or more compression stages for the working fluid, the compressor wheel(s) (2) being driven in rotation by one or more motors (11), the expansion mechanism (7) comprising one or more turbines (7) arranged optionally in series and / or in parallel in the working circuit (10) 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) driving in rotation at least one compressor wheel (2). Device according to claim 7, characterized in that it comprises several motors (11), the electronic controller (12) being configured to control the rotational speed (V) of all or part of the motors (11) to supply said cold power demand. Device according to any one of claims 1 to 8, characterized in that the cooling exchanger (8) intended to extract heat from at least one component (25) includes a fluid circulation passage for cooling a component (25) consisting of a fluid flow. A method for refrigerating at a low temperature, i.e. at a temperature between -100 degrees Celsius and -273 degrees Celsius, an element (25) such as a fluid flow using a refrigeration device according to any one of claims 1 to 9, comprising regulating the cooling power delivered by the device (1) by controlling the maximum operating speed (Vmf) of the motor (1). Method according to claim 10, characterized in that it comprises a step of receiving a signal (13) of cold power demand (P) determined to be delivered by the device (1), a step of determining a rotation speed (V) determined of the motor to provide said power demand, a step of fixing the maximum operating speed (Vmf) at the value of the determined rotation speed and a step of maintaining the rotation speed (V) of the motor at said maximum operating speed (Vmf).

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