Compressor device and operation method thereof

Abstract

The present invention relates to a compressor unit (1) comprising a screw compressor (3) capable of producing a compressed air-oil mixture, a compressor unit outlet (13), an oil separator (11) to which the compressed air-oil mixture can be transferred and to which the compressed air and oil from the compressed air-oil mixture can be separated from each other and the compressed air can be discharged at the compressor unit outlet (13), an oil separation duct (15) connecting the oil separator (11) to the screw compressor (3) and constituting a fan unit (19) of an oil cooler (17), and a control unit (21) capable of adjusting the speed (n) of the fan (19) and thus the cooling of the oil in the oil cooler (17).

Description

[Technical Field]

[0001] The present invention relates to a compressor device and a method for operating the same. [Background technology]

[0002] Conventional compressor designs typically incorporate measures to mitigate condensation of humidity from the air drawn into the compressor. However, the effect of the cooling intensity on the specific power output of the compressor at the corresponding operating point is often overlooked or ignored.

[0003] Typically, an expansion element may be installed, in which case the compression end temperature of the air-oil mixture is preset to a specific value. This set point may be configured to reduce condensation of intake air humidity in the oil-injected screw compressor, but may be inefficient in terms of cooling intensity and the associated achievable specific power at the respective operating point.

[0004] Prior art document WO 0246617 describes a method for controlling a compressor system comprising at least one oil-cooled compressor element.

[0005] SUMMARY OF THE INVENTION It is therefore a basic object of the present invention to provide a compressor unit and a method for operating the same, which allows the compressor unit to be operated in a particularly energy-efficient manner. Summary of the Invention

[0006] This problem is solved by the features of the independent claims. Further preferred embodiments are disclosed in the dependent claims.

[0007] According to independent claim 1, the following is provided: a screw compressor capable of producing a compressed air-oil mixture; a compressor unit outlet; an oil separator to which the compressed air-oil mixture can be transferred and to which the compressed air and oil can be separated from each other from the compressed air-oil mixture, and to which the compressed air can be discharged at the compressor unit outlet; an oil separation duct connecting the oil separator to the screw compressor and comprising a fan unit in the oil cooler; and a control device capable of adjusting the speed of the fan and therefore the cooling of the oil in the oil cooler, wherein the control device is capable of determining a current operating point of the compressor unit; the control device determines a value of the oil cooling parameter from the plurality of operating parameters using a predetermined performance map or formula reflecting a relationship between the plurality of operating parameters characterizing a current operating point and the oil cooling parameter, the plurality of operating parameters including at least a speed of the screw compressor and a pressure of the generated air-oil mixture or a pressure of the generated compressed air, and the oil cooling parameter includes a temperature of the generated air-oil mixture, an oil temperature downstream of the oil cooler, or a speed of the fan device; The determined values ​​of the oil cooling parameters are ,Ko Compressor device at a defined specific power or within a predefined range from the minimum specific power value driving do Therefore, it can be adjusted by the control device. the law of nature , The specific power is the quotient of the total power consumption of the compressor device and the volumetric flow rate of the compressed air produced, It is a compressor device.

[0008] Furthermore, according to independent claim 4, the following is provided: compression was a screw compressor capable of generating an air-oil mixture; a compressor unit outlet; an oil separator to which the compressed air-oil mixture can be transferred and to which the compressed air and oil from the compressed air-oil mixture can be separated from each other and which can discharge the compressed air from the compressor unit outlet; an oil separation duct connecting the oil separator to the screw compressor and provided with a fan unit in the oil cooler; and a control device capable of adjusting the speed of the fan and therefore the cooling of the oil in the oil cooler, wherein a current operating point of the compressor unit can be determined by the control device; The control device uses a predetermined performance map or a formula reflecting the relationship between a plurality of operating parameters characterizing a current operating point and the oil cooling parameter to determine a value of the oil cooling parameter from the two operating parameters, the plurality of operating parameters including at least a speed of the screw compressor and a pressure of the generated air-oil mixture or a pressure of the generated compressed air, and the oil cooling parameter includes a temperature of the generated air-oil mixture, an oil temperature downstream of the oil cooler, or a speed of the fan device; The determined values ​​of the oil cooling parameters are ,Ko Compressor device at a defined specific power or within a predefined range from the minimum specific power value driving do To achieve this, the control device adjusts wherein the specific power is the quotient of the total power consumption of the compressor device (1) and the volumetric flow rate of the compressed air generated. A method for operating a compressor device.

[0009] In this way, it is possible to influence the cooling intensity of an air-cooled, fluid-injected compressor unit ("package") equipped with at least one fan with variable speed for conveying a variable amount of cooling air through the cooler, with the aim of operating the machine within predetermined limits at the respective operating point with the optimum (minimum) specific power. This operating mode helps to reduce the energy consumption of the compressor unit. The compressor unit can be a single-stage or multi-stage compressor unit with at least one screw compressor driven at a fixed or variable speed.

[0010] The specific power of a compressor unit is calculated as the quotient of the total power consumption of the compressor unit (dividend) and the discharge rate of the compressor unit (divisor). It should be noted that power is consumed during operation by many components, including the control unit, the fan unit drive, and the screw compressor drive. The discharge rate can be defined as the volumetric flow rate of compressed air, preferably generated downstream of the oil separator. The volumetric flow rate can be measured using an appropriate measuring device.

[0011] The objective is to change and adjust the intensity of the cooling process of the compressor unit by influencing the fan speed in such a way as to optimize the specific power of the compressor unit at the corresponding operating point, i.e., to bring it as close as possible to the optimum level (i.e., minimum value). External constraints may impose upper and lower limits on the intensity of the cooling process. These include the maximum allowable temperature of components or working materials, or the minimum allowable temperature to avoid condensation of moisture drawn into the compressor unit. The cooling intensity can be changed within these allowable limits, but even with higher or lower cooling intensities outside these limits, further improvements in specific power can be achieved.

[0012] According to a specific example embodiment, the compressor unit may comprise an air-cooled, single-stage, oil-injected screw compressor with a variable speed fan for variable drive speed of the screw compressor and for conveying a variable amount of cooling air through a fan unit in the oil circuit.

[0013] In this embodiment, the operating point can be characterized by the pressure at the compressor unit outlet or the internal pressure of the compressor unit (oil separator wet side), the speed of the screw compressor, the temperature and density of the available cooling air at the inlet to the screw compressor, the flow resistance of the cooling air at the inlet or outlet resulting from the compressor's installation conditions, the current oil properties (e.g., viscosity class and viscosity index), the fouling state of the oil separator cartridge, and the fouling state of the cooler. This operating point results from external boundary conditions, the current aging state of components or working materials within the compressor, the pressure or volumetric flow control method (discharge control method) implemented in the compressor control system, and / or control commands from a higher-level control system to the compressor control system. The operating point is time-variable and can be considered to be predetermined at any given time.

[0014] Increasing the fan speed not only increases the power consumption of the fan drive unit, but also increases the amount of cooling air, resulting in more intensive cooling of the compressor (and in a specific embodiment, the oil in the fan unit). This more intensive cooling also reduces the temperature at which the oil is injected into the screw compressor and the temperature at which the air and oil mixture leaves the screw compressor (the compression end temperature, VET). Lower oil temperatures increase the oil's working viscosity, which increases the viscosity loss during oil transport within the screw compressor, thereby increasing the required shaft power. Higher working viscosity improves the oil's sealing effect within the screw compressor, thereby reducing internal leakage losses during the compression process, which in turn affects the screw compressor's discharge volume and required shaft power.

[0015] The strength and sign of the effect of increasing the fan speed or increasing the cooling on the discharge rate and required shaft power of the screw compressor depend on the current operating point and the current fan speed. For example, an increase in the fan speed always results in an increase in the power consumption of the fan drive, but an increase in the fan speed can increase or decrease the discharge rate or required shaft power of the screw compressor depending on the current operating point and the current fan speed.

[0016] A reduced fan speed has a similar effect, though with a different manifestation.

[0017] Varying the fan speed has the following effects at each operating point: - Changes in power consumption of fan drive - Changes in the required shaft power of the screw compressor - Changes in power consumption of fan drive

[0018] These variables are included in the specific power output of the compressor unit (the quotient of the total power consumption and the discharge volume). When the above effects are combined, there exists a fan speed at each operating point at which the specific power output of the compressor unit is optimal, i.e., minimal. This can be called the optimal fan speed, and includes the optimal cooling power, in particular the optimal VET or optimal oil injection temperature.

[0019] The objective is to essentially adjust the optimum fan speed or optimum cooling power, in particular the associated optimum VET, during operation of the compressor unit, to track the changes in the operating point over time, provided that the cooling power is maintained within the tolerance limits, or to approach this optimum as closely as possible, provided that this is possible while respecting the tolerance limits of the cooling power.

[0020] These tolerance limits can be fixed or variable. An example of a fixed limit on cooling intensity is the VET upper limit to counteract oil degradation over time.

[0021] In a preferred embodiment, the compressor unit has an oil temperature sensor between the fan unit and the screw compressor. The compressor unit may have at least one air temperature sensor for the air drawn in by the screw compressor and / or the ambient air. The compressor unit may further have a temperature sensor for measuring the temperature of the air-oil mixture, particularly at the outlet of the screw compressor. Furthermore, the compressor unit may have a pressure sensor for measuring the pressure of the generated air-oil mixture, particularly in or at the oil separator. The compressor unit may also have a pressure sensor for measuring the pressure of the generated compressed air, particularly downstream of the oil separator or at the compressor unit outlet. The control unit may be connected to at least one of these sensors and configured to read them.

[0022] The control device can adjust, in particular manually or automatically, multiple defined pressures for the compressed air generated by the compressor device. For variable operation, multiple defined and / or variable speeds of the screw compressor can be adjusted by the control device. The control device can then approach different speeds, for example, depending on the pressure resulting from the user's compressed air demand. In a preferred method, multiple, in particular two, operating points of the compressor device can be determined using a relationship reflecting the relationship between the operating parameter and the oil cooling parameter to determine the current operating point. By taking into account the two operating parameters that characterize the operating point in the relationship, operation can be optimized particularly simply and effectively.

[0023] To determine the current operating point, it is particularly preferred to determine the speed of the screw compressor as an operating parameter and the pressure of the air-oil mixture, particularly generated in or at the oil separator, as an operating parameter. The oil cooling parameter is therefore determined via a relationship as a function of these two operating parameters. Determining the pressure of the air-oil mixture is advantageous here, since an increase in the pressure loss in the oil separator, particularly in the oil separator cartridge of the oil separator, does not affect the pressure of the air-oil mixture or the pressure on the wet side of the oil separator.

[0024] Alternatively, the current operating point can be determined by determining the speed of the screw compressor as an operating parameter and the pressure of the compressed air generated downstream of the oil separator, in particular at the compressor unit outlet, as an operating parameter, and the oil cooling parameter is therefore determined via a relationship as a function of these two operating parameters.

[0025] In principle, the oil cooling parameter can be formed by the speed of the fan assigned to the fan device, and the fan device is controlled in a defined manner by the control device to adjust the speed derived from the relationship, thereby adjusting the speed.

[0026] Preferably, however, the oil cooling parameter is formed in particular by the temperature of the air-oil mixture produced at the outlet of the screw compressor, the temperature of the air-oil mixture being derived from the relationship and being adjusted and / or regulated by the control device and the fan device.

[0027] A particularly simple design involves modifying the VET control method, which is typically present in compressor units and uses fan speed as a control variable. This involves determining and using a VET setpoint for each operating point, and adjusting this setpoint to achieve the optimum fan speed or the optimum cooling power, which corresponds to the optimum or minimum specific power.

[0028] Alternatively, the oil cooling parameter can be formed by the oil temperature downstream of the oil cooler, in particular at the oil inlet of the screw compressor, and the oil temperature resulting from the relationship is adjusted and / or regulated by the control device and the fan device.

[0029] The relationship can be specifically designed as a performance map and / or a formula derived from a mathematical expression. Preferably, the mathematical expression is a performance map approximation of a performance map determined in tests. Alternatively, the relationship can be designed as a performance map and stored in the control device.

[0030] For example, a series of tests can be run at multiple operating points to determine the optimum VET setting for each operating point, which will optimize the specific power output. A performance map can be created from the series of tests, from which the optimum VET setting for each operating point can be obtained or calculated, and adjustments by changing the fan speed can provide a good approximation of the optimum specific power output for the screw compressor. This performance map can then be used to determine the optimum VET setting for the current operating point.

[0031] When deriving the performance map, individual variables characterizing the operating point that have a relatively small influence on the optimal cooling intensity can be omitted. For example, if an operating point is characterized only by the pressure at the outlet of the compressor unit and the speed of the screw compressor, and fixed reference values ​​are used for all other variables characterizing the operating point, a method is obtained that works reliably in practice and achieves the optimal specific power to a good approximation.

[0032] An example of a fixed reference value that can be used as a basis for creating a performance map is the temperature of the available cooling air (the performance map created is based on a cooling air temperature of, for example, 20°C) and the particular oil in the new conditions (viscosity class and viscosity index).

[0033] In a preferred method, the temperature of the air drawn in by the compressor device and / or the ambient air can be determined by the control device, and the oil cooling parameter determined by the relationship is corrected according to a predetermined correction model, particularly in the form of a mathematical formula, that takes the determined air temperature into account, whereby the oil cooling parameter corrected by the correction model is preferably adjusted by the control device. In this way, the current air temperature can be taken into account simply and effectively.

[0034] A drawback of the embodiment based solely on the performance map is that the method does not receive feedback on whether or how the setting of the setpoint based on the performance map value actually leads to an adjustment of the optimal cooling intensity or the optimal specific power. If the performance map does not take into account relevant variables characterizing the operating point, there may be a relevant difference between the actual optimal cooling intensity at each operating point and the cooling intensity set based on the performance map value, and the actual specific power may not reach the optimum. For example, if the temperature of the available cooling air is not considered when creating the performance map and the series of tests used to create the performance map were performed only at a reference temperature, different temperatures of the available cooling air will affect the cooling intensity set by the process when the process is actually performed. The series of tests shows that when the temperature of the available cooling air is high and there is no change in the variables characterizing the operating point, the optimal specific power will be adjusted to a higher VET, which includes the optimal fan speed or the optimal cooling intensity.

[0035] For example, if the current temperature of the available cooling air is taken into account, the target VET determined from the performance map can be mathematically corrected at the operating point. As a first approximation, the deviation from the reference temperature when calculating the target VET can be written as follows:

[0036] VET Soll,korr =VET Soll +[(ta-tr)×n / n max ] where ta is the temperature of the available cooling air, tr is the reference temperature when the performance map was created, and n is the screw compressor speed.

[0037] In a further preferred method, a search, in particular an iterative search, for a second value, in particular an optimum value, of the oil cooling parameter at which the compressor unit operates with a lower specific power than at the first value of the oil cooling parameter derived from the relationship, in particular corrected, can be carried out by the control device at the current operating point, in this way an operating mode of the compressor unit with a particularly low specific power can be achieved.

[0038] Preferably, if a second value is found during the search, the second value is adjusted by the controller at the current operating point.

[0039] In a preferred specific embodiment, multiple values ​​of the oil cooling parameter are adjusted by the control device, in particular for the iterative search for the second value, and the specific power of the compressor device is determined and / or estimated by the control device for each adjusted value.

[0040] If the oil cooling parameter considered in the relationship is fan speed, some values ​​for the fan speed can be adjusted when searching for the second value. If the oil cooling parameter considered in the relationship is VET, some values ​​for VET or fan speed can be adjusted when searching for the second value. If the oil cooling parameter considered in the relationship is oil injection temperature, some values ​​for the oil injection temperature or fan speed can be adjusted when searching for the second value.

[0041] The iterative search can be performed, for example, as follows. Starting point (e.g., |VET Soll -VET IstStarting from a specific power output (|<0.5K), iterative incremental changes to the cooling intensity can be performed. The effect of the change steps on the specific power output is then evaluated, and based on this, a next change step that is likely to improve the specific power output can be determined. For example, if a previous change step that increased the fan speed by one speed increment improved (i.e., reduced) the specific power output, the fan speed can be increased again by one speed increment in the next change step. Otherwise, the fan speed can be decreased by one speed increment. The size of the speed increment for changing the fan speed can be, for example, 20 rpm at the start of the iteration. The amount of the speed increment can advantageously be adapted to the change in specific power observed in the previous change step relative to the previous speed increment (step size control). This advantageously allows for small incremental changes when the cooling intensity is close to optimal, and large incremental changes when the current cooling intensity is far from optimal.

[0042] There are several options for evaluating specific power output changes during incremental iterations. For example, the total power consumption and discharge rate of the screw compressor can be measured by suitable sensors and made available to the process. From this, the process can calculate the specific power output as the quotient of the total power consumption and discharge rate of the screw compressor. The evaluation of the change consists of comparing the specific power output calculated based on measurements before and after the change step. Alternatively, all or part of these measurements can be replaced by so-called "virtual sensors" or "virtual sensor values." These are calculated or simulated values ​​based on appropriate models and represent a good approximation of the actual values ​​of physical variables, even when measurements from actual sensors for these physical variables are not available or used. For example, conventional frequency inverters provide an approximation of the frequency inverter's power consumption via an interface based, at least in part, on such "virtual sensors."

[0043] The compressor device may advantageously be characterized by the features and advantages already mentioned in the context of the method, and vice versa. [Brief explanation of the drawings]

[0044] The invention will now be described in more detail with reference to the drawings in which: [Figure 1] 1 is a schematic diagram showing a first embodiment of a compressor device according to the present invention. [Figure 2] FIG. 2 is a diagram illustrating the operation of the compressor device. [Figure 3] FIG. 2 is a schematic diagram of a performance map for the operation of the compressor unit; [Figure 4] 10 is a table illustrating a method for determining a performance map. [Figure 5] FIG. 3 is a diagram showing a second embodiment of the compressor device according to the present invention shown in FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0045] 1 shows a schematic representation of a compressor unit 1. The compressor unit 1 comprises an oil-injected screw compressor 3 for generating compressed air. The compressor 3 is driven by a drive motor 5, here designed as an electric motor.

[0046] During operation of the compressor 3, air 8 is drawn in through the air inlet 6, compressed in the compression chamber of the compressor 3, and mixed with oil. The air-oil mixture 9 leaving the compressor 3 is fed to an oil separator vessel 11 for separating oil from the resulting compressed air. From the oil separator 11, the oil-free compressed air 12 is led to the compressor unit outlet 13 of the compressor unit 1. A compressed air cooler (not shown) can be arranged between the oil separator 11 and the compressor unit outlet 13 to cool the resulting compressed air. The separated oil 15 is returned to the compressor 3 via an oil separation duct 16 equipped with a fan unit 17 and injected into its compression chamber.

[0047] A fan 19 is attached to the fan device 17 for feeding cooling air to the fan device 17. The fan or ventilation device 19 is driven here by a speed-controlled drive motor 20. The speed of the fan 19 can be variably adjusted to defined speed values ​​via a control device 21 of the compressor device 1. In this way, the cooling air supplied by the fan 19 to the fan device 17, and thus also the cooling of the oil 15, is regulated.

[0048] The speed of the screw compressor 3 can also be variably adjusted at defined speed values ​​by the control device 21. Furthermore, measured values ​​from several sensors 25, 29, 31, 35, 36 are sent to the control device 21.

[0049] The temperature T of the air 8 drawn in by the screw compressor 3 is measured by a temperature sensor 25. Instead of the temperature of the drawn in air, the temperature of the ambient air can also be measured. A temperature sensor 29 is used to measure the temperature T of the air-oil mixture 9 at the outlet 37 of the compressor 3 (compression end temperature, VET). A pressure sensor 31 is used to measure the internal pressure p of the air-oil mixture 9 in the oil separator 11, upstream of the oil separation element 39 or on the wet side of the oil separator 11, as viewed in the flow direction. A pressure sensor 35 arranged downstream of the oil separator 11 is used to measure the pressure p of the compressed air produced at the compressor unit outlet 13 (final system pressure). Furthermore, a temperature sensor 36 measures the temperature T of the oil 15 downstream of the fan unit 17 at the oil inlet 18 of the compressor 3 (oil injection temperature).

[0050] The relationship in the form of a mathematical equation is also stored in the control device 21. This equation is used to map or approximate a performance map 41 (FIG. 3) determined in a series of tests. This equation is used by the control device 21 to determine the compression end temperature (VET) as an oil cooling parameter when the compressor unit 1 is operated at its current operating point with a particularly low specific power and, correspondingly, a particularly high energy efficiency. This VET can be adjusted by the control device 21 via the adjustable speed of the fan 19 and the temperature sensor 29.

[0051] 3, the internal pressure p of the air-oil mixture 9 in the oil separator 11 and the current speed n of the compressor 3 are entered into a performance map 41 as operating parameters characterizing the current operating point of the compressor unit 1. In principle, further or other operating parameters can also be taken into account in the performance map 41.

[0052] In the case of a speed-controlled screw compressor, the current speed n of the screw compressor is already available in the control device and this value can be calculated in the frequency converter of the drive motor. It is also possible to measure the current speed n of the compressor 3 during operation.

[0053] The VET is also entered into the performance map 41. In the schematic representation of the performance map 41 in Figure 3, three temperature ranges 43, 45, 47 of the VET are shown by way of example with different hatching. The temperature ranges 43, 45, 47 are shown on a temperature scale 49.

[0054] The performance map 41 reflects the relationship between the operating parameters and the VET. Depending on the values ​​of the operating parameters, the control device 21 can derive an assigned value of the VET from the performance map 41. The assigned value is the VET when the compressor device 1 is operated at a particularly low specific power at the current operating point. Depending on the pressure p and the speed n, the VET when the compressor device 1 is operated at a particularly low specific power varies.

[0055] It can also be seen from the performance map 41 that at a certain internal pressure p at a higher speed n, a higher VET is derived from the performance map 41 than at a lower speed n. Therefore, at a higher speed n, the control device 21 adjusts or sets a higher VET than at a lower speed n in order to operate the compressor device 1 at a particularly low specific power.

[0056] It can also be seen from the performance map 41 that at a particular speed n at a higher internal pressure p, a lower VET is derived from the performance map 41 than at a lower internal pressure p.

[0057] The mathematical formula stored in the controller 21 for mapping or approximating the performance map 41 may be, for example, as follows:

[0058] y(x;z)=P0+P1×c+P2×x 2 +P3×x 3 +P4×1 / x +P5×z+P6×z 2 +P7×z 3 +P8×x×z where y is the VET, x is the speed n of the screw compressor 3, and z is the internal pressure p. As an alternative to a mathematical formula, the performance map 41 can be stored in the control device 21 as a relationship.

[0059] Instead of the compression end temperature (VET), the oil injection temperature or the fan 19 speed can be considered as an oil cooling parameter in the performance map 41 or formula.

[0060] Instead of the internal pressure p of the oil separator 11, the final system pressure p can be considered as an operating parameter in the relationship.

[0061] An exemplary operation of the compressor unit 1 will now be described with reference to FIG.

[0062] First, the control device 21 determines the VET to be set in step 51. SollDepending on the determined current internal pressure p of the screw compressor 3 and the determined current speed n, the VET at which the compressor unit 1 is operated at a particularly low specific power is determined using a relationship in the form of the formula: VET Soll Also known as VET Soll is determined continuously during operation of the compressor unit 1.

[0063] Subsequently, in step 53, the control device 21 calculates the determined VET Soll A check is made as to whether an additional mathematical correction of the temperature Ta of the intake air should be performed. One criterion for whether a mathematical correction is performed or not can be the deviation of the current temperature Ta of the intake air from a defined reference temperature Tr, for example |Ta-Tr|>1 K (Kelvin).

[0064] In a specific operating situation, the mathematical correction is calculated by the VET at the current operating point, i.e., the current internal pressure p and the current speed n of the compressor 3, which is derived from the formula target can be used to determine a VET that has a higher energy efficiency than m is set to 0 K (Kelvin). If mathematical correction is performed, the value ΔVET m is the defined reference temperature Tr, the current temperature Ta of the intake air, the current speed n of the compressor 3, and the defined maximum speed n of the compressor 3. max is determined in step 55 as a function of . For example, the following equation stored in the control device 21 can be used as the correction model:

[0065] ΔVET m = [(Ta-Tr)×n / n max ]

[0066] The defined reference temperature Tr is the temperature of the cooling air delivered by the fan 19, selected in a series of tests to determine the performance map 41. Also, the current intake air temperature Ta of the compressor measured by the temperature sensor 25 is assumed to correspond to the current cooling air temperature of the compressor.

[0067] In step 56, the control device 21 Soll and ΔVET m The sum of VET and Soll,korr1 It was decided that:

[0068] VET Soll,korr1 =VET Soll +ΔVET m

[0069] Finally, in step 57, the control unit 21 Soll,korr1 It is checked whether an additional iterative search for a VET with a specific power (second VET value) lower than the specific power (first VET value) should be performed at the current operating point. The iterative search can be performed, for example, if the compressor unit 1 has the option to evaluate, for example, using a suitable sensor system, the influence of different VET values ​​set during the iterative search on the specific power of the compressor unit 1. If an additional iterative search is not performed, the value ΔVET i is set to 0K. If an iterative search is performed, the following conditions are first checked in step 59:

[0070] |VET Soll,korr1 -VET Ist |<0.5K (Kelvin)

[0071] VET Ist is the current temperature of the VET measured by the temperature sensor 29. The value 0.5 K represents an exemplary value of the defined temperature difference. If the condition is met, an iterative search (iteration loop) is performed in step 61. If the condition is not met, the iterative search is not performed, which is the case, for example, when the speed changes during load operation, resulting in a new VET Soll In this case, ΔVET i The value of is set to 0K.

[0072] In an iterative search, the specific power of the compressor unit 1 is determined for each different adjusted VET. For this purpose, the power consumption of the control device 21, the drive 5 of the compressor 3 and the drive 20 of the fan 19, as well as the discharge rate of the compressor unit 1, can be measured by a suitable sensor system during operation of the compressor unit 1.

[0073] For example, the iterative search starts with VET Soll,korr1 The VET can then be increased or decreased by a defined value and the specific power determined at each set VET. Alternatively, the speed of the fan 19 can also be increased or decreased by a defined value and the specific power determined at each set speed.

[0074] Finally, a VET is determined at which the specific power of the compressor unit 1 is relatively low and therefore the most energy efficient.

[0075] Correction value ΔVET i is derived from the results of the iterative search in step 63.

[0076] In step 64, the control device 21 Soll,korr1 and ΔVET i The sum of VET and Soll,korr2 Determine.

[0077] VET Soll,korr2 =VET Soll,korr1 +ΔVET i

[0078] Furthermore, the control device 21 determines the VET Soll,korr2 Check whether it is within the following tolerance range:

[0079] VET min ≦VET Soll,korr2 ≦VET max

[0080] VET Soll,korr2 is the defined VETmin VET should not be less than 0.05, which prevents the formation of condensation in the compressor unit 1. min is determined by the control device 21 depending on the temperature of the intake air and the relative humidity of the ambient air. Furthermore, to counteract deterioration of the oil 15, the VET Soll,korr2 is the defined VET max VET max is a constant value here. Soll,korr2 If is not within the tolerance range, VET min or VET max Either of the following is VET Soll,korr2 The value is defined as VET min If it is below VET min VET Soll,korr2 and VET max If it exceeds VET max VET Soll Let's say.

[0081] In step 65, the determined VET Soll,korr2 is transmitted to the VET adjusting device (VET control device) of the control device 21. The speed of the fan 19 to be adjusted is determined via this in step 67. This speed is adjusted in step 69 via the drive motor 20 of the fan 19.

[0082] A similar operating mode to the compressor unit 1 according to FIG. 2 can be realized if the oil injection temperature instead of the VET is taken into account as the oil cooling parameter in the relational formula.

[0083] FIG. 4 shows an example of how a performance map 41 is determined in a series of tests.

[0084] The series of tests is carried out at defined reference values, that is, a defined temperature of the cooling air delivered by the fan 19 to the fan unit 17 and the type and condition of the oil 15 delivered by the compressor unit 1, in this example new conditions.

[0085] According to FIG. 4, in order to determine the specific power P of the compressor device 1, several measurements are carried out in a series of tests, in this example 18 measurements. Each determination of the specific power P is carried out at a different operating point of the compressor device 1. The operating points set in the series of tests are also called characteristic map points. The specific power P is the quotient of the power consumption and the discharge rate of the compressor device 1. To determine the specific power P, the power consumption and the discharge rate of the compressor device 1 are measured.

[0086] As an example, three series of measurements 71 are performed, each with six measurements, at pressures p1, p2, and p3, defined as the internal pressure p of the oil separator 11. In each series of measurements 71, two exemplary series of measurements 73 are performed, each with three measurements at speeds n1 and n2, defined as the speed n of the compressor 3. Furthermore, the defined temperatures T1, T2, and T3 are adjusted as the compression end temperature T(VET) for each series of measurements 73. Each measurement therefore represents a different operating point of the compressor device 1.

[0087] After carrying out the measurements, it is determined at which operating point of the compressor unit 1 the specific power P of the compressor unit 1 is relatively low and therefore the most energy efficient. It is therefore determined at which VET must be adjusted at a given pressure p and a given speed n to achieve particularly energy-efficient operation of the compressor unit 1. From these values ​​a performance map 41 is created.

[0088] Next, with reference to FIG. 5, another operation mode of the compressor device 75 will be described.

[0089] In the case of the compressor unit 75, a mathematical formula is stored in the control device as a relationship reflecting the relationship between the internal pressure of the oil separator 11 as an operating parameter, the speed of the compressor 3 as an operating parameter, and the speed n of the fan 19 as an oil cooling parameter. Depending on the values ​​of the operating parameters, the control device 21 can derive an assigned value of the speed n of the fan 19 from the formula. The assigned value of the speed n is the speed n of the fan 19 at which the compressor unit 75 operates with a particularly low specific power at the current operating point. This speed n of the fan 19 is n Soll It is also called.

[0090] In the following, only the essential differences between the operation mode of the compressor device 75 and the operation mode of the compressor device 1 will be described.

[0091] In step 51, the fan speed n derived from the relationship Soll This determines the speed value n available after step 64. L,Soll,korr2 is determined in a speed determination unit 81 highlighted by a dashed line, similar to the compressor device 1. L,Soll,korr2 The allowable range of values ​​for is the defined maximum speed n L,max,max The minimum speed n defined from L,min It is in the range of up to.

[0092] The following conditions are also checked for compressor unit 75 in step 59:

[0093] |ΔVET Ist / Δt|≦0.01K / s (Kelvin / second)

[0094] ΔVET Ist is the measured VET Ist is the difference value changed over a defined time interval Δt. The value 0.01 K / s represents an example value for a defined temperature change over time.

[0095] If the condition of step 59 is met, then in step 61, n Soll,Korr1An iterative search is performed at a rate n that is more energy efficient than in Soll,korr1 The specific power at can first be determined. Then the speed is increased or decreased by a defined amount and the specific power at each set speed is determined.

[0096] If the condition is not met, the iterative search is not performed, which means that, for example, a new n Soll is obtained, so that VET is currently adjusted, in this case after a speed change in load operation.

[0097] n in the speed determination unit 81 L、Soll、korr2 In parallel with or simultaneously with the continuous determination of VET, the controller determines in step 77 the measured current VET Ist Continuously check whether satisfies the following conditions:

[0098] VET Ist ≦VET max

[0099] If this condition is not met, the system proceeds to step 85. If this condition is met, the controller determines in step 79 the measured current VET Ist Check whether the following conditions are also satisfied:

[0100] VET Ist ≧VET min

[0101] If this condition is not met, proceed to step 87. VET min and VET max is the same value as in the case of the compressor unit 1. In steps 77 and 79, the measured current VET Ist However, VET min and VET max If it is determined that the VET is not within the tolerance range between 0 and 1, then step 85 or step 87 is performed by the control system depending on the measured VET.

[0102] In step 85, VET max However, VET should be adjusted Soll In step 87, the VET min VET should be adjusted Soll The VET to be set in steps 85 and 87 is specified as Soll After specifying the speed n of the fan 19, the VET adjusting device (VET regulator) of the control device 21 is activated in step 89. In the following step 91, the speed n of the fan 19 to be adjusted is determined. VETRegler is supplied by the VET regulator.

[0103] Finally, in step 93, the speed to which the fan 19 should be adjusted is determined. VETRegler is the speed n determined in parallel from the speed determination unit 81. Soll,korr2 takes precedence over

[0104] Therefore, the VET adjustment device of the control device is inactive (this is the VET Ist is within the tolerance range), the n determined in step 65 Soll,korr2 is set as the speed of the fan 19 to be adjusted. The VET adjustment device of the control device is activated (VET Ist is not within the tolerance range), in step 91, VETRegler is set as the speed of the fan 19 to be adjusted. The speed thus determined is adjusted in step 69 via the drive motor 20 of the fan 19.

[0105] Instead of using a VET regulator, max If this is exceeded, the fan 19 will operate at its maximum speed n max You can simply increase the speed of the fan 19 until it reaches VET min If the fan speed is less than n min The speed of the fan 19 is reduced until

Claims

1. A compressor device, a screw compressor (3) capable of producing a compressed air-oil mixture; a compressor unit outlet (13); an oil separator (11) through which the compressed air-oil mixture can be transferred, through which compressed air and oil can be separated from each other from the air-oil mixture, and through which the compressed air can be discharged to an outlet (13) of the compressor unit; an oil separation duct (16) connecting the oil separator (11) to the screw compressor (3) and equipped with a fan device provided in the oil cooler; a control device (21) capable of adjusting the speed (n) of the fan device and thus the cooling of the oil in the oil cooler; the current operating point of the compressor unit (1) is determinable by the control device (21); the control device (21) determines a value of the oil cooling parameter from a plurality of operating parameters characterizing the current operating point using a predetermined performance map or formula reflecting a relationship between the plurality of operating parameters and the oil cooling parameter; the plurality of operating parameters comprises at least the speed of the screw compressor (3) and the pressure (p) of the air-oil mixture produced or the pressure of the compressed air produced; the oil cooling parameters include the temperature of the air-oil mixture produced, the oil temperature downstream of the oil cooler, or the speed of the fan device; The determined value of the oil cooling parameter is adjustable by the control device (21) to operate the compressor device (1) at a defined specific power output or within a predefined range from a minimum value of the specific power output, the specific power output being the quotient of the total power consumption of the compressor device (1) and the volumetric flow rate of the compressed air produced.

2. 2. The compressor unit according to claim 1, further comprising an oil temperature sensor (36) between the fan unit and the screw compressor (3), and / or at least one air temperature sensor (25) for the air drawn in by the screw compressor (3) and / or for the ambient air, and / or a temperature sensor (29) for the temperature of the air-oil mixture at the outlet (37) of the screw compressor (3), and / or a pressure sensor (31) for the pressure of the air-oil mixture in or at the oil separator (11), and / or a pressure sensor (35) for the pressure of the compressed air produced downstream of the oil separator (11) and / or at the compressor unit outlet (13), and the control device (21) is connected to at least one of these sensors and is configured to read these sensors.

3. 3. Compressor unit according to claim 1 or 2, wherein several defined and / or variable speeds of the screw compressor (3) are adjustable by the control device (21) and / or several defined pressures of the compressed air produced by the compressor unit (1) are adjustable by the control device (21).

4. A screw compressor (3) for producing a compressed air-oil mixture; a compressor unit outlet (13); an oil separator (11) into which the air-oil mixture is transferred, in which compressed air and oil are separated from each other from the air-oil mixture, and the compressed air is discharged from the compressor unit outlet (13); an oil separation duct (16) connecting the oil separator (11) to the screw compressor (3) and equipped with a fan device for the oil cooler; a control device (21) for adjusting the speed of the fan device and thus the cooling of the oil in the oil cooler; The control device (21) determines the current operating point of the compressor device (1), The control device (21) determines a value of the oil cooling parameter from two of the operating parameters by using a predetermined performance map or a mathematical formula that reflects a relationship between a plurality of operating parameters that characterize the current operating point and an oil cooling parameter; the plurality of operating parameters comprises at least the speed of the screw compressor (3) and the pressure (p) of the air-oil mixture produced or the pressure of the compressed air produced; the oil cooling parameters include the temperature of the air-oil mixture produced, the oil temperature downstream of the oil cooler, or the speed of the fan device; The determined value of the oil cooling parameter is adjusted by the control device (21) in order to operate the compressor device (1) at a defined specific power output or within a predefined range from a minimum value of the specific power output, the specific power output being the quotient of the total power consumption of the compressor device (1) and the volumetric flow rate of the compressed air produced.

5. 5. The method according to claim 4, wherein the speed (n) of the screw compressor (3) and the pressure (p) of the air-oil mixture generated upstream of or in the oil separator (11) are determined as operating parameters for determining the current operating point.

6. 5. The method according to claim 4, wherein the speed (n) of the screw compressor (3) and the pressure of the compressed air generated downstream of the oil separator and / or at the compressor unit outlet are determined as operating parameters for determining the current operating point.

7. 7. The method according to claim 4, wherein the oil cooling parameter is formed by the speed of the fan device, the fan device being controlled by the control device to set the derived speed.

8. 7. The method according to any one of claims 4 to 6, wherein the oil cooling parameter is formed by the temperature of the air-oil mixture produced at the outlet (37) of the screw compressor (3), the temperature being regulated and / or adjusted by the control device (21) and the fan device.

9. 7. The method according to claim 4, wherein the oil cooling parameter is formed by an oil temperature downstream of the oil cooler, and the derived oil temperature is adjusted and / or regulated by the control device (21) and the fan device.

10. 10. The method according to claim 4, wherein the temperature of the air taken in by the compressor unit and / or the ambient air is determined by the control device (21), the determined oil cooling parameter is corrected according to a predetermined correction model that takes into account the determined air temperature, and the oil cooling parameter corrected by the correction model is adjusted by the control device (21).

11. 11. The method according to claim 4, wherein the control device (21) searches for a second value of the oil cooling parameter at which the compressor device (1) operates at the current operating point with a lower specific power output than at the derived first value of the oil cooling parameter.

12. 12. The method of claim 11, wherein if the second value is found during the search, this second value is adjusted by the control device (21) at the current operating point.

13. A method as described in claim 11 or 12, wherein, for the search of the second value, multiple different values ​​of the oil cooling parameter are adjusted by the control device (21), and at each adjusted value, the specific output of the compressor device (1) is determined by the control device (21).

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