Compressor device and method for controlling such compressor device

Abstract

The present disclosure relates to a compressor arrangement, which includes an oil-injected compressor element (2). The outlet (4) of the compressor element is connected to an oil separator (9) via an outlet line (8). The oil separator (9) is connected to the compressor element (2) via an injection line (10). A controllable cooling device (15) for the oil is provided. The compressor arrangement (1) is provided with a control unit (21) and measuring devices (22a, 22b) connected thereto for controlling the cooling device (15) to control the temperature (T_uit_afsch) downstream of the oil separator (9). The measuring devices include a device (22a) for determining the temperature (T_uit) at the outlet (4) and a temperature sensor (22b) for determining the temperature downstream of the oil separator (9). The control unit (21) includes a controller (25) for controlling the cooling device (15) based on signals from the measuring devices and based on the dew point. The present disclosure also relates to a method for controlling a compressor arrangement.

Description

Technical Field

[0001] The present invention relates to a compressor device, which includes an oil-injected compressor element having an inlet for the gas to be compressed and an outlet for compressing the gas. The outlet is connected to an oil separator, and the oil separator is connected to the compressor element via an injection line for oil injection. The injection line includes a cooler that can be bypassed by a bypass line. A controlled mixing valve having an inlet and two outlets is provided. One of the outlets of the mixing valve and its inlet are connected to the injection line, and the other outlet is connected to the bypass line. The compressor device is also provided with a control unit for controlling the mixing valve. Background Art

[0002] From US2009 / 252632, a device is known in which the control unit controls the mixing valve by controlling the temperature of the injected oil to prevent condensation from forming in the compressed gas.

[0003] In this regard, the control unit will determine the dew point at the outlet of the compressor element based on ambient parameters (such as temperature, pressure, and humidity) and based on the pressure at the outlet.

[0004] The mixing valve will then be controlled by the control unit such that the temperature at the outlet is above the dew point.

[0005] Normally, a temperature several degrees above the dew point is used as the control temperature for the temperature at the outlet.

[0006] The disadvantage of this method is that the temperature of the gas after the oil separator will drop, such that the temperature of the gas will be below the dew point. Therefore, condensation may occur in the compressed gas downstream of the oil separator and also upstream of the subsequent filter, which will separate the last oil from the compressed gas.

[0007] This is not desirable because it is always desired to avoid condensation before all the oil has been separated from the compressed gas.

[0008] Therefore, the control temperature must be set sufficiently above the dew point, usually 20°C, however, a much lower setting would actually be desired.

[0009] After all, the higher the temperature, the shorter the life of the oil and the lower the efficiency of the compressor device.

[0010] Controlling the temperature of the compressed gas downstream of the oil separator to be above the dew point instead of controlling the temperature at the outlet of the compressor element does not provide a solution because this control takes effect too late and leads to instability. Summary of the Invention

[0011] The present invention aims to solve at least one of the above and other drawbacks.

[0012] The object of the present invention is to provide a compressor device, which comprises an oil-injected compressor element having an inlet for the gas to be compressed and an outlet for the compressed gas, wherein the outlet is connected via an outlet line to an oil separator, which is connected to the compressor element via an injection line for oil injection, wherein a controllable cooling device for the oil is provided, and the compressor device further has a control unit and measuring means connected to the control unit for controlling the cooling device to control the temperature T_uit_afsch of the compressed gas downstream of the oil separator, characterized in that the measuring means comprises means for determining the temperature T_uit of the compressed gas at the outlet and a temperature sensor for determining the temperature T_uit_afsch of the compressed gas downstream of the oil separator, and the control unit comprises a controller for controlling the cooling device based on signals from the means and the temperature sensor and based on the dew point of the compressed gas.

[0013] The advantage is that by controlling based on both the temperature T_uit of the compressed gas at the outlet and the temperature T_uit_afsch of the compressed gas downstream of the oil separator, the control takes place on the temperature T_uit_afsch downstream of the oil separator and is adjusted using the temperature T_uit at the outlet, and the control will be more stable.

[0014] "The control takes place on..." means that the temperature will be controlled to the dew point.

[0015] Another advantage is that by effectively controlling the temperature T_uit_afsch of the compressed gas downstream of the oil separator, the temperature of the oil can be kept as low as possible with no or only a very low safety margin to avoid condensation at this location.

[0016] The means for determining the temperature T_uit of the compressed gas at the outlet can be, for example, a temperature sensor or a pressure sensor for measuring the pressure at the outlet. After all, the temperature T_uit can also be determined based on, for example, the pressure at the outlet.

[0017] In a practical form of the embodiment, the controller of the control unit comprises a feedforward control, which calculates a corrected temperature setpoint T_set_corr based on the temperature T_uit of the compressed gas and the dew point, and the corrected temperature setpoint is used by the controller to control the cooling device based on the difference between the corrected temperature setpoint T_set_corr and the temperature T_uit_afsch of the compressed gas downstream of the oil separator, such that the temperature T_uit_afsch of the compressed gas downstream of the oil separator is higher than the dew point.

[0018] The principle of feedforward is well-known and is based on information or knowledge that is known in advance in the system to control the process at subsequent times.

[0019] In another practical form of the embodiment, the control unit includes a main controller and a slave controller, wherein the main controller determines a corrected temperature setpoint T_set_corr for the slave controller based on the dew point and the temperature T_uit_afsch of the compressed gas downstream of the oil separator, and the main controller controls the cooling device based on the corrected temperature setpoint T_set_corr and the temperature T_uit of the compressed gas at the outlet such that the temperature T_uit_afsch of the compressed gas downstream of the oil separator is higher than the dew point.

[0020] The principle of master-slave control is also well-known, and in this case the main controller will form a large and slow control loop, and the slave controller will make small and fast corrections thereto.

[0021] By means of feedforward control or master-slave control, it is possible to control the temperature T_uit_afsch of the compressed gas downstream of the oil separator by also taking into account the temperature T_uit of the compressed gas at the outlet (i.e., using the temperature T_uit during correction).

[0022] The invention also relates to a method for controlling a compressor device according to the invention, characterized in that the method comprises the following steps:

[0023] A - determining or measuring the temperature T_uit of the compressed gas at the outlet and the temperature T_uit_afsch of the compressed gas downstream of the oil separator;

[0024] B - determining the dew point of the compressed gas;

[0025] C - controlling the cooling device based on the temperature T_uit of the compressed gas at the outlet, the temperature T_uit_afsch of the compressed gas downstream of the oil separator, and the dew point.

[0026] The advantages of this method are of course the same as those of the compressor device.

[0027] In a practical embodiment, the method comprises the step of calculating a corrected temperature setpoint T_set_corr based on the temperature T_uit of the compressed gas at the outlet and the dew point of the compressed gas, wherein the method subsequently comprises the step of controlling the cooling device based on the difference between the corrected temperature setpoint T_set_corr and the temperature T_uit_afsch of the compressed gas downstream of the oil separator such that the temperature T_uit_afsch of the compressed gas downstream of the oil separator is higher than the dew point.

[0028] In an alternative practical embodiment, the method comprises the step of determining a corrected temperature setpoint T_set_corr based on the dew point and the temperature T_uit_afsch of the compressed gas downstream of the oil separator, wherein the method subsequently comprises the step of controlling the cooling device based on this corrected temperature setpoint T_set_corr and the temperature T_uit of the compressed gas at the outlet such that the temperature T_uit_afsch of the compressed gas downstream of the oil separator is higher than the dew point.

[0029] For the cooling device, a controlled mixing valve is preferably used, which is provided with

[0030] - an input and two outputs, the mixing valve being incorporated in the injection line upstream of the cooler, which is incorporated in the injection line and can be bypassed by means of a bypass line, such that the input and one of the two outputs are connected to the injection line and the other output is connected to the bypass line;

[0031] - or two inputs and an output, the mixing valve being incorporated in the injection line downstream of the cooler, such that one of the two inputs and the output are connected to the injection line and the other input is connected to the bypass line.

[0032] For the cooling device, a controllable cooler arranged in the injection line is preferably used. Description of the Drawings

[0033] To better illustrate the features of the present invention, several preferred variants of the compressor device and method according to the present invention are described below by way of example without any restrictive features and with reference to the drawings, wherein:

[0034] Figure 1 A compressor device according to the present invention is schematically shown;

[0035] Figure 2 and Figure 3 Two possible control diagrams are shown. Specific Embodiment

[0036] Figure 1 The compressor device 1 schematically shown in [the figure] comprises an oil-injected compressor element 2, which has an inlet 3 for the gas to be compressed and an outlet 4 for the compressed gas.

[0037] The compressor element 2 is provided with a drive 5.

[0038] The inlet 3 is provided with an inlet line 6 having an inlet filter 7.

[0039] The outlet 4 is connected via an outlet line 8 to an oil separator 9.

[0040] The oil separator 9 is in turn connected to the compressor element 2 by means of an injection line 10 so that the separated oil can be injected.

[0041] In the example shown, this connection is made via the drive 5, which is connected to the injection line 10 for injecting oil into the drive 5.

[0042] Obviously, the injection line 10 can also be connected directly to the compressor element 2 itself to provide a direct connection to the oil separator 9, rather than via the drive 5.

[0043] The pressure line 11 is also connected to the oil separator 9 to discharge the purified gas. The pressure line 11 in turn includes: an oil filter 12 for separating the last remaining oil in the compressed gas, and a cooler 13 for cooling the compressed gas before it is delivered to the user of the compressed gas or the pressure network.

[0044] The oil filter 12 is connected to the compressor element 2 via an oil line 14 to enable the injection of the oil separated by the oil filter 12.

[0045] Furthermore, the compressor device 1 is provided with controllable cooling means 15 for the oil.

[0046] In this case, they are implemented in the following manner:

[0047] In the injection line 10, a cooler 16 is provided, which can be bypassed via a bypass line 17. The controllable cooling means 15 is formed by a controlled mixing valve 18 provided with an input 19 and two outputs 20a, 20b. The mixing valve 18 is incorporated into the injection line 10 upstream of the cooler 16 such that the input 19 and one of the two outputs 20a are connected to the injection line 10 and the other output 20b is connected to the bypass line 17.

[0048] It should be clear that by controlling the mixing valve 18, the amount of oil passing through the cooler 16 can be controlled, and in this way the degree of oil cooling, or in other words, the temperature of the oil, can be controlled.

[0049] The cooler 16 can take various forms, such as an oil-air heat exchanger or an oil-water heat exchanger provided with a cooling fan.

[0050] The controllable cooling means 15 can alternatively be formed by a controlled mixing valve 18 provided with an output and two inputs. The mixing valve 18 is incorporated into the injection line 10 downstream of the cooler 16 such that one of the two inputs and the output are connected to the injection line 10 and the other input is connected to the bypass line 17.

[0051] To control these controllable cooling devices 15, the compressor device 1 is provided with a control unit 21.

[0052] The control unit 21 is connected to a number of measuring devices 22a, 22b.

[0053] These measuring devices 22a, 22b according to the invention at least include:

[0054] - device 22a, which is arranged at the outlet 4 to measure or determine the temperature T_uit of the compressed gas at the outlet 4;

[0055] - temperature sensor 22b, which is used to determine the temperature T_uit_afsch of the compressed gas downstream of the oil separator 9.

[0056] In this case, device 22a is a temperature sensor, but it does not exclude that these devices 22a include pressure sensors.

[0057] In this case, the second temperature sensor 22b is arranged downstream of the oil filter 12.

[0058] In addition, additional sensors 23a, 23b are provided, and these additional sensors are also connected to the control unit 21:

[0059] - inlet state sensor 23a, which is represented by sensor S in the figure;

[0060] - pressure sensor 23b arranged in the oil separator 9, which determines or measures the working pressure p_werk in the oil separator.

[0061] The inlet state sensor 23a measures or determines the pressure, temperature and humidity at the inlet 3.

[0062] As will be clarified later, the inlet state sensor 23a and this pressure sensor 23b are used to determine the dew point at the outlet 4. However, these additional sensors 23a, 23b are optional and do not exclude determining the dew point by estimation.

[0063] To determine the dew point, the control unit 21 is provided with a separate calculation unit 24.

[0064] "Connected to the control unit 21" means that the relevant measuring devices 22a, 22b or additional sensors 23a, 23b transmit their signals, that is, the temperatures, pressures, etc. they have recorded, to the control unit 21.

[0065] In addition, the control unit 21 is provided with a controller 25.

[0066] This controller 25 includes one or more PID or PD controllers.

[0067] Of course, it is not excluded that the controller 25 can include one or more fuzzy controllers instead of a PID or PD controller.

[0068] The controller 25 will control the cooling device 15 based on signals from the device 22a and the temperature sensor 22b and based on the dew point at the outlet 4.

[0069] Furthermore, the oil separator 9 and the oil filter 12 are arranged in a sealed isolation housing 26.

[0070] The operation of the compressor device 1 and the method for controlling the compressor device 1 are very simple and are described as follows.

[0071] During operation of the compressor device, the compressor element 2 will compress the gas sucked in via the inlet filter 7.

[0072] Via the injection line 10 and the oil line 14, oil is injected into the compressor element 2 and the drive 5 to cool and lubricate the compressor element 2 and the drive 5.

[0073] The compressed gas will leave the compressor element 2 via the outlet 4.

[0074] This compressed gas also contains oil.

[0075] Via the outlet line 8, this oil-gas mixture will reach the oil separator 9, where most of the oil will be separated from the compressed gas.

[0076] Thereafter, the compressed gas also passes through the oil filter 12 and through the cooler 13 before being sent to the pressure network or the user of the compressed gas, where the last of the oil is separated.

[0077] The oil separated in the oil separator 9 is injected back into the compressor element 2 via the injection line 10 and the bypass line 17, and this oil first passes through the drive 5 before reaching the compressor element 2.

[0078] The oil separated in the oil filter 12 is injected back into the compressor element 2 via the oil line 14, for example at the height of the bearings.

[0079] The control unit 21 will control the mixing valve 18 during operation of the compressor device 1 to control the temperature of the injected oil by determining how much oil is cooled via the cooler 16.

[0080] When doing so, the control will be carried out in such a way that the temperature of the compressed gas downstream of the oil separator 9 (and in this case also the temperature downstream of the oil filter 12) is high enough to avoid condensation. In practice, this means that this temperature of the compressed gas must be above the dew point.

[0081] The control applied here is based on signals from the device 22a and the temperature sensor 22b and on the dew point at the outlet 4.

[0082] In the example shown, the dew point is determined by the control unit 21 with the help of the calculation unit 24 based on signals from the inlet state sensor 23a and the pressure sensor 23b.

[0083] The output of the calculation unit 24 is the temperature setpoint T_set based on the dew point.

[0084] The controller 25 can then be implemented in two different ways, which are schematically shown in Figure 2 and 3 respectively.

[0085] Figure 2 A controller 25 with a feed - forward principle is shown.

[0086] The control unit 21 contains a feed - forward controller 27, which calculates a corrected temperature setpoint T_set_corr based on the temperature T_uit of the compressed gas at the outlet 4 and the dew point. The controller 28 uses this corrected temperature setpoint to appropriately control the cooling device 15 based on the difference between the corrected temperature setpoint T_set_corr and the temperature T_uit_afsch of the compressed gas downstream of the oil separator 9.

[0087] Figure 3 A controller 25 with a master - slave principle is shown.

[0088] The control unit 21 contains a master controller 29 and a slave controller 30. The master controller 29 determines a corrected temperature setpoint T_set_corr for the slave controller 30 based on the dew point and the temperature T_uit_afsch of the compressed gas downstream of the oil separator. The slave controller will appropriately control the cooling device 15 based on this corrected temperature setpoint T_set_corr and the temperature T_uit of the compressed gas at the outlet 4.

[0089] The advantage of the insulated housing 26 that houses the oil separator 9 and the oil filter 12 is that the temperature difference between T_uit and T_uit_afsch is minimized, making both control principles more stable and accurate.

[0090] Optionally, a device can be provided in this housing 26 to control the temperature of the housing 26.

[0091] Although in the previous example the controllable cooling device 15 is formed by a controllable mixing valve 18, they can be implemented in various ways.

[0092] The cooling device 15 can also be formed by a controllable cooler arranged in the injection line 10.

[0093] The controllable cooler is then controlled by the control unit 21, and the cooling capacity is adjustable, for example, by controlling the speed of the cooling fan of the air - oil cooler or, in the case of a water - oil cooler, by controlling the temperature or flow rate of the cooling water.

[0094] The controllable cooler can optionally be bypassed by means of a bypass line 17. In this case, the thermostat is provided with an input and two outputs. The input of the thermostat and one of the two outputs are connected to the injection line 10 and the other output is connected to the bypass line 17.

[0095] The thermostat will then become a passive component.

[0096] The operation of such a compressor device 1 with a controllable cooler is further the same as that of the compressor device described in the foregoing Figure 1 as described.

[0097] The present invention is in no way limited to the embodiments described by way of example and shown in the drawings, but such compressor devices and methods according to the present invention can be implemented in different variants without departing from the scope of the present invention.

Claims

1. A compressor device, said compressor device comprising an oil-injected compressor element (2), said compressor element having an inlet (3) for the gas to be compressed and an outlet (4) for the compressed gas, wherein the outlet (4) is connected via an outlet line (8) to an oil separator (9), said oil separator (9) being connected via an injection line (10) to said compressor element (2) for injecting oil, wherein a controllable cooling device (15) for the oil is provided, said compressor device (1) further being provided with a control unit (21) and measuring means (22a, 22b) connected to said control unit for controlling the cooling device (15) to control the temperature (T_uit_afsch) of the compressed gas downstream of the oil separator (9), characterized in that, The measuring device (22a, 22b) includes means (22a) for determining the temperature (T_uit) of the compressed gas at the outlet (4) and a temperature sensor (22b) for determining the temperature (T_uit_afsch) of the compressed gas downstream of the oil separator (9), and the control unit (21) includes a controller (25) for controlling the cooling device (15) based on signals from the means (22a) for determining the temperature of the compressed gas at the outlet and the temperature sensor (22b) and based on the dew point of the compressed gas, and wherein the controller (25) of the control unit (21) includes: - A feed - forward controller (27) and an additional controller (28), the feed - forward controller calculating a corrected temperature set - point (T_set_corr) based on the temperature (T_uit) and the dew point of the compressed gas, and the additional controller (28) using the corrected temperature set - point to control the cooling device (15) based on the difference between the corrected temperature set - point (T_set_corr) and the temperature (T_uit_afsch) of the compressed gas downstream of the oil separator (9) such that the temperature (T_uit_afsch) of the compressed gas downstream of the oil separator (9) is higher than the dew point, or - A main controller (29) and a slave controller (30), wherein the main controller (29) determines a corrected temperature set - point (T_set_corr) for the slave controller (30) based on the dew point and the temperature (T_uit_afsch) of the compressed gas downstream of the oil separator (9), and the slave controller controls the cooling device (15) based on the corrected temperature set - point (T_set_corr) and the temperature (T_uit) of the compressed gas at the outlet (4) such that the temperature (T_uit_afsch) of the compressed gas downstream of the oil separator (9) is higher than the dew point.

2. The compressor device according to claim 1, characterized in that, A cooler (16) is arranged in the injection line (10), and the cooler can be bypassed by means of a bypass line (17), and the cooling device (15) is formed by a controlled mixing valve (18), and the mixing valve is provided with: - An input (19) and two outputs (20a, 20b), the mixing valve (18) being incorporated in the injection line (10) upstream of the cooler (16) such that the input (19) and one of the two outputs (20a) are connected to the injection line (10) and the other output (20b) is connected to the bypass line (17); - An or - output and two inputs, the mixing valve (18) being incorporated in the injection line (10) downstream of the cooler (16) such that one of the two inputs and the output are connected to the injection line (10) and the other input is connected to the bypass line (17).

3. The compressor device according to claim 1, characterized in that, The cooling device (15) is formed by a controllable cooler arranged in the injection line (10).

4. The compressor device according to claim 3, characterized in that, The controllable cooler can be bypassed by means of a bypass line (17), wherein a thermostat having an input and two outputs is provided, the input of the thermostat and one of the two outputs being connected to the injection line (10) and the other output being connected to the bypass line (17).

5. The compressor device according to claim 1, characterized in that, The controller (25) comprises a PID controller and / or a PD controller.

6. The compressor device according to claim 1, characterized in that, The controller (25) comprises a fuzzy controller.

7. The compressor device according to claim 1, characterized in that, The compressor device (1) is further provided with an inlet state sensor (23a) and a pressure sensor (23b), the inlet state sensor being connected to the control unit (21), the pressure sensor being connected to the control unit (21) and determining the pressure (p_werk) in the oil separator (9), wherein the control unit (21) can determine the dew point at the outlet (4) based on signals from the inlet state sensor (23a) and the pressure sensor (23b).

8. The compressor device according to claim 1, characterized in that, The oil separator (9) and any oil filter (12) downstream of the oil separator (9) are arranged in a sealed isolation housing (26).

9. The compressor device according to claim 1, wherein, The means (22a) for determining the temperature (T_uit) of the compressed gas at the outlet (4) comprises a temperature sensor or a pressure sensor capable of determining the pressure at the outlet (4).

10. A method for controlling a compressor arrangement (1), said compressor arrangement comprising an oil-injected compressor element (2), said compressor element having an inlet (3) for the gas to be compressed and an outlet (4) for the compressed gas, wherein said outlet (4) is connected via an outlet line (8) to an oil separator (9), said oil separator being connected to said compressor element (2) by means of an injection line (10) for oil injection, wherein a controllable cooling device (15) for the oil is provided, characterized in that, The method comprises the following steps: A - determining or measuring the temperature (T_uit) of the compressed gas at the outlet (4) and the temperature (T_uit_afsch) of the compressed gas downstream of the oil separator (9); B - determining the dew point of the compressed gas; C - controlling the cooling device (15) based on the temperature (T_uit) of the compressed gas at the outlet (4), the temperature (T_uit_afsch) of the compressed gas downstream of the oil separator (9), and the dew point; D - calculating a corrected temperature setpoint (T_set_corr) based on the temperature (T_uit) of the compressed gas at the outlet (4) and the dew point of the compressed gas, wherein the method subsequently comprises controlling the cooling device (15) based on the difference between the corrected temperature setpoint (T_set_corr) and the temperature (T_uit_afsch) of the compressed gas downstream of the oil separator (9) such that the temperature (T_uit_afsch) of the compressed gas downstream of the oil separator (9) is higher than the dew point; or determining a corrected temperature setpoint (T_set_corr) based on the dew point and the temperature (T_uit_afsch) of the compressed gas downstream of the oil separator (9), the method subsequently comprising controlling the cooling device (15) based on the corrected temperature setpoint (T_set_corr) and the temperature (T_uit) of the compressed gas at the outlet (4) such that the temperature (T_uit_afsch) of the compressed gas downstream of the oil separator (9) is higher than the dew point.

11. The method according to claim 10, wherein A controlled mixing valve (18) is used for the cooling device (15), the mixing valve being provided with - An input (19) and two outputs (20a, 20b), the mixing valve (18) being incorporated in the injection line (10) upstream of the cooler (16), which cooler (16) is incorporated in the injection line (10) and can be bypassed by means of a bypass line (17), such that the input (19) and one of the two outputs (20a) are connected to the injection line (10) and the other output (20b) is connected to the bypass line (17); - Or an output and two inputs, the mixing valve (18) being incorporated in the injection line (10) downstream of the cooler (16), such that one of the two inputs and the output are connected to the injection line (10), and the other input is connected to the bypass line (17).

12. The method according to claim 10, wherein A controllable cooler arranged in the injection line (10) is used for the cooling device (15).

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