Oil injection type multi-stage compressor system and procedure for controlling such a compressor system

Abstract

An oil-injected multi-stage compressor system comprising at least a low-pressure stage compressor element (2) having an inlet (4a) and an outlet (5a) and a high-pressure stage compressor element (3) having an inlet (4b) and an outlet (5b), the outlet (5a) of the low-pressure stage compressor element (2) being connected to the inlet (4b) of the high-pressure stage compressor element (3) via a pipeline (6), wherein the compressor elements (2, 3) are provided with their own drives in the form of electric motors (2a, 3a), and the compressor elements (2, 3) are coupled to the electric motors (2a, 3a) either directly or via a transmission, and an intercooler (9) is provided in the pipeline (6) between the low-pressure stage compressor element (2) and the high-pressure stage compressor element (3). [Selected Figure] Figure 1

Description

Technical Field

[0001] The present invention relates to an oil injection type multi-stage compressor system.

Background Art

[0002] Conventionally, it has been known to perform gas compression in two or more stages, i.e., "multi-stage", by oil-free compression. Therefore, due to technical constraints particularly regarding the maximum allowable discharge temperature, two or more compressor elements are arranged in series.

[0003] These technical constraints can be overcome by injecting a cooling medium such as water or oil into the compressor element, which enables single-stage compression.

[0004] The implementation of "multi-stage" involves considerable complexity and additional costs. Therefore, currently, an oil or water injection type single-stage compressor system is a preferred option.

[0005] The fact that the maintenance of a multi-stage compressor system is more extensive and complex also means that a single-stage compressor system is still often a preferred option.

[0006] The improved efficiency of the second and subsequent stages of a multi-stage compressor system would be an advantage over the above-mentioned drawbacks. This improved efficiency would be made possible by cooling the gas that reduces the consumption of the second and subsequent stages. However, it is not easy to achieve this.

[0007] A multi-stage compressor system already exists. In this system, for example, cooling oil is injected between two stages for cooling purposes using an oil curtain that lowers the temperature of the gas.

[0008] However, such a solution only enables limited cooling of the gas and thus provides only limited improved efficiency compared to an oil-free multi-stage compressor system. Also, more oil is added to the gas, which is not necessarily desirable.

[0009] An oil injection type multi-stage compressor system can be utilized, whereby, for example, a cooler can be provided between the first compressor element and the second compressor element, which will actively remove heat from the gas after the first compression stage.

[0010] However, this is not done for the following reasons. - First, a pressure drop is expected in this cooler, which necessarily means an efficiency loss. - Also, intermediate cooling can lead to the formation of condensate. The condensate must always be prevented from flowing into the next compressor element. Therefore, it is not possible to overcool to reliably prevent condensate in all operating states. Nevertheless, if condensate occurs, it will end up in the oil and then in the bearings and other parts where this oil is used. - Furthermore, this solution method is necessarily more complex and may also be more costly than an oil-free multi-stage compressor system.

[0011] Due to all the drawbacks associated with this, in principle, in order to ensure a favorable final result, a very large benefit in efficiency can be obtained by cooling, but this benefit may be limited by the generation of condensate.

[0012] Even if the problem of condensate does not occur, it is assumed that cooling still cannot be carried out sufficiently simply because the temperature rise of the oil-gas mixture after the first compression stage is not sufficient.

Summary of the Invention

Problems to be Solved by the Invention

[0013] It is an object of the present invention to provide a solution to at least one of the above and other drawbacks.

Means for Solving the Problems

[0014] The subject of the present invention is an oil-injection multi-stage compressor system, which comprises at least a low-pressure stage compressor element having an inlet and an outlet, and a high-pressure stage compressor element having an inlet and an outlet. The outlet of the low-pressure stage compressor element is connected to the inlet of the high-pressure stage compressor element via a pipeline. The compressor elements are provided with a drive device in the form of their own electric motor, and the compressor elements are directly coupled to the electric motor or coupled via a transmission. An intercooler is provided in the pipeline between the low-pressure stage compressor element and the high-pressure stage compressor element, and the intercooler is - an air-cooling unit that can be adjusted by a fan and the air flow rate can be controlled by adjusting the speed of the fan, or - a water-cooling unit that can be adjusted by a valve capable of adjusting the water flow rate, either of which, The intercooler can also be adjusted by changing the temperature of the air or water by means of a bypass pipeline and / or by shielding a part of the intercooler so that the gas to be cooled touches only a part of the intercooler.

[0015] It has been found that cooling after the low-pressure stage can result in a much larger temperature drop than that described in the literature. The temperature of the oil-gas mixture is measured when measuring the temperature at the outlet of the low-pressure stage compressor element. The measured temperature will be lower than the actual temperature of the gas due to the wet-bulb effect.

[0016] This means that the potential temperature drop of the resulting gas is actually much larger than that described in the literature.

[0017] Also, this means that the potential benefits of efficiency due to cooling are much greater than conventional assumptions, so the above disadvantages do not offset the improved efficiency. One advantage is that such an oil-injection multi-stage compressor system can provide better performance than known compressors equipped with oil injectors in the form of no cooling or oil curtains.

[0018] According to a preferred feature of the present invention, the intercooler is adjustable, and the compressor system further comprises a control unit or regulator for controlling or adjusting the intercooler such that the temperature at the inlet of the high-pressure stage compressor element is above the dew point. By keeping the temperature at the inlet of the high-pressure stage compressor element above the dew point, the generation of condensate at this point can be prevented.

[0019] By making the intercooler adjustable, maximum cooling can always be achieved without the risk of condensate formation. Therefore, it is not necessary to use the worst-case scenario when determining the cooling capacity of the intercooler. As soon as the dew point rises, the intercooler cools the gas excessively and condensate is formed. The intercooler can then be adjusted to cool the gas less in order to prevent the formation of condensate.

[0020] The intercooler can be made adjustable in various ways. The requirement for an adjustable intercooler is the degree of cooling of the gas or the temperature drop of the gas, which can be changed. This can be done, for example, by changing the cooling capacity of the intercooler and / or by sending a portion of the gas through a bypass pipeline instead of through the intercooler.

[0021] It is known that the dew point is not a fixed value and depends on various parameters such as the temperature, humidity, and pressure of the gas. There are several possibilities for determining this dew point. The potential presence of condensate can be estimated from the dew point.

[0022] In a preferred feature of the present invention, the intercooler comprises a heat pump. The advantage of this approach is that further cooling becomes possible. When there is no risk of condensate formation after the intercooler, the maximum cooling capacity can be obtained, and the high-pressure stage compressor element will be more efficient. Therefore, the total benefit in terms of efficiency or performance will be very high.

[0023] The present invention also includes a procedure for controlling an oil-injected multistage compressor system, the oil-injected multistage compressor system comprising a low-pressure stage compressor element having at least an inlet and an outlet and a high-pressure stage compressor element having an inlet and an outlet, the outlet of the low-pressure stage compressor element being connected to the inlet of the high-pressure stage compressor element via a pipeline, The compressor elements are provided with a drive in the form of their own electric motor, the compressor elements being directly coupled to the electric motor or coupled via a transmission, an intercooler being incorporated into the pipeline between the low-pressure stage compressor element and the high-pressure stage compressor element, the intercooler being adjustable, the compressor system further comprising a control unit or regulator for controlling or adjusting the intercooler such that the temperature at the inlet of the high-pressure stage compressor element exceeds the dew point, the procedure being - a step for calculating or determining the dew point at the inlet of the high-pressure stage compressor element, and - a step of adjusting the intercooler such that the temperature at the inlet of the high-pressure stage compressor element exceeds the dew point.

[0024] The advantages of this procedure are of course the same as those of the above-described oil-injected multistage compressor system.

[0025] To further illustrate the features of the present invention, a plurality of variations of the oil-injected multistage compressor system according to the present invention and the procedure applied thereto are described below by way of non-limiting and exemplary reference to the accompanying drawings.

Brief Description of the Drawings

[0026]

Figure 1

Modes for Carrying Out the Invention

[0027] The oil-injected multistage compressor system 1 shown in FIG. 1 in this case comprises two stages, namely a low-pressure stage with a low-pressure stage compressor element 2 and a high-pressure stage with a high-pressure stage compressor element 3, i.e., "multistage". Both compressor elements 2 and 3 are, for example, screw compressor elements, but this is not an essential requirement in the present invention.

[0028] In the present invention, the compressor elements 2 and 3 each comprise a drive device in the form of an electric motor 2a and 3a, respectively, whereby, in this case, the compressor elements 2 and 3 are directly connected to the electric motors 2a and 3a. It is obvious that the compressor elements 2 and 3 can be coupled to the electric motors 2a and 3a via a transmission.

[0029] Also, the compressor elements 2 and 3 comprise an oil circuit for injecting oil into the compressor elements 2 and 3. For the sake of clarity, these oil circuits are not shown. The low-pressure stage compressor element 2 has an inlet 4a for gas and an outlet 5a for compressed gas. This outlet 5a is connected to the inlet 4b of the high-pressure stage compressor element 3 via a pipeline 6.

[0030] Also, the high-pressure stage compressor element 3 comprises an outlet 5b, and the outlet 5b is connected to a liquid separator 7. The outlet 8 of the liquid separator 7 can be connected to a final cooler.

[0031] The intermediate cooler 9 is incorporated into the above-mentioned pipeline 6 between the low-pressure stage compressor element 2 and the high-pressure stage compressor element 3. In this case, the intermediate cooler 9 is adjustable, but this is not essential in the present invention.

[0032] This intermediate cooler 9 can be designed in various ways. For example, the intermediate cooler 9 can be an air-cooled unit, and the air-cooled unit is adjustable by a fan, and the air flow rate can be controlled by adjusting the speed of the fan.

[0033] Alternatively, the intermediate cooler 9 can be a water cooler, and the water cooler can be adjusted by a valve capable of adjusting the water flow rate. The intermediate cooler 9 can also be controlled by changing the temperature of air or water.

[0034] It is also possible to provide a pipeline that can bypass a part of the gas so that the gas can directly proceed from the low-pressure stage compressor element 2 to the high-pressure stage compressor element 3 without passing through the intercooler 9. It is also possible to shield a part of the intercooler 9 with, for example, a plate so that the entire intercooler is not used. This means that the gas to be cooled does not come into contact with the entire intercooler 9.

[0035] In this case, the intercooler 9 is provided with a heat pump 10, but this is not essential in the present invention. The heat pump 10 can be adjustable, but this is not essential. With the help of the heat pump 10, it is also possible to further remove heat from the gas.

[0036] Further, the compressor system 1 includes a control unit or regulator 11 for adjusting or controlling the intercooler 9. If the heat pump 10 is adjustable, the control unit or regulator 11 can also control the heat pump 10. In this case, a sensor 12 is provided. The sensor 12 is connected to the above-mentioned control unit or regulator 11.

[0037] In this regard, the sensor 12 can measure one or more environmental parameters at the inlet 4a of the low-pressure stage compressor element 2. For example, the sensor 12 can measure pressure, temperature, and humidity.

[0038] Providing a sensor 13 at the inlet 4b of the high-pressure stage compressor element 3 instead of or in addition to the sensor 12 is not excluded. This is schematically shown by a dotted line in the figure. Therefore, the sensor 13 can measure the humidity at the inlet 4b.

[0039] Furthermore, the device 1 includes a sensor 14 for measuring temperature at the inlet 4b. Finally, it is not excluded that the apparatus 1 comprises an oil injector 15 so that oil can be injected into the pipeline 6 on the downstream side of the intercooler 9. This is schematically indicated by the dotted line.

[0040] As shown below, the operation of the oil injection type multi-stage compressor system 1 is very simple. During operation, the gas to be compressed, for example air, is sucked through the inlet 4a of the low-pressure stage compressor element 2 and the first compression will be carried out.

[0041] The partially compressed gas passes through the pipeline 6 and flows into the intercooler 9, where it is cooled and then flows into the inlet 4b of the high-pressure stage compressor element 3, where the next compression is carried out. Oil is injected into both the low-pressure stage compressor element 2 and the high-pressure stage compressor element 3, which enables the lubrication and cooling of the compressor elements 2, 3.

[0042] The compressed gas exits the high-pressure stage compressor element 3 through the outlet 5b and is led to the oil separator 7. The injected oil is separated, and then the compressed gas can be transferred to the final cooler before being supplied to the consumer.

[0043] In order to ensure that no condensate is generated when the gas is cooled in the intercooler 9, this intercooler 9 needs to be controlled in an appropriate way to adapt to changes in the environment of the compressor elements 2, 3 and / or changes in the drive parameters.

[0044] For this purpose, the control unit or regulator 11 will adjust the intercooler 9 so that the temperature at the inlet 4b of the high-pressure stage compressor element 3 is above the dew point. As described above, this means that no condensate will occur at the inlet 4b of the high-pressure stage compressor element 3 after the intercooler 9.

[0045] In the first step, the dew point, that is, the presence of condensate, is determined or calculated at the inlet 4b of the high-pressure stage compressor element 3. The dew point depends on various parameters and, in other words, is not a fixed value but a variable. There are multiple options or methods for specifying the dew point.

[0046] In the case of FIG. 1, the dew point is specified by measuring the environmental parameters with the help of sensor 12. For this purpose, the measured values from sensor 12 are sent to the control unit or regulator 11, and the dew point is calculated based on this.

[0047] When the oil injection type multistage compressor system 1 is equipped with a humidity sensor 13 at the inlet 4b of the high-pressure stage compressor element 3, in other words, to directly identify the presence of condensate, the humidity at the inlet 4b can be measured. In this case, the humidity sensor 13 will similarly send the measured values to the control unit 11.

[0048] Another alternative means is, for example, to monitor the temperature at the inlet 4b of the high-pressure stage compressor element 3 using a temperature sensor 14 at the inlet 4b of the high-pressure stage compressor element 3 or other sensors specially designed for this purpose to identify the dew point.

[0049] In this case, the temperature sensor 14 sends the measured value of the temperature at the inlet 4b to the control unit or regulator 11, and the control unit or regulator 11 monitors and evaluates the change in the measured temperature and identifies the dew point based on this. Once the dew point is identified, the control unit or regulator 11 will adjust the intercooler 9 so that the temperature at the inlet 4b of the high-pressure stage compressor element 3 exceeds the dew point.

[0050] For this purpose, the control unit or regulator 11 requests the temperature at the inlet 4b from the temperature sensor 14 and compares this with the set dew point. When the temperature at the inlet 4b is higher than the dew point, the control unit 11 will enable the intercooler 9 to further cool so that the temperature of the gas can be further reduced without the occurrence of condensate.

[0051] When the temperature is still higher than the dew point when the intermediate cooler 9 is already cooling at maximum capacity, the control unit 11 will activate the heat pump 10. It is also possible for the heat pump 10 to operate constantly and for the adjustment to be made only at the intermediate cooler 9.

[0052] It is also possible to make the heat pump 10 adjustable, so that when the dew point is low, and thus when the required cooling capacity is high, the control unit 11 can increase the cooling capacity of the first intermediate cooler 9, subsequently the heat pump 10, or vice versa, or both simultaneously or alternately.

[0053] When the temperature at the inlet 4b is at or below the dew point, the control unit 11 will reduce the cooling of the intermediate cooler 9 so that the temperature of the gas rises, thereby preventing the formation of condensate. Also, when the heat pump 10 is adjustable, the control unit 11 can first reduce the cooling capacity of the heat pump 10, or alternatively reduce the cooling capacity of the intermediate cooler 9 and the heat pump 10.

[0054] When the dew point drops, the control unit or regulator 11 can cause the intermediate cooler 9 to cool again so that the temperature of the gas drops again. This makes it possible to always achieve maximum cooling without generating condensate.

[0055] The performance of the high-pressure stage compressor element can be maximized by always being able to optimize the cooling. If the device 1 is equipped with an oil injector 15, this can be used to perform additional cooling of the gas. In addition, the injected oil will enable additional lubrication of the high-pressure stage compressor element 3.

[0056] Although the present invention is described by way of example and is not limited to the embodiments shown in the drawings, the oil injection type multistage compressor system according to the present invention and the procedure applied thereto can be realized in various modified forms without departing from the scope of the present invention.

Claims

1. An oil-injected multi-stage compressor system comprising at least a low-pressure stage compressor element (2) having an inlet (4a) and an outlet (5a), and a high-pressure stage compressor element (3) having an inlet (4b) and an outlet (5b), wherein the outlet (5a) of the low-pressure stage compressor element (2) is connected to the inlet (4b) of the high-pressure stage compressor element (3) via a pipeline (6). The compressor elements (2, 3) are provided with a drive device in the form of their own electric motors (2a, 3a), the compressor elements (2, 3) are connected to the electric motors (2a, 3a) directly or via a transmission, and an intercooler (9) is provided in the pipeline (6) between the low-pressure stage compressor element (2) and the high-pressure stage compressor element (3). The intercooler (9) is adjustable, and the oil-injected multi-stage compressor system (1) further comprises a control unit or regulator (11) for controlling or adjusting the intercooler (9) such that the temperature at the inlet (4b) of the high-pressure stage compressor element (3) exceeds the dew point. The intercooler (9) is an air-cooling unit adjustable by a fan and capable of controlling the air flow rate by adjusting the speed of the fan, or a water-cooling unit adjustable by a valve capable of adjusting the water flow rate, and is selected from the group consisting of these. The intercooler (9) is additionally adjusted by shielding a part of the intercooler (9) such that the gas to be cooled touches only a part of the intercooler (9). An oil-injected multi-stage compressor system, characterized by the above.

2. The oil-injected multi-stage compressor system (1) comprises a sensor (12) connected to the control unit or regulator (11) for measuring environmental parameters selected from the group consisting of pressure, temperature and humidity, and the control unit or regulator (11) can specify or calculate the dew point based on the measured values of the sensor (12). The oil-injected multi-stage compressor system according to Claim 1.

3. The oil injection type multistage compressor system (1) further comprises a humidity sensor (13) connected to the control unit or regulator (11) at the inlet (4b) of the high-pressure stage compressor element (3), the humidity sensor (13) being capable of measuring or specifying humidity, and the control unit or regulator (11) being capable of specifying or calculating the dew point based on the measured value of the humidity sensor (13). The oil injection type multistage compressor system according to claim 1.

4. The oil injection type multistage compressor system (1) further comprises a temperature sensor (14) connected to the control unit or regulator (11) at the inlet (4b) of the high-pressure stage compressor element (3), the temperature sensor (14) being capable of measuring or specifying temperature, and the control unit or regulator (11) being provided with an algorithm that enables it to specify the dew point based on the temperature measured by the temperature sensor (14). The oil injection type multistage compressor system according to claim 1.

5. The intercooler (9) comprises a heat pump (10). The oil injection type multistage compressor system according to any one of claims 1 to 4.

6. The cooling capacity of the heat pump (10) is adjustable. The oil injection type multistage compressor system according to claim 5.

7. Oil is injected into the pipeline (6) downstream of the intercooler (9). The oil injection type multistage compressor system according to any one of claims 1 to 6.

8. In a method of controlling an oil injection type multistage compressor system (1) comprising a low-pressure stage compressor element (2) having at least an inlet (4a) and an outlet (5a) and a high-pressure stage compressor element (3) having an inlet (4b) and an outlet (5b), the outlet (5a) of the low-pressure stage compressor element (2) being connected to the inlet (4b) of the high-pressure stage compressor element (3) via a pipeline (6). The compressor elements (2, 3) are provided with a drive in the form of their own electric motors (2a, 3a), the compressor elements (2, 3) are connected directly or via a transmission to the electric motors (2a, 3a), an intercooler (9) is incorporated into the pipeline (6) between the low-pressure stage compressor element (2) and the high-pressure stage compressor element (3), the intercooler (9) is adjustable, and the oil-injected multistage compressor system (1) further comprises a control unit or regulator (11) for controlling or adjusting the intercooler (9) such that the temperature at the inlet (4b) of the high-pressure stage compressor element (3) exceeds the dew point. The intercooler (9) is adjustable by a fan and is an air-cooling unit capable of controlling the air flow rate by adjusting the speed of the fan, or is a water-cooling unit adjustable by a valve capable of adjusting the water flow rate, and is selected from the group consisting of The method is - a step for calculating or specifying the dew point at the inlet (4b) of the high-pressure stage compressor element (3), - a step of additionally adjusting the intercooler (9) such that the temperature at the inlet (4b) of the high-pressure stage compressor element (3) exceeds the dew point by shielding a part of the intercooler (9) such that the gas to be cooled touches only a part of the intercooler (9), characterized by the above.

9. The calculation or specification of the dew point is performed by measuring environmental parameters selected from the group consisting of pressure, temperature, and humidity. The method according to claim 8.

10. The calculation or specification of the dew point is performed by measuring the humidity at the inlet (4b) of the high-pressure stage compressor element (3). The method according to claim 8.

11. The calculation or specification of the dew point is performed by following the temperature trend at the inlet (4b) of the high-pressure stage compressor element (3). The method according to claim 8.

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