OIL-INJECTED MULTI-STAGE COMPRESSOR SYSTEM AND PROCEDURE FOR CONTROLLING SUCH A COMPRESSOR SYSTEM

Abstract

An oil-injected multi-stage compressor system that comprises at least a low-pressure stage compressor element (2) with an inlet (4a) and an outlet (5a) and a high-pressure stage compressor element (3) with an inlet (4b) and an outlet (5b), whereby 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) through a pipeline (6), characterized in that the compressor elements (2, 3) are provided with their own drive in the form of an electric motor (2a, 3a), whereby the compressor elements (2, 3) are connected to the electric motor (2a, 3a) either directly or through a gearbox and that an intercooler (9) is provided in the aforementioned pipeline (6) between the low-pressure stage compressor element (2) and the high-pressure stage compressor element (3).

Claims

1. An oil-injected multi-stage compressor system that comprises at least a low-pressure stage compressor element (2) with an inlet (4a) and an outlet (5a) and a high-pressure stage compressor element (3) with an inlet (4b) and an outlet (5b), whereby 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) through a pipeline (6), characterized in that the compressor elements (2, 3) are provided with their own drive in the form of an electric motor (2a, 3a), whereby the compressor elements (2, 3) are connected to the electric motor (2a, 3a) either directly or through a gearbox and that an intercooler (9) is provided in the aforementioned pipeline (6) between the low-pressure stage compressor element (2) and the high-pressure stage compressor element (3), whereby the intercooler (9) is an air-cooling system, which is adjustable by means of a fan, whereby the flow rate of the air can be controlled by adjusting the speed of the fan; or a water cooling unit, which is adjustable by means of a valve that can regulate the flow of the water, whereby the intercooler (9) can also be regulated by changing the temperature of the air or water by means of a bypass pipeline and/or by screening a part of the intercooler (9) so that the gas to be cooled is exposed to only a part of the intercooler (9).

2. Oil-injected multi-stage compressor system according to claim 1, characterized in that the intercooler (9) is adjustable, whereby the compressor system (1) is also equipped with a control unit or regulator (11) to control or regulate the intercooler (9), so that the temperature at the inlet (4b) of the high-pressure stage compressor element (3) is above the dew point.

3. Oil-injected multi-stage compressor system according to claim 2, characterized in that the compressor system (1) is provided with a sensor (12) that is connected to the control unit or regulator (11) to measure the environmental parameters, where the control unit or regulator (11) can determine or calculate the dew point based on the measurements of the sensor (12).

4. Oil-injected multi-stage compressor system according to claim 2, characterized in that the compressor system (1) is also provided with a humidity sensor (13) at the inlet (4b) of the high-pressure stage compressor element (3) that is connected to the control unit or regulator (11), which humidity sensor (13) can measure or determine the humidity, whereby the control unit or regulator (11) can determine or calculate the dew point on the basis of the measurements of the sensor (13).

5. Oil-injected multi-stage compressor system according to claim 2, characterized in that the compressor system (1) is also provided with a temperature sensor (14) at the inlet (4b) of the high-pressure stage compressor element (3) that is connected to the control unit or regulator (11), which temperature sensor (14) can measure or determine the temperature, whereby the control unit or regulator (11) is provided with an algorithm that allows determining the dew point based on the course of the temperature measured by the temperature sensor (14).

6. Oil-injected multi-stage compressor system according to one of the preceding claims, characterized in that the intercooler (9) is provided with a heat pump (10).

7. Oil-injected multi-stage compressor system according to claim 6, characterized in that the heat pump (10) is adjustable.

8. Oil-injected multi-stage compressor system according to the preceding claims, characterized in that oil is injected into the pipeline (6) that is downstream from the intercooler (9).

9. Procedure for controlling an oil-injected multi-stage compressor system (1) comprising at least a low-pressure stage compressor element (2) with an inlet (4a) and an outlet (5a) and a high-pressure stage compressor element (3) with an inlet (4b) and an outlet (5b), whereby 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) through a pipeline (6), characterized in that the compressor elements (2, 3) are provided with their own drive in the form of an electric motor (2a, 3a), whereby the compressor elements (2, 3) are connected either directly or by means of a gearbox to the electric motor (2a, 3a) and that an intercooler (9) is installed in the above pipeline (6) between the low-pressure stage compressor element (2) and the high-pressure stage compressor element (3), whereby this intercooler (9) is adjustable, whereby the compressor system (1) is also provided with a control unit or regulator (11) for controlling or regulating the intercooler (9) so that the temperature at the inlet (4b) of the high-pressure stage compressor element (3) is above the dew point, and that the procedure comprises the following steps: calculating or determining the dew point at the inlet (4b) of the high-pressure stage compressor element (3); regulating the intercooler (9) so that the temperature at the inlet (4b) of the high-pressure stage compressor element (3) is above the dew point.

10. Procedure according to claim 9, characterized in that the calculation or determination of the dew point is done by measuring environmental parameters such as pressure, temperature and/or humidity.

11. Procedure according to claim 9, characterized in that the calculation or determination of the dew point is done by measuring the humidity at the inlet (4b) of the high-pressure stage compressor element (3).

12. Procedure according to claim 9, characterized in that the calculation or determination of the dew point is carried out by following the course of the temperature at the inlet (4b) of the high-pressure stage compressor element (3).

Description

[0039] With the insight to better demonstrate the characteristics of the invention, a number of preferred variants of an oil-injected multi-stage compressor system according to the invention and a procedure applied therewith are described below, as an example without any restrictive character, with reference to the accompanying drawing in which:

[0040] FIG. 1 provides a schematic representation of an oil-injected multi-stage compressor system according to the invention.

[0041] The oil-injected multi-stage compressor system 1 shown in FIG. 1 comprises in this case two steps or “stages”: 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.

[0042] Both compressor elements 2, 3 are, for example, screw compressor elements, but that is not a necessary requirement for the invention.

[0043] According to the invention, compressor elements 2, 3 are provided with their own drive in the form of electric motors 2a and 3a respectively, whereby in this case compressor elements 2, 3 are directly coupled to electric motors 2a, 3a. It is clear that compressor elements 2, 3 can be connected to electric motors 2a, 3a through a gearbox.

[0044] Compressor elements 2, 3 are also equipped with an oil circuit for the injection of oil into compressor elements 2, 3. For the sake of clarity, these oil circuits are not shown in the figure.

[0045] Low-pressure stage compressor element 2 has an inlet 4a for gas and an outlet 5a for compressed gas.

[0046] This outlet 5a is connected to inlet 4b of the high-pressure stage compressor element 3 through a pipeline 6.

[0047] High-pressure stage compressor element 3 is also provided with an outlet 5b, where outlet 5b is connected to a liquid separator 7. It is possible for outlet 8 of liquid separator 7 to be connected to an aftercooler.

[0048] Intercooler 9 is included in the aforementioned pipeline 6 between low-pressure stage compressor element 2 and high-pressure stage compressor element 3.

[0049] In this case, the intercooler 9 is adjustable, but that is not necessary for the invention.

[0050] This intercooler 9 can be designed in different ways.

[0051] For example, intercooler 9 can be an air-cooling unit, which is adjustable by means of a fan, whereby the flow rate of the air can be controlled by adjusting the speed of the fan.

[0052] Alternatively, intercooler 9 can be a water cooler, which is adjustable by means of a valve that can regulate the flow rate of the water.

[0053] It is also possible that intercooler 9 can be controlled by changing the temperature of the air or water.

[0054] It is also possible to provide a bypass pipeline that can divert part of the gas so that it can go directly from low-pressure stage compressor element 2 to high-pressure stage compressor element 3, without passing through intercooler 9.

[0055] It is also possible for a part of the intercooler 9 to be screened, e.g. with a plate or the like, so that not the entire intercooler is used. This means that the gas to be cooled is not exposed to the entire intercooler 9.

[0056] In this case, intercooler 9 is equipped with heat pump 10, but this is not necessary for the invention.

[0057] Heat pump 10 can also be adjustable, but this is not necessarily the case.

[0058] It will be possible to extract even more heat from the gas with the assistance of heat pump 10.

[0059] Compressor system 1 is also equipped with a control unit or regulator 11 for regulating or controlling intercooler 9. If heat pump 10 is adjustable, this control unit or regulator 11 will also be able to control heat pump 10.

[0060] In this case, sensor 12 is also provided. Sensor 12 is connected to the aforementioned control unit or regulator 11.

[0061] This concerns sensor 12, which can measure one or more environmental parameters at inlet 4a of low-pressure stage compressor element 2.

[0062] For example, sensor 12 can measure pressure, temperature and humidity.

[0063] It is not excluded that instead of or in addition to sensor 12, sensor 13 is provided at inlet 4b of the high-pressure stage compressor element 3. This is shown schematically in the figure with a dotted line.

[0064] This sensor 13 can then measure the humidity at inlet 4b.

[0065] Furthermore, device 1 is equipped with sensor 14 at inlet 4b to measure the temperature.

[0066] Finally, it is not excluded for device 1 to be provided with an oil injection 15, so that oil can be injected into pipeline 6 downstream of the intercooler 9. This is shown schematically with a dotted line.

[0067] The operation of the oil-injected multi-stage compressor system 1 is very simple, as described below.

[0068] During operation, gas to be compressed, e.g. air, is sucked in through inlet 4a of low-pressure stage compressor element 2, and will undergo a first compression stage.

[0069] The partially compressed gas flows through pipeline 6 to intercooler 9 where it is cooled, and then to inlet 4b of high-pressure stage compressor element 3, where it undergoes a subsequent compression.

[0070] Oil is injected both in low-pressure stage 2 and in high-pressure stage compressor element 3, which will provide the lubrication and cooling for compressor elements 2, 3.

[0071] The compressed gas leaves high-pressure stage compressor element 3 through the outlet 5b and is led to oil separator 7.

[0072] The injected oil is separated and the compressed gas can then be transported to an aftercooler before being sent to the consumers.

[0073] To ensure that no condensate forms when the gas is cooled by intercooler 9, this intercooler 9 must be controlled in a suitable manner to accommodate changes in the environmental and/or drive parameters of compressor elements 2, 3.

[0074] For this purpose, the control unit or regulator 11 will regulate intercooler 9 so that the temperature at inlet 4b of high-pressure stage compressor element 3 is above the dew point. As stated previously, this means that no condensate will occur after intercooler 9 at inlet 4b of high-pressure stage compressor element 3.

[0075] In a first step, the dew point, i.e. the presence of condensate, is determined or calculated at inlet 4b of high-pressure stage compressor element 3. The dew point depends on different parameters and is in other words not a fixed value, but a variable.

[0076] There are several options or ways to determine the dew point.

[0077] In the case of FIG. 1, the dew point is determined by measuring the environmental parameters with the assistance of sensor 12.

[0078] For this purpose, the measured values from sensor 12 are transferred to the control unit or regulator 11, which calculates the dew point on the basis thereof.

[0079] If oil-injected multi-stage compressor system 1 is provided with humidity sensor 13 at inlet 4b of high-pressure stage compressor element 3, it is also possible to measure the humidity at inlet 4b to directly determine the dew point, or in other words, the presence of condensate. Here, humidity sensor 13 will also transmit the measured value to control unit 11.

[0080] Another alternative is to determine the dew point by monitoring the temperature at inlet 4b of high-pressure stage compressor element 3, e.g. by using temperature sensor 14 at inlet 4b of high-pressure stage compressor element 3 or another sensor specially designed thereto.

[0081] In this case, temperature sensor 14 will transmit the measured values of the temperature to inlet 4b to the control unit or regulator 11, which will monitor and evaluate the course of the measured temperatures to determine the dew point on the basis thereof.

[0082] When the dew point has been determined, the control unit or regulator 11 will regulate intercooler 9 so that the temperature at inlet 4b of high-pressure stage compressor element 3 is above the dew point.

[0083] For this purpose, the control unit or regulator 11 will request the temperature at inlet 4b through temperature sensor 14 and compare it with the established dew point.

[0084] Control unit 11 will allow intercooler 9 to cool more when the temperature at inlet 4b is higher than the dew point, as the temperature of the gas can drop even further without condensate occurring.

[0085] If the temperature is still higher than the dew point when intercooler 9 is already cooling to its maximum, control unit 11 will put heat pump 10 into operation.

[0086] It is also possible that heat pump 10 is always in operation and that regulation is only carried through intercooler 9.

[0087] It is also possible for heat pump 10 to be adjustable, so that when the dew point is lowered and the required cooling capacity therefore increases, the control unit 11 will allow the first intercooler 9 and then heat pump 10, or vice versa or both at the same time or alternately, to increase their cooling capacity.

[0088] If the temperature at inlet 4b is lower than or equal to the dew point, control unit 11 will reduce the cooling of intercooler 9 so that the temperature of the gas will rise, thereby avoiding the formation of condensate.

[0089] If heat pump 10 is also adjustable, control unit 11 can also first lower the cooling capacity of heat pump 10, or alternately lower the cooling capacity of intercooler 9 and heat pump 10.

[0090] In the event of a drop in the dew point, the control unit or regulator 11 may allow intercooler 9 to cool down again so that the temperature of the gas will drop again.

[0091] This always allows maximum cooling to be achieved without condensate occurring.

[0092] The performance of the high-pressure stage compressor element can be maximized by being able to cool optimally at all times.

[0093] If device 1 is provided with oil-injection 15, additional cooling of the gas can be obtained with this. In addition, the injected oil will provide additional lubrication for high-pressure stage compressor element 3.

[0094] This invention is by no means limited to the embodiments described by way of example and shown in the figures, but an oil-injected multi-stage compressor system according to the invention and a procedure applied thereto can be realized according to different variants, without going beyond the scope of the invention.