Method for controlling a rotary screw compressor

Abstract

The invention relates to a method for controlling a rotary screw compressor, having at least a first and a second air-end, wherein both air-ends are driven separately from one another and speed controlled. According to the invention, the following steps are carried out: detection of a volume flow taken at the outlet of the second air-end; adjustment of the rotational speed of both air-ends, when the removed volume flow fluctuates in a range between a maximum value and a minimum value; opening of a pressure-relief valve, if the volume flow falls below the minimum value; and reduction of the rotational speed of at least the first air-end to a predetermined idling speed (V1.sub.L) to reduce the volumetric flow delivered by the first to the second air-end.

Claims

1. A rotary screw compressor, comprising: a first air-end configured to compress a gaseous medium; a second air-end configured to further compress the gaseous medium; a first variable speed drive configured to drive the first air-end; a second variable speed drive configured to drive the second air-end; and a control unit communicatively coupled with each of the first variable speed drive and the second variable speed drive, the control unit configured to determine a flow of the compressed gaseous medium at an outlet of the second air-end; adjust a rotation speed of the first air-end with the first variable speed drive when the flow fluctuates in a range between a maximum value and a predetermined minimum value, while maintaining a predetermined outlet pressure; adjust a rotational speed of the second air-end with the second variable speed drive when the flow fluctuates in the range between the maximum value and the predetermined minimum value, while maintaining the predetermined outlet pressure; and reduce the rotational speed of the first air-end to a predetermined idling speed via the first variable speed drive when the flow falls below the predetermined minimum value to reduce the flow delivered by the first air-end to the second air-end, wherein a speed ratio between the second air-end and the first air-end when the flow determined at the outlet of the second air-end fluctuates in a range between the maximum value and the predetermined minimum value is different than the speed ratio between the second air-end and the first air-end when the flow determined at the outlet of the second air-end falls below the predetermined minimum value.

2. The rotary screw compressor of claim 1, wherein the control unit is further configured to reduce the rotational speed of the second air-end to a second predetermined idling speed via the second variable speed drive when the flow falls below the predetermined minimum value.

3. The rotary screw compressor of claim 2, wherein a ratio of the second predetermined idling speed of the second air-end to the predetermined idling speed of the first air-end is within a range from 2 to 3.

4. The rotary screw compressor of claim 1, wherein an inlet of the first air-end is in direct communication with an atmosphere in which the rotary screw compressor is positioned.

5. The rotary screw compressor of claim 1, further comprising a volumetric flow sensor communicatively coupled with the control unit, the volumetric flow sensor configured to measure the flow of the compressed gaseous medium at the outlet of the second air-end.

6. The rotary screw compressor of claim 1, further comprising a pressure-relief valve in fluid communication with the outlet of the second air-end.

7. The rotary screw compressor of claim 6, wherein the control unit is further configured to open the pressure-relief valve when the flow falls below the predetermined minimum value to at least partially discharge compressed gaseous medium delivered by the second air-end via the pressure-relief valve.

8. A rotary screw compressor, comprising: a first air-end configured to compress a gaseous medium; a second air-end configured to further compress the gaseous medium; a first variable speed drive configured to drive the first air-end; a second variable speed drive configured to drive the second air-end; a pressure-relief valve in fluid communication with an outlet of the second air-end; and a control unit communicatively coupled with the first variable speed drive, the second variable speed drive, and the pressure-relief valve, the control unit configured to determine a flow of the compressed gaseous medium at the outlet of the second air-end; adjust a rotation speed of the first air-end with the first variable speed drive when the flow fluctuates in a range between a maximum value and a predetermined minimum value; adjust a rotational speed of the second air-end with the second variable speed drive when the flow fluctuates in the range between the maximum value and the predetermined minimum value; and reduce the rotational speed of the first air-end to a predetermined idling speed via the first variable speed drive when the flow falls below the predetermined minimum value to reduce the flow delivered by the first air-end to the second air-end, wherein a speed ratio between the second air-end and the first air-end when the flow determined at the outlet of the second air-end fluctuates in a range between the maximum value and the predetermined minimum value is different than the speed ratio between the second air-end and the first air-end when the flow determined at the outlet of the second air-end falls below the predetermined minimum value.

9. The rotary screw compressor of claim 8, wherein the control unit is further configured to reduce the rotational speed of the second air-end to a second predetermined idling speed via the second variable speed drive when the flow falls below the predetermined minimum value.

10. The rotary screw compressor of claim 9, wherein a ratio of the second predetermined idling speed of the second air-end to the predetermined idling speed of the first air-end is within a range from 2 to 3.

11. The rotary screw compressor of claim 8, wherein an inlet of the first air-end is in direct communication with an atmosphere in which the rotary screw compressor is positioned.

12. The rotary screw compressor of claim 8, further comprising a flow sensor communicatively coupled with the control unit, the flow sensor configured to measure the flow of the compressed gaseous medium at the outlet of the second air-end.

13. The rotary screw compressor of claim 8, wherein the control unit is further configured to open the pressure-relief valve when the flow falls below the predetermined minimum value to at least partially discharge compressed gaseous medium delivered by the second air-end via the pressure-relief valve.

14. The rotary screw compressor of claim 8, wherein the control unit is further configured to control operation of at least one of the first variable speed drive or the second variable speed drive to maintain a predetermined outlet pressure when the flow fluctuates in the range between the maximum value and the predetermined minimum value.

15. The rotary screw compressor of claim 8, wherein at least one of the first variable speed drive or the second variable speed drive is a speed-controlled direct drive.

16. A rotary screw compressor, comprising: a first air-end and a second air-end, the first air-end configured to compress a gaseous medium, the second air-end configured to further compress the gaseous medium, wherein each of the first air-end and the second air-end is driven separately and speed controllable; a pressure-relief valve in fluid communication with an outlet of the second air-end; and a control unit configured to determine a flow of the compressed gaseous medium at an outlet of the second air-end; adjust a rotation speed of the first air-end when the flow fluctuates in a range between a maximum value and a predetermined minimum value, while maintaining a predetermined outlet pressure; adjust a rotational speed of the second air-end when the flow fluctuates in the range between the maximum value and the predetermined minimum value, while maintaining the predetermined outlet pressure; open the pressure-relief valve when the flow falls below the predetermined minimum value to at least partially discharge compressed gaseous medium delivered by the second air-end via the pressure-relief valve; and reduce the rotational speed of the first air-end to a predetermined idling speed when the flow falls below the predetermined minimum value to reduce the flow delivered by the first air-end to the second air-end, wherein a speed ratio between the second air-end and the first air-end when the flow determined at the outlet of the second air-end fluctuates in a range between the maximum value and the predetermined minimum value is different than the speed ratio between the second air-end and the first air-end when the flow determined at the outlet of the second air-end falls below the predetermined minimum value.

17. The rotary screw compressor of claim 16, wherein the control unit is further configured to reduce the rotational speed of the second air-end to a second predetermined idling speed when the flow falls below the predetermined minimum value.

18. The rotary screw compressor of claim 17, wherein a ratio of the second predetermined idling speed of the second air-end to the predetermined idling speed of the first air-end is within a range from 2 to 3.

19. The rotary screw compressor of claim 16, wherein an inlet of the first air-end is in direct communication with an atmosphere in which the rotary screw compressor is positioned.

20. The rotary screw compressor of claim 16, further comprising a flow sensor communicatively coupled with the control unit, the flow sensor configured to measure the flow of the compressed gaseous medium at the outlet of the second air-end.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages and details emerge from the following description of a preferred embodiment with reference to the drawing. Shown are:

(2) FIG. 1 illustrates a simplified representation of the operating parameters in a rotary screw compressor with two air-ends during load operation

(3) FIG. 2 illustrates a simplified illustration of the operating parameters in the rotary screw compressor during idle mode.

DETAILED DESCRIPTION

(4) Before any embodiments of the disclosure are explained in detail, it is to be understood that the disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The disclosure is capable of supporting other embodiments and of being practiced or of being carried out in various ways.

(5) FIG. 1 shows the basic structure of a compressor, which is designed as a rotary twin screw compressor 200. In addition to the individual elements of the rotary twin screw compressor, typical parameters are also given, how they occur during load operation, if compressed air with a volume flow above a predetermined minimum value and not greater than a system-dependent maximum value is required.

(6) A first air-end 201 has a first direct drive 202 which is speed-controlled. The inlet of the first air-end 201, via which ambient air is drawn in, is coupled without the interposition of an intake regulator directly to an intake manifold 203, at which ambient atmosphere with a pressure of 1.0 bar at a temperature of, for example, 20° C. is applied. Thus, at the inlet of the first air-end 201, a pressure of 1.0 bar is applied.

(7) The first air-end 201 is operated, for example, at a speed of 15,500 min−1 in order to compress the air. At the outlet of the first air-end 201, a pressure of 3.2 bar prevails, so that the first air-end has a compression ratio of 3.2 during load operation. Through the compression the temperature of the medium (compressed air) increases to 170° C. The compressed air is conducted from the outlet of the first air-end 201 via an inter-stage cooler 204 to the inlet of a second air-end 206, which has a second, speed-controlled direct drive 207. After the inter-stage cooler 204, at the inlet of the second air-end 206, the compressed air has a temperature of, for example, 30° C. and further a pressure of 3.2 bar. In load operation, the second air-end 206 with a speed of, for example, 22,000 min−1 is operated, so that it comes to a further compression. The compressed air therefore has a pressure of 10.2 bar and a temperature of 180° C. at the outlet of the second air-end 206. The second air-end thus also has a compression ratio of about 3.2. The compressed air is passed from the outlet of the second air-end 206 through an after-cooler 208 and cooled there to about 35° C. Finally, at the output of the rotary twin screw compressor 200, a pressure-relief valve 209 is arranged, which is actuated by a control unit (not shown).

(8) The rotary twin screw compressor 200, described by way of example, exhibits a power consumption of 150 kW at maximum rotational speed to the direct drives 202, 207, and supplies compressed air with a maximum pressure of 12 bar and a minimum pressure of 6 bar. The speed ratio between the air-ends is approximately 1.4 during load operation.

(9) FIG. 2 shows the rotary twin screw compressor 200 in idle mode, that is, if essentially no compressed air is removed. In addition to the elements of the rotary twin screw compressor, typical parameters are given in turn, as they occur in idle mode. To enter into idle mode, the pressure-relief valve is opened and the speed of both air-ends is reduced. The inlet of the first air-end 201, via which ambient air continues to be sucked in, albeit in a reduced amount, is still coupled without the interposition of an intake regulator directly to the intake manifold 203, at which ambient atmosphere is applied at a pressure of 1.0 bar at a temperature of 20° C. At the inlet of the first air-end 201, an unchanged pressure of 1.0 bar is thus applied.

(10) The first air-end 201 is now operated at an idling speed V1L=2,500 min−1 in order to compress the air. At the outlet of the first air-end 201, a pressure of 1.5 bar prevails, so that the first air-end has a compression ratio of 1.5 in idle mode. Due to the reduced compression, the temperature of the medium (compressed air) only increases to 90° C. The compressed air is supplied from the outlet of the first air-end 201 via the inter-stage cooler 204 led to the inlet of the second air-end 206. After the inter-stage cooler 204, at the inlet of the second air-end 206, the compressed air has at idle a temperature of, for example, 30° C. and further a pressure of 1.5 bar. After the intercooler 204, at the inlet of the second compressor stage 206, the compressed air has at idle a temperature of for example 30° C. and further a pressure of 1.5 bar (Intermediate pressure). The necessary cooling capacity for the intermediate cooling is thus reduced during idle mode. In idle mode, the second air-end 206 is operated at an idling speed V2L of 7,500 min−1 rpm. At the outlet of the second air-end 206, the compressed air has a reduced pressure of about 1.2 bar and a temperature of 70° C., compared to the intermediate pressure. The second air-end thus has a compression ratio of about 0.8 (Expansion). The compressed air is passed from the outlet of the second air-end 206 through the after-cooler 208 and cooled there to about 30° C.

(11) The rotary twin screw compressor 200, described by way of example, exhibits a power consumption of 7 kW during idle mode and delivers a maximum pressure of 1.2 bar. The speed ratio between the air-ends is about 3.

REFERENCE NUMERAL LIST

(12) 200 Rotary twin screw compressor 201 First rotary screw compressor 202 First direct drive 203 Intake air duct 204 Inter-stage cooler 205 — 206 Second rotary screw compressor 207 second direct drive 208 After-cooler 209 Pressure-relief valve

(13) Various features and advantages of the disclosure are set forth in the following claims.