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 method for controlling a rotary screw compressor with a first air-end and a second air-end, wherein the first air-end compresses a gaseous medium and leads to the second air-end, which further compresses the medium, the method comprising: detecting a flow of the compressed gaseous medium at an outlet of the second air-end; adjusting a rotation speed of the first air-end with a first speed-controlled direct drive when the detected flow fluctuates in a range between a maximum value and a predetermined minimum value, while maintaining a predetermined outlet pressure; adjusting a rotational speed of the second air-end with a second speed-controlled direct drive when the detected flow fluctuates in the range between the maximum value and the predetermined minimum value, while maintaining the predetermined outlet pressure; opening a pressure-relief valve when the detected 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; reducing the rotational speed of the first air-end to a predetermined idling speed (V1L) via the first speed-controlled direct drive when the detected flow falls below the predetermined minimum value to reduce a 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 detected flow 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 taken at the outlet of the second air-end falls below the predetermined minimum value.

2. A rotary screw compressor comprising a first air-end and a second air-end, wherein the first air-end is configured to compress a gaseous medium, wherein the second air-end is configured to further compress the gaseous medium, and wherein both air-ends are driven separately and speed controllable, characterized in that the compressor further comprises a control unit which is configured to carry out a method according to claim 1.

3. The rotary screw compressor according to claim 2, characterized in that the inlet of the first air-end lacks a flow limiting, controllable throttle element and is in direct communication with the atmosphere.

4. The rotary screw compressor according to claim 2, characterized in that a pressure-relief valve is arranged at the outlet of the second air-end and configured to open in response to the flow decreasing below the predetermined minimum value.

5. The method of claim 1, wherein reducing the rotational speed of the first air-end takes place simultaneously with the opening of the pressure-relief valve.

6. The method of claim 1, further comprising reducing the rotational speed of the second air-end to a second predetermined idling speed (V2L) via the second speed-controlled direct drive when the detected flow falls below the predetermined minimum value.

7. The method of claim 6, the ratio of the second predetermined idling speed (V2L) of the second air-end to the predetermined idling speed (V1L) of the first air-end is within a range from 2 to 3.

8. A method for controlling a rotary screw compressor with a first air-end and a second air-end, wherein the first air-end compresses a gaseous medium and leads to the second air-end, which further compresses the medium, and wherein both air-ends are driven separately and speed controlled, the method comprising: detecting a flow of the compressed gaseous medium at an outlet of the second air-end; adjusting a rotation speed of the first air-end with a first speed-controlled direct drive when the detected flow fluctuates in a range between a maximum value and a predetermined minimum value, while maintaining a predetermined outlet pressure; adjusting a rotational speed of the second air-end with a second speed-controlled direct drive when the detected flow fluctuates in the range between the maximum value and the predetermined minimum value, while maintaining the predetermined outlet pressure; opening a pressure-relief valve when the detected 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; reducing the speed of the first air-end to a first predetermined idling speed when the detected flow falls below the predetermined minimum value; and reducing the speed of the second air-end to a second predetermined idling speed when the detected flow falls below the predetermined minimum value, wherein a speed ratio between the second air-end and the first air-end in response to the detected flow being above the predetermined minimum value differs from the ratio of the second predetermined idling speed to the first predetermined idling speed.

9. 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 speed-controlled first direct drive configured to drive the first air-end; and a speed-controlled second direct drive configured to drive the second air-end, wherein the compressor further comprises a control unit configured to carry out a method according to claim 8.

10. The method according to claim 8, wherein the ratio of the second predetermined idling speed to the first predetermined idling speed is within a range from 2 to 3.

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.