Method for controlling a rotary screw compressor
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 L ) to reduce the volumetric flow delivered by the first to the second air-end.
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;
an inter-stage cooler coupled between the first air-end and the second air-end and configured to cool the compressed gaseous medium from the first air-end prior to directing the cooled, compressed gaseous medium to the second air-end;
a sensor configured to measure a flow of the compressed gaseous medium at an outlet of the second air-end; and
a control unit configured to
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; 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 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 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 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. 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 sensor configured to measure a flow of the compressed gaseous medium at an outlet of the second air-end; and
a control unit configured to
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; 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 taken 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 of the compressed gaseous medium taken at the outlet of the second air-end falls below the predetermined minimum value.
6. The rotary screw compressor of claim 5 , 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.
7. The rotary screw compressor of claim 6 , 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.
8. The rotary screw compressor of claim 5 , wherein an inlet of the first air-end is in direct communication with an atmosphere in which the rotary screw compressor is positioned.
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 pressure-relief valve in fluid communication with an outlet of the second air-end;
a sensor configured to measure a flow of the compressed gaseous medium at the outlet of the second air-end; and
a control unit communicatively coupled the sensor, the control unit configured to
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 from the second air-end via the pressure-relief valve; and
reduce the rotational speed of the first air-end to 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 taken 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 of the compressed gaseous medium taken at the outlet of the second air-end falls below the predetermined minimum value.
10. The rotary screw compressor of claim 9 , 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.
11. The rotary screw compressor of claim 10 , 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.
12. The rotary screw compressor of claim 9 , wherein an inlet of the first air-end is in direct communication with an atmosphere in which the rotary screw compressor is positioned.