System and methods for controlling rotary screw compressors

• US 6,077,051 A
• Filed: 10/08/1997
• Issued: 06/20/2000
• Est. Priority Date: 11/23/1994
• Status: Expired due to Term

• Current Assignee: Quincy Compressor LLC (Atlas Copco AB)
• Original Assignee: Coltec Industries Incorporated (Enpro Industries Incorporated)
• Inventors: Burrell, Paul, Centers, Steven D.
• Primary Examiner(s): Thorpe, Timothy S.
• Assistant Examiner(s): Gartenberg, Ehud
• Application Number:
  US08/946,635
• Time in Patent Office: 986 Days
• Field of Search: 417/53, 417/280, 417/310
• US Class Current: 417/280
• CPC Class Codes: F04B 2205/06 Pressure in a (hydraulic) circuit
• CPC Class Codes: F04B 49/065 and making use of computers
• CPC Class Codes: F04C 2270/01 Load
• CPC Class Codes: F04C 2270/02 Power
• CPC Class Codes: F04C 2270/18 Pressure
• CPC Class Codes: F04C 2270/19 Temperature
• CPC Class Codes: F04C 2270/56 Number of pump/machine units in operation
• CPC Class Codes: F04C 2270/72 preventing reverse rotation
• CPC Class Codes: F04C 2270/78 Warnings
• CPC Class Codes: F04C 2270/80 Diagnostics
• CPC Class Codes: F04C 2270/86 Detection
• CPC Class Codes: F04C 28/06 specially adapted for stopping, starting, idling or no-load operation
• CPC Class Codes: F04C 28/12 using sliding valves
• CPC Class Codes: F04C 28/24 characterised by using valves controlling pressure or flow rate, e.g. discharge valves or unloading valvesF04C28/10 takes precedence
• CPC Class Codes: G05B 23/0213 Modular or universal configuration of the monitoring system, e.g. monitoring system having modules that may be combined to build monitoring program; monitoring system that can be applied to legacy systems; adaptable monitoring system; using different communication protocols
• CPC Class Codes: G05B 23/0286 Modifications to the monitored process, e.g. stopping operation or adapting control
• CPC Class Codes: G05D 16/2066 using controlling means acting on the pressure source
• CPC Class Codes: G06F 11/006 Identification G06F11/2289 takes precedence
• CPC Class Codes: G06F 11/2294 by remote test
• CPC Class Codes: G06F 11/327 Alarm or error message display
• CPC Class Codes: G07C 3/00 : Registering or indicating the condition or the working of machines or other apparatus, other than vehicles

Abstract

An electronic control system dynamically varies the output capacity of a compressor by controlling plural valves associated with the compressor to provide pressurized air to a distribution system at an appropriate rate. The control system operates in any of three modes for standalone operation, including continuous run, auto/dual pressure band, and target pressure modes. In the first two modes, pressure bands are dynamically calculated based on load and unload values entered by an operator. These electronic control systems can also be connected in a peer-to-peer network to coordinate control of up to 16 compressors feeding the same distribution system, so as to maintain a desired target pressure in the system. A modem connected to the system supports remote diagnostics, monitoring, and control. Specialized startup, operating, and shutdown diagnostic algorithms prevent damage to the compressor and avert unsafe operating conditions.

Claims

1. An electronic control apparatus for maintaining desired pressures in an air pressure system fed by at least one rotary screw compressor having an inlet valve, comprising:

inlet valve closing means for selectively closing the inlet valve of the compressor;

inlet valve modulation means for selectively partially closing the inlet valve of the compressor;

processing means connected to the inlet valve closing means and the inlet valve modulation means for selectively reducing output capacity of the compressor by selectively actuating the inlet valve closing means and inlet valve modulation means, the processing means selectively operable in at least two modes, including a first mode wherein the inlet valve closing means is periodically actuated and deactuated to provide an inlet valve duty cycle appropriate to a desired compressor output level, and a second mode wherein the inlet valve modulation means is actuated to partially close the inlet valve; and

mode switching means associated with the processing means for monitoring the number of actuations of the inlet valve closing means during a defined time period in the first mode, and if the number of actuations in the defined time period is greater than a defined value, causing the processing means to switch to the second mode of operation.

2. The apparatus of claim 1 wherein said mode switching means is provided with default values for the defined time period and defined value, said default values changeable by an operator.

3. The apparatus of claim 1 wherein the default value of the defined time period is 30 seconds and the default value of the defined value is 10 cycles.

4. A method for electronically maintaining desired pressures in an air pressure system fed by at least one rotary screw compressor having an inlet valve, the method comprising the steps of:

providing the inlet valve with both means for closing the inlet valve and means for partially closing the inlet valve;

determining when an output capacity of the compressor should be reduced to maintain desired pressure in the pressure system, and automatically periodically actuating and deactuating the means for closing the inlet valve to provide an inlet valve duty cycle appropriate to a desired compressor output level;

automatically monitoring the number of actuations of the inlet valve closing means during a defined time period, and if the number of actuations in the defined time period is greater than a defined value, actuating the means for partially closing the inlet valve, whereby the operating mode of the compressor is changed to prevent rapid cycling of the inlet valve.

5. The method of claim 4 wherein default values are provided for the defined time period and defined value, said default values changeable by an operator.

6. The method of claim 5 wherein the default value of the defined time period is 30 seconds and the default value of the defined value is 10 cycles.

7. A method for automated shutdown of a rotary screw air compressor having an inlet valve and an output connected to a sump with a blowdown valve, comprising the steps of:

storing a defined maximum shutdown sump pressure value;

detecting an instruction for implementing an orderly shutdown of the compressor;

automatically closing the inlet valve to unload the compressor;

after closing the inlet valve, automatically opening the blowdown valve to release pressure in the sump;

electronically monitoring pressure in the sump until sump pressure is less than said defined maximum shutdown sump pressure value, then stopping compressor rotation, whereby oil foaming is reduced.

8. The method of claim 7 comprising the further step of sensing disengagement of a contactor associated with compressor rotation and turning off a cooling fan motor of the compressor only when the contactor associated with compressor rotation is opened.

9. The method of claim 8 comprising the further steps of:

detecting an instruction for countermanding said orderly shutdown instruction prior to stopping compressor rotation; and

in response to said countermanding instruction, closing the blowdown valve, closing the inlet valve, and continuing compressor operation.

10. The method of claim 9 wherein an operator gives said orderly shutdown instruction, observes closing of the inlet valve, and then gives said countermanding instruction to reopen the inlet valve and continue compressor operation, whereby proper closing operation of the inlet valve is verified by the operator.

11. A system for electronically maintaining desired pressures in an air pressure system fed by at least one rotary screw compressor comprising:

at least one inlet valve having both means for closing the inlet valve and means for partially closing the inlet valve;

means for determining when an output capacity of the compressor should be reduced to maintain desired pressure in the pressure system, and automatically periodically actuating and deactuating the means for closing the inlet valve to provide an inlet valve duty cycle appropriate to a desired compressor output level; and

means for automatically monitoring the number of actuations of the inlet valve closing means during a defined time period, and if the number of actuations in the defined time period is greater than a defined value, actuating the means for partially closing the inlet valve, whereby the operating mode of the compressor is changed to prevent rapid cycling of the inlet valve.

12. The system of claim 11 wherein default values are provided for the defined time period and defined value, the default values being changeable by an operator.

13. The system of claim 12 wherein the default value of the defined time period is 30 seconds and the default value of the defined value is 10 cycles.

14. A system for automated shutdown of a rotary screw air compressor having an inlet valve and an output connected to a sump with a blowdown valve, the system comprising:

a stored defined maximum shutdown sump pressure value;

means for detecting an instruction for implementing an orderly shutdown of the compressor;

means for automatically closing the inlet valve to unload the compressor;

means for, after closing the inlet valve, automatically opening the blowdown valve to release pressure in the sump; and

means for electronically monitoring pressure in the sump until sump pressure is less than the defined maximum shutdown sump pressure value;

means for stopping compressor rotation, such that oil foaming is reduced.

15. The system of claim 14 further comprising:

means for sensing disengagement of a contactor associated with compressor rotation and turning off a cooling fan motor of the compressor only when the contactor associated with compressor rotation is opened.

16. The system of claim 14 further comprising:

means for detecting an instruction for countermanding the orderly shutdown instruction prior to stopping compressor rotation; and

means, in response to said countermanding instruction, for closing the blowdown valve, closing the inlet valve, and continuing compressor operation.

17. The system of claim 16 wherein when an operator gives the orderly shutdown instruction, observes closing of the inlet valve, and then gives the countermanding instruction to reopen the inlet valve and continue compressor operation, whereby proper closing operation of the inlet valve is verified by the operator.