System and a Method for Capacity Control in a Screw Compressor

Abstract

A system and a method for implementing capacity control in a screw compressor, said system comprising; a screw compressor, said compressor driven by a multi-capacity (speed and power) motor to compress air or gas medium, a bypass inlet member with a bypass valve, extending from the high pressure zone to the low pressure zone of the screw compressor to recirculate the gaseous medium, a bypass valve controller functionally connected to said bypass valve, a motor controller functionally connected to the motor to effect multi-capacity (speed and power) operations, a main processing control unit disposed to control the bypass valve and multi-capacity (speed and power) operations, measuring means disposed on the compressed medium passage for measuring the changes in the pressure and/or temperature changes in the form of signals, a signal converter functionally connected to the main processing unit and the measuring means to receive the signals, and said motor controller and bypass valve controller are functionally connected to the main processing unit to perform the capacity control of the screw compressor.

1 . A system for implementing capacity control in a screw compressor, said system comprising;
 (a) a screw compressor, said compressor driven by a multi-speed motor to compress a medium,   (b) a bypass inlet member with a bypass valve, extending from the high pressure zone to the low pressure zone of the screw compressor to recirculate the gaseous medium,   (c) a bypass valve controller functionally connected to said bypass valve,   (d) a motor controller functionally connected to the motor to effect multi-speed operations,   (e) a main processing control unit disposed to control the bypass valve and multi-speed operations,   (f) measuring means disposed on the compressed medium passage for measuring the changes in the pressure and/or temperature changes in the form of signals,   (g) a signal converter functionally connected to the main processing unit and the measuring means to receive the signals, and   (h) said motor controller and bypass valve controller are functionally connected to the main processing unit to perform the capacity control of the screw compressor.   
   
   
       2 . The system as claimed in  claim 1 , wherein the measuring means is pressure or temperature transducers. 
   
   
       3 . The system as claimed in  claim 1 , wherein the bypass inlet member on the compressor where pressure of the air or gas moving through the screw compressor has a positive pressure. 
   
   
       4 . The system as claimed in  claim 1 , wherein the screw compressor is without the bypass inlet member and the bypass controller. 
   
   
       5 . A method for capacity control in a screw compressor as claimed in  claim 1 , said method comprising the steps of;
 (a) setting a plurality of pressure values along with corresponding motor speed values for the compressor,   (b) measuring discharge pressure of the compressor,   (c) comparing the discharge pressure value with the pre-set pressure value,   (d) running initially the multi-speed motor at a maximum speed with bypass valve closed, to deliver the compressed medium, when the discharge pressure value is equal to pre-set pressure value, and   (e) controlling the compressor capacity by relative regulation of the bypass valve and the speed of multi-speed motor, through the main processing unit, to achieve the desired capacity of the compressor.   
   
   
       6 . The method as claimed in  claim 5 , wherein the controlling of the compressor capacity is performed by;
 (a) measuring the discharge pressure,   (b) comparing the discharged pressure with pre-set pressure value,   (c) running the motor at the motor speed value corresponding to the pre-set pressure value, and   (d) controlling the bypass valve to achieve the desired capacity of the compressor.   
   
   
       7 . The method as claimed in  claim 6 , wherein the initial motor speed value is varied to the corresponding pre-set pressure value whenever the discharge pressure value is equal to pre-set pressure value. 
   
   
       8 . The method as claimed in  claim 6 , wherein the opening of the bypass valve is regulated when the discharge pressure value is hot equal to pre-set pressure value.