Methods and systems for controlling turbocompressors

Abstract

A method for regulating a turbocompressor to prevent surge, is described. The method comprises the following steps: providing at least one surge limit line of turbocompressor; continuously determining an actual value of a corrected speed of the turbocompressor; continuously determining at least a maximum admissible pressure ratio on the surge limit line, corresponding to the actual value of the corrected speed; continuously determining an actual pressure ratio; acting upon an antisurge arrangement, if the actual pressure ratio is equal to or higher than the maximum admissible pressure ratio.

What is claimed is: 
     
         1 . A method for regulating a turbocompressor to prevent surge, comprising the following steps:
 providing at least one surge limit line and/or at least one choke line of said turbocompressor;   determining continuously an operating point of the compressor measuring a processing gas temperature at a compressor inlet, the rotary speed of the compressor, a delivery pressure value and a suction pressure value;   continuously determining an actual value of a corrected speed of the turbocompressor, the corrected speed being proportional to a ratio of the rotary speed to a square root of the processing gas temperature;   continuously determining at least a maximum admissible pressure ratio on said surge limit line and/or at least a minimum admissible pressure ratio on said choke line, corresponding to the actual value of the corrected speed;   continuously determining an actual pressure ratio, equal to a ratio between the delivery pressure value and the suction pressure value; and   acting upon an antisurge arrangement to recirculate a fraction of a the compressed gas in the compressor through a suction line, if the actual pressure ratio is equal to or higher than the maximum admissible pressure ratio or equal to or lower than the minimum admissible pressure ratio.   
     
     
         2 . The method of  claim 1 , further comprising the step of calculating a surge parameter defined as a ratio of
 the maximum admissible pressure ratio to the actual pressure ratio   and using said surge parameter to control the antisurge arrangement.   
     
     
         3 . The method of  claim 1 , further comprising the step of calculating a choke parameter defined as a ratio of
 the minimum admissible pressure ratio to the actual pressure ratio,   and using said choke parameter to control the antichoke arrangement.   
     
     
         4 . The method of  claim 1 , further comprising the steps of:
 providing at least one maximum admissible corrected speed and at least one minimum admissible corrected speed of the turbocompressor;   if the actual value of the corrected speed is higher than the maximum admissible corrected speed, reducing the rotary speed of the compressor; and   if the actual value of the corrected speed is lower than the minimum admissible corrected speed, increasing the rotary speed of the compressor.   
     
     
         5 . The method of  claim 1 , further comprising the steps of:
 determining a parameter indicative of a position of variable stator vanes located at the inlet of said turbocompressor; and   selecting said surge limit line and/or said choke line as a function of said parameter, among a plurality of surge limit lines and/or a plurality of choke lines, each corresponding to a respective position of the variable stator vanes.   
     
     
         6 . The method of  claim 1 , further comprising the steps of:
 setting a maximum admissible corrected speed and a minimum admissible corrected speed corresponding to a position of variable stator vanes located at the inlet of said turbocompressor; and   if the actual value of the corrected speed is higher than the maximum admissible corrected speed or if the actual value of the corrected speed is lower than the minimum admissible corrected speed, acting upon the variable stator vanes.   
     
     
         7 . The method of  claim 1 , further comprising the preceding step of detecting the kind of gas entering in the turbocompressor. 
     
     
         8 . An apparatus for providing an antisurge control for a compression system comprising at least one compressor, said apparatus being arranged and configured for performing a method according to  claim 1 . 
     
     
         9 . An apparatus for providing an antisurge control for a compression system comprising at least one compressor, said apparatus comprising:
 a data storage device containing data defining at least one surge limit line and/or at least one choke line of the compressor;   an arrangement for determining continuously an operating point of the compressor comprising: a temperature sensor for measuring processing gas temperature at a compressor inlet, a rotary speed sensor for measuring rotary speed of the compressor, and pressure sensors for measuring a delivery pressure value and a suction pressure value;   an arrangement for continuously determining an actual value of a corrected speed of the turbocompressor, the corrected speed being proportional to a ratio of the rotary speed to a square root of the processing gas temperature;   an arrangement for continuously determining at least a maximum admissible pressure ratio on said surge limit line and/or at least a minimum admissible pressure ratio on said choke line, corresponding to the actual value of the corrected speed;   an arrangement for continuously determining an actual pressure ratio, equal to a ratio between the delivery pressure value and the suction pressure value;   an antisurge arrangement to recirculate a fraction of compressed gas in the compressor through a the suction line, acted upon if the actual pressure ratio is equal to or higher than the maximum admissible pressure ratio or equal to or lower than the minimum admissible pressure ratio.   
     
     
         10 . The apparatus of  claim 9 , further comprising devices for calculating a surge parameter defined as a ratio of
 the maximum admissible pressure ratio to the actual pressure ratio.   
     
     
         11 . The apparatus of  claim 9 , further comprising devices for calculating a choke parameter defined as a ratio of
 the maximum admissible pressure ratio to the actual pressure ratio.   
     
     
         12 . The apparatus of  claim 9 , wherein said storage device contains data defining at least one maximum admissible corrected speed and one minimum admissible corrected speed of said compressor; and wherein a speed control arrangement is provided, which controls a rotary speed of said compressor such that: if the actual value of the corrected speed is higher than the maximum admissible corrected speed, the rotary speed of the compressor is reduced, and if the actual value of the corrected speed is lower than the minimum admissible corrected speed, the rotary speed of the compressor increased. 
     
     
         13 . The apparatus of  claim 9 , further comprising an actuation device for controlling a position of variable stator vanes of said compressor and wherein said storage device contains data defining a plurality of surge lines and/or choke lines corresponding to a plurality of respective positions of the variable stator vanes. 
     
     
         14 . A compression system comprising at least one compressor and an apparatus according to  claim 9 , for antisurge-control of said compressor. 
     
     
         15 . The compression system of  claim 14 , further comprising an arrangement for detecting the kind of gas entering in the turbocompressor. 
     
     
         16 . The apparatus of  claim 10 , further comprising devices for calculating a choke parameter defined as a ratio of the maximum admissible pressure ratio to the actual pressure ratio.