Compressor anti-surge protectoin under wet gas conditions

Abstract

A method for anti-surge protection of a compressor under wet gas conditions is described. The compressor includes a suction side and a delivery side. An anti-surge system is arranged between the delivery side and the suction side of the compressor. The method includes: calculating a surge limit line in a compression ratio vs. corrected power diagram; determining a compressor operating point in the compression ratio vs. corrected power diagram; detecting a distance between the operating point and the surge limit line; acting on the anti-surge system of the compressor if the distance is below a minimum safety distance.

What is claimed is: 
     
         1 . A method for anti-surge protection of a compressor under wet gas conditions, the compressor comprising a suction side, a delivery side and an anti-surge system; the method comprising:
 calculating a surge limit line in a compression ratio vs. corrected power diagram;   determining a compressor operating point in said compression ratio vs. corrected power diagram;   detecting a distance between the operating point and the surge limit line; and   acting on the anti-surge system of the compressor if the distance is below a minimum safety distance.   
     
     
         2 . The method of  claim 1 , wherein the corrected power is a dimensionless parameter dependent upon the power required to drive the compressor. 
     
     
         3 . The method of  claim 1 , wherein the surge limit line extends from a first end point corresponding to a dry gas condition to a second end point corresponding to a maximum liquid content. 
     
     
         4 . The method of  claim 1 , further comprising:
 determining a rotational speed of the compressor; and   determining a suction temperature and a suction pressure of the gas at the compressor suction side;   wherein the surge limit line is calculated based on the rotational speed, suction temperature and suction pressure of the gas.   
     
     
         5 . The method of  claim 4 , further comprising:
 determining a mean molar mass of the gas; and   determining the compressibility of the gas;   wherein the surge limit line is calculated as a function of the mean molar mass and compressibility of the gas.   
     
     
         6 . The method of  claim 1 , wherein the corrected power is a dimensionless parameter. 
     
     
         7 . The method of  claim 1 , wherein the corrected power is a function of an actual compressor driving power, gas pressure at the compressor suction side, gas temperature at the compressor suction side, and chemical parameters of the gas. 
     
     
         8 . The method of  claim 5 , wherein the corrected power is calculated as follows: 
       
         
           
             
               
                 W 
                 corr 
               
               = 
               
                 W 
                 
                   
                     P 
                     s 
                   
                   * 
                   
                     
                       ( 
                       
                         
                           
                             Z 
                             s 
                           
                            
                           
                             RT 
                             s 
                           
                         
                         
                           M 
                           w 
                         
                       
                       ) 
                     
                     0.5 
                   
                   * 
                   
                     k 
                     vs 
                     1.5 
                   
                   * 
                   
                     
                       π 
                        
                       
                           
                       
                        
                       
                         D 
                         2 
                       
                     
                     4 
                   
                 
               
             
           
         
         wherein 
         W is the actual measured power absorbed by the compressor; 
         Ps, Ts are the gas pressure and temperature at the suction side of the compressor; 
         Mw is the mean molar mass of the gas processed by compressor; 
         Zs is the compressibility of the gas at the compressor suction side; 
         R is the gas constant; 
         kvs is the isentropic volume exponent of the gas at the compressor suction side; and 
         D is the impeller diameter. 
       
     
     
         9 . The method of  claim 1 , wherein the anti-surge system comprises an anti-surge valve, which is opened when acting on the anti-surge system is performed, to recirculate gas from the delivery side to the suction side of compressor. 
     
     
         10 . A wet gas compressor system, comprising:
 a compressor having a suction side and a delivery side;   an anti-surge system; and   a control unit, functionally coupled to the anti-surge system;   wherein the control unit is configured and arranged for performing a method according to  claim 1 .