Method of surge protection for a dynamic compressor using a surge parameter

Abstract

A method of surge protection for a dynamic compressor that has a corresponding compressor map. A control system continually calculates an equivalent polytropic head parameter in order to define a surge limit line. The system then calculates a control parameter and determines the distance the control parameter to the surge limit line wherein the control parameter is dynamic to changes in compressor load and invariant to changes in suction conditions and gas compressibility. As a result of the distance of the control parameter to the surge limit line, the surge valve of a dynamic compressor is actuated to prevent surge.

1 . A method of surge protection for a dynamic compressor having a corresponding compressor map steps comprising:
 continually calculating an equivalent parameter with a controller;   defining a surge limit line on the compressor map as a function of the equivalent parameter;   continually calculating a distance a control parameter is from the surge limit line, wherein the control parameter is dynamic to changes in compressor load; and   actuating an surge valve based on the distance.   
     
     
         2 . The method of  claim 1  wherein the equivalent parameter is an equivalent polytropic head parameter. 
     
     
         3 . The method of  claim 2  wherein the equivalent polytropic head is a function of 
       
         
           
             
               Hp 
               
                 V 
                 c 
                 2 
               
             
           
         
       
       where Hp is polytropic head and V c   2  is equal to NZRT where N is a polytropic exponent, R is equal to 
       
         
           
             
               Ro 
               MW 
             
           
         
       
       where Ro is a gas constant and MW is molecular weight and T is the temperature of gas at flow conditions at the compressor. 
     
     
         4 . The method of  claim 2  wherein the surge limit line is defined based on the polytropic compression process equation, Pv n =constant. 
     
     
         5 . The method of  claim 2  wherein the surge limit line is defined based on modeling of the compressor based on flow, pressure, speed, compressibility and temperature. 
     
     
         6 . The method of  claim 2  wherein the equivalent polytropic head parameter is based on similitude theory. 
     
     
         7 . The method of  claim 2  wherein the equivalent polytropic head parameter is based on polytropic head correction using sonic velocity of gas at flowing condition of the compressor. 
     
     
         8 . The method of  claim 2  wherein the equivalent polytropic head parameter is based on gas compressibility. 
     
     
         9 . The method of  claim 2  wherein the equivalent polytropic head parameter is based on n=constant. 
     
     
         10 . The method of  claim 1  wherein the control parameter is determined based on an equivalent flow parameter. 
     
     
         11 . The method of  claim 10  wherein the equivalent flow parameter is a function of q 2   eq  wherein q 2  equals 
       
         
           
             
               
                 Q 
                 2 
               
               
                 V 
                 c 
                 2 
               
             
           
         
       
       where Q is volumetric flow and V c  is the sonic velocity of gas at flowing conditions. 
     
     
         12 . The method of  claim 10  wherein the equivalent flow parameter is based on similitude theory. 
     
     
         13 . The method of  claim 10  wherein the equivalent flow parameter is based on mach number determination using sonic velocity of gas at flowing condition of the compressor. 
     
     
         14 . The method of  claim 10  wherein the equivalent flow parameter is based on gas compressibility. 
     
     
         15 . The method of  claim 10  wherein the equivalent flow parameter is based on n=constant. 
     
     
         16 . The method of  claim 1  wherein the control parameter is determined based on R=(q 2   eq |op)/(q 2   eq |surge) where q 2   eq |op=an equivalent volumetric flow parameter at an operating condition and q 2   eq |surge=an equivalent volumetric flow parameter at a surge condition. 
     
     
         17 . The method of  claim 1  wherein the distance a control parameter is from the surge limit line is determined based on the control parameter and is a function of [((q 2   eq |op)/f(h eq ))−1] where q 2   eq |op is an equivalent flow parameter at an operating condition and f(h eq ) is a function of the equivalent polytropic head parameter. 
     
     
         18 . The method of  claim 17  wherein when the distance a control parameter is from the surge limit line is greater than 0 then the compressor is operating to the right of the surge limit line and when the distance a control parameter is from the surge limit line is less than or equal to 0 then the compressor is operating to the left of the surge limit line. 
     
     
         19 . The method of  claim 1  further comprising the step of continually calculating a distance the control parameter is from a surge control line. 
     
     
         20 . The method of  claim 19  where the surge control line is determined based on the control parameter and is a function of [((q 2   eq |op)/f(h eq ))−SM]−1 where q 2   eq |op is the equivalent flow parameter at an operating condition, f(h eq ) is a function of the equivalent polytropic head parameter defining the surge limit line and SM is the safety margin. 
     
     
         21 . The method of  claim 20  wherein when the distance a control parameter is from the surge control line is equal to or greater than 0 the surge valve is closed and when the distance the control parameter from the surge control line is less than 0 the surge valve is opened.