Method for operating a multistage compressor

Abstract

A method for operating a multistage compressor is provided. The method includes monitoring the pump limit, wherein at least a first measurement parameter measured during operation is compared to a reference parameter. The reference parameter is characteristic of reaching the surge limit or a specific distance of the operating point from the surge limit. A multistage compressor is also provided. In order to enlarge the operating range without risking safety, it is proposed that each stage to be monitored individually for the onset of the surge.

1 . A method for operating a multistage compressor with a monitoring means for reaching of the surge limit or a defined gap from the surge limit, comprising:
 measuring a first measured variable at an inlet of each stage of the compressor;   providing an evaluation module which monitors each stage separately for the reaching of the surge limit or a defined gap from the surge limit using a reference variable which is specific for the stage;   comparing the reference variable, specific for each stage, with the stage-specific measured variable using the evaluation module; and   determining a state of the surging when a defined gap from the surge limit is reached,   wherein the reference variable is characteristic of reaching the surge limit or the defined gap from the surge limit.   
     
     
         2 . The method as claimed in  claim 1 , wherein the first measured variable is an input pressure in front of the corresponding stage. 
     
     
         3 . The method as claimed in  claim 2 ,
 wherein a second measured variable is measured at the inlet of each stage,   wherein the second measured variable is a temperature in front of the corresponding stage, and   wherein the temperature is forwarded for evaluation in the evaluation module.   
     
     
         4 . The method as claimed in  claim 1 , wherein a third measured value is a volumetric flow, a mass flow or a mass throughput of process gas. 
     
     
         5 . The method as claimed in at  claim 4 , wherein the volumetric flow, mass flow or mass throughput of the process gas is measured only at one location of the compressor. 
     
     
         6 . The method as claimed in  claim 1 ,
 wherein each stage is assigned a dedicated regulating line which delimits an operating range, in which the compressor is operated without surging, and   wherein a first gap exists between the dedicated regulating line and the surge limit.   
     
     
         7 . The method as claimed in  claim 1 ,
 wherein each stage is assigned a control line for controlling an opening of a surge limit regulating valve, and   wherein the control line delimits an extended operating range, in which the compressor is operated without surging,   wherein a second gap exists between the control line and the surge limit.   
     
     
         8 . The method as claimed in  6 ,
 wherein the control line and/or the regulating line are represented as a plot of a relationship between a volumetric flow or a dimensionless equivalent and a pressure number or a pressure-related equivalent, and   wherein the regulating line and/or control line are/is fixed by a gap from the surge limit by a first ratio of >1 of the volumetric flow or of the dimensionless equivalent to that of the surge limit, or a second ratio of <1 of the measured pressure number or of the pressure-related equivalent to the corresponding value of the surge limit.   
     
     
         9 . The method as claimed in  claim 8 , wherein the regulating line or the control line is fixed by the ratio, the first ratio or the second ration, whichever results in a greater operating range. 
     
     
         10 . The method as claimed in  claim 7 , wherein an adjusting run of the compressor comprises:
 approaching of the surge limit;   measuring of operating parameters, by means of which the surge limit is clearly fixed;   determining of standardized characteristic numbers which no longer have any dependencies on each individual operating parameter and are assigned to the surge limit; and   storing of the determined characteristic values in a first evaluation means.   
     
     
         11 . The method as claimed in  claim 10 , wherein a standardized surge limit is stored in the first evaluation means, which surge limit is standardized in such a way that there is no dependency on operationally variable influencing variables. 
     
     
         12 . The method as claimed in  claim 1 , wherein the surge limit for each individual stage is stored in an internal memory as a pressure number and/or a delivery coefficient or standardized delivery coefficient. 
     
     
         13 . The method as claimed in  claim 12 , wherein at least one or more stages includes an adjustable inlet guide vane apparatus, an angle of attack of which is measured and the surge limit is stored in the internal memory as a function of the angle of attack. 
     
     
         14 . The method as claimed in  claim 13 , further comprising:
 measuring a rotational speed and/or the angle of attack of an inlet guide vane apparatus;   determining the surge limit for each stage as at least one standardized characteristic variable which is called up from an internal memory independently of an inlet pressure and/or an inlet temperature and/or a volumetric flow and/or a mass throughput and/or a longitudinal flow;   measuring the inlet pressure and/or the inlet temperature and/or the volumetric flow and/or the mass throughput and/or the mass flow;   determining the surge limit for each stage and each standardized characteristic variable using the measurements for the operating point; and   determining the surge limit from the characteristic variable for each stage which affords the greatest operating range, and   fixing the surge limit of that stage by a surge limit regulator as criterion which is closest to the current operating point.   
     
     
         15 . The method as claimed in  claim 1 , wherein a fourth evaluation module is provided which evaluates a fluctuation range of the measured values and, as an evaluation result, determines a safety number which increases the gap of the regulating line for the surge limit regulating valve from the surge limit when a fluctuation range of the measurement increases. 
     
     
         16 . A multistage compressor, comprising:
 an evaluation module for monitoring the reaching of the surge limit or of a defined gap from the surge limit; and   a measuring apparatus for detecting a first measured variable during operation,   wherein the evaluation module is configured in such a way that it compares the first measured variable with a reference variable,   wherein the reference variable is characteristic of the reaching of the surge limit or a defined gap from the surge limit,   wherein the evaluation module is configured in such a way that the first measured variable is measured at an inlet of each stage of the compressor,   wherein at least one evaluation module is provided which monitors each stage separately for the reaching of the surge limit or a defined gap from the surge limit using the reference variable which is specific for the stage being compared with the stage-specific measured variable, and   wherein a variable is provided which includes a first assignment for a state of the surging and, when the surge limit or a defined gap from the surge limit is reached, the variable is the first assignment.   
     
     
         17 . The multistage compressor as claimed in  claim 16 , wherein the compressor is configured for carrying out a method, the method comprising:
 measuring a first measured variable at an inlet of each stage of the compressor;   providing an evaluation module which monitors each stage separately for the reaching of the surge limit or a defined gap from the surge limit using a reference variable which is specific for the stage;   comparing the reference variable, specific for each stage, with the stage-specific measured variable using the evaluation module; and   determining a state of the surging when a defined gap from the surge limit is reached,   wherein the reference variable is characteristic of reaching the surge limit or the defined gap from the surge limit.   
     
     
         18 . The multistage compressor as claimed in  claim 17 , wherein the first measured variable is an input pressure in front of the corresponding stage. 
     
     
         19 . The multistage compressor as claimed in  claim 19 ,
 wherein a second measured variable is measured at the inlet of each stage,   wherein the second measured variable is a temperature in front of the corresponding stage, and   wherein the temperature is forwarded for evaluation in the evaluation module.   
     
     
         20 . The multistage compressor as claimed in  claim 17 , wherein a third measured value is a volumetric flow, a mass flow or a mass throughput of process gas.