Method and control unit for operating a compressor

A method for operating a compressor configured to compress a process gas, comprising:

• determining a flow rate of the process gas through the compressor or a variable corresponding to the flow rate;
• determining a delivery head of the compressor or a variable corresponding to the delivery head dependent on a measured inlet pressure of the compressor and dependent on a measured outlet pressure of the compressor;
• determining, by a surge limit controller, a control variable for a control element interacting with the compressor dependent on the flow rate or the variable corresponding to the flow rate and dependent on the delivery head or the variable corresponding to the delivery head;
• operating the compressor along a control line, which has a defined distance from a surge limit of the compressor;
• determining a proportion of steam of the process gas or a variable corresponding to the proportion of steam;
• and
• adapting the control line, along which the compressor is operated, dependent on the proportion of steam or the variable corresponding to the proportion of steam.