Patent ID: 8840358

Claim:
A method of controlling a compressor comprising: (a) providing a compressor feed stream; (b) passing the compressor feed stream to an inlet of the compressor to provide a compressed stream at an outlet of the compressor; (c) calculating one or more controlled variables (CO 1 , CO 2 ) that are invariant to compressor inlet conditions of the compressor feed stream, said inlet conditions comprising at least the ratio of specific heats (Cp/Cv) of the compressor feed stream, said one or more controlled variables comprising a surge controlled variable (CO 1 ) representing the surge characteristics of the compressor; (d) providing one or more set points, that are invariant to the compressor inlet conditions of the compressor feed stream, said inlet conditions comprising at least the ratio of the specific heats (Cp/Cv) of the compressor feed stream, said one or more set points comprising an anti-surge set point (SP 1 ) corresponding to a surge control line which is invariant to the compressor inlet conditions; (e) providing a compressor recycle line around the compressor from the compressed stream to upstream of the inlet of the compressor, said compressor recycle line comprising an in-line recycle valve; (f) controlling at least one of the in-line recycle valve and the speed of the compressor in response to the difference between the surge controlled variable (CO 1 ) calculated in step (c) and the anti-surge set point (SP 1 ) provided in step (d).