| abstract |
The present invention relates to a method of controlling a compressor and an apparatus therefor, the method, comprising at least the steps of : (a) providing a compressor feed stream (10); (b) passing the compressor feed stream (10) to an inlet (48) of the compressor (50) to provide a compressed stream (60) at an outlet (52) of the compressor (50); (c) calculating one or more controlled variables (CO1, CO2) that are invariant to compressor inlet conditions of the compressor feed stream (10), said inlet conditions comprising at least the ratio of specific heats (Cp/Cv) of the compressor feed stream (10), said one or more controlled variables comprising a surge controlled variable (CO1) representing the surge characteristics of the compressor (50); (d) providing one or more set points (SP1, SP2), that are invariant to the compressor inlet conditions of the compressor feed stream (10), said inlet conditions comprising at least the ratio of specific heats (Cp/Cv) of the compressor feed stream (10), said one or more set points comprising an anti-surge set point (SP1); and (e) providing a compressor recycle line (30) around the compressor (50) from the compressed stream (60) to upstream of the inlet (48) of the compressor (50), said compressor recycle line (30) comprising a in-line recycle valve (34); and controlling at least one of the in-line recycle valve (34) and the speed of the compressor (50) in response to the difference between the surge controlled variable (CO1) calculated in step (c) and the anti-surge set point (SP1) provided in step (d). |