Abstract: An industrial system for compressing a waste gas product, such as CO2, including a compressor train having an upstream rotor portion and a downstream rotor portion arranged in flow series with said upstream portion. Each rotor portion includes one or more compressor stages and said downstream portion is arranged to rotate at a variable relative speed to that of the upstream rotor portion. Sensing equipment for the compressor train is arranged to determine one or more flow conditions and a controller is arranged to receive data indicative of said one or more sensed flow conditions. The controller is arranged to set the rotational speed of the upstream rotor portion based upon the pressure or flow rate of gas upstream of said compressor train and to set operational parameters for said downstream portion so as to maintain a desired surge margin for said upstream rotor portion.