A compressor consumes shaft work to raise the pressure of a flowing gas or vapor.

For steady, approximately adiabatic operation with negligible kinetic and potential-energy changes,

$$w_{in}\approx h_2-h_1.$$

If a compressor raises a gas enthalpy from $300$ to $450\ \mathrm{kJ/kg}$, the idealized specific shaft-work input is

$$w_{in}\approx150\ \mathrm{kJ/kg}.$$

At $2\ \mathrm{kg/s}$, the shaft power required is approximately

$$\dot W_{in}=2(150)=300\ \mathrm{kW}.$$

Compressing a gas generally raises its temperature as well as its pressure. Cooling between compression stages can reduce required work because the gas enters later stages in a different thermodynamic state.

Real compressor losses modify the outlet state and required work; those effects can be quantified later by comparison with an ideal reference process.