Centrifugal compressor

The centrifugal compressor comprises a primary impeller, the primary impeller is installed at an air inlet of a diffuser, the diffuser is communicated with a backflow device through an air supply channel, the air supply channel comprises a diffusion channel, a reversing channel and a backflow channel, a cooling coil is installed on the backflow channel, and an air supply opening is formed in an air outlet of the backflow device. The utility model has the benefits that the cooling coil is used for cooling the gas in the backflow channel, so that the difference value between the gas pressure in the backflow channel and the gas pressure in the diffusion channel is increased, the gas flow can pass through the reversing channel more smoothly, the primary compression is close to isothermal compression as much as possible, and the energy consumption of the next-stage compression is saved; the air supply port is formed in the air outlet of the backflow device, it is guaranteed that the amount of compressed air enteri