Is an expander considered a compressor?

A turboexpander is a machine that utilizes the principle of gas expansion and pressure reduction to generate mechanical work, thereby reducing the gas temperature and obtaining energy.

The expander does work externally, which can drive the compressor

The flow-through section of the expander consists of three parts: the nozzle, the impeller, and the diffuser. The gas expands inside the nozzle, resulting in an increase in flow velocity to around 200 m/s; at the same time, temperature and pressure decrease. The cooling capacity provided by this process accounts for about 50% of the total cooling capacity. The gas then enters the impeller, driving it to perform work as it continues to expand, with further decreases in flow velocity, pressure, and temperature, to levels of 70–100 m/s. Once it reaches the diffuser, the flow velocity decreases while temperature and pressure increase, thereby recovering kinetic energy and reducing frictional losses. To prevent the expander from running away, braking is required, which can be either regenerative or non-regenerative; regenerative types include generators and boosters, among others. Which one to choose is determined by the process. I used to study by reading books, so I might not have the correct figures; I hope this is helpful to you.