Centrifugal Compressors & Their Working

All gases have large spaces among there molecules, these spaces could be enhanced further and decreased by doing some work. Work done which is used for the enhancement of these spaces is called expansion, and work done to minimize these spaces is called compression. All gases while expansion produces cooling effect and while compression of gases raises there temperature. Compression is a term used to force gases to occupy smaller volumes by increasing their pressure. Volume of gases is interlinked with temperature and pressure of the gas, which is cleared by 2 laws, govern gas compressions.

·         Boyles Law

·         Charles Law

Centrifugal compressor are machines in which velocity and pressure given to air or gas in a radial direction by one or more impellers diffuser combination.

       

The centrifugal compressor may be single stage or multistage. Multistage limits containing a series of impellers on a single shaft rotating at high speed in a massive casing internal channel lead from the discharge of one impeller to the in let of next these machines compress enormous volumes of air or process gas up to 200000 ft3/min,(340000m3/hr).At the inlet to an outlet pressure of20atm, similar capacity machines discharge at pressure up to several hundred atmospheres, interstage cooling is needed on high pressure units.

WORKING  PRINCIPLE:

                                                               

In a centrifugal compressor the mechanical energy is increased by centrifugal action. The gas enters the suction eye of a high speed rotary element called the impeller which caries radial vanes integrally cast in it. As the impeller rotates, the blades of the impeller force the gas outward from the center the impeller to the outer rim of impeller, the increase in velocity of the gas creates a flow pressure area at the eye of the impeller. The gas at the outer rim of the impeller is forced in to a passage way called a diffuser where the velocity decreases in the pressure of the gas.

      In a multistage compressor different sets of impellers and diffusers the pressure of the gas in stages. Labryrinths are installed between the impellers the prevents gas leakage between the stages, each stage has its own casing drain to insure that no liquid is in the compressor before starting.

  To balance the axial thrust developed from the discharge end to the suction end of machine, a balancing drum connected to the suction discharge end of the machine to stop gas leakage along the shaft, a seal is formed with seal oil.