Compounding of steam turbines
Each stage of a compounded steam turbine has its own set of nozzles and rotors.
[1][2] Compounded steam turbines are used to reduce rotor speeds to achieve optimal operating revolutions per minute.
The steam produced in the boiler has sufficiently high enthalpy when superheated.
Curtis to solve the problem of single stage Impulse turbine for use of high pressure and temperature steam.
This high velocity steam is directed on to the first set (ring) of moving blades.
The figure also shows the changes in the pressure and the absolute steam velocity as it passes through the stages.
The ratio of work produced in a 2-stage turbine is 3:1 as one move from higher to lower pressure.
This is used to solve the problem of high blade velocity in the single-stage impulse turbine.
The steam coming from the boiler is fed to the first set of fixed blades i.e. the nozzle ring.
Then it is fed into the next set of moving blades, and this process is repeated until the condenser pressure is reached.
As shown in the figure, pressure drop takes place in the nozzles and is distributed in many stages.
An important point to note here is that the inlet steam velocities to each stage of moving blades are essentially equal.
An important point to note from the above velocity diagram is that the fluid exit angle (δ) is 90⁰.
The steam coming from the boiler is passed to the first ring of fixed blades, where it gets partially expanded.
This process is shown diagrammatically in figure 5. where, symbols have their usual meaning.
As explained earlier a reaction turbine is one in which there is pressure and velocity loss in the moving blades.
In this type of turbine the pressure drops take place in a number of stages.
The steam passes over a series of alternate fixed and moving blades.
The fixed blades act as nozzles i.e. they change the direction of the steam and also expand it.
