What is the compounding steam turbine?
Velosity compounding:This is a combination of pressure-velocity
compounding.
Lets say you have superheated steam coming out of the boiler at
70 bar, which is suppose to drive a steam turbine. How many stages
of blading required to reduce the pressure to acceptable exhaust
pressure so that it does not overheat the condenser?Remember, when
you reduce the pressure the kinetic energy increases so is the
steam speed. In order to reduce the pessure you must have pressure
compounded arrangement. In order to reduce speed you must have
velocity compounded. So what is pressure componded?This is an array
of nozzles and impulse blades laid out accordingly to mainly reduce
the steam pressure as it pass through the respected stages.Notice
the pressure drop gradually as it pass through a fixed blade stage,
but the speed increases as it pass the same stage. The velocity
compounded which is arranged so that you have nozzles,moving and
fixed blades laid accordingly. As it enters the nozzle the pressure
is dropped, steam velocity inctreased.Then it pass through moving
blades which reduces the steam velocity but maintain steam
pressure.Then the steam is pass through guide blades or fixed
blades where further reduction in velocity but none in
pressure.Last stage is moving blades where velocity is reduced but
pressure is maintained.
How is pressure-velocity compounding accomplished?
Answers:
It is a combination of pressure compounding and velocity
compounding.
Steam is expanded partially in a row of nozzles whereupon its
velocity gets increased. This high velocity steam then enters a few
rows of velocity compounding whereupon its velocity gets
successively reduced.
The velocity of the steam is again increased in the subsequent
row of nozzles and then again it is allowed to pass onto another
set of velocity compounding that brings about a stage-wise
reduction of velocity of the steam.
This system is continued.