the boiler is the biggest and the most
critical part of a thermal power plant
in this video we will learn about the
operation and construction of a typical
power plant boiler
we will also clarify a popular
misconception associated with boiler
operation near the end of the video
the function of the boiler is to convert
energy contained in the coal into high
temperature steam
large power plants typically use a type
of boiler called a water tube boiler
where water flows through the tubes and
fire surrounds it
water tube boilers are ideal for high
pressure applications
there are also fire tube boilers but
they are used for small scale
applications
burners in the boiler convert chemical
energy in the pulverized coal into
thermal energy
the hot gas that is produced travels all
over the boiler
the first heat absorption unit of the
boiler is an economizer highly
pressurized water supplied by the feed
water pump enters here
the economizer absorbs energy from the
flue gas which raises the temperature of
the liquid
from there the water flows into a steam
drum to the down comer
it then passes through a narrow tube
section called a water wall the phase
change of the water happens in the water
wall
the steam that is produced in addition
to some water droplets enters the steam
drum again
the real function of the steam drum is
to separate the water droplets from the
steam
as a result the steam leaving the steam
drum is saturated and pure
now here are some thermodynamics facts
according to the second law of
thermodynamics the greater the
temperature of the heat source the more
efficient the cycle
therefore making the steam temperature
very high will result in a highly
efficient power plant but this
temperature increase has certain
limitations the steam turbine blade
material cannot withstand temperatures
greater than 600 degrees celsius
so one more heat exchanger is added
after the steam drum to superheat the
steam and it is heated to the maximum
allowable limit
superheating also reduces the moisture
content in the steam
the steam is then supplied to the
turbine inlet
after the first turbine stage the
temperature drops
a clever idea to increase the power
plant efficiency is to bypass the steam
completely after the first stage and add
more heat
this process is known as reheating a
heat exchanger known as a reheater is
used for this purpose
reheating and super heating also
increase the power plant capacity along
with the efficiency
now let's discuss an important
misconception about boilers
we know that the temperature rises
across the boiler but what about
pressure consider this droplet of water
assume it is surrounded by a cover
if it gets converted to steam obviously
the pressure will rise
now consider the same droplet with no
cover here if the liquid gets converted
to steam the pressure will remain the
same because the fluid does not have a
fixed volume here it is free to expand
water inside the boiler is also like the
water droplet without a cover it's an
open flowing system the water is free to
expand when the liquid is converted into
steam which means that the pressure
should remain the same throughout an
ideal boiler
in actual practice due to friction and
other irregularities a small drop in
pressure occurs across the boiler
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