La Mont Boiler Working and Construction
A forced circulation
boiler was first introduced by La-Mont in the year 1925 which is used in Europe
and America. This is a modern high pressure boiler (water tube type
steam boilers) working on forced circulation system.
Working principle
of La Mont Boiler
The image shows the
flow circuit of La Mont Boiler.
explained working of each and every
part in La Mont boiler one by one.
Steam separator
drum
The la Mont boiler
consists of a steam separator drum which is placed wholly outside the
boiler setting . The drum receives a mixture
of steam and water from the evaporator tubes and feed water from the
economizer. The steam is separated from water in the drum.
Circulating pump
The water from the
drum is then drawn to the circulating (centrifugal) pump through the
down-comer. The pump circulates water (“forced circulation”) equal to 8 to 10
times the weight of steam evaporated. This prevents the tubes from being
overheated.
Distributing
header
The circulating pump
delivers the feed water to the distributing header with orifices at a pressure
above the drum pressure.
Evaporator
The header
distributes water through orifices into the evaporator tubes acting in
parallel. Orifice in the header controls the flow of water to the evaporator
tubes. Here part of the water is evaporated and a mixture of steam and water
from these tubes enters the drum.
Convection superheater
The steam produced
in the boiler is nearly saturated. This steam as such should not be used in the
steam turbine. The presence of moisture in it will cause corrosion of turbine
blades, etc. to raise the temperature of steam and thereby to increase the
turbine efficiency, superheater is used.
The principle of
convection superheater is similar to steam
generating tubes of the boiler. The hot flue gases at high temperature sweep
over convection superheated tubes and raise the temperature of steam.
Convection superheater thus receives heat
from the flue gases flowing from the combustion chamber, entirely by convective
heat transfer. Such a superheater may be
more conveniently located since it is not necessary for it to “see” the furnace.
Saturated steam from
the top of the drum enters the convection superheater placed
in the path of the flue gases and is superheated.
Steam outlet
Superheated steam
from the superheater passes out to the
steam turbine through the steam outlet.
Economizer
The quantity of
superheated steam thus delivered to turbine is continuously made up in the form
of feed water. Feed water supplied by the feed pump is heated in the economizer
on its way to the steam separator drum.
The economizer is a
device used to preheat the feed water using the hot gases leaving the boiler.
Before the gases are let off to the atmosphere, they are made to flow in a
definite passage in the economizer so that some of the heat in the hot gases,
which otherwise gets wasted, can be used to preheat the feed water. The
preheated water requires only a small amount of heat to be supplied in the
boiler, resulting in some saving of the fuel burnt. This results in an increase
in the boiler efficiency.
Air preheater
Since the heat of
the exit gases cannot be fully extracted through the economizer, the air
preheater is employed to recover some of the heat escaping in these gases.
These exit gases preheat the air from the blower in the air preheater. The
preheated air is supplied to the furnace for combustion.
Capacity
The capacity of la-mont boiler is about 50 Tonnes/hr of superheated steam
at a pressure of 170 kgf/sq.cm. and at a temperature of 500’C.