Loeffler Boiler
This is also a
modern high pressure water tube boiler using the forced circulation principle
and named after Prof.Loeffler.
Salient features
of Loeffler Boiler
The novel feature of
the Loeffler Boiler is to evaporate water
solely by means of superheated steam. The furnace heat is supplied only to
economiser and superheater. In other words,
steam is used as a heat absorbing medium.
The major difficulty
experienced in La-Mont boiler is deposition of salt and sediment on the inner
surfaces of water tubes. The deposition reduces the heat transfer, ultimately,
the generating capacity. This difficulty was solved in Loeffler boiler
by preventing the flow of water into the boiler tubes. Feed water is evaporated
in the drum using part of the superheated steam coming out from the
water-heater. Thus only the dry saturated steam passes through the tubes. Poor
feed water can, therefore, be used without any difficulty in the boiler, which
is great advantage of this boiler.
Working principle
of Loeffler Boiler
The image shows the
outline diagram of Loeffler Boiler.
Economiser
The feed water from
the feed tank is supplied to the economiser by feed pump. In the economiser the
feed water is made to flow through a number of tubes surrounding which the hot
gases leaving the furnace pass over. There is a heat exchange from the hot
gases to the feed water, which is preheated in the economiser.
Evaporated Drum
It is housed away
from the furnace. It contains a mixture of steam and water. The feed water from
the economiser tubes enters the evaporator drum into which is also passed
two-thirds of the superheated steam generated by the boiler. The superheated
steam gives its superheat to the water in the drum and evaporates it to saturated
steam.
Mixing Nozzles
The nozzles
distribute and mix the superheated steam throughout the water in the evaporator
drum.
Steam circulating
pump
A steam circulating
pump forces this saturated steam from the evaporator drum to the radiant superheater through the tube of the furnace wall.
Radiant superheater
The radiant superheater is placed in the furnace. The hot gases in
the furnace are used for superheating the saturated steam from the drum. The
radiant superheater receives heat from the
burning fuel through radiation process.
Convection superheater
Steam from the
radiant superheater enters the
convection superheater where it is finally
heated to the desired temperature of 500’C. The convection superheater receives heat from the flue gases entirely
by convective heat transfer. Both radiant and convection superheater are arranged in series in the path of the
flue gases.
Steam outlet
About one-third of
the superheated steam from the convection superheater passes
to the steam turbine while the remaining two-thirds is passed on to evaporator
drum to evaporated the feed water to saturated
steam.
Capacity
Capacity of
the Loeffler boiler is about 100 Tonnes/Hr
of superheated steam generated at a pressure of 140 kgf/sq.cm and at a
temperature of 500’C.