Benson Boiler
The presence of
steam bubbles in contact with the surface of tubes seriously impairs heat
transmission from the flue gases to water. By rising the boiler pressure to the
critical pressure of steam (225 kgf/sq.cm.),
this difficulty is overcome, as suggested by Mark Benson in 1922. At the
critical pressure water and steam have the same density and no bubbles are
formed.
The first modern
high pressure drumless boiler developed
by benson was put into operation in 1927 in
west Germany power station.
Working principle
of Benson Boiler:
This boiler has a
unique characteristic of absence of steam separating drum. The entire process
of heating, steam generation and superheating is done in a single continuous
tube.
Economiser
The feed water by
means of the feed pump is circulated through the economiser tubes. Hot flue
gases pass over the economiser tubes and the feed water is preheated.
Radiant evaporator
The feed water from the economiser flows into the radiant
evaporator with radiant parallel tube sections. The radiant evaporator receives
heat from the burning fuel through radiation process and majority of water is
converted into steam in it.
Convection
Evaporator
The remaining water
is evaporated in the convection evaporator, absorbing the heat from the hot
gases by convection. Thus the saturated high pressure steam at a pressure of
210 kg/sq.cm is produced.
Convection superheater
The saturated steam
is now passed through the convection superheater where
the saturated steam os superheated to
650’C. The radiant evaporator, the convection evaporater and
the convection superheater are all arranged
in the path of the flue gases.
Steam outlet
The superheated
steam is supplied to the steam turbine through the steam outlet.
Capacity
Capacity of benson boiler is about 150 tonnes/hr
at a pressure of 210 kgf/sq.cm. and at a temperature of 650’C. (Efficiency may be
improved by running the boiler at a pressure slightly lower than the critical
pressure).
Salient features
of Benson Boiler
1. As there are no drums, the
total weight of benson bolier is
20% less than other boilers. This also reduces the cost of the boilers.
2. As no drums are required, the
transfer of the benson parts is easy.
Majority of the parts may be carried to the site without pre-assembly.
3. Since no drum is used, this
is an once-through boiler and the feed water
entering at one end is discharged as superheated steam at the other end.
4. Circulating pump and downcomers are dispensed with.