Super Heater
SUPER
HEATER
Super heater is a device used to convert
saturated steam or dry steam in to super heated steam with out raising its
pressure .
Super heater are used to super heat the wet
steam or dry steam generated by boiler . Its function is to removed the last
traces of moisture [1% to 2%] from the saturated steam coming out of boiler.
RSH inlet flue gas temperature 700 0C to 750 0C
RSH outlet flue gas temperature 500 0C to 600 0C
Super heater is important boiler
accessory which is placed in the path of flue gases to recovery some amount of
their heat & through which steam passed . Chromium nickel or Chrome
molybdenum alloys to with stand temperature as high as 650 0C to prevent metal
crack .
Super heater – Low carbon steel is used
when the temperature of superheater is below 427 0C .
Superheated steam gives saving in water
consumption from 10% to 12% over that with saturated steam . By superheating
process nearly fuel consumption is reduced up to 10% to 15% . Every 5% C raise of temperature of steam will reduce
steam cost as 1% is boiler .
Classification of Superheater
In non-drainable SH : - condensate can’t be
drain out completely from vertical SH when boiler is in shut down condition .
Non drainable SH required more careful
handling in start up to remove condensate by evaporation at temperature below
5500C to avoid overheating the tube metal .
In drainable SH : - Sufficient slope is made
so that condensate from SH tube is
completely drained out .
Act to movement of flue gas & steam
A. Counter flow super heater
B. Parallel flow super heater
C. Mixed flow super heater
1) Counter flow SH:- Steam flow and flue gas flow
in the opposite direction to each other .
2) In parallel flow SH :- Steam flow and flue
gas flow in same direction .
3) Mixed flow SH : - In this type of super health
combination of counter flow SH & parallel flow SH found .
Classification of super heater according to mode of heat transformer : -
Classification of SH Act to design
of tube
1. Pendent tube SH
2. Platen tube SH
In
platen type super heater :-
Platen is vertical single loop has set of closely packed tubes appearing like
plate . they are placed in upper part of furnace so entire heat is pick up by
radiation .
Platen coils are place 600mm to 1000mm apart
to avoid the formation of ash build up . the temperature of steam from radiant
super heater drops downward with increase in boiler output .
In
pendent type super heater :-
This is vertical or horizontal multi loop SH placed in convection section of
boiler . the heat transformer is by a combination of radiation & convection .
With increase in steam load the
temperature of steam increases .
According to position of SH unit
i.
Internal
Super heater
ii.
External
/ separate super heater
Draft :
- The pressure difference between furnace combustion products and outside cold
air is called draft .
Start up vent
Uses
During
starting of boiler
1) To increase main steam temperature .
2) To prevent over heating of super heater tubes .
3) To escape condensate .
4) Release excess pressure during sudden load cut off .
5) Running minimum load during no load on
turbine .
Steam vent Silencer
i.
Boiler
drum safety valve .
ii.
Super
heater safety valve .
iii.
Start
up vent
iv.
Deaerator
safety valve
v.
It made
out of concentric annular acoustic
cylinder enclosed with robust steel casing .
vi.
A
weather down is provided for protection from rain .
Purpose
:- Main function is to release large quantity steam from high pressure to
atmosphere and reduce high level of noise .
Air
vent close to reclosed air & dissolved gases .
Air
vent open to prevent vacuum formation in boiler .
Types
of Economizer (1) Plain tube type (2)
Finned tube type
Thank
you
Suvendu Singha . (Asia , India , Odisha , Balasore)
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