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SUPER HEATING• HEATING STEAM
ABOVE SATURATION TEMPERATURE
– IMPROVES THERMAL CYCLE EFFICIENCY
– STEAM CAN BE RETAINED IN VAPOUR FORM TILL THE LAST STAGE OF TURBINE
– NO CONDENSATION OF STEAM BETWEEN BOILER AND TURBINE
SUPER HEATERS
CLASSIFICATION
RADIANT CONVECTIVE
SUPER HEATERS
SUPER HEATERS CLASSIFICATION
H O R IZO N T AL L SH APED
DRAINABLE
VER T C AL
NON DRAINABLE
SUPER HEATERS
SUPER HEATERS CLASSIFICATION
PARALLEL FLOW COUNTER FLOW
SUPER HEATERS
SUPER HEATERS DESIGN CONSIDERATIONS
• STEAM TEMPERATURE REQUIRED• SUPER HEATER SURFACE AREA
REQUIRED• RATE OF STEAM FLOW THROUGH
TUBES (MASS FLOW)• MATERIAL BEST SUITED• GAS TEMPERATURE ZONES WHERE THE
SURFACES ARE TO BE LOCATED• ARRANGEMENT OF SURFACES
– SPACING OF TUBES
SUPER HEATERS DESIGN CONSIDERATIONS
• STEAM TEMPERATURE– MINIMUM
• BASED ON APPLICATION AND ECONOMICS
– MAXIMUM• BASED ON METALLURGICAL
LIMITATIONS
SUPER HEATERS DESIGN CONSIDERATIONS
• SURFACE AREA– GIVE MINIMUM PRESSURE DROP WITHOUT
INCREASING METAL TEMPERATURE
– GIVE HIGH MASS FLOW TO KEEP METAL TEMPERATURE LOW
– REQUIRE ALLOY OF LESSER COST
– PROPER SPACING WITH REFERENCE TO FUEL CHARACTERISTICS
– LOW DRAUGHT LOSS
SUPER HEATERS DESIGN CONSIDERATIONS
• MASS FLOW– HIGHER THAN NECESSARY
• PRESSURE LOSS WILL BE MORE
• LESS EFFICIENCY
– LESSER• HIGH TUBE METAL TEMPERATURE
– PRESSURE DROP NOT MORE THAN 10%
– STEAM FILM TEMPERATURE NOT MORE THAN 380C
MATERIALS USED FOR S.H.
ASME CODE NOMINAL
COMPOSITION
TEMP.LIMIT 0C
SA 213 CARBON STEEL 450
SA 213 T1 C-1/2 Mo. 470
SA 213 T11 11/4 Cr. –1/2 Mo. 550
SA 213 T22 21/4 Cr.-1 Mo. 580
SA 213 T9 9 Cr.-1 Mo. 635
SA 213 TP 304 H 18 Cr.-8 Ni. 705
SA 213 TP 347 H 18 Cr.-10 Ni. 705
SA 213 TP 316 H 16 Cr.-12 Ni.-2
Mo.
705
S.H.SECTIONS IN C.E BOILERS
• STEAM COOLED WALL AND ROOF SECTION
• LOW TEMPERATURE SUPER HEATER
• PLATEN SUPER HEATER
• FINAL SUPER HEATER
500 MW BOILER
C.E.DESIGN
TOWER TYPE BOILER
STEIN DESIGN
OPERATING FACTORS AFFECTING STEAM TEMPERATURE
• BOILER LOAD
• EXCESS AIR
• FEED WATER TEMPERATURE
• USE OF SATURATED STEAM
• BLOW DOWN
• BURNER OPERATION
• HEATING SURFACE CLEANLINESS
• FUEL
MEANS FOR CONTROLLING STEAM TEMPERATURE
• SEPARATELY FIRED SUPER HEATER
• EXCESS AIR
• GAS RECIRCULATION
• BURNER SELECTION
• TILTING BURNERS
• ATTEMPERATION
300 UPWARDS HORIZONTAL 300 DOWNWARDS
DESUPERHEATING
• CONTROL OF STEAM TEMPERATURE BY INJECTING WATER– SURFACE TYPE– DIRECT MIXING
• ATTEMPERATION
SUPER HEATER LENGTH
TE
MP
ER
AT
UR
E
3400C
4100C
3600C
5400C
6000C
CONCEPT OF ATTEMPERATION
ATTEMPERATION WATER STANDARDS
• PURITY– AS PURE AS THAT OF STEAM
• PRESSURE– HIGHER THAN STEAM PRESSURE
• TEMPERATURE– SATURATION TEMPERATURE
CORRESPONDING TO STEAM PRESSURE
ATTEMPERATION WATER SOURCES
• BOILER CONDENSER
• FEED WATER TAPPED BEFORE FEED CONTROL STATION