Presentation on BHEL Steam Generators
BHEL Steam Generators
Material Selection Overview
by
Veerendar Aluvala
DM/BHEL/Trichy
Bharat Heavy Electricals Limited - Trichy
Presentation on BHEL Steam Generators
Presentation Summary
Pulverised Coal Combustion (PCC)
Design Aspects
Boiler Parameters
Drum Type Boilers
OTSC Boilers
Fuel Analysis
Site Conditions
Material Selection
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Technology Developments
Pulverised Coal Combustion (PCC)
Fluidised Bed Combustion (FBC)
Circulating Fluidised Bed Combustion (CFBC)
Combined Cycle Gas Turbine/Co-generation Plants
Integrated Gasification Combined Cycle (IGCC)
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Pulverised Coal ?
Fineness of pulverised coal not being less than
70% thru 200 mesh (75 microns) and 98% thru 50
mesh (300 microns).
Pulveriser is required
Gas velocities 10-12 m/s
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Tower Type
Basic Boiler Configurations
Conventional Two Pass
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Boiler Parameters
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Heat Balance Diagram (Typ.)
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Boiler Parameters define
heat duty of the boiler
Heat fired
= (SH + RH) heat duty
÷ Boiler Efficiency
Coal fired
= Heat fired / HHV of coal
Air quantity = kg. of air/kg. of fuel x Qty. of
coal fired
Gas quantity = Coal + Air – Ash in coal
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Increase of Plant Cycle Efficiency due to
Steam Parameters
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Implications of Steam Parameters on
Boiler Design
Boiler type
Materials
Reliability and Availability
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Types of boilers
Drum type
Once-through type
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Drum type boiler
Steam generation takes place in furnace
water walls
Fixed evaporation end point - the drum
Steam -water separation takes place in
the drum
Separated water mixed with incoming
feed water
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Drum Type Boiler
Natural Circulation Boiler
Circulation thru water walls by
thermo-siphon effect
Controlled Circulation Boiler
Thermo-siphon effect supplemented
by pumps
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Types of Circulation
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Types of Circulation
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Supercritical:
Pressure > Supercritical
(221 bar)
Ultra Supercritical:
Supercritical with SHO
temperature > 593 deg.C
Adavnced
Supercritical:
Ultra
Supercritical with SHO
temperature > 700 deg.C
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Once Through Boiler
• Once -through flow through all sections of
boiler (economiser, water walls &
superheater)
• Feed pump provides the driving head
• Suitable for sub critical & super critical
pressures
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Operating Pressure Range
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Once-thru Boiler
Major differences
type boiler :
from
Drum
• Evaporator system
• Low load circulation system
• Separator
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Once -thru Boiler-Furnace Wall
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Spiral Tube Arrangement
Features
 Reduced number of
tubes with pitch.
 Increased mass flow.
 Mass flow rate can
be selected by
number of tubes.
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Evaporator – heat absorption
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SPIRAL TO VERTICAL TRANSITION
Presentation on Supercritical Boilers
21th Nov. 2014
Presentation on BHEL Steam Generators
Transition Area Vertical Wall Tubes
Vertical Tube
Forgings
Spiral Wall Tubes
Spiral Tube Forgings
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Spiral Furnace
Windbox Panel
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Supercritical boiler Spiral Furnace Wall Assembly
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Spiral Wall Burner panel (SlidingPressureSupercriticalDesign)
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Sliding Pressure Supercritical Design
Spiral to Vertical Transition Area - Load Transfer
Support
Fingers
SPIRAL WALL SUPPORT
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Vertical Wall
Windbox
Only a Few
Bends at the
Top and Bottom
Straight
Tubes
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FRONT WALL
RIFLED TUBING
VerticalWallSlidingPressure
SupercriticalDesign
SIDE WALL
RIFLED TUBING
SCREEN TUBES
SMOOTH TUBING
HANGER TUBES
SMOOTH TUBING
ARCH
RIFLED TUBING
SIDE WALL
RIFLED TUBING
REAR WALL
RIFLED TUBING
FRONT WALL
RIFLED TUBING
SMOOTH TUBING
FROM THIS ELEVATION
ALL WALLS
Presentation on Supercritical Boilers
21th Nov. 2014
Presentation on BHEL Steam Generators
Spiral vs. Vertical Wall Comparison
•
Spiral Furnace System Applicable for
all size units
•
Benefits from averaging of lateral heat
absorption variation (each tube forms a
part of each furnace wall)
Simplified inlet header arrangement
Large number of operating units
•
•
•
•
•
Use of smooth bore tubing
throughout entire furnace wall
system
One material utilized throughout entire
waterwall system
No individual tube orifices – Less
maintenance & pluggage potential
•
Vertical Furnace Wall System
Limited to larger capacity units (>600
MW depending on fuel)
•
Less complicated windbox openings
•
Traditional furnace water wall support
system
•
Elimination of intermediate furnace
wall transition header
•
Less welding in the lower furnace wall
system
Easier to identify and repair tubes leaks
•
•
Lower water wall system pressure
drop thereby reducing required feed
pump power
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Once -thru Boiler
 Low load circulation system :
 At part loads once -thru flow not adequate to cool the tubes
 To maintain required mass velocities boiler operates on circulating
mode at low loads
 Excess flow supplied by feed pump or a dedicated circulating pump
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ONCE - THROUGH OPERATING RANGE
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Once - thru’ Boiler
Low load circulation system :
 The excess flow over the once-thru flow
separated in separator and
– Returned to the condenser thru’ a heat
exchanger
or
– Recirculated back to the boiler directly by
the dedicated circulating pump
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Once -thru Boiler
Separator :

Separates steam and water during the
circulating mode operation


Runs dry during once-thru flow mode
Smaller in size compared to drum in a
drum type boiler
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Separator
Separatorvessel
forsupercritical
steamgenerator
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Start-up System with Circulating pump
WW
C
ECO
Flash
Tank
Separator
SH
HWL
C
MEFCV
To Condenser
BRP
Deaerator
Mixing Sphere
HPH
BFP
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SUB CRITICAL Vs SUPER CRTICAL
Particulars
Sub critical
Super critical
Type
Drum type
Once through
Once through
Operating pressure
Below 221.1 bar
Below 221.1 bar
Above 221.1 bar
Steam generation
process
Boiling (Two phase
heat transfer)
Boiling (Two
phase heat
transfer)
No boiling process.
Phase change is
gradual.
Thick walled
component
Thick walled drum is
provided
Smaller vertical separators provided
Start up and load
change rates
Base
Better start up and load change rates
Water wall
construction
Vertical
Circulation
Circulation at all loads
Higher loads: Once through
Lower loads : Circulation
Water quality
Base
More stringent requirements
Generally spiral wall.
Vertical wall for higher capacity
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Materials used in various Pressure Parts
of Subcritical Boilers
Area of
application
Material
Drum
Water walls,
Economizer
SH and RH
ASME specification
Tubes
Pipes
Carbon steel /
Low Alloy steel
-
SA 299
Carbon Steel
SA192
SA210 Gr.A1
SA210 Gr.C
SA106 Gr.B
SA106 Gr.C
1 ¼ Cr ½ Mo
SA213 T11
SA335 P11
2¼ Cr 1 Mo
SA213 T22
SA335 P22
9 Cr 1 Mo ¼V
SA213 T91
SA335 P91
18 Cr 8 Ni
SA213 TP304 H
-
18 Cr 10 Ni Cb
SA213 TP347 H
-
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Materials
Section
Supercritical
Boilers
Economiser
SA 210 Gr C
Water wall
SA 213 T11 / T22 / T23
Superheater & Reheater Tubing
SA 213 T11 / T22 / T23 / T91 / T92 /
S304H / TP347H
Superheater & Reheater Headers & Piping
SA 106 Gr B / Gr C,
SA 335 P11 / P22 / P91 / P92
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Materials in typical OTSC Boiler
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Furnace design
Furnace for Burning Pulverised Coal are Designed
To prevent formation of slag deposits
To allow complete combustion by providing adequate
retention time.
Temperature at entry to closely spaced SH/ RH sections is
brought down well below the lowest of the ash softening
temperatures.
Adequate mass flow through water wall tubes so that tube
metal temperatures are well within allowable limits.
Ensuring the above in design stage will lead to high boiler
availability
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Furnace Design ( contd…..)
The furnaces of BHEL boilers are conservatively sized with low
heat release rates to ensure maximum output all the times.

The possibility of slagging and fouling of heat transfer
surfaces is minimised even while firing

worst
type of fuels.
Furnace design accommodates wider range of coals
normally experienced by Indian utilities.
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Furnace Selection Criteria
Cross Sectional Area Heat Release Rate - NHI / PA
Effective Projected Radiating Surface Loading - NHI/ EPRS
Volumetric Heat Release Rate - Q Fired / Volume
Burner Zone Heat Release Rate – Q Fired / FZS
Furnace Residence Time
Distance Between Furnace Bottom-hopper & Lower Most Fuel Nozzle
Distance Between Upper Most Fuel - Nozzle & Bottom of SH
Furnace Exit Gas Temperature (FEGT)
Furnace Bottom Opening
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SH / RH / ECONOMISER
Design criteria
Adequate heating surface to get rated SHO / RHO
temperature over control load for the range of
coals.
Low
gas velocity to minimise pressure part
erosion
Proper tube spacing to prevent plugging and
fouling of heat transfer surfaces
Proper pressure part support and alignments
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APPLICABILITY OF CODE REGULATIONS
IBR:
“Boiler” means any closed vessel exceeding 22.75 litres (five
gallons) in capacity which is used expressly for generating steam
under pressure and includes any mounting or other fitting attached
to such vessel, which is wholly or partly under pressure when steam
is shut off
ASME Sec. I:
Applicable to boilers in which the steam or any other vapour is
generated at a pressure more than 15 PSI (g).
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MAXIMUM ALLOWABLE WORKING PRESSURE
IBR: (Reg. 2)
It is the working pressure of any component of the boiler.
“Calculation Pressure”, in relation to a boiler, means the design pressure of any part
adjusted to take into account the pressure drops corresponding to the most severe
conditions of pressure drop and hydraulic head;
IBR: (Reg. 2)
"Design Pressure" means:(i) in relation to a natural or assisted circulation boiler, the maximum allowable
working pressure in the steam drum of the boiler;
(ii) in relation to a once through forced-circulation boiler, the maximum
allowable working pressure at the final superheater steam outlet;
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DESIGN PRESSURE
Operating Pressure
Design Pressure
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SAFETY VALVE – IBR Reg. 621
Each boiler shall be equipped with two safety valves for relieving the
steam pressure. The diameter of the valve shall not be less than 19
mm.
The minimum relieving capacity of the safety valve shall be sufficient
to discharge all the steam that can be generated by the boiler without
allowing the pressure to rise more than 10% above maximum
allowable working pressure.
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DESIGN PRESSURE
ASME Sec. I:
(PG 21.1)
No boiler, except a forced-flow steam generator with no fixed steam
and water line that meets the special provisions of PG-67, shall be
operated at a pressure higher than the maximum allowable working
pressure except when the pressure relief valve or valves are
discharging, at which time the maximum allowable working pressure
shall not be exceeded by more than 6%.
(PG 21.2)
In a forced-flow steam generator with no fixed steam and waterline it is
permissible to design the pressure parts for different pressure levels
along the path of water-steam flow. The maximum allowable working
pressure of any part shall be not less than that required by the rules of
Part PG for the expected maximum sustained conditions of pressure
and temperature to which that part is subjected except when one or
more of the overpressure protection devices covered by PG-67.4 is in
operation.
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Requirement of Overpressure Protection
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DESIGN TEMPERATURES - ALLOWANCES
Area
IBR
ASME
Radiant SH/RH
50oC
Convective SH/RH
39oC
Economiser
11oC
Furnace & Boiler
Tubes
28oC
Gas touched Headers
28oC
Actual Metal
Temperature
for Gas
Touched Portion
or 371C (Min)
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DESIGN - CALCULATION OF THICKNESS REQUIRED
Description
IBR (Reg. 338, 350, 270)
ASME (PG 27)
Minimum Tube
thickness
PD
------------2S + P
PD
--------- + 0.005D + f
2S + P
Minimum
Pipe/Shell
thickness
PD
----------- + 0.75
2SE  P
+ C
PD
---------- + C
2SE+2yP
(or)
PR
------------------ + C
SE  (1 y) P
A-317 Formula:
D ( 1- e^(-P/SE))/2 + C + f
Where,
C = 0.75 for P  70 kg/cm²
C = 0 for P > 70 kg/cm²
P = Design Pressure
D = OD for Tubes, ID for Pipes/Shell
S = Allowable Stress
E = Ligament Efficiency
C = Threading and Structural stability allowance
P = Design Pressure
D = Outside diameter
S = Allowable Stress
E = Ligament Efficiency
f = factor for expanded tube ends
y = Temperature coefficient (0.4 to 0.7)
R = Inside Radius of cylinder
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ALLOWABLE MAXIMUM FLUID TEMPERATURES AND METAL TEMPERATURES FOR DIFFERENT MATERIALS (Reg. 47)
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THE PRESSURE AND TEMPERATURE LIMITS WITHIN WHICH
PIPES, TEES, BRANCHES, ETC., (REG. 349 )
Method of manufacture
Maximum
permissible
working
pressure
Maximum
Form
permissible
temp, °C
Cold drawn seamless
No restriction
454
Hot finished seamless
Do
454
Straights, bends
or fittings.
Do
Butt welded [Max. nominal
21 kg/cm²
bore allowable 102 mm. (4 in)]
260
Do
Electric resistance welded
No restriction
454
Cast steel
Castings
No restriction
454
Straights
Straights, bends
or fittings
Molybdenu
m steel
Chromium
molybdenu
m Steel
Cold drawn seamless and
castings.
No restriction
524
Do
Cold drawn seamless and hot
No restriction
finished seamless
621
Do
Solid drawn up to and including
12.6 kg/cm²
127 mm.(5 in.) dia.
Not allowed Straights and
for SH steam bends.
Material
Carbon
steel
Copper
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ALLOWABLE MAXIMUM FLUID TEMPERATURES AND METAL TEMPERATURES FOR DIFFERENT MATERIALS
Material
ASME Alloy
Oxidation Limit, Deg. C IBR Allowable,
Deg. C
Carbon steel
454
427
454
552
649
18 Cr-10 Ni Cb
SA -210 Gr A1
SA-106-C/B
SA -299 (drums)
SA-515, 70
SA-213, T12
SA-335, P12
SA-213, T11
SA-335, P11
SA-213, T22
SA-335, P22
SA-213, T23
SA-335, P23
SA-213, T91
SA-335, P91
SA-213, T92
SA-335, P92
SA-213, TP347H
18 Cr-9 Ni -3Cu-Cb-N
SA-213, Super 304H
1 Cr-1/2 Mo
1-1/4 Cr-1/2 Mo
2-1/4 Cr-1Mo
2-1/4 Cr-1.6W-V-Cb
9 Cr-1 Mo. V
9 Cr-2W
593
649
740
816
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