1. BOILERS FUNDAMENTALS/COMBUSTION
AJAY SHUKLA
DGM NTPC PMI
23rd March ,10
Boiler give importance and function of boiler , then history

2. In early 19th Century boiler were low pressure
Invention of water tube removed the pr barrier and boiler pr rise to super critical
Between utility operated conservatively and used low steam pr in boiler .
Now renewed interest in high efficiency supercritical boiler .The interest arose from the environmental need to attain higher efficiency and dividend of higher eff is reduce CO2
Give history of boiler

3. Five minute over view

4. 1 to 2: Isentropic expansion (Steam turbine)
Rankine Cycle
1 to 2: Isentropic expansion (Steam turbine)
2 to 3: Isobaric heat rejection (Condenser)
3 to 4: Isentropic compression (Pump)
4 to 1: Isobaric heat supply (Boiler)
Rankine cycle is a heat engine with vapor power cycle. The common working fluid is water. The cycle consists of four processes:
Explain cycle

5. Boiler/ steam generator
Steam generating device for a specific purpose.
Capable to meet variation in load demand
Capable of generating steam in a range of operating pressure and temperature
For utility purpose, it should generate steam uninterruptedly at operating pressure and temperature for running steam turbines.
Slide :5 Explain function how it maintains function then explain it , Most lethargic

7. 500 MW Boiler – Typical Arrangement Drum type
Slide 27 : Before going to general arrangement of once through , we will first see the arrangement of , explain location of each components
This is 500MW drum type boiler explain. More SH and SH is in radiant zone .

8. OUTLINE Boiler fundamentals Boiler components (water side)
Boiler combustion (air side)
Boiler classification

9. Basic Knowledge of Boiler

10. Basic boiler : Steam / water system Mixing of fuel and air Furnace
Heat transfer
Surface
Steam
Water
Blow down
Flue gas
Explain it : Water side then water cycle explained by other , air cycle , from where each comes explain it
AIR
Ash
FUEL

12. Phenomenological Model
Hot Flue
Gas
Thermal Structure SH
Steam
Convection &
Radiation HT
Convection HT
Drop in Enthalpy
of Flue Gas
Rise in Enthalpy of
Steam
Mechanism of Heat Transfer
Explain it : Combustion is happening , heat transfer is happening , how heat is exchanged ,how heat is being
Source/Supply
Thermal Structure
Sink /Demand

13. STEAM GENERATOR COMPONENTS
FURNACE
DRUM
BOILER CIRCULATING PUMPS
CONVECTION PASS
SUPERHEATER
REHEATER
ECONOMISER
AIR HEATER
STEAM COILED AIR PREHEATER
SOOT BLOWERS
COAL FEEDERS
PULVERIZERS
COAL PIPING
BURNERS
IGNITOR AND WARM UP BURNERS
DUCTWORK AND
INSULATION AND LAGGING
Explain function of each component , 10 min

14. BOILER LAYOUT AND PA FAN
Hoe each component is placed

15. DPNL Platen SHTR SHTR LTSH Reheater S Drum C R E n Gooseneck Chimney
Downcomer
waterwall
Fireball
Economiser
Expaion water and air circuit
ID fan
ESP
APH
Bottom Ash

16. Boiler fundamentals -BOILER=CONTROLLED COMB.+HEAT TRANSFER
-CHEMICAL =THERMAL
-COMBUSTION-FUEL,TEMP,O2
-FUEL - BITUMINOUS COAL

17. Boiler fundamentals Combustion in furnace :- Reactions:-
Pulverized fuel by coal burners
Ignition temp. By oil firing
O2 by means of fans.
Reactions:-
C+O2 = CO2,
2H2+O2 = 2H2O
S+O2 = SO2
Theoretical air = O2/.233

18. Boiler fundamentals FACTORS AFFECTING COMBUSTION-
TIME,TEMP., INTER MIXING OF AIR WITH FUEL(TTT), COAL FINENESS,
I. Excess Air:-
- (20%)-bituminous coal
-(15%)-lignite
A. Lower excess air:-
-High unburnt loss
B. Higher excess air:-
-Higher heat loss (ma*cpa*dt)

19. Water and Steam Circulation System
Economiser
Boiler drum
Down Comers
Water walls
Primary super heater
Platen super heater
Final super heater
Reheater

21. Drum
The boiler drum forms a part of the circulation system of the boiler. The drum serves two functions, the first and primary one being that of separating steam from the mixture of water and steam discharged into it. Secondly, the drum houses all equipments used for purification of steam after being separated from water. This purification equipment is commonly referred to as the Drum Internals.

23. Type of Circulation Density difference & height of water column
Assisted by external circulating pump (CC/ BCW pump)
Below bar
bar
Natural circulation (upto 165 ksc)
Forced/ assisted circulation ( ksc)
Once thru boiler
1. Sub critical
2. Supercritical

24. Circulation ratio
It may be defined as the ratio of feed water flow thru down comers to the steam generated in water wall.
CR = Industrial boilers
CR = 6-8 Natrual cir. Boilers
CR = 2-3 Forced cir. Boilers
CR = 1 Once thru boilers (Sub critical)
CR = 1 Supercritical boilers

28. Waterwall construction
Made of carbon steel (Grade-C) hollow circular tubes and DM water flows inside
Waterwalls are stiffened by the vertical stays and buck stays to safeguard from furnace pressure pulsation & explosion/ implosion
The boiler as a whole is hanging type, supported at the top in large structural columns.
Vertical expansion is allowed downwards and provision is made at bottom trough seal near ring header.

29. Superheater & Reheater
Heat associated with the flue gas is used in superheaters & Reheater, LTSH, economiser.
Maximum steam temperature is decided by the operating drum pressure and metallurgical constraints of the turbine blade material.
Reheating is recommened at pressure above 100 ksc operating pressure. Reheating is done at 20-25% of the operating pressure.
Carbon steel, alloy steel & SS used for tubing of SH & RH.

30. Superheaters
Convection Superheaters
Radiant Superheaters

31. Important Components of Boiler
Economizer
Boiler drum
Water wall
Superheater
Reheater
Boiler Pressure Part Design
Code – IBR/ASME.
Selection of Material based on:
Creep and Fatigue strength at design temperature.
Fire side oxidation resistance.
Design Temperature and thickness: as per IBR.
Allowable stress for chosen material – as per ASME.
TWO PASS BOILER ARRANGEMENT

32. More Details of Pulverized Fuel fired SG

33. Additional allowance on tube design thickness to take care of erosion.
Selection of Material
Upto 4000C: Carbon Steel for boiler tubes and plates.
Upto 5500C: Low Alloy Steels like T11/P11, T22/P22, T23 etc.
Upto 5900C: Medium Alloy Steel like T91/P91.
Above 5900C: Austenitic Stainless Steel like TP347H, Super 304H.
Drum internals designed for removal of maximum moisture and provide required purity.
TDS in Feed Water restricted to 15 to 20 ppm
Dissolved solids carryover not to exceed
Silica carry over <10 ppb
Sodium carry over - <3 ppb
Chloride carry over - <2 ppb
Copper carry over - <1 ppb
Iron carry over not detectable
Erosion shield/Cassette baffles on erosion prone areas.

34. Boiler Auxiliaries

35. Steam Theory
Within the boiler, fuel and air are forced into the furnace by the burner.
There, it burns to produce heat.
From there, the heat (flue gases) travel throughout the boiler.
The water absorbs the heat, and eventually absorb enough to change into a gaseous state - steam.
To the left is the basic theoretical design of a modern boiler.
Boiler makers have developed various designs to squeeze the most energy out of fuel and to maximized its transfer to the water.

36. Why Steam is so popular as heat conveying media in industry?
Highest specific heat and latent heat
Highest heat transfer coefficient
Easy to control and distribute
Cheap and inert

37. Properties of Steam Enthalpy of Evaporation Liquid Enthalpy
Liquid enthalpy is the "Enthalpy" (heat energy) in the water when it has been raised to its boiling point is measured in kcal/kg, its symbol is hf
Also known as "Sensible Heat”
Enthalpy of Evaporation
It is the heat energy to be added to the water in order to change it into steam.
There is no change in temperature, the steam produced is at the same temperature as the water from which it is produced.
Also known as latent heat and its symbol is hfg

38. The temperature at which water boils, also called as boiling point or saturation temperature (It increases as the pressure increases. )
As the steam pressure increases, the usable heat energy in the steam (enthalpy of evaporation), which is given up when the steam condenses, actually decreases.
The total heat of dry saturated steam or enthalpy of saturated steam is given by sum of the two enthalpies
hf +hfg
When the steam contains moisture the total heat of steam will be hg = hf +q hfg where q is the dryness fraction.

39. Superheated Steam Degree of Superheat
Superheat is the addition of heat to dry saturated steam without increase in pressure.
Degree of Superheat
The temperature of superheated steam, expressed as degrees above saturation corresponding to that pressure.

42. Steam Properties : a re-look

43. Steam generation principle
Steam power plants operate on Rankine Cycle, DM water as working fluid.
Sensible heat is added in economiser +furnace
Steam generation takes place in waterwall.
Heat transfer in furnace and enclosed superheater takes place thru radiation. SH RH
w/w
HPT
HPH+Eco
IPT
BFP
LPT
LPH
CEP
condenser

44. Basic Knowledge of Boiler
Purpose
To produce steam (Main Steam and Reheat Steam) at rated pressure and temperature
To Convert the heat of combustion of coal/oil/gas to thermal energy of steam
Steam Parameters are decided by Turbine Cycle Requirements
Steam Parameters adopted by NTPC
200 MW: 157 bar MS Pressure, 5400C/5400C
500 MW: 179 bar MS Pressure, 5400C/5400C
660 MW: 246 bar MS Pressure, 5450C/5630C
Advanced Supercritical Parameter
310 bar MS Pressure, 6100C/6100C

45. Engineering Function Selection of Unit Size
Based on load demand, coal and water availability.
Input from Feasibility Report
Selection of Steam Parameters
Choice of steam parameters is governed by overall cost of the plant.
Sub-critical boilers are more suited in places where fuel cost is low.
Both drum type and once through boilers are acceptable based on manufacturer’s experience.
Super-critical boilers are costly because of greater use of high temperature material in boiler pressure parts.
Selection of Firing System
Firing systems are generally left to manufacturer’s discretion as each manufacturer prefers his standard design.

49. OT Boiler Tower type Typical Layout
Slide 29 : Now coming to OT boiler , it can have many arrangement , one arrangement I have shown you that is tower type which is our talcher thermal plant is operating. Other can be two pass arragement which our Sipat is having and mostly manufacturere are going for 2 pass design

52. Boiler Classification (contd…)
Once Through Boiler
Continuous Path of water through economizer to water walls and to superheaters.
These are necessarily forced circulation boilers.
They are suited for fast start-up and load cycling, as the thick drum is eliminated.
Once Through Boiler

53. Boiler Classification (contd…)
Drum Type Boiler (Natural Circulation)
Drum Type Boiler (Assisted Circulation)

54. Boiler Classification (contd…)
Supercritical Boiler (Universal Pressure)
Supercritical Boiler (Sliding Pressure)

55. Boiler
Combustion

56. Combustion Burning of fuel (chemical reaction)
Rapid combination of o2 with fuel, resulting in the release of heat
For fuel to burn ,the following conditions must be present
The fuel must be gasified
The oxygen and fuel mixture should be proper.
Temp should be above ignition

57. FUELS
Combustible substances which, when combined with oxygen in air & ignited, burn giving heat.

58. CLASSIFICATION OF FUELS
Solids Liquids Gaseous
Coal Kerosene Natural gas
Lignite Petrol Methane
Peat HSD LPG
Bagasse LDO Producer Gas
Husk FO
LSHS

59. MAIN CONSTITUENTS OF FUEL
Carbon
Hydrogen
Sulphur
Nitrogen
Oxygen
Water Vapour
Ash

61. PROPERTIES OF FUEL (Typical Analysis of F.O.)
Carbon %
Hydrogen %
Sulphur %
Calorific value 10,000 Kcal/kg
Sp. Gravity at 30oC 0.95
Flash point 65oC
Viscosity at 40oC RW Sec No 1
Water Percentage 0.15
Sediment Percentage 0.3 (Variable)

62. COMBUSTION
Combustion is rapid oxidation of fuel resulting in constituents getting converted into respective oxides, liberating heat.
Fuel +Air Oxides + Heat (Prs of combustion)
C +O2 : CO Heat 43,968 Kcal
2H2 +O2 : 2H2O + Heat 61,979 Kcal
S +O2 : SO Heat Kcal
Incomplete Combustion
2C + O2 : 2CO Heat 26,429 Kcal
1 Kg of liquid fuel + 15 Kg of Air Oxides + Heat
(5.26M3)

63. COMBUSTION PROCESS PRESSURISED + PREHEATED HEATED BY FURNACE HEAT
LIQUID FUEL
PRESSURISED + PREHEATED
ATOMISED
HEATED BY FURNACE HEAT
VAPORISED
IGNITED BY FLAME
COMBUSTION

64. COMBUSTION REACTIONS COMBUSTION INCOMPLETE C O C O C O
2C + O2 2CO + LESS HEAT O C
COMBUSTION INCOMPLETE

65. COMBUSTION REACTIONS O C C O O O CO2 + HEAT C + O2 H O H O H H H H O
2H2 + O2 2H20 + HEAT O H H
COMBUSTION COMPLETE

66. COMBUSTION FLAME & FLAME FRONT
IT IS AN ENVELOPE OR ZONE WITHIN WHICH COMBUSTION REACTION IS OCCURRING AT SUCH A RATE AS TO PRODUCE VISIBLE RADIATION.
FLAME FRONT :
IT IS THE 3 D CONTOUR ALONG WHICH COMBUSTION STARTS
IT IS THE DIVIDING LINE BETWEEN FUEL-AIR MIXTURE AND COMBUSTION PRODUCTS.
REF. : NORTH AMERICAN COMBUSTION HANDBOOK

67. EXCESS AIR FOR COMPLETE COMBUSTION... Fuel has to be atomised.
Fuel + Theoretical air required + 15% to 40% T.A.
Combustion
FOR COMPLETE COMBUSTION...
Fuel has to be atomised.
Raise the temperature to ignition temperature.
Electrical spark of ignition.
Proper mixing of fuel and air.
Distribution of Primary and Secondary air.

68. GOOD COMBUSTION REQUIRES .......
3 T’s - TIME, TEMPERATURE & TURBULENCE
PROPER PROPORTIONING OF FUEL & AIR
CORRECT CONTROL OF FUEL & AIR
THOROUGH MIXING OF FUEL & AIR
INITIAL & SUSTAINED IGNITION

69. MEASUREMENT OF COMBUSTION
SMOKE INDEX : 2 - 3
STACK TEMPERATURE : As per design.
O2 : 3%

70. Arrangement of fuel input in furnace
Coal is pulverized in mills at a fineness of 70% thru 200 mesh. Dried powdered coal is conveyed to furnace (at a temperature < oC)
Total coal flow is distributed among running mills and fed thru coal burners at m/sec.
Coal flow is arranged in tiers. Maximum heat release rate must not exceed plain area heat loading. It generates excessive NOx and making ash fused.

71. Combustion air arrangement in furnace
Fuel air is supplied around coal nozzles (at velocity of m/sec).
Secondary air is supplied in adjacent tiers of sec. air dampers from wind box (Hot air from Secondary APH)
Overfire/ Tempering air is supplied at the top of the burnaer zone for NOx control.
Gas recirculation is adopted for steam temperature control in oil/ gas fired units.
Furnace draft is maintained at -5 mmwcl with Forced and Induced draft fans (balanced draft)

74. Pulverized Fuel Boiler (Contd..)
Advantages
Its ability to burn all ranks of coal from anthracitic to lignitic, and it permits combination firing (i.e., can use coal, oil and gas in same burner). Because of these advantages, there is widespread use of pulverized coal furnaces.
Disadvantages
High power demand for pulverizing
Requires more maintenance, flyash erosion and pollution complicate unit operation

75. SAFETIES
Unauthorised flame presence during pre-purge and after controlled shut down.
Pilot flame safety
Main flame safety
High gas pressure safety
Low gas pressure safety (optional)
Double Block & Bleed valves in main gas line
Combustion air failure safety
Interlock with boiler safeties

76. Any question please ?

77. THANK YOU