Jiang Wu，

Professor, Ph.D.

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 Jiang Wu，
Professor, Ph.D.

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1 Boiler and its classification

2 Fuel and its characteristics

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PART
Boiler and its classification
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1.1 Working Process
1.2 Boiler System
1.3 Boiler Classification

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Power Plant System Diagram
Power Plant System Diagram
 What is a boiler?

boiler pot stove

A container with heating surfaces, The equipment with enough

which can hold water, withstand pressure space for fuel to combust and
and absorb enough heat energy to make get its heat energy to heat the
water become vapor at high pressure. working substance.
1.1 Working process of boiler

Heating, evaporation
Combustion Heat transfer and superheating
process of working
process of fuel process substance

Chemical energy Flue gas heat

Thermodynamic change
of working substance
thermal energy working substance heat
 Energy Transformation

Boiler Steam turbine

Fuel chemical energy heat energy
equipment equipment

Electricity
electric energy Generator mechanical energy
 Process and Transformation of media

evaporation
water steam
condensation

coal coal grinding pulverized burning ash

coal
cold hot flue
heating burning
air air gas
 flue
slag gas
and emission
ash removal
Pulverizing
boiler
combustion system
circuit system
system

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 Pulverizing
System

Raw Coal Bunker → Feeder → Mill → Pulverized Coal Separation

→ Qualified Pulverized Coal → Air into Furnace for Combustion

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 Combustion System oxygen supply system

burner secondary air nozzle

Air needed for Combustion
Furnace
F.D. Fan
Pulverized Coal Conveying system
Air Preheater
Primary Air Nozzle of Burner

Two Hot Air Channels Furnace 17

Working Substance Boiler Circuit
Water Supply Economizer Sub-cooled Water Wall Superheater

High Pressure
Cylinder Exhaust

Boiler Reheater

Steam Turbine Low

Pressure Cylinder
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Combustion System

cold air

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Slag cleaning system

Large slag water wall cooling slag crusher

Ash particles in flue gas dust collector ash field

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Flue gas Pollutant Emission Control system

Flue gas in the Boiler Superhearter Reheater Economizer

Stack WFGD ESP air preheater SCR

1.3 Boiler Classification Classified by cycle mode

Classified by application Natural Circulation Boiler

Once-through Boiler
Industrial Boiler Forced Circulation Boiler
Marine Boiler
Central power station
Classified by structure

Fire Tube Boiler

Water Tube Boiler
 1.3 Boiler Classification outlet steam pressure
Low Pressure Boiler ≤2.5MPa
Medium Pressure Boiler 3.8-5.4MPa

High Pressure Boiler 9.8-13.7MPa

Classified by
working substance’s Ultra High Pressure Boiler 13.7-16.7MPa
pressure Subcritical Pressure boiler 16.7-22.1MPa
Supercritical Pressure boiler 22.1-25.0MPa
Ultra supercritical ≥25MP
 Flow pattern of working substnce in boiler evaporating heating surface

Natural Circulation Boiler Forced Circulation Boiler Once-through Boiler

Carnot Cycle
Rankine Cycle
The Rankine cycle is a simplifiedideal steam power
cycle, which consists of four idealized

reversible processes :
3-4: reversible adiabatic compressionof water in
the feed pump;

4-5-6-1: reversible constant pressure heating

process of water and steam in boiler;

1-2: Reversible adiabatic expansion

process of water vapor in steam turbine;

2-3: constant pressure exothermic process in

condenser.
1.4 The classification and model of boiler
model：

△△–×××/×××–△
Serial number of product design

Capacity and steam pressure of boiler

The abbreviations of boiler

manufacturer
HG－231/9.81－L.HM

It refers to the coal fired boiler manufactured by Harbin Boiler Co., Ltd., with
capacity of 231 t/h and superheated steam pressure 9.81Mpa.
 Summary of this chapter
1. Power produced by thermal power
plants needs to undergo multiple energy
conversions.
2. There are lots of sub-systems in boiler
system.
3. According to the working pressure,
the boiler can be divided into various
forms of boilers.
 Thinking Questions

1. Heating Surface and Function of Boiler

2. Main sub-systems of boilers

3. Classification of boiler by flow patterns

 Fuel and its characteristics
PART
2.1 Proximate analysis and ultimate analysis of coal

2 2.2
2.3
Calculation benchmark of coal composition
Calorific value of coal
2.4 Coal ash fusibility
2.5 Classification of coal

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2.1.1 Proximate analysis of coal

Moisture Volatile Fixed carbon Ash content

Water volatilization Fixed carbon combustion

Coal Coke Ash content
Dry Heating Ignite

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2.1.1 Ultimate analysis of coal
C Main combustible components

H Combustible component, low content

O Combustion-supporting, low content

N NOX will be generated, harmful
S Burnable, SOx will be generated, harmful
M External moisture, Internal moisture
A Harmful to the environment, abrasion heating surface
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2.2 Calculation benchmark

As received basis

Air-dried basis

Dry basis

Dry ash-free basis

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2.2.1 Calculation benchmark of coal composition
As received basis

Air-dried basis

Dry basis

Dry ash-free basis

A C H O N S Mad M

Ash content Fixed carbon Volatilization Moisture

Coke Volatile matter

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2.2.2 Conversion of benchmark
dry ash-free
as received basis air-dried basis dry basis
basis

as received basis 1

air-dried basis 1

dry basis 1

dry ash-free
1
basis

Conversion coefficients of different benchmarks.→k 35

2.3 Calorific value of coal
The total amount of heat released when 1kg fuel is completely burned.
Gross calorific value
It includes the latent heat of vaporization released when water vapor in
Qgr
flue gas condenses into water.

Net calorific value The latent heat of vaporization released by water vapor condensation is
Qnet subtracted from the Gross calorific value.
> >

At the boiler exhaust gas temperature (110 ~ 160 ℃), the water vapor in the flue gas will not condense and
can only obtain net calorific value.
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Conversion between gross and net calorific value:
As received basis
9
, = , − + = , − 226 − 25.1
100 100

Dry basis
9
, = , − = , − 226
100

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2.4 Coal ash fusibility
Method of determination : Pyramid method

DT(Deforming ST(Softening
FT (Fusion Temperature)
Temperature) Temperature)

The top of the ash cone B e n d i n g c o n e t o p t o The cone can flow along
begins to turn round or contact bottom plate. The the plane in a fluid state.
bend. cone becomes spherical.

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2.5 Classification of coal

Classification of coal based on Vdaf

Anthracite Lean coal Bituminous coal Lignite

≤ 10% 10% < ≤ 20% 20% < ≤ 37% 37% <

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 Anthracite Lignite

Bituminous Coal Lean Coal 40

 Anthracite Lignite

• The carbon content is very high, up to 95%. • The carbon content is low, 40 ~ 50%.
• Impurities are few. • High moisture and ash content.
• The calorific value is very high, about 25000～ • The calorific value is low, about 10000~21000
32500kJ/kg; kJ/kg;
• It is difficult to ignite and burn out. • Both ignition and combustion are easier.
Bituminous Coal Lean Coal

• The carbon content is high, 40 ~ 60%. • Its properties are between anthracite and
• Less impurities. bituminous coal, and its combustion performance
• The calorific value is high, about 20000 ~ 30000 is close to anthracite.
kJ/kg. • It is not easy to ignite and coke.
• Both ignition and combustion are easier.
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 Summary of this chapter
1. Ultimate analysis of coal
2. Four bases for ultimate analysis of coal.
3.Coal’s gross/net calorific value.
4.The fusibility of coal ash.
5. Proximate analysis: Coal is divided into
4 categories based on Vdaf.
1. What is the difference between gross
and net calorific value?

2.What do DT, ST and FT represent

respectively in the fusibility of coal ash?
What is the significance to boiler design?
Thank you

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