Coal Combustion Theory _ Electrical4u

8/17/2019 Coal Combustion Theory _ Electrical4u

1/11

5/9/2016 Coal Combustion Theory | Electrical4u

http://www.electrical4u.com/coal-combustion-theory/

« Previous Next »

Coal Combustion Theory

Combustion is a rapid chemical reaction

between fuel and oxygen. When combustible

elements of f uel combine with O2, heat energy

comes out. During combustion combustible

elements like Carbon, Sulfur, Hydrogen etc

combine with oxygen and produce respective

oxides. The source of oxygen in fuelcombustion is air. By volume there is 21 % of

Oxygen presents in air and by weight it is

23.2 %. Although there is 79 % (by volume)

nitrogen in air but it plays no role in

combustion.

Actually Nitrogen carries heat produced during combustion to steam boiler stack. As per

combustion theory the quantity of air required for combustion is that which provides

sufficient O2 to completely oxidize combustible elements of fuel. This quantity of air is

normally known as STOICHIOMETRIC AIR requirement. This amount of air depends upon

the nature of fuel. STOICHIOMETRIC AIR requirements for different fuels are obtained by

analysis of fuel and they are given in tabular form below,

MENU

http://www.electrical4u.com/steam-boiler-working-principle-and-types-of-boiler/http://electrical4u.com/fluidized-bed-combustion-types-and-advantages-of-fluidized-bed-combustion/http://electrical4u.com/boiler-feed-water-treatment-process-demineralization-plant/http://www.electrical4u.com/


2/11


http://www.electrical4u.com/coal-combustion-theory/ 2

Fuel STOICHIOMETRIC AIR mass / unit mass of fuel

Bituminous Coal 11.18

Anttiasite Coal 10.7

Coke 9.8

Liquite 7.5

Peat 5.7

Residual Fuel Oil 13.85

Distillate Fuel Oil(Gas Oil) 14.48

Natural Gas(Methane Base) 17.3

Combustion of Coal

For sufficient air,


3/11



We have already said that mass wise there is 23.2 % O2 presents in air. Hence the

amount of air required to provide 2.67 gm of O 2 is

As per ideal combustion theory, after combustion of one gm carbon(C), product ofcombustion contains only 3.67 gm of CO2 and (11.5 - 2.67 =) 8.83 gm of N2

Coal Combustion for Insufficient Air


4/11



By weight, the requirement of air for providing this much O2 is

After combustion of one gm carbon(C), product of combustion contains only 2.33 gm of

CO and (5.75 - 1.33 =) 4.42 gm of N2.

From equation (1) and (2) it is clear that due to insufficient air combustion, the heat

lose during 1 gm of coal combustion is (33.94 - 10.12) = 23.82 kj

Combustion of Sulfur

So, air required for 1 gm sulfur combustion, is

So, combustion product, after completing 1 gm of sulfur combustion, contains 2 gm of

SO2 and (4.31 - 1 = ) 3.31 gm of N2

Combustion of Hydrogen

From combustion theory of C, S and H2 it is found that 2.67 gm oxygen is required for 1


5/11



gm carbon combustion, which implies 2.67C gm oxygen is required for C gm carbon, 1

gm oxygen is required for 1 gm sulfur combustion, which implies S gm oxygen is

required for S gm sulfur and 8 gm oxygen is required for 1 gm hydrogen combustion,

which implies 8H gm oxygen is required for H gm hydrogen.

Hence 1 gm of coal (fuel) which contains C gm carbon, S gm sulfur and H gm hydrogen,

requires (2.67C + S + 8H) gm of oxygen for efficient combustion.

Some amount of oxygen may be contained in the fuel itself in form of differentcompounds and it takes part in combustion also. If O is the original weight of the oxygen

presents in 1 gm of fuel, net requirement of oxygen for sufficient coal combustion is

(2.67C + S + 8H - O) gm.For that the amount of air required is

This above mentioned analysis is called coal analysis for combustion.Before efficient combustion can take place, several basic requirements must be fulfilled,

most important of them are,

a) The combustion must be done with sufficient oxygen

b) There must be sufficient turbulence to promote throughout mixing of combustible and

oxygen.

Coal Content in Proximate Analysis

Moisture = 8 %, volatile material = 20 to 25 %, fixed carbon = 40%, ash = 30%. Fixed

carbon's combustion temperature = 900°C. Basic component of ash is Si, Al and others.

Now fusion temperature of Si is 1200°C.

If the furnace temperature raises above 1100°C then Si will be fused and deposited on

the tubes, as slag, causing improper heat transfer.

Now to dilute the temperature excess air and complete combustion are required.

Now, the volatile material plays important role in combustion. Less the volatile material

flame will be high which may be chance for flame impingement of S/H coil.

For fulfilling the point some practical steps to taken. In practice it is always necessary to

supply more air to the combustion system than it is theoretically required. Reason for

that air and fuel mixing process in any combustion system, as it is not possible to

ensure complete and intimate mixing of the fuel with the necessary oxygen at the point

of injection. So some excess air is required for proper combustion to a reasonable

minimum power, stack loss and unburnt carbon in ash.


6/11



Generally 20% excess air is allowed.

% of Excess

Air

Unburnt Carbon in

Ash

C.V. Liberated in

FurnaceUnburnt Gas Loss

0 % 10 % 75 %CO2, O2, N2, H2O, CO,

CH4(15 %)

15 % 2 % 97 % CO2, O2, N2, H2, CO(1 %)

100 % 0.5 % 99.5 % CO2, O2, N2

Third process is unsatisfactory for extra fan power and convey huge amount of heat.

The coal particles should be at least 74 microns in 200 mesh. So pulveriser is required

for

i) better utility of coal

ii) saving of time.

There are mainly three losses occurred during coal combustion,

1) Unburnt gas loss

2) Dry flue gas loss

3) Combustible in ash loss.

Unburnt Gas Loss

Remember the unburnt gas loss is mainly the result of burning carbon to carbon

monoxide instead of carbon dioxide. It is seen that heat release in CO reaction is onethird of that in CO2 reaction. So adequate supply of oxygen or excess air will quickly

reduce this loss to zero.

Dry Flue Gas Loss

A further loss of heat is that due to dry flue gas. It is often referred to as the stack loss.

If more excess air is admitted, this loss increases.

Combustible in Ash Loss

This loss is very high when there is little or no excess air because mixing of combustible

material and oxygen is so poor. As the air quantity is increased, the loss falls rapidly.

However it does not reach to "zero" because the loss depends upon two factors firstly on

air - coal mixture and secondly on fineness of pulverized coal grain. More fine grain of

pulverized coal helps to complete combustion more perfectly and resulting less

combustible in ash loss. In practice, though, a stage is reached where it is not worth

grinding the coal any finer because it will cost more to grind than the extra heat release.

Practically the loss does not reach to zero. generally a high volatile coal is crushed until


7/11



Objective Questions on Electrical Power Generation (MCQs)

« Previous Next »

75% of its bulk passes through a 200 mesh whereas a low volatile coal is crushed until

80% passes through similar mesh.

The loss gets less as excess air is added, reaches a minimum and then increases as still

more excess air is added. Thus there is only one quantity of excess air which will give

lower loss for the combustion of a particular fuel. For bituminous coal 15.5% excess air

is optimum requirement for Coal Combustion.

Closely Related Articles

Steam Boiler | Working principle and Types of Boiler

Methods of Firing Steam Boiler

Fire Tube Boiler | Operation and Types of Fire Tube Boiler

Water Tube Boiler | Operation and Types of Water Tube Boiler

Steam Boiler Furnace Grate Firebox Combustion Chamber of Furnace

Feed Water and Steam Circuit of Boiler

Boiler Feed Water Treatment Demineralization Reverse Osmosis Plant Deaerator

Fluidized Bed Combustion | Types and Advantages of Fluidized Bed Combustion

More Related Articles

Steam Condenser of Turbine

Jet Condenser | Low Level High Level Ejector Jet Condenser

Surface Steam Condenser

Economics of Power Generation

Cooling Tower Useful Terms and Cooling Tower Performance

Cooling Tower Material and Main Components

Power Plant Fire Protection System

Hydrant System for Power Plant Fire Protection

Medium Velocity Water Spray or MVWS System for Fire Protection

http://electrical4u.com/medium-velocity-water-spray-(mvws)-system-for-fire-protection/http://electrical4u.com/hydrant-system-for-power-plant-fire-protection/http://electrical4u.com/power-plant-fire-protection-system/http://electrical4u.com/cooling-tower-material-and-main-components/http://electrical4u.com/cooling-tower-useful-terms-and-cooling-tower-performance/http://electrical4u.com/economics-of-power-generation/http://electrical4u.com/surface-steam-condenser/http://electrical4u.com/jet-condenser-low-level-high-level-ejector-jet-condenser/http://electrical4u.com/steam-condenser-of-turbine/http://electrical4u.com/fluidized-bed-combustion-types-and-advantages-of-fluidized-bed-combustion/http://electrical4u.com/boiler-feed-water-treatment-process-demineralization-plant/http://electrical4u.com/feed-water-and-steam-circuit-of-boiler/http://electrical4u.com/steam-boiler-furnace-grate-firebox-combustion-chamber-of-furnace/http://electrical4u.com/water-tube-boiler-operation-and-types-of-water-tube-boiler/http://electrical4u.com/fire-tube-boiler-operation-and-types-of-fire-tube-boiler/http://electrical4u.com/methods-of-firing-steam-boiler/http://electrical4u.com/steam-boiler-working-principle-and-types-of-boiler/http://electrical4u.com/fluidized-bed-combustion-types-and-advantages-of-fluidized-bed-combustion/http://electrical4u.com/boiler-feed-water-treatment-process-demineralization-plant/http://www.electrical4u.com/electrical-engineering-objective-questions-mcq/#Objective-Questions-on-Electrical-Power-Generation


8/11



Foam Fire Protection System

Fire Detection and Alarm System

Gas Extinguishing System

Electric Power Generation

Power Plants and Types of Power Plant

Thermal Power Generation Plant or Thermal Power Station

Why Supply Frequency is 50 Hz or 60 Hz?

Hydro Power Plant | Construction Working and History of Hydro power plant

Nuclear Power Station or Nuclear Power Plant

Diesel Power Station

Cogeneration | Combined Heat and Power

Economiser in Thermal Power Plant | Economiser

MHD Generation or Magneto Hydro Dynamic Power Generation

Thermoelectric Power Generators or Seebeck Power Generation

Solar Energy Solar Electricity

Solar Energy System | History of Solar Energy

Types of Solar Power Station

Components of a Solar Electric Generating System

What is photovoltaic effect?

Staebler Wronski Effect

Working Principle of Photovoltaic Cell or Solar Cell

Solar Cell

Characteristics and Parameters of a Solar Cell

Solar Cell Manufacturing Technology

What is a Solar PV Module?

What is Standalone Solar Electric System?

http://electrical4u.com/what-is-standalone-solar-system/http://electrical4u.com/what-is-a-solar-pv-module/http://electrical4u.com/solar-cell-manufacturing-technology/http://electrical4u.com/characteristics-and-parameters-of-a-solar-cell/http://electrical4u.com/solar-cell/http://electrical4u.com/working-principle-of-photovoltaic-cell-or-solar-cell/http://electrical4u.com/staebler-wronski-effect/http://electrical4u.com/what-is-photovoltaic-effect/http://electrical4u.com/components-of-a-solar-electric-generation-system/http://electrical4u.com/types-of-solar-power-station/http://electrical4u.com/solar-energy-system-history-of-solar-energy/http://electrical4u.com/solar-energy-solar-electricity/http://electrical4u.com/thermoelectric-power-generators-or-seebeck-power-generation/http://electrical4u.com/mhd-generation-or-magneto-hydro-dynamic-power-generation/http://electrical4u.com/economiser-in-thermal-power-plant-economiser/http://electrical4u.com/cogeneration-combine-heat-and-power/http://electrical4u.com/diesel-power-station/http://electrical4u.com/nuclear-power-station-or-nuclear-power-plant/http://electrical4u.com/hydro-power-plant-construction-working-and-history-of-hydro-power-plant/http://electrical4u.com/why-supply-frequency-is-50-hz-or-60-hz/http://electrical4u.com/thermal-power-generation-plant-or-thermal-power-station/http://electrical4u.com/power-plants-types-of-power-plant/http://electrical4u.com/electric-power-generation/http://electrical4u.com/gas-extingiushing-system/http://electrical4u.com/fire-detection-and-alarm-system/http://electrical4u.com/foam-protection-system/


9/11



Solar Lantern

Steam

Steam Dryness Fraction

Superheated Steam and Steam Phase Diagram

Vapour Properties Mollier Chart Heat Capacities

What is Steam Flashing?

How to Calculate Steam Consumption During Plant Start Up

Effective Steam Distribution System

What is Water Hammer?

Engineering Thermodynamics Part 1

Science of Engineering Thermodynamics Part 2

Basic Law of Conservation and First Law of Thermodynamics

Carnot Cycle and Reversed Carnot Cycle

Enthalpy Entropy and Second Law of Thermodynamics

Rankine Cycle

Rankine Cycle and Regenerative Feed Heating

Rankine Cycle for Closed Feed Water Heaters and Rankine Cycle Cogeneration

Ideal Verses Actual Rankine Cycle

Rankine Cycle Efficiency Improvement Techniques

Basic Wind Energy

Wind Turbine | Working Types and History of Wind Turbine

Theory of Wind Turbine

New Articles

What is Zener Diode?

Applications of Shift Registers

Dynamic Shift Register

http://electrical4u.com/dynamic-shift-register/http://electrical4u.com/applications-of-shift-registers/http://electrical4u.com/what-is-zener-diode/http://electrical4u.com/theory-of-wind-turbine/http://electrical4u.com/wind-turbine-working-types-and-history-of-wind-turbine/http://electrical4u.com/basic-wind-energy/http://electrical4u.com/rankine-cycle-efficiency-improvement-techniques/http://electrical4u.com/ideal-verses-actual-in-rankine-cycle/http://electrical4u.com/rankine-cycle-for-closed-feed-water-heaters-and-cogeneration/http://electrical4u.com/rankine-cycle-and-re-generative-feed-heating/http://electrical4u.com/rankine-cycle/http://electrical4u.com/enthalpy-entropy-and-second-law-of-thermodynamics/http://electrical4u.com/carnot-cycle-and-reversed-carnot-cycle/http://electrical4u.com/basic-law-of-conservation-and-first-law-of-thermodynamics/http://electrical4u.com/science-of-engineering-thermodynamics-part-2/http://electrical4u.com/engineering-thermodynamics/http://electrical4u.com/all-about-water-hammer/http://electrical4u.com/effective-steam-distribution-system/http://electrical4u.com/how-to-calculate-steam-consumption-during-plant-start-up-/http://electrical4u.com/what-is-steam-flashing/http://electrical4u.com/vapour-properties-mollier-chart-heat-capacities/http://electrical4u.com/superheated-steam-and-steam-phase-diagram/http://electrical4u.com/steam-dryness-fraction/http://electrical4u.com/steam/http://electrical4u.com/solar-lantern/


10/11



Universal Shift Registers

Transistor as Switch

Bidirectional Shift Register

Please provide your valuable comments

Name : -

Enter your name here

Email : -

Enter your email here

Location : -

Enter your location here

Your content : -

Enter your content here

Enter the above code here

Regenerate Code

Submit

Reset

http://electrical4u.com/bidirectional-shift-register/http://electrical4u.com/transistor-as-switch/http://electrical4u.com/universal-shift-registers/


11/11


© 2011-2016 electrical4u.The content is copyrighted to electrical4u and may not

be reproduced on other websites.
http://www.electrical4u.com/http://www.electrical4u.com/https://play.google.com/store/apps/details?id=com.welectrical4ucomhttps://www.facebook.com/electrical4u/

Coal Combustion Theory _ Electrical4u

Documents

Transcript of Coal Combustion Theory _ Electrical4u