119657695 fuels and combustion
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1. FUELS AND COMBUSTION
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Introduction to Fuels liquid, solid and gaseous fuels Criteria for fuel selection
Availability
Storage
Handling
landed cost of fuel
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Properties of Liquid Fuels
Specific gravity
Viscosity
Flash Point
Pour Point
Specific Heat
Calorific Value
Carbon Residue Water Content
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Physical Properties Heating Value
Analysis of Coal
ultimate analysis
proximate analysis
Table 1.4 GCV for Various CoalsParameter Lignite
(Dry
Basis)
IndianCoal
IndonesianCoal
South AfricanCoal
GCV(kcal/kg)
4,500* 4,000 5,500 6,000
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Properties of Coal
Anthracite, bituminous, and lignite
Grade Calorific Value Range
( in kCal/kg)A
BC
DE
FG
Exceeding 6200
5600 62004940 5600
4200
49403360 4200
2400 33601300 2400
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Storage, Handling and Preparation of Coal carpet loss
spontaneous combustion
http://images.google.co.in/imgres?imgurl=www.dfd.dlr.de/projects/coalfire/Overview/images/coal_process.jpg&imgrefurl=http://www.dfd.dlr.de/projects/coalfire/Overview/html/spontaneous_combustion.html&h=368&w=640&prev=/images%3Fq%3Dspontaneous%2Bcombustion%2Bof%2Bcoal%26svnum%3D10%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26sa%3DN -
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Preparation of Coal
Sizing of CoalS. No. Types of Firing System Size (in mm)
1. Hand Firing
(a) Natural draft
(b) Forced draft
25-75
25-40
2. Stoker Firing(a) Chain grate
i) Natural draft
ii) Forced draft
(b) Spreader Stoker
25-40
15-25
15-25
3. Pulverized Fuel Fired 75% below 75
micron*
4 Fluidized bed boiler < 10 mm
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3 Ts of Combustion
TIME
All combustion requires sufficient Time which depends
upon type of Reaction
TEMPERATURE
Temperature must be more than ignition temperature
TURBULENCE
Proper turbulence helps in bringing the fuel and air in
intimate contact and gives them enough time to
complete reaction.
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Air for combustion
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Combustion of Coal Excess air required for coal combustion
depends on the type of coal firing equipment Hand fired boilers use large lumps of coal and hence need
very high excess air.
Stoker fired boilers use sized coal and hence require less
excess air. Also in these systems primary air is suppliedbelow the grate and secondary air is supplied over thegrate to ensure complete combustion.
Fluidised bed combustion in which turbulence is created
leads to intimate mixing of air and fuel resulting in furtherreduction of excess air.
The pulverized fuel firing in which powdered coal is firedhas the minimum excess air due to high surface area ofcoal ensuring complete combustion.
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Coal Combustion
Presence of silica,calcium oxide,magnesiumoxides etc. in ash
lead to a lowfusiontemperature andClinker formation.
Ash fusiontemperature aslow as 1100oC
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Draft Natural Draft
It is the draft produced by a chimney alone. It is caused by the
difference in weight between the column of hot gas inside thechimney and column of outside air of the same height and crosssection
Balanced Draft Forced-draft (F-D) fan (blower) pushes air into the furnace and
an induced-draft (I-D) fan draws gases into the chimneythereby providing draft to remove the gases from the boiler
Negative 0.05 to 0.10 in wg in boiler and slightly + ive inFurnace
Induced Draft
An induced-draft fan draws enough draft for flow into thefurnace, causing the products of combustion to discharge toatmosphere
Forced Draft The Forced draft system uses a fan to deliver the air to the
furnace, forcing combustion products to flow through the unitand up the stack
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THANKS
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