fuel technology solid fuels
DESCRIPTION
UNIT IIITRANSCRIPT
-
FUEL TECHNOLOGY-SOLID FUELS
1
UNIT III
-
FUEL
COMBUSTION OF FUEL
CLASSIFICATION OF FUEL
2
CLASSIFICATION OF FUEL
CALORIFIC VALUE
CHARACTERISTICS OF GOOD FUEL
-
FUEL
The combustible substances which
on burning in air produces large
amount of heat that can be used
3
amount of heat that can be used
economically for domestic and
industrial purposes are called fuels.
Eg. Wood , Coal etc
-
COMBUSTION OF FUEL
The term combustion refers to the
exothermal oxidation of a fuel, by air or
oxygen occurring at a sufficiently rapid
rate to produce a high temperature,
4
rate to produce a high temperature,
usually with the appearance of a flame.
-
As most of the fuels contain carbon or
carbon and hydrogen, the combustion
involves the oxidation of carbon to carbon
dioxide and hydrogen to water. Sulphur, if
present, is oxidised to sulphur dioxide while
the mineral matter forms the ash.
5
the mineral matter forms the ash.
Complex fuels like coal undergo thermal
decomposition during combustion to give
simpler products which are then oxidised to
carbon dioxide, water etc.
-
e.g.: Coke on combustion gives carbon
dioxide
Coal Coke + Coal gas
6
C (coke) + O2 CO2
-
CLASSIFICATION OF FUEL
FUEL
7
OCCURENCE PHYSICAL STATE
-
On the basis of occurrence
FUEL
8
PRIMARY OR
NATURAL FUELSECONDARY OR
ARTIFICIAL FUEL
-
CLASSIFICATION OF FUEL
Fuels are classified as
Primary fuels Fuels which occur naturally such as coal, crude petroleumand natural gas. Coal and crude petroleum, formed from organic matter many millions of years ago, are referred
9
many millions of years ago, are referred to as fossil fuels.
Secondary fuels Fuels which are derived from naturally occurring ones by a treatment process such as coke, gasoline, coal gas etc.
-
On basis of physical state
FUEL
10
SOLID LIQUID GAS
-
FUEL
Primary Fuels Secondary fuels
11
Solid
Eg. Wood,peat Liquid
Eg.crude oil
Gas
Eg.Natural gas
Solid
EgCoke,charcoal
Liquid
Eg. Petrol ,LPG
Gas
Eg.coal gas ,water gas
-
CHARACTERISTICS OF
GOOD FUEL
1.HIGH CALORIFIC VALUE:
A good fuel should have high
12
A good fuel should have high
calorific value i.e. it should
produce large amount of heat on
burning.
-
CALORIFIC VALUE
The calorific value of a fuel is defined as
the quantity of heat (expressed in
calories or kilo calories) liberated by the
complete combustion of unit weight
13
complete combustion of unit weight
(1gm or 1kg) of the fuel in air or oxygen,
with subsequent cooling of the
products of combustion to the initial
temperature of the fuel.
-
contd
The calorific value of a fuel depends
upon the nature of the fuel and the
relative proportions of the elements
present, increasing with increasing
amounts of hydrogen. Moisture if
14
amounts of hydrogen. Moisture if
present, considerably reduces the
calorific value of a fuel. The calorific
value may be theoretically
calculated from the chemical
composition of the fuel.
-
contd
If both hydrogen and oxygen are
present, it may be assumed that all the
oxygen are already combined with 1/8
of its weight of hydrogen to form water.
This fraction is then deducted from the
hydrogen content of the fuel in the
15
hydrogen content of the fuel in the
calculation. Thus for a fuel containing
carbon, hydrogen, oxygen and sulphur,
the calorific value of the fuel is given
by DULONG FORMULA
-
Determination of calorific value
from Dulong formula
Calorific value =
1/100[8080 C + 34500 {H O/8 } +2240 S] kcal/kg
16
where C, H, O, S refer to % of carbon, hydrogen, oxygen and sulphur respectively.
-
GROSS AND NET CALORIFIC VALUE
With fuels containing hydrogen, two calorific values are distinguished, the gross and the net calorific value.
GROSS CALORIFIC VALUE
17
The gross calorific value refers to the heat evolved when the water produced by combustion is condensed as a liquid. The net value gives the heat liberated when water is in the form of steam or water vapour.
-
contd
Thus the gross calorific value (or the
higher heating value) is the quantity of
heat liberated by the complete
combustion of unit weight of the fuel with
18
combustion of unit weight of the fuel with
subsequent cooling of the products of
combustion to the initial temperature of
the fuel.
-
NET CALORIFIC VALUE
Under normal working conditions,
water vapours produced during
combustion are not condensed
and escape as such along with the
19
and escape as such along with the
hot gases.Hence lesser amount of
heat is available, which is called
Lower or net calorific value.
-
Contd.
Net calorific value is the heat
produced when unit mass of fuel
is burnt completely and products
of combustion are allowed to
20
of combustion are allowed to
escape.
-
contd
The net calorific value (or the
lower heating value) is defined as
the gross calorific value minus
the latent heat of condensation of
water (at the initial temperature of
21
water (at the initial temperature of
the fuel), formed by the
combustion of hydrogen in the
fuel.The latent heat of steam at
ordinary temperature may be
taken as 587cal/g
-
contd
Net calorific value=Gross calorific
value-Latent heat of water vapours
NCV=GCV-weight of hydrogen x 9 x
Latent heat of water vapours
22
Latent heat of water vapours
Latent heat of water vapours is 587
kcal/kg
-
Calculation of Net calorific valueHydrogen in the fuel reacts with oxygen to
give water
H2 + 1/2 O2 H2O
2H = 1/2O = H O
23
2H = 1/2O2 = H2O
2parts = 16parts = 18parts
1parts = 8parts = 9parts
-
Contd
Let H is the percentage of hydrogen in
the fuel
Amount of water produced by burning
unit mass of fuel=9H/100 g
Latent heat of steam=587cal/g
24
Latent heat of steam=587cal/g
Amount of heat produced by
condensation of steam=9H/100 x587 cal
NCV=[GCV-9H/100 x 587]
=[GCV-0.09 x 587] cal/g
-
25
-
Energy Units
Need to distinguish between energy and
power
Common energy units:
Btu (British Thermal Unit)- energy required to Btu (British Thermal Unit)- energy required to
heat one lbm of water one degree Fahrenheit
1 Btu = 778.16 ft-lbf = 1.055 kJ = 0.252 Cal
Commonly used measure of fuel energy, heating and
cooling quantities
1 MBtu = 1000 BTU; 1 MMBtu = 106 Btu
1 Quad = 1015 Btu (billion 109, trillion 1012, quadrillion)
1 Q = 1018 Btu
-
Energy Units
kJ- standard SI-mks energy unit
1 kJ = 1000 J = 1000 N-m
kJ used to measure fuel energy and heating and
cooling quantities
kWh- used to measure electrical energy kWh- used to measure electrical energy
1 kWh = 3412 Btu = 3600 kJ = 860 Cal
Calorie- used to measure food energy,
technically should be called a kilocalorie.
Chemists calorie (lower case c) is the energy
needed to raise 1 g of water 1 degree C.
1 Cal = 1000 cal = 4.186 kJ = 3.968 Btu
-
Power Units
Horsepower- used to measure rate of
mechanical work
1 hp = 2545 Btu/hr = 0.746 kW
kW- SI power unit used for both work and kW- SI power unit used for both work and
heat transfer. Sometimes see kWth for
thermal kW.
1 kW = 3412 Btu/hr = 1.34 hp = 0.2843 Tons
Ton- American unit of cooling rate commonly
employed to measure air conditioning
capacity
1 Ton = 12,000 Btu/hr = 3.517 kWth
-
2. MODERATE IGNITION
TEMPERATURE:
Ignition temperature: the lowest
temperature to which fuel must be
preheated so that it starts burning
smoothly. If ignition temp. is low, the
fuel catches fire easily. Low ignition
29
fuel catches fire easily. Low ignition
temperature is dangerous for storage
and transportation of fuel. High
temperature causes difficulty in
kindling. So ,a good fuel should have
moderate ignition temperature.
-
3.LOW MOISTURE CONTENT:Agood fuel should have low moisture
content as moisture content reduces
30
content as moisture content reduces
the calorific value.
-
4.LOW NON-COMBUSTIBLE
MATTER CONTENT
A good fuel should have low
contents of non-combustible
31
contents of non-combustible
material as non-combustible matter
is left in form of ash which
decreases the calorific value of fuel
-
5.MODERATE RATE OF
COMBUSTION:
The temperature of combustion of
fuel depends upon the rate of
combustion . If the rate of
combustion is low ,then required
32
combustion is low ,then required
high temperature may not be
reached soon. On the other hand
,too high combustion rate causes
high temperature very quickly.
-
6.MINIMUM SMOKE AND NON-
POISONOUS GASES
On burning, Fuel should not give
out objectionable and poisonous
gases. In other words, gaseous
products should not pollute the
33
products should not pollute the
atmosphere. Gases like
CO,SO2,H2S etc. are some of
harmful gases.
-
7.CHEAP: A good fuel should be cheap and readily available.
8.EASY TRANSPORTATION :
34
8.EASY TRANSPORTATION : A good fuel should be easy to
handle and transport at low cost
-
9.CONTROLLABLE
COMBUSTION:
Combustion of fuel should be easy
to start or stop when required.
35
10.NON SPONTANEOUS
COMBUSTION: Combustion of fuel
should be non-spontaneous
otherwise it can cause fire hazards.
-
Contd.
11.LOW STORAGE COST:A good fuel should be easily stored at
low cost.
36
-
The substance to be burned is massed into the
bomb, which is fitted with a device that can
deliver a spark and with a tube that can deliver
oxygen under pressure.
The bomb is then sealed and immersed in a
well-insulated vat of water.
Oxygen is let into the bomb, the sparkOxygen is let into the bomb, the spark
generated, the reaction occurs, and no products
escape as the heat is generated.
-
The heat warms the bomb and thus
the water surrounding it.
The stuff absorbing the heat is not
only the water, but also anything
immersed in it.
It includes the thermometer and the It includes the thermometer and the
stirrer which ensures that any heat is
uniformly distributed before the final
temperature is read.
-
Bomb Calorimetry
To obtain precise heat measurements, you
must know or find out the heat capacity of
the bomb calorimeter
Heat capacity takes into account all the Heat capacity takes into account all the
parts of the calorimeter that can lose or
gain.
ctotal= cwater + cthermometer + cstirrer + ccontainer
-
Bomb Calorimetry
Since mass of the other parts are
constant, there is no need for the mass
units in the heat capacity value.
Manufacturers include the heat capacity Manufacturers include the heat capacity
(C) of a calorimeter when it is purchased.
Therefore, qcal= CT
C= heat capacity of the calorimeter
-
Coal in truth stands not beside but
entirely above all other commodities. It is
the material energy of the country- the
universal aid, the factor in everything weuniversal aid, the factor in everything we
do with coal, almost any feat is possible;
without it we are thrown back into the
laborious poverty of early times
(DiCiccio, 1996).
-
What is Coal?
Coal:
A sedimentary rock that burns
Mineralized vegetative material deposited over a
long period of time (although miniscule long period of time (although miniscule
geologically)
altered chemical composition
Formed by increased T and P
Partial decay resulting from restricted access to
oxygen
-
Coal Composition
Carbon > 50%
Impurities Volatile Matter
Sulphur
Chlorine Chlorine
Phosphorus
Nitrogen
Trace amounts Dirt
Other elements
-
Classification of coal
Classification means classifying or categorizing
objects as per their characteristics or property.
Objective is to place like things together and
separate things that differs.
Coal is a naturally available heterogeneous organic
mass. So very difficult to classify.
Hence for last 150 years many attempts have been
made according to different classification basis.
-
Classification by visual characters
Category Attributes Flame
Brown coal/lignite Brown colour, woody
structure
----------------
Bituminous coal Black and banded Smoky yellow flame
Anthracite Black and lustrous Burns without flame
-
Changes in the average composition from wood to anthracite
47
-
Where Does The Carbon
Come From? Coke: pure carbon obtained from heating wood at high temperatures. This heating evaporates volatile organic compounds and leaves essentially pure carbon.
Coke was the originally used source of carbon in Coke was the originally used source of carbon in iron smelting. However, population growth and rapid industrial development caused an increase in price and resulted in a declining source of supply (trees) created need for a cheaper substitute for the charcoal.
-
Welcome to
Coke-Land
Coke = charcoal made from coal
Heating value 25million BTUs/ton Heating value 25million BTUs/ton
Process of coke-making discovered in Sixteenth Century England:. Originally called (charking).
Obtained by heating coal at high temperatures (900-1150 C) in the absence of oxygen; much the same way as charcoal was made from wood.
-
Beehive Coke Ovens First Beehive coke oven was made in Connellsville,
Fayette County, PA during the 1830s.
Widespread use of these ovens was delayed until the
1850s.
These ovens proved much more efficient, producing These ovens proved much more efficient, producing
coke with carbon contents of up to 67%.
-
Beehive oven: A fire brick chamber shaped like a dome is
used. It is 4 m wide and 2.5 m high.
The roof has a hole for charging the coal from the top. The
discharging hole is provided in the circumference of the
lower part of the wall. Number of ovens is built in a row with
common walls between neighboring ovens.
Coal is introduced from the top and produces an even layer
about 60-90 cm deep. Air is supplied initially to ignite the
coal. Carbonization starts and volatile matter burns insidecoal. Carbonization starts and volatile matter burns inside
the partially closed side door. Carbonization proceeds from
top to bottom and is completed in 2-3 days.
Heat is supplied by burning of volatile matter and hence no
by-products recovered. The exhaust gases are allowed to
escape to the atmosphere. The hot coke is quenched with
water and discharged, manually through the side door. The
walls and roof retain enough heat to initiate, carbonization
of the next charge.
The yield of coke is about 60-80%.
-
Beehive Coke Ovens
Demerits:
No recovery of by-products
Lower coke yield due to partial combustion
Lack of flexibility in operation
-
Otto Hoffmann oven or by product oven
-
Construction:
A number of narrow rectangular chambers made of silica
bricks 12-14 m in length, 4-5 m in height, 0.5 m width ire
used.
It is tightly closed so that no air can enter.
Each chamber at the top has three holes for charging coal,
Otto Hoffmann oven or by product oven
Each chamber at the top has three holes for charging coal,
a gas take off and refractory lined cast iron door for
discharging the coke.
The carbonization chambers are erected side by side with
vertical flues or interspaced for combustion in between
them. 10-100 ovens are set together.
One oven is capable of holding 16-24 tones of coal.
-
Recovery of byproducts