WTP
CHEMICALS
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SL
NO.
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CHEMICAL
NAME
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FUNCTION
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APPLICATION
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1
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Sodium
Hypochlorite
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To kill microorganisms
(bacteria. Algae and other germs)
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Clarifier
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Ultra
Filter (UF)
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Cooling
tower
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2
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Ferric
chloride
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Coagulation
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Clarifier
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3
|
Polyelectrolyte
|
Flocculation
|
Clarifier
|
4
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Hydrochloric
acid
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Regeneration by cation exchange
|
Regeneration of SAC, MB
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Membrane
cleaning
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UF
& RO Membranes
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||
5
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Caustic
soda lye
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Regeneration by anion exchange
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Regeneration of SBA, MB.
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Membrane
Alkali Cleaning
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UF
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||
6
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Caustic
flakes
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Regeneration by anion exchange
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Regeneration of SBA, MB.
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7
|
Trisodium
phospate
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Sludge Conditioner & Corrosion
inhibitor
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Boiler steam drum Drum (Through
HP dosing pump)
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8
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Hydrazine
Hydrate
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To remove Oxygen
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1-Deaerator outlet feed water line
(Through LP dosing)
2-Boiler Wet Preservation |
9
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Morpholine
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pH
boosting
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Deaerator outlet feed water line
(Through LP dosing)
2-MB outlet 3-Boiler Wet Preservation |
MB
outlet
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Boiler
Wet Preservation
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10
|
Antiscalant
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Prevention of scale
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RO Membranes
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11
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Sodium
Meta bisulphite
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To reduce chlorine
|
RO Membranes
|
12
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Biocide
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Reduce Algae, bacteria & fungi
growth
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RO Membranes cleaning
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13
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Acidic
cleaner
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Salts removing
|
RO membranes
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14
|
Alkaline
Cleaner
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Salts removing (Cleaning inorganic
scales)
|
RO membranes
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15
|
Scale
inhibitor
|
Prevents scaling
|
Cooling Tower
|
16
|
Corrosion inhibitor
|
Prevents Corrosion
|
Cooling Tower
|
17
|
Bio-Dispersant
|
Bio-Dispersion
|
Cooling Tower
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18
|
Non
oxidising Micro Biocide
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To kill microorganisms
|
Cooling Tower
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19
|
Non
oxidising Micro Biocide
|
To kill microorganisms
|
Cooling Tower
|
20
|
Sulphuric
acid
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To maintain pH (To reduce
Alakalinity of water)
|
Cooling Tower
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21
|
Chlorine
Granuals
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Bacteria killing
|
Cooling Tower
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22
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Zinc
base chemical
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To prevent corrosion of Copper
base alloy
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Cooling Tower
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23
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Oxidising
Biocide (Chlorine activator)
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Controls biofouling in heat
exchangers like Condensers, oil coolers)
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Cooling Tower
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Water treatment plant chemicals and their functions
Shaft couplings & selection guide
A shaft coupling is a mechanical
device used to connect rotating shafts and absorb misalignments between
them. A coupling is a mechanical device, which is used to connect driver
and driven shaft permanently or semi permanently.
Couplings can be rigid or flexible depending
on the alignment accuracies of the system and torque requirements. Shaft
couplings are used for power and torque transmission between two rotating
shafts such as on motors and pumps, compressors, and generators.
Functions of couplings:
- Connects the shafts of two units, which are manufactured separately.
- Transfers motion, power and torque
- To reduce transmission shock loads from one shaft to another
- Protection against overloads.
- Introduces mechanical flexibility.
Design considerations for
couplings:
- Type of drive & driven equipments
- Alignment accuracy
- Operating & surrounding temperatures
- Type operation (Intermediate, continuous, frequent ON/OFF etc)
- Shafts diameters to be connected
- Maximum & minimum bores size
- Operating & design power
- Maximum & peak loads
- Space available
- Operation & Maintenance cost
- Service factor (Generally, for medium duty use a service factor of 1.5. For heavy duty use a factor of 2 and for extra heavy duty a factor of 3 should be used)
Types of couplings:
Main types of couplings: Rigid coupling and
Flexible coupling
Regid couplings:
Rigid coupling is used to connect two shafts
which are perfectly aligned. Most of the rigid couplings are made of aluminum, steel,
or stainless steel.
Types of Regid couplings:
- Sleeve or muff coupling
- Clamp/compression
- Flange coupling
Considerations for regid coupling
selection:
- Angular misalignment tolerance
- Parallel misalignment tolerance
- Axial motion allowed
- Dimensions like Bore diameter,Coupling diameter,Coupling length & Design units
- 3 if shaft size is up to 40 mm
- 4 if shaft size is 40–80 mm
- 6 if shaft size is 80–180 mm
Flexible
Couplings:
- Pin bush coupling (Protected and unprotected type)
- Jaw/spider/love joy coupling
- Gear coupling
- Bibby/grid coupling
- Metaflex/flexible disc coupling
- Tyre coupling
- Fluid coupling
- Oldham’s coupling
- Coupling size
- Coupling flange diameter
- Hub diameter
- Coupling gap
- Coupling maximum & minimum bore diameters
- No.of pins or bolts
- Maximum speed
- Torque
Gear couplings also transmit high
torques. They have misalignment capabilities generally about 0.01-0.02 inch in
parallel and 2 degrees in angular. Gear couplings are often used in pairs with
spacer shafts to span the distance between the driving and driven equipment.
They generally require lubricant although some designs intended for lighter
duty use lubricant free nylons or other polymers for the center sleeve.
Grid Couplings:
Grid couplings employ spring-like
connecting elements that weave between slots machined in the coupling hubs.
They are capable of high torque transmission with an added bonus of shock
absorption and torsional vibration dampening. They operate without lubricant.
They are appropriate for power transmission and capable of handling parallel
misalignment up to 0.30 inch and angular misalignment of about ¼ degree.
Disc Couplings:
Disc couplings use single or multiple
discs and single or double stages which bolt to the shaft hubs. They are used
for power transmission and rely on the flexibility of their thin metal discs to
transmit torque and accommodate angular misalignment. They are not especially
good at managing parallel misalignment. They are capable of transmitting high
torques and are often used to couple high horsepower motors, gas turbines, etc.
to loads.
Oldham Couplings:
Oldham couplings handle high degrees
of parallel misalignment owing to their sliding element design. Use of an
elastomer center element instead of metal is popular in modern versions. Some
manufacturers claim an ability to tolerate up to 5-degree angular misalignment
through the use of cylindrical, rather than rectangular, sliders.
Fluid Couplings:
Fluid
couplings or hydraulic couplings work on the hydrodynamic principle. In drives
consisting fluid couplings, there is no mechanical contact between the driver
and the driven machine and power is transmitted by means of a fluid. Due to the
mechanical separation between the driver and the driven machine, a fluid
coupling enables to achieve two separate value of acceleration in the drive,
the fast value of acceleration for the driver and simultaneously the slow value
of acceleration for the driven machine.
Fluid couplings are often used to drive large
inertia machines in combination with squirrel cage motors. They permit a load
free acceleration of the motor and consequently with increasing oil fill,
provide a soft/gentle quasi steady state start-up of the machine. The maximum
torque occurring during the start-up process is restricted to lowest possible
level. As fluid coupling allows quick acceleration of the motor and short
duration of high value starting current, it results into economical design for
electrical system. In addition, systems that use multiple motors can be
switched on in a staggered sequence to limit the current demanded during the
motor acceleration. This avoids grid overloading caused by simultaneous motor
starts.
Fluid
couplings are used in drives for conveyor systems such as belt conveyors, bucket
elevators and chain conveyors. The smooth application of fluid coupling torque
provides a smooth start-up of belt conveyor to protect the belt from damaging
stresses. In heavy industry, they are used for applications such as crushers,
roller presses, mixers, large ventilators, boiler feed pumps, large
compressors, centrifuges, etc
Types of fluid couplings:
Constant fill type:
Constant-fill
Couplings Couplings of this type are mainly used for start-up (to limit torque)
and to cushion the torsional vibration of the drive chain. In this type of
couplings, various designs mainly differ through adjoining chambers, who’s
automatically controlled filling and emptying have a significant influence on
the start-up behavior. Constant-fill couplings are sealed to the outside.
Filling of the operating fluid in a coupling is carried out before its
commissioning.
Drive
requirements determine the design and filling quantity. The ratio of the
operating fluid volume filled to the overall volume of the coupling is called
the fill level.
Variable-speed
Couplings:
Couplings
of this type are used to control or regulate the speed of the driven machine
over a wide range below the drive speed. These couplings have devices that
seamlessly change the transmission behavior during operation. This mainly
occurs by changing the fill level. The fill level can be changed during
operation either via a radially movable scoop tube or by controlling the
operating fluid inlet and outlet via valves and nozzles. These couplings always
have an external fluid circuit for filling changes that can also aid cooling.
Missalignment tolerances for angular & parallel alignments
Speed (RPM)
|
Angular
misalignment in Mills/inch of coupling diameter
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Parallel misalignment Mills
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Good
|
Acceptable
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Good
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Acceptable
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600
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1
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1.5
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5
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9
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900
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0.7
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1
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3
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6
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1200
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0.5
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0.8
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2.5
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4
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1800
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0.3
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0.5
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2
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3
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3600
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0.2
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0.3
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1
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1.5
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7200
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0.1
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0.2
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0.5
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1
|
Calculations:
Example-1:What is the size of muff coupling, which is required to
fit on 50 mm shaft Outer diameter of muff or sleeve = 2 X shaft diameter + 13 mm
=
2 X 50 + 13 = 113 mm
Length
of sleeve = 3.5 X shaft diameter =3.5 X 50 =175mm
Example-2: Calculate the
flange coupling dimensions required to fit on a shaft of 65 mm diameter.
Based on shaft diameter we can calculate the following dimensions
of flange coupling.
Outside diameter of hub = 2 X shaft diameter (d) ==2 X 65 = 130 mm
Length of the hub = 1.5 X d = 1.5 X 65 = 97.5 mm
Pitch circle diameter (PCD) of the bolts = 3 X d = 3 X 65 = 195 mm
Outside diameter of the flange = 4 X d = 4 X 65 = 260 mm
Thickness of flanges =
0.5 X d = 0.5 X 65 = 32.5 mm
Example-3:What is the
maximum torque developed on a gear coupling mounted for pump & motors of
power rating 525 KW & speed 3000 RPM
Torque = 9550 X
Power/Speed
T = 9550 X 525/3000
T = 1671.25 Nm
Basic calculations on fuels & combustion
Fuel:
It is a substance which releases heat energy on combustion. The principal combustible elements of each fuel are carbon and hydrogen.
Fuels classification:
Primary Fuels: These fuels directly available in nature, Ex: Wood, Peat, Lignite coal, Petroleum and Natural gas.
Secondary Fuel: These are prepared fuels, Ex: Coke, Charcoal, Briquettes, Kerosene, fuel oil, petroleum gas, producer gas etc.
Fuels are also classified as Solid fuels, liquid fuel and Gaseous fuel.
Different types of coals: Peat, Lignite, Bituminous coal, Anthracite coal and Coke.
Gaseous fuels:Natural gas, Coal gas, Coke oven gas, Blast furnace gas, producer gas, Water gas and Sewer gas.
Energy producing elements in fuel: Carbon, oxygen, hydrogen and Sulphur.
Formation of Charcoal & Coke:
Charcoal:It is obtained by destructive distillation of wood.
Coke is formed by destructive distillation of certain types of coal.
Calorific value of fuel: Calorific value (GCV) is the amount of heat released on complete combustion of unit quantity of fuel.It is measured in kcal/kg.
GCV is also known as Higher Calorific Value (HCV),it is given by following formula
GCV or HCV = (8084 X C% + 28922 X (H2%–O2%/8) + 2224 X S%)/100…kcal/kg
Where C, H2, O2 and S are percentage of Carbon, hydrogen, oxygen and Sulphur respectively in fuel.
Net Calorific Value (NCV) or Lower Calorific Value (LCV):
The total heat
released by fuel during combustion is not completely utilized. Some heat is
taken out by water vapour which is produced during combustion of hydrogen. Such
heat value taken by considering heat taken away by water vapour is called NCV
or LCV.
LCV = HCV – (9 X H2% X 586), Where H2 = Hydrogen% in fuel and 586 is latent heat of steam
in kcal/kg.
Useful heat Value (UHV) of coal:
NCV = GCV - 10.02 X Percentage of total moisture.
Ultimate analysis:Ultimate analysis indicates the various elemental chemical constituents such as Carbon, Hydrogen, Oxygen, Sulphur etc.
Proximate analysis of coal:Proximate analysis determines fixed carbon, Volatile matter, moisture and percentages of ash.
Volatile Matter (VM) & is its significance:
VM is generally a composition of methane, hydrocarbons, hydrogen and carbon monoxide and other incombustible gases like CO2 and Nitrogen. It is the indication of presence of gaseous fuel in the fuel.
Significance:
- Helps in easy ignition of coal by increasing the flame length
- Sets minimum limit on the furnace height and volume.
·
Caking Index: Indicates binding property of coal.
·
Swelling
Index: Indicates caking capacity of coal.
·
Slacking
Index: Indicates the stability of
coal when exposed to open atmosphere.
·
Grinding
Index: It gives the idea of ease of
grinding of coal.
·
Abrasive
Index: Indicates the hardness of
coal.
Combustion:
Combustion
is the rapid oxidation of fuel accompanied by the production of heat
Oxygen
is the major element on earth, making up to 21% (by volume) of our air. Carbon,
hydrogen and Sulphur in the fuel combine with oxygen in the air to form carbon
dioxide, water vapour and Sulphur dioxide releasing tremendous heat.
Oxygen is the major element on earth, making up to 21% (by volume) of our air. Carbon, hydrogen and Sulphur in the fuel combine with oxygen in the air to form carbon dioxide, water vapour and Sulphur dioxide releasing tremendous heat.
Basic requirements of combustion:Fuel, Oxygen and 3T’s
C + O2 = CO2+ Heat 8084 kcal/kg of Carbon.
2C + O2 = 2CO + Heat 2430 kcal/kg of Carbon.
2H2 + O2 = 2H2O 1 Heat 28922 kcal/kg of Hydrogen.
S + O2 = SO2 + Heat 2224 kcal/kg of Sulphur.
Products of Combustion: CO2, CO, O2, SO2 and ash.
Spontaneous combustion: is a phenomenon in which coal bursts into flame without any external ignition source but by itself due to gradual increase in temperature as a result of heat released by combination of oxygen with coal.
Major contents of ash:
- Silica
(SiO2)
- Aluminum
oxide (AlO3)
- Iron
Oxide (Fe2O3)
- Sodium
Oxide (Na2O)
- Potassium
Oxide (K2O)
- Calcium Oxide (CaO)
- Magnesium Oxide or Magnesia (MgO)
Fly ash & Bottom ash :
Fly ash 70–80%, Bottom ash 20–30%.
Fly ash at Economiser : 7–8%, APH: 10–12% and ESP: 80–82% of total fly ash.
Stoichiometric air fuel ratio: A mixture of air and fuel, which contains sufficient amount of oxygen for complete combustion.
Rich mixture: Mixture with deficiency of air
Lean mixture: Mixture with excess air
Theoretical air of combustion:
Minimum amount of air that supplies the sufficient amount of oxygen for the complete combustion of all carbon, hydrogen and any other elements in the fuel that may oxidize is called theoretical air.
Theoretical air required for combustion of carbon:
We know that Carbon on oxidation with Oxygen forms Carbon dioxide.
C + O2 = CO2
12 + 32 = 44 (Molecular weights of Carbon and Oxygen are 12 and 16 respectively)
1 + 2.67 = 3.67
So, 1 kg of Carbon requires 2.67 Kg of Oxygen for complete combustion into 3.67 kg of carbon dioxide.
Similarly
Hydrogen on oxidation forms Water
2H2 + O2 = 2H2O
4 + 32 = 36 (Molecular weights of Hydrogen and Oxygen are 1 and 16 respectively)
1 + 8 = 9
So, 1 Kg of Hydrogen requires 8 Kg of Oxygen for its combustion & forms into water.
Excess air: Amount of extra air given to ensure complete combustion is called excess air.
3T’s of combustion:
- Temperature: High enough to maintain the ignition of the fuel.
- Turbulence: Is the mixing of fuel and air.
- Time: Sufficient enough for combustion.
Specific heat Cp and Cv:
Specific heat is the amount of heat in kcal needed to raise the temperature of 1 kg of substance by 1 °C. Cp and Cv are the specific heat at constant pressure and constant volume of gas.
Solved examples:
Example-1:A Biomass (Bagasse) contains 23% of carbon, 22% of oxygen, 3.5% of Hydrogen and 0.05% of Sulphur, then calculate the theoretical air required for its combustion.
We have, Theoretical air requirement = (11.6 X %C + 34.8 3 (%H2 - %O2/8) + 4.35 X %S)/100…
Kg/kg of fuel.
Therefore, Th air requirement will be = (11.6 X 23 + 34.8 X (3.5 – 22/8) + 4.35 X 0.05))/100
= 2.9 kg of air/kg of fuel.
Example-2:What is the quantity of excess air, if O2 measured in the Boiler outlet flue gas is 6%?
We have, Excess air = (O2%/( 21 - O2%)) X 100
= (6/(21 – 6)) X 100 = 40%
Example-3:A complete combustion requires 2.9 kg of theoretical
and 20% of excess air, then calculate the total air consumed for complete
combustion per kg of fuel burnt.
Actual quantity of air supplied = (1 + Excess air %/100) X theoretical air
= (1 + 20/100) X 2.9 = 3.48 kg of air/kg of fuel.
Example-4: A flue gas has 10% of CO2 and theoretical calculated CO2 is 12%, then calculate percentage of the excess air.
% of Excess air = ((Theoretical CO2%/Actual CO2%) - 1)) X 100
= (12/10) - 1) X 100 = 20%
Example-5: A Coal sample contains 10% of ash, coal required is 300 MT/day, assuming 100% combustion calculate the mass of ash generated in a day.
Mass of ash generated = (300 X10)/100
= 30 MT
Example-5:A Indonesian coal contains 58% of Carbon, 4.2% of Hydrogen, 11.8% of Oxygen and 0.5% of Sulphur, also needs 20% of excess air for its complete combustion. Calculate the Total air required for complete combustion and O2% in flue gas.
We know that,
Theoretical air required for combustion is = (11.6 X 58 + 34.8 3 (4.2 - 11.8/8) + 4.35 X 0.5)/100
= 5 7.7 Kg/Kg of Coal
Total air = (1 + EA/100) X Theoretical air
= (1 + 20/100) X 7.7
= 9.24 Kg/Kg of Coal
Also we know that EA = (O2 %/(21 - O2%)) X 100
20 = (O2/(21 - O2)) X 100
O2= 3.5%
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