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1. COMBUSTION –
IMPROVED CHULHAS
J. JOHN GUNASEKAR
Professor (Bio-Energy)
Anbil Dharmalingam Agricultural College and
Research Institute
Trichy
Lecture 7
ERG 211 RENEWABLE ENERGY AND GREEN TECHNOLOGY (1+1)

2. CONTENT
 Combustion
 Improved chulha
 Single pot – double pot – conventional chulha
 Biomass gas stove – constructional features – principles and
applications

3. THERMOCHEMICAL CONVERSION TECHNOLOGY :
COMBUSTION, GASIFICATION AND PYROLYSIS
Combustion of Fuels
Fuel - is a combustible substance burns in presence
of air/oxygen and generates heat
Can be utilized for domestic and Industrial
purposes.
Elements present in fuel: C,H,N,O,S
Principally classified based on the
 reaction temperature
 availability of oxygen
 residence time
 type of product

4. COMBUSTION OF FUELS
Combustion of organic materials generate heat,
carbon dioxide and water and also produce
carbonaceous residues, smoke and tar and
obnoxious gases of carbonyl derivatives,
unsaturated compounds and carbon monoxide.

5. COMBUSTION OF FUELS
The selection of right type of fuel depends on
various factors such as availability, storage,
handling, pollution and cost of fuel at the utility
point.
The knowledge on the fuel properties helps in
selecting the right fuel for the right purpose.

6. DIRECT COMBUSTION
In combustion, the waste fuel is burnt in excess
air in a controlled manner to produce heat.
The combustion heat is used to produce steam in
a boiler.
The steam is expanded through a turbine
connected to a generator, thereby producing
electricity.

7. DIRECT COMBUSTION
Flue gases from efficient combustion are mainly
carbon dioxide and water vapour, with small amounts
of other air emissions (obnoxious gases of carbonyl
derivatives, NOx and carbon monoxide), depending on
the nature of the biomass fuel.
The flue gases are cleaned using flue gas scrubbers,
bag filters and electrostatic precipitators, and if
required, further chemical processing to reduce
emission of oxides of nitrogen (NOx) and other
pollutants.

8. Direct Combustion

9. PRINCIPLES OF COMBUSTION
 Combustion refers to the rapid oxidation of fuel
accompanied by the production of heat or heat and light.
 Complete combustion of a fuel is possible only in the
presence of an adequate supply of oxygen.
 Oxygen (O2) is one of the most common elements on earth
making up 20.9% of atmospheric air.
 Rapid fuel oxidation results in large amounts of heat.
 Solid or liquid fuels must be changed to a gas before they
will burn. Usually heat is required to change liquids or
solids into gases.

10. PRINCIPLES OF COMBUSTION
N2 reduces combustion efficiency by absorbing
heat from the combustion of fuels and diluting the
flue gases.
Nitrogen also increases the volume of combustion
by-products, which then have to travel through the
heat exchanger and up the stack faster to allow the
introduction of additional fuel-air mixture.

11. PRINCIPLES OF COMBUSTION
This nitrogen also can combine with oxygen
(particularly at high flame temperatures) to
produce oxides of nitrogen (NOx), which are toxic
pollutants.
C, H and S in the fuel combine with O2 in the air to
form CO2, water vapour and SO2, releasing 8,084
kcal, 28,922 kcal and 2,224 kcal of heat
respectively.

12. PRINCIPLES OF COMBUSTION
Under certain conditions, carbon may also combine
with oxygen to form CO, which results in the release of
a smaller quantity of heat (2,430 kcal/kg of carbon).
Carbon burned to CO2 will produce more heat per unit
of fuel than when CO or smoke is produced.
Each kilogram of CO formed means a loss of 5654 kcal
of heat (8084-2430).
C + O2 → CO2 + 8084 kcal/kg of Carbon
2C + O2 → 2 CO + 2430 kcal/kg of Carbon
2H2 + O2 → 2H2O + 28,922 kcal/kg of Hydrogen
S + O2 → SO2 + 2,224 kcal/kg of Sulphur

13. 3 T’S OF COMBUSTION
1) Temperature high enough to ignite and maintain ignition of the
fuel,
2) Turbulence or intimate mixing of the fuel and oxygen, and
3) Time sufficient for complete combustion.
 Too much fuel with the available combustion air may result in
unburned fuel and CO generation.
 A very specific amount of O2 is needed for perfect combustion
and excess air is required for ensuring complete combustion.

14. CONDITIONS FOR EFFICIENT COMBUSTION
Combustion Controls
 Combustion controls assist the burner in regulation of fuel
supply, air supply, (fuel to air ratio), and removal of gases
of combustion to achieve optimum boiler efficiency.
Conditions for efficient combustion of any fuel in a furnace:
 A sufficient amount of air (higher than stoichiometric
amount of air) must be supplied for completion of the
combustion reactions.
 The fuel mass and the oxygen of the air must be in free and
intimate contact.

15. CONDITIONS FOR EFFICIENT COMBUSTION
Conditions for efficient combustion of any fuel in a
furnace:
While burning solid biomass and other solid fuels,
the volatile combustion products leaving the fuel
bed must be intimately mixed with the secondary
air.
The volatile combustion products leaving the fuel
bed must not be allowed to cool below the ignition
point until the reactions are complete.

16. STOICHIOMETRIC CALCULATION OF AIR
REQUIREMENT
 The amount of air needed to burn one kg of fuel completely
based on combustion equations.
Kg of Air = 11.53 C + 34.34 (H2 – O2/8) + 4.29 S Kg of Fuel
Where, C, H2, O2 and S are the fractions by weight of each
chemical constituent of the fuel.
Excess Air
 During combustion, insufficient amount of air causes a
reduction in fuel efficiency, creates highly toxic carbon
monoxide gas and produces soot.
 To ensure enough oxygen to completely react with the fuel,
extra combustion air is usually supplied.

17. STOICHIOMETRIC CALCULATION OF AIR
REQUIREMENT
Excess Air
 This extra air, called “Excess Air,” is expressed as the
percent air above the amount theoretically (Stoichiometric)
needed for complete combustion.
 In real-world combustion, the excess air required for
gaseous fuels is typically about 15%.
% O2 measured
% Excess Air = ------------------------------------ x 100
20.9 - % O2 measured

18. STOICHIOMETRIC CALCULATION OF AIR
REQUIREMENT
Combustion efficiency
 Combustion efficiency is a measure of how effectively
energy from the fuel is converted into useful energy.
 Combustion efficiency is determined by subtracting the
heat content of the exhaust gases, expressed as a % of the
fuel’s heating value, from the total fuel-heat potential, or
100%.
Stack heat losses
% Combustion Efficiency = 100% - ----------------------- x
100
Fuel heating value

19. BIOMASS COMBUSTION
Biomass combustion simply
means burning organic
material.
For ages, humans have used
this basic technology to create
heat and, later, to generate
power through steam.
Direct combustion is the most
common method for converting
biomass to useful energy.

20. WOOD BURNING STOVES
 In India, 80 per cent of total population
lives in villages.
 The major energy demand of rural
population is for cooking which contributes
to about 98 per cent of their total energy
consumption.
 Wood, agricultural waste and biomass are
used as fuel in rural kitchen.
 The cooking appliances which are
commonly used in rural houses have very
low thermal efficiency (10 to 15 per cent)
and hence per capita energy consumption
in rural areas is much higher than that in

21. WOOD BURNING STOVES

22. CONVENTIONAL STOVES
 Conventional stoves waste a lot of energy and
pose many pollution hazards.
 Most traditional stoves can utilize only 2 – 10
per cent of the energy generated by the fuel.
 Black smoke emission consists of particles of
sizes up to 5, CO, CO2, oxides of nitrogen
and sulphur, hydrocarbons, aldehydes,
ketones etc.
 These pollutants are detrimental to
environment and to the health of rural women.
 It causes headache, watery eyes, common
cold and sneezing.

23. CONVENTIONAL STOVES
 Conventional stoves (chulha) take more time for cooking, more
difficult to fire and consume more fuel.
 The growing gap between availability and demand for fire wood,
poor thermal performance and pollution caused by traditional
stoves forced the technologists to concentrate their attention on
improving the thermal efficiencies of stoves.
Change Those Stoves And Save Our

24. TNAU SINGLE POT CHULHA
 The single pot chulha has a double
wall with a gap of 2.5 cm.
 It has a grate at the bottom of the
combustion chamber.
 The ash can be collected below the
grate.
 The outer wall has two rectangular
secondary air openings on both
sides at the lower portion.
 The inner wall has 1cm diameter
holes which maintain a triangular
pitch of approximately 3 cm.

25. TNAU SINGLE POT CHULHA
Separate mounds are provided
for holding bigger and smaller
vessels.
The secondary air enters
through the rectangular
opening in the outer wall, gets
heated in the annular chamber
and distributed through the
holes in the combustion
chamber.
The preheated air helps in

26. TNAU SINGLE POT CHULHA
TNAU Single Pot Stove
1. Outer wall
2. Inner wall
3. Mount
4. Air hole
5. Leg
Salient features
Height : 21 cm.
Inner wall diameter : 18 cm.
Outer wall diameter : 24 cm.
Fuel inlet opening : 15.5 x 15 cm.
Leg height : 5 cm.
Efficiency : 24%

27. TNAU DOUBLE POT CHIMNEYLESS CHULHA
This double pot portable chulha
(Chimneyless) is made with two
walls with an air gap of 2.5 cm.
There are two secondary air inlets,
one on the outer wall with
rectangular shape (17 cm x 1 cm)
near the combustion chamber and
the other circular hole of diameter 5
cm at the bottom of the second pot.
A cast iron grate is placed at the
bottom of the combustion chamber.

28. TNAU DOUBLE POT CHIMNEYLESS CHULHA
Salient features
Overall dimension : 55 x 30 x 25 cm (L x B x H)
Fuel inlet opening : 15.5 x 15 cm
Air inlet : 17x1 cm
Size and No. of legs : 5x5 cm 6nos
Efficiency : 26%
Figure 70 TNAU Double Pot Stove
1. First pot hole
2. Second pot hole
3. Tunnel
4. Outer wall
5. Fire box
6. Air hole

29. BIOMASS GAS STOVE
The biomass gas stove has been
developed for small scale thermal
application in Agriculture and
allied industries.
This stoves widens the market for
agro wastes, makes possible a
higher efficiency and in some
cases reduce the time and
investment, all by comparison
with combustion.

30. BIOMASS GAS STOVE
The biomass gas stove is a
natural convection type updraft
gasifier consisting of a cylindrical
body made of clay, sand and
paddy husk with its top open and
bottom closed.
The diameters and height of the
stove are 290mm and 630mm
respectively.
The dimensions can be changed
depending on the applications.

31. BIOMASS GAS STOVE
An iron grate to hold the
biomass is fixed at 50 mm
from the base of the reactor.
The bottom is provided with an
air opening cum ash removal
door.
At the top, provision is made
to place vessel for cooking,
boiling etc.

32. EFFICIENCY OF BIOMASS GAS STOVE
The conventional wood burning stoves give a
thermal efficiency of 12-15 percent and the
temperature of the flame obtained by direct
combustion of biomass in the stove is in the range
of 400-500° C only, whereas in the biomass gas
stove the efficiency is 25 per cent and the
temperature of the flame obtained is in the range
of 600-700° C.
The saving in fuel and time over the conventional
wood stoves are 10 per cent and 40 per cent
respectively.

33. APPLICATIONS OF BIOMASS GAS STOVE
The biomass gas stove
can be used for thermal
applications in farm
households, tea shops,
jaggery manufacturing,
small scale paddy
parboiling, arecanut
boiling and other agro-
industrial applications.

34. THANK YOU 