Combustion is the rapid reaction between a substance and oxygen that releases heat and light energy. Complete combustion of hydrocarbons produces carbon dioxide and water, while incomplete combustion occurs when there is insufficient oxygen and produces carbon monoxide and soot as well. Combustion technologies for biomass depend on factors like the fuel type, size, moisture content, and intended application. Solid biomass combustion in domestic applications uses stoves, while larger systems above 1 MWth are used for industrial plants.

1. Combustion of Biomass
BET 1 2017
Jackson Mutegeki,
Nyabyeya Forestry College

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When a substance burns,
it is said to combust.
A fuel is a substance that reacts with oxygen (combusts) to
release useful energy.
Combustion- Definition
Many fractions obtained from crude oil are used as fuels
because they contain hydrocarbons that burn easily and
release a large amount of useful energy.
Combustion is a rapid
reaction between a
substance and oxygen
that releases heat and
light energy.

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What are the products of the
complete combustion of a hydrocarbon?
Plenty of air is needed to provide enough oxygen for a
hydrocarbon fuel to burn completely.
oxygen
carbon
dioxide
fuel + +
 water
The blue flame of a gas hob
or a Bunsen burner is an
example of complete
combustion of a hydrocarbon
(in this case, natural gas).
Complete combustion of fuel

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Example - Complete combustion of
propane
Propane is a hydrocarbon used in camping gas. What is the
equation for its combustion?
oxygen
carbon
dioxide
propane + +
 water
5O2 3CO2
C3H8 + +
 4H20
How would the equations change if wood was used?

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If there is a shortage of air (oxygen), incomplete combustion
of fuel takes place.
Instead of producing just
carbon dioxide and water,
incomplete combustion
also produces carbon
monoxide and/or carbon
(soot). It also releases less
energy than complete
combustion.
Carbon monoxide is a poisonous gas because it reduces the
ability of blood to carry oxygen.
Incomplete combustion of fuel

7. Energy Release
• During the free radical reactions, carbon and hydrogen in
the fuel react with oxygen to form carbon dioxide and
water while liberating useful heat
– C+O2 CO2 -111 MJ/kmol
– H+ ½O2 H2O -283 MJ/kmol
• Oxygen is provided in excess to ensure complete
combustion of the fuel. This minimizes the production of
CO and maximizes heat generation

8. Combustion - Applications
• Designed on the basis of different factors:
– fuels
– fuel particle sizes
– moisture contents
– ash contents and compositions
– application purposes
– application sizes
– emission regulations
– etc.

9. SOLID FUEL COMBUSTION

10. Solid Biomass Composition

11. Fuelwood Combustion Theory
• When wood gets hot it releases volatile gases
which then burn if there is sufficient oxygen and
temperature
• Some of the radiant heat from the flame strikes
the wood, heating it and causing further
decomposition hence maintaining the cycle
• The gases are released at about 200 - 300oC
• But complete combustion takes place at about
650oC
• The unburnt gases escape as smoke – hence
smoke is wasted energy
John Kuteesakwe

15. Combustion Technologies
Applications
• For solid biomass utilisation, combustion
technologies depend on the application
– Domestic applications involve stoves
– Small furnaces up to a thermal output of 15 kWth,
– Middle-sized firing systems up to 1 MWth,
– Industrial plants above 1 MWth
• For liquid and gaseous biofuels, some form of
burner must be used