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V.
Discussion
Wood, like other fuels is made up of various amounts of carbon, hydrogen, and other
elements. The burning of wood is a chemical reaction that depends on many factors. The
essential factors to complete wood burning are time, temperature, and turbulence. Some other
factors to take into consideration are: intake air; amount and placement, density and moisture
content of the fuel, size of the firebox compared to the size of the wood load, and adequate room
for the combustion process to take place.
The smoke that is seen coming out of a chimney is essentially a combination of unburned
fuel (carbon and hydrogen) and moisture in the form of water vapor. The reason for the smoke is
usually attributed to: (i) not enough time for complete combustion, (ii) not enough mixing
(turbulence) to complete the chemical process, (iii) not enough temperature to get the fuel to that
chemical conversion stage, or (iv) a combination of the above. In many cases, excessive smoke
can be reduced by adopting practices that improve complete combustion, reducing visible
emissions in the form of smoke.
A.
Fuel
1.
Moisture Content
Moisture content of the wood, either too high or too low, will affect the amount of visible
smoke. Wood with a low moisture content (less than 10%) will burn relatively quicker, resulting
in some of the fuel going up the chimney in the form of smoke, i.e., time was insufficient to
complete the burn process. Wood with a moisture content too high (more than 35%) can quench
the flame causing smoke, i.e., temperature was insufficient to burn completely.
Wood moisture in the 20% to 30% range can be the best of both scenarios. It is dry
enough to burn without quenching the flame, yet the moisture is high enough to self-regulate the
burn, giving it plenty of time to complete combustion.
2.
Density
The density of wood plays a part in the combustion process in the same way as moisture
content. Softwoods are by definition less dense and tend to burn more rapidly than hardwoods.
Softwoods tend to create more smoke – due generally to insufficient time to complete the burn.
Denser hardwoods will burn more slowly and evenly, allowing more time for the conversion of
fuel to heat.
3.
Size
The size of the wood can also be a factor in the amount of smoke produced. The surface
area of a piece of wood is one of the factors that will affect burn rate. Larger diameter logs tend
to burn slower than smaller logs, allowing for a more complete burn.
4.
Improper Fuels
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