The Combustion Process; Drying Phase; Degasifi Cation Phase; Burn-Off Phase - HASE Ottawa Mode D'emploi

21. The Combustion Process

EA piece of wood burns in three phases. In a wood fi re,
however, these processes occur both consecutively and
simultaneously.

21.1 Drying Phase

The moisture still remaining in the air-dried wood (approx.
15 - 20%) is evaporated. This takes place at temperatures of
approx. 100°C. For the evaporation to occur, the wood must
be supplied with heat during the warming up phase; this is
achieved by using small wood logs.
21.2 Degasifi cation Phase
At temperatures between 100°C and 150°C, the contents of
the wood start - slowly at fi rst – to disintegrate and gasify and
the wood begins its thermal decomposition. At tempera-
tures above 150°C, the gas development accelerates. The
proportion of volatile components makes up around 80%
of the wood substance. The actual combustion begins at a
temperature of about 225°C (ignition temperature) with the
ignition of the resultant gases and the release of heat. There
must be an adequate supply of oxygen available for this
purpose. The peak of the combustion process is reached at
approx. 300°C. The reaction process is now so rapid that the
largest amount of heat is released at this point; fl ames can
reach temperatures of up to 1100°C.

21.3 Burn-off Phase

Glowing charcoal embers remain after the volatile compon-
ents have been burned off. These burn slowly, almost without
fl ames, at a temperature of approx. 800°C.
Crucial to a clean and effi cient combustion process is a
complete as possible chemical
reaction of the wood gases with the oxygen in the combustion
air. In your Hase stove, the combustion air is pre-heated and
guided into the fi re box via wide air inlet openings, so that at
high temperatures, there is a good, thorough mixing of the
gases with the air. An important variable in any combustion
phase is the amount of combustion air. Too little air leads
to an oxygen defi ciency and incomplete combustion, while
too much air reduces the fi re box temperature and thus the
effi ciency. Incomplete combustion can generate air pollutants
such as dust, carbon monoxide, and hydrocarbons.
Burn-off
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21.4 Expansion Noises

Steel expands upon heating and contracts as it cools. These
movements occur during the warming up and cooling down
phases, as well as when adding fuel. They can cause your
stove to emit audible expansion sounds. However, the design
and construction of your stove takes this into account and
prevents this physical process from damaging the stove.

22. The Chemistry of Wood

Wood predominantly consists of the elements carbon,
hydrogen, and oxygen. It contains virtually no environmental-
ly hazardous substances such as sulphur, chloride and heavy
metals. As a result, complete wood combustion produces
mainly carbon dioxide and water vapour as the primary
gaseous products as well as a small quantity of wood ash as
the solid combustion residue. On the other hand, incomplete
combustion can generate a number of pollutant substances,
such as carbon monoxide, acetic acid, phenols, methanol,
formaldehyde, soot, and tar.

23. Contribution to Environmental Protection

Whether your Ottawa burns in an environmentally-friendly
or environmentally hazardous manner depends to a large
Degasifi cation
extent on how you operate it and the type of fuel you use (see
Section 11, „The Right Fuel").
Therefore, use only dry wood; hardwoods such as birch and
beech are most suitable.
Only use small pieces of wood to light the fi re. They burn
Drying
faster than large logs and as a result, the temperature required
for complete combustion is reached more quickly.
For continuous heating, adding smaller quantities of wood
more frequently is more effi cient and more ecological.

24. Evaluating the Combustion Quality

The following characteristics can help you easily evaluate the
quality of the combustion:
– Colour and composition of the ash
If the combustion process is clean and effi cient, the
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