When we burn wood, it is sublimation

How does wood burn and which substances are released in the process?

Besides a flame, other things are created during combustion

A corresponding amount of firewood is of course burned in a fireplace. The result is a great play of flames in the stove and pleasant warmth. But of course that is not the only thing that arises when burning firewood. You can see that in the exhaust gases alone. But what exactly is it that is released when the wood is burned? We will shed light on this exciting topic in the following article.

What substances are produced when wood is burned?

In the Burning wood Mainly carbon is released in the form of carbon monoxide and carbon dioxide. There is also a large amount of hydrogen. Wood also has some non-flammable components that remain as ash after burning. In addition, other gases such as a very small amount of tar and acids are also produced during combustion. These are in the smoke.


The three phases of wood burning

The burning of wood is a process that has been studied very closely in science. In the true sense of the word, wood does not burn - it gasifies. The fire ignites the gases in the wood and uses them to generate energy. Wood combustion is generally divided into three different phases: drying, degassing and oxidation.

1. The drying

The first phase of wood combustion is called a temperature range between 100 and 150 degrees Celsius. The water in the wood is heated and evaporated. At this point it should be noted that wood with a residual moisture level of more than 20 percent should not be placed in the stove. If the wood is too moist, the energy yield would drop significantly and considerably more pollutants would be released. In the long run, this increases the risk of a chimney fire. A moisture meter for wood can be used to quickly and easily determine the residual moisture in the wood. You can recognize the drying phase by the fact that you can literally hear the evaporating water hissing if you leave the fireplace door ajar.

2. The degassing

In this second phase we speak of a temperature range of 150 to 600 degrees Celsius. The flames lick very violently. From around 150 degrees Celsius, volatile wooden parts become gaseous. The wood is then severely decomposed from over 200 degrees. This decomposition phase lasts up to around 600 degrees Celsius. During this phase we speak of the so-called pyrolysis reaction. The following numbers are impressive. The wood has already lost 85 percent of its original mass. What remains is charcoal. The degassing phase is a very crucial phase for wood combustion, as 70 percent of the calorific value of the fire is released here.

3. The oxidation

This phase extends over a temperature range of 600 to 1,300 degrees Celsius. In this phase you can influence the fire by means of air throttling. The flames react to the supply of oxygen. At the end of this phase, the ash remains as a residue. The ashes make up just 0.5 to 1 percent of the original total weight. Wood burns almost completely.

When wood is burned, carbon monoxide, hydrogen, carbon dioxide and organic compounds are essentially produced. Incidentally, when burning wood, you can have a positive influence on the Co2 emissions of a wood-burning stove through optimal combustion.