Since time immemorial, people have been faced with burning wood. And since then they have been using wood as the main type of fuel, which is used for heating various rooms and cooking. Despite the diversity of combustible substances, wood remains a common fuel in the 21st century, due to the low cost, availability and ease of handling. For effective and safe use of it in stoves and fireplaces, it is necessary to possess some information about its physical and chemical characteristics.
Factors Affecting Combustion Temperature
The maximum burning temperature of wood depends on the species and can be achieved under the following conditions:
- the amount of moisture content is not more than 20%;
- a closed space is used for combustion;
- the availability of oxygen in the required volume.
It is possible to burn fresh firewood with a moisture content of 40 to 60%, while:
- raw firewood is ignited only in a well-melted stove;
- heat transfer will decrease by 20–40%;
- there will be an increase in the consumption of firewood, about twice;
- soot will settle on the walls of the stove and chimney.
The combustion efficiency will be significantly reduced due to the need for an increased temperature, which goes to the evaporation of water and the burning of resin in conifers. Under ideal conditions, the highest burning temperature is for beech and ash, and the lowest is for poplar. Beech, larch oak and hornbeam are valuable species of wood and are not used as fuel. In domestic conditions, birch and coniferous trees are used for burning wood in stoves, believing that they give the highest temperature during combustion.
What kind of firewood burns hotter?
As already mentioned, firewood is one of the most used types of fuel for heating homes outside the city. Given that all firewood burns at different temperatures, you need to choose the ones that are better. The main condition for burning wood is the presence of oxygen, and this largely depends on the design of the stove. In addition, each wood has its own chemical composition and density. The denser the tree, the greater the heat transfer from it. Of particular importance for greater heat transfer of wood during combustion? in addition to density and the presence of oxygen, firewood has humidity.
Dry ones burn better and produce more heat than raw firewood. Therefore, after cutting, they are stacked in woodpiles and dried under a canopy for a year. Everyone who used to burn wood with a stove noticed that some of them burn brightly, giving off a lot of heat, while others smolder and heat the stove a little. Everything, it turns out, depends on the heat output of firewood. According to this indicator, the most suitable breeds for burning in furnaces are birch, pine and aspen.
What stands out when burning a tree?
When a tree burns, smoke is formed consisting of solid particles (soot) and gaseous combustion products. They include substances found in wood. The products released during the combustion of wood consist of nitrogen, carbon dioxide, water vapor, sulfur dioxide and carbon monoxide, which can burn further.
It is estimated that each kilogram of wood emits about 800 g of gaseous products and 200 g of coal during combustion. The composition of the wood combustion products also depends on the conditions under which this process occurs. He can be:
- Incomplete - occurs with insufficient access to oxygen. As a result of combustion, substances are released that can burn again. These include soot, carbon monoxide and various hydrocarbons.
- Full - occurs with sufficient access to oxygen. As a result of combustion, products are formed - carbon dioxide and sulfur dioxide, water vapor - which are no longer able to burn.
Description of the combustion process
In the process of burning wood, several stages are noted:
- Warming up - occurs at a temperature of at least 150 degrees Celsius and in the presence of an external source of fire.
- Ignition - the required temperature is from 450 to 620 degrees Celsius depending on the moisture and density of the wood, as well as on the shape and amount of firewood.
- Combustion - consists of two phases: flame and decay. For some time, both species occur simultaneously. After the cessation of gas formation, only coal burns (smolders).
- Attenuation - occurs when the oxygen supply stops or when the fuel runs out.
Dense wood burns more slowly than less dense wood due to the fact that it has a higher thermal conductivity. When burning raw firewood, a lot of heat is expended on the evaporation of moisture, so they burn slower than dry firewood. Is wood burning a physical or chemical phenomenon? This question is of practical importance, and the conditions for maximum heat transfer and the duration of combustion will depend on its correct interpretation. On the one hand, this is a chemical phenomenon: when wood is burned, a chemical reaction occurs and new substances are formed - oxides, heat and light are released. On the other hand, physical: during the process, the kinetic energy of the molecules increases. As a result, it turns out that the process of burning wood is a complex physicochemical phenomenon. Familiarity with it will help you choose the right type of wood to provide yourself with a long-term and sustainable source of heat.
Features of smoke arising from burning a fire
When tossing firewood into the fire, there is an increased emission of smoke and carbon monoxide - carbon monoxide. Moreover, smoke appears in various colors:
- White is an aerosol consisting of small droplets of water and tar vapors that comes out of cold wood. Smoke has a specific smell of soot. As the log is heated, it evaporates, flames with flame and disappears.
- Gray - comes from red-hot, but not burning logs and firebrands. It is formed at high temperature from boiling oils and resins and condenses into fog. Its particles are much smaller than that of white smoke, and it is lighter and drier than it.
- Black - charred tar, called soot. It is formed during the decomposition of hydrocarbons in a flame with insufficient oxidation.
Smoke from a bonfire lingers in the body for a long time and contains a large amount of harmful substances. This must be remembered to everyone who likes to sit around the fire.
Wood properties
Different tree species have the following physical properties:
- Color - climate and wood species influence it.
- Shine - depends on how the heart-shaped rays are developed.
- Texture - associated with the structure of wood.
- Humidity is the ratio of moisture removed to the mass of wood in the dry state.
- Shrinkage and swelling - the first is obtained as a result of evaporation of hygroscopic moisture, swelling - the absorption of water and an increase in volume.
- Density - approximately the same for all tree species.
- Thermal conductivity - the ability to conduct heat through the thickness of the surface depends on the density.
- Sound conductivity - characterized by the speed of sound propagation, depending on the location of the fibers.
- Conductivity - resistance to the passage of electric current. It is influenced by rock, temperature, humidity, fiber direction.
Before using wood raw materials for certain purposes, first of all they get acquainted with the properties of wood, and only then it goes into production.
Advantages and disadvantages of wood
The following advantages are inherent in wood:
- excellent machinability;
- light nails;
- it is well painted, polished, varnished;
- has the ability to absorb sounds;
- resistance to acids;
- high bending ability.
The disadvantages of wood include:
- change in shape and size due to shrinkage and swelling;
- low cracking resistance;
- decay;
- spoilage by insects;
- tanning due to non-compliance with safety regulations.
The use of wood in various sectors of the economy
Wood is widely used in the following industries:
- plywood - veneer, plywood;
- woodworking - wood boards, matches, joinery, furniture;
- logging - raw materials used in the chemical industry, consumer goods, firewood of all kinds;
- sawmill - various lumber;
- Wood chemical - tar, charcoal, acetic acid;
- pulp and paper - paper, cardboard, pulp;
- hydrolysis - fodder yeast, ethyl alcohol.
Conclusion
Wood is one of the most common materials in the world. It has been used for centuries in construction, furniture manufacturing and for heating residential premises. Wooden structures are used in every family. Wood is increasingly being used in various industries. The main advantages of this material are environmental cleanliness, high strength, easy machinability, the ability to use waste for fuel and other purposes.