From time immemorial, people have experienced burning wood. And since then, wood has been used as the main type of fuel, which is used to heat various rooms and cook food. Despite the variety of combustible substances, wood remains a common fuel in the 21st century due to its low cost, availability and ease of handling. For its effective and safe use in stoves and fireplaces, it is necessary to have some information about its physical and chemical characteristics.
Factors affecting combustion temperature
The maximum combustion temperature of wood depends on the species and can be reached under the following conditions:
- moisture content - no more than 20%;
- enclosed space used for combustion;
- availability of oxygen in the required amount.
It is also possible to burn fresh firewood with a moisture content of 40 to 60%, while:
- raw firewood ignites only in a well-heated stove;
- heat dissipationwill decrease by 20–40%;
- there will be an increase in firewood consumption, approximately twice;
- soot will settle on the walls of the stove and chimney.
Combustion efficiency will be significantly reduced due to the need for increased temperature, which goes to the evaporation of water and the burning of resin in softwoods. Under ideal conditions, beech and ash have the highest combustion temperature, and poplar has the lowest. Beech, larch, oak and hornbeam are valuable wood species and are not used as fuel. In domestic conditions, birch and coniferous trees are used to burn wood in stoves, considering that they give the highest temperature during combustion.
Which wood burns hotter?
As already mentioned, wood is one of the most used fuels for heating homes outside the city. Considering that all firewood burns at different temperatures, you need to choose those 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 more heat transfer from it. Of particular importance for the greater heat transfer of wood during combustion? in addition to the density and the presence of oxygen, it has the moisture content of firewood.
Dry wood burns better and produces more heat than damp wood. Therefore, after cutting them, they are stacked in woodpile and dried under a canopy for a year. Everyone who has ever heated a stove with wood has noticed that some of them are burning.bright, releasing 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 species for burning in stoves are birch, pine and aspen.
What is released when a tree burns?
When wood is burned, smoke is produced, consisting of solid particles (soot) and gaseous products of combustion. They include substances found in wood. The products released when wood is burned 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 approximately 800 g of gaseous products and 200 g of coal during combustion. The composition of wood combustion products also depends on the conditions under which this process occurs. It can be:
- Incomplete - occurs when there is insufficient access to oxygen. As a result of combustion, substances are released that are able to 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
There are several stages in the process of burning wood:
- Heating up - takes place at a temperature of at least 150 degrees Celsius and in the presence of an external fire source.
- Ignition - the required temperature is from 450 to 620 degrees Celsius independing on the moisture and density of the wood, as well as the shape and quantity of firewood.
- Combustion - consists of two phases: fiery and smoldering. For some time, both types proceed simultaneously. After the formation of gases ceases, only coal burns (smolders).
- Fading - Occurs when oxygen is cut off or when fuel runs out.
Dense wood burns more slowly than less dense wood due to its higher thermal conductivity. When burning wet firewood, a lot of heat is spent on the evaporation of moisture, so they burn more slowly than dry firewood. Is burning wood a physical or chemical phenomenon? This question is of practical importance, and the conditions for maximum heat transfer and burning duration 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, it is physical: during the process, an increase in the kinetic energy of molecules occurs. As a result, it turns out that the process of burning wood is a complex physical and chemical phenomenon. Getting to know him will help you choose the right wood species to provide yourself with a long-term and sustainable source of heat.
Features of the smoke that occurs when burning a fire
When throwing firewood into a fire, there is an increased emission of smoke and carbon monoxide - carbon monoxide. Moreover, the smoke appears in various colors:
- White is an aerosol, consisting of small droplets of water and tar vapor, comes outcold wood. The smoke has a specific smell of soot. As the log heats up, it evaporates, bursts into flames 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 a mist. Its particles are much smaller than that of white smoke, and it is lighter and drier than it.
- Black - burnt tar, called soot. It is formed during the decomposition of hydrocarbons in a flame with insufficient oxidation.
Smoke from a fire lingers in the body for a long time and contains a large amount of harmful substances. This should be remembered by everyone who loves to sit by the fire.
Properties of wood
Different tree species have the following physical properties:
- Color - influenced by climate and wood species.
- Shine - depends on how the heart-shaped rays are developed.
- Texture - related to the structure of wood.
- Moisture - the ratio of moisture removed to the mass of wood in a dry state.
- Shrinkage and swelling - the first is obtained as a result of the evaporation of hygroscopic moisture, swelling - the absorption of water and an increase in volume.
- Density - about 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, depends on the location of the fibers.
- Electrical conductivity - resistance to passageelectric current. It is influenced by breed, 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
Wood has the following advantages:
- excellent machinability;
- light nailiness;
- well stained, polished, varnished;
- has the ability to absorb sounds;
- acid resistance;
- high bending ability.
Disadvantages of wood include:
- change in shape and size due to shrinkage and swelling;
- low splitting resistance;
- rotting;
- damage by insects;
- fire when safety rules are not followed.
Use of wood in various sectors of the economy
Wood is widely used in the following industries:
- plywood - veneer, plywood;
- woodworking - wood boards, matches, carpentry, furniture;
- logging - raw materials used in the wood 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, alcoholethyl.
Conclusion
Wood is one of the most widely used 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 used in various industries. The main advantages of this material are environmental friendliness, high strength, easy processing, the ability to use waste for fuel and other purposes.
