Large coals after combustion and uniform heat are a sign of good raw materials
Main criteria
The most important indicators for combustion material: density, humidity and heat transfer. All of them are closely related to each other and determine how effective and useful wood burning is. It is worth considering each of them in more detail, taking into account different types of wood and methods of harvesting it.
Density
The first thing a competent buyer pays attention to when ordering wood heating material is its density. The higher this indicator, the better the quality of the breed.
All wood species are divided into three main categories:
- low-density (soft);
- medium-dense (moderately hard);
- high-density (solid).
Each of them has a different density, and therefore specific heat combustion of wood. The hard varieties are considered to be of the highest quality. They burn longer and produce more heat. In addition, they form a lot of coals, which maintain heat in the firebox.
Due to its hardness, such firewood is difficult to process, so some consumers prefer medium-density wood, such as birch or ash. Their structure allows special effort splitting logs by hand.
Humidity
The second indicator is humidity, that is, the percentage of water in the wood structure. The higher this value, the greater the density, while the resource used will generate less heat with the same effort expended.
The specific heat of combustion of dry birch firewood is characterized as more productive than wet ones. It is worth noting this feature of birch: it can be placed in the firebox almost immediately after cutting, because it has low humidity. To maximize the beneficial effect, it is better to prepare the material properly.
To improve the quality of wood by reducing the percentage of moisture content in it, the following approaches are used:
- Fresh firewood is left for a certain period of time under a canopy to dry. The number of days depends on the season and can range from 80 to 310 days.
- Some firewood is dried indoors, which increases its calorific value.
- The best option is artificial drying. The calorific value is brought to the maximum level by bringing the humidity percentage to zero, and a minimum of time is required to prepare the wood.
Heat dissipation
An indicator such as the heat transfer of firewood seems to summarize the previous two characteristics. It is he who indicates how much heat the selected material can provide under specific conditions.
The heat of combustion of wood is greatest for hardwood. Accordingly, the situation is opposite with soft wood. At equal conditions and natural shrinkage, the difference in readings can reach almost 100%. That is why, in order to save money, it makes sense to purchase high-quality firewood that is more expensive to purchase, since its production is more efficient.
Here it is worth mentioning such a property as the combustion temperature of wood. It is greatest in hornbeam, beech and ash, more than 1000 degrees Celsius, and it produces maximum amount heat at 85-87%. Oak and larch are close to them, and the lowest indicators are poplar and alder with a production of 39-47% at temperatures around 500 degrees.
Wood species
Calorific value The amount of firewood depends to the greatest extent on the type of wood. There are two main categories: coniferous and deciduous. High-quality combustion material belongs to the second group. There is also a classification here, since not all varieties are suitable for a particular purpose in terms of their density.
Conifers
Often the most accessible wood is pine needles. Its low cost is determined not only by the prevalence of spruce and pine trees, but also by its properties. The fact is that the heat capacity of firewood of this type is low, and there are also a lot of other disadvantages.
Main disadvantage coniferous species- presence of a large number of resins. When such firewood is heated, the resin begins to expand and boil, which results in the scattering of sparks and burning fragments over a long distance. The resin also leads to the formation of soot and burning, which clog the fireplace and chimney.
Deciduous
It is much more profitable to use hardwood. All varieties are divided into three categories, depending on their density. Soft breeds include:
- Linden;
- aspen;
- poplar;
- alder;
They burn out quickly and therefore have little value in terms of heating a home.
Medium-density trees include:
- maple;
- birch;
- larch;
- acacia;
- cherry.
The specific heat of combustion of birch firewood is close to that of species that are classified as hard, in particular oak.
- hornbeam;
- nut;
- dogwood;
The calorific value of this type of firewood is maximum, but wood processing is difficult due to its high density.
Oak is another popular type of fuel
The useful qualities of such breeds determine their higher cost, but this allows you to reduce the amount of material that will be needed to maintain a comfortable temperature in the house.
Material selection
Even the most high quality timber can be negated if it is selected incorrectly for a particular type of activity. For example, it practically doesn’t matter what was used for the night fire when gathering with friends. Lighting a fireplace or stove in a bathhouse is a completely different matter.
For the fireplace
Heating your home can become a problem if you load your stove with the wrong wood. This is especially dangerous when using a fireplace, since a sparkling log can even lead to a fire.
The unobtrusive burning of wood and the heat emanating from the fireplace are the highlight of the living room
For long burning and emitting a large amount of heat, you should give preference to oak, acacia, as well as birch and walnut. To clean the chimney, you can burn aspen and alder from time to time. The density of these rocks is small, but they have the ability to burn soot.
For the bath
To provide high temperature In the steam room of a bathhouse, maximum heat transfer from wood is required. In addition, you can improve your relaxation conditions if you use breeds that saturate the room with a pleasant smell, without emitting harmful substances and resins.
Read also about in addition to this article.
For heating the steam room optimal choice will, of course, be oak and birch logs. They are solid, give good heat in a small volume and also emit pleasant fumes. Linden and alder can also provide an additional healing effect. You can only use well-dried materials, but not older than one and a half to two years.
For barbecue
When cooking on a grill or barbecue, the main point is not the combustion of wood itself, but the formation of coals. That is why it makes no sense to use thin, loose branches. They can only be used to light a fire, and then add large, hard logs to the firebox. In order for the smoke to have a special aroma, it is recommended to use fruit firewood for the barbecue. You can combine them with oak and acacia.
Using different varieties wood, pay attention to the size of the chocks. For example, oak will take longer to burn and smolder than apple wood, so it makes sense to take thicker fruit logs.
Alternative fuel materials
The calorific value of certain types of firewood is quite high, but far from the maximum possible. In order to save money and space for storing fuel material, today more and more attention is paid to alternative options. It is optimal to use pressed briquettes.
For the same oven load, pressed wood produces much more heat. This effect is possible by increasing the density of the material. In addition, there is a much lower percentage of humidity. Another plus is minimal ash formation.
Briquettes and pellets are made from sawdust and wood chips. By pressing waste, it is possible to create an incredibly dense combustion material that even the most the best varieties wood With a higher cost per cubic meter of briquettes, the final savings can amount to a very significant amount.
It is necessary to prepare and purchase combustion materials based on a thorough analysis of their properties. Only high-quality firewood can provide you with the necessary heat without causing harm to your health or the heating structure itself.
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The calorific value of firewood depends on the type of tree and its humidity
We call firewood pieces of wood used in rapid oxidation reactions with atmospheric oxygen to produce light and heat. We simply light a fire on the ground after going on a picnic. Or in special devices - barbecues, hearths, boilers, stoves, takyrs or others.
There are various types of firewood, the amount of heat obtained from burning it, divided by mass (volume), is called the specific heat of combustion of heating oil. The calorific value of firewood depends on the type of tree and its moisture content. In addition, the completeness of combustion and the efficiency of combustion energy utilization depend on other factors. Different stoves, draft force, chimney design - everything affects the result.
The essence of the physical parameter
Energy is measured in “joules” - the amount of work done to move 1 meter when a force of 1 newton is applied in the direction of application. Or in “calories” - the amount of heat required to heat 1 g of water by 1 °C at a pressure of 760 mm Hg. An international calorie corresponds to 4.1868 Joules.
The specific heat capacity of a fuel is the amount of heat produced by complete combustion divided by the mass or volume of the fuel.
The value is not constant, since firewood can vary greatly, and this parameter also varies accordingly. In the laboratory, specific heat is measured by combustion in special devices. The result is true for a specific sample, but only for that sample.
The total specific heat of heating oil is measured with simultaneous cooling of combustion products and condensation of evaporated water - to take into account the ENTIRE amount of energy received.
In practice, working rather than specific heat of combustion is more often used, without taking into account all the energy received.
The essence of the combustion process
If you heat wood, at 120–150 ˚C it becomes dark in color. This is a slow charring, turning into charcoal. Raising the temperature to 350–350 ˚С, we will see thermal decomposition, blackening with the release of white or brown smoke. When heated further, the released pyrolysis gases (CO and volatile hydrocarbons) will ignite, turning into flames. After burning for some time, the amount of volatile substances will decrease, and the coals will continue to burn, but without a flame. In practice, to ignite and maintain combustion, the wood must be heated to 450–650 ˚C.
Wood burning process
Subsequently, the combustion temperature of heating oil in the firebox ranges from approximately 500 ˚С (poplar) to 1000 and higher (ash, beech). This value greatly depends on the draft, the design of the furnace and many other factors.
Humidity dependent
The higher the humidity, the worse the combustion, the lower the efficiency of the stove, and the more difficult it is to ignite and maintain the fire. And the calorific value of firewood is lower.
Indicators of calorific value (the amount of heat released during complete combustion of 1 kg of firewood, depending on humidity)
Both the specific heat of heating oil and its utilization rate decrease. The reasons are as follows.
- The water in the composition reduces the amount of fuel as such: at a humidity of 50%, the firewood contains half the water. And it won’t burn...
- Part of the heating oil energy will be spent on heating and evaporation of moisture.
- Wet wood conducts heat better, which makes it difficult to warm up the part of the log being ignited to combustion temperature.
Freshly cut wood varies in moisture content depending on the time of felling, the type of tree, and the place of growth, but on average it contains about 50% water.
That's why they put it in woodpiles under a canopy. During storage, some of the moisture will evaporate. When humidity decreases from 50 to 20%, the specific heat of combustion of heating oil approximately doubles.
Density dependence
Oddly enough, the composition of trees of different species is similar: 35–46% cellulose, 20–28% lignin + esters, resins, and other substances. And the difference in the heat of combustion of heating oil is due to porosity, that is, how much space the voids occupy. Accordingly, the denser the tree, the greater the calorific value of firewood from it. High-quality fuel pellets obtained by drying and pressing wood waste have a density of 1.1 kg/dm 3, that is, higher than the density of water. In which they drown.
Economic features of various firewood
The shape matters: the smaller the logs, the easier they ignite and burn faster. It is clear that the length also depends on the design: too long cannot be placed in a stove or fireplace; the ends stick out. Too short - extra labor when cutting or chopping. The combustion temperature of firewood depends on the amount of humidity, the type of wood, and the amount of air supplied. The temperature is lowest when burning firewood from poplar, highest when burning hardwood: ash, mountain maple, oak.
The importance of humidity was written above. Not only the heat transfer of fuel in the furnace, but also the labor costs for splitting or sawing greatly depend on it. It is easier to split and saw damp, freshly cut wood. However, it is too wet and viscous, which makes it hurt badly. The butt part is denser, and uprooted stumps and areas near knots have increased strength. There the layers of wood are intertwined, which makes it much stronger. Oak splits well in the longitudinal direction, which has been used by coopers since ancient times. Getting shingles, shingles, and splitting firewood has its secrets.
Spruce is a “shooting” species, which is why it is undesirable for use in fireplaces or fires. When heated, the internal “bubbles” with resin boil and throw burning particles quite far away, which is dangerous: it is easy to burn clothes near a fire. Or it may cause a fire near the fireplace. In a closed furnace firebox this does not matter. Birch produces a hot flame and is excellent firewood. But when bad traction it produces a lot of resinous substances (they used to make birch tar), and a lot of soot is deposited. Alder and aspen, on the contrary, produce little soot. Matches are mainly made from aspen.
In practice, it is convenient to immediately saw and split freshly cut firewood. Then stack it under the awnings, making woodpiles so that air passes through, drying the fuel and increasing heat transfer. Chopping wood is a labor-intensive task, so when buying, pay attention to this. In addition, they will bring you stacked or bulk firewood.
In the second case, heating oil is placed in a “loose” body, and the client pays partly for the air. In addition, the liquid or gaseous fuel has a plus: it is easy to automate the feed. They require a lot of firewood self made. All this should be taken into account when choosing a stove or boiler for your home.
Video: How to choose firewood for the firebox
Table 1 - Content of ash and ash elements in wood of various tree species
|
Woody plant |
Ash, |
|||||||||||||
|
Sum |
||||||||||||||
|
Pine |
0,27 |
1111,8 |
274,0 |
53,4 |
4,08 |
5,59 |
1,148 |
0,648 |
0,141 |
0,778 |
0,610 |
0,191 |
1461,3 |
|
|
Spruce |
0,35 |
1399,5 |
245,8 |
11,0 |
9,78 |
12,54 |
7,76 |
1,560 |
1,491 |
0,157 |
0,110 |
0,091 |
0,041 |
1689,8 |
|
Fir |
0,46 |
1269,9 |
1001,9 |
16,9 |
16,96 |
6,85 |
6,16 |
1,363 |
2,228 |
0,237 |
0,180 |
0,098 |
0,049 |
2322,8 |
|
Larch |
0,22 |
845,4 |
163,1 |
23,80 |
13,34 |
3,41 |
1,105 |
0,790 |
0,194 |
0,141 |
0,069 |
0,154 |
1057,4 |
|
|
Oak |
0,31 |
929,7 |
738,3 |
14,4 |
7,88 |
3,87 |
1,29 |
2,074 |
0,987 |
0,524 |
0,103 |
0,082 |
0,024 |
1699,2 |
|
Elm |
1,15 |
2282,2 |
2730,3 |
19,2 |
4,06 |
10,05 |
4,22 |
2,881 |
1,563 |
0,615 |
0,116 |
0,153 |
0,050 |
5055,4 |
|
Linden |
0,52 |
1860,9 |
792,6 |
12,3 |
9,40 |
8,25 |
2,58 |
1,199 |
1,563 |
0,558 |
0,136 |
0,102 |
0,043 |
2689,6 |
|
Birch |
0,45 |
1632,8 |
541,0 |
17,8 |
23,81 |
4,30 |
20,12 |
1,693 |
1,350 |
0,373 |
0,163 |
0,105 |
0,081 |
2243,6 |
|
Aspen |
0,58 |
2100,7 |
781,4 |
12,4 |
5,70 |
9,19 |
12,99 |
1,352 |
1,854 |
0,215 |
0,069 |
0,143 |
0,469 |
2926,5 |
|
Poplar |
1,63 |
4759,3 |
1812,0 |
18,1 |
8,19 |
17,18 |
15,25 |
1,411 |
1,737 |
0,469 |
0,469 |
0,273 |
0,498 |
6634,8 |
|
Alder black |
0,50 |
1212,6 |
599,6 |
131,1 |
15,02 |
4,10 |
5,08 |
2,335 |
1,596 |
0,502 |
0,251 |
0,147 |
0,039 |
1972,4 |
|
Gray alder |
0,43 |
1623,5 |
630,3 |
30,6 |
5,80 |
6,13 |
9,35 |
2,059 |
1,457 |
0,225 |
0,198 |
0,152 |
0,026 |
2309,8 |
|
Bird cherry |
0,45 |
1878,0 |
555,6 |
4,56 |
11,49 |
4,67 |
1,599 |
1,287 |
0,347 |
0,264 |
0,124 |
0,105 |
2466,0 |
|
All tree species, based on the content of ash elements in their wood, are combined into two large clusters (Fig. 1). The first, headed by Scots pine, includes black alder, aspen and balsam poplar (Berlin), and the second includes all other species, led by spruce and bird cherry. A separate subcluster consists of light-loving species: silver birch and Siberian larch. The smooth elm stands apart from them. The greatest differences between clusters No. 1 (pine) and No. 2 (spruce) are noted in the content of Fe, Pb, Co and Cd (Fig. 2).
Figure 1 - Dendrogram of the similarity of tree species based on the ash composition of their wood, constructed using the Ward method using a matrix of normalized data
Figure 2 - The nature of the differences between woody plants belonging to different clusters according to the ash composition of their wood
Conclusions.
1. Most of all the wood of all tree species contains calcium, which is the basis of the cell membrane. This is followed by potassium. There is an order of magnitude less iron, manganese, strontium and zinc in wood. Ni, Pb, Co and Cd close the rank series.
3. Tree species growing within the same floodplain biotope differ significantly from each other in the efficiency of their use nutrients. The most effective use of soil potential is Siberian larch, 1 kg of whose wood contains 7.4 times less ash than poplar wood, the most environmentally wasteful species.
4.High consumption property minerals A number of woody plants can be used in phytomelioration when creating plantations on technogenically or naturally polluted lands.
List of sources used
1. Adamenko, V.N. Chemical composition tree rings and the state of the natural environment / V.N. Adamenko, E.L. Zhuravleva, A.F. Chetverikov // Dokl. Academy of Sciences of the USSR. - 1982. - T. 265, No. 2. - P. 507-512.
2. Lyanguzova, I.V. Chemical composition of plants under atmospheric and soil pollution / I.V. Lyanguzova, O.G. Devil // Forest ecosystems and atmospheric pollution. - L.: Nauka, 1990. P. 75-87.
3. Demakov, Yu.P. Variability of the content of ash elements in wood, bark and needles of Scots pine / Yu.P. Demakov, R.I. Vinokurova, V.I. Talantsev, S.M. Shvetsov // Forest ecosystems in a changing climate: biological productivity, monitoring and adaptation technologies: materials international conference with elements of a scientific school for youth [Electronic resource]. - Yoshkar-Ola: MarSTU, 2010. P. 32-37. http://csfm.marstu.net/publications.html
4. Demakov, Yu.P. Dynamics of the content of ash elements in the annual rings of old-growth pines growing in floodplain biotopes / Yu.P. Demakov, S.M. Shvetsov, V.I. Talantsev // Bulletin of MarSTU. Ser. "Forest. Ecology. Nature management". 2011. - No. 3. - P. 25-36.
5. Vinokurova, R.I. Specificity of the distribution of macroelements in the organs of woody plants of spruce-fir forests of the Republic of Mari El / R.I. Vinokurova, O.V. Lobanova // Bulletin of MarSTU. Ser. "Forest. Ecology. Nature management." - 2011. - No. 2. - P. 76-83.
6. Akhromeyko A.I. Physiological justification for creating sustainable forest plantations / A.I. Akhromeiko. – M.: Forest industry, 1965. – 312 p.
7. Remezov, N.P. Consumption and circulation of nitrogen and ash elements in the forests of the European part of the USSR / N.P. Remezov, L.N. Bykova, K.M. Smirnova.- M.: MSU, 1959. – 284 p.
8. Rodin, L.E. Dynamics of organic matter and biological cycle of ash elements and nitrogen in the main types of vegetation of the globe / L.E. Rodin, N.I. Bazilevich. – M.-L.: Nauka, 1965. -
9. Methodology for measuring the gross content of copper, cadmium, zinc, lead, nickel, manganese, cobalt, chromium using atomic absorption spectroscopy. – M.: FGU FCAO, 2007. – 20 p.
10. Methods of biogeochemical research of plants / Ed. A.I. Ermakova. – L.: Agropromizdat, 1987. – 450 p.
11. Afifi, A. Statistical analysis. Computer approach / A. Afifi, S. Eisen. - M.: Mir, 1982. - 488 p.
12. Factor, discriminant and cluster analysis / J. Kim, C. Muller, U. Klekka, etc. - M.: Finance and Statistics, 1989. - 215 p.
The calorific value of a wood substance of any species and any density in an absolutely dry state is determined by the number 4370 kcal/kg. It is also believed that the degree of rottenness of wood has virtually no effect on the calorific value.
There are concepts of volumetric calorific value and mass calorific value. The volumetric calorific value of firewood is a rather unstable value, depending on the density of the wood and, therefore, on the type of wood. After all, each rock has its own density; moreover, the same rock from different areas can differ in density.
It is most convenient to determine the calorific value of firewood by mass calorific value depending on humidity. If the humidity (W) of the samples is known, then their calorific value (Q) can be determined with a certain degree of error using a simple formula:
Q(kcal/kg) = 4370 – 50 * W
Based on moisture content, wood can be divided into three categories:
- room-dry wood, humidity from 7% to 20%;
- air-dried wood, humidity from 20% to 50%;
- driftwood, humidity from 50% to 70%;
Table 1. Volumetric calorific value of firewood depending on humidity.
| Breed | Calorific value, kcal/dm3, at humidity, % | Calorific value, kW h/m 3, at humidity, % | ||||
|---|---|---|---|---|---|---|
| 12% | 25% | 50% | 12% | 25% | 50% | |
| Oak | 3240 | 2527 | 1110 | 3758 | 2932 | 1287 |
| Larch | 2640 | 2059 | 904 | 3062 | 2389 | 1049 |
| Birch | 2600 | 2028 | 891 | 3016 | 2352 | 1033 |
| Cedar | 2280 | 1778 | 781 | 2645 | 2063 | 906 |
| Pine | 2080 | 1622 | 712 | 2413 | 1882 | 826 |
| Aspen | 1880 | 1466 | 644 | 2181 | 1701 | 747 |
| Spruce | 1800 | 1404 | 617 | 2088 | 1629 | 715 |
| Fir | 1640 | 1279 | 562 | 1902 | 1484 | 652 |
| Poplar | 1600 | 1248 | 548 | 1856 | 1448 | 636 |
Table 2. Estimated mass calorific value of firewood depending on humidity.
| Humidity degree, % | Calorific value, kcal/kg | Calorific value, kW h/kg |
|---|---|---|
| 7 | 4020 | 4.6632 |
| 8 | 3970 | 4.6052 |
| 9 | 3920 | 4.5472 |
| 10 | 3870 | 4.4892 |
| 11 | 3820 | 4.4312 |
| 12 | 3770 | 4.3732 |
| 13 | 3720 | 4.3152 |
| 14 | 3670 | 4.2572 |
| 15 | 3620 | 4.1992 |
| 16 | 3570 | 4.1412 |
| 17 | 3520 | 4.0832 |
| 18 | 3470 | 4.0252 |
| 19 | 3420 | 3.9672 |
| 20 | 3370 | 3.9092 |
| 21 | 3320 | 3.8512 |
| 22 | 3270 | 3.7932 |
| 23 | 3220 | 3.7352 |
| 24 | 3170 | 3.6772 |
| 25 | 3120 | 3.6192 |
| 26 | 3070 | 3.5612 |
| 27 | 3020 | 3.5032 |
| 28 | 2970 | 3.4452 |
| 29 | 2920 | 3.3872 |
| 30 | 2870 | 3.3292 |
| 31 | 2820 | 3.2712 |
| 32 | 2770 | 3.2132 |
| 33 | 2720 | 3.1552 |
| 34 | 2670 | 3.0972 |
| 35 | 2620 | 3.0392 |
| 36 | 2570 | 2.9812 |
| 37 | 2520 | 2.9232 |
| 38 | 2470 | 2.8652 |
| 39 | 2420 | 2.8072 |
| 40 | 2370 | 2.7492 |
| 41 | 2320 | 2.6912 |
| 42 | 2270 | 2.6332 |
| 43 | 2220 | 2.5752 |
| 44 | 2170 | 2.5172 |
| 45 | 2120 | 2.4592 |
| 46 | 2070 | 2.4012 |
| 47 | 2020 | 2.3432 |
| 48 | 1970 | 2.2852 |
| 49 | 1920 | 2.2272 |
| 50 | 1870 | 2.1692 |
| 51 | 1820 | 2.1112 |
| 52 | 1770 | 2.0532 |
| 53 | 1720 | 1.9952 |
| 54 | 1670 | 1.9372 |
| 55 | 1620 | 1.8792 |
| 56 | 1570 | 1.8212 |
| 57 | 1520 | 1.7632 |
| 58 | 1470 | 1.7052 |
| 59 | 1420 | 1.6472 |
| 60 | 1370 | 1.5892 |
| 61 | 1320 | 1.5312 |
| 62 | 1270 | 1.4732 |
| 63 | 1220 | 1.4152 |
| 64 | 1170 | 1.3572 |
| 65 | 1120 | 1.2992 |
| 66 | 1070 | 1.2412 |
| 67 | 1020 | 1.1832 |
| 68 | 970 | 1.1252 |
| 69 | 920 | 1.0672 |
| 70 | 870 | 1.0092 |
