The correct heating of the heating device (wood or coal stove of any type) affects not only the temperature in the house and the consumption of firewood, but also the life of the stove. Overheating, that is, burning too much firewood, leads to the destruction of the masonry of the brick oven and an increase in the likelihood of a fire in the room where the metal stove is installed. Poor air supply causes soot deposits on the walls of the heater, roughness and chimney, which often leads to a fire. After all, when the oven door is opened, enough oxygen is supplied to the red-hot soot to ignite it. As a result, the masonry of the walls weakens, the stove and chimney collapse, and there is also a high probability of a fire. Excess air leads to cooling internal surfaces ovens and rough, which reduces efficiency.
How is wood or coal converted into heat?
The temperature in the furnace loaded with wood or coal reaches 900–1200 degrees, but the surface temperature of a well-heated furnace is 50–70 degrees. The temperature of the rough, which is used to increase the efficiency of the heater, is 45–60 degrees. At the same time, the temperature of the smoke coming out of the chimney opening is 150–250 degrees. How does the high-temperature flame in the furnace turn into heat radiated from the walls of the furnace?
During combustion, carbon from coal or wood is oxidized, releasing large amounts of heat and open fire. This reaction occurs not only in the lower, but also in the upper part of the firebox, because the tongues of fire just appear due to the oxidation of gaseous carbon. Depending on the design of the furnace, the temperature at the outlet of the furnace can be 600–800 degrees (furnaces with a rough or channel chimney) or 200–300 degrees in bell-shaped ones.
This is due to the fact that in bell-type furnaces, the firebox is part of the bell, which absorbs heat from hot flue gases and, when heated, radiates heat from the outer walls. In channel stoves, the same function is performed by chimneys (channels), which are heated by hot smoke chimneys and store heat, gradually radiating into the room through the outer walls. What determines the efficiency of heat removal and the amount of stored thermal energy? The efficiency of heat extraction from flue gases depends on:
- speed of movement of gases through the chimney;
- their temperatures;
- states internal walls stoves and chimneys;
- moisture content of firewood;
- free air flow.
The faster the smoke moves through the hood or channels, the more efficiently and evenly it heats the stone or brick. At a low speed of smoke movement, the internal surfaces located next to the firebox become very hot, however, the farther from the firebox, the weaker the heating. That is why, with the wrong firebox (smoldering with a small air flow), one part of the furnace overheats with insufficient heating of the other part. This mode is acceptable only for heated stoves with coarse, because it allows you to maintain the temperature all night, but even in this case, a strong temperature drop cannot be avoided. different parts heater and rough.
Frequent combustion in the mode of lack of oxygen (smoldering) leads to the formation of a large amount of soot, which settles on the walls of the cap and channels. In addition to the risk of fire, it also reduces the heating rate of the furnace body or coarse, which reduces the efficiency of the heating device and increases the consumption of firewood or coal. Equally important is the condition of the wood. Raw firewood can give a strong heat with a sufficient supply of fresh air, but, in addition to this heat, there will be a lot of water vapor and free air in the smoke, which will lead to a decrease in the temperature of the gases moving through the hood or channels. The same problem arises when the additional loading of firewood or coal is too long.
The only way to reduce the impact of this problem is to build a heater with a gas view, which is sometimes called a dry joint. The gas view separates the smoke into hot and cold streams. The hot stream goes into the cap or channels, giving them heat, and the cold one immediately enters the chimney and exits. Most often, a dry seam is used in Kuznetsov furnaces and other bell-type furnaces. heating devices, but they are also suitable for channel stoves if a direct channel for cold smoke is provided.
What kind of firewood is best for the firebox
If you have the opportunity to choose, then these types of firewood are best suited for heating:
- birch;
- alder;
- acacia.
After the tree has been cut down, sawn into chocks and chopped into logs, the firewood must be dried to a moisture content of 10–13%. To do this, finished firewood must be kept in a dry, ventilated garage for one to two years. During this time excess moisture will come out and the logs will acquire the desired moisture content. If you dry the wood in logs or chocks, then the drying process will take 3-5 years. Therefore, dry firewood from less calorific species will give more heat than raw firewood from more calorific species.
How to prepare the stove for the heating season
Preparing for heating season begins with cleaning the chimney, the boletus, the rough and the stove itself. During cleaning, soot deposits are removed from the walls and bottom of the channels, which impede the movement of flue gases and create a fire hazard. After that, they carefully check the condition of all metal parts, such as doors, grates, blizzards and blowers. If any of these parts is defective, it is changed. Then check the condition of the outer surfaces of the furnace and rough. Cracks are expanded and sealed with clay-based masonry mortar. After making sure that everything is in order, they check the draft, for this they bring a burning match to the open door and blower.
With an open blizzard, the flame should noticeably deviate into the furnace. If there is no draft or it is weak (the fire almost does not deviate), then the integrity of the boletus and the chimney is checked, most likely, there are gaps or cracks somewhere in them. It is also possible for individual bricks to fall out. If you can’t restore traction yourself, you need to invite an experienced craftsman.
How to load the stove with fuel
Most properly designed and built furnaces are designed for a single charge of fuel. If the power of the furnace is less than necessary for the normal heating of all heat-radiating surfaces, then it is necessary to add fuel 1-2 times. Therefore, the power of the furnace, as well as the size of the furnace, directly affect the way the fuel is loaded. The larger the firebox, the larger firewood you can use. At the same time, it is necessary to remember - optimal dimensions a log of 6x6 cm (width and thickness), and the length should be slightly shorter than the length of the firebox.
Much smaller logs will give more heat, but will burn out less time, because of which the body of the furnace and the rough will not have time to absorb the right amount of energy. A strong increase in the size of the logs will reduce the intensity of the fire and the emission of flue gases, but they will burn noticeably longer.
Therefore, ready-made firewood is laid in one direction as close to each other as possible, filling the firebox to the top edge of the door. Kindling can be laid both from below (in this case it will be necessary to make a chamber from logs) and from above. The first method is suitable for firewood of any humidity, the second only for dry ones. For kindling, paper, bark and wood are used. A small layer of finely planed (not thicker than one mm) chips of bark and wood is poured onto dry paper.
Instead of paper, dry fuel works well - it will not ignite from an accidental spark and gives enough heat to ignite large chips. Moreover, these chips are not laid close to each other, but so that air can freely move between them. A layer of chips 3–5 mm thick is laid above them. The next layer is laid from chips 10–15 mm thick. If the firewood is dry, then three layers are enough; to ignite damp firewood, a fourth layer of wood planks 30–40 mm thick is needed.
Do not use any light oil products (gasoline, kerosene, etc.) to ignite the stove, but liquids based on paraffins can be used. In this case, only the two lower layers of kindling are poured with liquid, and not more than one cm 3 per furnace. Used machine oil can be used in the same way.
If one bookmark of firewood is not enough, then after burning to the coals, you must quickly open the door and throw in a few chocks, and then immediately close the door. It is undesirable to keep the door open for more than fifteen seconds, because this will lead to a decrease in the temperature in the firebox and a change in the mode of burning firewood. Therefore, for the second bookmark, it is better to use thick chocks or whole logs, the size of which does not exceed 10x10 cm. Thicker firewood can only be used in stoves high power heating area over 150 m 2 .
If the draft is weak or the house is very cold, then at first only kindling from three layers is loaded into the firebox. After the kindling flares up and warms up the chimneys and chimney, the fourth layer of kindling is loaded into the furnace, and after 5 minutes, firewood is laid on the burning kindling, trying not to knock down the fire. Moreover, firewood is laid in batches of 4–6 pieces, after which the door is closed and the next batch is laid in 5 minutes. This method of loading the furnace provides maximum efficiency with weak traction and a cold house. With normal draft and regular firing, the stove is fired only after full load firewood.
In coal-fired ovens, coal is first poured into the shaft, then kindling is placed on top, over which 5–7 medium-sized chocks are folded. You can also first load firewood with top kindling into the shaft, and after burning it to golden coals, fill the shaft with coal in 3-5 (with a frequency of 3-5 minutes) steps.
How to light and set up the stove
Before lighting the stove, all blizzards and blowers are fully opened, and the draft is also checked. Some heaters have a door for heating the chimney. In such ovens, this door is opened and ignited paper is inserted there, which will warm the air in the chimney and increase the draft in the furnace. After the paper burns out, the door is closed and the kindling is immediately ignited. In stoves without such a door, the ignition method depends on the moisture content of the wood. If the firewood is dry, then they are put into the oven, after which the kindling is ignited, if the firewood is damp, then the kindling is first kindled, then the firewood is added as described above.
After the firewood has flared up, in 2-3 steps they block the blizzard of the summer operation of the furnace, through which the flue gases pass directly into the chimney. It is not possible to close this door at one time, because the chimney draft may not be enough to immediately ensure the normal movement of smoke through cold ducts, due to which carbon monoxide will begin to come out through the slightest cracks and fill the air in the room. Bell-type furnaces are devoid of this drawback, because their design does not provide for any summer mode work.
After the closing of the summer blizzard, the furnace gradually enters the operating mode and warms up its body and rough. From time to time it is necessary to listen to the sound of the stove, if it starts to buzz, then the draft is too strong (this happens during severe frost and wind), so the blower is covered by a third. If the buzz has not stopped, then the blower is covered by another third, and the blizzard is also covered by 1–3 cm.
In Russian stoves, after the closing of the summer blizzard, the draft is regulated, focusing on both the sound and the color of the flame - blue fire indicates too strong draft and excess oxygen, and red indicates insufficient draft. Under normal thrust, the fire will yellow color with small red patches. Due to the lack of a blower in the Russian stove, draft is regulated only by a blizzard. In metal ovens with a glass door, they are guided by the color of the flame (should be yellow with barely noticeable red patches) and work with a normal sound without a loud buzz.
Optimal firing time
The optimal firing time depends on the design of the furnace and the roughness. For metal heaters, which are a modern analogue of a potbelly stove, the burning time can be any, because they cannot store heat and have an extremely low efficiency. Firebox time metal furnaces with a brick rough connected to them depends on the power of the heating device. If the furnace power is sufficient to warm up the rough, then the furnace time is 1-2 hours. Optimum time for burning wood brick ovens, regardless of their design, is 1–1.5 hours, coal 2–2.5 hours. This is caused by the properties of brick and masonry mortar.
Despite the fact that the coefficient of thermal expansion of these materials is very close, when overheated, they expand and increase in linear dimensions unequally, which causes a rupture of the masonry mortar and the appearance of cracks in the masonry. Each slot is an influx of additional air, which cools the flue gases and reduces the efficiency of the heater. Therefore, it is highly undesirable to reheat the stove, it is better to heat it 2 times a day. If, even with such a furnace mode, it is cold in the house, then it is necessary either to insulate the house, or to make a more powerful or efficient stove that can generate more heat.
Firebox Completion
IN wood stoves the blower must be closed after all the firewood has turned into coals and low (2-5 cm) flames will flicker above them. Further afterburning of these coals will lead to a decrease in the temperature of the smoke and cooling of all channels and internal surfaces. It is necessary to detect how long it takes the firewood to burn to the state of coals and then complete the firebox in time. This will protect the heater and rough from exposure to cold air and increase their efficiency. In coal-fired ovens, during the combustion process, it is necessary to agitate the fuel with a poker 1-3 times (depending on the size and quality of the coal), so that the slag falls into the ash pan, and the air passes through the coal more easily. When the height of the tongues of fire is reduced to two or three cm, the firebox must be stopped and the blower completely closed.
In Russian stoves, the coals remaining after the firebox are either raked into a pocket intended for them, from where the flue gases go directly into the chimney, or they are pulled out and thrown into a bucket of water or taken out into the street, after which the firebox is closed with a special door to protect it from the penetration of cold air.
The closing of the gate (blizzard) depends on the type of fuel - when burning with wood, they close it, leaving a gap of 1 cm, and after 15 minutes they close it completely (in Russian stoves they close it completely immediately after removing the coals). When burning coal, they close it, leaving a gap of 2 cm, and after half an hour they cover it almost completely. It is advisable to drill a hole with a diameter of 10 mm in the blizzard valve of a coal furnace, so that half an hour after the end of the furnace, when the coal cools down and the emission of flue gases decreases sharply, it was possible to close the gate completely.
Before the next filling of fuel, it is necessary to empty the furnace from ash and remaining coals, then clean the ash pan. It is advisable to do this with fully open gates, because inside the furnace a temperature of 40–60 degrees is maintained, which is enough to warm up the chimney.
How not to heat the oven
In many villages, this type of firebox is popular, in which wood or coal slowly smolders, due to which flue gases constantly move along the rough. In this mode, the efficiency of the heater is very low, because the fuel burns with a strong lack of oxygen, which means that little heat is released and a lot of carbon is released in the form of soot, which settles on the inner walls of the smoke channels. Improper laying of wood or coal can cause soot to ignite in the channels, and this often ends in a fire that completely destroys the house.
If you properly heat the stove with wood, you can reduce fuel consumption by 15-20%, improve heat transfer and prevent increased soot formation in the chimney. From compliance with the recommendations, the service life of the furnace depends.
What kind of wood is better to heat the stove
As general rule, manufacturers indicate that for the oven better firewood non-coniferous hard rock tree. When burned, wood does not emit resins, maintains the required combustion temperature. An additional plus, minimal soot deposits on the inner walls of the chimney.It is not recommended to heat the stove with pine and spruce firewood, garbage. If necessary, peat and wood briquettes or sawdust are used as an alternative. Optimal Humidity fuel 20%, which corresponds to the annual storage of firewood in a dry room.
What type of wood is best for firewood
Wood different breeds, differs in calorific value and combustion characteristics. Therefore, when deciding what type of fuel the furnace will be fired with, the working and other characteristics of the selected firewood are taken into account:
In addition to the already listed types of wood, peat briquettes are popular. The advantage of briquettes is the absence of the need for splitting, drying and any other preparations for burning.
As an alternative to lump wood, it can be fired with sawdust. Kindling is done with firewood. After the fire has flared up, sawdust is added to the furnace at the rate of no more than 30% of the total fuel volume.
What kind of wood to heat to clean the chimney
From time to time, it is recommended to carry out preventive maintenance of the chimney, removing soot and tar deposits from the internal cavity. This is necessary for the following reasons:
Prevention of the condition of the chimney is carried out in several ways. If the deposits are small, they burn aspen firewood (similar to alder). The oven heats up well. Some craftsmen bring the combustion mode to such an intensity that there is a buzz in the pipes. In addition to firewood, special chemical briquettes are burned.
Resin burning is effective preventive measure, but does not help if deposits inside the chimney have reached critical levels. In such cases, you will need mechanical cleaning pipes.
Is it possible to heat a wood stove with charcoal
To decide what to heat, coal or firewood, you can answer a few questions:
The temperature in the oven when burning firewood is maintained at 300-350°C, rarely, the heating rises to 450°C. The combustion temperature of coal is much higher. Under certain conditions, the air in the furnace is heated up to 1000-2000°C.
Furnace rules
To reduce the consumption of firewood and optimize the combustion process, certain rules for ignition and combustion are observed. To make it easier to kindle, a few recommendations will help:- standard wood size- logs are placed in the oven, approximately 5 cm less than the length of the combustion chamber. If during the preparation of firewood, try to make logs of approximately the same size, you can greatly facilitate the process of kindling.
- Correct bookmark- the logs are stacked so that there are gaps between them for the free passage of air.
- Humidity of firewood - the stove is allowed to be heated with raw firewood, but at the same time it is released a large number of tar and smoke. Therefore, as general recommendation, there is a rule: you should heat with dry fuel, with a moisture content of 20-25%.
How to properly fire wood stove
Kindling the stove is an art. If it is wrong to kindle and maintain the fire, the temperature in the furnace will not exceed 40-50 ° C, which is not enough for heating the room.The kindling of the furnace is carried out in several stages: 
It is somewhat easier to heat with fuel briquettes. Pressed firewood is laid out on a burnt-out seed. The calorific value of briquettes is greater than that of ordinary firewood, therefore, heating will be 20-30% faster.
How to heat a stove with raw wood
The cost of high-quality dry firewood is not so much more that you can save a lot. But, if there are no other options, you can melt the stove with raw fuel.To kindle the stove with raw wood, follow the step-by-step plan:
- Firewood is chopped into small pieces.
- The seed is made from small chips.
- Gradually begin to enclose larger fractions of wood.
- After the coals have appeared, you can add ordinary logs.
Raw birch firewood, it is better not to use. When kindling, smoke and resin are released, which leads to a quick failure of the furnace and the smoke exhaust system.
How to heat a brick oven in winter
The metal furnace, equally smoothly works in the winter and in the summer. Precautions are necessary when operating a brick stove.A private bath is an unheated room, often used once every few days. During this time, the masonry has time to cool and freeze. A similar situation is observed in country houses left without heating for a long period.
The combustion temperature of firewood in the oven is at least 300°C. Dry fuel burns, heating flue gases up to 400-450°C. The temperature difference between frozen bricks and burning wood leads to cracking of the masonry and joints. As a result, after the season of operation, you will need to do overhaul brick oven.
To avoid unpleasant consequences, the furnace is carried out slowly, allowing the walls to slowly warm up. The filling of fuel should not exceed 30% of the total volume of the combustion chamber until the temperature of the masonry rises to the required level (the brick becomes warm). After that, the furnace will continue as usual.
How to heat the stove correctly so as not to burn out
Carbon monoxide is a product of the combustion of wood in smoke. At correct operation stoves, flue gases are discharged to the street through the chimney. The ingress of carbon monoxide into the room is dangerous.In order not to burn out, you will need to follow a few recommendations:
- It is forbidden to completely close the dampers and blower in order to increase the burning time of firewood.
- Before kindling, check the presence of traction.
- The furnace is heated gradually, when the chimney is heated, the draft increases.
- Regular maintenance is carried out - if necessary, the chimney is cleaned, malfunctions are eliminated.
- Use good quality dry wood.
Be especially careful when using coal. During combustion, coal requires more oxygen than wood. After the air burns out in the furnace, the draft will deteriorate, carbon monoxide will go into the room.
When can I heat the stove after masonry
It is impossible to heat the stove immediately after laying. The brick is placed on the clay mortar. Clay hardens when heated. But, when overheated, it quickly loses moisture, strength and cracks.Brickwork is initially dried. They do it like this:
- It is important to avoid dampness in the furnace and smoke channels, for this, open all doors and windows, only after that they light a fire.
- Works are carried out at least after 2-3 days after the completion of masonry work. The firebox is carried out for 0.5-1 hour not for full power. The oven is heated 2 times a day.
- As fuel, finely chopped firewood, wood chips, shavings are used. You can not drown full-fledged logs.
- The process of forced drying lasts 4-6 days.
The stove fire is not to be taken lightly. Following several simple principles, you can kindle the stove easily and safely for yourself and your loved ones.
We clean the ash pan and the grate from the ashes. This will allow air to flow better to all the firewood. With the blower tightly closed, open the oven door. If you open the door and blew together, smoke and fire will go into the house with a strong wind. Crumpled paper and newspapers should be placed on the oven grate. Then there are chips that need to be prepared in advance.
Never place flammable objects near the oven. Leaving the oven unattended for a long time is not recommended.
What type of firewood to choose is an important factor. You need to select them specifically for your oven. In some designs, they do not burn out completely. If the stove is done correctly, only a handful of ash should remain from the firewood.
What type of firewood to choose is an important factor. You need to select them specifically for your oven. In some designs, they do not burn out completely. If the stove is done correctly, only a handful of ash should remain from the firewood.
Firewood differs in heat transfer:
Birch. Logs from this tree are perhaps the leaders in popularity. Wood has a high heat transfer and surpasses all other types by 20 percent. However, it is worth excluding oak from the list, which is the leader in all respects.
Spruce, pine are also quite hot firewood, they contain a large amount of resins, due to which efficiency increases. When burning, they produce a characteristic crack, which many people like. Cooking high-quality firewood Attention: pine, birch and spruce, although they have good heat dissipation, but when burned, they form a lot of soot, so you should refrain from using them in a bath or sauna.
Aspen and alder emit little soot, but a lot of heat. Such firewood is used for heating the bath.
Oak, although it is more of a valuable species of wood, is also used for heating, in particular, its waste. It has the highest efficiency.
How to lay firewood? What kind of firewood is better for the stove, you will understand from the foregoing. Now we will talk about styling methods. This is an important factor that contributes to rapid ignition and better combustion.
So:
Firewood can simply be laid, but it is better to make the stacking a well. At the same time, gaps are made and air is better supplied to the places of combustion and contributes to this process. You can do styling while standing, with a cone up. This design contributes to the rapid ignition.
Attention! When laying wood, make sure that the firewood lies freely in the firebox. Don't stuff them in there. This will only make things worse for the combustion process. For burning, select a long wood chip and feed it to the wood, in the middle of the cone there should be paper, from which further fire will occur.
Proper kindling without blower
DETERMINING THE VOLUME OF LOADING THE FURNACE
How much to put firewood is determined by the volume of the load and the type of stove:
Furnaces that are intended for heating a room should be fully loaded. Only not to the end, it is necessary to leave a gap from the upper part of the order of 15 percent. The stove for a bath is characterized by a different approach. To begin with, small firewood and kindling material are laid out. After the material has completely ignited, a full portion of firewood should be loaded. It is recommended to load clean and chopped firewood for the stove-heater.
Before starting laying firewood, fully open the damper on the pipe and ensure the removal of exhaust gases: Check the draft in the pipe and ventilate the room. After that, carry out a complete cleaning of the grate. We cover the blower. We put kindling material on the grate, we use only dry. We put thicker firewood on top. Laying is done horizontally or crosswise. We set fire to firewood, as described above. After they flare up normally, it is necessary to partially cover the blower door. After that, we adjust the thrust using a valve in the pipe.
Attention! Do not open the damper all the way just because it burns better. Heat should not be thrown into the chimney, but on the contrary, completely warm up the furnace. The increase in heat transfer is carried out due to the minimum supply of oxygen to the place of combustion, this increases the temperature of the flue gases and heating occurs, and not heat is released. At this time, do not open the furnace door and do not add firewood. When the flue gas temperature becomes 200°C and higher, then there is no soot deposit in the duct. The fuel burns out completely. And at a lower temperature, the walls of the heating unit, on the contrary, are covered with soot.
When firing a stove, there are some rules to remember:
During the firebox, you should stir them about 3 times, this will contribute to high-quality combustion. Normal burning of the furnace is about 1.5-3.5 hours of one bookmark. It depends on the size of the combustion chamber and the temperature. environment. If there are unburned firebrands, they should be moved to the center of the grate. In this place they will burn out faster.
Attention! Many people close the valve completely early. This can only be done when the blue light above the firewood disappears. The rules for firing outdoor stoves are slightly different from the usual ones. They use a smaller firebox, at the top it is limited by a flooring in the form of a cast-iron stove, on which food is cooked.
Do not load such a firebox completely. You should leave a space from the firewood to the stove at least 15 cm. In the construction of such a stove, two entrances are used, summer and winter. In this design, the top valve must be fully open at the start of the firebox. The summer valve opens only when the internal shield does not need to be warmed up.
Proper combustion
The correctness of laying firewood and burning can be judged by several signs:
The color of the flame is straw-gold, and at the same time a rustling sound is heard with a slight crackle. If the flame is very bright and a rumble is heard in the pipe, then this indicates an excessive air supply and that it is necessary to cover the blower. If dark smoke comes out of the pipe, this indicates poor combustion of the fuel. This may be due to a lack of air flow, so the blower should be opened. What kind of wood is better to heat the stove, you can now decide for yourself, but you should not forget that you should heat the stove, which is made to warm up, at least a couple of times a day. Such a design should not overcool, this should not be allowed. If this happens, it may lose traction. Before burning, simply burn the newspaper in the firebox to begin with, and this must be done after closing the blower. At first, smoke will be released, and when stable combustion begins, this will be a signal that the draft has appeared and you can load a portion of firewood. If the oven has not been used long time you will have to do this several times.
Now you know what kind of firewood is best for the stove, and you can do everything perfectly with your own hands.
From a conversation on a building forum:
- If the stove-potbelly stove on dry wood stoked the room up to 20 degrees, then on wet wood it was barely 15 degrees. And, the burning time is the same (if you count by the number of logs). Most best option(if there is no dry firewood) - dry the fuel right next to the stove, at least for a few days. The effect is very noticeable. If there is no dry firewood at all, you have to breed it slightly dried, and then report it raw. Damp firewood burns badly, but for a long time. They heat at half the strength, however, they burn longer. Why this is so is not clear...
- The energy (heat) of combustion of wood is spent on heating the excess moisture (water) contained to the boiling point and evaporation of this water
- Third Nobel and guaranteed guarantees
Calculation of the mass calorific value of raw firewood
In order to clarify once and for all the topic of calorific value for raw and firewood, I found a calculation method on one of the forums, took out a school textbook and sat down to count.
It turned out this:
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The heat of combustion of wood is 4752.9 kcal/kg x 0.8 kg = 3802 kcal Let's calculate the heat that water (0.2 kg) will take when heated to 100 degrees, and then - to turn into steam and heat the steam to a temperature of 800 degrees: Water heating from 20 to 100 degrees: 1 kcal / kg ° C x 80 ° C x 0.2 kg = 1.6 kcal Total |
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For firewood, with a relative humidity of 40% Estimated weight of firewood 1kg, incl. The heat of combustion of wood is 4752.9 kcal/kg x 0.6 kg = 2852 kcal Let's calculate the heat that water (0.4 kg) will take when heated to 100 degrees, and then - to turn into steam and heat the steam to a temperature of 800 degrees: Water heating from 20 to 100 degrees: 1 kcal / kg ° C x 80 ° C x 0.4 kg = 3.2 kcal Total |
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For firewood, with a relative humidity of 60% Estimated weight of firewood 1kg, incl. The heat of combustion of wood is 4752.9 kcal/kg x 0.4 kg = 1901 kcal We calculate the heat that water (0.6 kg) will take when heated to 100 degrees, and then - to turn into steam and heat the steam to a temperature of 800 degrees: Water heating from 20 to 100 degrees: 1 kcal / kg ° C x 80 ° C x 0.6 kg = 4.8 kcal Total |
When analyzing the results of the calculation, the following becomes obvious:
- The mass calorific value of room-dry and freshly cut firewood varies, more than twice
- The decrease in the mass calorific value of firewood occurs mainly due to a decrease in the weight fraction of dry combustible matter per unit mass of fuel. Heat losses for heating and evaporation of water, as well as for heating water vapor, are relatively small. Accordingly, 180, 362 and 542 (kcal). Of the total figure for the mass calorific value of absolutely dry wood (4752.9 kcal / kg), this is (only) - 3.7%, 7.6% and 11.4% for relative humidity in 20%, 40% and 60%.
- However, wood with a moisture content of 60% practically does not burn. What are 11.4% of heat loss here. Obviously, this is something else. Right now, let's try to get to the bottom...
- The only reassurance is that approximately the same figures were obtained using a completely different method of wood calorific value. This suggests the plausibility of the results and the chosen path.
Yes! In mass units, some unconvincing calculation is obtained ...
And if everything is repeated for volume units?
Calculation of the volumetric calorific value of raw firewood
To calculate the volumetric calorific value of firewood of different humidity, let's take as an example oak firewood with a density of 0.81 kg / dm 3 and a calorific value of 3240 kcal / dm 3, at a moisture content of 12% (see). Suppose there is a batch of firewood with a volume of each log 1 dm 3 and weighing, respectively, 0.81 kg each (for ease of calculation). It is quite obvious that each such log will contain the same amount of dry combustible substance (0.81 kg each). Moreover, this amount of combustible substance will remain unchanged, even if some log is soaked in water for a long time. And if the amount of combustible substance is the same, and in dry, and in raw, and in wet logs, therefore, their calorific value will also be the same.
Nobel Prize for calculating the calorific value of raw firewood
The conclusion clearly draws on the Nobel Prize!
The volumetric calorific value of both raw and dry wood is the same.
In principle, the way it is, if we recall the definition for and calorific value of wood. The heat required to heat and evaporate the water contained in the wood is called the latent heat of combustion. The heat required to remove water from wood during combustion is the famous difference between absolute and operating calorific value.
In the case of volumetric calorific value (as opposed to mass), when the moisture content of firewood changes, their volume does not change. Water is simply absorbed into the voids of the wood, but the volume of the combustible wood substance does not change. Subsequently, during the burning of firewood, this water will be evaporated and removed into the atmosphere. Thus, the volumetric calorific value of raw firewood is equal to the volumetric calorific value of dry firewood minus the latent heat of combustion required to remove water from the wood.
In our case, with oak firewood:
From the absolute calorific value of dry oak wood (moisture content 0%)
4752.9 kcal / kg x 0.81 kg / dm 3 \u003d 3849 kcal / dm 3
you need to subtract the latent heat of combustion required to remove water from the wood, which is calculated based on the degree of its moisture content.
Another Nobel Prize for calculating calorific value
Let's check our correctness by the method of limit modeling of the situation.
Suppose we managed to moisten our oak log (with a volume of 1 dm 3) to such a state that it absorbed 1 dm 3 of water. Then, the wood of such a super-wet oak will be:
The heat of combustion of wood is 3849 kcal / dm 3 minus the heat that water will take (1 dm 3 \u003d 1 kg) when heated to 100 degrees, followed by evaporation and heating of the steam to a temperature of 800 degrees:
Water heating from 20 to 100 degrees: 1 kcal/kg°C x 80°C x 1 kg = 80 kcal
Vaporization: 1 kg x 539 kcal/kg = 539 kcal
Steam heating: 1kg x 700°С x 0.51kcal/kg°С = 357 kcal
Total
3849 - 80 - 539 - 357 = 2873 (kcal)
Well, it turned out to be a good result.
There is still quite a lot of calories to support combustion and evaporation of the second liter of water. It turns out that if we could moisten oak firewood to an incredibly fantastic degree so that 1dm 3 of firewood absorbed 2dm 3 of water, then even such firewood could burn. In other words, wood of any humidity should burn hot and bright, even right in the water?
Despite the absurdity of the conditions of the problem, a stupid result is also a result. In order not to undersign his own idiocy, the author will immediately stop distorting the theory of combustion and take it as an axiom:
- 1 dm 3 oak wood is enough to heat 2 liters of water to a temperature of 100°C, evaporate it and then heat the resulting steam to 700°C (assuming a hearth efficiency of 50%)
- 1 dm 3 oak firewood, 70% humidity contains approximately 0.56 liters of water. Such firewood is not able to burn on its own. Proven by practice.
Why is that?
Why does raw firewood not burn (burn badly)?
Because the wood itself is directly (does not oxidize). Burn (oxidize) only products of thermal decomposition of wood - pyrolysis. The first signs of the process of thermal decomposition of wood (pyrolysis) appear at 400...500°C. A stable pyrolysis requires a temperature of 700...900°C. To start pyrolysis, the wood must be heated to a pyrolysis temperature of external source heat (set on fire). If there is no heat loss in the high-temperature pyrolysis zone, the wood will catch fire and burn. The high-temperature pyrolysis zone will heat up neighboring wood sections and move to them. Thus, the burning of firewood will occur.
Now, our water.
Water in wood is located in pericellular and intracellular voids. That is, the water in raw wood is located directly in the high-temperature pyrolysis zone and cools it. Until the water has evaporated from the wood, it is impossible to warm it up to 400...500°C, and even more so, up to 700...900°C. Thus, the evaporation of water from the wood thickness is an obligatory process that precedes the pyrolysis of wood and the combustion of pyrolysis products. And before that, wood is just a non-combustible substance, so to speak. But, that's half the trouble...
After the water has evaporated, the water vapor mixes with the gaseous products of wood pyrolysis and cools them down. There is much more harm from water here. If in the case of water evaporation we are talking simply about heat losses, then when water vapor is mixed with gaseous pyrolysis products - we are talking about the direct loss of a precious combustible substance. Because, the combustion (oxidation) of gases occurs on a thin line between its heated volume and the surrounding air, where there is oxygen. Water vapor, mixing with combustible gases, lowers their concentration and temperature, and contributes to the removal from the combustion zone in an unburned (not oxidized) form. Thick white smoke from raw firewood is nothing more than water vapor mixed with unburned pyrolysis gases.
