Coal combustion temperature in a boiler and furnace: properties of different types of fuel

Chemical process

After entering the chamber, gradual smoldering of the firewood occurs.
This process occurs due to the presence in the firebox of a sufficient amount of oxygen gas that supports combustion. As the smoldering process occurs, a sufficient amount of heat is released and excess liquid is converted into steam. The smoke released during the reaction goes to the secondary processing compartment, where it burns completely and heat is released. A charcoal kiln performs several important functional tasks. With its help, charcoal is formed, and a comfortable temperature is maintained in the room.

But the process of obtaining such fuel is quite delicate, and with the slightest delay, complete combustion of the wood is possible. It is necessary to remove charred pieces from the oven at a certain time.

Types and grades of coal

Coal is classified according to many parameters (geography of extraction, chemical composition), but from a “domestic” point of view, when buying coal for use in furnaces, it is enough to understand the labeling and the possibility of use in ThermoRobot.

According to the degree of coalification, three types of coal are distinguished: brown

,
stone
and
anthracite.
The following coal designation system is used:
Grade
= (
grade)
+ (
size class).
In addition to the main grades given in the table, intermediate grades of coal are also distinguished: DG (long-flame gas), GZh (gas fatty), KZh (coke fatty), PA (semi-anthracite), brown coals are also divided into groups. Coking grades of coal (G, coke, Zh, K, OS) are practically not used in thermal power engineering, since they are a scarce raw material for the coke-chemical industry. According to the size class (size of pieces, fractions), graded coal is divided into:

In addition to graded coal, there are combined fractions and screenings available for sale (PK, KO, OM, MS, SSh, MSSh, OMSSh). The size of coal is determined based on the smaller value of the finest fraction and the larger value of the largest fraction indicated in the name of the coal grade. For example, the OM fraction (M - 13–25, O - 25-50) is 13–50 mm.

In addition to the above-mentioned types of coal, you can find coal briquettes on sale, which are pressed from low-enriched coal slurry.

How coal burns

Coal consists of two flammable components: volatiles

and
solid (coke) residue
.

During the first stage of combustion, volatile substances are released; When there is an excess of oxygen, they burn quickly, producing a long flame but little heat.

After this, the coke residue burns out; the intensity of its combustion and ignition temperature depend on the degree of coalification, that is, on the type of coal (brown, hard, anthracite). The higher the degree of carbonization (the highest is for anthracite), the higher the ignition temperature and heat of combustion, but the lower the combustion intensity.

Coal grades D, G

Due to the high content of volatile substances, such coal flares up quickly and burns out quickly. Coal of these grades is available and suitable for almost all types of boilers, however, for complete combustion, this coal must be supplied in small portions so that the released volatile substances have time to completely combine with oxygen in the air. Complete combustion of coal is characterized by a yellow flame and clear flue gases; incomplete combustion of volatile substances produces a purple flame and black smoke. To effectively burn such coal, the process must be constantly monitored; this operating mode is implemented in the Termorobot automatic boiler room.

Coal grade A

It is more difficult to light, but it burns for a long time and produces much more heat. Coal can be loaded in large batches, since they burn mainly coke residue and there is no mass release of volatile substances. The blowing mode is very important, since if there is a lack of air, combustion occurs slowly, it may stop, or, on the contrary, an excessive increase in temperature, leading to heat loss and burnout of the boiler.

Everyone knows that fuel use plays a huge role in our lives. The fuel is used in almost every branch of modern industry. Fuel derived from oil is especially often used: gasoline, kerosene, diesel fuel and others. Combustible gases (methane and others) are also used.

Carbon

Carbon

Carbon is a non-metallic element of group IV of the periodic table D.I. Mendeleev, is the most important part of all organic substances in nature.

General characteristics of group IVa elements

From C to Pb (from top to bottom in the periodic table) there is an increase in: atomic radius, metallic, basic, reducing properties. Electronegativity, ionization energy, and electron affinity decrease.

Of the elements of group IVa, carbon and silicon are non-metals, germanium, tin and lead are metals.

The electronic configurations of these elements are similar, since they are in the same group (main subgroup!), the general formula ns 2 np 2:

• C - 2s 2 2p 2
• Si - 3s 2 3p 2
• Ge - 4s 2 4p 2
• Sn - 5s 2 5p 2
• Pb - 6s 2 6p 2

Natural compounds

In nature, carbon occurs in the form of the following compounds:

• Allotropic modifications - graphite, diamond, fullerene
• MgCO3 - magnesite
• CaCO3 - calcite (chalk, marble)
• CaCO3*MgCO3 - dolomite

Receipt

Carbon is obtained during the pyrolysis of hydrocarbons (pyrolysis - heating without access to oxygen). The production of carbon compounds: wood and coal is also used.

Chemical properties

When heated, carbon reacts with many non-metals: hydrogen, oxygen, fluorine.

2C + O2 → (t) 2CO (carbon monoxide is a product of incomplete oxidation of carbon, formed when there is a lack of oxygen)

C + O2 → (t) CO2 (carbon dioxide is a product of complete oxidation of carbon, formed when there is a sufficient amount of oxygen)

Reactions with metals

When heated, carbon reacts with metals, exhibiting its oxidizing properties. Let me remind you that metals can only take positive oxidation states.

Ca + C → CaC2 (calcium carbide, CO carbon = -1)

Al + C → Al4C3 (aluminum carbide, CO carbon -4)

Obviously, the degree of oxidation of carbon in combination with different metals may differ.

Carbon is a good reducing agent. With its help, the metallurgical industry copes with the task of obtaining pure metals from their oxides:

Carbon reduces not only metals from their oxides, but also nonmetals in a similar way:

SiO2 + C → (t) Si + CO

It can also reduce its own oxide:

The well-known reaction of interaction of coal with water vapor, also called gasification of coal, peat, shale, is extremely important in industry:

Reactions with acids

In reactions with acids, carbon acts as a reducing agent:

Carbon monoxide II - CO

Carbon monoxide II is a product of incomplete oxidation of carbon. Non-salt-forming oxide. This extremely dangerous substance is often formed during fires in confined spaces, or when a car is warmed up in a garage.

Dissolving in the blood, carbon monoxide (which has a 300 times greater affinity for hemoglobin than oxygen) easily outcompetes oxygen and takes its place in red blood cells. Carbon monoxide poisoning is often fatal.

In industry, carbon monoxide is produced by the reduction of carbon monoxide IV or gasification of coal (t = 1000 °C).

In the laboratory, carbon monoxide is obtained from the decomposition of formic acid in the presence of sulfuric acid:

Completely oxidizes to carbon dioxide in reaction with oxygen, reducing metal oxides.

FeO + CO → Fe + CO2

Formation of carbonyls - extremely toxic substances.

Carbon monoxide IV - CO2

Product of complete oxidation of carbon. Refers to acidic oxides, corresponds to carbonic acid H2CO3. Colorless gas, odorless.

In industry, carbon dioxide is obtained from the decomposition of limestone, during the production of alcohol, and from the alcoholic fermentation of glucose.

In laboratory conditions, the reaction of chalk (marble) with hydrochloric acid is used.

Carbon dioxide is formed when organic substances burn:

Reaction with water

As a result of the reaction with water, unstable carbonic acid is formed, which immediately breaks down into water and carbon dioxide.

Reactions with basic oxides and bases

During reactions with bases and basic oxides, carbon dioxide forms salts of carbonic acid: medium - carbonates (with an excess of base), acidic - bicarbonates (with an excess of acidic oxide).

2KOH + CO2 → K2CO3 + H2O (base-acid oxide ratio 2:1)

KOH + CO2 → KHCO3 (base-acid oxide ratio 1:1)

When heated, it is capable of oxidizing metals to their oxides.

Zn + CO2 → (t) ZnO + CO

Pyrolysis furnace: charcoal burning temperature

Charcoal is not a fossil at all. This fuel is produced by humans in special pyrolysis furnaces. The process of obtaining it is quite simple and consists of processing wood by pyrolysis. Simply put, you need to remove all moisture from the wood.

During the entire smoldering process, a lot of heat is generated, and moisture evaporates and evaporates. The smoke that is produced is recycled in a special compartment and burns completely there, generating heat.

Stages of producing charcoal:

• The critical stage is drying;
• The most important is pyrolysis;
• Then - calcination;
• And finally - cooling.

A charcoal-fired pyrolysis furnace can heat both small and large houses

Charcoal begins to ignite at a temperature of 100 - 200 degrees, and flares up to 800 - 900. When it burns, a sufficient amount of heat is released that can warm the room.

Production technology

On an industrial scale, the product is made from waste from wood processing enterprises. Therefore, furnace installations are located in close proximity to them. The main essence of the technology comes down to the maximum preliminary purification of raw materials from various kinds of organic and inorganic components, and then subsequent heat treatment under special conditions - so that the output is almost pure carbon.

The production cycle consists of the following main 4 stages:

• Pre-drying of raw materials. The procedure proceeds at 1500C until the material loses most of the moisture that is harmful for subsequent stages.
• Pyrolysis. In a closed chamber with a lack of oxygen, dried wood languishes at a heating level of about 200-3000C. As a result, cellulose decomposes into carbon and gases.
• Calcination. Due to the hard-melting resins remaining in the structure, the raw material is subjected to heat treatment up to 6000C - which transforms all excess components into a gaseous state and allows them to be separated from the base material.

Source stroitelcentr.ru

• Recovery. The procedure is carried out by cooling the raw material to ambient temperature.

Note! In production, charcoal is made in a special installation, equipped with separate compartments for each stage - however, this does not mean that this procedure is not feasible for domestic purposes, for example, for barbecue. To make it at home, you will need an ordinary metal barrel or just a pit.

Open mining method

The main advantage of open-pit coal mining is its relative safety. The thing is that it is used only if the depth of the rock is no more than 100 meters. In other words, a shaft is not created that could collapse during an accident. The extraction process itself is carried out according to the following procedure.

First you need to remove the top layer of soil that covers the rock. This layer is called overburden, and the method of removing it is called stripping. This procedure, depending on the type of soil, is carried out using bulldozers, draglines, rotary excavators or scrapers. After the soil layer has been removed, you can proceed to crushing the rock itself. For this, crushers, water cannons, bulldozers and other equipment are used. If the rock in a coal deposit is too dense, then in rare cases, drilling and blasting of coal is used. This mining method usually covers a fairly large area.

As for the disadvantages of the method, they are as follows:

• Firstly, causing significant harm to the environment at the mining site.
• Secondly, all the rock that is mined in this way contains a large amount of harmful impurities in its composition.

The main advantages of open-pit coal mining, in addition to safety, are high speed and cost-effectiveness.

Coal

In terms of formation time, this type of coal comes next after brown coal. It has a black or gray-black color, as well as a resinous, sometimes metallic sheen.

The moisture content of hard coal is significantly less than brown coal: only 1-12%. The content of volatile substances in coal varies greatly depending on the location of mining. It can be minimal (from 2%), but can reach values ​​similar to brown coal (up to 48%). The elemental composition is as follows:

From this we can conclude that the chemical formula of hard coal consists of more carbon than that of brown coal. This makes this type of coal a higher quality fuel.

Activated carbon

Activated carbon is a type of carbon with a high specific pore surface area, which makes it even more absorbent than wood. The raw materials used for its production are charcoal and coal, as well as coconut shells. The starting material is subjected to an activation process. Its essence is to open clogged pores using high temperature, electrolyte solutions or water vapor.

During the activation process, only the structure of the substance changes, therefore the chemical formula of activated carbon is identical to the composition of the raw materials from which it was made. The moisture content of activated carbon depends on the specific pore surface area and is usually less than 12%.

Source

"Coal plus water"

The substances that will be discussed further are, in their composition, like a combination of coal and water, for which they were called carbohydrates
.
(Note that since 1844, when this term was proposed, many carbohydrates have become known that do not correspond to this formula, but the name has remained; the other common name for this class of compounds is sugars
.) The composition of the vast majority of such compounds can be expressed by the general formula C
n
(H20)
m
.

But how do carbon atoms and water molecules combine in one molecule? Let's consider this issue using the example of one of the most common carbohydrates - glucose.

So, let's try to “establish” the structure of the glucose molecule. Its formula is C6H12O6. If you act on glucose with acetic anhydride, then five molecules of anhydride react per one molecule of glucose and an ester is formed. Hence the conclusion - a glucose molecule contains five hydroxyl groups, i.e. it is a five-atomic alcohol.

We will further investigate glucose. Glucose is a reducing agent, gives a silver mirror reaction (reduces silver salts), and upon careful oxidation itself forms monobasic gluconic acid. Hence the second conclusion: the glucose molecule contains an aldehyde group.

If you treat glucose with hydrogen iodide, you get 2-iodohexane. The third conclusion is that the glucose molecule has a normal, i.e., unbranched hydrocarbon skeleton. This data is sufficient to construct the structural formula of glucose. This is a five-hydroxy aldehyde alcohol:

Reactions confirming the structure of glucose (D - forms)

However, let's continue our experiments. Let's try to perform other reactions characteristic of the aldehyde group. Thus, aldehydes form compounds with bisulfite NaHSO3 and give color with fuchsulfuric acid. Glucose does not give such reactions. Let's heat glucose with methyl alcohol in the presence of dry hydrogen chloride. An ether is formed, but only one of the five hydroxyls participates in the reaction. This means that this hydroxyl is somehow different from the others.

All these seemingly incomprehensible features can be explained in this way. Glucose exists in two forms: aldehyde and cyclic. In the first form, an aldehyde group is clearly present, it reduces silver, and it is oxidized into a carboxyl group. However, the proportion of this form in the solution is small, and therefore there is no reaction with either bisulfite or fuchsulfurous acid. At the same time, in the cyclic form, one of the hydroxyls has a special, privileged position - it is attached to a carbon atom, which is connected to another oxygen atom. It is this hydroxyl that forms a derivative with methyl alcohol. This hydroxyl has another interesting feature - it can be located below or above the six-membered ring (we assume that the ring is always located so that the oxygen entering the ring is in the far right corner from us). The first form is denoted by the letter α, the second by β.

Source

Creating optimal conditions for combustion

Due to the high temperature, all internal elements of the furnace are made of special refractory bricks. Fireproof clay is used for their installation. If special conditions are created, it is quite possible to obtain a temperature in the furnace exceeding 2000 degrees. Each type of coal has its own flash point.

After reaching this indicator, it is important to maintain the ignition temperature by continuously supplying excess oxygen to the firebox

Among the disadvantages of this process, we highlight heat loss, because part of the released energy will escape through the pipe. This leads to a decrease in the temperature of the firebox. In the course of experimental studies, scientists were able to establish the optimal excess amount of oxygen for various types of fuel. Thanks to the choice of excess air, you can count on complete combustion of the fuel. As a result, you can count on minimal losses of thermal energy.

Formation and origin of coal seams

The appearance of coal on Earth dates back to the distant Paleozoic era, when the planet was still in the development stage and had a completely alien appearance to us. The formation of coal seams began approximately 360,000,000 years ago. This happened mainly in the bottom sediments of prehistoric reservoirs, where organic materials accumulated over millions of years.

Simply put, coal is the remains of the bodies of giant animals, tree trunks and other living organisms that sank to the bottom, decayed and were pressed under the water column. The formation process of deposits is quite long, and it takes at least 40,000,000 years to form a coal seam.

Comparative table of indicators

The table presents the values ​​of the mass specific heat of combustion of liquid, solid, and gaseous fuels.

The table shows that hydrogen has the highest TST indicators of all substances, not just gaseous ones. It belongs to high-energy fuels.

The product of hydrogen combustion is ordinary water. The process does not emit furnace slag, ash, carbon dioxide and carbon dioxide, which makes the substance an environmentally friendly combustible. But it is explosive and has a low density, so this fuel is difficult to liquefy and transport.

Examples of problem solving

ω (X) = n × Ar (X) / M (HX) × 100%

Let's calculate the mass fraction of phosphorus in the compound:

ω(P) = 100% - ω(Cl) = 100% - 77.5% = 22.5%

Let us denote the number of moles of elements included in the compound as “x” (phosphorus) and “y” (chlorine). Then, the molar ratio will look like this (the values ​​of relative atomic masses taken from D.I. Mendeleev’s Periodic Table are rounded to whole numbers):

x:y = ω(P)/Ar(P) : ω(Cl)/Ar(Cl);

x:y= 22.5/31 : 77.5/35.5;

x:y= 0.726 : 2.183 = 1 : 3

This means that the formula for combining phosphorus with chlorine will be PCl3. This is phosphorus(III) chloride.

ω (X) = n × Ar (X) / M (HX) × 100%

Let's calculate the mass fraction of oxygen in the compound:

ω (P) = 100% - ω(K) - ω(Mn) = 100% - 24.7% - 34.8% = 40.5%

Let us denote the number of moles of elements included in the compound as “x” (potassium), “y” (manganese) and “z” (oxygen). Then, the molar ratio will look like this (the values ​​of relative atomic masses taken from D.I. Mendeleev’s Periodic Table are rounded to whole numbers):

x:y:z = ω(K)/Ar(K) : ω(Mn)/Ar(Mn) : ω(O)/Ar(O);

x:y:z= 24.7/39 : 34.8/55 : 40.5/16;

x:y:z= 0.63:0.63:2.53 = 1:1:4

This means that the formula for the compound of potassium, manganese and oxygen will be KMnO4. This is potassium permanganate.

Source

Features of different types of fuel

Let's consider the two main, most common types of solid fuel raw materials - firewood and coal. Firewood contains a significant amount of moisture, so the moisture first evaporates, which will require a certain amount of energy. After the moisture evaporates, intense combustion of the wood begins, but, unfortunately, the process does not last long.

Therefore, to maintain it, regular addition of firewood to the firebox is required. The ignition temperature of wood is about 300°C.

In terms of the amount of heat generated and the duration of combustion, coal is superior to wood. Depending on the age of the fossil material, the mineral is divided into types:

• brown;
• stone;
• anthracite.

Brown coals

Among fossil coals, the youngest are brown coals. The fuel got its name from its brown color. This type of fuel is characterized by a large amount of volatile impurities and high moisture content - up to 40%. In this case, the amount of pure carbon can reach 70%.

Due to high humidity, brown coal has a low combustion temperature and low heat transfer. Fuel ignites at 250°C, and the combustion temperature of brown coal reaches 1900°C. The calorific value is approximately 3600 kcal/kg.

As an energy carrier, brown coal in its natural form is inferior to firewood, so it is rarely used for stoves and solid fuel units in private homes. But briquetted fuel is in steady demand.

Brown coals

Brown coal in briquettes is a fuel that has undergone special preparation. By reducing humidity, its energy efficiency increases. The heat transfer of briquetted fuel reaches 5000 kcal/kg.

Stone coals

Hard coals are older than brown coals; their deposits are located at a depth of up to 3 km. In this type of fuel, the content of pure carbon can reach 95%, and volatile impurities - up to 30%. This energy carrier contains no more than 12% moisture, which has a positive effect on the thermal efficiency of the mineral.

The combustion temperature of coal under ideal conditions reaches 2100°C, but in a heating furnace the fuel is burned at a maximum of 1000°C. The heat transfer of coal fuel is 7000 kcal/kg. It is more difficult to ignite - it requires heating up to 400°C to ignite.

Coal energy is most often used to heat residential buildings and other buildings.

Stone wall

Anthracite

The oldest solid fossil fuel, which contains practically no moisture and volatile impurities. The carbon content in anthracite exceeds 95%.

The specific heat transfer of the fuel reaches 8500 kcal/kg - this is the highest indicator among coals. Under ideal conditions, anthracite burns at 2250°C. It ignites at a temperature of at least 600°C - this is an indicator for the lowest calorie types. Ignition requires the use of wood to create the necessary heat.

Characteristics of anthracite

Anthracite is primarily an industrial fuel. Its use in a furnace or boiler is irrational and expensive. In addition to high heat transfer, the advantages of anthracite include low ash content and low smoke.

Anthracite

Anthracite is the oldest form of fossil coal. It is characterized by a dark black color and has a characteristic metallic sheen. This is the best coal in terms of the amount of heat it releases during combustion.

The amount of moisture and volatile substances in it is very small. About 5-7% for each indicator. And the elemental composition is characterized by an extremely high carbon content:

• Carbon over 90%.
• Hydrogen 1-3%.
• Oxygen 1-1.5%.
• Nitrogen 1-1.5%.
• Sulfur up to 0.8%.

More coal is contained only in graphite, which is a further stage of anthracite coalification.

Coal options

In winter, the issue of heating residential premises is especially relevant. Due to the systematic increase in the cost of coolants, people have to look for alternative options for generating thermal energy. The best way to solve this problem is to select solid fuel boilers that have optimal performance characteristics and retain heat well.

The specific heat of combustion of coal is a physical quantity that shows how much heat can be released during the complete combustion of a kilogram of fuel

In order for the boiler to operate for a long time, it is important to select the correct fuel for it. The specific heat of combustion of coal is high (22 MJ/kg), so this type of fuel is considered optimal for efficient boiler operation

The combustion temperature of charcoal is much higher, so this fuel option is an excellent alternative to conventional firewood. We also note the excellent heat transfer rate, the duration of the combustion process, and low fuel consumption. There are several types of coal, related to the specifics of mining, as well as the depth of occurrence in the bowels of the earth: hard, brown, anthracite.

Coal has an ignition temperature of 400 degrees. Moreover, the calorific value of this type of coal is quite high, so this type of fuel is widely used for heating residential premises.

Anthracite has maximum efficiency. Among the disadvantages of such fuel, we highlight its high cost. The combustion temperature of this type of coal reaches 2250 degrees. No solid fuel extracted from the bowels of the earth has such an indicator.

Burning rules

When a consumer becomes familiar with the combustion temperature of a particular coal, he needs to take into account that manufacturers indicate only those figures that are relevant for ideal conditions. Of course, it is simply impossible to recreate the necessary parameters in an ordinary household boiler or oven. Modern heat generators made of metal or brick are simply not designed for such high temperatures, since the main coolant in the system can quickly boil. That is why the combustion parameters of a particular fuel are determined by its combustion mode.

In other words, it all depends on the intensity of the air supply. Both fossil and charcoal heat a room well if the oxygen supply level reaches 100%. To restrict the air flow, you can use a special damper/gate. This approach makes it possible to create the most favorable combustion conditions for filled fuel (up to 950˚C).

If coal is used in a solid fuel boiler, then boiling of the coolant must not be allowed. The main danger is that the safety valve may simply not work, which can lead to a large explosion. In addition, a mixture of water and hot steam has a bad effect on the functionality of the circulation pump. Experts have developed two most effective methods that allow you to control the combustion process:

1. Crushed or powdered fuel must enter the boiler exclusively in a dosed volume (the same scheme applies as in pellet devices).
2. The main energy carrier is loaded into the firebox, after which the intensity of the air supply is adjusted.

Making at home

The simplest ways to make coal at home are:

1. In a metal container.
2. In the hole.

Let's look at the features of each of them.

In a barrel

To prepare using this method, you will need a metal barrel with a volume of 100-200 liters with fairly thick walls. Moreover, if the container was previously used for petroleum products or other toxic material, it must first be thoroughly burned.

Source khabaroff.com

Instructions for obtaining coal are as follows:

• Fire-resistant bricks are laid edgewise on the bottom of the barrel (for a 200-liter version, 6 pieces will be required).
• A small fire is made from dry shavings or wood chips between them.
• A metal grating is installed on top of the bricks.
• Next, wood is laid out in small sections of 0.3-0.5 m to the top.
• When the flame begins to come out, the container is closed with a steel sheet, maintaining a small gap at the edge.

Video example of making coal in a barrel:

• When bluish smoke appears, indicating that the material is burning, the container is closed completely.
• After cooling, the finished product is unloaded.

Advice! To speed up the process, small holes are made at the bottom of the barrel. You can also force the air flow through them using a special blower.

In the hole

To make coals for barbecue or other household use, you can use a simpler method:

• A cylindrical hole is dug in the ground.
• The bottom is well compacted.
• A fire is lit for kindling.
• Next, the wood is laid gradually - as it burns out.
• When filled to the top, the hole is covered with branches, leaves, grass and a layer of soil.
• The finished product is dug out after 48 hours and, if necessary, sifted.

Important! When making charcoal for barbecues at home, it is important to choose well-dried and bark-free wood. It also needs to be first sawed and chopped into small pieces. However, in any case, the quality of the product will be slightly lower than in factory production.

Video instructions for making charcoal in a pit:

Coal: varieties and characteristics

Coals primarily differ in origin. Charcoal, which is obtained by burning wood, as well as fossil fuels are used as an energy source.

Fossil coals are fuels created by nature. They consist of the remains of ancient plants and bitumen masses, which underwent a number of transformations in the process of sinking underground to great depths. The transformation of starting substances into effective fuel took place at high temperatures and in conditions of oxygen deficiency under the earth. Fossil fuels include brown and hard coals, as well as anthracite.

Brown coals

Among fossil coals, the youngest are brown coals. The fuel got its name from its brown color. This type of fuel is characterized by a large amount of volatile impurities and high moisture content - up to 40%. In this case, the amount of pure carbon can reach 70%.

Due to high humidity, brown coal has a low combustion temperature and low heat transfer. Fuel ignites at 250°C, and the combustion temperature of brown coal reaches 1900°C. The calorific value is approximately 3600 kcal/kg.

As an energy carrier, brown coal in its natural form is inferior to firewood, so it is rarely used for stoves and solid fuel units in private homes. But briquetted fuel is in steady demand.

Brown coals

Brown coal in briquettes is a fuel that has undergone special preparation. By reducing humidity, its energy efficiency increases. The heat transfer of briquetted fuel reaches 5000 kcal/kg.

Stone coals

Hard coals are older than brown coals; their deposits are located at a depth of up to 3 km. In this type of fuel, the content of pure carbon can reach 95%, and volatile impurities - up to 30%. This energy carrier contains no more than 12% moisture, which has a positive effect on the thermal efficiency of the mineral.

The combustion temperature of coal under ideal conditions reaches 2100°C, but in a heating furnace the fuel is burned at a maximum of 1000°C. The heat transfer of coal fuel is 7000 kcal/kg. It is more difficult to ignite - it requires heating up to 400°C to ignite.

Coal energy is most often used to heat residential buildings and other buildings.

Stone wall

Anthracite

The oldest solid fossil fuel, which contains practically no moisture and volatile impurities. The carbon content in anthracite exceeds 95%.

The specific heat transfer of the fuel reaches 8500 kcal/kg - this is the highest indicator among coals. Under ideal conditions, anthracite burns at 2250°C. It ignites at a temperature of at least 600°C - this is an indicator for the lowest calorie types. Ignition requires the use of wood to create the necessary heat.

Characteristics of anthracite

Anthracite is primarily an industrial fuel. Its use in a furnace or boiler is irrational and expensive. In addition to high heat transfer, the advantages of anthracite include low ash content and low smoke.

Charcoal – Gosstandart

The main part of charcoal is carbon. Charcoal is similar in composition to coal, in which carbon is also the main element. In fact, both charcoal and hard coal are based on wood. Only in coal did wood decompose for many centuries with a limited supply of oxygen, and charcoal is charred wood that was partially burned with a lack of oxygen.

During the charring process, the composition of charcoal leaves most of the moisture, sulfur, phosphorus and oxygen. At the same time, losses of carbon and hydrogen are minimal. Ash also remains, which is not removed during charring. Moreover, the higher the combustion temperature, the less carbon remains in the composition. So, for example, at a temperature of 450°C the level of carbon is 85%, and hydrogen is 3%. The phosphorus content depends on the type of wood: birch charcoal contains 0.037%, spruce charcoal contains 0.017%, and pine charcoal contains 0.016%.

With a low oxygen content and at normal temperature, charcoal has the ability to add oxygen. Therefore, one of its properties is the tendency to spontaneous combustion. Humidity at the end of the charring process is 2-4%, but it increases significantly during storage - up to 7-15%. The calorific value of charcoal produced at a temperature of 400-500°C is 7000-8100 Kcal/kg. For comparison, the calorific value of coal is 7200-8600 Kcal/kg.

Charcoal is very porous. Moreover, the ratio of pore volume to piece volume depends on the type of wood: for birch charcoal it is 72%, and for spruce charcoal it is 80%. The weight of coal also depends on the type of wood: 1 m3 of bulk dry spruce coal weighs about 100 kg, the same volume of birch coal weighs about 180 kg, and beech coal weighs about 195 kg.

There is a distinction between the apparent density of charcoal and the true density. Apparent density is the weight of the coal as it is, with all its pores. It also depends on the type of wood: dense wood produces dense coal, and soft wood produces soft coal. So, spruce charcoal has an apparent density of 260 kg/m2, aspen charcoal has an apparent density of 290 kg/m2, and birch charcoal has an apparent density of 380 kg/m2. The true density increases with the charring temperature. For example, at a temperature of 350°C, the density of coal is 1500 kg/m

2. If the temperature increases to 1500°C, then the density increases to 1869 kg/m2.

High-quality charcoal has a shiny black color with a blue tint. The fracture shows that it has well preserved the structure of the wood. And its entire surface is covered with cracks. From these cracks you can determine the time of charring (the more there are, the faster it passed). When struck, pieces of coal make a fairly loud sound. The charcoal itself is easy to light and produces a lot of heat.

There are two types of charcoal: black and white. White coal chars at low temperatures. Only at the end is it sharply increased to 1000°C. The hot pieces are taken out of the flame and covered with a mixture of sand, ash and earth to cool. It is this mixture that makes the surface of the coal white. White coal has no bark; it is burned off during the charring process. Whereas black coal usually retains its bark. The surface of white coal is smooth and hard. In Japan, white coal is created from holm or iron oak. This type of coal is very hard and burns for a long time, so it is considered the best.

There are charcoal made from mixed hardwood and hardwood (this type of wood is preferred). They are also classified according to the size of the pieces: 6-12 mm - small and more than 25 mm - large. Coal is also divided according to GOST: A – highest grade, B – first grade.

The process of producing charcoal is quite simple: it is burned in a closed space without access to air. This operation is called pyrolysis. When treated at high temperatures, wood produces: charcoal, as well as liquid and gaseous products (acetone, methanol, acetic acid, resins, etc.). But, despite its simplicity, the pyrolysis process must be strictly regulated. Otherwise, the amount of charcoal obtained will be less, and the charcoal itself will be fine and smell like resin. The main rule: during production there should be no air access to the process. By the way, the best charcoal is considered to be the one that is burned at a temperature not exceeding 400-500°C.

Modern enterprises that produce charcoal are equipped with special retort furnaces. The entire process takes place directly in such a furnace. It is preceded by a firebox, followed by a chamber in which the pyrolysis process occurs. The next part is the drying chamber. On both sides of the furnace there are retorts, on the left with prepared firewood, and on the right with cooling coal. An exhaust pipe completes the installation. The pyrolysis and coal drying chambers are separated, so the heat is used more efficiently. Moreover, the flame is formed due to the combustion of volatile products, and not due to the combustion of firewood. Volatile products that are released during combustion are transferred back to the firebox and burned there.

According to statistics, about 9 million tons are currently produced in the world. charcoal per year. Moreover, most of this amount is produced by Brazil - about 7.5 million tons. Russia's share in the total amount of coal produced is 100 thousand tons. in year. We use imported charcoal from China, Ukraine and Belarus. And the amount of coal consumed per person per year is only 100 grams. The leader in charcoal consumption is Japan - about 60 kg per person per year. In European countries this figure is approximately 20 kg.

The use of charcoal lies in many areas:

- the metallurgical industry uses it as a reducing agent, that is, to separate metal from ore, and also to protect the cast metal from oxidation. The valuable quality of coal is the minimum percentage of sulfur and phosphorus in its composition.

— non-ferrous metallurgy and the production of ferroalloys use it as a component of the charge.

- the radio electronics industry uses it for the production of crystalline materials

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Coal combustion - What is the formula for coal combustion? — 22 answers



Coal burning

In the Other Education section, answer the question What is the formula for burning coal? given by the author Maria Nasonova, the best answer is Coal + oxygen and fire = Ayyyyyyy hot!!!

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Reply from CoBRA79922C+O2—>2CO just like that!!

Answer from Irina Zarechkova Finding out the chemical formula of coal is the same as figuring out the chemical formula of borscht. Coal (coals, they are very different and have different compositions) is a mixture of different chemicals, mainly high molecular weight polycyclic aromatic compounds (arenes) with a high carbon content. Coal is not pure carbon with a crystalline lattice, as many people believe. The most obvious way to think of coal is as solidified oil. After all, oil is also a mixture of hydrocarbons, even with a higher carbon content in relation to coal, but no one claims that oil is liquid carbon in its pure form. Thus, if you are interested in the composition of a specific grade of coal, then look for information on arenes (anthracene C14H10 is one of the largest molecules, consisting of three benzene rings, a large amount of carbon in it is noticeable even from the simplified formula; naphthalene C10H8 - two benzene rings; benzene C6H6 - one benzene ring; as well as their modifications and other variants). In addition to polycyclic hydrocarbons, coals contain varying amounts of water and mineral impurities. Based on hydrocarbon content, coals are divided into brown (65-70% carbon, up to 50% volatiles and about 43% water), hard coal (about 80% carbon, up to 32% volatiles and up to 12% water), anthracite (up to 96% water). carbon, less than 8% volatiles). Anthracite - this ancient, shiny and dense coal, which even gives its name to noble black shades of paint, is already similar to what coal is generally considered to be: pure carbon, well, slightly contaminated with impurities. Anthracites are formed at elevated pressure and temperature at greater depths, therefore their composition is closest to graphite, which is precisely an allotropic modification of carbon in its pure form (with a crystal lattice) and can also be considered coal.

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Formula of coal in chemistry

Definition and formula of coal

The structure of the carbon atom is shown in Fig. 1. In addition to charcoal, carbon can exist in the form of a simple substance: diamond or graphite, belonging to the hexagonal and cubic systems, coke, soot, carbyne, polycumulene graphene, fullerene, nanotubes, nanofibers, astralen, etc.

Rice. 1. Structure of the carbon atom.

Chemical formula of coal

The chemical formula of coal is C. It shows that the molecule of this substance contains one carbon atom (Ar = 12 amu). Using the chemical formula, you can calculate the molecular weight of coal:

M(C) = Mr (C) × 1 mol = 12.0116 g/mol

Structural (graphic) formula of coal

More visual is the structural (graphical) formula of coal . It shows how atoms are connected to each other inside a molecule (Fig. 2).

Rice. 2. Structure of allotropic modifications of carbon: a) diamond; b – graphite; c) – fullerene.

Electronic formula

An electronic formula showing the distribution of electrons in an atom across energy sublevels is shown below:

6С 1s22s22p2

It also shows that carbon belongs to the elements of the p-family, as well as the number of valence electrons - there are 4 electrons in the outer energy level (2s22p2).

Examples of problem solving

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History of the formation of coal and its types

The entire process of coal formation can be divided into two main stages: the formation of peat and the actual process of coalification - the conversion of peat into coal.

Peat formed on vast water-covered areas from plant remains of varying degrees of decomposition. Some plants rotted completely to a gel-like state, while others retained their cellular structure. Their remains accumulated at the bottom of reservoirs, which gradually turned into swamps. A prerequisite for the formation of peat is the absence of oxygen. There was little oxygen under the water column; during the decomposition of the residues, hydrogen sulfide, methane and carbon dioxide were released, which contributed to the hardening of the residues. Peat formed.

History of coal. It all started many millions of years ago

But not all peatlands were converted to coal. The carbonization process requires: high pressure, high temperature and a long period of time. Depending on the presence of these conditions, the formation of coal occurred or not. First, the peat was carried over by sedimentary rocks, which increased the pressure and temperature inside the peat layer. Under such conditions, brown coal was formed - the first stage of coalification. In some areas, strata displacement occurred, causing brown coal seams to sink (some of the discovered deposits are at depths of more than 6,000 meters). In some places, these processes were accompanied by the rise of magma and volcanic eruptions. High pressure, lack of oxygen and high temperatures contributed to the fact that there was less and less moisture and natural gases in brown coal, and more and more carbon. As water and gases were displaced, brown coal turned into bituminous coal, then, in the presence of high temperatures, into anthracite. The main difference between brown coal and hard coal: brown coal contains more moisture and natural gases and less carbon, which affects the amount of heat released during combustion.

The age of coal is determined by the vegetation remains it contains. Sometimes the prints are very clear

Today, the age of coal deposits is determined by plant remains. The oldest ones date back to the Carboniferous period (345-280 million years ago). During this period, most of the coal basins of North America (eastern and central USA), central and western Europe, southern Africa, China, and India were formed. In Eurasia, most of the coal deposits were formed in the Permian period, some of the small coal basins in Europe date back to the Triassic period. The activity of coal formation increases towards the end of the Jurassic and in the Cretaceous. Around this time, deposits were formed in eastern Europe, the American Rocky Mountains, Indochina and central Asia. Later, mainly brown coals and peat deposits were formed.

Types of coal

Coal is classified according to its moisture, natural gas and carbon content. As the amount of carbon increases, its calorific value increases. The less moisture and volatile substances (gases), the better it tolerates storage and transportation.

Lignite is coal at the first stage of coalification. It differs from brown coal in the smaller amount of water (45%) in its composition and greater heat generation. The structure is fibrous, the color is from brown to black (higher quality). Most often used in the energy sector (at thermal power plants), it is rarely used for heating private houses, as it is poorly stored and has a low calorific value in conventional stoves.

Coal. Lignite. Has a loose layered structure

Subbitominous coal is black in color, has a less pronounced fibrous structure, has a higher calorific value compared to lignite, and has a lower moisture content (30%). It crumbles during transportation and dissipates in the open air. When burned, it emits 5-6 kW/kg. It is used both in the energy sector and in housing and communal services for heating.

Bituminous coal has the highest calorific value and does not lose its qualities during transportation and storage. When burning, it releases 7-9 kW/kg of heat. Some of its types are used for coking.

Anthracite is pitch-black coal. It has the highest hydrocarbon content. It is difficult to light, but it burns for a long time and without soot, and produces a large amount of heat (more than 9 kW/kg). It is anthracite that is most often used for heating.

Anthracite. It has a deep black color and a shiny surface.

Chemical formula of coal, the process of its formation and use in industry

Coal in its various modifications can have a color from brown to black. It is a good fuel, so it is used in converting thermal energy into electrical energy. It is formed as a result of the accumulation of plant mass and the passage of physical and chemical processes in it.

Various modifications of coal

The accumulation of wood pulp in marshy soil leads to the formation of peat, which is a precursor to coal. The formula of peat is quite complex; in addition, there is no specific stoichiometric ratio for this type of coal. Dry peat consists of carbon, hydrogen, oxygen, nitrogen and sulfur atoms.

Further, under prolonged exposure to high temperatures and high pressures resulting from geological processes, peat undergoes a number of the following coal modifications:

1. Brown coal or lignite.
2. Bitumen.
3. Coal.
4. Anthracite.

The end product of this chain of transformations is solid graphite or graphite-like carbon, the formula of which is pure carbon C.

Carboniferous wood

About 300 million years ago, during the Carboniferous period, most of the land on our planet was covered with giant fern forests. Gradually these forests died out, and the wood accumulated in the marshy soils on which they grew. Large amounts of water and dirt created barriers to oxygen penetration, so the dead wood did not decompose.

For a long time, newly dead wood covered older layers, the pressure and temperature of which gradually increased. Associated geological processes eventually led to the formation of coal deposits.

Carbonation process

The term “carbonization” implies metamorphic transformations of carbon associated with an increase in the thickness of woody layers, tectonic movements and processes, as well as an increase in temperature depending on the depth of the strata.

An increase in pressure primarily changes the physical properties of coal, the chemical formula of which remains unchanged. In particular, its density, hardness, optical anisotropy and porosity change. An increase in temperature changes the very formula of coal towards an increase in carbon content and a decrease in oxygen and hydrogen. These chemical processes lead to an increase in the fuel properties of coal.

Coal

This modification of coal is very rich in carbon, which leads to a high heat transfer coefficient and determines its use in the energy industry as the main fuel.

The formula of coal consists of bituminous substances, the distillation of which allows the separation of aromatic hydrocarbonates and a substance known as coke, which is widely used in metallurgical processes. In addition to bitumen compounds, coal contains a lot of sulfur. This element is the main source of air pollution when burning coal.

Coal is black in color and burns slowly, producing a yellow flame. Unlike brown coal, its calorific value is higher and amounts to 30-36 MJ/kg.

The formula of coal has a complex composition and contains many compounds of carbon, oxygen and hydrogen, as well as nitrogen and sulfur. Such a variety of chemical compounds became the beginning of the development of a whole direction in the chemical industry - carbochemistry.

Currently, coal has been practically replaced by natural gas and oil, but two important areas of its use continue to exist:

• the main fuel at thermal power plants;
• a source of coke produced by oxygen-free combustion of coal in closed blast furnaces.

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Conclusions and useful video on the topic

About the calorific value of different types of wood. Comparison of indicators per m3 and kg.

TCT is the most important thermal and operational characteristic of a fuel. This indicator is used in various areas of human activity: heat engines, power plants, industry, home heating and cooking.

Calorific values ​​help to compare different types of fuel according to the degree of energy released, calculate the required mass of fuel, and save on costs.

Do you have anything to add or have questions about the calorific value of different types of fuel? You can leave comments on the publication and participate in discussions - the contact form is in the lower block.

Pellets

Pellets (fuel granules) are solid fuels created industrially from wood and plant waste: shavings, bark, cardboard, straw.

The raw material, crushed to dust, is dried and poured into a granulator, from where it comes out in the form of granules of a certain shape. To add viscosity to the mass, a plant polymer, lignin, is used. The complexity of the production process and high demand determine the cost of pellets. The material is used in specially equipped boilers.