Different types of fuel have different characteristics. This depends on the calorific value and the amount of heat released when the fuel is completely burned out. For example, the relative heat of combustion of hydrogen affects its consumption. Calorific value is determined using tables. They provide comparative analyzes of the consumption of different energy resources.

There is a huge amount of combustibles. each of which has its own pros and cons

Comparison tables

With the help of comparison tables it is possible to explain why different energy resources have different calorific values. For example, such as:

• electricity;
• methane;
• butane;
• propane-butane;
• diesel fuel;
• firewood;
• peat;
• coal;
• mixtures of liquefied gases.

Propane is one of the popular types of fuel

Tables can demonstrate not only, for example, the specific heat of combustion of diesel fuel. Other indicators are also included in the comparative analysis reports: calorific value, volumetric densities of substances, price per part of conditional power supply, efficiency of heating systems, cost of one kilowatt per hour.

In this video you will learn about how fuel works:

Fuel prices

Thanks to comparative analysis reports, the prospects for using methane or diesel fuel are determined. Gas price in a centralized gas pipeline tends to increase. It may be higher even than diesel fuel. That is why the cost of liquefied petroleum gas will hardly change, and its use will remain the only solution when installing an independent gasification system.

There are several types of names for fuels and lubricants (fuels and lubricants): solid, liquid, gaseous and some other flammable materials, in which, during the heat-generating reaction of oxidation of fuels and lubricants, its chemical heat energy is converted into temperature radiation.

The heat energy released is called the calorific value of various types of fuel during complete combustion of any flammable substance. Its dependence on chemical composition and humidity is the main indicator of nutrition.

Thermal susceptibility

Determination of the OTC of fuel is carried out experimentally or using analytical calculations. The experimental determination of thermal susceptibility is carried out experimentally by establishing the volume of heat released during fuel combustion in a heat store with a thermostat and a combustion bomb.

If necessary, determine the specific heat of combustion of fuel from the table First, calculations are made according to Mendeleev's formulas. There are higher and lower grades of OTC fuel. At the highest relative heat, a large amount of heat is released when any fuel burns out. This takes into account the heat spent on evaporating the water in the fuel.

At the lowest degree of burnout, the TTC is less than at the highest degree, since in this case less evaporation is released. Evaporation occurs from water and hydrogen when fuel burns. To determine the properties of the fuel, engineering calculations take into account the lower relative calorific value, which is an important parameter of the fuel.

The following components are included in the tables of the specific heat of combustion of solid fuels: coal, firewood, peat, coke. They include the values ​​of the GTC of solid flammable material. The names of fuels are entered in the tables alphabetically. Of all solid forms of fuels and lubricants, coking, hard coal, brown and charcoal, as well as anthracite, have the greatest heat transfer capacity. Low productivity fuels include:

• wood;
• firewood;
• powder;
• peat;
• combustible shale.

Indicators of alcohol, gasoline, kerosene, and oil are entered in the list of liquid fuels and lubricants. The specific heat of combustion of hydrogen, as well as various forms of fuel, is released with the unconditional combustion of one kilogram, one cubic meter or one liter. Most often, such physical properties are measured in units of work, energy and the amount of heat released.

Depending on the degree to which the OTC of fuel and lubricants is high, this will be its consumption. This competence is the most significant parameter of the fuel, and this must be taken into account when designing boiler installations using different types of fuel. Calorific value depends on humidity and ash content, as well as from flammable ingredients such as carbon, hydrogen, volatile combustible sulfur.

SG (specific heat) of burnout of alcohol and acetone is much lower than classic motor fuel and lubricants and it is equal to 31.4 MJ/kg; for fuel oil this figure ranges from 39-41.7 MJ/kg. The indicator of combustion efficiency of natural gas is 41-49 MJ/kg. One kcal (kilocalorie) is equal to 0.0041868 MJ. The caloric content of different types of fuel differs from each other in terms of burnout. The more heat any substance gives off, the greater its heat transfer. This process is also called heat transfer. Liquids, gases and hard particles take part in heat transfer.

Recently, due to the regular increase in the price of natural gas, the issue of both installation and conversion/modernization of heating systems to alternative (renewable) energy sources, such as coal, firewood, pellets, solar and wind energy, has become relevant.

In this section we will focus on solid fuel boilers.

Depending on the type of fuel, they can be divided into solid fuel boilers (fuel - coal, wood) and pellet boilers (fuel - pellets). In turn, solid fuel boilers are made of cast iron and steel. Each of them is designed to burn a specific type of fuel.

In cast iron boilers, the main type of fuel is coal. Therefore, the rated power of such boilers according to the passport, as a rule, is indicated based on the combustion of coal in cast iron boilers. But, in addition to coal, cast iron boilers can operate on wood and briquettes. But in this case, you need to understand that the rated power of the bute boiler is somewhat less than that stated in the manufacturer’s passport.

Steel boilers are designed for burning brown coal and wood. As a rule, the rated power of such boilers is indicated based on the use of brown coal as fuel. When using wood, depending on its calorific value, the rated power of a steel boiler may differ slightly. Brown coal as a fuel is, as a rule, widespread in Europe (Germany, Poland, etc.) due to its fairly large deposits in this area. In view of the fact that brown coal is not relevant for Ukraine, wood should be taken as a basis.

Since we are talking about the calorific value of solid fuel, I propose to consider this concept and compare different types of fuel according to their calorific value.

Specific calorific value of fuel is a physical quantity that shows how much heat is released during the complete combustion of fuel weighing 1 kg or volume 1 m3. The specific heat of combustion is measured in J/kg (J/m3) or calorie/kg (calorie/m3). To experimentally measure this quantity, calorimetric methods are used.

The higher the specific heat of combustion of the fuel, the lower the specific fuel consumption at the same value of the coefficient of performance (efficiency) of the boiler.

The table below shows the main types of boiler fuel used in everyday life, common in Ukraine.

This table gives a distinctive idea of ​​the maximum possible level of that energy, which is often called the specific heat of combustion for dry (when it makes sense to talk about it) fuels.

Also, from the values ​​​​presented in the table, you can determine how much the rated power of the boiler will change depending on the type of fuel used. So, for example, if the rated power of a boiler using unprocessed brown coal is 20 kW, then if oak is used as fuel, the rated power of the same boiler will decrease to 17.7 kW.

Any fuel, when burned, releases heat (energy), quantified in joules or calories (4.3 J = 1 cal). In practice, to measure the amount of heat released during fuel combustion, they use calorimeters - complex laboratory devices. The heat of combustion is also called calorific value.

The amount of heat obtained from burning fuel depends not only on its calorific value, but also on its mass.

To compare substances by the amount of energy released during combustion, the specific heat of combustion is more convenient. It shows the amount of heat generated during the combustion of one kilogram (mass specific heat of combustion) or one liter, cubic meter (volume specific heat of combustion) of fuel.

The units of specific heat of combustion of fuel accepted in the SI system are kcal/kg, MJ/kg, kcal/m³, MJ/m³, as well as their derivatives.

The energy value of the fuel is determined precisely by the value of its specific heat of combustion. The relationship between the amount of heat generated during the combustion of fuel, its mass and specific heat of combustion is expressed by a simple formula:

Q = q m, where Q is the amount of heat in J, q is the specific heat of combustion in J/kg, m is the mass of the substance in kg.

For all types of fuel and most combustible substances, the values ​​of the specific heat of combustion have long been determined and compiled into tables, which are used by specialists when calculating the heat released during the combustion of fuel or other materials. There may be slight discrepancies in different tables, which are obviously explained by slightly different measurement techniques or different calorific values ​​of similar combustible materials extracted from different deposits.

Coal has the highest energy intensity among solid fuels - 27 MJ/kg (anthracite - 28 MJ/kg). Charcoal has similar indicators (27 MJ/kg). Brown coal has a much lower calorific value - 13 MJ/kg. It also usually contains a lot of moisture (up to 60%), which, when evaporated, reduces the total heat of combustion.

Peat burns with a heat of 14-17 MJ/kg (depending on its condition - crumbled, pressed, briquette). Firewood dried to 20% humidity releases from 8 to 15 MJ/kg. At the same time, the amount of energy received from aspen and birch can vary almost twice. Pellets from different materials give approximately the same indicators - from 14 to 18 MJ/kg.

Liquid fuels differ much less in their specific heat of combustion than solid fuels. Thus, the specific heat of combustion of diesel fuel is 43 MJ/l, gasoline - 44 MJ/l, kerosene - 43.5 MJ/l, fuel oil - 40.6 MJ/l.

The specific heat of combustion of natural gas is 33.5 MJ/m³, propane - 45 MJ/m³. The most energy-intensive gaseous fuel is hydrogen gas (120 MJ/m³). It is very promising for use as fuel, but to date no optimal options for its storage and transportation have been found.

Comparison of energy intensity of different types of fuel

When comparing the energy value of the main types of solid, liquid and gaseous fuels, it can be established that one liter of gasoline or diesel fuel corresponds to 1.3 m³ of natural gas, one kilogram of coal - 0.8 m³ of gas, one kg of firewood - 0.4 m³ of gas.

The heat of combustion of a fuel is the most important indicator of efficiency, but the breadth of its distribution in areas of human activity depends on the technical capabilities and economic indicators of use.

Different types of fuel (solid, liquid and gaseous) are characterized by general and specific properties. General properties of fuel include specific heat of combustion and humidity, specific properties include ash content, sulfur content (sulfur content), density, viscosity and other properties.

The specific heat of combustion of a fuel is the amount of heat that is released during complete combustion of \(1\) kg of solid or liquid fuel or \(1\) m³ of gaseous fuel.

The energy value of a fuel is primarily determined by its specific heat of combustion.

The specific heat of combustion is denoted by the letter \(q\). The unit of specific heat of combustion is \(1\) J/kg for solid and liquid fuels and \(1\) J/m³ for gaseous fuels.

The specific heat of combustion is experimentally determined using rather complex methods.

Table 2. Specific heat of combustion of some types of fuel.

Solid fuel

Liquid fuel

Gaseous fuel

(under normal conditions)

From this table it is clear that the specific heat of combustion of hydrogen is the highest, it is equal to \(120\) MJ/m³. This means that with the complete combustion of hydrogen with a volume of \(1\) m³, \(120\) MJ \(=\)\(120\) ⋅ 10 6 J of energy is released.

Hydrogen is one of the high-energy fuels. In addition, the product of hydrogen combustion is ordinary water, unlike other types of fuel, where the combustion products are carbon dioxide and carbon monoxide, ash and furnace slag. This makes hydrogen the most environmentally friendly fuel.

However, hydrogen gas is explosive. In addition, it has the lowest density compared to other gases at the same temperature and pressure, which creates difficulties with the liquefaction of hydrogen and its transportation.

The total amount of heat \(Q\) released during complete combustion of \(m\) kg of solid or liquid fuel is calculated by the formula:

The total amount of heat \(Q\) released during complete combustion of \(V\) m³ of gaseous fuel is calculated by the formula:

Humidity (moisture content) of the fuel reduces its calorific value, as the heat consumption for evaporation of moisture increases and the volume of combustion products increases (due to the presence of water vapor).
Ash content is the amount of ash formed during the combustion of minerals contained in fuel. Mineral substances contained in fuel reduce its calorific value, since the content of combustible components decreases (the main reason) and the heat consumption for heating and melting the mineral mass increases.
Sulfur content (sulfur content) refers to a negative factor in fuel, since its combustion produces sulfur dioxide gases that pollute the atmosphere and destroy the metal. In addition, the sulfur contained in the fuel partially passes into the smelted metal and welded glass melt, reducing their quality. For example, for melting crystal, optical and other glasses, you cannot use fuel containing sulfur, since sulfur significantly reduces the optical properties and color of the glass.

Substances of organic origin include fuels that, when burned, release a certain amount of thermal energy. Heat production must be characterized by high efficiency and the absence of side effects, in particular, substances harmful to human health and the environment.

For ease of loading into the firebox, wood material is cut into individual elements up to 30 cm long. To increase the efficiency of their use, the firewood must be as dry as possible and the combustion process must be relatively slow. In many respects, wood from hardwoods such as oak and birch, hazel and ash, and hawthorn are suitable for heating premises. Due to the high resin content, increased burning rate and low calorific value, coniferous trees are significantly inferior in this regard.

It should be understood that the value of the calorific value is affected by the density of wood.

It is a natural material of plant origin, extracted from sedimentary rock.

This type of solid fuel contains carbon and other chemical elements. There is a division of material into types depending on its age. Brown coal is considered the youngest, followed by hard coal, and anthracite is older than all other types. The age of a combustible substance also determines its moisture content, which is more present in young material.

During the combustion of coal, environmental pollution occurs, and slag is formed on the boiler grates, which to a certain extent creates an obstacle to normal combustion. The presence of sulfur in the material is also an unfavorable factor for the atmosphere, since in the air space this element is converted into sulfuric acid.

However, consumers should not fear for their health. Manufacturers of this material, taking care of private customers, strive to reduce the sulfur content in it. The heating value of coal can vary even within the same type. The difference depends on the characteristics of the subspecies and its mineral content, as well as the geography of production. As a solid fuel, not only pure coal is found, but also low-enriched coal slag, pressed into briquettes.

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.

Types of fuel are determined depending on the material from which they are processed:

• round timber of trees of any species;
• straw;
• peat;
• sunflower husk.

Among the advantages that fuel pellets have, it is worth noting the following qualities:

• environmental friendliness;
• inability to deform and resistance to fungus;
• easy storage even outdoors;
• uniformity and duration of combustion;
• relatively low cost;
• Possibility of use for various heating devices;
• suitable granule size for automatic loading into a specially equipped boiler.

Briquettes

Briquettes are solid fuels that are in many ways similar to pellets. For their manufacture, identical materials are used: wood chips, shavings, peat, husks and straw. During the production process, raw materials are crushed and formed into briquettes by compression. This material is also an environmentally friendly fuel. It is convenient to store even outdoors. Smooth, uniform and slow combustion of this fuel can be observed both in fireplaces and stoves, and in heating boilers.

The types of environmentally friendly solid fuel discussed above are a good alternative for generating heat. Compared to fossil sources of thermal energy, which have a negative impact on the environment when burned and are, moreover, non-renewable, alternative fuels have clear advantages and a relatively low cost, which is important for certain categories of consumers.

At the same time, the fire hazard of such fuels is much higher. Therefore, it is necessary to take some safety measures regarding their storage and the use of fire-resistant materials for walls.

Liquid and gaseous fuels

As for liquid and gaseous flammable substances, the situation is as follows.