Fuel is how it is burned. Methods for burning gaseous fuels. Major deposits of fossil fuels

April 18, 2011

Gaseous fuels are burned in three ways.

In the first combustion method, gas and air under low pressure are supplied simultaneously to the burner, where they are partially mixed, however, complete mixing of gas with air is completed only at the entrance to the furnace, where the mixture burns, forming a relatively short torch. Burners that partially mix gas and air are called low pressure flame burners.

Gas enters the mixing chamber 7 in a thin annular jet. The air supplied (under a pressure somewhat greater than the gas) tangentially to the body 10 by swirling jets enters the mixing chamber through the slots 8 and breaks the moving gas jet.

The gas-air mixture mixed in this way, after passing through the lined hole of the burner 9, burns in the working space of the furnace, forming a short torch.

In the second method of combustion, gas and air are fed into a special device - a mixer, in which they are completely mixed into a gas-air mixture and sent under high pressure to the burner for combustion. Combustion takes place quickly, without creating a flame in the working space of the oven.

In the third combustion method, gas is fed into the burner under high pressure, in which the required air is sucked in from the atmosphere. Mixing of gas with air takes place in an injection-type mixer built into the burner.

Burners for burning gas according to the second and third methods are called high pressure flameless burners.

"Free forging", Ya.S. Vishnevetsky

Rotary Bottom Carousel Heating Furnace Electric resistance furnaces are used to heat small billets. To heat the workpieces to a temperature of 1200-1250 ° C, furnaces with silicon carbide heaters (selite resistance elements) produced by the Electric Furnace Trust are used. Non-ferrous alloy blanks are heated in furnaces with metal heaters operating at temperatures up to 900-950 ° C. These furnaces are used ...

Electrical contact heating devices are used to heat workpieces using the resistance method. 1 - generator, 2 - inductor, 3 - heated workpiece, 4 - capacitor bank, 5 - contactor. Inductors, depending on the shape and size of the heated workpiece, are: cylindrical, oval, square and slotted. The shapes of the inductors and the location of the heated workpieces in them are shown in Fig. 1 -…

Electric resistance furnace Н75 1 - heating elements, 2 - refractory masonry, 3 - thermal insulation, 4 - door lifting mechanism, 5 - counterweight, 6 - door, 7 - lift shaft, 8 - limit switch, 9 - heel bricks, 10 - hearth plate. The essence of the method consists in supplying an electric current of industrial frequency to the ends of the workpiece (or ...

The schematic electrical diagram of heating by the resistance method is shown in Fig. A large current is supplied to the workpiece clamped in the contacts with a voltage of 5.6 to 13.6 V. The current required to heat the metal increases in proportion to the square of the diameter of the workpiece. 1 - contacts, 2 - heated workpiece, 3 - supply busbars, 4 - power transformer. As…

The main indicators when assessing the operation of furnaces are: furnace productivity, specific fuel consumption and efficiency. The productivity of the furnace is the amount of metal in kilograms that can be heated in it to a given temperature per unit of time (kg / h). Productivity depends on the number of simultaneously heated workpieces, the way they are positioned on the hearth, the size of the workpiece, steel grade, temperature, heating and ...

1 TYPES OF FUEL

Solid fuel - flammable substances, the main component of which is carbon. Solid fuels include coal and brown coal, oil shale, peat and wood. Fuel properties are largely determined by its chemical composition - the content of carbon, hydrogen, oxygen, nitrogen and sulfur. The same amounts of fuel give different amounts of heat during combustion. Therefore, to assess the quality of the fuel, its calorific value is determined, that is, the largest amount of heat released during the complete combustion of 1 kg of fuel (the highest calorific value of coal). Basically, solid fuels are used to obtain heat and other types of energy, which are spent on obtaining mechanical work. In addition, more than 300 different chemical compounds can be obtained from solid fuel with appropriate processing (distillation); processing of brown coal into valuable types of liquid fuel - gasoline and kerosene is of great importance.

Briquettes

Briquettes are solid fuels formed in the process of compressing waste from the woodworking process (shavings, chips, wood dust) as well as household waste (straw, husks), peat.

Fuel briquettes are convenient for storage, no harmful binders are used in the manufacture, therefore this type of fuel is environmentally friendly. When burning, they do not spark, do not emit foul gas, they burn evenly and smoothly, which ensures a sufficiently long combustion process in the boiler chamber. In addition to solid fuel boilers, they are used in home fireplaces and for cooking (for example, on the grill).

There are 3 main types of briquettes:

1. RUF-briquettes. Formed rectangular bricks.

2. NESTRO-briquettes. Cylindrical, can also be with holes inside (rings).

3. Rini& Kau - briquettes. Faceted briquettes (4,6,8 sides).

Advantages of fuel briquettes:

Environmentally friendly.

Long and convenient storage. Thanks to heat treatment, they are not affected by fungi. And thanks to the formation, they are conveniently used.

Long and even burning is due to the high density of the briquettes.

High calorific value. Almost twice as high as that of ordinary firewood.

Constant combustion temperature. Due to the uniform density.

Cost effective.

Minimum ash content after burning: 1-3%

Pellets or fuel pellets.

Essentially the same production principle as for briquettes. Lignin (plant polymer) is used as a binder.

The materials are the same as for briquettes: bark, shavings, straw, cardboard. First, the raw material is crushed to the state of pollen, then, after drying, a special granulator forms granules of a special shape from the mass. Used in pellet heating boilers. Prices for this type of solid fuel are the highest - this is due to the complexity of production and popularity with buyers.

There are the following types of this solid fuel:

Processing round timber of hard and soft tree species into pellets.

Peat pellets

Pellets obtained from sunflower husk processing.

Straw pellets

The advantages of pellets:

Environmentally friendly.

Storage. Due to special production technologies, pellets can be stored directly in the open air. They do not swell, do not become covered with fungus.

Long and even burning.

Low cost.

Due to their small shape, the pellets are suitable for boilers with automatic loading.

Wide range of applications (boilers, stoves, fireplaces)

Firewood

Pieces of wood intended for obtaining heat by burning in boilers for heating with solid fuels, fireboxes intended for firewood. For convenience, the length of the logs is most often 25-30 cm. For the most effective use, "the lowest possible moisture level is required. For heating, it is necessary to burn as slow as possible. Also, in addition to heating, firewood can be used, for example, in boilers for solid fuel. Best for these parameters. hardwoods are suitable: oak, ash, hazel, hawthorn, birch .. Worse - coniferous firewood, as they contribute to the deposition of resin and have a low calorific value, while quickly burn out.

Firewood is presented in two types:

Sawed.

Chipped.

2 FUEL COMPOSITION

For the formation of coal, an abundant accumulation of plant matter is necessary. In ancient peat bogs, starting from the Devonian period, organic matter accumulated, from which fossil coals were formed without access to oxygen. Most of the commercial deposits of fossil coal date from this period, although there are also younger deposits. The oldest coals are estimated to be about 350 million years old. Coal is formed when rotting plant material accumulates faster than bacterial decomposition occurs. An ideal environment for this is created in swamps, where stagnant water, depleted in oxygen, interferes with the vital activity of bacteria and thereby protects the plant mass from complete destruction? At a certain stage of the process, the acids released during the process prevent further bacterial activity. This is how peat is formed - the initial product for the formation of coal. If then it is buried under other sediments, then the peat is compressed and, losing water and gases, is converted into coal. Under the pressure of sediment layers 1 kilometer thick, a layer of brown coal 4 meters thick is obtained from a 20-meter layer of peat. If the depth of burial of plant material reaches 3 kilometers, then the same layer of peat will turn into a layer of coal 2 meters thick. At a greater depth, about 6 kilometers, and at a higher temperature, the 20-meter layer of peat becomes an anthracite layer 1.5 meters thick. As a result of the movement of the earth's crust, the coal seams experienced uplift and folding. Over time, the raised parts were destroyed due to erosion or spontaneous combustion, and the lowered ones remained in wide shallow basins, where coal is at least 900 meters from the earth's surface.

Brown coals. They contain a lot of water (43%) and therefore have a low calorific value. In addition, they contain a large amount of volatile substances (up to 50%). They are formed from dead organic residues under pressure of loading and under the influence of elevated temperatures at depths of about 1 kilometer.

Coals. They contain up to 12% moisture (3-4% internal moisture), therefore they have a higher calorific value. They contain up to 32% volatile substances, due to which they are quite flammable. Formed from brown coal at depths of about 3 kilometers.

Anthracites. Almost entirely (96%) are carbon. They have the highest calorific value, but are poorly flammable. Formed from coal and in the form of oxidesBUT NS. They refer to the harmful components of combustion products, the amount of which should be limited.

Sulfur - found in solid fuels as organic compoundsSOand pyriteS xthey are combined into volatile sulfurS l... Sulfur is also included in the fuel in the form of sulphurous salts - sulfates - which are incapable of burning. Sulfate sulfur is usually referred to as fuel ash. The presence of sulfur significantly reduces the quality of solid fuels, since sulfurous gasesSO 2 andSO 3 combining with water, they form sulfuric acid - which in turn destroys the metal of the boiler, and getting into the atmosphere harms the environment. It is for this reason that the sulfur content in fuels - not only in solid ones - is highly undesirable.

Ash - fuel is a ballast mixture of various minerals remaining after the complete combustion of the entire combustible part of the city. Ash directly affects the quality of fuel combustion - it reduces combustion efficiency.

Questions:

1. What are the main types of solid fuels?

2. What is ash?

3 FUEL APPLICATION

The use of coal is diverse. It is used as a household, energy fuel, raw material for the metallurgical and chemical industries, as well as for the extraction of rare and trace elements from it. Liquefaction (hydrogenation) of coal with the formation of liquid fuel is very promising. For the production of 1 ton of oil, 2-3 tons of coal are consumed, some countries almost completely provided themselves with fuel due to this technology. Artificial graphite is obtained from coal.

Brown coal outwardly differs from coal by the color of a line on porcelain plastic - it is always brown. The most important difference from bituminous coal is its lower carbon content and significantly higher VOC and water content. This explains why brown coal burns more easily, gives more smoke, smell, as well as the aforementioned reaction with caustic potassium and produces little heat. Due to its high water content for combustion, it is used in powder, into which it inevitably turns during drying. The nitrogen content is significantly inferior to coal, but the sulfur content is increased.

The use of brown coal - as a fuel, brown coal is used in many countries much less than coal, however, due to its low cost in small and private boiler houses, it is more popular and sometimes takes up to 80%. It is used for pulverized combustion (during storage, brown coal dries up and crumbles), and sometimes the whole. In small provincial CHP plants, it is also often burned for heat. However, in Greece and especially in Germany, lignite is used in steam power plants, generating up to 50% of electricity in Greece and 24.6% in Germany. The production of liquid hydrocarbon fuels from brown coal by distillation is spreading at a high speed. After distillation, the residue is suitable for the production of soot. Combustible gas is extracted from it, and carbon-alkali reagents and methane-wax (mountain wax) are obtained. In scanty quantities, it is also used for crafts.

Peat is a combustible mineral formed in the process of natural withering away and incomplete decay of marsh plants in conditions of excessive moisture and difficult air access. Peat is a product of the first stage of the coal educational process. The first information about peat as a "combustible soil" used for cooking dates back to the 26th century AD.

Sedimentary rock of plant origin, composed of carbon and other chemical elements. The composition of coal depends on age: anthracite is the oldest, coal is younger, and the youngest brown. Depending on aging, it has different moisture content; the younger, the more moisture. Coal in the process of burning pollutes the environment, plus it is sintered into slag and deposited on the grates in the boiler. This prevents normal combustion.

Questions:

Fuel application?

Is fuel combustion harmful to the environment, and which type is the most ?

4 WAYS OF FUEL BURNING

There are three ways of fuel combustion: layer, flare or chamber and vortex.

1 - grate; 2 - igniter door; 3 - loading door; 4 - heating surfaces; 5 - combustion chamber.

Figure 4.1 - Layered furnace scheme

This drawing shows a layered method of fuel combustion, where a layer of lumpy fuel lies motionless on the grate and is blown with air.

The layered method is used to burn solid fuels.

And here is shown a flare and vortex method of fuel combustion.

1 - burner; 2 combustion chamber; 3 - lining; 4 - furnace screen; 5 - ceiling-mounted radiant steam superheater; 6 - scallop.

Figure 4.2 - Chamber furnace

Figure 4.3 - Vortex fuel combustion

With the flare and vortex method, all types of fuel can be burned, only solid fuel is preliminarily subjected to breaking, turning it into dust. When fuel is burned, all heat is transferred to the combustion products. This temperature is called the theoretical combustion temperature of the fuel.

In industry, continuous boilers are used to burn solid fuels. The principle of continuity is supported by a grate, to which solid fuel is constantly supplied.

For a more rational combustion of fuel, boilers are built that are capable of burning it in a dusty state. Liquid fuels are burned in the same way.

Questions:

What is the most rational combustion method?

Explain the advantages of the chamber combustion method.

5 OPERATING PROCESSES IN BOILERS

Working processes in boilers:

Steam formation

In boiler plants, processes such as the formation of steam occur:

The conditions under which steam is formed in boilers are constant pressure and continuous heat supply.

Steps in the vaporization process: water heating to saturation temperature, vaporization and steam heating to a predetermined temperature.

Even in boilers, one can observe the corrosion of heating surfaces:

The destruction of metal under the influence of the environment is called corrosion.

Corrosion from the side of combustion products is called external, and from the side of the heated medium - internal.

There is low temperature and high temperature corrosion.

To reduce the destructive force of corrosion, it is necessary to monitor the water regime of the boiler. Therefore, raw water before use forboiler feed is pretreated in order to improve its quality.

Boiler water quality is characterized by dry residue, total salt content, hardness, alkalinity and content of corrosive gases

Sodium cation filter - where the water is purified

Deaerator - aggressive agents, air oxygen and carbon dioxide are removed.

Samples of pipes that have corroded outside and inside.

Corrosion of heating surfaces

Internal corrosion of steam and hot water boilers is mainly of the following types: oxygen, steam-water, alkaline and sub-sludge.

The main appearance of oxygen corrosion is ulcers, usually with iron oxides.

Steam-water corrosion is observed during the operation of boilers with increased thermal loads. As a result of this corrosion, on the inner surfaces of the wall tubes and brittle damage in the places where the boiler water is evaporated.

Pits are formed as a result of undersludge corrosion.

External corrosion can be low temperature and high temperature.

Low temperature corrosion can occur when any fuel is burned. High-temperature corrosion can occur when burning fuel oil.

The combustion device, or firebox, being the main element of the boiler unit, is designed to burn fuel in order to release the heat contained in it and obtain combustion products with the highest possible temperature. At the same time, the furnace serves as a heat exchange device, in which heat is transferred by radiation from the combustion zone to the colder surrounding heating surfaces of the boiler, as well as a device for capturing and removing some of the focal residues when burning solid fuel.

According to the method of fuel combustion, furnace devices are divided into layer and chamber. In layered furnaces, solid lump fuel is burned in a layer, in chamber furnaces - gaseous, liquid and pulverized fuels in suspension.

Modern boilers usually three main methods of solid fuel combustion are used: layer, flare, vortex.

Layer furnaces. Furnaces in which layered combustion of lump solid fuel is carried out are called layered. This firebox consists of a grate that supports a layer of lumpy fuel and a combustion space in which flammable volatiles are burned. Each furnace is designed to burn a specific type of fuel. The designs of the furnaces are varied, and each of them corresponds to a specific combustion method. The efficiency and economy of the boiler plant depend on the size and design of the furnace.

Layer furnaces for burning various types of solid fuels are divided into internal and external ones, with horizontal and inclined grates.

Furnaces located inside the lining of the boiler are called internal, and those located outside the lining and additionally attached to the boiler are called remote.

Depending on the method of fuel supply and the organization of maintenance, layered furnaces are subdivided into manual, semi-mechanical and mechanized.

Manual furnaces are those in which all three operations - supplying fuel to the furnace, shuraing it and removing slag (focal residues) from the furnace - are performed manually by the driver. These furnaces have a horizontal grate.

Semi-mechanical furnaces are those in which one or two operations are mechanized. These include mine ones with inclined grate grates, in which the fuel loaded into the furnace manually, as the lower layers burn out, moves along the inclined grates under the action of its own mass.

Mechanized fireboxes are those in which the supply of fuel to the confusion, its skimming and removal of focal residues from the firebox are made by a mechanical drive without manual intervention of the driver. Fuel enters the furnace in a continuous flow.

Layer furnaces for solid fuel combustion are divided into three classes:

• fireboxes with a fixed grate and a layer of fuel lying on it, which include a furnace with a manual horizontal grate. All types of solid fuels can be burned on this grate, but due to manual maintenance, it is used under boilers with a steam capacity of up to 1-2 t / h. Furnaces with projectors, into which fresh fuel is continuously mechanically loaded and scattered over the grate surface, are installed under boilers with a steam capacity of up to 6.5-10 t / h;
• furnaces with a fixed grate and a layer of fuel moving along it, which include furnaces with a rustling bar and furnaces with an inclined grate. In furnaces with a rustling bar, the fuel moves along a fixed horizontal grate with a special bar of a special shape, which reciprocates along the grate. They are used for burning brown coal under boilers with a steam capacity of up to 6.5 t / h; In furnaces with an inclined grate, fresh fuel loaded into the furnace from above, as it burns under the influence of gravity, slides into the lower part of the furnace. Such furnaces are used for burning wood waste and peat under boilers with a steam capacity of up to 2.5 t / h; high-speed shaft furnaces of the V.V. Pomerantsev system are used for burning sod peat under boilers with a steam capacity of up to 6.5 t / h for burning wood waste under boilers with a steam capacity of 20 t / h;
• furnaces with moving mechanical chain grates of two types: forward and reverse. The forward-running chain grate moves from the front wall towards the rear wall of the furnace. Fuel is supplied to the grate by gravity. The return chain grate moves from the rear to the front wall of the firebox. Fuel is supplied to the Grate by a spreader. Furnaces with chain grate grates are used to burn coal, brown coal and anthracite under boilers with a steam capacity of 10 to 35 t / h.

Chamber (flare) furnaces. Chamber furnaces are used to burn solid, liquid and gaseous fuels. In this case, solid fuel must be preliminarily ground into a fine powder in special pulverizing installations - coal grinding mills, and liquid fuel must be atomized into very small droplets in fuel oil nozzles. Gaseous fuel does not require preliminary preparation.

The flare method allows burning various and low-grade fuels with high reliability and efficiency. Solid fuels in a pulverized state are burned under boilers with a steam capacity of 35 t / h and above, and liquid and gaseous fuels under boilers of any steam capacity.

Chamber (flare) furnaces are rectangular prismatic chambers made of refractory bricks or refractory concrete. The walls of the combustion chamber are covered from the inside with a system of boiling pipes - furnace water screens. They represent an effective boiler heating surface, which absorbs a large amount of heat emitted by the torch, at the same time, they protect the masonry of the combustion chamber from wear and tear under the action of the high temperature of the torch and molten slag.

According to the method of slag removal, flare furnaces for pulverized fuel are divided into two classes: with solid and liquid slag removal.

The furnace chamber with solid bottom ash removal has a funnel shape, called a cold funnel. Drops of slag falling out of the torch fall into this funnel, solidify due to the lower temperature in the funnel, granulate into individual grains and enter the slag receiver through the throat. The furnace chamber b with liquid slag removal is performed with a horizontal or slightly inclined hearth, which is thermally insulated in the lower part of the furnace walls to maintain a temperature higher than the ash melting temperature. The molten slag that has fallen from the torch to the bottom remains in a molten state and flows out of the furnace through the tap hole into the slag collection bath filled with water, solidifies and cracks into small particles.

Furnaces with liquid slag removal are divided into single-chamber and two-chamber.

In two-chamber furnaces, the furnace is divided into a fuel combustion chamber and a combustion product cooling chamber. The combustion chamber is reliably covered with thermal insulation to create a maximum temperature in order to reliably obtain liquid slag. Flare furnaces for liquid and gaseous fuels are sometimes made with a horizontal or slightly inclined hearth, which is sometimes not shielded. The location of the burners in the combustion chamber is done on the front and side walls, as well as at the corners of it. Burners are available as direct-flow and swirling ones.

The method of fuel combustion is selected depending on the type and type of fuel, as well as the steam capacity of the boiler unit.

Solid fuel combustion methods.

Major deposits of fossil fuels.

The distribution of fossil solid fuels across the territory of the USSR is extremely uneven. The most industrially developed regions of the European part of the USSR are poor in fuel. The Donetsk Basin is of the greatest importance here, which has various grades of coal and anthracite, but the fuel reserves in it no longer satisfy the needs. At the same time, seams with weak thickness, extraction from deep mines make this fuel expensive (14-16 rubles / ton of equivalent fuel). The bulk of fossil fuels is located in Central and Western Siberia, Kazakhstan. These fuels are cheaper than Donetsk ones (8-10 rubles / ton of standard fuel - mine production and 4 rubles / ton of standard fuel - open-pit mining). Even taking into account the cost of transportation, they turn out to be cheaper in the European part of the USSR than Donetsk ones. There are reserves of brown coal in the Kansk-Achinsk basin (Central Siberia). Its close location to the surface of the earth, thick layers make it possible to develop open-pit mining of this fuel, which makes it the cheapest fuel in the USSR (estimated costs are 2.5-3 rubles / ton of standard fuel). The Ekibastuz coal deposit (East Kazakhstan) has the same characteristics. With regard to the Kansk-Achinsk brown coals, a plan is also being developed for their complex energy-technological processing with the production of valuable chemicals, lignite fuel oil and coke - fuel with a high calorific value (about 29.3 MJ / kg).

Oil reserves are being intensively developed in the Tyumen region. Oil and gas condensate production in this area accounts for about 50% of all production in the country.

There are natural gas deposits in many regions of our country. The most famous are Shebelinskoe, Dashavskoe, Gazliyskoe. In recent years, unique fields have been discovered and began to be actively exploited in Turkmenistan, in the South Urals and in the Tyumen region (Shatlykskoye, Orenburgskoye, Medvezhye, Urengoyskoye, Yamburgskoye). Gas reserves here account for almost 50% of all known natural gas reserves in the country. Gas and oil seals were discovered on the territory of the Komi ASSR. The proximity of this region to the industrial centers of the European part of the USSR makes it necessary to accelerate the development of fuel production in this region, which is difficult in terms of natural and climatic conditions. Data are quoted in 1977 ᴦ prices.

Combustion of solid fuel in furnaces can be organized in different ways: flare, cyclonic, in a fluidized bed (Fig. 1.7). Of these, the most common in modern large-scale power engineering is the flare.

The classification of combustion methods is based on the aerodynamic characteristic of the process, which determines the conditions for the oxidant washing the burning fuel.

An almost unlimited increase in the power of combustion devices is associated with the combustion of coal dust in the volume of the combustion chamber in a suspended state. This method of fuel combustion is usually called torch... In this case, small particles of fuel are easily transported by the flow of air and formed gases in the section of the combustion chamber. Fuel combustion occurs in this case in the volume of the combustion chamber for a very limited residence time of particles in the furnace (1-2 s). The combustion rate of the fuel is determined by the combustion surface.

At cyclonic method burning fuel particles are in intense vortex motion. In contrast to the flare combustion method, the fuel particles are intensively blown by the flow and burn quickly. The cyclonic method allows you to burn coarser coal dust and even crushed pieces. A higher combustion temperature develops in the cyclone, which makes the slags turn into a liquid state.

Recently, a new method of fuel combustion in the so-called fluidized bed(Fig. 1.7, c). The crushed fuel with particles of 1-6 mm in size located on the grate is blown by an air stream at such a speed that the particles float above the grate and make reciprocating movements in the vertical plane. In this case, the velocity of the gas-air flow within the fluidized bed is greater than above them. Smaller and partially burnt particles rise to the upper part of the fluidized bed, where the flow rate decreases, and there they burn. The fluidized bed increases in volume by 1.5-2 times, its height is usually 0.5-1 m.

Heat-sensing surfaces in the form of a corridor or staggered tube bundle are placed inside the fluidized bed volume and above it. Due to the developed conductive (contact) heat transfer from incandescent particles to the heating surface, the specific heat perception of surfaces within the fluidized bed increases significantly. At the same time, the temperature of the gases in the burning layer remains relatively low (800-1000 ° C), which excludes overheating of the metal and reduces the formation of harmful nitrogen oxides in the combustion products. At the same time, this combustion method allows solid additives (for example, limestone) to be introduced into the fluidized bed to neutralize the formed sulfur oxides.

Large power plants consume over 1000 t / h of coal. Even when fuel is delivered by wagons with a larger carrying capacity (60 - 125 t) at a power plant, it is extremely important to constantly unload 15-30 wagons of fuel in 1 hour, which is ensured by the use of high-performance car dumpers for unloading wagons.

The transformation of lump fuel into coal dust is carried out in two stages. Initially, the raw fuel is exposed to fragmentation up to a size not exceeding 15 - 25 mm. Then shredded fuel - crushed enters raw coal bunkers, after which it is subjected to grinding in coal grinding mills to the final product - coal dust with a particle size of up to 500 microns. Simultaneously with grinding, the fuel is dried to ensure good fluidity of the dust.

If we take the air velocity as the defining parameter w c relative to the speed of movement of fuel particles v t, then according to this parameter four technologies of fuel combustion are distinguished.

1. In a dense filtering layer(w in >> v T).

Applies only to lumpy solid fuel that is distributed on the grate. The fuel layer is blown through with air at a rate at which the stability of the layer is not disturbed and the combustion process has an oxygen and reduction zone.

The apparent thermal stress of the grate is Q R= 1.1 ... 1.8 MW / m 2.

2. In a fluidized or fluidized bed(w in> v T).

With an increase in air speed, the dynamic head can reach and then exceed the gravitational force of the particles. The stability of the layer will be violated and a random movement of particles will begin, which will rise above the lattice, and then reciprocate up and down. The flow rate at which the stability of the layer is violated is called critical.

Its increase is possible up to the speed of particle soaring, when they are carried out by the gas flow from the layer.

A significant part of the air passes through the fluidized bed in the form of "bubbles" (gas volumes), strongly mixing the fine-grained material of the layer, as a result, the combustion process along the height proceeds at an almost constant temperature, which ensures the completeness of fuel burnout.

A boiling fluidized bed is characterized by an air velocity of 0.5 ... 4 m / s, a fuel particle size of 3 ... 10 mm, a bed height of no more than 0.3 ... 0.5 m. Thermal stress of the furnace volume Q V= 3.0 ... 3.5 MW / m 3.

A non-combustible filler is introduced into the fluidized bed: fine quartz sand, chamotte chips, etc.

The fuel concentration in the layer does not exceed 5%, which makes it possible to burn any fuel (solid, liquid, gaseous, including combustible waste). A non-combustible filler in a fluidized bed can be active against harmful gases generated during combustion. The introduction of a filler (limestone, lime or dolomite) makes it possible to solidify up to 95% of sulfur dioxide.

3. In a stream of air(w at ≈ v t) or flare direct-flow process. Fuel particles are suspended in the gas-air flow and begin to move with it, burning during movement within the combustion chamber. The method is characterized by low intensity, extended combustion zone, sharp non-isothermality; requires a high temperature of the medium in the ignition zone and careful preparation of the fuel (spraying and premixing with air). Thermal stress of the volume of the furnace Q V≈ 0.5 MW / m 3.