Gas combustion methods. Open Library - open library of educational information Methods of burning solid fuels in boiler rooms

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 largest calorific value near 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), great importance has the processing of brown coal into valuable types of liquid fuel - gasoline and kerosene.

Briquettes

Briquettes are solid fuel 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 given view 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 susceptible to fungal attack. 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 from the mass special form... 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 1 kilometer thick layers of sediment, 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, a 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%). Formed from dead organic residues under load pressure and under the influence of elevated temperatures at depths of about 1 kilometer.

Coals. They contain up to 12% moisture (3-4% internal), 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 fuel, energy fuel, raw material for metallurgical and chemical industry, 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 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 when boilers operate 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.

Depending on the method of formation of the gas-air mixture, the methods of gas combustion are subdivided (figure below):

• for diffusion;
• mixed;
• kinetic.

Gas combustion methods

a - diffusion; b - mixed; в - kinetic; 1 - inner cone; 2 - primary combustion zone; 3 - main combustion zone; 4 - combustion products; 5 - primary air; 6 - secondary air

In the diffusion method of combustion, the gas is supplied to the combustion front under pressure, and the air required for combustion is supplied from the surrounding space due to molecular or turbulent diffusion. Mixing here occurs simultaneously with the combustion process, therefore the rate of the combustion process is mainly determined by the rate of mixture formation.

The combustion process begins after contact between gas and air and the formation of a gas-air mixture of the required composition. Air diffuses to the gas stream, and gas diffuses from the gas stream into the air. Thus, a gas-air mixture is created near the gas jet, as a result of the combustion of which a primary combustion zone of gas 2 is formed. The combustion of the main part of the gas occurs in zone 3, and combustion products move in zone 4.

The emitted combustion products complicate the mutual diffusion of gas and air, as a result of which combustion proceeds slowly, with the formation of soot particles. This explains why diffusion combustion is characterized by a significant length and luminosity of the flame.

The advantage of the diffusion method of gas combustion is the ability to regulate the combustion process in a wide range. The mixture formation process can be easily controlled using various adjusting elements. The area and length of the flare can be adjusted by crushing the gas jet into separate flares, by changing the diameter of the burner nozzle, by adjusting the gas pressure, etc.

The advantages of the diffusion combustion method include: high flame stability when changing thermal loads, no flame breakthrough, temperature uniformity along the flame length.

The disadvantages of this method are: the likelihood of thermal decomposition of hydrocarbons, low combustion intensity, the likelihood of incomplete combustion of the gas.

In a mixed combustion method, the burner pre-mixes the gas with only a part of the air required for complete combustion of the gas, the rest of the air flows from the environment directly to the torch. In this case, at first, only a part of the gas mixed with the primary air burns out, and the remaining part of the gas, diluted with the combustion products, burns out after the addition of oxygen from the secondary air. As a result, the torch is shorter and less luminous than with diffusion combustion.

With the kinetic combustion method, a gas-air mixture is supplied to the combustion site, completely prepared inside the burner. The air-gas mixture is burned in a short flame. The advantage of this combustion method is the low probability of chemical underburning, short flame length, and high heat output of the burners. The disadvantage is the need to stabilize the gas flame.

There are three ways of fuel combustion: layer, in which the fuel in the layer is blown with air and burned; flare, when the fuel-air mixture burns in a flare in a suspended state while moving through the combustion chamber, and vortex (cyclonic), in which the fuel-air mixture circulates along a streamlined circuit due to centrifugal forces. Flare and vortex methods can be combined into a chamber one.

Process layer combustion of solid fuel occurs in a fixed or fluidized bed (pseudo-liquefied). In a fixed bed (Fig. 2.6, a) pieces of fuel do not move relative to the grate, under which the air necessary for combustion is supplied. In a fluidized bed (Fig. 2.6, b) particles of solid fuel under the action of the high-speed pressure of air intensively move one relative to the other. The flow rate at which the stability of the layer is violated and the reciprocating motion of particles over the lattice begins is called critical... The fluidized bed exists in the range of speeds from the beginning of pseudoliquefaction to pneumatic transport mode.

Rice. 2.6. Fuel combustion schemes: a- in a fixed bed; b- in a fluidized bed; v- straight-through flare process; G- vortex process; d- the structure of the fixed layer during fuel combustion and the change a, О 2 , CO, CO 2 and t by layer thickness: 1 - lattice; 2 - slag; 3 - burning coke;
4– fuel; 5 - over-layer flame

In fig. 2.6, d the structure of the fixed layer is shown. Fuel 4, poured onto the burning coke, is warmed up. The evolved volatiles burn, forming an over-layer flame 5. The maximum temperature (1300 - 1500 ° C) is observed in the area of ​​combustion of coke particles 3. In the layer, two zones can be distinguished: oxidizing, a> 1; restorative, a< 1.
In the oxidizing zone, the reaction products of the fuel and the oxidizer are as follows: CO 2 and CO... As air is used, the rate of formation CO 2 slows down, its maximum value is reached with an excess of air a = 1. In the reduction zone due to insufficient amount of oxygen (a< 1) начинается реакция между CO 2 and burning coke (carbon) to form CO... Concentration CO in combustion products increases, and CO 2 decreases. The length of the zones depending on the average size d to fuel particles are as follows: L 1 = (2 – 4) d to; L 2 = (4 – 6) d to... By the length of the zones L 1 and L 2 (towards their decrease) are influenced by an increase in the content of volatile fuels, a decrease in ash content A r, the rise in air temperature.

Since in zone 2, apart from CO contained H 2 and CH 4, the appearance of which is associated with the release of volatiles, then for their afterburning, part of the air is supplied through the blowing nozzles located above the layer.

In a fluidized bed, coarse fuel fractions are in suspension. The fluidized bed can be high temperature and low temperature. Low-temperature (800 - 900 ° C) fuel combustion is achieved by placing the boiler heating surface in the fluidized bed. Unlike a fixed bed, where the fuel particle size reaches 100 mm, crushed coal with d to£ 25mm.
The layer contains 5 - 7% fuel (by volume). The heat transfer coefficient to the surfaces located in the layer is quite high and reaches 850 kJ / (m2 × h × K). When burning low-ash fuels, to increase heat transfer, fillers are introduced into the layer in the form of inert granular materials: slag, sand, dolomite. Dolomite binds sulfur oxides
(up to 90%), which reduces the likelihood of low-temperature corrosion. A lower level of gas temperatures in a fluidized bed helps to reduce the formation of nitrogen oxides during combustion, which, when released into the atmosphere, pollute the environment. In addition, slagging of the screens is excluded, i.e. the adhesion of the mineral part of the fuel to them.

A characteristic feature of the circulating fluidized bed is the approach to the bed operation in pneumatic transport mode.

Chamber way solid fuel combustion carried out mainly in powerful boilers. In chamber combustion, the solid fuel ground to a pulverized state and pre-dried is supplied with part of the air (primary) through the burners to the furnace. The rest of the air (secondary) is introduced into the combustion zone most often through the same burners or through special nozzles to ensure complete combustion of the fuel. In the furnace, pulverized fuel burns in suspension in a system of interacting gas-air flows moving in its volume. With a greater crushing of fuel, the area of ​​the reacting surface increases significantly, and, consequently, the chemical reactions of combustion.

The characteristic of grinding solid fuel is the specific area F pl dust surface or the total surface area of ​​dust particles weighing 1 kg (m 2 / kg). For spherical particles of the same (monodisperse) size, the quantity F pl is inversely proportional to the diameter of the dust particles.

In fact, the dust obtained during grinding has a polydisperse composition and a complex shape. To characterize the quality of grinding of polydisperse dust, along with the specific surface area of ​​the dust, the results of its sifting on sieves of various sizes are used. According to the sifting data, the grain (or grinding) characteristic of dust is built in the form of the dependence of the residues on the sieve on the size of the sieve meshes. R 90 and R 200. The preliminary preparation of the fuel and the heating of the air ensure the burnout of solid fuel in the furnace in a relatively short period of time (several seconds) when the dust-air flows (torches) are in its volume.

Technological methods combustion organizations are characterized by a certain input of fuel and air into the furnace. In most dust preparation systems, fuel is transported to the furnace by primary air, which is only part of the the total air required for the combustion process. The supply of secondary air to the furnace and the organization of its interaction with the primary are carried out in the burner.

The chamber method, in contrast to the layer method, is also used for burning gaseous and liquid fuels. Gaseous fuel enters the combustion chamber through the burner, and liquid fuel is sprayed through the nozzles.

Layer furnaces

The fixed bed furnace can be manual, semi-mechanical or mechanical with a chain grate. Mechanical furnace a layer furnace is called, in which all operations (fuel supply, slag removal) are performed by mechanisms. When servicing semi-mechanical furnaces, along with mechanisms, manual labor... There are fire chambers with a straight line (Fig. 2.7, a) and reverse (fig. 2.7, b) by the course of the grids 1, driven by sprockets 2. The fuel consumption supplied from the bunker 3 is regulated by the installation height of the gate 4 (see Fig. 2.7, a) or the speed of movement of dispensers 7 (Fig. 2.7, b). In grids with a reverse stroke, the fuel is supplied to the canvas by spreaders 8 mechanical (Fig.2.7, b, c) or pneumatic (fig. 2.7, G) type. Small fractions of the fuel burn in a suspended state, and large ones - in a layer on the grate, under which air is supplied 9. Heating, ignition and combustion of the fuel occur due to the heat transferred by radiation from the combustion products. Slag 6 using a slag remover 5 (Fig.2.7, a) or under the action of its own weight (Fig. 2.7, b) enters the slag bunker.

The structure of the burning layer is shown in Fig. 2.7, a. Region III combustion of coke after zone II heating of incoming fuel (zone I) is located in the central part of the lattice. There is also a recovery zone. IV. The unevenness of the degree of fuel combustion along the length of the grate leads to the need for sectional air supply. Most of the oxidant must be fed to the zone III, the smaller one - to the end of the coke reaction zone and a very small amount - to the zone II preparation of fuel for combustion and the zone V burning out slag. This condition is met by the stepwise distribution of the excess air a 1 along the length of the grating. The supply of the same amount of air to all sections could lead to increased excess air at the end of the grate sheet, as a result of which it would not be enough for coke combustion (curve a 1) in the zone III.

The main disadvantage of chain grate furnaces is the increased heat loss from incomplete combustion of the fuel. The area of ​​application of such grates is limited to boilers with a steam capacity. D= 10 kg / s and fuels with volatile release = 20% and reduced humidity.

Fluidized bed furnaces are characterized by a reduced emission of harmful compounds such as NO x, SO 2, the low probability of slagging of the screens, the possibility (due to the low gas temperature) of saturation of the furnace volume with heating surfaces. Their disadvantages are increased incompleteness of fuel combustion, high aerodynamic resistance of the grate and layer, and a narrow range of regulation of the boiler steam output.

Rice. 2.7. Schemes of chain grate operation and types of fuel spreaders: a, b- furnaces with forward and backward grates, respectively; v, G- mechanical and pneumatic spreaders;
1 - lattice; 2 - asterisks; 3 - bunker; 4 - gate; 5 - slag remover; 6 - slag; 7 - fuel dispenser; 8 - spreader; 9 - air supply; I - zone of fresh fuel; II - fuel heating zone;
III - area of ​​combustion (oxidation) of coke; IV - recovery zone; V - zone of fuel burning

The layered method of fuel combustion is characterized by relatively low rates of the combustion process, reduced efficiency and reliability. Therefore, he did not find application in boilers of high productivity.

Chamber pulverized coal furnaces

Chamber pulverized coal furnaces consist of pulverized coal burners and a combustion chamber.

Combustion chamber is called a device designed to complete the combustion process and isolate it from external conditions.

Burners are designed to enter and mix fuel and air into the furnace, to ensure stable ignition and burnout of the mixture. They must meet the following requirements: tightness of the connection with the firebox; maintainability; ensure stable combustion at reduced load and when using reserve fuel (gas or fuel oil).

According to the method of slag removal, furnaces for burning solid fuels are divided into furnaces with dry ash removal (Figure 2.8) and furnaces with liquid bottom ash removal (Figure 2.9).

In fig. 2.8 shows a schematic diagram of a flare (pulverized coal) furnace with dry ash removal, where fuel burns in suspension in the volume of the combustion chamber.

b

a

In furnaces with dry ash removal, the core of the flame is located slightly below the combustion chamber, covered with screen heating surfaces that receive the heat emitted by the combustion products and the burning torch and protect the walls of the combustion chamber from high temperatures. Such furnaces are single-chamber with a cold funnel in the lower part. In the zone of the cold funnel and in the upper part of the furnace, the temperatures of the combustion products are lower than in the torch core. The ash particles suspended in the flue gas flow, getting from the torch core in the region of relatively low temperatures, cool and solidify. A small part of the ash (10 - 15% of the total ash content of the fuel) falls into the slag hopper located under the cold funnel. The rest of the ash is carried away with the combustion products into the boiler gas ducts.

Furnaces with liquid slag removal are single-chamber and two-chamber.
In single-chamber ones, the bottom of the combustion chamber is made in the form of a horizontal or inclined hearth. At a height of 4 - 5 m from the hearth, the screens are covered with a heat-insulating material to reduce heat absorption, which allows maintaining high temperatures of 1500 - 1600 o C near the hearth of the furnace, at which the slag is in a liquid state. Liquid slag is continuously removed through the taphole into a slag bath filled with water.
In two-chamber furnaces, the processes of fuel combustion and cooling of combustion products are separated.

Schematic diagrams of two-chamber cyclone furnaces with liquid slag removal are shown in Fig. 2.9. The main components of cyclonic furnaces are a vortex combustion chamber, which is a cylinder with tangential concentrated or dispersed fuel and air input, and a prismatic cooling chamber.

The fuel is fed into a vortex chamber with primary air. The fuel-air mixture is introduced through a swirler (snail) into the central part of the chamber. Crushed is introduced along the axis. Coal dust enters through tangentially located nozzles. Secondary air is fed into the chamber tangentially through nozzles-slits at a high speed (more than 100 m / s), providing the movement of fuel particles to the chamber walls. The vortices formed in the cyclone chamber contribute to the intensive formation of the fuel-air mixture and the combustion of fuel both in the volume of the cyclone and on its walls. Between the combustion and cooling chambers there is a slag catcher bundle of lined (closed with heat-insulating material) pipes designed to trap molten slag droplets contained in the combustion products. Uncaptured ash particles solidify in the cooling chamber.

The walls of the combustion chamber for insulation are made of studded screens covered with a refractory coating (Fig. 2.10), and the walls of the cooling chamber have non-insulated smooth-tube or fin screens.

Depending on the principle of organizing the process of introducing a dust-air mixture, pulverized coal burners can be divided into three types: vortex, direct-flow and flat-flare.

The principle of operation of the vortex burner (Fig.2.11, a) next. Primary streams I and secondary II air is introduced into the furnace through the annular concentric channels in which the swirlers are installed. The flow direction is the same. A characteristic feature of such a flow is the comparability in magnitude of all three velocity components: axial (longitudinal) w a, tangent w t(circumferential) and radial w r. The presence of the tangential component of the velocity leads to a noticeable expansion of the jet, which forms a parabolic body of revolution in space. In the central inner part of the 1 jet, a vacuum zone is formed, the value of which is determined by the sleeve ratio t = D o / D a and the flow rate at the outlet of the burners.

Under the influence of the pressure difference, reverse currents of high-temperature combustion products arise, which stabilize the ignition of the dust-air mixture. When driving, the primary I and secondary II the air is mixed, and the combustion process spreads to the outer surface of the jet.

Depending on the design of the swirlers, scroll-blade burners are distinguished (Fig. 2.12, v), snail-snail (Fig. 2.12, a), scapular-scapular, straight-coiled (Fig. 2.12, b) and straight-blade. The name first indicates the type of primary air swirler.

Rice. 2.12. Types of swirl pulverized coal burners: a- snail-snail burner;
b- ORGRES co-current coiled burner; v- Scroll-blade burner TsKTI - TKZ;
1 - a snail of a dust-air mixture; 1 "- dust-air mixture inlet pipe; 2 - secondary air snail; 2" - secondary air inlet box; 3 - annular channel for the exit of the dust-air mixture into the furnace; 4 - the same for secondary air; 5 - main fuel oil nozzle;
5 "- fuel oil nozzle; 6 - diffuser at the outlet of the dust-air mixture;
7 - swirl blades for secondary air; 8 - supply of tertiary air through the axial channel; 9 - control of the position of the splitter; 10 - swirler of axial air flow;
11 - furnace lining; АБ - dust-air mixture ignition limit; B - suction of flue gases to the torch root

In the vortex burner, the primary I and secondary II individual air (Fig. 2.11). The secondary air inlet can be either top or bottom, and the primary air inlet - only the top, which is explained by the need to prevent dust deposits in the dust pipe. The primary and secondary air ducts are circular, concentric.

Flare opening, the amount of ejected gases, the distribution of velocities, the range in the vortex burner are determined by the swirling intensity of the flows, which is estimated by the parameter NS twist, depending on the design of the swirler.

It is advisable to supply all types of fuel through vortex burners, except for milled peat. The disadvantages of these burners include: increased hydraulic resistance, structural complexity, the need to make the outlet part of heat-resistant materials in order to avoid burnout, an increased tendency to fuel separation, a slightly larger (compared to burners of other designs) emission of nitrogen oxides into the atmosphere.

In direct-flow burners, in contrast to the vortex flows of the primary I and secondary II air do not swirl and have a unidirectional (passing) movement (Fig. 2.11, b). The tangential component of the velocity is absent, and the radial one is much less than the longitudinal component.

Stabilization of ignition is carried out due to the ejection of combustion products 1 along the periphery 2 of the jet. The required degree of air mixing is achieved by the corresponding ratio of the speeds of the primary I and secondary II air.

The resistance of direct-flow burners is less than that of vortex burners, they are easier to manufacture, and the amount of nitrogen oxides formed is less. The disadvantages of direct-flow burners include a higher range and worse conditions for mixing the mixture in comparison with vortex ones.

Direct-flow burners are used for hard and brown coal. Premixing burners with a mixing chamber are mainly used for peat and brown coal.

The principle of operation of flat-flame burners (Fig. 2.13) is based on the use of the effect of the collision of two air jets directed at an angle to each other. The torch range of flat-flame burners is less than that of direct-flow burners. A "triangle" is formed between the streams of secondary air and the burner, into which fuel is supplied, ignited by the hot combustion products ejected into it. As a result of the crushing of the jets after the collision, a flat jet with a large surface is formed. Due to the expansion of the jet in one plane and its intense ejection of combustion products from below and from above, the jet velocity drops sharply. The inclination of the flame is regulated by changing the ratio of the secondary air flow rates supplied to the upper and lower nozzles. This property of the burner is used when the quality of the burned fuel changes, as well as the load of the boiler unit or its mode of operation.

Furnaces for burning liquid fuel (fuel oil)

Mainly fuel oil is used as a liquid fuel for industrial boilers. In order to burn fuel oil, it must first be sprayed to improve the evaporation conditions, since when fuel oil is burned, the gaseous products of its evaporation burn. For spraying and introducing fuel oil into the furnace, special devices are used, called nozzles.

The furnace for burning fuel oil consists of a combustion chamber, radiation-receiving heating surfaces and nozzles.

The combustion chamber and radiant heating surfaces during fuel oil combustion are made in such a way that the bottom of the chamber is limited by a horizontal or slightly inclined tray. The chamber itself is made relatively smaller, since fuel oil can be burned at a significantly higher thermal stress of the furnace space than pulverized fuel. In boilers of small steam capacity, the furnaces are often not shielded in order to simplify the implementation of the shield system.

FUEL COMBUSTION METHODS.
TYPES OF HEATING DEVICES.

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 during solid fuel combustion.
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.
In modern boiler plants, three main methods of burning solid fuel are usually used (Fig. 14): layer, flare, vortex.
Layer furnaces. Furnaces in which layered combustion of lumpy solid fuel is carried out are called layered. This firebox consists of a grate supporting a layer of lumpy fuel and a furnace 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.

Rice. fourteen. Fuel combustion processes: a - layer, 6 - flare, in - vortex

Layer furnaces for burning various types of solid fuels are divided into internal and external ones, with horizontal and inclined grates.
The shafts located inside the lining of the boiler are called internal, and those located outside the lining and additionally attached to the boiler are called external ones.
Depending on the method of fuel supply and organization of service, layered thin films 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 call those in which one or two operations are mechanized. These include mine with our
inclined grate grates, in which fuel, manually loaded into the furnace, as it burns out lower layers moves along inclined grates under the action of its own weight.
Mechanized furnaces are called those in which the supply of fuel to the furnace, its shurovka and removal of focal residues from the furnace.

Ryas 15 Burner diagrams for burning solid fuel in a layer.
a - with a manual horizontal grate, b - with a spreader onto a fixed bed, c - with a scuffing bar, d - with an inclined grate, e - vertical, e - with a forward chain grate, g - with a backward grate with a spreader mechanical drive without manual intervention of the driver.

Fuel enters the furnace in a continuous flow.
Layer furnaces for burning solid fuels (Fig. 15) are divided into three classes:
furnaces with a stationary grate and a layer of fuel that is motionlessly lying on it, which include a firebox, with a manual horizontal grate (Fig. 15, a and b). 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 spreaders, 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 (Fig. 15, c, guide), which include fireboxes with a rustling bar and fireboxes 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, but as it burns under the influence of gravity, slides into the lower part of the furnace.
Such furnaces are used for burning wood waste of peat under boilers with a steam capacity of up to 2.5 t / h.The high-speed mine furnaces of V.V. t / h furnaces with moving mechanical grate grates (Fig. 15, f and g) 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 for burning bituminous, brown coal and anthracite under boilers with a steam capacity of 10 to 35 t / h.
Chamber (flare) furnaces. Chamber furnaces (Fig. 16) 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 and destruction 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 (Fig. 16, a) has a funnel-shaped bottom, called cold funnel 1. Drops of slag falling out of the torch fall into this funnel, solidify due to the lower temperature in the funnel, and granulate. into individual grains and through the neck 3 fall into the slag receiving device 2. The furnace chamber b with liquid slag removal (Fig. 16, b) is performed with a horizontal or slightly inclined hearth 7, which in the lower part of the furnace walls has thermal insulation to maintain a temperature higher than the temperature ash melting. The molten slag, which has fallen from the torch onto the bottom, remains in a molten state and flows out of the furnace through the tap hole 9 into the slag collection tank 8 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 can be direct-flow or swirl.
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.

Holders of the patent RU 2553748:

The invention relates to heat power engineering and can be used in furnaces and heat generators of various types that use fossil fuel for combustion.

There is a known method for efficient combustion of fuel by separating gas (combustion reaction products), for example, a Method for separating gases using membranes with permeate purging to remove CO 2 from combustion products according to patent 2489197 (RU) BAKER Richard (US), VIDZHMANS Johannes Gee (US) et al.

The implementation of this combustion method is carried out in several stages: the stage of capturing carbon dioxide, the stage of membrane separation of gases, working in combination with compression and condensation to obtain a product from carbon dioxide in the form of a liquid, and a stage based on blowing, in which incoming air or oxygen is used for the furnace. as a purge gas. The disadvantage of this method is its complexity in implementation, since it includes many additional stages of a standard type, such as heating, cooling, compression, condensation, pumping, various types of separation and / or fractionation, as well as monitoring pressures, temperatures, flows, etc. with this method, the capture of carbon dioxide occurs from the waste stream formed by the combustion of fuel diluted with ballast gases, which therefore has a lower temperature.

The closest technical solution (prototype) is a Method for burning solid fuel in household heating furnaces according to patent 2239750 (RU), the authors of Ten V.I. (RU) and Ten G.Ch. (RU), Patent holder Ten Valery Ivanovich (RU).

This method includes loading fuel onto the grate of the furnace, creating thrust in its working space, igniting and burning the fuel with the removal of combustion products into the atmosphere, regulating the thrust and the amount of combustion products removed from the furnace by slightly opening the blower and chimney flaps.

The disadvantage of this method of burning solid fuel is its complexity in implementation, due to the breakdown of the process into a number of separate periods, in each of which the fuel is re-ignited, brought to an intensive combustion mode, and after reaching a predetermined temperature of the furnace, the combustion process is transferred to the damping mode, then ignition is performed again with the help of sophisticated automation and using already liquid or gaseous fuel. The disadvantage of these and other similar methods of fuel combustion is the mixing of combustion products, heat sources (CO 2 and H 2 O), in the reaction zone, into a single flow with ballast gases (nitrogen, excess air, etc.), which worsen the conditions for fuel combustion and use of the released heat (useful heat is taken and carried out into the atmosphere).

The proposed invention aims to improve the conditions for fuel combustion and increase the amount of thermal energy released by the fuel.

The technical result of the proposed method is to increase the efficiency of furnaces and heat generators by burning combustible gases in the middle zone of the furnace bell and removing ballast gases from the combustion zone, as well as by exposing the incandescent carbon to superheated steam.

The proposed method of fuel combustion is illustrated by graphic material, where the following designations are adopted: 1 - combustion reaction zone; 2 - blower (ash pan); 3 - supply of primary air for ignition, maintenance of combustion and gasification of fuel (volatile combustible gases); 4 - combustion chamber with fuel; 5 - hydrocarbon (volatile gases); 6 - supply of secondary air to the combustion zone for burning volatile combustible gases; 7 - harmful non-combustible ballast gases that do not participate in combustion; 8 - supply of superheated steam; 9 - useful hot products - heat carriers, carbon dioxide and water vapor; 10 - heat exchange zone; 11 - grate; 12 - outlet of gases from the furnace bell.

The proposed method is carried out as follows. Solid fuel is loaded onto the grate 11, it is ignited, while the primary air enters through the blower 2 and the grate 11. Then, after ignition, secondary air 6 enters the bell directly into the combustion zone for combustion of volatile combustible gases. As a result of the combustion reaction, a mixture of unrelated gases arises: incandescent carbon dioxide and water vapor and conditionally cold ballast gases - excess air and released nitrogen in its composition (excess air with an increased nitrogen content). The peculiarity of the bell structure is that during the combustion reaction, the generated gases are separated in it. Hot gases rise upward, giving off thermal energy to the bell, while cold particles of ballast gases go down through the bell zones with a low temperature. Fuel combustion reactions are expressed by the well-known combustion equations. The ratios of the reacting substances are maintained, as is their composition. That is, carbon C, hydrogen H 2 enter into a reaction with oxygen O 2 in the amount determined by the chemical equations:

other substances cannot react. The combustion reaction takes place in the combustion zone between hydrocarbon and oxygen without the participation of ballast gases, while the nitrogen released from the air in the composition of excess air, as less heated, is pushed out through the lower part of the bell (the outlet pipe is not shown in the diagram). After warming up the combustion chamber and the presence of incandescent carbon in it, superheated water vapor 8 is fed into the bell below the secondary air supply zone. As a result of the interaction of carbon with water vapor at high temperatures, flammable gases arise in accordance with the well-known chemical equations

at a low temperature with a total positive thermal effect, which enhance the process of fuel combustion and increase heat transfer from it. Implementation of the proposed method of fuel combustion will increase the efficiency of furnaces and heat generators. The proposed method is quite simple to implement, does not require complex equipment and can be widely used in industry and in everyday life.

SOURCES OF INFORMATION

1. Patent Russian Federation No. 2489197, IPC B01D 53/22 (2006.01). Gas separation method using membranes with permeate purging to remove carbon dioxide from combustion products. Patentee, MEMBRANE TECHNOLOGY AND RESERCH, INC. (US).

2. Patent of the Russian Federation No. 2239750, IPC F24C 1/08, F24B 1/185. A method of burning fuel in household heating stoves. The patentee is Ten Valery Ivanovich.

3. Mäkelä K. Stoves and fireplaces. Reference manual. Translated from Finnish. Moscow: Stroyizdat, 1987.

4. Ginzburg D.B. Solid fuel gasification. State publishing house of literature on construction, architecture and building materials... M., 1958.

A method of fuel combustion in furnaces having a bell with a fuel combustion chamber and a grate, including loading fuel, igniting and burning fuel due to the primary air entering through the blower, characterized in that the movement of gases in the bell is carried out without using the draft of the pipe, with the possibility of accumulating of hot gases in the upper part of the bell, while secondary air is supplied to the bell, directly to the combustion zone, while hot gases rise upward, giving thermal energy to the bell, and cold particles of ballast gases go down through the bell zones with a low temperature, after the chamber is heated combustion into it, below the secondary air supply, superheated water vapor is supplied to the incandescent carbon and combustible gases are obtained.

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