Combustion of fuel is a chemical process of combining its combustible elements with atmospheric oxygen, which occurs at high temperature and accompanied by the release of a significant amount of heat. Depending on the type of fuel differentiate homogeneous, heterogeneous combustion and pulsating (PULSAR). Homogeneous combustion occurs in volume (in mass), while the fuel and oxidizer are in the same state of aggregation (for example, gaseous fuel and air). Heterogeneous combustion occurs at the interface between two phases, that is, during the combustion of solid and liquid fuel. There are two combustion methods: in a layer of lump fuel and in a torch of pulverized fuel (layer and flare combustion methods). Gaseous and liquid fuels are burned only in a torch. The method of supplying air to the fuel is essential when burning it in a torch. The total combustion time t is determined by the time of mixture formation td and the time of occurrence of chemical combustion reactions tk. Since these stages of processes can overlap, the total combustion time t = tд+tк.
A device designed to burn fuel is called firebox. Classification: by fuel combustion method- layer, chamber (flare) and cyclone; in the layer only solid fuel is burned, and in other cases - solid, liquid and gaseous; according to fuel supply mode- with periodic and continuous feeding; in connection with the boiler- internal, i.e. located inside the boiler, external, arranged outside the heated surface of the boiler; according to the method of fuel supply and maintenance organization- manual, semi-mechanical and mechanical. Furnaces for layer combustion of fuel can be of the following varieties: a) fireboxes with a fixed grate and a motionless layer of fuel lying on it; b) fireboxes with a fixed grate and a layer of fuel moving on it; c) fireboxes with a moving grate that moves the layer of fuel lying on it . Manual firebox with a horizontal fixed grate allows you to burn all types of solid fuel during manual maintenance of the operations of loading, blasting and removing slag, used in boilers with a steam capacity of 1-2 t/h. Fireboxes with a rustling strip: during the forward stroke, it moves fuel from the loading hopper deep into the furnace and throws slag off the grate, and during the reverse stroke, it stirs up the fuel layer. A- manual with horizontal grate; b - firebox with thrower onto a fixed bed; V- firebox with rustling strip; G- firebox with inclined grate; d- firebox of the Pomerantsev system; e - firebox with a chain mechanical grate; and- the same reverse motion and thrower; h- chamber combustion chamber for pulverized fuel; To- furnace for burning liquid and gaseous fuels Fireboxes with inclined grate. In them, fuel is loaded into the firebox from above, and as it burns, under the influence of gravity, it slides to the bottom of the firebox, creating the opportunity for new portions of fuel to enter the firebox (2.5-20 t/h). High-speed mine 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. Fireboxes with moving grate. These include fireboxes with a mechanical chain grate of forward and reverse motion. The direct motion chain grate moves from the front wall of the firebox to the rear, while the fuel flows by gravity to the grate. (10-150 t/h). In chamber fireboxes fuel is burned in the form of coal dust. It is fed mixed with air into the furnace, where it burns in suspension. Chamber fireboxes for liquid and gaseous fuel. Direct-flow and vortex burners are used. The operation of fireboxes is characterized by the following indicators: thermal power, thermal loads of the grate and combustion volume, efficiency.
5.1. Methods of burning solid fuels
5.2. Combustion of liquid fuels
5.2.1. Fuel oil quality.
5.2.2. Problems of preparing fuel oil for combustion
5.2.3. Problems when using fuel oil in boiler houses and thermal power plants
5.3. Combustion of gaseous fuels
5.3.1. Gas preparation
5.3.2. Features of the natural gas combustion process
5.3.3. Combustion of gaseous fuels
5.3.4. Gas-burners
5.4. Combination burners
5.5. Flame control devices
5.6. Gas analyzers
5.7. Examples of gas burners
5.7.1. BK-2595PS
5.7.3.BIG-2-14
5.8. Removing combustion products.
5.1. Methods of burning solid fuels
Combustion methods. The combustion device, or firebox, is the main element of a boiler unit or industrial combustion furnace and serves to burn fuel in the most economical way and convert its chemical energy into heat. In the furnace, fuel burns, part of the heat of combustion products is transferred to the heating surfaces located in the combustion zone, as well as the capture of a certain amount of focal residues (ash, slag). In modern boiler units and furnaces, up to 50% of the heat released in the firebox is transferred to heating surfaces by radiation. In combustion technology, the following main methods of burning solid fuels are usually used: layer, flare (chamber), vortex and fluidized bed combustion (Fig. 5.5). Each of these methods has its own characteristics concerning the basic principles of organizing aerodynamic processes occurring in the combustion chamber. For the combustion of liquid and gaseous fuels, only the flare (chamber) combustion method is used.
Layer method. The combustion process in this way is carried out in layered furnaces
(see Fig. 5.5a ), having a variety of designs. The layer combustion process is characterized by the fact that in it the air flow meets a stationary or slowly moving layer of fuel during its movement and, interacting with it, turns into a flow of flue gases.
An important feature of layered fireboxes is the presence of a fuel reserve on the grate, linked to its hourly consumption, which allows for primary control of the firebox power only by changing the amount of supplied air. The fuel supply on the grate also ensures a certain stability of the combustion process.
In the conditions of modern combustion technology, the layered method of fuel combustion is outdated, since its various schemes and options are unsuitable or difficult to adapt to large power plants. However, layered methods of burning solid fuels will be used for a long time in boiler houses of small and medium-sized power plants.
In Fig. 5.6 6 shows the schematic diagrams of layered furnaces. With the layer combustion method, the air necessary for combustion is supplied from the ash pit 1 to the fuel layer 3 through the free section of the grate 2. In the combustion chamber 4 Above the layer, gaseous products of thermal decomposition of the fuel and small fuel particles removed from the layer burn. Combustion products, together with excess air from the furnace, enter the boiler flues.
Layer furnaces are widely used in boilers of low and medium power. They are divided according to several classification criteria. Depending on the method of maintenance, there are manually operated fireboxes (see Fig. 5.6, A), non-mechanized, semi-mechanized (see Fig. 5.6, b, c) and mechanized (see Fig. 5.6, d, e). Shown in Fig. 5.6 layer fireboxes can be divided into three groups
Rice. 5.5. Methods of burning solid fuels
a – in a dense layer; b – in a dusty state; c – in a cyclone furnace; d – in a fluidized bed.
Fireboxes with a fixed grate and movinglayer of fuel running over it(see Fig. 5.6, b, d).
Fireboxes with a layer moving together with the grateeat fuel(see Fig. 5.6, d).
The simplest layer firebox with a fixed grate and manual operation (see Fig. 5.6, A) used for burning all types of solid fuels. Only boilers with very low steam output - 0.275...0.55 kg/s (1...2 t/h) are equipped with such fireboxes.
In a firebox with a fixed inclined grate (see Fig. 5.6, b) As the fuel burns, it moves along the grate under the influence of gravity. These fireboxes are used for burning wet fuels (wood waste, lump peat) under boilers with a steam capacity of 0.7...1.8 kg/s (2.5...6.5 t/h).
In a semi-mechanized firebox (see Fig. 5.6, V), Fuel is supplied to the stationary grate using a spreader 5. In these furnaces, hard and brown coals and sorted anthracite are burned under boilers with a steam capacity of 0.55...2.8 kg/s (2...10 t/h).
The simplest mechanized firebox is a firebox with a screwing strip (see Fig. 5.6, G). It consists of a fixed glossy grille, over the entire width of which a bar slides b wedge-shaped section. The bar makes reciprocating movements using a special device. These furnaces are used for burning brown coal under boilers with a steam capacity of up to 2.8 kg/s (10 t/h).
The most common type of mechanized layer firebox is the firebox with a mechanical chain grate (see Fig. 5.6, d). The mechanical chain grate is made in the form of an endless grate, moving along with a layer of burning fuel lying on it. Each new portion of fuel entering the grate moves after the fuel layer. The speed of the grate movement can be changed depending on the fuel consumption (boiler operating mode) from 2 to 16 m/h. These fireboxes are used for burning sorted anthracite and non-caking coals with moderate humidity and ash content and the release of volatile substances U T = 10...25%. Existing modifications of fireboxes with chain grates allow them to be used for burning other fuels. Fireboxes with chain grates are installed under boilers with a steam capacity of 3...10 kg/s (10.5...35 t/h) and higher.
Torch method. Unlike the layer process, this process (See Fig. 5.5, b) characterized by the continuity of movement of fuel particles in the combustion space along with the flow of air and combustion products, in which they are suspended.
To ensure the stability and uniformity of the burning torch, and consequently the gas-air flow with the fuel suspended in it, solid fuel particles are ground to a dust-like state, to sizes measured in microns (from 60 to 90% of all particles have a size of less than 90 microns). Liquid fuel is pre-sprayed into very small droplets in nozzles so that the droplets do not fall out of the flow and have time to burn completely in a short time in the firebox. Gaseous fuel is supplied to the furnace through burners and does not require any special preliminary preparation.
A special feature of flare furnaces is the small amount of fuel in the combustion chamber, which makes the combustion process unstable and very sensitive to changes in the regime. The power of the firebox can be adjusted only by simultaneously changing the supply of fuel and air to the combustion chamber. During flare combustion (Fig. 5.7), solid fuel is pre-crushed in a dust preparation system and blown into the furnace in the form of dust, where it burns in suspension. Grinding the fuel sharply increases its reaction surface, which promotes better combustion.
The disadvantages of this method include the high cost of equipment for the dust preparation system and energy consumption for grinding, lower specific heat loads of the combustion chamber (about twice) than with layer fireboxes, which significantly increases the volume of combustion spaces.
Dust preparation from lump fuel consists of the following operations:
removal from fuel metal objects using magnetic separators;
crushing large pieces of fuel in crushers;
drying and grinding of fuel in special mills.
With working moisture W R < 20 % сушка топлива производится в мельнице одновременно с процессом размола, для чего в мельницу подается горячий воздух из воздухоподогревателя котла. Температура воздуха доходит до 400 °С, и он одновременно служит для выноса пыли из мельницы.
When grinding fuel, dust particles measuring 0...500 microns are formed. The main characteristic of dust is the fineness of its grinding, which according to GOST 3584-53 is characterized by the residue on sieves with cells of 90 and 200 microns, designated R 90 and R 2 oo. So, R 90 = 10% means that 10% of the dust remained on the 90 micron sieve and all the remaining dust passed through the sieve.
The optimal grinding fineness (fineness) is determined by a total factor: the minimum energy consumption for grinding fuel and losses from mechanical underburning. The fineness of grinding depends on the reactivity of the fuel, characterized mainly by the release of volatile substances. The higher the content of volatile substances in the fuel, the coarser the grind.
The grinding properties of fuel are characterized by the grindability coefficient (for anthracite Clo = 1; for lean coal TO lo = 1.6; For brown coal near Moscow, Cl 0 = 1.75).
The main disadvantages of this scheme are the lack of dust reserve, which reduces the reliability of the boiler, and severe wear of the mill fan, through which all the coal dust is passed.
In Fig. 5.9 shows a diagram of dust preparation with an intermediate hopper. Its difference is that a cyclone is placed behind the separator 6, into which the finished dust is sent. In the cyclone, 90...95% of the dust is separated from the air and precipitated, and then sent to an intermediate bunker 9. Dust from the cyclone is released into the bunker through valves (flashing lights) 8, which open when a certain portion of dust is pressed on them. Air with the remaining fine dust is sucked out of the cyclone by a mill fan 12 and is forced into the primary air pipeline, which in turn receives dust from the intermediate hopper using auger or bladed dust feeders 10. The dust preparation scheme with an intermediate hopper, as the most flexible and reliable, has become the most widely used.
Various types of mills are used to grind fuel. The choice of mill type depends on the grinding characteristics of the fuel, the yield of volatile substances and the moisture content of the fuel. There are low-speed and high-speed mills.
To grind anthracite and hard coals with a small yield of volatile substances, burned by boilers of medium and high steam capacity, low-speed ball drum mills (SBM) are used (Fig. 5.10). The main advantages of a drum mill are good adjustability of grinding fineness and grinding reliability. The disadvantages of these mills include: bulkiness, high cost, increased specific energy consumption, and significant noise accompanying the operation of the mill.
There are two types of high-speed mills: hammer mills and fan mills.
The fan mill (MB) is designed for grinding mainly high-moisture brown coals and milled peat. Furnaces with MV are used in boiler units of medium productivity. The grinding element of the MV is a massive impeller 1 (Fig. 5.12) with a rotation speed of 380... 1470 rpm, located in an armored housing 6.
INtheir way. IN In the flare furnaces considered, fuel particles burn in the volume of the furnace on the fly. The duration of their stay in the combustion space does not exceed the time the combustion products remain in the furnace and is 1.5... 3 s. In cyclone furnaces, which are designed for burning finely crushed fuel and coarse dust, large coal particles are suspended for as long as how much is necessary for their complete burnout, regardless of the length of time the combustion products remain in the furnace.
Quite small particles of coal are burned in them (usually smaller than 5 mm), and the air necessary for combustion is supplied at enormous (up to 100 m/s) velocities tangentially to the cyclone generatrix. A powerful vortex is created in the furnace, drawing the particles into a circulation movement in which they are intensively blown by the flow (see Fig. 5.5, V).
Significant specific surface of small particles, large values of mass transfer coefficients between the flow and particles, high concentrations of fuel in the chamber ensure the production of high thermal stresses of the furnace volume (q = 0.65... 1.3 MW/m 3 at a = 1.05... 1.1), as a result of which temperatures close to adiabatic (up to 2000 °C) develop in the furnace. Coal ash melts, liquid slag, flowing down the walls, slows down the movement of particles adhering to its surface, which further increases the speed of their washing by the flow, and hence the mass transfer coefficient.
Since the centrifugal effect decreases with increasing radius of the cyclone, the diameter of the latter usually does not exceed 2 m, which makes it possible to obtain a thermal power of 40...60 MW.
In our country, technological cyclone combustion chambers are mainly used, for example, for burning sulfur (in order to obtain SO 2 - raw material for the production of H 2 SO 4; the heat of combustion is also used), for melting and roasting ores and non-metallic materials (for example, phosphorites) etc. Recently, fire neutralization has been carried out in cyclone furnaces. Wastewater, i.e., burning out the harmful impurities contained in them by supplying additional (usually gaseous or liquid) fuel.
In combustion chambers in which fuel burns at high temperatures, large amounts of extremely toxic nitrogen oxides are formed. The maximum permissible concentration (MPC) of N0, safe for human health, in the air of populated areas is 0.08 mg/m 3 .
Since the formation of nitrogen oxides significantly decreases with decreasing temperature, in recent years power engineers have shown increasing interest in the so-called low-temperature (as opposed to high-temperature - with a temperature of 1100 ° C and above) combustion in a fluidized bed, when stable and complete combustion of hard and brown coals it is possible to provide at 750...950 "C.
Fluidized bed combustion. A layer of fine-grained material, blown from the bottom up with air at a speed exceeding the stability limit of the dense layer, but not sufficient to remove particles from the layer, creates circulation. The intense circulation of particles in the limited volume of the chamber creates the impression of a rapidly boiling liquid. A significant portion of the air passes through such a layer in the form of bubbles, vigorously mixing the fine-grained material, which further enhances the resemblance to a boiling liquid and explains the origin of the name.
The combustion method in a fluidized (fluidized) bed (see Fig. 5.5, d) is in a certain sense intermediate between layer and chamber. Its advantage is the ability to burn relatively small pieces of fuel (usually smaller than 5...10 mm) at an air speed of 0.1...0.5 m/s.
Fluidized bed furnaces are widely used in industry for burning pyrites to produce SO 2, roasting various ores and their concentrates (zinc, copper, nickel, gold), etc.
If we take air speed as the determining parameter w in relative to the speed of movement of fuel particles v t, then according to this parameter there are four fuel combustion technologies.
1. In a dense filter layer(w in >> v T).
It is used only for lump solid fuel, which is distributed on the grate. The fuel layer is blown with air at a speed at which the stability of the layer is not violated and the combustion process has an oxygen and reduction zone.
The apparent thermal stress of the grate is QR= 1.1...1.8 MW/m 2.
2. In a fluidized or fluidized bed(w in > v T).
As air speed increases, the dynamic pressure can reach and then exceed the gravitational force of the particles. The stability of the layer will be disrupted and a random movement of particles will begin, which will rise above the lattice and then reciprocate up and down. The flow speed at which the stability of the layer is disrupted is called critical.
It can be increased up to the soaring speed of particles, when they are carried out of the layer by a flow of gases.
A significant part of the air passes through the fluidized bed in the form of “bubbles” (gas volumes), which strongly mix the fine-grained material of the layer; as a result, the combustion process along the height occurs at an almost constant temperature, which ensures complete combustion of the fuel.
A fluidized fluidized bed is characterized by an air speed of 0.5...4 m/s, fuel particle size of 3...10 mm, layer 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.
Non-flammable filler is introduced into the fluidized bed: fine quartz sand, fireclay chips, etc.
The fuel concentration in the layer does not exceed 5%, which allows the combustion of any fuel (solid, liquid, gaseous, including combustible waste). A non-flammable 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 convert up to 95% of sulfur dioxide into a solid state.
3. In the air flow(w in ≈ v t) or flare direct-flow process. Fuel particles become suspended in the gas-air flow and begin to move with it, burning while moving within the combustion volume. The method is characterized by low intensity, extended combustion zone, and sharp non-isothermal properties; a high ambient temperature in the ignition zone and careful preparation of the fuel (atomization and pre-mixing with air) are required. Thermal stress of the furnace volume Q V≈ 0.5 MW/m3.
1 TYPES OF FUEL
Solid fuel - flammable substances, main integral part which is carbon. Solid fuels include coal and brown coals, oil shale, peat and wood. The properties of the fuel are largely determined by its chemical composition - the content of carbon, hydrogen, oxygen, nitrogen and sulfur. Identical amounts of fuel produce different amounts of heat when burned. Therefore, to assess the quality of fuel, its calorific value is determined, that is, the greatest amount of heat released during complete combustion of 1 kg of fuel (the highest calorific value of coal). Basically, solid fuel is used to produce heat and other types of energy that are spent on obtaining mechanical work. In addition, more than 300 different chemical compounds can be obtained from solid fuel with its appropriate processing (distillation); the processing of brown coal into valuable types of liquid fuel - gasoline and kerosene is of great importance.
Briquettes
Briquettes are solid fuel formed during the compression of waste from the woodworking process (shavings, chips, wood dust) as well as household waste (straw, husks), peat.
Fuel briquettes are easy to store; no harmful binders are used in production, which is why this type of fuel is environmentally friendly. When burning, they do not spark, do not emit fumes, burn evenly and smoothly, which ensures a fairly long combustion process in the boiler chamber. In addition to solid fuel boilers, they are used in home fireplaces and for cooking (on the grill, for example).
There are 3 main types of briquettes:
1. RUF- briquettes. Formed “bricks” of rectangular shape.
2. NESTRO- briquettes. Cylindrical in shape, can also have holes inside (rings).
3. Rini&Kau - briquettes. Faceted briquettes (4,6,8 faces).
Advantages fuel briquettes:
Environmentally friendly.
Long and convenient storage. Thanks to heat treatment, they are not susceptible to fungi. And thanks to the formation, they are convenient to use.
Long and even burning is due to the high degree of density of the briquettes.
High calorific value. Almost twice as high as regular firewood.
Constant combustion temperature. Due to uniform density.
Economically beneficial.
Minimum amount of ash after combustion: 1-3%
Pellets or fuel granules.
Essentially the same production principle as briquettes. Lignin (a plant polymer) is used as a binder.
The materials are the same as for briquettes: bark, shavings, straw, cardboard. First, the raw materials are 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 solid fuel of this type are the highest - this is justified by the complexity of production and popularity among buyers.
The following types of this solid fuel are distinguished:
Processing round timber from hard and soft trees into pellets.
Peat pellets
Pellets obtained as a result of processing sunflower husks.
Straw pellets
Advantages of pellets:
Environmentally friendly.
Storage. Thanks to special production technology, pellets can be stored directly in the open air. They do not swell or 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
Wooden pieces intended to produce heat by burning in solid fuel heating boilers, fireboxes designed for firewood. For convenience, the length of the logs is most often 25-30 cm. For the most effective use, the lowest level of moisture is required. For heating, combustion must be as slow as possible. Also, in addition to heating, firewood can be used, for example, in boilers for solid fuels. Best for these parameters Deciduous wood is suitable: oak, ash, hazel, hawthorn, birch.Coniferous firewood is worse, as it promotes the deposition of resin and has a low calorific value, and burns out quickly.
Firewood comes in two types:
Sawn.
Stab.
2 FUEL COMPOSITION
For the formation of coal, 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. Majority industrial deposits fossil coal dates back to this period, although younger deposits also exist. The oldest coals are estimated to be about 350 million years old. Coal is formed when decaying plant material accumulates faster than bacterial decomposition occurs. An ideal environment for this is created in swamps, where stagnant water, depleted of oxygen, prevents the 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 it is then buried under other sediments, the peat experiences compression and, losing water and gases, is converted into coal. Under the pressure of sediment layers 1 kilometer thick, a 20-meter layer of peat produces a layer of brown coal 4 meters thick. 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 a layer of anthracite 1.5 meters thick. As a result of the movement of the earth's crust, coal seams experienced uplift and folding. Over time, the raised parts were destroyed by erosion or spontaneous combustion, and the lower parts were preserved in wide, shallow basins where the 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 load pressure and under the influence of elevated temperature at depths of about 1 kilometer.
Stone 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 ignite well. They are formed from brown coal at depths of about 3 kilometers.
Anthracites. Almost entirely (96%) consists of carbon. They have the highest heat of combustion, but do not ignite well. Formed from coal and in the form of oxidesBUT X. They belong to the harmful components of combustion products, the quantity of which must be limited.
Sulfur - found in solid fuels in the form of organic compoundsSOand pyritesS xthey are combined into volatile sulfurS l. Sulfur is also included in the fuel in the form of sulfur salts - sulfates - which are not capable of burning. Sulfate sulfur is commonly referred to as fuel ash. The presence of sulfur significantly reduces the quality of solid fuel, since sulfur dioxideSO 2 AndSO 3 combine with water to form sulfuric acid- which in turn destroys the metal of the boiler and, when released into the atmosphere, harms the environment. It is for this reason that sulfur content in fuel - not just solid fuel - is extremely undesirable.
Fuel ash is a ballast mixture of various mineral substances remaining after 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 fuel?
2. What is ash?
3 FUEL APPLICATION
The uses of coal are varied. It is used as household, energy fuel, raw material for metallurgical and chemical industry, as well as for extracting rare and trace elements from it. The liquefaction (hydrogenation) of coal to form liquid fuel is very promising. To produce 1 ton of oil, 2-3 tons of coal are consumed; some countries almost completely provided themselves with fuel using this technology. Artificial graphite is obtained from coal.
Brown coal differs in appearance from hard coal in the color of the line on the porcelain plastic - it is always brown. The most important difference from hard coal is its lower carbon content and significantly higher content of bituminous volatiles and water. This explains why brown coal burns easier, produces more smoke, smell, as well as the above-mentioned reaction with caustic potassium, and produces little heat. Due to its high water content, it is used for combustion in powder form, into which it inevitably turns when dried. The nitrogen content is significantly lower than that of hard coals, but the sulfur content is higher.
The use of brown coal - as fuel, brown coal in many countries is used significantly less than hard coal, however, due to its low cost, it is more popular in small and private boiler houses and sometimes takes up to 80%. It is used for pulverized combustion (during storage, brown coal dries out and crumbles), and sometimes entirely. At small provincial thermal power plants, it is also often burned to produce heat. However, in Greece and especially in Germany, brown coal is used in steam power plants, generating up to 50% of electricity in Greece and 24.6% in Germany. WITH high speed The production of liquid hydrocarbon fuels from brown coal by distillation is spreading. After distillation, the residue is suitable for obtaining 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 death and incomplete decay of marsh plants under conditions of excess 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 earth” 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, hard coal is the youngest, brown coal is the youngest. Depending on aging, it has different humidity. The younger, the more moisture. During the combustion process, coal pollutes the environment, plus it is sintered into slag and deposited on the grates in the boiler. This prevents normal combustion.
Questions:
Scope of fuel?
Does burning fuel harm the environment, and which type is the most ?
4 METHODS OF FUEL COMBUSTION
There are three ways of burning fuel: layer, flare or chamber and vortex.
1 – grate; 2 – igniter door; 3 – loading door; 4 – heating surfaces; 5 – combustion chamber.
Figure 4.1 – Scheme of a layered firebox
This drawing shows a layered method of burning fuel, where a layer of lump fuel lies motionless on a grate and is blown with air.
The layer method is used to burn solid fuel.
And here the flare and vortex method of fuel combustion is shown.
1 – burner; 2 combustion chamber; 3 – lining; 4 – combustion screen; 5 - ceiling radiation superheater; 6 – scallop.
Figure 4.2 – Chamber firebox
Figure 4.3 - Vortex method of fuel combustion
With the flare and vortex method, all types of fuel can be burned, only solid fuel is first subjected to fracture, turning it into dust. When fuel is burned, all heat is transferred to 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 maintained by the grate, which is constantly supplied with solid fuel.
For more efficient 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 efficient combustion method?
Explain the advantages chamber method incineration.
5 WORKING PROCESSES IN BOILERS
Working processes in boilers:
Steam formation
In boiler installations, processes such as steam formation occur:
The conditions under which steam formation occurs in boilers are constant pressure and continuous heat supply.
Stages of the steam formation process: heating water to saturation temperature, steam formation and heating of steam to a given temperature.
You can also observe corrosion of heating surfaces in boilers:
Destruction of metal under the influence environment 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 water regime boiler Therefore, raw water before use forBoiler feed is pre-treated to improve its quality.
The quality of boiler water is characterized by solids, total salt content, hardness, alkalinity and content of corrosive gases
Sodium-cation filter - where the water is purified
Deaerator – removal of aggressive agents, air oxygen and carbon dioxide.
Samples of pipes that are corroded inside and out.
Corrosion of heating surfaces
Internal corrosion of steam and hot water boilers is mainly the following types: oxygen, steam-water, alkaline and sludge.
The main appearance of oxygen corrosion is pitting, usually with iron oxides.
Steam-water corrosion is observed when boilers operate under high thermal loads. As a result of this corrosion, on the internal surfaces of the screen pipes and brittle damage in places where boiler water evaporates.
As a result of sludge corrosion, shells are formed.
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 oils.
Loading...