Fuel combustion methods. Methods of burning gaseous fuels Methods of burning solid fuels

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 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.
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 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.

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 the fuel loaded into the furnace manually, as the lower layers burn out, moves along the 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 fixed 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 coals and anthracites 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 you to burn a wide variety of 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 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 throat 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 and swirl.
The method of fuel combustion is selected depending on the type and type of fuel, as well as the steam output of the boiler unit.

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 the 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, changing the diameter of the burner nozzle, regulating the gas pressure, etc.

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

With a mixed combustion method, the burner ensures that the gas is premixed with only a part of the air necessary 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.

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.

The gas enters the mixing chamber 7 in a thin annular jet. The air supplied (under a pressure slightly 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 supplied to 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 billets 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 ...

A 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 in 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 ...

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 of efficient combustion of fuel by separating gas (combustion reaction products), for example, Method of gas separation using membranes with purging of permeate 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 traction in its working space, igniting and burning 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 furnace temperature, the combustion process is transferred to a 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 hot 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 resulting gases are separated. 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 well-known combustion equations. The ratios of the reacting substances are maintained, as is their composition. That is, carbon C, hydrogen H 2 with oxygen O 2 enter into the reaction 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 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 supplied to 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 low temperatures 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 of the 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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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. The technical result is an increase in the efficiency of furnaces and heat generators. The method of fuel combustion in furnaces having a bell with a fuel combustion chamber and a grate, includes loading fuel, igniting and burning the fuel due to the primary air entering through the blower. The movement of gases in the bell is carried out without using the draft of the pipe, with the possibility of accumulating hot gases in the upper part of the bell. In this case, secondary air is fed into the bell, directly into the combustion zone. 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. After warming up the combustion chamber, superheated water vapor is supplied to the incandescent carbon into it, below the secondary air supply, and combustible gases are obtained. 1 ill.

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 the 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 integrated energy-technological processing to obtain 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 various 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 through 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.