The combustion of natural gas is a complex physical and chemical process of the interaction of its combustible components with an oxidizer, while the chemical energy of the fuel is converted into heat. Burning can be complete or incomplete. When gas is mixed with air, the temperature in the furnace is high enough for combustion, the fuel and air are continuously supplied, complete combustion of the fuel is carried out. Incomplete combustion of fuel occurs when these rules are not observed, which leads to less heat release, (CO), hydrogen (H2), methane (CH4), and as a result, to soot deposition on heating surfaces, worsening heat transfer and increasing heat loss, which in turn, leads to excessive fuel consumption and a decrease in the efficiency of the boiler and, accordingly, to air pollution.
The excess air ratio depends on the design of the gas burner and furnace. The excess air coefficient must be at least 1, otherwise it may lead to incomplete combustion of the gas. And also an increase in the excess air coefficient reduces the efficiency of the heat-using installation due to large heat losses with the exhaust gases.
The completeness of combustion is determined using a gas analyzer and by color and smell.
Complete combustion of gas. methane + oxygen \u003d carbon dioxide + water CH4 + 2O2 \u003d CO2 + 2H2O In addition to these gases, nitrogen and the remaining oxygen enter the atmosphere with combustible gases. N2 + O2 If the combustion of gas is incomplete, then combustible substances are emitted into the atmosphere - carbon monoxide, hydrogen, soot.CO + H + C
Incomplete combustion of gas occurs due to insufficient air. At the same time, soot tongues appear visually in the flame. The danger of incomplete combustion of gas is that carbon monoxide can cause poisoning of boiler room personnel. The content of CO in the air 0.01-0.02% can cause mild poisoning. A higher concentration can lead to severe poisoning and death. The resulting soot settles on the walls of the boilers, thereby impairing the transfer of heat to the coolant and reducing the efficiency of the boiler room. Soot conducts heat 200 times worse than methane. Theoretically, 9 m3 of air is needed to burn 1 m3 of gas. In real conditions, more air is needed. That is, an excess amount of air is needed. This value, denoted alpha, shows how many times more air is consumed than theoretically necessary. The alpha coefficient depends on the type of a particular burner and is usually prescribed in the burner's passport or in accordance with the recommendations of the commissioning organization. With an increase in the amount of excess air above the recommended one, heat losses increase. With a significant increase in the amount of air, flame separation can occur, creating an emergency. If the amount of air is less than recommended, then combustion will be incomplete, thereby creating a risk of poisoning the boiler room personnel. Incomplete combustion is determined by:
The combustion of gaseous fuel is a combination of the following physical and chemical processes: mixing combustible gas with air, heating the mixture, thermal decomposition of combustible components, ignition and chemical combination of combustible elements with atmospheric oxygen.
Stable combustion of a gas-air mixture is possible with a continuous supply of the necessary amounts of combustible gas and air to the combustion front, their thorough mixing and heating to the ignition or self-ignition temperature (Table 5).
The ignition of the gas-air mixture can be carried out:
- heating the entire volume of the gas-air mixture to the auto-ignition temperature. This method is used in internal combustion engines, where the gas-air mixture is heated by rapid compression to a certain pressure;
- the use of foreign sources of ignition (igniters, etc.). In this case, not the entire gas-air mixture is heated to the ignition temperature, but part of it. This method is used when burning gases in the burners of gas appliances;
- existing torch continuously in the combustion process.
To start the combustion reaction of gaseous fuel, it is necessary to spend a certain amount of energy necessary to break molecular bonds and create new ones.
The chemical formula for the combustion of gas fuel, indicating the entire reaction mechanism associated with the emergence and disappearance of a large number of free atoms, radicals and other active particles, is complex. Therefore, for simplification, equations are used that express the initial and final states of gas combustion reactions.
If hydrocarbon gases are denoted C m H n, then the equation for the chemical reaction of combustion of these gases in oxygen will take the form
C m H n + (m + n/4)O 2 = mCO 2 + (n/2)H 2 O,
where m is the number of carbon atoms in the hydrocarbon gas; n is the number of hydrogen atoms in the gas; (m + n/4) - the amount of oxygen required for complete combustion of the gas.
In accordance with the formula, the equations for the combustion of gases are derived:
- methane CH 4 + 2O 2 \u003d CO 2 + 2H 2 O
- ethane C 2 H 6 + 3.5O 2 \u003d 2CO 2 + ZH 2 O
- butane C 4 H 10 + 6.5O 2 \u003d 4CO 2 + 5H 2 0
- propane C 3 H 8 + 5O 3 \u003d ZSO 2 + 4H 2 O.
In practical conditions of gas combustion, oxygen is not taken in its pure form, but is part of the air. Since air consists of 79% nitrogen and 21% oxygen by volume, 100:21 = 4.76 volumes of air or 79:21 = 3.76 volumes of nitrogen is required for each volume of oxygen. Then the combustion reaction of methane in air can be written as follows:
CH 4 + 2O 2 + 2 * 3.76N 2 \u003d CO 2 + 2H 2 O + 7.52N 2.
The equation shows that for the combustion of 1 m 3 of methane, 1 m 3 of oxygen and 7.52 m 3 of nitrogen or 2 + 7.52 = 9.52 m 3 of air are required.
As a result of the combustion of 1 m 3 of methane, 1 m 3 of carbon dioxide, 2 m 3 of water vapor and 7.52 m 3 of nitrogen are obtained. The table below shows these data for the most common combustible gases.
For the process of combustion of a gas-air mixture, it is necessary that the amount of gas and air in the gas-air mixture be within certain limits. These limits are called flammability limits or explosive limits. There are lower and upper flammability limits. The minimum gas content in the gas-air mixture, expressed as a percentage by volume, at which ignition occurs, is called the lower flammability limit. The maximum gas content in the gas-air mixture, above which the mixture does not ignite without the supply of additional heat, is called the upper flammability limit.
The amount of oxygen and air during the combustion of certain gases
|
To burn 1 m 3 of gas is required, m 3 |
When burning 1 m 3 gas is released, m 3 |
Heat of combustion He, kJ / m 3 |
|||||
|
oxygen |
dioxide carbon |
||||||
|
carbon monoxide |
|||||||
If the gas-air mixture contains gas less than the lower flammable limit, then it will not burn. If there is not enough air in the gas-air mixture, then combustion does not proceed completely.
Inert impurities in gases have a great influence on the magnitude of the explosive limits. An increase in the ballast content (N 2 and CO 2) in the gas narrows the flammability limits, and when the ballast content increases above certain limits, the gas-air mixture does not ignite at any ratio of gas and air (table below).
The number of volumes of inert gas per 1 volume of combustible gas at which the gas-air mixture ceases to be explosive
The smallest amount of air required for complete combustion of gas is called the theoretical air flow and is denoted by Lt, that is, if the net calorific value of gas fuel is 33520 kJ / m 3 , then the theoretically required amount of air for burning 1 m 3 gas
L T\u003d (33 520/4190) / 1.1 \u003d 8.8 m 3.
However, the actual air flow always exceeds the theoretical one. This is explained by the fact that it is very difficult to achieve complete combustion of gas at theoretical air flow rates. Therefore, any gas combustion plant operates with some excess air.
So, practical air flow
L n = αL T,
where L n- practical air consumption; α - coefficient of excess air; L T- theoretical air consumption.
The excess air coefficient is always greater than one. For natural gas it is α = 1.05 - 1.2. Coefficient α shows how many times the actual air flow exceeds the theoretical one, taken as a unit. If a α = 1, then the gas-air mixture is called stoichiometric.
At α = 1.2 gas combustion is carried out with an excess of air by 20%. As a rule, combustion of gases should take place with a minimum value of a, since with a decrease in excess air, heat losses with exhaust gases decrease. The air involved in combustion is primary and secondary. Primary called the air entering the burner for mixing with gas in it; secondary- air entering the combustion zone is not mixed with gas, but separately.
Gas combustion is a combination of the following processes:
Mixing combustible gas with air
heating the mixture
thermal decomposition of combustible components,
Ignition and chemical combination of combustible components with atmospheric oxygen, accompanied by the formation of a torch and intense heat release.
The combustion of methane occurs according to the reaction:
CH 4 + 2O 2 \u003d CO 2 + 2H 2 O
Conditions required for gas combustion:
Ensuring the required ratio of combustible gas and air,
heating up to ignition temperature.
If the gas-air mixture of gas is less than the lower flammable limit, then it will not burn.
If there is more gas in the gas-air mixture than the upper flammable limit, then it will not burn completely.
The composition of the products of complete combustion of gas:
CO 2 - carbon dioxide
H 2 O - water vapor
* N 2 - nitrogen (it does not react with oxygen during combustion)
Composition of products of incomplete combustion of gas:
CO - carbon monoxide
C - soot.
Combustion of 1 m 3 of natural gas requires 9.5 m 3 of air. In practice, air consumption is always higher.
Attitude actual consumption air to theoretically required flow is called the excess air coefficient: α = L/L t .,
Where: L- actual expense;
L t - theoretically required flow.
The excess air coefficient is always greater than one. For natural gas, it is 1.05 - 1.2.
2. Purpose, device and main characteristics of instantaneous water heaters.
Flowing gas water heaters. Designed to heat water to a certain temperature during drawdown. Flowing water heaters are divided according to the load of thermal power: 33600, 75600, 105000 kJ, according to the degree of automation - into the highest and first classes. efficiency water heaters 80%, oxide content is not more than 0.05%, the temperature of the combustion products behind the draft interrupter is not less than 180 0 C. The principle is based on heating water during the drawdown period.
The main units of instantaneous water heaters are: a gas burner, a heat exchanger, an automation system and a gas outlet. The low pressure gas is fed into the injection burner. The combustion products pass through the heat exchanger and are discharged into the chimney. The heat of combustion is transferred to the water flowing through the heat exchanger. To cool the fire chamber, a coil is used, through which water circulates, passing through the heater. Gas instantaneous water heaters are equipped with gas exhaust devices and draft breakers, which, in the event of a short-term violation of draft, prevent the flame of the gas burner from extinguishing. There is a flue pipe for connection to the chimney.
Gas instantaneous water heater - VPG. On the front wall of the casing there are: a gas cock control knob, a button for turning on the solenoid valve and a viewing window for observing the flame of the pilot and main burners. At the top of the device there is a smoke exhaust device, at the bottom there are branch pipes for connecting the device to the gas and water systems. The gas enters the solenoid valve, the gas shut-off valve of the water and gas burner block sequentially turns on the pilot burner and supplies gas to the main burner.
Blocking the flow of gas to the main burner, with the obligatory operation of the igniter, is carried out by an electromagnetic valve operating from a thermocouple. Blocking the gas supply to the main burner, depending on the presence of water intake, is carried out by a valve driven through the stem from the membrane of the water block valve.
Ld. - the actual amount of air supplied to the furnace, it is usually supplied in excess. The relationship between theoretical and actual flow is expressed by the equation:where α is the excess air coefficient (usually greater than 1).
Incomplete combustion of gas leads to excessive fuel consumption and increases the risk of poisoning by products of incomplete combustion of gas, which also include carbon monoxide (CO).
Products of gas combustion and control over the combustion process.
The combustion products of natural gas are carbon dioxide (carbon dioxide), water vapour, some excess oxygen and nitrogen. Excess oxygen is contained in the combustion products only in those cases when combustion occurs with excess air, and nitrogen is always contained in the combustion products, since it is an integral part of the air and does not take part in combustion.
The products of incomplete combustion of gas can be carbon monoxide (carbon monoxide), unburned hydrogen and methane, heavy hydrocarbons, soot.
The combustion process can be most correctly judged by flue gas analysis devices that show the content of carbon dioxide and oxygen in it. If the flame in the boiler furnace is elongated and has a dark yellow color, this indicates a lack of air, and if the flame becomes short and has a dazzling white color, then its excess.
There are two ways to regulate the operation of the boiler unit by changing the thermal power of all burners installed in the boiler, or by turning off part of them. The method of regulation depends on local conditions and must be specified in the production instructions. A change in the thermal power of the burners is permissible if it does not go beyond the limits of stable operation. Deviation of thermal power beyond the limits of stable operation can lead to separation or flashback of the flame.
Adjust the operation of individual burners in two steps, slowly and gradually changing the flow of air and gas.
When reducing the heat output, first reduce the air supply, and then gas; with an increase in thermal power, first increase the gas supply, and then air.
In this case, the vacuum in the furnace should be regulated by changing the position of the gate valve with the boiler or the blades of the guide vane in front of the smoke exhauster.
If it is necessary to increase the heat output of the burners, increase vacuum in the furnace; with a decrease in thermal power, the operation of the burners is first regulated, and then the vacuum in the furnace is reduced.
Gas combustion methods.
Depending on the method of education DHW combustion methods can be divided into diffusion, mixed and kinetic.
At diffusion In this method, gas enters the combustion front under pressure, and air from the surrounding space due to molecular or turbulent diffusion, mixture formation proceeds simultaneously with the combustion process, therefore the rate of the combustion process is determined by the rate of mixture formation.
The combustion process begins after the formation of contact between gas and air and the formation of hot water of the required composition. In this case, air diffuses to the gas jet, and gas diffuses from the gas jet into air. Thus, a hot water supply is created near the gas jet, as a result of the combustion of which a zone of primary gas combustion is formed (2) . The combustion of the main part of the gas occurs in the zone (Z), in the zone (4) moving combustion products.
This combustion method is mainly used in everyday life (ovens, gas stoves, etc.)
With the mixed method of gas combustion, 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 comes from the environment directly to the torch.
In this case, only part of the gas mixed with primary air (50%-60%), and the rest of the gas, diluted with combustion products, burns out after the addition of oxygen from the secondary air.
The air surrounding the flame is called secondary .
With the kinetic method of gas combustion, DHW is supplied to the combustion site fully prepared inside the burner.
Classification of gas burners .
A gas burner is a device that provides stable combustion of gaseous fuel and regulation of the combustion process.
The main functions of gas burners:
Supply of gas and air to the combustion front;
mixture formation;
Stabilization of the ignition front;
Ensuring the required intensity of the gas combustion process.
According to the gas combustion method, all burners can be divided into three groups:
Diffusion - without preliminary mixing of gas with air;
Diffusion-kinetic - with incomplete preliminary mixing of gas with air;
Kinetic - with complete pre-mixing of gas with air.
According to the method of air supply, the burners are divided into:
Blow-free - in which air enters the furnace due to the discharge in it.
Injection - in which air is sucked in due to the energy of the gas jet.
Blast - in which air is supplied to the burner or furnace using a fan.
According to the pressure of the gas on which the burners operate:
- low pressure up to 0.05 kgf/cm 2 ;
- medium pressure over 0.05 to 3 kgf/cm 2 ;
- high pressure over 3 kgf/cm 2 .
General requirements for all burners:
Ensuring the completeness of gas combustion;
Stability when changing thermal power;
Reliability during operation;
Compactness;
Serviceability.
Physical and chemical properties of natural gas
Natural gas is colorless, odorless and tasteless, non-toxic.
Density of gases at t = 0°C, Р = 760 mm Hg. Art.: methane - 0.72 kg / m 3, air -1.29 kg / m 3.
The autoignition temperature of methane is 545 - 650°C. This means that any mixture of natural gas and air heated to this temperature will ignite without an ignition source and will burn.
The combustion temperature of methane is 2100°C in furnaces of 1800°C.
Calorific value of methane: Q n \u003d 8500 kcal / m 3, Q in \u003d 9500 kcal / m 3.
Explosiveness. Distinguish:
- the lower explosive limit is the lowest gas content in the air at which an explosion occurs, it is 5% for methane.
With a lower content of gas in the air, there will be no explosion due to a lack of gas. When introducing a third-party energy source - pops.
- the upper explosive limit is the highest gas content in the air at which an explosion occurs, it is 15% for methane.
With a higher content of gas in the air, there will be no explosion due to lack of air. When a third-party source of energy is introduced - fire, fire.
For a gas explosion, in addition to keeping it in the air within the limits of its explosibility, an external source of energy (spark, flame, etc.) is needed.
During a gas explosion in a closed volume (a room, a firebox, a tank, etc.), there is more destruction than in the open air.
When burning gas with underburning, i.e., with a lack of oxygen, carbon monoxide (CO), or carbon monoxide, is formed in the combustion products, which is a highly toxic gas.
Flame propagation speed is the speed at which the flame front moves relative to the fresh mixture jet.
Estimated flame propagation speed methane - 0.67 m / s. It depends on the composition, temperature, pressure of the mixture, the ratio of gas and air in the mixture, the diameter of the flame front, the nature of the movement of the mixture (laminar or turbulent) and determines the stability of combustion.
Gas odorization- this is the addition of a strong-smelling substance (odorant) to the gas to give the gas an odor before delivery to consumers.
Requirements for odorants:
- a sharp specific smell;
- must not prevent combustion;
- should not dissolve in water;
– must be harmless to humans and equipment.
Ethyl mercaptan (C 2 H 5 SH) is used as an odorant, it is added to methane - 16 g per 1000 m 3, in winter the rate doubles.
A person should smell the odorant in the air when the gas content in the air is 20% of the lower explosive limit for methane - 1% by volume.
This is a chemical process of combining combustible components (hydrogen and carbon) with oxygen contained in the air. Occurs with the release of heat and light.
When carbon is burned, carbon dioxide (CO 2) is formed, and hydrogen is formed into water vapor (H 2 0).
Combustion stages: supply of gas and air, formation of a gas-air mixture, ignition of the mixture, its combustion, removal of combustion products.
Theoretically, when all the gas burns out and all the necessary amount of air takes part in combustion, the combustion reaction of 1 m 3 of gas:
CH 4 + 20 2 \u003d CO 2 + 2H 2 O + 8500 kcal / m 3.
To burn 1 m 3 of methane, 9.52 m 3 of air is needed.
Practically not all the air supplied to combustion will take part in combustion.
Therefore, in addition to carbon dioxide (CO 2) and water vapor (H 2 0), the following will appear in the combustion products:
- carbon monoxide, or carbon monoxide (CO), if it enters the room, can cause poisoning of the attendants;
- atomic carbon, or soot (C), being deposited in gas ducts and furnaces, worsens traction, and heat transfer on heating surfaces.
- unburned gas and hydrogen - accumulating in furnaces and gas ducts, form an explosive mixture.
With a lack of air, incomplete combustion of the fuel occurs - the combustion process occurs with underburning. Underburning also occurs with poor mixing of gas with air and low temperature in the combustion zone.
For complete combustion of gas, combustion air is supplied in sufficient quantity, air and gas must be well mixed, and a high temperature is required in the combustion zone.
For complete combustion of gas, air is supplied in a larger amount than theoretically required, i.e., with excess, not all air will take part in combustion. Part of the heat will be spent on heating this excess air and will be released into the atmosphere.
The excess air coefficient α is a number showing how many times the actual consumption for combustion is greater than it is theoretically required:
α = V d / V t
where V d - actual air consumption, m 3;
V t - theoretically necessary air, m 3.
α = 1.05 - 1.2.
Gas flaring methods
Combustion air can be:
- primary - is fed into the burner, mixed with gas, and the gas-air mixture is used for combustion;
- secondary - enters the combustion zone.
Gas combustion methods:
1. Diffusion method - gas and combustion air are supplied separately and mixed in the combustion zone, all air is secondary. The flame is long, a large furnace space is required.
2. Mixed method - part of the air is supplied into the burner, mixed with gas (primary air), part of the air is supplied to the combustion zone (secondary). The flame is shorter than with the diffusion method.
3. Kinetic method - all air is mixed with gas inside the burner, i.e. all air is primary. The flame is short, a small furnace space is required.
Gas burner devices
Gas burners are devices that supply gas and air to the combustion front, form a gas-air mixture, stabilize the combustion front, and ensure the required intensity of the combustion process.
A burner equipped with an additional device (tunnel, air distribution device, etc.) is called a gas burner device.
Burner requirements:
1) must be factory-made and pass state tests;
2) must ensure the completeness of gas combustion in all operating modes with a minimum excess of air and a minimum emission of harmful substances into the atmosphere;
3) be able to use automatic control and safety, as well as measuring the parameters of gas and air in front of the burner;
4) must have a simple design, be accessible for repair and revision;
5) must work stably within the operating regulation, if necessary, have stabilizers to prevent separation and flashback of the flame;
6) for working burners, the noise level should not exceed 85 dB, and the surface temperature should not exceed 45 ° C.
Parameters of gas burners
1) thermal power of the burner N g - the amount of heat released during the combustion of gas in 1 hour;
2) the lowest limit of stable operation of the burner N n. .P. . - the lowest power at which the burner operates stably without separation and flashover of the flame;
3) minimum power N min - the power of the lower limit, increased by 10%;
4) the upper limit of stable operation of the burner N in. .P. . - the highest power at which the burner operates stably without separation and flashover of the flame;
5) maximum power N max - power of the upper limit, reduced by 10%;
6) rated power N nom - the highest power with which the burner operates for a long time with the highest efficiency;
7) operating control range - power values from N min to N nom;
8) coefficient of working regulation - the ratio of the rated power to the minimum.
Classification of gas burners:
1) according to the method of supplying air for combustion:
- blastless - air enters the furnace due to rarefaction in it;
- injection - air is sucked into the burner due to the energy of the gas jet;
- blast - air is supplied to the burner or to the furnace using a fan;
2) according to the degree of preparation of the combustible mixture:
– without preliminary mixing of gas with air;
- with complete pre-mixing;
- with incomplete or partial pre-mixing;
3) by the speed of the outflow of combustion products (low - up to 20 m / s, medium - 20-70 m / s, high - more than 70 m / s);
4) according to the gas pressure in front of the burners:
- low up to 0.005 MPa (up to 500 mm water column);
- average from 0.005 MPa to 0.3 MPa (from 500 mm water column to 3 kgf / cm 2);
- high more than 0.3 MPa (more than 3 kgf / cm 2);
5) according to the degree of automation of burner control - with manual control, semi-automatic, automatic.
According to the method of air supply, burners can be:
1) Diffusion. All air enters the torch from the surrounding space. The gas is supplied to the burner without primary air and, leaving the collector, mixes with the air outside it.
The simplest burner in design, usually a pipe with holes drilled in one or two rows.
Variety - hearth burner. It consists of a gas collector made of a steel pipe, plugged at one end. Holes are drilled in two rows in the pipe. The collector is installed in a slot, made of refractory bricks, based on a grate. Gas through the holes in the collector exits into the gap. Air enters the same slot through the grate due to rarefaction in the furnace or with the help of a fan. During operation, the refractory lining of the slot heats up, ensuring flame stabilization in all operating modes.
Advantages of the burner: simple design, reliable operation (flame flashback is impossible), noiselessness, good regulation.
Disadvantages: low power, uneconomical, high flame.
2) Injection burners:
a) low pressure or atmospheric (applies to burners with partial premixing). The jet of gas leaves the nozzle at high speed and, due to its energy, captures air into the confuser, dragging it inside the burner. Mixing of gas with air takes place in a mixer consisting of a neck, a diffuser and a fire nozzle. The vacuum created by the injector increases with increasing gas pressure, while changing the amount of primary air drawn in. The amount of primary air can be changed using an adjusting washer. By changing the distance between the washer and the confuser, the air supply is regulated.
To ensure complete combustion of the fuel, part of the air enters due to rarefaction in the furnace (secondary air). The regulation of its consumption is carried out by changing the vacuum.
They have the property of self-regulation: with increasing load, the pressure of the gas increases, which injects an increased amount of air into the burner. As the load decreases, the amount of air decreases.
Burners are limitedly used on high-capacity equipment (more than 100 kW). This is due to the fact that the burner collector is located directly in the furnace. During operation, it heats up to high temperatures and quickly fails. They have a high excess air ratio, which leads to uneconomical gas combustion.
b) Medium pressure. When the gas pressure is increased, all the air required for complete combustion of the gas is injected. All air is primary. They operate at gas pressure from 0.005 MPa to 0.3 MPa. Relate to burners of complete pre-mixing of gas with air. As a result of good mixing of gas and air, they work with a small excess air ratio (1.05-1.1). Burner Kazantsev. Consists of primary air regulator, nozzle, mixer, nozzle and plate stabilizer. When leaving the nozzle, the gas has enough energy to inject all the air needed for combustion. In the mixer, the gas is completely mixed with air. The primary air regulator at the same time dampens the noise that occurs due to the high speed of the gas-air mixture. Advantages:
- simplicity of design;
- stable operation when the load changes;
- lack of air supply under pressure (no fan, electric motor, air ducts);
– the possibility of self-regulation (maintaining a constant gas-air ratio).
Disadvantages:
- large dimensions of the burners along the length, especially burners with increased productivity;
– high noise level.
3) Burners with forced air supply. The formation of the gas-air mixture begins in the burner and ends in the furnace. Air is supplied by a fan. The supply of gas and air is carried out through separate pipes. They operate on low and medium pressure gas. For better mixing, the gas flow is directed through the holes at an angle to the air flow.
To improve mixing, the air flow is given a rotational motion using swirlers with a constant or adjustable blade angle.
Swirl gas burner (GGV) - gas from the distribution manifold exits through holes drilled in one row, and at an angle of 90 0 enters the air flow swirling with a bladed swirler. The blades are welded at an angle of 45 0 to the outer surface of the gas manifold. Inside the gas collector there is a pipe for monitoring the combustion process. When working on fuel oil, a steam-mechanical nozzle is installed in it.
Burners designed to burn several types of fuel are called combined.
Advantages of the burners: high thermal power, wide range of operating regulation, the ability to control the excess air ratio, the possibility of preheating gas and air.
Disadvantages of burners: sufficient design complexity; detachment and breakthrough of the flame are possible, in connection with which it becomes necessary to use combustion stabilizers (ceramic tunnel, pilot torch, etc.).
Burner accidents
The amount of air in the gas-air mixture is the most important factor affecting the speed of flame propagation. In mixtures in which the gas content exceeds the upper limit of its ignition, the flame does not spread at all. With an increase in the amount of air in the mixture, the flame propagation speed increases, reaching the highest value when the air content is about 90% of its theoretical amount necessary for complete combustion of the gas. Increasing the air flow to the burner creates a mixture that is poorer in gas, capable of burning faster and causing a flash of flame into the burner. Therefore, if it is required to increase the load, first increase the gas supply, and then the air. If it is necessary to reduce the load, they do the opposite - first reduce the air supply, and then the gas. At the time of starting the burners, air should not enter them and the gas is ignited in a diffusion mode due to the air entering the furnace, followed by a transition to air supply to the burner
1. Flame separation - movement of the torch zone from the burner outlets in the direction of fuel combustion. Occurs when the speed of the gas-air mixture becomes greater than the speed of flame propagation. The flame becomes unstable and may go out. Gas continues to flow through the extinguished burner, which leads to the formation of an explosive mixture in the furnace.
Separation occurs when: an increase in gas pressure above the permissible one, a sharp increase in the supply of primary air, an increase in vacuum in the furnace, the operation of the burner in transcendental modes relative to those indicated in the passport.
2. Flashback - moving the flame zone towards the combustible mixture. It happens only in burners with a preliminary mixture of gas and air. Occurs when the speed of the gas-air mixture becomes less than the speed of flame propagation. The flame jumps inside the burner, where it continues to burn, causing the burner to deform from overheating. In case of a slip, a small pop is possible, the flame will go out, gassing of the furnace and gas ducts will occur through the idle burner.
The breakthrough occurs when: the gas pressure in front of the burner drops below the permissible value; ignition of the burner when the primary air is supplied; large gas supply at low air pressure, reducing the performance of burners by pre-mixing gas and air below the values \u200b\u200bspecified in the passport. Not possible with the diffusion method of gas combustion.
Actions of personnel in case of an accident at the burner:
- turn off the burner,
- ventilate the furnace,
- find out the cause of the accident,
- make a journal entry
