The location of the automation device elements is shown in Fig. 7. It shows that the electromagnet is covered with a protective cap. The wires from the sensors are located inside thin-walled tubes. The tubes are attached to the electromagnet using union nuts. The body terminals of the sensors are connected to the electromagnet through the housing of the tubes themselves.
Now let’s look at the method for finding the above fault.
The check begins with the “weakest link” of the automation device - the traction sensor. The sensor is not protected by a casing, so after 6... 12 months of operation it becomes “overgrown” with a thick layer of dust. The bimetallic plate (see Fig. 6) quickly oxidizes, which leads to deterioration of contact.
The dust coat is removed with a soft brush. Then the plate is pulled away from the contact and cleaned with fine sandpaper. We should not forget that it is necessary to clean the contact itself. Good results cleaning of these elements with a special spray “Contact” gives. It contains substances that actively destroy the oxide film. After cleaning, apply a thin layer of liquid lubricant to the plate and contact.
The next step is to check the serviceability of the thermocouple. She works hard thermal mode, since it is constantly in the pilot flame, naturally, its service life is significantly less than the other elements of the boiler.
The main defect of a thermocouple is burnout (destruction) of its body. In this case, the transition resistance at the welding site (junction) increases sharply. As a result, the current in the Thermocouple - Electromagnet circuit
- The bimetallic plate will be lower than the nominal value, which leads to the fact that the electromagnet will no longer be able to fix the rod (Fig. 5).
To check the thermocouple, unscrew the union nut (Fig. 7), located on the left 
sides of the electromagnet. Then turn on the igniter and use a voltmeter to measure the constant voltage (thermo-EMF) at the thermocouple contacts (Fig. 8). A heated, serviceable thermocouple generates an EMF of about 25...30 mV. If this value is less, the thermocouple is faulty. To final check it, disconnect the tube from the electromagnet casing and measure the resistance of the thermocouple. The resistance of the heated thermocouple is less than 1 Ohm. If the resistance of the thermocouple is hundreds of Ohms or more, it must be replaced. A low value of thermo-EMF generated by a thermocouple can be caused by the following reasons: - clogging of the igniter nozzle (as a result, the heating temperature of the thermocouple may be lower than the nominal one). They “treat” such a defect by cleaning the igniter hole with any soft wire of a suitable diameter;
- shifting the position of the thermocouple (naturally, it may also not heat up enough). Eliminate the defect as follows - loosen the screw securing the liner near the igniter and adjust the position of the thermocouple (Figure 10);
- low gas pressure at the boiler inlet.
If the EMF at the thermocouple terminals is normal (while the symptoms of malfunction indicated above remain), then check the following elements:
- integrity of contacts at the connection points of the thermocouple and draft sensor.
Oxidized contacts must be cleaned. The union nuts are tightened, as they say, “by hand.” In this case, it is not advisable to use a wrench, since you can easily break the wires suitable for the contacts;
- integrity of the electromagnet winding and, if necessary, solder its terminals.
The functionality of the electromagnet can be checked as follows. Disconnect 
thermocouple connection. Press and hold the start button, then light the igniter. From a separate source DC voltage a voltage of about 1 V is applied to the released contact of the electromagnet (from the thermocouple) relative to the housing (at a current of up to 2 A). For this, you can use a regular battery (1.5 V), the main thing is that it provides the necessary operating current. The button can now be released. If the igniter does not go out, the electromagnet and draft sensor are working;
- traction sensor. First, check the force of pressing the contact against the bimetallic plate (with the indicated signs of malfunction, it is often insufficient). To increase the clamping force, release the lock nut and move the contact closer to the plate, then tighten the nut. In this case, no additional adjustments are required - the clamping force does not affect the response temperature of the sensor. The sensor has a large margin of plate deflection angle, ensuring reliable breaking of the electrical circuit in the event of an accident.
Natural gas is the most common fuel today. Natural gas is called natural gas because it is extracted from the very depths of the Earth.
The process of gas combustion is a chemical reaction in which interactions occur natural gas with oxygen contained in the air.
In gaseous fuel there is a combustible part and a non-combustible part.
The main flammable component of natural gas is methane - CH4. Its content in natural gas reaches 98%. Methane is odorless, tasteless and non-toxic. Its flammability limit is from 5 to 15%. It is these qualities that have made it possible to use natural gas as one of the main types of fuel. A methane concentration of more than 10% is life-threatening; suffocation can occur due to lack of oxygen.
To detect gas leaks, the gas is odorized, in other words, a strong-smelling substance (ethyl mercaptan) is added. In this case, the gas can be detected already at a concentration of 1%.
In addition to methane, natural gas may contain flammable gases - propane, butane and ethane.
To ensure high-quality combustion of gas, it is necessary to supply sufficient air to the combustion zone and ensure good mixing of gas with air. The optimal ratio is 1: 10. That is, for one part of gas there are ten parts of air. In addition, it is necessary to create the necessary temperature regime. In order for a gas to ignite, it must be heated to its ignition temperature and in the future the temperature should not fall below the ignition temperature.
It is necessary to organize the removal of combustion products into the atmosphere.
Complete combustion is achieved if there are no flammable substances in the combustion products released into the atmosphere. In this case, carbon and hydrogen combine together and form carbon dioxide and water vapor.
Visually, with complete combustion, the flame is light blue or bluish-violet.
In addition to these gases, nitrogen and remaining oxygen are released into the atmosphere with flammable gases. N2+O2
If gas combustion does not occur completely, flammable substances are released into the atmosphere - carbon monoxide, hydrogen, soot.
Incomplete combustion of gas occurs due to insufficient air. At the same time, tongues of soot visually appear in the flame.
The danger of incomplete combustion of gas is that carbon monoxide can cause poisoning of boiler room personnel. A CO content in the air of 0.01-0.02% can cause mild poisoning. Higher concentrations can cause severe poisoning and death.
The resulting soot settles on the walls of the boiler, 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, 9m3 of air is needed to burn 1m3 of gas. In real conditions, more air is required.
That is, an excess amount of air is needed. This value, designated alpha, shows how many times more air is consumed than is theoretically necessary.
The alpha coefficient depends on the type of specific burner and is usually specified in the burner passport or in accordance with the recommendations for organizing the commissioning work being carried out.
As the amount of excess air increases above the recommended level, heat loss increases. With a significant increase in the amount of air, a flame may break off, creating an emergency situation. If the amount of air is less than recommended, combustion will be incomplete, thereby creating a risk of poisoning for boiler room personnel.
For more accurate control of the quality of fuel combustion, there are devices - gas analyzers, which measure the content of certain substances in the composition of exhaust gases.
Gas analyzers can be supplied complete with boilers. If they are not available, the corresponding measurements are carried out commissioning organization using portable gas analyzers. A regime map is drawn up in which the necessary control parameters are prescribed. By adhering to them, you can ensure normal complete combustion of the fuel.
The main parameters for regulating fuel combustion are:
- the ratio of gas and air supplied to the burners.
- excess air coefficient.
- vacuum in the furnace.
- coefficient useful action boiler
In this case, the efficiency of the boiler means the ratio of useful heat to the amount of total heat expended.
Air composition
| Gas name | Chemical element | Contents in the air |
| Nitrogen | N2 | 78 % |
| Oxygen | O2 | 21 % |
| Argon | Ar | 1 % |
| Carbon dioxide | CO2 | 0.03 % |
| Helium | He | less than 0.001% |
| Hydrogen | H2 | less than 0.001% |
| Neon | Ne | less than 0.001% |
| Methane | CH4 | less than 0.001% |
| Krypton | Kr | less than 0.001% |
| Xenon | Xe | less than 0.001% |
Alexander Pavlovich Konstantinov
Chief Inspector for Safety Control of Nuclear and Radiation Hazardous Facilities. Candidate of Technical Sciences, Associate Professor, Professor of the Russian Academy of Natural Sciences.
A kitchen with a gas stove is often the main source of air pollution throughout the apartment. And, what is very important, this applies to the majority of Russian residents. Indeed, in Russia, 90% of urban and over 80% of rural residents use gas stoves Khata, Z. I. Human health in the modern environmental situation. - M.: FAIR PRESS, 2001. - 208 p..
In recent years, publications by serious researchers have appeared on the high health hazards of gas stoves. Doctors know that in houses with gas stoves, residents get sick more often and for longer than in houses with electric stoves. Moreover, we are talking about many different diseases, and not just respiratory diseases. The decline in health levels is especially noticeable in women, children, as well as in older and chronically ill people who spend more time at home.
It was not for nothing that Professor V. Blagov called the use of gas stoves “a large-scale chemical war against one’s own people.”
Why using domestic gas is harmful to health
Let's try to answer this question. There are several factors that combine to make the use of gas stoves hazardous to health.
First group of factors
This group of factors is determined by the very chemistry of the natural gas combustion process. Even if household gas burned completely to water and carbon dioxide, this would lead to a deterioration in the composition of the air in the apartment, especially in the kitchen. After all, at the same time, oxygen is burned out of the air, and at the same time the concentration of carbon dioxide increases. But this is not the main problem. In the end, the same thing happens to the air that a person breathes.
It is much worse that in most cases gas combustion does not occur completely, not 100%. Due to incomplete combustion of natural gas, much more toxic products are formed. For example, carbon monoxide (carbon monoxide), the concentration of which can be many times, 20–25 times higher than permissible norm. But this leads to headaches, allergies, ailments, weakened immunity Yakovleva, M. A. And we have gas in our apartment. - Business environmental magazine. - 2004. - No. 1(4). - P. 55..
In addition to carbon monoxide, sulfur dioxide, nitrogen oxides, formaldehyde, and benzopyrene, a strong carcinogen, are released into the air. In cities, benzopyrene enters the air from emissions from metallurgical plants, thermal power plants (especially coal-fired ones) and cars (especially old ones). But the concentration of benzopyrene, even in polluted atmospheric air, cannot be compared with its concentration in an apartment. The figure shows how much more benzopyrene we get while in the kitchen.
Entry of benzopyrene into the human body, mcg/day Let's compare the first two columns. In the kitchen we get 13.5 times more harmful substances than on the street! For clarity, let us estimate the intake of benzopyrene into our body not in micrograms, but in a more understandable equivalent - the number of cigarettes smoked daily. So, if a smoker smokes one pack (20 cigarettes) per day, then in the kitchen a person receives the equivalent of two to five cigarettes per day. That is, a housewife who has gas stove, as if “smoking” a little.
Second group of factors
This group is related to the operating conditions of gas stoves. Any driver knows that you cannot be in the garage at the same time as a car with the engine running. But in the kitchen we have just such a case: burning hydrocarbon fuels indoors! We lack that device that every car has - an exhaust pipe. According to all hygiene rules, each gas stove must be equipped with an exhaust ventilation hood.
Things are especially bad if we have a small kitchen in small apartment. Minimal area, minimal ceiling height, poor ventilation and a gas stove that works all day. But when low ceilings gas combustion products accumulate in the upper layer of air up to 70–80 centimeters thick Boyko, A. F. Health 5+. - M.: Rossiyskaya Gazeta, 2002. - 365 p..
The work of a housewife at a gas stove is often compared to harmful working conditions in production. This is not entirely correct. Calculations show that if the kitchen is small and there is no good ventilation, then we are dealing with particularly harmful working conditions. A type of metallurgist servicing coke oven batteries.
How to reduce harm from a gas stove
What should we do if everything is so bad? Maybe it’s really worth getting rid of the gas stove and installing an electric or induction one? It's good if there is such an opportunity. And if not? For this case there are several simple rules. It is enough to follow them, and you can reduce the harm to health from a gas stove tenfold. Let us list these rules (most of them are the recommendations of Professor Yu. D. Gubernsky) Ilnitsky, A. It smells like gas. - Be healthy!. - 2001. - No. 5. - P. 68–70..
- It is necessary to install an exhaust hood with an air purifier above the stove. This is the most effective technique. But even if for some reason you cannot do this, then the remaining seven rules in total will also significantly reduce air pollution.
- Monitor the complete combustion of gas. If suddenly the color of the gas is not what it should be according to the instructions, immediately call gas workers to regulate the malfunctioning burner.
- Do not clutter the stove with unnecessary dishes. Cookware should only be placed on working burners. In this case, free access of air to the burners and more complete combustion of gas will be ensured.
- It is better to use no more than two burners or an oven and one burner at the same time. Even if your stove has four burners, it is better to turn on a maximum of two at a time.
- The maximum continuous operation time of a gas stove is two hours. After this, you need to take a break and thoroughly ventilate the kitchen.
- When the gas stove is operating, the doors to the kitchen should be closed and the window should be open. This will ensure that combustion products are removed through the street, and not through living rooms.
- After finishing the operation of the gas stove, it is advisable to ventilate not only the kitchen, but the entire apartment. Through ventilation is desirable.
- Never use a gas stove to heat or dry clothes. You wouldn’t start a fire in the middle of the kitchen for this purpose, right?
The fuel for the boiler house is natural gas supplied from the gas distribution station. Natural gas with a pressure of 1-2 MPa, the temperature, flow and pressure of which are recorded by commercial metering devices, enters the first stage of reduction. The pressure after the first reduction stage is regulated by a pressure regulator valve.
Next, fuel gas with a pressure of about 0.5 MPa enters the tube space of the heater, the coolant of which is steam of 0.3-0.6 MPa. The temperature of the fuel gas after the heater is changed by a control valve installed on the steam pipeline. After the heater, the pressure of the fuel gas is reduced by the second stage of reduction to 3-80 kPa. After the second stage of reduction, the gas enters the boiler burners through standard gas equipment units (SBG). Before the SBG of each boiler, pressure, flow, and gas temperature are measured and recorded. The gas pressure after the SBG of each boiler is also recorded
5.3.2. Features of the natural gas combustion process.
The choice of the type and number of gas burners, their placement and organization of the combustion process depend on the characteristics of the thermal and aerodynamic operating conditions of the industrial installation. The correct solution of these problems determines the intensity of the technological process and the efficiency of the installation. Theoretical premises and operational experience indicate that when designing new gas installations, the main indicators of their operation, as a rule, can be improved. However, it should be noted here that an incorrectly chosen method of gas combustion and poor placement of burners reduce the productivity and efficiency of installations.
When designing industrial gas installations the tasks of intensifying the technological process and increasing fuel efficiency must be solved with the least material costs and in compliance with a number of other conditions, such as operational reliability, safety, etc.
When burning natural gas, unlike the combustion of other types of fuel, the characteristics of the torch can be varied within a wide range. Therefore, it can be used for almost any installation. Here you should only remember that the required maximum intensification of the technological process, increase in efficiency, as well as satisfaction of other requirements for the installation, cannot be ensured only by choosing one or another gas burner, but will be achieved by the right decision the whole complex of issues of heat transfer and aerodynamics, starting from the supply of air and gas and ending with the removal of waste combustion products into the atmosphere. Of particular importance is the initial stage of the process - the organization of gas combustion.
Natural gas is a colorless gas. Significantly lighter than air. The presence of gas in the air of premises, wells, pits of more than 20% causes suffocation, dizziness, loss of consciousness and death. According to sanitary standards, natural gas (methane) belongs to hazard class 4 (low-hazard substance). Low toxicity, not poisonous.
Composition of natural gas:
Methane 98.52%;
Ethane 0.46%;
Propane 0.16%;
Butane 0.02%;
Nitrogen 0.73%;
Carbon dioxide 0.07%.
If natural gas has passed all stages of purification, then its properties differ little from the properties of methane. Methane is the simplest element of the methane hydrocarbon series. Properties of methane:
Specific heat of combustion 7980 Kcal/m3;
It liquefies at t°=-161°С, hardens at t°=-182°С;
Methane density is 0.7169 kg/m3 (2 times lighter than air);
Ignition temperature t°=645°С;
Combustion temperature t°=1500 ÷ 2000°С
Explosion limits 5 ÷ 15%.
When interacting with air, highly explosive mixtures are formed that can explode and cause destruction.
The combustion of any fuel, including gas, is a reaction of its chemical combination with oxygen and is accompanied by the release of heat. The amount of heat obtained from the complete combustion of 1 m 3 (or 1 kg) of gas is called its calorific value. There is a distinction between the lowest heat of combustion, in which the latent heat of formation of water vapor contained in the combustion products is not taken into account, and the highest, when this heat is taken into account. The difference between the higher and lower calorific values depends on the amount of water vapor generated during fuel combustion and is approximately 2500 kJ per 1 kg or 2000 kJ per 1 m 3 of water vapor.
The heating value of different types of fuels can vary significantly. For example, firewood and peat have a lower calorific value of up to 12,500, the best coals have a calorific value of up to 31,000, and oil has a calorific value of about 40,000 kJ/kg. Natural gas has a lower calorific value of 40-44 MJ/kg.
The total combustion time is determined by the time d of mixture formation (diffusion processes) and the time k of chemical combustion reactions (kinetic processes). Taking into account the fact that these stages of the process may overlap, we obtain d + k.
At to d (combustion occurring simultaneously with mixture formation in the furnace is called diffusion, since this mixture formation includes processes of turbulent (in the final stage - molecular) diffusion).
At d k k (combustion of a pre-prepared mixture is often conventionally called kinetic, it is determined by the kinetics of chemical reactions).
When d and k are commensurate, the combustion process is called mixed.
The next stage of mixture formation is heating and ignition of the fuel. When a stream of flammable gas is mixed with a stream of air and their temperature gradually increases, at a certain temperature the mixture will ignite. The minimum temperature at which a mixture ignites is called the flash point.
The ignition temperature is not a physicochemical constant of the substance, since in addition to the nature of the flammable gas it depends on the concentration of the gas and the oxidizer, as well as on the intensity of heat exchange between the gas mixture and the environment.
There are upper and lower limits on the concentration of gas and oxidizer, and outside these limits at a given temperature the mixtures do not ignite. When the temperature of the gas-air mixture increases, according to the Arrhenius law, the reaction rate increases in proportion to e -E/ RT, and the heat release is proportional to the same value. If the heat loss of the combustion zone associated with heat exchange with the environment exceeds the heat release, then ignition and combustion are impossible. Typically, heating occurs simultaneously with mixture formation.
A gas-air mixture in which the gas content is between the lower and upper flammability limits is explosive. The wider the range of flammable limits (also called explosive limits), the more explosive the gas is. In chemical essence, an explosion of a gas-air (gas-oxygen) mixture is a very fast (almost instantaneous) combustion process, leading to the formation of combustion products that have a high temperature and a sharp increase in their pressure. The calculated excess pressure during the explosion of natural gas is 0.75, propane and butane - 0.86, hydrogen - 0.74, acetylene - 1.03 MPa. In practical conditions, the temperature of the explosion does not reach maximum values and the resulting pressures are lower than those indicated, but they are quite sufficient to destroy not only the lining of boilers and buildings, but also metal containers if an explosion occurs in them.
As a result of ignition and combustion, a flame appears, which is an external manifestation of intense reactions of the oxidizing substance. The movement of a flame through a gas mixture is called flame propagation. In this case, the gas mixture is divided into two parts - the burned gas, through which the flame has already passed, and the unburned gas, which will soon enter the flame area. The boundary between these two parts of the burning gas mixture is called the flame front.
A torch is a flow containing a mixture of air, burning gases, fuel particles and combustion products, in which heating, ignition and combustion of gaseous fuel occurs.
At normal temperatures in furnaces (1000-1500 °C), hydrocarbons, including methane, even in very short periods of time as a result of thermal decomposition give noticeable amounts of elemental carbon. As a result of the appearance of elemental carbon in the torch, the combustion process to a certain extent acquires elements of heterogeneous combustion, i.e., occurring on the surface of solid particles. The presence of catalysts (iron and nickel oxides) significantly accelerates the process of decomposition of methane and other hydrocarbons.
Thus, in the furnace or working space of the furnace, between the moment of introducing gas and air and the production of final combustion products as a result of the superposition of the process of thermal decomposition of hydrocarbons and the chain reaction of oxidation, a very complex picture is observed, characterized by the presence of both oxidation products CO 2 and H 2 O, and CO, H 2 , elemental carbon and products of incomplete oxidation (of the latter, formaldehyde is of particular importance). The ratio between these components will depend on the conditions and duration of heating of the gas preceding the oxidation reactions.
When fuel burns, chemical processes of oxidation of its combustible components occur, accompanied by intense heat release and a rapid rise in the temperature of combustion products.
A distinction is made between homogeneous combustion, which occurs in the volume, when the fuel and the oxidizer are in the same state of aggregation, and heterogeneous combustion, which occurs at the phase interface, when the combustible substance and the oxidizer are in different states of aggregation.
The combustion of gaseous fuel is a homogeneous process. During combustion, the rate of the direct process is incommensurably greater than the rate of the reverse process, so the reverse reaction can be neglected. Let us recall that for a homogeneous combustion reaction the expression for the rate of the direct reaction will be:
where -time; T- absolute temperature; TO- universal gas constant; k- reaction rate constant, depending on the nature of the reactants, the action of catalysts, and temperature; k 0 - empirical constant; E- activation energy, which characterizes the smallest excess energy that colliding particles must have for a reaction to occur.
From the expressions (the second of them is called the Arrhenius equation) it follows that the reaction rate increases with increasing concentrations (pressure in the system) and temperature and with decreasing activation energy. Experimental measurements give the activation energy a significantly smaller value than the given laws of chemical kinetics. This is explained by the fact that gas combustion processes are chain reactions and proceed through intermediate stages with the continuous formation of active centers (atoms or radicals).
For example, during the combustion of hydrogen (Fig. 3), with the help of free oxygen atoms and hydroxyl radicals, three active hydrogen atoms are formed instead of the one present at the beginning of the reaction stage under consideration. This tripling occurs at each stage, and in chain reactions the number of active centers increases like an avalanche. In addition, the interaction between unstable intermediates occurs much faster than between molecules.
Rice. 3. Scheme of a chain reaction of hydrogen combustion
The total rate of the hydrogen combustion reaction is determined by the rate of the slowest reaction (expressed by the equation H+O 2 OH+H 2) =kC n Co, where C n, Co are the concentrations of atomic hydrogen and molecular oxygen.
The oxidation processes of hydrocarbons that make up the organic part of natural and associated gases are the most complex. Until now, there is no clear understanding of the kinetic mechanism of reactions, although it can be said with confidence that combustion has a chain nature in the presence of an induction period and occurs with the formation of numerous intermediate products of partial oxidation and decomposition.
An approximate diagram of the staged combustion of methane can be represented by a set of the following reactions:
Although the initial and final products of the combustion reaction are gases, the intermediate products, in addition to gases, may contain elemental carbon in the form of a tiny soot suspension.
The rate of the combustion reaction of carbon monoxide depends on the concentrations of carbon monoxide and water vapor in the reaction zone, and the rate of chain combustion of methane and other hydrocarbons depends on the concentrations of atomic hydrogen, oxygen and water vapor.
The combustion of gas fuel is a combination of complex aerodynamic, thermal and chemical processes. The combustion process of gaseous fuel consists of several stages: mixing gas with air, heating the resulting mixture to the ignition temperature, ignition and combustion.
Characteristics of methane
§ Colorless;
§ Non-toxic (non-poisonous);
§ Odorless and tasteless.
§ Methane consists of 75% carbon, 25% hydrogen.
§ Specific gravity is 0.717 kg/m 3 (2 times lighter than air).
§ Flash point is the minimum initial temperature at which combustion begins. For methane it is 645 o.
§ Combustion temperature- This Maximum temperature, which can be achieved with complete combustion of gas if the amount of air required for combustion exactly corresponds to the chemical formulas of combustion. For methane it is 1100-1400 o and depends on the combustion conditions.
§ Heat of combustion– this is the amount of heat that is released during the complete combustion of 1 m 3 of gas and it is equal to 8500 kcal/m 3.
§ Flame propagation speed equal to 0.67 m/sec.
Gas-air mixture
Which gas contains:
Up to 5% does not burn;
From 5 to 15% explodes;
Over 15% burns when additional air is supplied (all this depends on the ratio of the volume of gas in the air and is called explosive limits)
Combustible gases are odorless; in order to timely detect them in the air and quickly and accurately detect leaks, the gas is odorized, i.e. give off a smell. For this purpose, ETHYLMERCOPTAN is used. The odorization rate is 16 g per 1000 m 3. If there is 1% natural gas in the air, you should smell it.
Gas used as fuel must comply with GOST requirements and contain harmful impurities per 100m 3 no more than:
Hydrogen sulfide 0.0 2 G /m.cube
Ammonia 2 gr.
Hydrocyanic acid 5 g.
Resin and dust 0.001 g/m3
Naphthalene 10 gr.
Oxygen 1%.
Using natural gas has a number of advantages:
· absence of ash and dust and removal of solid particles into the atmosphere;
· high heat of combustion;
· ease of transportation and combustion;
· the work of service personnel is facilitated;
· sanitary and hygienic conditions in boiler houses and surrounding areas are improved;
· wide range of automatic control.
When using natural gas, special precautions are required because... leakage is possible through leaks at the junction of the gas pipeline and fittings. The presence of more than 20% of gas in a room causes suffocation; its accumulation in a closed volume of more than 5% to 15% leads to an explosion of the gas-air mixture. Incomplete combustion releases carbon monoxide, which is poisonous even at low concentrations (0.15%).
Natural gas combustion
Burning called the rapid chemical combination of combustible parts of the fuel with oxygen in the air, occurs when high temperature, is accompanied by the release of heat with the formation of flame and combustion products. Combustion happens complete and incomplete.
Full combustion– Occurs when there is sufficient oxygen. Lack of oxygen causes incomplete combustion, in which less heat is released than with full carbon monoxide (has a poisonous effect on operating personnel), soot is formed on the surface of the boiler and heat loss increases, which leads to excessive fuel consumption, a decrease in boiler efficiency, and air pollution.
The products of natural gas combustion are– carbon dioxide, water vapor, some excess oxygen and nitrogen. Excess oxygen is contained in combustion products only in cases where combustion occurs with excess air, and nitrogen is always contained in combustion products, because is a component of air and does not take part in combustion.
Products of incomplete combustion of gas can be carbon monoxide, unburned hydrogen and methane, heavy hydrocarbons, soot.
Methane reaction:
CH 4 + 2O 2 = CO 2 + 2H 2 O
According to the formula For the combustion of 1 m 3 of methane, 10 m 3 of air is required, which contains 2 m 3 of oxygen. In practice, to burn 1 m 3 of methane, more air is needed, taking into account all kinds of losses; for this, a coefficient is used TO excess air, which = 1.05-1.1.
Theoretical air volume = 10 m3
Practical air volume = 10*1.05=10.5 or 10*1.1=11
Completeness of combustion fuel can be determined visually by the color and nature of the flame, as well as using a gas analyzer.
Transparent blue flame - complete combustion of gas;
Red or yellow with smoky streaks – combustion is incomplete.
Combustion is regulated by increasing the air supply to the firebox or decreasing the gas supply. This process uses primary and secondary air.
Secondary air– 40-50% (mixed with gas in the boiler furnace during combustion)
Primary air– 50-60% (mixed with gas in the burner before combustion) a gas-air mixture is used for combustion
Combustion characterizes flame distribution speed is the speed at which the flame front element distributed by relatively fresh stream of gas-air mixture.
The rate of combustion and flame propagation depends on:
· on the composition of the mixture;
· on temperature;
· from pressure;
· on the ratio of gas and air.
The burning rate determines one of the main conditions for the reliable operation of the boiler room and characterizes it flame separation and breakthrough.
Flame break– occurs if the speed of the gas-air mixture at the burner outlet is greater than the combustion speed.
Reasons for separation: excessive increase in gas supply or excessive vacuum in the firebox (draft). Flame separation is observed during ignition and when the burners are turned on. The separation of the flame leads to gas contamination of the furnace and gas ducts of the boiler and to an explosion.
Flame breakthrough– occurs if the speed of flame propagation (burning speed) is greater than the speed of outflow of the gas-air mixture from the burner. The breakthrough is accompanied by combustion of the gas-air mixture inside the burner, the burner becomes hot and fails. Sometimes a breakthrough is accompanied by a pop or explosion inside the burner. In this case, not only the burner, but also the front wall of the boiler can be destroyed. Overshoot occurs when there is a sharp decrease in gas supply.
If the flame comes off and breaks through, the maintenance personnel must stop supplying fuel, find out and eliminate the cause, ventilate the firebox and flue ducts for 10-15 minutes and re-ignite the fire.
The combustion process of gaseous fuel can be divided into 4 stages:
1. Gas leaking from the burner nozzle into the burner device under pressure at an increased speed.
2. Formation of a mixture of gas and air.
3. Ignition of the resulting combustible mixture.
4. Combustion of a flammable mixture.
Gas pipelines
Gas is supplied to the consumer through gas pipelines - external and internal– to gas distribution stations located outside the city, and from them through gas pipelines to gas regulatory points hydraulic fracturing or gas control device GRU industrial enterprises.
Gas pipelines are:
· high pressure first category over 0.6 MPa up to 1.2 MPa inclusive;
· high pressure of the second category over 0.3 MPa to 0.6 MPa;
· average pressure of the third category over 0.005 MPa to 0.3 MPa;
· low pressure fourth category up to 0.005 MPa inclusive.
MPa - means Mega Pascal
Only medium and low pressure gas pipelines are laid in the boiler room. The section from the network gas distribution pipeline (city) to the premises together with the disconnecting device is called input.
The inlet gas pipeline is considered to be the section from the disconnecting device at the inlet if it is installed outside the room to the internal gas pipeline.
There should be a valve at the gas inlet into the boiler room in a lighted and convenient place for maintenance. There must be an insulating flange in front of the valve to protect against stray currents. At each branch from the gas distribution pipeline to the boiler, at least 2 shut-off devices are provided, one of which is installed directly in front of the burner. In addition to fittings and instrumentation on the gas pipeline, in front of each boiler, it is necessary to install automatic device, providing safe work boiler To prevent gases from entering the boiler furnace in the event of faulty shut-off devices, purge candles and safety gas pipelines with shut-off devices are required, which must be open when the boilers are idle. Low pressure gas pipelines are painted in boiler rooms in yellow, and medium pressure in yellow with red rings.
Gas-burners- a gas burner device designed to supply to the combustion site, depending on the technological requirements, a prepared gas-air mixture or separated gas and air, as well as to ensure stable combustion of gaseous fuel and control the combustion process.
The following requirements apply to burners:
· the main types of burners must be mass-produced in factories;
· burners must ensure the passage of a given amount of gas and the completeness of its combustion;
· ensure a minimum amount of harmful emissions into the atmosphere;
· must operate without noise, flame separation or breakthrough;
· must be easy to maintain, convenient for inspection and repair;
· if necessary, could be used for reserve fuel;
· samples of newly created and existing burners are subject to GOST testing;
The main characteristic of burners is its thermal power , which is understood as the amount of heat that can be released during complete combustion of the fuel supplied through the burner. All these characteristics can be found in the burner data sheet.
