Concentration limits of explosiveness of natural gas. Physical and chemical properties of natural gas

Gas-air mixtures can ignite (explode) only when the gas content in the mixture is within certain (for each gas) limits. In this regard, there are lower and upper concentration limits of flammability. The lower limit corresponds to the minimum, and the upper - to the maximum amount of gas in the mixture, at which they ignite (during ignition) and spontaneous (without heat influx from the outside) flame propagation (self-ignition). The same limits correspond to the conditions of explosiveness of gas-air mixtures.

Table 8.8. The degree of dissociation of water vapor H2O and carbon dioxide CO2 depending on the partial pressure

Temperature,

Partial pressure, MPa

Water vapor H2O

Carbon dioxide CO2

If the gas content in the gas-air mixture is less than the lower flammability limit, such a mixture cannot burn and explode, since the heat released near the ignition source is not enough to heat the mixture to the ignition temperature. If the gas content of the mixture is between the lower and upper flammability limits, the ignited mixture ignites and burns both near the ignition source and when it is removed. This mixture is explosive.

The wider the range of flammability limits (also called explosive limits) and the lower the lower limit, the more explosive the gas. And finally, if the gas content in the mixture exceeds the upper flammability limit, then the amount of air in the mixture is insufficient for complete combustion of the gas.

The existence of flammability limits is caused by heat loss during combustion. When a combustible mixture is diluted with air, oxygen or gas, heat losses increase, the flame propagation speed decreases, and combustion stops after the ignition source is removed.

Flammability limits for common gases in mixtures with air and oxygen are given in Table. 8.11-8.9. With an increase in the temperature of the mixture, the flammability limits expand, and at a temperature exceeding the autoignition temperature, mixtures of gas with air or oxygen burn at any volume ratio.

The flammability limits depend not only on the types of combustible gases, but also on the conditions of the experiments (vessel capacity, heat output of the ignition source, mixture temperature, flame propagation up, down, horizontally, etc.). This explains the different values ​​of these limits in various literary sources. In table. 8.11-8.12 shows relatively reliable data obtained at room temperature and atmospheric pressure during flame propagation from bottom to top in a tube with a diameter of 50 mm or more. When the flame spreads from top to bottom or horizontally, the lower limits increase slightly, and the upper ones decrease. The flammability limits of complex combustible gases that do not contain ballast impurities are determined by the additivity rule:

L g \u003d (r 1 + r 2 + ... + r n) / (r 1 / l1 + r2 / l2 + ... + rn / ln) (8.17)

where L g is the lower or upper flammability limit of the compound gas (8.17)

where 12 is the lower or upper flammability limit of a complex gas in a gas-air or gas-oxygen mixture, vol. %; r, r2 ,..., rn is the content of individual components in the complex gas, vol. %; r, + r2 + ... + rn = 100%; l, l2,..., ln are the lower or upper flammability limits of individual components in a gas-air or gas-oxygen mixture according to Table. 8.11 or 8.12, vol. %.

In the presence of ballast impurities in the gas, the flammability limits can be determined by the formula:

L6 = LJ 1 + B/(1 - B);00]/ (8.18)

where Lg is the upper and lower flammability limits of the mixture with ballast impurities, vol. %; L2 - upper and lower flammability limits of a combustible mixture, vol. %; B is the amount of ballast impurities, fractions of a unit.

Table 8.11. Flammability limits of gases mixed with air (at t = 20°C and p = 101.3 kPa)

					Maximum explosion pressure, MPa	Excess air coefficient a at flammable limits
	Within flammable limits		With a stoichiometric composition of the mixture	With the composition of the mixture giving the maximum explosion pressure
	lower	upper				lower	upper
carbon monoxide
Isobutane
Propylene
Acetylene

T table 8.12. Flammability limits of gases mixed with oxygen (at t = 20ºC and p =

When calculating, it is often necessary to know the excess air coefficient a at different flammability limits (see Table 8.11), as well as the pressure that occurs during the explosion of the gas-air mixture. The excess air coefficient corresponding to the upper or lower flammability limits can be determined by the formula

α = (100/L - 1) (1/VT) (8.19)

The pressure arising from the explosion of gas-air mixtures can be determined with sufficient approximation by the following formulas: for the stoichiometric ratio of a simple gas to air:

Р vz = Рн(1 + β tк) (m/n) (8.20)

for any ratio of complex gas to air:

Рvz = Рн(1 + βtк) Vvlps /(1 + αV m) (8.21)

where Rz is the pressure arising from the explosion, MPa; рн is the initial pressure (before the explosion), MPa; c - coefficient of volumetric expansion of gases, numerically equal to the pressure coefficient (1/273); tK is the calorimetric combustion temperature, °C; m is the number of moles after the explosion, determined from the reaction of gas combustion in air; n is the number of moles before the explosion involved in the combustion reaction; V mn ,. - the volume of wet combustion products per 1 m 3 of gas, m 3; V„, - theoretical air consumption, m 3 / m 3.

Explosion pressures given in Table. 8.13 or determined by the formulas can only occur if the gas is completely burned inside the container and its walls are designed for these pressures. Otherwise, they are limited by the strength of the walls or their most easily destroyed parts - pressure pulses propagate through the unignited volume of the mixture at the speed of sound and reach the fence much faster than the flame front.

This feature - the difference in flame propagation speeds and pressure pulses (shock wave) - is widely used in practice to protect gas devices and premises from destruction during an explosion. To do this, easily opening or collapsing transoms, frames, panels, valves, etc. are installed in the openings of walls and ceilings. The pressure that occurs during an explosion depends on the design features of the protective devices and the relief factor kc6, which is the ratio of the area of ​​\u200b\u200bprotective devices to the volume of the room.

It is known that there is a certain limit value for the concentration of flammable substances in the surrounding atmosphere, which is called the lower explosive limit (LEL). If the concentration of flammable components in the air is below the LEL, then ignition is not possible: the mixture is not flammable. However, the LEL values ​​that are given in the reference literature are usually determined for a normal temperature of 20 °C. When designing gas control systems for operation in a high temperature environment, can it be assumed that methane, propane and other combustible gases retain the LEL values ​​​​known to us, at a temperature of, for example, 150 ° C?

No. Indeed, with an increase in temperature, the values ​​of the LEL of combustible gases decrease.

Let's find out what LEL concentration really means: it is the minimum concentration of flammable substances in the air at ambient temperature sufficient to initiate a self-sustained combustion. All the energy necessary to maintain combustion is released during the oxidation reaction (heat of combustion). When the concentration of the substance is below the LEL level, there is not enough energy to maintain combustion. We can state that the heat of combustion is necessary to heat the gas mixture from the ambient air temperature to the flame temperature. However, at high ambient temperatures, it will take less energy to heat the gas mixture to flame temperature, or in other words, you will need fewer flammable substances to get self-sustaining combustion. That is, as the temperature rises, the LEL decreases.

For most hydrocarbons, it has been found that LEL decreases at a rate of 0.14% LEL per degree. This speed value already includes a safety margin (equal to 2) to obtain a temperature dependence that is valid for all combustible gases and vapors.

Thus, at ambient temperature t, the LEL can be calculated using the following approximate formula:

LEL(t) = LEL(20°C)*(1 – 0.0014*(t – 20))

Naturally, this formula can only be applied to temperatures below the ignition temperature of a given gas.

The LEL of methane at normal temperature (20 °C) is 4.4% by volume.
At a temperature of 150 °C, the LEL of methane will be:

LEL(150°C) = 4.4*(1 - 0.0014*(150 - 20)) = 4.4*(1 - 0.0014*130) = 4.4*(1-0.182) = 3.6% v/v .d.

Dependence of the lower explosive limit of combustible gases on temperature

Dependence of the lower explosive limit of combustible gases on temperature It is known that there is a certain limit value for the concentration of flammable substances in the surrounding atmosphere, which

Occupational health and safety

Occupational health and safety

Labor protection in conditions of increased danger
Gas economy. Operation of gas equipment

Operation of gas equipment

In industry, along with the use of artificial gases, natural gas is increasingly being used. In its pure form, it has no color and odor, but after odorization, the gas acquires the smell of rotten eggs, by which its presence in the air is determined.

This gas, like many of its analogues, consists of the following components: methane - 90%, nitrogen - 5%, oxygen - 0.2%, heavy hydrocarbons - 4.5%, carbon dioxide - 0.3%.

If a mixture of air and gas is formed in an amount of at least a certain minimum, then the gas may explode. This minimum is called the lower explosive limit and is equal to 5% of the gas content in the air.

When the gas content of this mixture exceeds the maximum amount, the mixture becomes non-explosive. This maximum is called the upper explosive limit and is equal to 15% of the gas content in the air. Mixtures with a gas content lying within the specified range from 5 to 15%, in the presence of various sources of ignition (open flames, sparks, hot objects, or when this mixture is heated to a self-ignition temperature), lead to an explosion.

The ignition temperature of natural gas is 700 0 C. This temperature is significantly reduced due to the catalytic action of certain materials and heated surfaces (water vapor, hydrogen, sooty carbon deposits, hot fireclay surface, etc.). Therefore, to prevent explosions, it is necessary, firstly, to prevent the formation of a mixture of air with gases, i.e., to ensure reliable sealing of all gas devices and maintain positive pressure in them. Secondly, do not allow the gas to come into contact with any source of ignition.

As a result of incomplete combustion of natural gas, carbon monoxide CO is formed, which has a toxic effect on the human body. The permissible content of carbon monoxide in the atmosphere of industrial premises should not exceed 0.03. mg/l.

Each employee of the gas facilities of the enterprise is obliged to undergo special training and certification, to know the operating instructions for his workplace at the enterprise. For all gas hazardous places and gas hazardous work, a list is compiled, agreed with the head of the gas facilities of the plant, the safety department, which is approved by the chief engineer and posted at workplaces.

In the gas industry, success, trouble-free operation and safety of work are ensured by thorough knowledge of the matter, high work organization and discipline. No work not provided for by the job description, without the instructions or permission of the head and the necessary preparation, can be carried out. Gas workers in all cases should not leave their jobs without the knowledge and permission of their foreman. They are obliged to promptly, immediately report to the master about any comments, even the most minor malfunctions.

In the boiler room and other gas-powered units, the following should be hung out:

1. An instruction that defines the duties and actions of personnel both in normal operation and in emergency situations.
2. List of operators with numbers and expiration dates of their certificates for the right to work and a schedule for going to work.
3. A copy of the order or an extract from it on the appointment of a person responsible for the gas sector, his office and home phone numbers.

At the unit in the office there are logs: watch keeping, preventive repairs and inspections, records of control results.

As practice shows, most accidents and accidents at gas-fired units are associated with violation of the Rules, instructions, and the procedure for preparing to turn on the units and ignite the burners.

Before each start-up of boilers, furnaces and other units, their furnaces must be ventilated. The duration of this operation is determined by local regulations and is taken depending on the volume of the furnace and the length of the chimneys.

The smoke exhauster and the fan for supplying air to the burners are switched on when the furnaces and chimneys are ventilated. Prior to this, by rotating the smoke exhauster rotor manually, make sure that it does not touch the body and cannot cause sparks upon impact. Responsible work before starting gas is also purging gas pipelines. Prior to purging, make sure that there are no people in the zone of gas release from the purge candle, there are no light lamps and no open fire work is being carried out.

The end of the purge is determined by analyzing the gas leaving the purge gas pipeline, in which the oxygen content should not exceed 1%.

Before lighting the burners, check:

1. The presence of sufficient gas pressure in the gas pipeline in front of the boiler or other unit.
2. Air pressure when it is supplied from blowing devices.
3. The presence of vacuum in the furnace or hog (to the gate).

If necessary, adjust the tension.

The device that cuts off the gas supply in front of the burner should be opened smoothly and only after an igniter or torch has been brought to it. At the same time, the person performing this work should be on the side of the gas burner at the time of ignition of the gas. When igniting the gas on the burner, the smallest amount of air should be supplied to the furnace, upon receipt of which complete combustion of the gas would be ensured. Other burners are ignited in the same way. If, during ignition, regulation or operation, the flame goes out or it breaks off, flashes, it is necessary to immediately turn off the gas, ventilate the furnace and re-ignite in the order indicated above.

Violation of this requirement is one of the main causes of accidents.

It is forbidden to operate gas-fired units in case of any malfunctions, lack of traction, and also to leave the units switched on for work unattended.

Emergency shutdown of units operating on gas fuel is carried out immediately in cases of gas supply interruption; when the blower fans stop; in case of dangerous gas leakage into the room; in the event of a fire threat or outbreak.

During the preparation of repairs, the manager responsible for their implementation draws up a plan, taking into account the implementation of all measures that guarantee the safety of people. The plan must contain: a diagram of the object being repaired with the location of the repair work and an indication of their volume; a list of mechanisms, devices and tools permitted for use for repair work; surname list and arrangement of workers admitted to repair work; a complete list of measures to ensure the safe conduct of work, agreed with the gas rescue station, and a note on their implementation. The repair plan in each individual case must be signed by the head of the workshop, the person responsible for the repair and agreed with the head of the gas facilities.

The repair manager, in addition, instructs the personnel and monitors the implementation of the Rules during the preparation and implementation of repair work.

During repairs, only portable electric lighting with a voltage of not more than 12 - 24 V and in an explosion-proof version can be used. Work related to the stay of people at height should be carried out with the help of reliable ladders, platforms, scaffolds, as well as using, if necessary, safety belts (the places where the belts are caught are indicated by the repair manager). After the repair is completed, it is necessary to immediately remove cleaning and combustible materials, their traces. Then remove the plugs, purge the gas pipeline with gas and check for leaks. All joints, set up and adjust the equipment to the specified mode.

Occupational health and safety

Information portal - Occupational health and safety. Section - Labor protection in conditions of increased danger. Gas economy. Operation of gas equipment

Ecology HANDBOOK

Information

Ignition limit

Flammability limits change significantly with the addition of certain substances that can influence the development of pre-flame chain reactions. Known substances are both expanding and narrowing the limits of ignition. [ . ]

The ignition limits are influenced by the chemical composition of the fuel and oxidizer, temperature, pressure and turbulence of the medium, the concentration and type of additives or inert diluents, and the power of the ignition source during forced ignition. The effect of fuel type on flammability limits is shown in Table 3.4.[ . ]

The highest limit is such a concentration of fuel vapor in the mixture, with an increase in which the ignition of the combustible mixture does not proceed. [ . ]

The ignition temperature, flash point, and ignition temperature limits are fire hazard indicators. In table. 22.1 these indicators are presented for some technical products. [ . ]

The wider the ignition zone and the lower the lower concentration limit of ignition, the more dangerous the fumigant during storage and use. .[ . ]

Its ignition temperature is 290 ° C. The lower and upper limits of the explosive concentration of hydrogen sulfide in the air are 4 and 45.5 vol., respectively. %. Hydrogen sulfide is heavier than air, its relative density is 1.17. With the manifestations of hydrogen sulfide, explosions and fires are possible, which can spread over a vast territory and cause numerous victims and great losses. The presence of hydrogen sulfide leads to a dangerous destruction of the drilling tool and drilling equipment and causes their intense corrosion cracking, as well as corrosion of the cement stone. Hydrogen sulfide is very aggressive to clay drilling fluids in formation waters and gases. [ . ]

The ignition delay period of diesel fuel is measured by the cetane number. The cetane number of diesel fuel is the percentage (by volume) content of cetane (n. hexadecane) of a mixture with (-methylnaphthalene, which is equivalent to the test fuel in terms of engine hardness. taken as a standard within the limits of the ignition delay of the fuel (respectively 100 and 0 units).Mixtures of cetane with a-methylnaphthalene in different ratios have different flammability.

Hydrogen and acetylene have the widest flammability limits. Hydrocarbon mixtures of various compositions have close ignition limits. [ . ]

Tests of the engine with ignition by a finely focused laser beam generating plasma cores have shown that in this case the increase in pressure in the combustion chamber is more intense, the ignition limits are expanded, and the power and economic performance of the engine are improved.[ . ]

The values ​​​​of the temperature limits of ignition of substances are used in the calculation of fire and explosion-proof modes of operation of technological equipment, in the assessment of emergency situations associated with spills of flammable liquids, as well as for the calculation of the concentration limits of ignition. [ . ]

The lower concentration limit of ignition is the minimum concentration of fumigant vapor in the air, at which the vapor is ignited by an open flame or an electric spark. [ . ]

The expansion of the concentration limits of ignition creates the prerequisites for ensuring stable operation of the engine on lean mixtures. [ . ]

However, it must not be overlooked that the ignition limits are determined under static conditions, i.e., in a stationary environment. As a result, they1 do not characterize the stability of combustion in the flow and do not reflect the stabilizing ability of the burner. In other words, the same heavily ballasted gas can be successfully burned in a gas burner that stabilizes combustion well, while in another burner such an attempt may be unsuccessful. .[ . ]

With an increase in the turbulence of the combustible mixture, the ignition limits expand if the characteristics of the turbulence are such that they intensify the transfer of heat and active products in the reaction zone. The ignition limits can narrow if the turbulence of the mixture, due to the intensive removal of heat and active products from the reaction zone, causes cooling and a decrease in the rate of chemical transformations. [ . ]

With a decrease in the molecular weight of hydrocarbons, the ignition limits expand. [ . ]

In addition to the concentration limits, there are also temperature limits (lower and upper) of ignition, which are understood to mean such temperatures of a substance or material at which its saturated combustible vapors form concentrations in an oxidizing environment equal to the lower and upper concentration limits of flame propagation, respectively. ]

An oil spill resulting from the destruction of a tank(s), without igniting the oil. Represents the least danger to the environment and personnel if the oil does not spread beyond the dike. When the embankment breaks as a result of the hydrodynamic impact of the flowing oil, pollution of the main components of the environment on a significant scale is possible.[ . ]

The second condition is the existence of concentration limits beyond which neither ignition nor propagation of the combustion zone at a given pressure is possible.[ . ]

There are upper (higher) and lower (lower) concentration limits of ignition. [ . ]

Chemical properties. Flash point (in open cup) 0°; limits of ignition in air - 3-17 about. %.[ . ]

During combustion in engines with spark ignition, the concentration limits of ignition of the mixture do not coincide with the specified limits for the onset of soot formation. Therefore, the soot content in the exhaust gas of spark-ignition engines is negligible.[ . ]

The variety of substances and materials predetermined different concentration limits of flame propagation. There are such concepts as the lower and upper concentration limits of flame propagation (ignition) - this is, respectively, the minimum and maximum fuel content in the "combustible substance - oxidizing environment" mixture, at which flame propagation through the mixture is possible at any distance from the ignition source. The concentration interval between the lower and upper limits is called the area of ​​\u200b\u200bflame propagation (ignition). [ . ]

An increase in the initial temperature and pressure of the combustible mixture leads to an expansion of the ignition limits, which is explained by an increase in the rate of reactions of pre-flame transformations. [ . ]

With an increase in heat capacity, thermal conductivity and concentration of inert diluents, the ignition limits expand. [ . ]

The flammability of vapors (or gases) is characterized by the lower and upper concentration limits of ignition and the concentration zone of ignition. [ . ]

The level of measured temperatures along the axis and periphery of the loophole (Fig. 6-15, b) is less than the ignition temperature of the mixture of natural gas with air, equal to 630-680 ° C, and only at the outlet of the loophole, in its conical section, does the temperature reach 680-700 ° С, i.e., the ignition zone is located here. A significant increase in temperature is observed outside the embrasure at a distance of (1.0-1.6) Vgun.[ . ]

The fire hazard during gasification works increases significantly when the fumigant consumption rate per 1 m3 is within the ignition concentration zone. [ . ]

On fig. 2.21 shows the maximum pressure values ​​during the explosion of the mass Mg = 15 tons of superheated gasoline. In this case, the flame speed varied within: 103.4-158.0 m/s, which corresponds to the minimum and maximum cluttered spaces at the site of ignition of the mixture. An explosion of such an amount of overheated gasoline (accident type 1 according to scenario A) is possible during cold destruction of tanks K-101 or K-102. The frequency of such an event is 1.3 10 7 year-1, so it is unlikely.[ . ]

The disadvantage of the considered process is a long-range torch spraying paste-like precipitation at a small opening angle, which leads to a breakthrough of unburned particles outside the cyclone reactor and requires the construction of an afterburner. In addition, the combustion products of the organic part of the sediments do not participate in the process of initial heat treatment - drying and heating to the ignition temperature; for this, additional fuel is consumed, and the temperature of the exhaust gases exceeds that necessary for the complete oxidation of organic substances. [ . ]

As a rule, organic solvents are flammable, their vapors form explosive mixtures with air. Degree of flammability of solvents Characterized by flash point and ignition limits. In order to avoid an explosion, it is necessary to maintain the concentration of solvent vapors in the air below the lower flammable limit. [ . ]

Combustible gases, vapors of flammable liquids and combustible dust under certain conditions form explosive mixtures with air. Distinguish between lower and upper explosive concentration limits, beyond which mixtures are not explosive. These limits vary depending on the power and characteristics of the ignition source, the temperature and pressure of the mixture, the speed of propagation of the flame, the content of inert substances. [ . ]

Combustion stops when one of the following conditions is met: elimination of a combustible substance from the combustion zone or a decrease in its concentration; reducing the percentage of oxygen in the combustion zone to the limits at which combustion is impossible; lowering the temperature of the combustible mixture to a temperature below the ignition temperature. [ . ]

In addition, the formation of fireballs or the burning of drifting gas clouds may result in the death of all people located on the territory of the facility (up to 4 people working in a shift), as well as the defeat of people outside the gas filling station. Moreover, the number of victims when they enter the affected area of ​​the road will primarily depend on the intensity of traffic. People traveling on a highway can only be harmed if a fireball occurs or a drifting cloud ignites. Moreover, when a cloud burns, damage in the area of ​​\u200b\u200broads is possible provided that it ignited not on the drift path, but when vehicles hit it. Also, the risk indicators are significantly affected by the professional and emergency response training of personnel.[ . ]

Dusts of many solid combustible substances suspended in air form flammable mixtures with it. The minimum concentration of dust in the air at which it ignites is called the lower concentration limit of dust ignition. The concept of an upper flammable limit for dust does not apply, since it is not possible to create very high concentrations of dust in suspension. Information on the lower concentration limit of ignition (LEL) of some dusts is presented in Table. 22.2.[ . ]

In some refineries and petrochemical plants, the amount of discharged gases can sometimes reach 10,000-15,000 m3/h. Let us assume that within five minutes 1000 m3 of gases will be discharged, in which the lower concentration limit of ignition is about 2% (vol.) (which corresponds to the explosive characteristic of most gases from oil refining and petrochemical processes). Such an amount of gas, mixed with the surrounding air, can create an explosive atmosphere of about 50,000 m3 in a short period of time. If we assume that the explosive cloud is located so that its average height is about 10 m, then the area of ​​the cloud will be 5000 m2 or cover about 0.5 ha of the surface. It is highly probable that some kind of source of ignition may appear in such an area and then a powerful explosion will occur in this vast territory. There have been such cases. Therefore, in order to prevent an explosion, all emissions must be collected, preventing them from spreading in the atmosphere and either disposed of or burned. [ . ]

Specifications have been developed for Universine “B”. According to the conclusions about the fire and toxic properties, universin “B” belongs to class IV products and is considered a low-hazard and low-toxic compound. It is a combustible substance having an ignition temperature of 209°C and an autoignition temperature of 303°C. Temperature limits of vapor explosion: lower 100 °С, upper 180 °С. The main physical properties of universin “B” are given below.[ . ]

Let us evaluate the fire hazard (fire hazard) of various substances and materials, taking into account their state of aggregation (solid, liquid or gaseous). The main indicators of fire danger are the autoignition temperature and the concentration limits of ignition. [ . ]

Wastes from solvent gasolines, extractants, petroleum ether, which are narrow low-boiling fractions of direct distillation of oil, have a boiling point of 30-70 ° C, a flash point of -17 ° C, an autoignition temperature of 224-350 ° C, a lower concentration limit of ignition ( NKP) 1.1%, upper (VKP) 5.4%. [ . ]

The design of the neutralizer must ensure the necessary residence time of the processed gases in the apparatus at a temperature that guarantees the possibility of achieving a given degree of their neutralization (neutralization). The residence time is usually 0.1-0.5 s (sometimes up to 1 s), the operating temperature in most cases is oriented to the lower limit of self-ignition of the neutralized gas mixtures and exceeds the ignition temperature (Table 1.7) by 100-150 ° C. [ . ]

Of the existing gas cleaning devices, the main ones for converter production are Venturi pipes, electrostatic filters and fabric (bag) filters. Scrubbers, foamers and cyclones are usually used in combination with Venturi tubes and electrostatic precipitators. The content of combustible components in the gases entering the electrostatic precipitators must be significantly less than the lower flammability limit of the corresponding components. As a result, electrostatic precipitators cannot work in a gas exhaust system without afterburning. [ . ]

Calculations carried out in accordance with the method described above showed that a gas cloud with a high concentration is formed at the rupture site, which dissipates due to advective transport and turbulent diffusion in the atmosphere. Using the "RISK" program, the probabilities of exceeding two threshold values ​​of concentrations were calculated: 300 mg/m3 - the maximum allowable concentration of methane in the working area and 35,000 mg/m3 - the lower limit of ignition of the methane-air mixture.[ . ]

A fairly complex gravity current is formed near the earth's surface, which contributes to the radial propagation and dispersion of LNG vapors. As an illustration of the results of numerical calculations of the dispersion of the methane-air cloud in Fig. Figure 5 shows the evolution of the vapor cloud for the most unfavorable dispersion conditions (atmospheric stability - “B” according to the Gifford-Pasquile classification, wind speed - 2 m/s) in the form of isosurfaces of the LNG vapor concentration in the air. The contours shown correspond to the upper flammable limit of LNG vapor in air (15% vol.), the lower flammable limit (5% vol.) and half the lower flammable limit (2.5% vol.).[ . ]

Natural gas futures rose during the US session

On the New York Mercantile Exchange, natural gas futures for August delivery traded at $2.768 per million Btu, up 0.58% as of this writing.

The high of the session was USD per MMBtu. At the time of writing, natural gas has found support at $2.736 and resistance at $2.832.

Futures on the USD index, which shows the ratio of the US dollar to a basket of six major currencies, fell 0.17% to trade at $94.28.

Elsewhere on the NYMEX, WTI September crude oil futures edged down 3.95% to hit $67.19 a barrel, while August fuel oil futures edged down 3.19% to hit $67.19 a barrel. to $2.0654 per gallon.

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Before the start of the swimming season and on the eve of the summer holidays, the Department of Civil Defense and Emergencies of the Administration of the Municipal Civil Defense Organization "Ukhta" reminds parents of the need to talk with their children about the rules of behavior on the water

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Explosive limit of natural gas

July 25, 2018 from 10.00 to 13.00 GKU RK "Department of fire service and civil protection" will collect mercury-containing waste on the territory of the municipal defense organization "Ukhta" The main cause of death

Climatic conditions in mines. Their differences from the climatic conditions on the surface.

Climatic conditions (thermal regime) of mining enterprises have a great influence on the well-being of a person, his labor productivity, and the level of injuries. In addition, they affect the operation of equipment, the maintenance of workings, the condition of ventilation facilities.

The temperature and humidity of the air in underground workings depend on those on the surface.

When air moves through underground workings, its temperature and humidity change.

In winter, the air entering the mine cools the walls of the air supply workings, and heats up itself. In summer, the air heats the walls of the workings, and cools itself. Heat exchange occurs most intensively in the air supply workings and at some distance from their mouth it attenuates, and the air temperature becomes close to the temperature of the rocks.

The main factors that determine the air temperature in underground mine workings are:

1. Heat and mass transfer with rocks.

2. Natural compression of air as it moves down vertical or inclined workings.

3. Oxidation of rocks and lining materials.

4. Cooling of the rock mass during its transportation through workings.

5. Processes of mass transfer between air and water.

6. Heat release during the operation of machines and mechanisms.

7. Heat dissipation of people, cooling of electric cables, pipelines, burning of lamps, etc.

The maximum allowable air speed in various workings ranges from 4 m/s (in bottom-hole spaces) to 15 m/s (in ventilation shafts not equipped with a lift).

The air supplied to underground workings in winter must be heated to a temperature of +2 ° C (5 m from the junction of the heater channel with the shaft).

The optimal and permissible standards for temperature, relative humidity and air velocity in the working area of ​​industrial premises (including processing plants) are given in GOST 12.1.005-88 and SanPiN - 2.2.4.548-96.

Optimal microclimatic conditions are such combinations of meteorological parameters that provide a feeling of thermal comfort.

Permissible - such combinations of meteorological parameters that do not cause damage or health problems.

Thus, the permissible temperature range in the cold season for works of I category of severity is 19-25 ° C; II category - 15-23 o C; Category III - 13-21 o C.

In the warm period of the year, these ranges are 20-28 ° C, respectively; 16-27 about C; 15-26 about S.

Concentration limits of flammability and explosiveness of methane. Factors affecting the intensity of flammability and explosiveness

Methane (CH 4)- gas without color, smell and taste, under normal conditions is very inert. Its relative density is 0.5539, as a result of which it accumulates in the upper parts of workings and rooms.

Methane forms combustible and explosive mixtures with air, burns with a pale bluish flame. In underground workings, methane combustion occurs in conditions of lack of oxygen, which leads to the formation of carbon monoxide and hydrogen.

When the content of methane in the air is up to 5-6% (at a normal oxygen content), it burns near a heat source (open fire), from 5-6% to 14-16% it explodes, more than 14-16% does not explode, but can burn at supply of oxygen from outside. The strength of the explosion depends on the absolute amount of methane involved in it. The explosion reaches its greatest force when the air contains 9.5% CH 4 .

The ignition temperature of methane is 650-750 o C; the temperature of the explosion products in an unlimited volume reaches 1875 o C, and inside a closed volume 2150-2650 o C.

Methane was formed as a result of the decomposition of organic matter fiber under the influence of complex chemical processes without oxygen. An important role is played by the vital activity of microorganisms (anaerobic bacteria).

In rocks, methane is in free (fills the pore space) and bound state. The amount of methane contained in a unit mass of coal (rock) in natural conditions is called gas content.

There are three types of methane release into the mine workings of coal mines: ordinary, souffle, sudden emissions.

The main measure to prevent dangerous accumulations of methane is the ventilation of workings, which ensures the maintenance of permissible gas concentrations. According to safety rules, the content of methane in the mine air should not exceed the values ​​given in Table. 1.3.

Permissible content of methane in mine workings

If it is impossible to ensure the permissible content of methane by means of ventilation, degassing of mines is used.

To prevent the ignition of methane, it is prohibited to use open flames in mine workings and smoking. Electrical equipment used in gas-hazardous workings must be explosion-proof. For blasting, only safety explosives and explosives should be used.

The main measures to limit the harmful effects of the explosion: the division of the mine into independently ventilated areas; clear organization of the rescue service; familiarization of all employees with the properties of methane and precautionary measures.

Explosive limits

Explosive limits- Explosive limits (more correctly - ignition) usually mean the minimum (lower limit) and maximum (upper limit) amount of combustible gas in the air. When these concentrations are exceeded, ignition is impossible, the ignition limits are indicated in volume percent under standard conditions of the gas-air mixture (p = 760 mm Hg, T = 0 ° C). With an increase in the temperature of the gas-air mixture, these limits expand, and at temperatures above the self-ignition temperature of the mixture, they burn at any volume ratio. This definition does not include the explosive limits of gas and dust mixtures, the explosive limits of which are calculated using the well-known Le Chatelier formula.

Notes

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A mixture of natural gas with air can explode at a gas concentration in air of 5-15%.

A mixture of liquefied gas in air explodes at a concentration of 1.5-9.5%.

For an explosion, 3 conditions must be present simultaneously:

The gas-air mixture must be in a closed volume. In the open air, the mixture does not explode, but flares up.

The amount of gas in the natural mixture should be 5-15% for natural gas and 1.5-9.5% for liquefied gas. At a higher concentration, the sweep will light up and when the limit is reached, it will explode.

The mixture should be heated at one point to the flash point.

5 First aid for a victim of carbon monoxide poisoning

Symptoms:

There is muscle weakness

Dizziness

Noise in ears

Drowsiness

hallucinations

Loss of consciousness

convulsions

Assistance:

Stop the flow of carbon monoxide

Remove victim to fresh air

If the victim is conscious, lay down and provide rest and continuous access to fresh air

If there is no consciousness, it is necessary to start a closed heart massage and artificial respiration before the arrival of an ambulance or before regaining consciousness.

Ticket number 10

5 First aid for a burn victim

Thermal caused by fire, steam, hot objects and in-you. If the victim's clothes caught fire, you need to quickly throw on a coat, any dense fabric, or knock down the flame with water. You can not run in burning clothes, as the wind will fan the flames. When providing assistance in order to avoid infection, you should not touch the burned areas of the skin with your hands or lubricate with fats, oils, petroleum jelly, sprinkle with baking soda. It is necessary to apply a sterile bandage to the burnt area of ​​​​the skin. If pieces of clothing are stuck, then a bandage should follow over them, you can not tear it off.

Ticket number 11

5 Contents of the work permit for gas hazardous work.

Written permission, indicating the period of its validity, the start time of work, the end of work, their safety conditions, the composition of the team and persons responsible. for safety works. ND approved ch. engineer. List of persons entitled to issue ND approved. by order under predp. ND is issued in two copies. for one work foreman with one team; for one workplace. One copy is transferred to the manufacturer, the other remains with the person who issued the outfit. Accounting for ND is carried out according to the registration book; they enter: serial number, summary, position; FULL NAME. resp. guides; signature.

Ticket number 12

5 first aid to the victim of suffocation with natural gas

Remove victim to fresh air

In case of absence of consciousness and pulse on the carotid artery, proceed to the resuscitation complex

In case of loss of consciousness for more than 4 minutes - turn over on the stomach and apply cold to the head

In all cases, call an ambulance

Ticket number 13

1 classification of gas pipelines by pressure.

I- low (0-500 mm water column); (0.05 kg * s / cm 2)

II-medium (500-30,000 mm water column); (0.05-3 kg * s / cm 2)

Ticket number 14

3 requirement for lighting, ventilation and heating in hydraulic fracturing.

The need for heating the hydraulic fracturing room should be determined depending on climatic conditions.

In the premises of the GTP, natural and (or) artificial lighting and natural permanent ventilation should be provided, providing at least three air exchanges per hour.

For rooms with a volume of more than 200 m3, air exchange is carried out according to the calculation, but not less than a single air exchange in 1 hour.

The placement of equipment, gas pipelines, fittings and instruments should ensure their convenient maintenance and repair.

The width of the main passage in the premises should be at least 0.8 m.