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

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

The temperature and humidity in underground mines depend on those on the surface.

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

The main factors determining 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 support materials.

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

5. Processes of mass transfer between air and water.

6. Heat generation during operation of machines and mechanisms.

7. Heat dissipation of people, cooling electrical cables, pipelines, lighting of lamps, etc.

The maximum permissible speed of air movement in various workings ranges from 4 m/s (in bottomhole spaces) to 15 m/s (in ventilation shafts not equipped with lifting).

Air supplied to underground workings in winter time, must be heated to a temperature of +2 o C (5 m from the interface of the heater channel with the barrel).

Optimal and acceptable standards temperature, relative humidity and air speed in work area production 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.

Acceptable are such combinations of meteorological parameters that do not cause damage or health problems.

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

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

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

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

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

When the methane content in the air is up to 5-6% (with normal oxygen content), it burns near a heat source ( open fire), from 5-6% to 14-16% explodes, over 14-16% does not explode, but can burn with an influx of oxygen from the outside. The strength of the explosion depends on the absolute amount of methane involved. The explosion reaches its greatest force when the air contains 9.5% CH4.

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 fiber in organic matter under the influence of complex chemical processes without access to oxygen. The vital activity of microorganisms (anaerobic bacteria) plays a significant role in this.

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

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

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

Permissible methane content in mine workings

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

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

Basic measures to limit the harmful consequences of an explosion: dividing the mine into independently ventilated areas; clear organization of rescue service; familiarizing all workers with the properties of methane and precautions.

An explosion is a phenomenon associated with the release of large quantity energy in a limited amount in a very short period of time. And if a flammable substance ignites in the vessel gas mixture, but the vessel withstood the resulting pressure, then this is not an explosion, but a simple combustion of gases. If the vessel ruptures, it is an explosion.

Moreover - an explosion, even if there was no combustible mixture, and it ruptured, for example, due to excess air pressure or even without exceeding the design pressure, or, for example, due to loss of strength of the vessel as a result of corrosion of its walls.

If we imagine the scale of gas contamination of any volume (room, vessel, etc.) in volume percentages from 0% to 100%, it turns out that with CH4 gas contamination:

From 0% to 1% - combustion is impossible, since there is too little gas relative to air;

From 1% to 5% - combustion is possible, but not stable (gas concentration is low);

From 5% to 15% (option 1) - combustion is possible from an ignition source, and (option 2) - combustion is possible without an ignition source (heating the gas-air mixture to the auto-ignition temperature);

From 15% to 100% - combustion is possible and stable.

The combustion process itself can occur in two ways:

From the ignition source - to in this case the gas-air mixture ignites at the “point of entry” of the ignition source. Further, according to the chain reaction, the gas-air mixture ignites itself, forming a “flame propagation front”, with the direction of movement from the ignition source;

Without an ignition source - in this case, the gas-air mixture ignites simultaneously (instantaneously) at all points of the gas-filled volume. This is where concepts such as the lower and upper concentration limits of gas explosion come from, since such ignition (explosion) is possible only within the gas contamination range from 5% to 15% by volume.

Conditions under which a gas explosion will occur:

Gas concentration (gas content) in the gas-air mixture is from 5% to 15%;

Closed volume;

Introducing an open fire or an object with a gas ignition temperature (heating the gas-air mixture to the auto-ignition temperature);

Lower concentration limit of auto-ignition of combustible gases (LCPL)- this is the minimum gas content in the gas-air mixture at which combustion occurs without an ignition source (spontaneously). Provided that the gas-air mixture is heated to the auto-ignition temperature. For methane it is approximately 5%, and for a propane-butane mixture it is approximately 2% of gas from the volume of the room.

Upper concentration limit of self-ignition of flammable gases (UCPL)- this is the gas content in the gas-air mixture, above which the mixture becomes non-flammable without an open ignition source. For methane it is approximately 15%, and for a propane-butane mixture it is approximately 9% of the gas of the volume of the room.

The percentage ratio of LCPR and VCPR is indicated under normal conditions (T = 0°C and P = 101325 Pa).

The signal norm is 1/5 of the NKPR. For methane it is 1%, and for a propane-butane mixture it is 0.4% of gas from the volume of the room. All gas detectors, gas analyzers and gas indicators up to explosive concentrations are configured to this signal standard. When a signal norm is detected (according to the PLA), a GAS EMERGENCY is declared. Appropriate measures are being taken. 20% of the NKPR is taken so that workers have some time to eliminate the accident or evacuate. Also, the indicated signal norm is the “point” of the end of purging of gas pipelines with gas or air after various operational works.

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

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

Temperature,

Partial pressure, MPa

Water vapor H2O

Carbon dioxide CO2

If the gas content in a 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 in 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 is. 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 losses during combustion. When the flammable mixture is diluted with air, oxygen or gas, heat losses increase, the speed of flame propagation 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. As the temperature of the mixture increases, the flammability limits expand, and at temperatures above the auto-ignition 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 experimental conditions (vessel capacity, thermal power of the ignition source, mixture temperature, flame propagation up, down, horizontally, etc.). This explains the different meanings of these limits in various literary sources. In table 8.11-8.12 show relatively reliable data obtained at room temperature and atmospheric pressure when a flame propagates from bottom to top in a tube with a diameter of 50 mm or more. As the flame spreads from top to bottom or horizontally, the lower limits increase slightly and the upper limits decrease. The flammability limits of complex combustible gases that do not contain ballast impurities are determined according to the additivity rule:

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

If there are 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 the combustible mixture, vol. %; B - 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 at flammability limits
	Within flammability limits		With a stoichiometric mixture composition	With a mixture composition giving 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 making calculations, 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 during the explosion of gas-air mixtures can be determined with sufficient approximation using the following formulas: for the stoichiometric ratio of a simple gas with air:

Р in = Рн(1 + β tк) (m/n) (8.20)

for any ratio of complex gas to air:

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

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

The explosion pressures given in table. 8.13 or determined by formulas, can occur only if complete combustion of the gas occurs 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 throughout 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 the speed of flame propagation and pressure pulses (shock wave) - is widely used in practice for protection 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 arising during an explosion depends on the design features of the protective devices and the release coefficient kc6, which is the ratio of the area protective devices to the volume of the room.

Natural gas is understood as a whole mixture of gases that are formed in the bowels of the earth following the anaerobic decomposition of organic substances. It is one of the most important minerals. Natural gas lies in the depths of the planet. These may be individual clusters or a gas cap on oil field, however, can be presented in the form of gas hydrates, in a crystalline state.

Hazardous properties

Natural gas is familiar to almost all residents of developed countries, and even at school, children learn the rules for using gas in everyday life. Meanwhile, natural gas explosions are not uncommon. But besides this, there are a number of threats posed by such convenient devices running on natural gas.

Natural gas is toxic. Although ethane and methane are pure form are non-poisonous; if the air is saturated with them, a person will experience suffocation due to lack of oxygen. This is especially dangerous at night, while sleeping.

Explosion limit of natural gas

When in contact with air, or more precisely with its component - oxygen, natural gases are capable of forming a flammable detonating mixture, which can cause a large explosion from even the slightest source of fire, for example, a spark from wiring or the flame of a match or candle. If the mass of natural gas is relatively low, then the ignition temperature will not be high, but the force of the explosion depends on the pressure of the resulting mixture: the higher the pressure of the gas-air composition, the more force it will explode.

However, almost all people at least once in their lives have experienced some kind of gas leak, detected by a characteristic odor, and yet no explosions have occurred. The fact is that natural gas can explode only when it reaches certain proportions with oxygen. There are lower and higher explosive limits.

As soon as the lowest explosive limit of natural gas is reached (for methane it is 5%), that is, a concentration sufficient to initiate an explosion. Reducing the concentration will eliminate the possibility of fire. Exceeding the highest mark (15% for methane) will also not allow the combustion reaction to begin, due to the lack of air, or more precisely, oxygen.

The explosive limit of natural gas increases with increasing pressure of the mixture, and also if the mixture contains inert gases, such as nitrogen.

The pressure of natural gas in the gas pipeline can be different, from 0.05 kgf/cm 2 to 12 kgf/cm2.

Difference between explosion and combustion

Although at first glance it seems that explosion and combustion are somewhat different things, in fact these processes are of the same type. Their only difference is the intensity of the reaction. During an explosion in a room or any other confined space, the reaction occurs incredibly quickly. The detonation wave propagates at a speed several times higher than the speed of sound: from 900 to 3000 m/s.

Since the methane used in the domestic gas pipeline is a natural gas, the volume of oxygen required for ignition also follows the general rule.

The maximum force of the explosion is achieved if the oxygen present is theoretically sufficient for complete combustion. Other conditions must also be present: the gas concentration corresponds to the ignition limit (above the lower limit, but below the highest) and there is a source of fire.

A gas stream without oxygen, that is, exceeding the highest ignition limit, entering the air, will burn with an even flame, the combustion front propagates at a speed of 0.2-2.4 m/s at normal atmospheric pressure.

Properties of gases

Detonation properties are manifested in paraffin hydrocarbons from methane to hexane. The structure of molecules and molecular weight determine their detonation properties, which decrease with decreasing molecular weight, and the octane number increases.

B includes several hydrocarbons. The first of them is methane ( chemical formula CH 4). Physical properties gases are as follows: colorless, lighter than air and odorless. It is quite flammable, but nevertheless quite safe to store, if safety precautions are fully followed. Ethane (C 2 H 6) is also colorless and odorless, but is slightly heavier than air. It is flammable, but is not used as fuel.

Propane (C 3 H 8) is colorless and odorless, capable of liquefying under low pressure. This useful property allows not only to safely transport propane, but also to separate it from a mixture with other hydrocarbons.

Butane (C 4 H 10): the physical properties of the gas are similar to propane, but its density is higher, and butane is twice as heavy as air.

Familiar to everyone

Carbon dioxide (CO 2) is also part of the natural gas. Perhaps everyone knows the physical properties of gas: it has no odor, but is characterized by a sour taste. It is one of the gases with the lowest toxicity and is the only (with the exception of helium) non-flammable gas in the natural gas composition.

Helium (He) is a very light gas, second only to hydrogen, colorless and odorless. It is very inert and under normal conditions is not able to react with any substance, and does not participate in the combustion process. Helium is safe, non-toxic, high blood pressure, along with other inert gases, puts a person into a state of anesthesia.

Hydrogen sulfide (H 2 S) is a colorless gas with a characteristic odor of rotten eggs. Heavy and very poisonous, can cause paralysis of the olfactory nerve even in small concentrations. In addition, the explosive limit of natural gas is very wide, from 4.5% to 45%.

There are two more hydrocarbons that are similar in application to natural gas, but are not part of it. Ethylene (C 2 H 4) is a gas close in properties to ethane, with a pleasant odor and colorless gas. It is distinguished from ethane by its lower density and flammability.

Acetylene (C 2 H 2) is a colorless, explosive gas. It is very flammable and explodes if there is strong compression. Because of this, acetylene is dangerous to use in everyday life; it is mainly used for welding work.

Application of hydrocarbons

Methane is used as fuel in household gas appliances.

Propane and butane serve as fuel for cars (for example, hybrids), and in liquefied form, propane is used to fuel lighters.

But ethane is rarely used as fuel; its main purpose in industry is to produce ethylene, which is produced on the planet in huge quantities, because it is the raw material for polyethylene.

Acetylene is used for the needs of metallurgy; with its help, high temperatures for welding and cutting metals. Since it is extremely flammable, it cannot be used as fuel, and strict adherence to conditions when storing gas is necessary.

Although hydrogen sulfide is toxic, it is used in medicine in extremely small quantities. These are the so-called hydrogen sulfide baths, the action of which is based on the antiseptic properties of hydrogen sulfide.

The main useful thing is its low density. This inert gas is used when flying in balloons and airships; it is used to fill volatile balloons, popular among children. It is impossible to ignite natural gas: helium does not burn, so you can heat it over an open fire without fear. Hydrogen, next to helium on the periodic table, is even lighter, but Helium is the only gas that does not have a solid phase under any conditions.

Rules for using gas at home

Every person using gas appliances is required to undergo safety training. The first rule is to monitor the serviceability of the appliances, periodically check the draft and chimney if the appliance has an outlet. After turning off the gas appliance, you need to close the taps and turn off the valve on the cylinder, if there is one. If the gas supply is suddenly interrupted, or if any malfunctions are identified, you must immediately call the gas service.

If you smell gas in an apartment or other room, you must immediately stop any use of appliances, do not turn on electrical appliances, open a window or vent for ventilation, then leave the room and call the emergency service (phone 04).

It is important to follow the rules for using gas in everyday life, because the slightest malfunction can lead to disastrous consequences.

If the concentration of a flammable substance in a mixture is less than the lower limit of flame propagation, 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 concentration of the flammable substance in the mixture is between the lower and upper limits of flame propagation, 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 flame spread limits (also called flammability limits And explosive limits) and the lower the lower limit, the more explosive the gas is. If the concentration of a flammable substance in the mixture exceeds the upper limit of flame propagation, then the amount of oxidizer in the mixture is insufficient for complete combustion of the combustible substance.

The range of values ​​of the graph of the dependence of the CPRP in the “combustible gas - oxidizer” system, corresponding to the ability of the mixture to ignite, forms the ignition region.

The following factors influence the values ​​of NKPRP and VKPRP:

• Properties of reacting substances;
• Pressure (usually an increase in pressure does not affect the NCPRP, but the VCPRP can increase significantly);
• Temperature (increasing temperature expands the CPRP due to increasing activation energy);
• Non-flammable additives - phlegmatizers;

The dimension of the CPRP can be expressed as a volume percentage or in g/m³.

The addition of a phlegmatizer to the mixture reduces the value of the VCPRP almost proportionally to its concentration up to the phlegmatization point, where the upper and lower limits coincide. At the same time, the NPRRP increases slightly. To assess the ignition ability of the “Fuel + Oxidizer + Phlegmatizer” system, a so-called fire triangle- a diagram where each vertex of the triangle corresponds to one hundred percent content of one of the substances, decreasing towards the opposite side. Inside the triangle, the ignition area of ​​the system is identified. In the fire triangle, a line of minimum oxygen concentration (MCC) is marked, corresponding to the value of the oxidizer content in the system, below which the mixture does not ignite. Assessing and monitoring ICC is important for systems operating under vacuum, where leakage is possible atmospheric air through leaks in process equipment.

In relation to liquid media, temperature limits of flame propagation (TPLP) are also applicable - such temperatures of the liquid and its vapors in the oxidizer medium at which its saturated vapors form concentrations corresponding to the TPLP.

CPRP is determined by calculation or found experimentally.