What are lower and upper explosive limits (LEL and ERL)?
To form an explosive atmosphere, the presence of a flammable substance in a certain concentration is necessary.
Basically, oxygen is required for all gases and vapors to ignite. With an excess of oxygen and a lack of it, the mixture will not ignite. The only exception is acetylene, which does not require oxygen to ignite. Low and high concentrations are called "explosive limit".
- Lower explosive limit (LEL): the limit of concentration of a gas-air mixture below which the gas-air mixture cannot ignite.
- Upper explosive limit (ELL): the limit of concentration of a gas-air mixture above which the gas-air mixture cannot ignite.
Explosion limits for explosive atmosphere:
If the concentration of a substance in the air is too low (lean mixture) or too high (saturated mixture), then an explosion will not occur, but rather a slow combustion reaction may occur or not at all.
An ignition reaction followed by an explosion reaction will occur in the range between the lower (LEL) and upper (EL) explosive limits.
Explosion limits depend on the pressure of the surrounding atmosphere and the concentration of oxygen in the air.
Examples of lower and upper explosive limits for various gases and vapors:
Dust is also explosive at certain concentrations:
- Lower explosive limit of dust: ranging from approximately 20 to 60 g/m3 of air.
- Upper explosive limit of dust: approximately 2 to 6 kg/m3 of air.
These settings may change for different types dust. Particularly flammable types of dust can form a flammable mixture in substance concentrations of less than 15 g/m3.
1. Gas – colorless, tasteless and odorless. Non-poisonous, non-toxic. Has a suffocating effect, i.e. in case of leaks, it displaces oxygen from the volume of the premises.
2. Fire and explosion hazard.
3. Approximately two times lighter than air, so in case of leaks it accumulates in upper layers premises.
Air Density:rair.=1.29 kg/m3.
Gas Density:rgas.=0.72 kg/m 3 .
4. At a temperature of –162 O C and atmospheric pressure(760 mmHg. Art.), natural gas turns into a liquid state.
5. The temperature developed during gas combustion is from +1600 to +2000 O C.
6. Ignition temperature +645 O C.
7. When one cubic meter of gas is burned, 8500 Kcal of heat is released (calorific value of natural gas).
8. Gas explosion limits: from 5% to 15% by volume.
If the gas concentration in the indoor air is less than 5% or more than 15%, there will be no explosion. There will be a fire or fire. When it is less than 5%, there will be a lack of gas and less heat that supports combustion.
In the second case (concentration more than 15%) there will be little air, i.e. oxidizer, and a small amount of heat to support combustion.
June 3, 2011| – | Lower explosive limit | Upper explosive limit |
| Gasoline B-70 | 0,8 | 5,1 |
| Tractor kerosene | 1,4 | 7,5 |
| Propane | 2,1 | 9,5 |
| n-Butane | 1,5 | 8,5 |
| Methane | 5 | 15 |
| Ammonia | 15 | 28 |
| Hydrogen sulfide | 4,3 | 45,5 |
| Carbon monoxide | 12,5 | 75 |
| Hydrogen | 4 | 75 |
| Acetylene | 2 | 82 |
An explosion is an instantaneous chemical transformation accompanied by the release of energy and the formation of compressed gases.
During explosions of gas-air mixtures, it is released a large number of heat and a large amount of gases are formed.
Gases, due to the released heat, are heated to a high temperature, sharply increase in volume and, expanding, press with great strength on the enclosing structures of buildings or the walls of apparatus in which an explosion occurs.
The pressure at the moment of explosion of gas mixtures reaches 10 kgf/cm 2, the temperature fluctuates between 1500-2000 ° C, and the speed of propagation of the blast wave reaches several hundred meters per second. Explosions usually cause great destruction and fires.
The fire hazardous properties of combustible substances are characterized by a number of indicators: flash point, ignition temperature, self-ignition temperature, etc.
Other properties of flammable substances include explosion pressure, the minimum explosive oxygen content, below which ignition and combustion of the mixture becomes impossible at any concentration of flammable substance in the mixture, the nature of interaction with fire extinguishing agents, etc.
“Occupational health and safety in the gas industry”,
A.N. Yanovich, A.Ts. Astvatsaturov, A.A. Busurin
Indicators Methane Propane n-Butane Aviation gasoline Tractor kerosene Industrial oil Vapor flash point, °C -188 - -77 -34 27 200 Auto-ignition temperature, °C 537 600-588 490-569 300 250 380 Concentration limits of ignition, % by volume 6 .3—15 2.2—9.5 1.9—8.5 0.8—5.2 1.4—7.5 1—4 Temperature limits of ignition of vapors above liquid, °C —188/+180 — —(77/52) —(34/4) 27—69 146—191 Speed…
Explosive concentrations of liquefied and natural gases are formed during the shutdown of pipelines, tanks and devices, when the gas is not completely removed and when it is mixed with incoming air, an explosive mixture is created. In this regard, before work begins, gas pipelines and tanks are washed with water, steamed, and purged with inert gas. To prevent gas from entering from other tanks or pipelines, the repaired...
Analysis of fires that occurred at operating cluster bases liquefied gas, indicates that the main types of accidents are the following: the presence of gas leaks, ruptures of pipelines and flexible hoses, breakdowns of flange connections and breakdowns of plugs, breakdowns of stuffing box seals on shut-off valves, loosely closed valves, destruction of liquefied gas containers due to their overflow; various breakdowns in pipelines and tanks (destruction...
When gas evaporates, an explosive gas-air mixture is formed. In case of accidents in premises, explosive concentrations of gas arise first of all, near the point of gas leakage, and then spread throughout the premises. When gas evaporates in open areas near the leak site, a gas contamination zone is formed that spreads throughout the warehouse. The size of the gas contamination zone during an emergency gas leak depends on many...
The main difficulty in extinguishing gas fires is the fight against gas contamination and re-ignition after extinguishing the fire. None of the known extinguishing agents eliminates the danger of gas contamination and re-ignition. The main task when fighting gas fires is to localize the fire. It should be carried out by limiting the flow time and volume of escaping gas, as well as by thermal protection...
It is known that there is a certain limit value for the concentration of flammable substances in surrounding atmosphere, which is called the lower explosive limit (LEL). If the concentration of flammable components in the air is below the LEL, then fire is not possible: the mixture is not flammable. However, the LEL values given in the reference literature are determined, as a rule, for a normal temperature of 20 °C. When designing gas control systems for operation in high-temperature environments, is it possible to assume that methane, propane and other flammable gases retain their known LEL values at a temperature of, for example, 150 °C?
No you can not. Indeed, with increasing temperature, the LEL values of combustible gases decrease.
Let's find out what the LEL concentration really means: it is the minimum concentration of flammable substances in the air at a temperature environment, sufficient to initiate 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, the energy is insufficient to support combustion. We can assert that the heat of combustion is necessary to heat the gas mixture from the ambient temperature to the flame temperature. However, when high temperature environment, it will take less energy to heat the gas mixture to flame temperature, or in other words, to get self-sustained combustion, you will need less flammable substances. That is, as the temperature increases, the LEL decreases.
For most hydrocarbons, it has been established that the LEL decreases at a rate of 0.14% of the LEL per degree. This speed value already includes a safety margin (equal to 2) to obtain a temperature dependence valid for all flammable 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 used for temperatures below the ignition temperature of a given gas.
LEL of methane at normal temperature(20 °C) is 4.4% vol.d.
At a temperature of 150 °C the LEL of methane will be equal to:
LEL(150 °C) = 4.4*(1 – 0.0014*(150 – 20)) = 4.4*(1 – 0.0014*130) = 4.4*(1-0.182) = 3.6% vol. .d.
Dependence of the lower explosive limit of flammable gases on temperature
Dependence of the lower explosive limit of flammable gases on temperature It is known that there is a certain limiting value for the concentration of flammable substances in the surrounding atmosphere, which
Labor protection and safety
Labor protection and life safety
Occupational safety in high-risk environments
Gas industry. Operation of gas equipment
Operation of gas equipment
In industry, along with the use of artificial gases, natural gas is increasingly used. IN pure form it is colorless and odorless, but after odorization the gas acquires an odor rotten eggs, which determines its presence in the air.
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 not less than a certain minimum, 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 in this mixture exceeds maximum amount, the mixture becomes non-explosive. This maximum is called. the upper explosive limit is equal to 15% of the gas content in the air. Mixtures with a gas content within the specified limits from 5 to 15%, if available various sources ignition ( open fire, sparks, hot objects or when this mixture is heated to the auto-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, soot carbon deposits, hot fireclay surface, etc.). Therefore, to prevent explosions, it is necessary, firstly, to prevent the formation of a mixture of air and 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 ignition source.
As a result of incomplete combustion of natural gas, carbon monoxide CO is formed, which has a toxic effect on the human body. Acceptable Content carbon monoxide in the atmosphere production premises should not exceed 0.03. mg/l.
Each employee of the gas sector of an enterprise is required to undergo special training and certification and know the operating instructions for their workplace at the enterprise. For all gas-hazardous places and gas-hazardous work, a list is drawn up, agreed with the head of the plant's gas facilities, the safety department, which is approved by the chief engineer and posted at the workplace.
In the gas industry, success, accident-free operation and safety are ensured by thorough knowledge of the matter, high work organization and discipline. No work not provided job description, without the instructions or permission of the manager and necessary preparation cannot be conducted. Gas workers in all cases should not leave their workplaces without the knowledge and permission of their foreman. They are obliged to promptly and immediately report to the foreman any comments, even the most minor malfunctions.
The following must be posted in the boiler room and other gas-fired units:
- Instructions defining the responsibilities and actions of personnel as in the conditions normal operation, and in emergency situations.
- A list of operators indicating the numbers and expiration dates of their work permits and their work schedule.
- A copy of the order or an extract from it on the appointment of the person responsible for the gas sector, his office and home telephone numbers.
The unit has OFFICE PREMISES there are logs: watch, preventative repairs and inspections, records of control results.
As practice shows, most accidents on gas-heated units are associated with violation of the Rules, instructions and order preparation for turning on the units and igniting the burners.
Before each commissioning of boilers, furnaces and other units, their fireboxes must be ventilated. The duration of this operation is determined by local instructions and is taken depending on the volume of the firebox and the length of the chimneys.
The smoke exhauster and fan for supplying air to the burners are turned on when ventilating the fireboxes and chimneys. Before this, you should, by rotating the rotor of the smoke exhauster manually, make sure that it does not touch the housing and cannot cause sparking upon impact. A responsible job before starting gas is also purging gas pipelines. Before starting purge, you should make sure that there are no people in the area where gas is released from the purge spark plug, there are no lights, and no work involving open fire 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:
- The presence of sufficient gas pressure in the gas pipeline in front of the boiler or other unit.
- Air pressure when supplied from blowing devices.
- Presence of vacuum in the firebox or hog (up to the gate).
If necessary, the traction must be adjusted.
The device that turns off the gas supply in front of the burner should be opened smoothly and only after the igniter or torch has been brought to it. In this case, the person performing this work should be on the side of the gas burner device when the gas is ignited. When igniting gas on the burner, the smallest amount of air should be supplied to the firebox, which would ensure complete combustion of the gas. Other burners are lit in the same way. If, during ignition, regulation or operation, the flame goes out or it comes off or breaks through, you must immediately turn off the gas, ventilate the firebox and relight it in the above order.
Failure to comply with this requirement is one of the main causes of accidents.
It is prohibited to operate gas-fueled units in the event of any malfunctions, lack of traction, or leave units turned on 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 a dangerous gas leak into the room; in the event of a fire threat or occurrence.
During the preparation of repairs, the manager responsible for their implementation outlines a plan taking into account the implementation of all measures to guarantee the safety of people. The plan must contain: a diagram of the facility being repaired, indicating the locations of repair work and indicating their scope; a list of mechanisms, devices and tools approved for use for repair work; list by name and arrangement of workers admitted to repair work; a complete list of measures to ensure the safe performance 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 workshop manager, responsible person for repairs and agreed with the head of the gas facility.
The repair manager, in addition, instructs personnel and monitors compliance with the Rules during the preparation and implementation of repair work.
During repairs, you can only use portable electric lighting with a voltage not higher than 12 - 24 V and in an explosion-proof design. Work related to people staying at heights must be carried out using reliable ladders, platforms, scaffolding, and also using, if necessary, safety belts (the places where the belts are caught are indicated by the repair manager). After completing the repair, you must immediately remove cleaning and flammable materials and their traces. Then remove the plugs, purge the gas pipeline with gas and check all connections for leaks, set up and adjust the equipment to the specified mode.
Labor protection and safety
Information portal – Occupational Health and Life Safety. Section – Labor protection in high-risk conditions. Gas industry. Operation of gas equipment
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Information
Flammability limit
The flammability limits change significantly with the addition of certain substances that can influence the development of pre-flame chain reactions. Substances are known that both expand and narrow the flammability limits.[ . ]
Flammability limits are influenced by chemical composition fuel and oxidizer, temperature, pressure and turbulence of the environment, concentration and type of additives or inert diluents, power of the ignition source during forced ignition. The influence of the type of fuel on the ignition limits is shown in table 3.4.[. ]
The highest limit is the concentration of fuel vapor in the mixture, at an increase in which the flammable mixture does not ignite.[. ]
Ignition temperature, flash point, and flammable temperature limits refer to the indicators fire danger. In table 22.1 presents these indicators for some technical products.[ . ]
The wider the ignition zone and the lower the bottom concentration limit ignition, the more dangerous the fumigant is 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. When hydrogen sulfide occurs, explosions and fires are possible, which can spread over a vast area and cause numerous casualties and large losses. The presence of hydrogen sulfide leads to dangerous destruction of drilling tools and drilling equipment and causes their intense corrosion cracking, as well as corrosion of cement stone. Hydrogen sulfide is very aggressive to clayey drilling fluids in formation waters and gases.[ . ]
The ignition delay period of diesel fuel is estimated 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 operating severity. Cetane is a hydrocarbon with the lowest, and a-methylnaphthalene is a hydrocarbon with the highest, accepted as the standard limits of fuel ignition delay (100 and 0 units, respectively).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 flammability limits.[ . ]
Tests of an engine ignited by a finely focused laser beam generating plasma nuclei have shown that in this case the pressure build-up in the combustion chamber occurs more intensely, the ignition limits expand, and the power outputs improve. economic indicators engine operation.[ . ]
The values of the temperature limits of ignition of substances are used when calculating fire and explosion-proof operating modes technological equipment, when assessing emergency situations associated with spills of flammable liquids, as well as for calculating flammable concentration limits.[ . ]
Lower concentration flammability limit - the minimum concentration of fumigant vapor in the air at which the vapor ignites from an open flame or from electric spark.[ . ]
The expansion of ignition concentration limits creates the prerequisites for ensuring stable engine operation on lean mixtures.[ . ]
However, we must not lose sight of the fact that 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 device that stabilizes combustion well, while in another burner such an attempt may be unsuccessful. .[ . ]
With increasing turbulence of the combustible mixture, the ignition limits expand if the turbulence characteristics are such that they intensify the processes of transfer of heat and active products in the reaction zone. The flammability limits may narrow if turbulization 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.[. ]
As the molecular weight of hydrocarbons decreases, the flammability limits expand.[ . ]
In addition to concentration limits, there are also temperature limits (lower and upper) of ignition, which are understood as those temperatures of a substance or material at which its saturated flammable vapors form concentrations in the 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. Poses the least danger to natural environment and personnel, if the oil does not spread beyond the embankment. When an embankment breaks through as a result of the hydrodynamic impact of leaking oil, contamination of the main components of the environment is possible on a significant scale.[ . ]
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 flammability limits.[ . ]
Chemical properties. Flash point (in open cup) 0°; flammability limits in air - 3-17 vol. %.[ . ]
During combustion in spark-ignition engines, the concentration limits for the ignition of the mixture do not coincide with the specified limits for the onset of soot formation. Therefore, the soot content in the exhaust gases of spark-ignition engines is insignificant.[ . ]
The variety of substances and materials predetermined different concentration limits for flame propagation. There are such concepts as lower and upper concentration limits of flame propagation (ignition) - these are, respectively, the minimum and maximum content of fuel in the mixture “combustible substance - oxidizing medium”, at which it is possible for the flame to spread through the mixture to any distance from the ignition source. The concentration interval between the lower and upper limits is called the area of flame 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 pre-flame transformation reactions.[ . ]
With an increase in heat capacity, thermal conductivity and concentration of inert diluents, the flammability limits expand.[ . ]
The flammability of vapors (or gases) is characterized by lower and upper flammability concentration limits and ignition concentration zone.[ . ]
Level of measured temperatures along the axis and periphery of the embrasure (Fig. 6-15, b) less temperature ignition of a mixture of natural gas with air equal to 630-680 °C, and only at the exit from the embrasure, in its conical section, the temperature reaches 680-700 °C, i.e., the ignition zone is located here. A significant increase in temperature is observed outside the embrasure at a distance of (1.0-g-1.6) Vgun.[ . ]
The fire hazard during aeration work increases significantly when the fumigant consumption rate per 1 m3 is within the ignition concentration zone.[ . ]
In Fig. Table 2.21 shows the maximum pressure values during an explosion of a mass Mg = 15 tons of superheated gasoline. In this case, the flame speed varied within the range: 103.4-158.0 m/s, which corresponds to the minimum and maximum cluttered space at the point of ignition of the mixture. An explosion of such a quantity of superheated gasoline (type 1 accident under scenario A) is possible during the 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 the long-range spray torch of pasty sediments at a small opening angle, which leads to the slippage of unburned particles beyond the cyclone reactor and requires the construction of an afterburner chamber. 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 required for complete oxidation of organic substances.[. ]
Usually, organic solvents are flammable, their vapors form explosive mixtures with air. The degree of flammability of solvents is characterized by flash point and flammability limits. To avoid explosion, it is necessary to maintain the concentration of solvent vapors in the air below the lower flammability limit.[ . ]
Flammable gases, vapors of flammable liquids and combustible dust when certain conditions form explosive mixtures with air. They delimit the lower and upper concentration limits of explosion, 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 flame propagation, and the content of inert substances.[ . ]
Combustion stops when one of the following conditions: eliminating a flammable substance from the combustion zone or reducing its concentration; reducing the percentage of oxygen in the combustion zone to 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 combustion of drifting gas clouds may result in the death of all people located on the territory of the facility (up to 4 people working per shift), as well as injury to people outside the gas station. Moreover, the number of victims when entering the affected area of the road will primarily depend on the intensity of traffic. People traveling on a road can only be harmed if a fireball occurs or a drifting cloud ignites. Moreover, when a cloud burns, damage in the area of roads is possible provided that it ignited not along the drift path, but when vehicles got into it. Also, the risk indicators are significantly influenced by the professional and emergency training of personnel.[ . ]
Dusts of many solid flammable substances suspended in the 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 concentration limit for dust is not applied, since it is impossible to create very large concentrations of dust in suspension. Information on the lower flammability limit (LCEL) of some dusts is presented in table. 22.2.[ . ]
At some oil refineries and petrochemical plants, the amount of gases discharged can sometimes reach 10,000-15,000 m3/h. Let us assume that within five minutes 1000 m3 of gases will be discharged, for 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, mixing with the surrounding air, can create an explosive atmosphere with a volume of about 50,000 m3 in a short period of time. If we assume that the explosive cloud is positioned so that it average height will be about 10 m, then the cloud area will be 5000 m2 or cover about 0.5 hectares of surface. It is very likely that in such an area there may be some kind of ignition source and then in this vast area there will be powerful explosion. Such cases have happened. 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.[ . ]
Developed at Universin “B” technical specifications. 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 flammable substance with a flash point of 209 °C and a self-ignition temperature of 303 °C. Temperature limits of vapor explosion: lower 100 °C, upper 180 °C. Basic physical properties University “B” are given below.[ . ]
Let's assess the fire danger (fire hazard) various substances and materials, taking them into account state of aggregation(solid, liquid or gas). The main indicators of fire hazard are the auto-ignition temperature and ignition concentration limits.[ . ]
Waste from gasoline solvents, 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 auto-ignition 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 required time residence 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 towards the lower limit of spontaneous ignition of neutralized gas mixtures and exceeds the ignition temperature (Table 1.7) by 100-150 °C. [ . ]
Of the existing gas purification devices, the main ones for converter production are Venturi tubes, electrostatic filters and fabric (bag) filters. Scrubbers, foam apparatus and cyclones are usually used in combination with Venturi tubes and electrostatic precipitators. The content of flammable components in the gases entering the electrostatic precipitators must be significantly less than the lower flammability limit of the corresponding components. As a result, electric precipitators cannot operate in the gas exhaust system without afterburning.[. ]
Calculations carried out in accordance with the above methodology showed that a cloud of gas with a high concentration is formed at the rupture site, which is dissipated due to advective transport and turbulent diffusion in the atmosphere. Using the "RISK" program, the probabilities of exceeding two threshold concentration values were calculated: 300 mg/m3 - the maximum permissible concentration of methane in work area and 35000 mg/m3 - the lower flammability limit of the methane-air mixture.[ . ]
Near the surface of the earth, a rather complex gravitational current is formed, facilitating the radial spread and dispersion of LNG vapors. As an illustration of the results of numerical calculations of the dispersion of a methane-air cloud in Fig. Figure 5 shows the evolution of the vapor cloud for the most unfavorable conditions dispersion (atmospheric stability – “B” according to the Gifford-Pasquill classification, wind speed – 2 m/s) in the form of isosurfaces of 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 are trading at $2.768 per mmBtu, up 0.58% at the time of writing.
The maximum of the session was the level of dollars per million Btu. At the time of writing, natural gas found support at $2.736 and resistance at $2.832.
USD index futures, which measure the US dollar against a basket of six major currencies, fell 0.17% to trade at $94.28.
In other NYMEX commodities, WTI crude oil for September delivery fell 3.95% to $67.19 a barrel, while heating oil futures for August delivery fell 3.19% to $67.19 a barrel. to $2.0654 per gallon.
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The version of this document on English language shall govern and shall prevail in the event of any discrepancies between the English and Russian versions.
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The Sosnogorsk section of the GIMS of the Ministry of Emergency Situations of Russia informs that with the opening of navigation for a short period, cases of death of 12 people were recorded on the reservoirs of the Komi Republic
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Explosion limit of natural gas
On July 25, 2018, from 10.00 to 13.00, the State Public Institution of the Republic of Kazakhstan “Department of Fire Service and Civil Protection” will collect mercury-containing waste on the territory of ICGO “Ukhta” Main cause of death
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 NCPRP and VCPRP:
- 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 lowers 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 it saturated couples form concentrations corresponding to the CPRP.
CPRP is determined by calculation or found experimentally.