Concentration limit of oil flame propagation is ha 30. See what “NKPR” is in other dictionaries
Lower (upper) concentration limit flame spread - the minimum (maximum) concentration of fuel in the oxidizer that can ignite from a high-energy source with the subsequent spread of combustion to the entire mixture.
Calculation formulas
The lower concentration limit of flame propagation φ n is determined by the maximum heat of combustion. It has been established that 1 m 3 of various gas-air mixtures at the NKPR emits a constant average amount of heat during combustion - 1830 kJ, called the ultimate heat of combustion. Hence,
if we take the average value of Q equal to 1830 kJ/m 3, then φ n 6 will be equal to
(2.1.2)
Where Q n - lower heat of combustion of a combustible substance, kJ/m 3.
The lower and upper flame CPR can be determined using the approximation formula
(2.1.3)
Where n - stoichiometric coefficient for oxygen in the chemical reaction equation; a and b are empirical constants, the values of which are given in table. 2.1.1
Table 2.1.1.
Concentration limits for flame propagation of vapors of liquid and solid substances can be calculated if known temperature limits
(2.1.4)
Where R Not)- pressure saturated steam substances at a temperature corresponding
lower (upper) limit of flame spread, Pa;
p O-ambient pressure, Pa.
Saturated vapor pressure can be determined from Antoine's equation or from table. 13 applications
(2.1.5)
Where A, B, C- Antoine constants (Table 7 of the appendix);
t - temperature, 0 C, (temperature limits)
To calculate the concentration limits of flame propagation of mixtures of flammable gases, Le Chatelier’s rule is used
(2.1.6)
Where 
lower (upper) CPR of the gas mixture flame, % vol.;
- lower (upper) limit of flame propagation i-ro flammable gas%, vol.;
- mole fraction i-ro of combustible gas in the mixture.
It should be kept in mind that ∑μ i =1, i.e. the concentration of flammable components of the gas mixture is taken as 100%.
If the concentration limits of flame propagation at temperature T 1 are known, then at temperature T 2. they are calculated using the formulas
,
(2.1.7)
,
(2.1.8)
Where 
,
- lower concentration limit of flame propagation, respectively, at temperatures
T 2
. and T 1
;
And 
- upper concentration limit of flame propagation, respectively, at temperatures T 1
And T 2
;
T G- combustion temperature of the mixture.
Approximately when determining the LFL of a flame T G take 1550 K, when determining the VKPR of the flame -1100K.
When the gas-air mixture is diluted with inert gases (N 2 , CO 2 H 2 O vapors, etc.), the ignition region narrows: the upper limit decreases, and the lower limit increases. The concentration of an inert gas (phlegmatizing agent), at which the lower and upper limits of flame propagation close, is called the minimum phlegmatizing concentration φ
f .
Oxygen content
Such a system is called the minimum explosive oxygen content MVSC. Some oxygen content below the MVSC is called safe 
.
The calculation of these parameters is carried out according to the formulas
(2.1.9)
(2.1.10)
(2.1.11)
Where 
- standard heat of formation of fuel, J/mol;
,
,
- constants depending on the type of chemical element in the fuel molecule and the type of phlegmatizer, table. 14 applications;
- the number of atoms of the i-th element (structural group) in a fuel molecule.
Example 1. Using the maximum heat of combustion, determine the lower concentration limit of ignition of butane in air.
Solution. To calculate using formula (2.1.1) in table. In Appendix 15 we find the lowest heat of combustion of the substance to be 2882.3 kJ/mol. This value must be converted to another dimension - kJ/m 3:
kJ/m 3
Using formula (2.1.1), we determine the lower concentration limit of flame propagation (LCFL)
According to the table 13 Appendix we find that the experimental value 
- 1.9%. The relative calculation error, therefore, was
.
Example 2. Determine the concentration limits of ethylene flame propagation in air.
We calculate the flame CPR using the approximation formula. Determine the value of the stoichiometric coefficient for oxygen
C 3 H 4 + 3 O 2 = 2 CO 2 + 2 H 2 O
Thus, n = 3, then
Let us determine the relative calculation error. According to the table 13 appendices experimental values of the limits are 3.0-32.0:
Consequently, when calculating the LEL of ethylene, the result is overestimated by 8%, and when calculating the LEL, it is underestimated by 40%.
Example 3. Let us determine the concentration limits of flame propagation of saturated methanol vapors in the air, if it is known that its temperature limits are 280 - 312 K. The atmospheric pressure is normal.
To calculate using formula (2.1.4), it is necessary to determine the saturated vapor pressure corresponding to the lower (7 ° C) and upper (39 ° C) limits of flame propagation.
Using the Antoine equation (2.1.5), we find the saturated vapor pressure, using the data in Table 7 of the Appendix.
Р Н =45.7 mmHg=45.7·133.2=6092.8 Pa
Р Н =250 mmHg=250·133.2=33300 Pa
Using formula (2.1.3) we determine the NKPR
Example 4. Determine the concentration limits of flame propagation of a gas mixture consisting of 40% propane, 50% butane and 10% propylene.
To calculate the flame coefficient of a mixture of gases using the Le Chatelier rule (2.1.6), it is necessary to determine the flame coefficient of individual combustible substances, the calculation methods of which are discussed above.
C 3 H 8 -2.1÷9.5%; C 3 H 6 -2.2÷10.3%; C 4 H 10 -1.9÷9.1%
Example 5. What is the minimum amount of diethyl ether, kg, capable of producing an explosive concentration upon evaporation in a container with a volume of 350 m3.
The concentration will be explosive if φ n =φ pg Where ( φ pg- concentration of vapors of a flammable substance). By calculation (see examples 1-3 of this section) or according to the table. 5 of the application we find the LCPR of the diethyl ether flame. It is equal to 1.7%.
Let us determine the volume of diethyl ether vapor required to create this concentration in a volume of 350 m3
m 3
Thus, to create an LCPR of diethyl ether with a volume of 350 m 3, it is necessary to introduce 5.95 m 3 of its vapor. Taking into account that 1 kmol (74 kg) of steam, reduced to normal conditions, occupies a volume equal to 22.4 m 1, we find the amount of diethyl ether
kg
Example 6. Determine whether the formation of an explosive concentration in a volume of 50 m3 is possible with the evaporation of 1 kg of hexane if the ambient temperature is 300 K.
Obviously, the steam-air mixture will be explosive if φ n ≤φ pg ≤φ V- At 300 K, we will find the volume of hexane vapor resulting from the evaporation of 5 kg of a substance, taking into account that with the evaporation of 1 kmol (86 kg) of hexane at 273 K, the volume of the vapor phase will be equal to 22.4 m 3
m 3
Hexane vapor concentration in room with a volume of 50m 3, therefore, will be equal to
Having determined the concentration limits of hexane flame propagation in air (1.2-7.5%), using tables or calculations we establish that the resulting mixture is explosive.
Example 7. Determine whether an explosive concentration of saturated vapors is formed above the surface of a tank containing 60% diethyl ether (DE) and 40% ethyl alcohol (EA) at a temperature of 245 K?
The vapor concentration will be explosive if φ cm n ≤φ cm np ≤φ cm V (φ cm np- concentration of saturated vapors of a mixture of liquids).
It is obvious that, as a result of different volatility of substances, the composition of the gas phase will differ from the composition of the condensed phase. Based on the known composition of the liquid phase, we determine the content of components in the gas phase using Raoult’s law for ideal solutions of liquids.
1. Determine the molar composition of the liquid phase
,
Where 
- mole fraction of the i-th substance;
- weight fraction of the i-th substance;
- molecular weight of the i-th substance; ( M DE =74,
M ES =46)
2. According to equation (2.1.5), using the values in Table 12 of the Appendix. Find the pressure of saturated ether and ethyl alcohol at a temperature of 19°C (245 K)
R DE=70.39 mmHg=382.6 Pa
R ES=2.87 mmHg=382.6 Pa
3. According to Raoult’s law, the partial pressure of saturated vapor of the i-th liquid above the mixture is equal to the product of the saturated vapor pressure above a pure liquid and its mole fraction in the liquid phase, i.e.
R DE(steam) =9384.4·0.479=4495.1 Pa;
R ES(steam)=382.6·0.521=199.3 Pa.
4. Taking the sum of the partial pressures of saturated vapors of diethyl ether and ethyl alcohol equal to 100%, we determine
a) vapor concentration in the air
b) molar composition of the gas phase (Raoult-Duartier law)
5. Having determined by calculation or from reference data (Table 16 of the appendix) the flame coefficient of individual substances (diethyl ether 1.7÷59%, ethyl alcohol 3.6÷19%). Using Le Chagelier's rule, we calculate the CPR of the vapor phase flame
6. Comparing the concentration of the steam-air mixture obtained in paragraph 4a with the concentration limits of flame propagation (1.7-46.1%), we conclude that at 245 K above this liquid phase an explosive concentration of saturated vapors in the air is formed.
From Table 15 in the appendix we find the heat of formation of acetone to be 248.1·10 3 J/mol. From chemical formula acetone (C3H 6 O) it follows that T With = 3, T n = 6, T O = 1. The values of the remaining parameters required for calculation using formula (2.8) are selected from the table. 11 for carbon dioxide
Consequently, when the oxygen concentration in a four-component system consisting of acetone, carbon dioxide, nitrogen and oxygen vapors is reduced to 8.6%, the mixture becomes explosion-proof. At an oxygen content equal to 10,7% this mixture will be extremely explosive. According to reference data (the reference book "Fire Hazard of Substances and Materials Used in the Chemical Industry." - M, Khimiya, 1979), the MVSC of an acetone-air mixture when diluted with carbon dioxide is 14.9%. Let us determine the relative calculation error
Thus, the results of calculating the MVSC are underestimated by 28%.
Independent work assignment
|
Substance liquid |
Substance gas |
|
|
Amylbenzene |
Acetylene |
|
|
N-Amyl alcohol | ||
|
Carbon monoxide |
||
|
Butyl acetate | ||
|
Butyl alcohol | ||
|
Hydrogen sulfide |
||
|
Diethyl ether | ||
|
Acetylene |
||
|
White Spirit | ||
|
Ethylene glycol |
Carbon monoxide |
|
|
Tert-Amyl alcohol | ||
|
Methyl alcohol | ||
|
Hydrogen sulfide |
||
|
Amyl methyl ketone | ||
|
Butylbenzene | ||
|
Butyl vinyl ether |
Carbon monoxide |
|
|
Acetylene |
||
|
Ethanol | ||
|
Acetylene |
||
|
Butyl alcohol |
Carbon monoxide |
|
2.1 Natural gas is a product extracted from the bowels of the earth, consisting of methane (96 - 99%), hydrocarbons (ethane, butane, propane, etc.), nitrogen, oxygen, carbon dioxide, water vapor, helium. At IVCHPP-3, natural gas is supplied as fuel through a gas pipeline from Tyumen.
The specific gravity of natural gas is 0.76 kg/m3, specific heat combustion - 8000 - 10000 kcal/m 3 (32 - 41 MJ/m 3), combustion temperature - 2080 ° C, ignition temperature - 750 ° C.
According to its toxicological characteristics, combustible natural gas belongs to substances of hazard class 4 (“low-hazardous”) in accordance with GOST 12.1.044-84.
2.2 Maximum permissible concentration (MPC) of natural gas hydrocarbons in the air working area equal to 300 mg/m 3 in terms of carbon, the maximum permissible concentration of hydrogen sulfide in the air of the working area is 10 mg/m 3, hydrogen sulfide mixed with hydrocarbons C 1 - C 5 - 3 mg/m 3.
2.3 Safety rules for the operation of gas facilities stipulate the following dangerous properties gaseous fuel:
a/ no odor or color
b/ the ability of gas to form fire and explosive mixtures with air
c/ gas suffocating ability.
2.4 Permissible gas concentration in the air of the working area, in the gas pipeline when performing gas hazardous work - no more than 20% of the lower concentration limit of flame propagation (LCFL):
3 Rules for sampling gas for analysis
3.1 Smoking and use open fire in gas-hazardous places, when checking the gas contamination of industrial premises, it is strictly prohibited.
3.2 The shoes of workers who measure gas levels and who are in gas-hazardous places should not have metal shoes or nails.
3.3 When performing gas-hazardous work, portable lamps of explosion-proof design with a voltage of 12 Volt should be used
3.4 Before performing the analysis, it is necessary to inspect the gas analyzer. Measuring instruments that have expired their verification period or are damaged are not allowed to be used.
3.5 Before entering the fracking room, you must: make sure that the emergency signal lamp “GASED” is not lit when entering the fracking room. The warning light turns on when the methane concentration in the air in the gas treatment facility reaches equal to or higher than 20% of the lower concentration limit of flame propagation, i.e. equal to or higher than vol. 1%.
3.6 Gas sampling in rooms (in the gas distribution center) is carried out with a portable gas analyzer from the upper zone of the room in the most poorly ventilated areas, because natural gas lighter than air.
Actions in case of gas contamination are specified in clause 6.
3.7 When taking air samples from a well, you need to approach it from the windward side, making sure that there is no smell of gas nearby. One side of the well cover should be raised by a special hook by 5 - 8 cm, and a wooden spacer should be placed under the cover during sampling. The sample is taken using a hose lowered to a depth of 20 - 30 cm and connected to a portable gas analyzer, or into a gas pipette.
If gas is detected in the well, ventilate it for 15 minutes. and repeat the analysis.
3.8 It is not allowed to go down into wells and other underground structures to take samples.
3.9 In the air of the working area, the content of natural gas should be no more than 20% of the lower concentration limit of flame propagation (1% for methane); the oxygen concentration must be at least 20% by volume.
At analysis of mixtures of various gases in order to determine their qualitative and quantitative composition, use the following basic units of measurement:
- “mg/m3”;
- “ppm” or “million -1”;
- "% about. d.";
- “% NKPR”.
The mass concentration of toxic substances and the maximum permissible concentration (MPC) of flammable gases are measured in “mg/m3”.
The unit of measurement “mg/m 3 ” (eng. “mass concentration”) is used to indicate the concentration of the measured substance in the air of the working area, atmosphere, as well as in exhaust gases, expressed in milligrams per cubic meter.
When performing gas analysis, end users typically convert gas concentration values from “ppm” to “mg/m3” and vice versa. This can be done using our Gas Unit Calculator.
Parts per million of gases and various substances is a relative value and is denoted in “ppm” or “million -1”.
“ppm” (eng. “parts per million”) - a unit of measurement of the concentration of gases and other relative values, similar in meaning to ppm and percentage.
The unit "ppm" (million -1) is convenient to use for estimating small concentrations. One ppm is one part in 1,000,000 parts and has a value of 1×10 -6 of the base value.
The most common unit for measuring the concentrations of flammable substances in the air of the working area, as well as oxygen and carbon dioxide is the volume fraction, which is denoted by the abbreviation “% vol. d." .
"% about. d." - is a value equal to the ratio of the volume of any substance in a gas mixture to the volume of the entire gas sample. The volume fraction of gas is usually expressed as a percentage (%).
“% LEL” (LEL - Low Explosion Level) - lower concentration limit of flame distribution, the minimum concentration of a flammable explosive substance in a homogeneous mixture with an oxidizing environment at which an explosion is possible.
BASIC TERMS AND CONCEPTS.
MPC (maximum permissible concentration) harmful substances in the air of the working area are the concentrations that, at daily work within 8 hours during the entire working time cannot cause diseases or health conditions in the worker that can be detected by modern research methods directly during work or at a later date. And also the maximum permissible concentration of harmful substances should not negatively affect the health status of subsequent generations. Measured in mg/cub.m
MPC of some substances (in mg/cub.m):
Petroleum hydrocarbons, kerosene, diesel fuel - 300
Gasoline - 100
Methane - 300
Ethanol - 1000
Methyl alcohol - 5
Carbon monoxide - 20
Ammonia ( ammonia) - 20
Hydrogen sulfide in pure form - 10
Hydrogen sulfide mixed with petroleum hydrocarbons - 3
Mercury - 0.01
Benzene - 5
NKPR – lower concentration limit of flame propagation. This is the lowest concentration of flammable gases and vapors at which an explosion is possible when exposed to an ignition pulse. Measured in %V.
LEL of some substances (in % V):
Methane - 5.28
Petroleum hydrocarbons - 1.2
Gasoline - 0.7
Kerosene - 1.4
Hydrogen sulfide - 4.3
Carbon monoxide - 12.5
Mercury - 2.5
Ammonia - 15.5
Methyl alcohol - 6.7
VKPR – upper concentration limit of flame propagation. This is the highest concentration of flammable gases and vapors at which an explosion is still possible when exposed to an ignition pulse. Measured in %V.
VKPR of some substances (in % V):
Methane - 15.4
Petroleum hydrocarbons - 15.4
Gasoline - 5.16
Kerosene - 7.5
Hydrogen sulfide - 45.5
Carbon monoxide - 74
Mercury - 80
Ammonia - 28
Methyl alcohol - 34.7
DVK - pre-explosive concentration, defined as 20% of the LEL. (at this point an explosion is not possible)
PELV - extremely explosive concentration, defined as 5% of the LEL. (at this point an explosion is not possible)
Relative density in air (d) shows how many times the vapor of a given substance is heavier or lighter than air vapor in normal conditions. The value is relative - there are no units of measurement.
Relative density in air of some substances:
Methane - 0.554
Petroleum hydrocarbons - 2.5
Gasoline - 3.27
Kerosene - 4.2
Hydrogen sulfide - 1.19
Carbon monoxide - 0.97
Ammonia - 0.59
Methyl alcohol - 1.11
Gas hazardous places – such places in the air of which there are or may suddenly appear toxic vapors in concentrations exceeding the maximum permissible concentration.
Gas hazardous areas are divided into three main groups.
Igroup – places where the oxygen content is below 18% V, and the content of toxic gases and vapors is more than 2% V. In this case, work is carried out only by gas rescuers, in isolating apparatus, or under their supervision according to special documents.
IIgroup– places where the oxygen content is less than 18-20%V, and sub-explosive concentrations of gases and vapors can be detected. In this case, the work is carried out according to work permits, excluding the formation of sparks, in appropriate protective equipment, under the supervision of gas rescue and fire supervision. Before carrying out work, an analysis of the gas-air environment (DHW) is carried out.
IIIgroup– places where the oxygen content is from 19% V, and the concentration of harmful vapors and gases may exceed the maximum permissible concentration. In this case, work is carried out with or without gas masks, but gas masks must be in good condition at the workplace. In places of this group, it is necessary to carry out analysis of hot water supply according to the schedule and selection map.
Gas hazardous work - all those works that carried out in a gas-polluted environment, or work during which gas may escape from gas pipelines, fittings, units and other equipment. Gas-hazardous work also includes work that is performed in a confined space with an oxygen content in the air of less than 20% V. When performing gas-hazardous work, the use of open flame is prohibited, and sparking must also be prevented.
Examples of gas hazardous work:
Work related to inspection, cleaning, repair, depressurization technological equipment, communications;
U removing blockages, installing and removing plugs on existing gas pipelines, as well as disconnecting units, equipment and individual components from gas pipelines;
Repair and inspection of wells, pumping water and condensate from gas pipelines and condensate collectors;
Preparation for technical inspection of LPG tanks and cylinders and its implementation;
Opening up the soil in areas of gas leaks until they are eliminated.
Hot work - production operations involving the use of open fire, sparking and heating to temperatures that can cause ignition of materials and structures.
Examples of hot work:
Electric welding, gas welding;
Electric cutting, gas cutting;
Application of explosive technologies;
Soldering works;
Educational cleaning;
Mechanical processing of metal with the release of sparks;
Warming up bitumen, resins.
NKPR- the lower concentration limit of flame propagation. For oil is 42000 mg/m3 at such a concentration an explosion is already possible if the ignition source is awakened.
VKPR- upper limit 195000 mg/m3. at such a concentration, an explosion is already possible if the ignition source is awakened.
Concentration between LEL and VKPR - explosive range.
An explosion from a fire differs in the speed of flame propagation through a flammable medium per unit time of 1 second. When burning, the speed of distribution flame in cm, and with an explosion in meters, tens of hundreds of m/s Acetylene = 400 m/s.
PDVC- the maximum permissible explosion-proof concentration is, for any explosive substance, 5% of the LEL = 2100 mg/m3, with it it is possible to carry out hot work but in PPE org. breathing.
Measures to prevent ignition and self-ignition of oil vapors.
Compliance with measures fire safety.
Use of non-sparking tools.
Use only explosion-proof equipment.
Safe work performance.
Decontamination or ventilation of the gas-contaminated area.
Use of grounding.
Bypass.
Spark arresters for equipment taking part in the work.
Minimum team size when monitoring hot water supply on the linear part.
The team consists of at least 3 people
List of gas hazardous work on the linear part, for which it is necessary to issue a work permit.
Excavation for opening an oil pipeline;
Cold tapping into existing oil pipelines under pressure special device;
Pumping (injecting) oil from barns, tanks, and a cut-off section of an oil pipeline;
Displacement of oil from an oil pipeline;
DHW inlet (outlet);
Cutting of oil pipelines using pipe cutting machines;
Cleaning (steaming) of an oil pipeline;
Oil pipeline sealing;
Cutting plungers, pipes, pipelines hand saws;
Insulation works on an oil pipeline;
Work in wells installed on process pipelines and pipelines of the linear part.
gas hazardous work: Work related to inspection, maintenance, repair, depressurization of process equipment, communications, incl. work inside containers (apparatuses, reservoirs, tanks, as well as collectors, tunnels, wells, pits and other similar places), during which there is or is not excluded the possibility of explosive, fire-hazardous or harmful vapors, gases and other substances entering the work site , capable of causing an explosion, fire, harmful effects on the human body, as well as work with insufficient oxygen content (volume fraction below - 20 %).
Arrangement of electrical equipment and equipment involved during pumping out of the pipeline and pumping the pumped product into the pipeline.
When carrying out work to clear an oil pipeline using mobile pumping units, the following requirements for the placement of machinery and equipment on prepared sites must be met (Figure 10.4):
a) the distance from the pumping pump to the pumping-injection site must be at least 50 m;
b) the distance between the PPU is at least 8 m;
c) the distance from the pump pumping station to the supporting unit is at least 40 m;
d) the distance from the diesel power station to the booster pumping units and the pumping/injection point is at least 50 m;
e) the distance from the equipment parking area to the pump pump unit, booster pump unit, repair pit - at least 100 m;
f) the distance from the fire tanker to the places of pumping and injection of oil, PPU, pit - at least 30 m.
Rules for the use of safety signs.
Safety signs can be basic, additional, combined and group
Depending on the type of materials used, safety signs can be non-luminous, retroreflective or photoluminescent.
Groups of basic safety signs
Basic safety signs must be divided into the following groups:
Prohibition signs;
Warning signs;
Fire safety signs;
Mandatory signs;
Evacuation signs and signs for medical and sanitary purposes;
Directional signs.
Signs should not interfere with passage or travel.
Should not contradict each other.
Be easy to read.
23. Work permit for carrying out fire, gas hazardous and other high-risk work, its contents.
The permit is valid for the period specified therein. The planned duration of the work should not exceed 10 days. The work permit may be extended for a period of no more than 3 days, while the duration of work from the planned date and time of the start of work, taking into account the extension, should not exceed 10 days.
PERMISSION WORKOUT NO.