Convert NKPR to volume fractions. Chow uts "new perspectives". Rules for the use of safety signs

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, the specific heat of combustion is 8000 - 10000 kcal/m3 (32 - 41 MJ/m3), the combustion temperature is 2080 °C, the ignition temperature is 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 The maximum permissible concentration (MPC) of natural gas hydrocarbons in the air of the working area is 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 regulations for the operation of gas facilities determine the following dangerous properties of 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 the use of open flames in gas hazardous places, when checking the gas contamination of industrial premises, 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 “GASED” emergency signal lamp 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 is 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.

Gas, tasteless, colorless, odorless. Air density 0.554. Burns well, with an almost colorless flame. Self-ignition temperature 537°C. Explosion limit 4.4 - 17%. The maximum permissible concentration in the air of the working area is 7000 mg/m3. It has no poisonous properties. A sign of suffocation with a methane content of 80% and 20% oxygen is a headache. The danger of methane is that with a strong increase in methane content, the oxygen content decreases. The danger of poisoning is reduced by the fact that methane is lighter than air, and when an unconscious person falls, he enters an atmosphere richer in oxygen. Methane is an asphyxiating gas, therefore, after bringing the victim to consciousness (if the victim has lost consciousness), it is necessary to inhale 100% oxygen. Give the victim 15-20 drops of valerian and rub the victim’s body. There are no methane filtering gas masks.

Ticket number 2

1. Define the concept of “Lower Explosive Limit (LEL) (lower concentration limit of flame propagation - LEL).” The minimum concentration of flammable gas in the air at which an explosion of a mixture of flammable gas and air occurs. At gas concentrations below the LEL, no reaction occurs.

2. Air monitoring at gas transportation facilities.

4.1. Before putting into operation a pipeline for the transport of natural gas, it is necessary to displace air from the pipeline with gas at a pressure of no more than 0.1 MPa (1 kgf/cm2) at the point of its supply, in compliance with safety measures. The displacement of air by gas can be considered complete when the oxygen content in the gas leaving the gas pipeline is no more than 1% according to the readings of the gas analyzer.

Analysis of residual oxygen in the pipe when purging a repaired section should be carried out with a specialized device that simultaneously analyzes the content of oxygen (low concentrations) and flammable gas (from 0 to 100% volume fraction).

The use of individual gas analyzers designed to ensure personnel safety in these cases is unacceptable, as it leads to failure of the sensors.

The equipment used must:

Have an explosion-proof design;

Have a sampling probe to take a sample from the pipe;

Have a built-in expense driver;

Have a lower operating temperature limit of minus 30° C;

Have automatic zero calibration (adjustment);

Have a display for simultaneous display of measured concentrations;

Ensure registration of measurement results.

4.2. The tightness of equipment, pipelines, welded, detachable joints and seals is monitored using explosion-proof leak detectors with the function of protecting the sensor from overloads.

The use of individual gas analyzers for these purposes is unacceptable, since these gas analyzers do not display leaks with a concentration of less than 0.1% LEL.

4.3. Monitoring of gas contamination in wells, including water supply and sewerage, underground premises and closed channels located on industrial sites, is carried out according to a schedule at least once a quarter, and in the first year of their operation - at least once a month, as well as every times immediately before starting work in the specified areas. Gas contamination control should be carried out using remote sampling with portable (individual) gas analyzers with a connected manual or built-in motorized sampling pump.

4.4. Monitoring of leaks and gas contamination along underground gas pipelines is carried out using leak detectors, similar to those used in monitoring the tightness of equipment.

4.5. Along with monitoring the air environment for gas contamination with stationary devices, it is necessary to carry out continuous monitoring (while in the danger zone) of the air environment with portable gas analyzers:

In rooms where gases and liquids containing harmful substances are pumped;

In rooms where the release and accumulation of harmful substances is possible, and in outdoor installations in places of their possible release and accumulation;

In rooms where there are no sources of emission, but harmful substances may enter from the outside;

In places where service personnel are permanently located, where there is no need to install stationary gas detectors;

During emergency work in a gas-contaminated area - continuously.

After eliminating the emergency situation, it is necessary to additionally analyze the air in places where harmful substances may accumulate.

4.7. In places of gas leaks and in areas of atmospheric pollution, a sign “Caution! Gas".

Yellow

black color

4.8. Start-up and operation of equipment and installations of gas transportation facilities with a switched off or faulty system for monitoring and signaling the content of flammable gases in the air is not allowed.

4.9. The operation of the automatic alarm system and the automatic activation of emergency ventilation is monitored by operational (duty) personnel when accepting a shift.

Information about the activation of the automatic gas detection system, the failure of sensors and associated measuring channels and automatic alarm channels, and equipment stops carried out by the automatic gas detection system is received by the operational (duty) personnel, who informs the head of the facility (service, section) about this entry in the operational journal.

The operation of automatic gas detection systems in indoor air is tested in accordance with the manufacturers' instructions.

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, the 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. Assessment and control of MCC is important for systems operating under vacuum, where suction of atmospheric air through leaks in process equipment is possible.

With regard to liquid media, temperature limits of flame propagation (FLPP) 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 FLPP.

CPRP is determined by calculation or found experimentally.

It is used to categorize premises and buildings according to explosion and fire hazards, to analyze the risk of an accident and assess possible damage, and to develop measures to prevent fires and explosions in technological equipment.

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See what “NKPR” is in other dictionaries:

NKPR- National Confederation of Industrial Workers trade union association Brazil, organization NKPR lower concentration limit of flame propagation Source: http://www.ecopribor.ru/pechat/signal03b.htm … Dictionary of abbreviations and abbreviations

NKPR- National Confederation of Industrial Workers... Dictionary of Russian abbreviations

LCL (lower concentration limit of flame propagation)- 3.37 NLPR (lower concentration limit of flame propagation): According to GOST 12.1.044. Source …

LKPR lower concentration limit of flame propagation- lower explosive limit, LEL The concentration of flammable gas or vapor in the air, below which an explosive gas atmosphere does not form... Electrical Dictionary

lower concentration limit of flame (ignition) propagation (LCPL)- 3.5 lower concentration limit of flame propagation (ignition): The minimum content of a combustible substance in a homogeneous mixture with an oxidizing medium (LCPR, % vol.), at which it is possible for a flame to spread through the mixture to any... ... Dictionary-reference book of terms of normative and technical documentation

lower concentration limit of flame propagation (ignition) (LCPL)- 2.10.1 lower concentration limit of flame propagation (ignition) (LCPR): The minimum content of flammable gas or vapor in the air at which a flame can spread through the mixture to any distance from the source.

BASIC TERMS AND CONCEPTS.

MPC (maximum permissible concentration) of harmful substances in the air of a working area are concentrations that, during daily work within 8 hours during the entire working time, cannot cause diseases or health conditions in the worker, detected by modern research methods directly in the process of work or more distant dates. 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

Ethyl alcohol - 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 under 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 of process equipment and 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.

The lower (upper) concentration limit of flame propagation is 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 the temperature limits are known

(2.1.4)

Where R Not)- saturated vapor pressure of a substance at a temperature corresponding to

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 the chemical formula of 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