RU2385750C1 - Non-flammable and explosion-proof methane-air mixture - Google Patents

Abstract

FIELD: medicine, life saving equipment. ^ SUBSTANCE: invention relates to fire and explosion protection. A non-flammable and explosion-proof methane-air mixture contains a fire retardant diluted in carbon dioxide and presented by propylene and/or isobutylene in the volume ratio of the fire retardant to carbon dioxide equal to 1 : 4-10, with the following content of said components in the protected capacity, vol %: Propylene and/or isobutylene 1.5 - 4.0; Carbon dioxide 8.0 - 15.0; Methane 4.0 - 13.0; Air up to 100. ^ EFFECT: lower consumption of the retardant. ^ 1 tbl

Description

The invention relates to the field of ensuring fire safety and explosion safety, in particular to gas compositions for preventing ignition and explosion of methane-air mixtures, and can be used in the mining industry, mainly in coal, to prevent catastrophes due to the explosion of methane-air mixture in the worked out space, as well as in areas of methane production and other areas related to either methane production or its use.

Known compositions and methods for volumetric fire extinguishing using gas inert diluents (carbon dioxide and nitrogen), which are effective ways of fire protection of premises by creating an environment that does not support combustion in a protected facility (Handbook "Fire Safety. Explosion Safety". - M. : Chemistry, 1987, p.134-137; RU 2210413 C1, 08.20.2003; RU 2235570 C2, 09/10/2004). However, gas inert diluents at a high flow rate are extremely ineffective in preventing the ignition and explosion of methane-air mixtures, since they do not have inhibitory properties.

A large number of combustion inhibitors of methane-air mixtures based on fluorine, or bromine, or chlorine, or fluorine-bromine, or fluorine-chlorine-containing hydrocarbons are known, which have a sufficiently high inhibitory ability (SU 981338 A, 12/15/1982; SU 1245714 A, 07/23/1986 ; RU 2079318 C1, 05.20.1997; RU 2156630 C1, 09/27/2000; RU 2169597 C1, 06/27/2001; RU 2225734 C2, 3/20/2004; RU 2321437 C1, 04/10/2008; US 4,826,610, 1989; US 5234613, 1993 ; US 5605647, 1997; US 5759430, 1998; US 6849194, February 1, 2005; US 7223351, May 29, 2007). However, the use of these hydrocarbons causes hard-to-solve problems on the part of proponents of environmental protection and safety engineering, which limits their widespread adoption in industry.

A known method of preventing ignition and explosion of combustible mixtures, in particular methane-air mixtures (RU 2187351, A62D 1/08, 08/20/2002), which describes an inhibitory gas composition containing a C ₂ -C ₈ hydrocarbon diluted with an inert gas. The inhibitor ratio is 5-10 vol.%, The inert gas is the rest. Preferably, the inhibitor is a mixture of saturated and unsaturated hydrocarbons propane, butane and propylene (brand name AKAM inhibitor containing in vol.%: 17 propylene, 41 butane and 42 propane). Inert gas: nitrogen, carbon dioxide, argon and mixtures thereof. The prepared composition is introduced into the combustible mixture in an amount of 5-43 vol.% Relative to the mixture. The result of the method is improving the efficiency of preventing ignition and explosion of combustible mixtures.

It was shown that the use of an inhibitor of 6.5 vol.% AKAM and 93.5 vol.% Carbon dioxide with a content of not more than 15 vol.% Allows the upper flammability limit to be reduced to 7.25 vol.% Methane in the methane-air mixture (explosive the limit lies in the range 5.25-14.8% of methane in the air). When the content of the composition is more than 17 vol.% In the methane-air mixture, complete prevention of ignition and explosion of methane-air mixtures of any composition is observed.

The known composition is non-combustible both during storage and when used as intended, effective in the entire range of methane content in methane-air mixtures.

The disadvantage of the described inhibitory gas composition is the significant consumption of the inhibitor (at least 10%).

The technical result of the invention is to reduce the consumption of the inhibitor and increase the inhibitory effect of the composition upon ignition and explosion of methane-air mixtures.

The technical result is achieved in that a non-flammable and non-explosive methane-air mixture comprising a combustion inhibitor diluted with carbon dioxide according to the invention contains propylene and / or isobutylene as a combustion inhibitor with a volume ratio of inhibitor to carbon dioxide of 1: 4-10, with the following content components in the protected volume, in vol.%:

Propylene and / or isobutylene 1.5-4.0 Carbon dioxide 8.0-15.0 Methane 4.0-13.0 Air Up to 100

The invention consists in the following.

The experiments to determine the prevention of ignition and explosion of methane-air mixtures were carried out in a closed cylindrical stainless steel reactor with a diameter of 12.6 cm and a height of 25.2 cm. The working mixtures were made in the reactor by the partial pressures of the components. The tests were also carried out in a large caisson reactor (4 m ³ ) in an explosive chamber. The relative error in the concentrations of CO ₂ and methane did not exceed 1%. The relative error of the concentration of inhibitors was 4%, since their concentration is small. The components were introduced into the evacuated reactor in the following sequence: inhibitor, methane, CO ₂ and then air. The initial pressure and temperature of the mixtures were 1.0 bar and 293K, respectively. The purity of the inhibitor and CO ₂ was 99%. The prepared combustible mixtures were ignited by a spark between electrodes mounted at the lower end of the reactor and powered by a capacitor bank. The energy of the initiating pulse was 3.6 J. Ignition in the caisson was carried out at a power of 3.0 J. Ignition was carried out 15 minutes later (the time required for complete mixing of the components) after the components were introduced into the reactor.

From the initiation of combustion to its completion, pressure and chemiluminescence were simultaneously recorded. Combustion is accompanied by a significant intermediate increase in pressure, which is the result of an increase in the temperature of the gas mixture. The kinetics of the pressure drop is largely determined by the cooling time of the gas after combustion. Inhibitor concentrations did not exceed the lower concentration limits of the flame propagation of their mixtures with air.

The experiments showed that the introduction of inhibitors into any methane-air mixture containing 1.5-4.0 vol.% Propylene (C ₃ H ₆ ) and / or isobutylene (iC ₄ H ₈ ) diluted 8-15 vol. % carbon dioxide (the volume ratio of inhibitor to carbon dioxide is 1: 4-10) prevents ignition and burning when trying to initiate them. After spark triggering, neither pressure changes nor chemiluminescence are recorded in such mixtures. There is also no change in pressure of the mixture after the experiment.

In the presence of, for example, 3 vol.% Propylene without carbon dioxide CO _2, combustion of mixtures containing less than 9% methane is more intense than without propylene. The introduction of 1% propylene and 10% CO ₂ into a mixture of 9% CH ₄ with air reduces the intensity of combustion, but does not prevent ignition.

The detected suppression of methane combustion by the proposed inhibitors is an indicator of the branched chain nature of methane combustion and is caused by the termination of reaction chains in the reactions of active intermediate particles with the inhibitor.

Indeed, given the experimental data on the measurement of the concentration of atomic hydrogen in a methane flame, which reaches 0.09% of the total mixture, the reaction rate constants

и радикалов

несравненно больше, чем в молекулярной реакции с метаном. Реакция (I), приводящая к размножению свободных атомов и радикалов, является начальным актом разветвления цепей. Действительно, за реакцией (I) следуют быстрые реакции образующихся атомов

и радикалов

с метаном:and intermolecular reaction of O ₂ with CH _4, equal respectively to 1.9 10 ¹⁴ exp (-8350K / T) and 2 × 10 ^{5 T 2,745 exp (-26040 K / T} ) cm ³ mol ^-1 c ^1, and the temperature in the combustion zone not exceeding 1800K, it is easy to verify that the reaction rate (I) in the methane flame is more than 200 times higher than the molecular reaction rate of O ₂ directly with CH ₄ . Thus, O ₂ is consumed in reaction (I), i.e. along the path of atom formation

and radicals

incomparably more than in a molecular reaction with methane. Reaction (I), leading to the multiplication of free atoms and radicals, is the initial act of chain branching. Indeed, reaction (I) is followed by fast reactions of the resulting atoms

and radicals

with methane:

при обычных температурах горения метана (выше 1500К) в значительной мере вступают в реакцииRadicals

at ordinary combustion temperatures of methane (above 1500K), they significantly react

These reactions are followed by the formation of CO and the regeneration of atoms.

The combination of these repeatedly repeated reactions forms a branched reaction chain. In a flame, reaction is also important.

и

а также продуктов их реакций в процессахWithout considering other reactions in the methane combustion mechanism, we note that in the absence of an inhibitor, chain termination occurs with the partial participation of radicals

and

as well as products of their reactions in the processes

recombination. Atomic hydrogen, on the other hand, carries out chain branching according to reaction (I).

In the reaction

atomic hydrogen is replaced by a significantly less active chain carrier. Therefore, to the extent that methyl radicals lead to chain termination, the reaction acts as chain termination and is a stage of self-inhibition of methane combustion. This is evidenced by the fact that small methane impurities inhibit the ignition of combustible mixtures.

к молекуле ингибитора (RH):In the presence of an inhibitor, an additional effective chain termination proceeds. This is primarily the reaction of attachment of atoms

to an inhibitor molecule (RH):

where R ₁ is an alkyl radical, which mainly leads to chain termination.

The activation energy of the reaction (XI) does not exceed 6.5 kJ / mol. Therefore, this reaction effectively competes with the reaction of the propagation of free valencies (I).

Since the rate of chain process is exponentially dependent on the reactant concentrations, the addition of CO _2, diluting the mixture to a large extent reduce the reaction rate and the self-heating, these contributing overspeed chain termination rate over the junction. This leads to the observed inhibition of ignition and combustion.

It is known that the most explosive range of methane content in the air, at which ignition occurs, and then an explosion, is from 4.0 vol.% To 13.0 vol.%, Therefore, the examples in the tables are presented specifically for this range.

The inhibiting data of the proposed gas composition with an optimal ratio of C ₃ H ₆ and / or iC ₄ H ₈ 1.5-4 vol.% And carbon dioxide not more than 15 vol.% In the protected volume are presented in the table.

The data in the table indicate that the proposed inhibitors with a content of not more than 4% of the volume of the gas mixture in the protected volume effectively prevent ignition and explosion in the entire dangerous range of methane in the air, which confirms the technical result.

The claimed technical solution can be used in mining operations, in methane leaks at pumping stations, in the technological process of its production, during storage and transportation.

Table The content of the components in the protected volume, vol.% C ₃ H ₆ , i-C ₄ H ₈ + CO ₂ Methane-air mixture Ignition Shock wave explosion C ₃ H ₆ iC ₄ H ₈ , CO ₂ Methane Air 3 - fifteen four 78 - - 2 - 8 6 84 - - 1,5 - 9.5 8 81 - - - 1,5 fifteen 8.5 75 - - one one 10 13 75 - - 2 2 13 9 74 - - - 1.8 10 12 76,2 - - - - 10 8 82 + + - - 10 10 80 + + - - - 10 90 + +

Claims (1)

Non-flammable and non-explosive methane-air mixture, including a combustion inhibitor diluted with carbon dioxide, characterized in that it contains propylene and / or isobutylene as a combustion inhibitor at a volume ratio of combustion inhibitor to carbon dioxide of 1: 4-10, with the following content of components in protected volume, vol.%:
Propylene and / or isobutylene 1.5-4.0 Carbon dioxide 8.0-15.0 Methane 4.0-13.0 Air up to 100