RU2776188C1 - Method for reducing the fire hazard of emergency spills of hydrocarbon liquids - Google Patents

Abstract

FIELD: fire protection.

SUBSTANCE: invention relates to methods for extinguishing a fire by isolating the surface of an emergency spill of hydrocarbon liquids. In the method for reducing the fire hazard of emergency spills of hydrocarbon liquids, based on the isolation of the surface of the spill with a layer of granular shielding material in a tank for collecting the spill and limiting the spread of hydrocarbon liquids equipped with a drain pipe, foam glass with spherical granules of 4-7 mm in size with a bulk density of 150-200 kg/m³ and a layer height, which is determined from conditions for the formation of a “dry” layer of critical thickness by the shielding material, at which the flame is extinguished.

EFFECT: increasing the efficiency of extinguishing the flame without the use of additional extinguishing agents, reducing the volume of granular material, reducing the specific mass rate of combustion of hydrocarbon liquids.

1 cl, 1 dwg, 1 tbl

Description

The invention relates to methods for extinguishing a fire by isolating the surface of an emergency spill of hydrocarbon liquids and can be used to limit the spread of fire in places where local leakage of hydrocarbon liquids is possible, for example, under the drain pipes of process equipment (tanks), sampling sites, under manifolds, in places of detachable connections of technological pipelines, etc.

A method is known that is carried out by a device for extinguishing a progressive fire by phlegmatization and localization (Description of the author's certificate SU971358 "Device for protecting equipment from a progressive fire", IPC A62C 3/12, 1982), which consists in using a device to protect equipment from a progressive fire , containing a container with a filler placed in it in the form of a granular non-combustible material with a granule size of 15-35 mm, and the height of the filler exceeds the level of the spilled combustible liquid by at least 30 mm, and the height of the container is equal to the level of the filler.

The disadvantages of this method are a significant decrease in the insulating effect with an increase in the level of flammable liquid in the tray due to the high bulk density of granular materials and their negative buoyancy (except for expanded clay), as well as the difficult transportability of the tray due to the severity of the filler.

A known method of extinguishing polar flammable liquids (Author's certificate SU1498507, IPC A62S 3/12, 1989), which consists in the fact that a shielding material is applied to the surface of the liquid and a sprayed foam solution is supplied to the shielded surface, granular material with with a density of granules of 0.25-0.60 t/m and a layer height of 0.05-0.12 m, expanded clay, gravel or expanded vermiculite is used as a screening granular material.

The disadvantage of this method is the need to use a fire extinguishing agent in the form of a foaming agent solution, as well as low efficiency and increased extinguishing time due to the fact that the liquid spill surface remains open until the granular material is supplied.

A known method of extinguishing polar liquids (Author's certificate SU1729521, IPC A62C 3/06, 1989), taken as a prototype, including the supply of a foaming agent solution to the surface of a liquid in a container equipped with a shielding material, gravel or crushed stone with the size of the granules is 5-40 mm in a volume equal to the volume of the container.

The disadvantages of this method are: the absence of the effect of extinguishing the flame without the additional use of a fire extinguishing agent in the form of medium expansion foam, a large consumption of granular material, as well as the threat of overflow and spreading of flammable liquid when spilling a volume of liquid exceeding the free volume of the container (tray).

The technical result consists in increasing the efficiency of extinguishing the flame without the use of additional fire extinguishing agents, in reducing the volume of granular material due to the use of granules of low bulk density that can be held on the surface of the liquid, forming a "dry" layer, and also in reducing the specific mass burnout rate of hydrocarbon liquids.

1. The technical result is achieved by the fact that in a method for reducing the fire hazard of emergency spills of hydrocarbon liquids, based on isolating the surface of the spill with a layer of granular screening material in a container for collecting spills and limiting the spread of hydrocarbon liquids equipped with a drain pipe, foam glass with spherical granules is used as a screening material. forms with a size of 4-7 mm with a bulk density of 150-200 kg / m ³ and a layer height H, which is determined from the condition for the formation of a “dry” layer of critical thickness H _cr by the shielding material, at which the flame is extinguished, by the expression:

,

,

where ρ _w is the density of the hydrocarbon liquid, kg / m ³ ,

ρ _g - bulk density of granules, kg / m ³ ,

N _cr - critical thickness of the "dry" layer of foam glass granules, m,

m - medium porosity,

h _to - the height of the capillary rise of the hydrocarbon liquid, m, for which H _kr is preliminarily calculated by the expression

,

,

where F is the area of the container for collecting the spill and limiting the spread of hydrocarbon liquids, m ² ,

k - medium permeability, 1.5⋅10 ^-12 m ² ,

P _n - saturated vapor pressure of the hydrocarbon liquid, Pa,

μ - dynamic viscosity of hydrocarbon liquid vapors, Pa⋅s.

The essence of the invention is illustrated by drawings.

In FIG. 1 shows an image of a container with a layer of foam glass granules (1.a - when ignited, 1.b - when the flame decreases, 1.c - when the flame is extinguished).

The way to reduce the fire hazard of emergency spills of hydrocarbon liquids is implemented as follows.

At the site where there are constant leaks of hydrocarbon liquids from technological apparatuses and pipelines, containers are installed to collect the spill and limit the spread of hydrocarbon liquids, for example, in the form of a metal pallet or a concreted area with sides. To prevent the overflow of hydrocarbon liquids during prolonged or intensive leaks, the indicated container 1 is equipped with a drain pipe 2 with a pipeline for draining the spilled liquid into an emergency container (reservoir) 3. Spherical foam glass granules of size 4-7 are placed in the container to collect the spill and limit the spread of hydrocarbon liquids. mm with a bulk density of 150-200 kg / m ³ and evenly distributed inside with a layer of thickness H. Due to the low bulk density of foam glass, with an increase in the level of hydrocarbon liquid in the tank, the granules float and stay afloat in an equilibrium state with the formation of a “dry” layer of foam glass granules ( SGP) above the surface of a liquid with a thickness of H _with and "wetted" SGP, located in a liquid with a thickness of H _cm (Fig. 1.a.). The presence of a "dry" layer of foam glass granules helps to reduce the specific mass rate of burnout of the hydrocarbon liquid by reducing the free surface of evaporation and increasing the resistance to the movement of vapor molecules when passing through the "dry" layer of granules. With an increase in the thickness of the “dry” layer of foam glass granules, the mass-specific burnout rate of the liquid decreases, when the thickness of the “dry” layer of foam glass granules reaches a critical value Hcr, the effect of extinguishing the flame is achieved (Fig. _1.c ). The use of spherical foam glass granules 4-7 mm in size ensures uniform flame extinguishing on the entire surface of the shielding material in the container to collect the spill and limit the spread of hydrocarbon liquids.

In case of leakage from technological apparatuses, the hydrocarbon liquid enters the container, it freely passes into the gaps between the foam glass granules to the bottom of the container. With an increase in the amount of hydrocarbon liquid in the container, the layer of foam glass granules will rise under the action of the Archimedean force. When the surface of the layer of foam glass granules reaches the upper level of the sides of the tank, the overflow of the hydrocarbon liquid is prevented by removing it through the drain pipe 2 into the emergency tank (reservoir) 3. When the hydrocarbon liquid ignites in the tank, its level decreases, the thickness of the "dry" SGP increases, and the height of the flame and the burning area decrease (Fig. 1.b), and when the critical thickness of the "dry" SGP (N _cr ) is reached, combustion stops (Fig. 1.c).

The thickness of the "dry" layer of foam glass granules in an equilibrium state on the surface of a hydrocarbon liquid is determined by the formula

where ρ _W is the density of the liquid, kg/m ³ ;

ρ _g - bulk density of granules, kg / m ³ ,

H is the total thickness of the layer of foam glass granules m;

m is the porosity of the medium (for a fraction of 4-7 mm equal to 0.385);

h _to - the height of the capillary rise, m.

The total height of the layer of granulated foam glass H placed in the container can be expressed from the formula (1)

The critical thickness of the "dry" layer of foam glass granules N _cr at which the flame is extinguished can be determined by the formula

where τ _Δp is the time of wave movement through the SGP layer to the liquid surface and back (pressure drop time), s;

k - medium permeability, 1.5⋅10 ^-2 m ² ;

P _n - saturated vapor pressure of the hydrocarbon liquid, Pa;

m is the porosity of the medium (for a fraction of 4-7 mm equal to 0.385);

μ - dynamic viscosity of hydrocarbon liquid vapor, Pa⋅s.

The pressure drop time τ _Δp is calculated by the formula

where F is the area of the container (tray) for collecting and limiting the spread of the spill of hydrocarbon liquids (m ² ).

Thus, the critical thickness of the "dry" layer of foam glass granules H _cr at which the flame is extinguished is preliminarily determined by the formula

Expression (4) for calculating the critical thickness of the "dry" layer of granulated foam glass with 4-7 mm granules was obtained using experimental data for various types of hydrocarbon liquids: acetone, n-hexane, AI-92 gasoline, ethyl alcohol, aviation kerosene, diesel fuel . The physicochemical properties of the studied liquids and the results of the experiments are summarized in Table 1.

The efficiency and effectiveness of the proposed method has been experimentally confirmed. The experiment was carried out in laboratory conditions in containers with a circular cross-section with a diameter of 0.150 mm and a rectangular cross-section of 0.112 x 0.157 m and a height of 0.020 m, as well as on a polygon in a pallet with dimensions a × b × h: 0.70 × 0.50 × 0.25 m , control tests on the efficiency of extinguishing the flame were carried out on pallets with dimensions of 1.19 × 0.85 × 0.27 m and 1.45 × 1.036 × 0.27 m.

The air temperature was +20°С (±1°С), the air velocity was 0.0-0.5 m/s, and the relative air humidity was 40-60%.

Thus, the use of the proposed method provides effective flame extinguishing without the use of additional fire extinguishing agents, as well as reducing the specific mass burnout rate of hydrocarbon liquids to critical values at which combustion becomes impossible.

Claims (13)

A method for reducing the fire hazard of accidental spills of hydrocarbon liquids based on isolating the surface of the spill with a layer of granular screening material in a container for collecting spills and limiting the spread of hydrocarbon liquids, characterized in that a container for collecting spills and limiting the spread of hydrocarbon liquids equipped with a drain pipe is used as The shielding material uses foam glass with spherical granules 4-7 mm in size with a bulk density of 150-200 kg/m ³ and a layer height H, which is determined from the condition of the shielding material forming a “dry” layer of critical thickness _Hcr , at which the flame is extinguished, according to expression:

, where ρ _w is the density of the hydrocarbon liquid, kg / m ³ , ρ _g - bulk density of granules, kg / m ³ , N _cr - critical thickness of the "dry" layer of foam glass granules, m, m - medium porosity, h _to - the height of the capillary rise of the hydrocarbon liquid, m, why pre-calculate H _kr by the expression

, where F is the area of the container for collecting the spill and limiting the spread of hydrocarbon liquids, m ² , k - medium permeability, 1.5⋅10 ^-12 m ² , P _n - saturated vapor pressure of the hydrocarbon liquid, Pa, μ - dynamic viscosity of hydrocarbon liquid vapors, Pa⋅s.

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