RU1806793C - Method for generation of foam for fire fighting - Google Patents

Abstract

Usage: in the field of firefighting. And labor protection, as well as in protecting the environment. SUMMARY OF THE INVENTION: the foaming solution is saturated with an absorbable gas under pressure, determined from the proposed relationship between the foam ratio, the Langmuir sorption constants and the required gas pressure with which the foam solution is saturated. 4 ill.

Description

FIELD OF THE INVENTION The invention relates to fire fighting equipment and can be used both for extinguishing flammable liquids and for extinguishing other materials.

Various fire fighting methods are known: water, powder, inhibitors, inert gases, foam.

Each of the listed methods of stewing has its own advantages and disadvantages. Thus, the use of inhibitors, powders and inert gases is effective in extinguishing a flame (a homogeneous combustion reaction), especially in closed or, especially, sealed volumes. But these methods are not very effective when it is necessary to cool walls and structures.

To extinguish solid fuels, water and foam are most effective, which not only reduce the temperature in the fire volume, but intensively cool the fuel, stopping heterogeneous combustion or evaporation (sublimation) of combustible substances.

The combination of the positive properties of the inert gases with the foam gives an inert-mechanical foam, obtained by filling foam bubbles with inert gases (e.g. carbon dioxide).

A known method of foaming to extinguish a fire, comprising mixing water, a foaming agent and saturating the resulting solution with gas under pressure in an airtight container, followed by transporting this solution through a pipeline to a fire source under pressure, where foam forms when leaving the pipeline.

The disadvantage of this method of foam formation, even for the prototype, is the impossibility of obtaining the necessary foam multiplicity at elevated water temperatures (more than 10-15 ° C) even at the maximum operating pressure of fire piping (1-2 MPa).

As is known, with the increase in the foam ratio up to K 100-200, the efficiency of foam fire extinguishing increases. So, the increase in the multiplicity of the foam with K 5, which corresponds to a water temperature of t 40 ° C at a pressure of a saturating foaming solution of carbon dioxide for P 1 MPa, to K 15, which corresponds to the temperature:

ate with

00

about about VI yu

water temperature t 3 ° C at the same pressure, increases the efficiency of fire extinguishing (reduces the duration of fire extinguishing or the consumption of foam) by almost 30%, respectively, with a decrease in water temperature at a constant pressure of saturation of the foaming solution with carbon dioxide (Fig. 1, where VB - weight solubility of CO2 in water; V-volume solubility of CO2 in water) the multiplicity of the resulting foam increases.

The proposed method of foaming to extinguish a fire involves mixing water, a foaming agent and saturating the solution with gas under pressure, and characterized in that in order to increase the extinguishing efficiency, the temperature of the foaming agent is lowered depending on the necessary multiplicity of the foam and the technical cooling capabilities of the foaming agent.

As can be seen from FIG. 1, which shows the dependence of the solubility of COa in water on its temperature, both weight solubility (curve 2 and 3 at P 0.68 MPa and P 0.102 MPa in weight% of water, respectively) and volumetric solubility (curve 1 at P 0.102 MPa in m3 of CO2 per m of H-gO) greatly increase with decreasing water temperature, which makes up about 95-98% of the composition of the foaming solution.

As is known, the isotherm of sorption (solubility) of carbon dioxide water can be described (approximated) by the Langmuir equation of the type

V- abpm - 1 + bP W

where V is the volume of gas dissolved in 1 volume of water, m3 CO2 / m3H20;

a and b are the sorption constant, respectively, m3C02 / m3N20 and

P is the pressure of the saturating (soluble) gas, MPa.

However, the Langmuir equation does not take into account the influence of water temperature, since it describes the sorption isotherm, i.e. gas dissolution at constant temperature as a function of pressure. To take into account the effect of temperature on gas solubility, this equation can be represented as abP -ct

1

V

(2)

° C.

1 + bp

where c is the coefficient of the exponent, deg-1;

t is the water temperature,

As shown by elementary calculations, the values of the constants a and b at a temperature of 0 ° С, taken as the base temperature due to the possibility of a phase transition (freezing) of water, in accordance with

the numerous data cited in the Solubility Handbook are accurate to 5% a 83.3 m3CO2 / m3H20 and b, 0.232.

Data were used to determine the numerical value of coefficient c, some of which are graphically shown in FIG. 1 and 2, which shows the solubility of CO2 in water at t 0 ° C (curve 1) nt 15 ° C (curve

2).

In accordance with these calculations, with 0.034 1 / deg C with an accuracy of about 7%.

The multiplicity of the foam for small values, when the volume of the foaming solution plays a significant role, is determined by the formula

K-t + v.-1 +.-A

R)

From this formula, using simple transformations, we can obtain the dependence

abP, -ct

ln (K-1) ln

1 + bp

(4)

Where from

5

t 1, „-abP

1 s 1P (K-1) (1 4-bp)

(5)

For water and carbon dioxide, this formula has a more specific form

t 1 Q4 in .... ,. . a (K-1) (1 + 0.232P)

0 calculations by which are graphically presented in FIG. 3.

As can be seen from these calculations, the possible multiplicity of the resulting foam strongly depends on the temperature of the foaming solution. So, in the case of obtaining foam on ships located in the temperate latitudes of the northern hemisphere, where in July the temperature of the deck and the upper part of the ship's hull reaches 25-30 ° C,

0, the maximum multiplicity of the resulting foam at a pressure of CO2 of 2.0 MPa is about K 10.

However, the temperature of the upper water layer in the ocean at this time is about

5 10 ° C, which allows, at the same gas pressure P 2.0 MPa, to obtain a foam with a multiplicity of about K 20, i.e. 2 times more. Therefore, in ships, in the case of obtaining foam by saturating the foaming solution with carbon dioxide, the tanks with the foaming solution must be cooled with sea water.

In the southern regions of our country, where in summertime the water temperature in open

In 5 fire water bodies it reaches 3 ° C, it is necessary to immerse water tanks in the soil to a depth of 5-6 m and are insulated from the earth's surface and to a depth of 2-3 m. Then the water temperature will be about 15 ° C, which at P 1 MPa can provide

the multiplicity of the foam is about K 12, while the use of water from open reservoirs provides a multiplicity of K 6-7.

 The implementation of the proposed method can be implemented according to the scheme shown in FIG. 4.

The circuit includes a pressurized container 1, into which pipelines 2-4 are introduced for supplying respectively water, a foaming agent and compressed gas, as well as a pipe 5 for transporting the carbonated solution to the place of use. Pipelines 2-4 are equipped with shut-off valves 6-8, and a remote-controlled valve 9 is provided at the outlet of pipe 5. At the end of pipe 5, a nozzle 10 is mounted to create a pressure drop and to better disperse the foaming solution. Pipelines 2 and 3 for supplying water and a foaming agent pass through a heat exchanger 12, in which they are cooled to the required temperature. Cold water or other coolant is supplied to the heat exchanger 12 via line 13 and discharged through line 14.

The method is carried out as follows.

The container 1 through pipelines 2 and 3, passing through the heat exchanger 12, is filled in certain proportions with chilled water and a foaming agent. Then, with closed valves 8 and 7, as well as valve 9, gas is supplied under pressure 4 to the container 1 through line 4, which dissolves in the liquid filling the container 1. When valve 9 is opened, the carbonated aqueous solution of the foaming agent is dispersed into the channels of the nozzle 10 and sprayed outward .. In this case, the pressure in the dispersed stream drops sharply, as a result of which the dissolved gas is rapidly released from the liquid, and the presence of a foaming agent in it contributes to the formation of foam, which is supplied to the fire 11.

With a relatively short pipeline length of 5 (200 m), even without thermal insulation on its surface, an increase in the temperature of the transported foaming solution saturated with gas is a fraction of a degree and does not significantly affect the process. At

long pipelines passing in areas of elevated temperatures, there may be a need for a small insulating layer on their surface. Compared with the prototype, a heat exchanger (refrigerator) 12 is added to the scheme of the method implementation, which allows to lower the temperature of the water. Thus, the essence of the proposed method for the formation of foam consists in changing the temperature of the foaming solution, as a result of which the foam is obtained with the necessary multiplicity in accordance with expression (5), which is a significant difference between prototype, wherein the temperature of foaming solution generally not referred to.

Using the proposed method allows to increase the efficiency of fire extinguishing by 20-30%, which can significantly reduce the amount of material

fire damage.

Claims (1)

SUMMARY OF THE INVENTION A method of forming a foam to extinguish a fire, comprising mixing water, a blowing agent and treating the resulting solution with gas, characterized in that, in order to increase the extinguishing efficiency, the water is pre-cooled to. temperature determined from expression 1, aP g with n (K-1) (1 + LB) where a and b are the Langmuir sorption constants, respectively m3C02 / m3H20 and c is a coefficient showing the intensity of the influence of temperature on the sorption capacity of water, 1 / MPa; P is the gas pressure, MPa; K is the multiplicity of the foam. 0. iO 20 3D 40 50 + ° b f 42 s, 4 C & t, f W -r 1. it, if r o o e r r, rf, r, Fie. 2 it P, KPO / Yfl- go%