RU2229908C1 - Method of creating gas-air screen to protect population against poisonous or intoxicating substances - Google Patents

Abstract

FIELD: collective security. SUBSTANCE: active collective protection of respiratory organs of people against poisonous or intoxicating substances is proposed in the form of gas-air screen, which is created by forming near-earth flat freely convective turbulent upward-directed gas-air current by way of heating near-earth layer of the air by a linear heat source located on the land surface against approaching poisonous air current. EFFECT: increased protection efficiency. 2 dwg

Description

The invention relates to active collective protection of respiratory organs from toxic or poisonous substances.

In the event of an accident at chemical plants using potent or toxic substances, or accidents during their transportation to the environment, a significant amount of such substances is poured or released. The resulting cloud of vapors spreads in the atmosphere over long distances, creating an infection zone with a concentration of toxic substances in the surface layer of the atmosphere, which is dangerous for people. A similar situation can occur during accidents at the facilities of storage or destruction of chemical poisonous substances.

There is a method of active collective protection of the population from toxic or poisonous substances, which consists in reducing the concentration of toxic or poisonous substances in the surface layer of the atmosphere in the residential zone to values that are not life-threatening to people by dispersing toxic or poisonous substances in the atmosphere using a protective surface flat directional vertically upwards of the air-gas jet curtain, located between the source of infection with toxic or poisonous substances and the residential area and having the shape in plan ugi with the center of the arc at the source of infection [1]. Due to the viscous friction forces, the protective gas-air curtain causes the surface part of the cloud of poisonous or poisonous substances moving downwind from the source of infection to rise to a height equal to the height of the curtain. Higher parts of the cloud rise to even greater heights. After the cloud rises, the curtain does not fall to the surface of the soil, but disperses in the atmosphere. At the same time, the concentration of toxic or poisonous substances in the surface layer along the cloud path is much lower than without raising it with a gas-air curtain.

The disadvantage of this method is the lack of installations for the formation of a protective air curtain of the required length and height.

The closest in technical essence and the achieved result to this invention is a method of forming a gas air curtain by forming a flat surface upward gas jet using a device containing a blower machine and a ground-based air outlet box connected to it with an air outlet slit nozzle located in the upper part with a confuser inlet section [2]. An air blower pumps atmospheric air into an air distribution box connected to it. Injection air when flowing out through an upwardly discharging slit-shaped nozzle forms a protective gas-air curtain.

The disadvantage of this method is the low efficiency of the curtain due to the limited range of operational characteristics of the installation, which does not allow you to create a gas curtain of the required length and height.

Typical example 2 considered in [1] provides for the formation in the air stream with a speed of V = 3 m / s of a transverse plane jet vertical air-blown protective air curtain with a height of H = 50 m and a length of L = 100 m. Available experimental data on the height of a plane air-gas lift the jets in the blowing air stream [3] show that for the formation of such a protective curtain it is necessary to blow air vertically upwards, for example, at a speed of W = 15 m / s through a surface slot with a length of L = 100 m and a width of = H · V / 6 W = 50 · 3/6 · 15 = 1.67 m. For the formation of one per linear meter l = 1 m of such a gas curtain, it is necessary to provide a volumetric air flow rate G ₁ = l · in · W = 1 · 1.67 · 15 = 25 m ³ / s (90,000 m ³ / h). In this case, the cross-sectional area F _{1 of the} air distribution duct in its initial part should be two times larger than the cross-sectional area of the air-outlet gap, i.e. F ₁ = 2 · l · in = 2 · 1 · 1.67 = 3.34 m ² . To form a protective curtain of the same height Н = 50 m, but with a length l = 10 m, the installation should provide 10 times greater operational characteristics, respectively: air volumetric flow rate G ₁₀ = 250 m ³ / s (900,000 m ³ / h) with a transverse area section of the initial part of the air distribution duct F ₁₀ = 3 · 3.4 m ² . Under these conditions, the dimensions of the installation - the cross-sectional area of the initial part of the square air duct is 33.4 m ² with the side of the square 5.78 m. Such operational characteristics of the installation (air blower performance and dimensions) are on the verge of practically feasible. A further increase in the length of the protective curtain requires a proportional increase in these characteristics, which is beyond the scope of modern capabilities.

The invention is aimed at increasing the efficiency of the air curtain to protect the population from toxic or poisonous substances by providing the necessary length and height.

This is achieved by the fact that the air curtain is formed by the method of forming a surface flat free convection turbulent upward air jet by heating the surface air layer with a linear heat source placed across the soil surface transversely containing toxic or poisonous substances from the incoming air flow.

The invention is illustrated in the drawing, where figure 1 shows a vertical cross section of a surface flat free convective gas-air jet in a stationary atmosphere (without wind), figure 2 is a vertical cross section of the same jet in the presence of wind with a speed V.

The positions in the drawing indicate: a linear source of heat - 1; axis of the jet - 2; streamlines (trajectories) of air particles - 3; jet boundaries - 4; vertical velocity profile in the stream - 5; temperature profile in the jet - 6.

In the absence of wind, air heated near a linear surface heat source 1, under the action of the lifting force of Archimedes, rises up, forming a vertical stream of heated gases. Turbulent viscous interaction with the surrounding atmospheric air ensures the gradual involvement of cold air into the stream, its expansion and decrease in temperature as the stream rises [4]. A feature of a free-convection jet of any shape is the constant flow of enthalpy through any of its cross sections equal to the amount of heat released from the surface heat source. A feature of a flat stream of atmospheric air under normal conditions above a linear heat source is the constancy of the vertical air velocity in the center of the stream U _m as it rises, which is maximum in the stream, does not change in height and is proportional to the linear heat density Q _{l of} heat in the heat source ( Q _l - the amount of heat released per unit time by a unit length of a linear source, W / m) to the extent of one third: U _m = 0.84 Q $\genfrac{}{}{0ex}{}{\text{1/3}}{\text{l}}$ . In this ratio, U _m is expressed in m / s, Q _l - in kW / m. It follows that the greater the heat release intensity Q _l in the heating source, the more intense the free convective jet is formed above it. In this case, the momentum flux at the beginning (bottom) of the jet is zero, but then, as it rises, it continuously increases due to the action of the lifting force on the heated air.

линейной плотности тепловыделения в приземном источнике теплотыWhen a wind occurs at a speed V in the direction across the free convective plane jet, it deflects it from the vertical. With increasing wind speed, the inclination of the axis of the jet increases, but remains the same in height, that is, the axis of the jet tilts, but remains straight. This happens until at a fixed linear density of heat release Q _l in the surface source the wind speed does not exceed a certain value at which the free-convection jet is destroyed. In this case, the heated air inside the jet is mixed with the oncoming air stream, the temperature of the mixed stream is leveled and the entire homogeneous stream formed moves mainly in the horizontal direction. The cause of the susceptibility of a free-convection jet to destruction by the transverse flow (in contrast to the jets injected into the transverse flow) is the absence of an initial momentum flow in the free-convection jet, as a result of which this jet has a weak dynamic counteraction to the transverse air flow in its initial section. The performed studies allowed us to establish the following relationship between the wind speed V and the corresponding critical value

linear heat density in a surface heat source

- в МВт/м.Here V is expressed in m / s,

- in MW / m.

); свободноконвективная струя разрушается и защитная завеса не формируется над линейным источником теплоты, если его мощность меньше критической (то есть если

).In the presence of a transverse air flow with a velocity V, a free-convective curtain forming above a linear heat source is stable if the heat density in the source is more than critical (i.e.

); a free-convection jet is destroyed and a protective curtain is not formed above a linear heat source if its power is less than critical (that is, if

)

Example 1. The air flow at a speed of V = 2 m / s carries toxic substances from the source of infection. To protect people in a village located in the direction downwind from the source of infection, between the source of infection and the village across the wind, a mobile active collective protection system for the population from toxic substances was quickly deployed by the method of forming an air curtain, which consists in the formation of a surface flat air-jet directed upwards by heating the surface layer of air with a linear source of heat placed on the surface of the soil. The linear source of heat is burning liquid fuel, poured into a horizontal tray with a length of L = 100 m. It is necessary to determine the fuel consumption that needs to be fed into the tray to replenish the burned so that the protective curtain is stable and fulfills its purpose. Kerosene is used as fuel, the lower heat of combustion of which is h = 43 MJ / kg.

=7,1 V³=7,12³=56,8 МВт/м. Количество теплоты, выделяющейся при горении керосина во всем лотке длиной L=100 м, должно быть Q>Q*=

L=56,8·100=5680 МВт (здесь Q* - критическая величина теплоты, выделившейся при горении керосина во всем лотке длиной L: Q*-

L, МВт). Массовый расход керосина для восполнения сгоревшего топлива должен быть больше минимальной величины М>М*=Q*/h-5680/43=132 кг/с (здесь М - критический (минимальный) массовый расход керосина, сгорающего во всем лотке длиной L: М*=Q*/h, кг/с). Если в лоток будет подаваться керосин с меньшим расходом, то сгорать он будет, но свободноконвективная струя над горящим керосином будет разрушаться поперечным потоком воздуха со скоростью V=2 м/с, и защитная завеса не сформируется.A free-convective gas-air jet formed as a result of burning kerosene from a free surface in a tray located across the air stream at a speed of V = 2 m / s will be stable if the linear heat density Q _l during combustion of kerosene in a section of the tray 1 m long exceeds a critical value

= 7.1 V ³ = 7.12 ³ = 56.8 MW / m. The amount of heat released during the burning of kerosene in the entire tray with a length of L = 100 m should be Q> Q * =

L = 56.8 · 100 = 5680 MW (here Q * is the critical value of the heat released during the combustion of kerosene in the entire tray of length L: Q * -

L, MW). The mass consumption of kerosene to make up for the burnt fuel should be greater than the minimum value M> M * = Q * / h-5680/43 = 132 kg / s (here M is the critical (minimum) mass consumption of kerosene burning in the entire tray of length L: M * = Q * / h, kg / s). If kerosene with a lower flow rate is fed into the tray, it will burn, but the free-convection jet above the burning kerosene will be destroyed by the transverse air flow at a speed of V = 2 m / s, and a protective curtain will not be formed.

газа, имеющего низшую теплоту сгорания h=36 МДж/м, нужно подавать в трубопровод на каждый его погонный метр при различных скоростях ветра V для того, чтобы газовоздушная завеса не разрушалась ветром. Используя соотношение (1), рассчитаем искомую величину

=

/h=7,1V³/36=0,197V³. Здесь

выражено в м³/с, V - в м/с. Из полученного соотношения следует, например, что при скорости ветра V=2 м/с на каждый погонный метр трубопровода должно подаваться не менее чем

=0,197·2³=0,197·8=1,58 м³/с природного газа.Example 2. Not far from the chemical weapons destruction facility in the direction of the nearest settlement, a stationary system of active protection of the population from toxic substances was mounted by the method of forming a gas-air curtain, which consists in the formation of a surface flat air-jet directed upwards by heating the surface layer of air with a linear heat source placed on the soil surface . A linear heat source is a pipeline located above the soil surface with longitudinal slots in its upper part. In the event of an accident at the facility, natural gas enters this pipeline and is ignited at the outlet to the atmosphere. When natural gas is burned in atmospheric air above the pipeline, a flat free convective gas-air curtain is formed. It is required to determine what is the minimum consumption

gas having a lower calorific value h = 36 MJ / m must be fed into the pipeline for each meter per meter at different wind speeds V so that the air curtain is not destroyed by the wind. Using relation (1), we calculate the desired value

=

/ h = 7,1V ^3/36 = 0,197V ^3. Here

expressed in m ³ / s, V - in m / s. From the obtained ratio it follows, for example, that at a wind speed of V = 2 m / s, at least one meter of pipeline should be supplied

= 0.197 · 2 ³ = 0.197 · 8 = 1.58 m ³ / s of natural gas.

In addition to the fact that a free-convection protective curtain raises a cloud of toxic or poisonous substances to a great height and scatters these substances in the atmosphere, there is an additional effect of their destruction. The free-convection plane jet is entirely formed from the air leaking from both sides, which is heated from a linear heat source, and part of the stream in the center of the stream is heated to a sufficiently high temperature. The air that gets into this jet and is heated in it from the windward side of it contains toxic or poisonous substances, which will also heat up in the stream and collapse upon heating, forming less toxic compounds.

Sources of information

1. RF patent No. 2179046, A 62 B 29/00, BI No. 4, 2002.

2. Elterman V.M. Air curtains. -M .: Engineering. -1966.-S.83-90.

3. Girshovich T.A. Turbulent jets in the cross flow. -M.: Engineering, 1993, p. 11.

4. Martynenko OG, Korovkin VN, Sokovishin Yu.A. Theory of floating jets and traces. -Minsk: Science and technology, 1991. -P.376-381.

Claims (1)

A method of forming a gas-air curtain to protect the population from toxic or poisonous substances, which consists in the formation of a surface flat free convective upward-directed gas-air jet by heating the surface layer of air with a linear heat source placed on the soil surface transversely containing the toxic or poisonous substances of the incoming air flow.

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