RU2210413C1 - Method of prevention of ignition and explosion of fire hazardous medium and device for method embodiment - Google Patents

Abstract

FIELD: methods and devices for prevention of ignition and explosion of fire hazardous media. SUBSTANCE: method includes two-stage injection to fire center of gaseous inhibitors; formation in fire hazardous medium of through ventilation cavities in which dynamics of temperature variation is observed; formation at the first stage of temperature rise in medium, prior to beginning of ignition, is periphery inflow velocity laminar flow of supply, to possible fire centers, of cooled nitrogen with temperature of 40-60C below temperature of ambient air; injection at the second stage, at beginning of ignition, to nitrogen laminar flow center zone of liquefied carbon dioxide with initial pressure of 60-70 atm. Supply of liquefied carbon dioxide shall satisfy the condition of the equation given in invention description. Device for method embodiment has fan and disk sprayer with electric drives, channels for supply of ingredients to fan and sprayer. Device includes coaxially secured in common casing: pipeline with diffuser for supply of compressed nitrogen, conical splitter of gas flow and longitudinal plates fastened to casing internal side. Disk sprayer is made in form of perforated hollow disks secured to perforated and rigidly interconnected branch pipes and blades installed on hollow sealed hub hydraulically connected to perforated branch pipes, disks and pipeline for supply of liquefied carbon dioxide to sprayer. Each branch pipe installed on hub has spring-loaded movable working piston. Holes on sprayer disks are made on side of sprayer rotation axis. Electric drives of fan and disk sprayer are made in form of d.c. motors electrically connected with temperature pickups and electropneumatic valves of cylinders with compressed nitrogen and liquefied carbon dioxide. EFFECT: increased efficiency of neutralization of fire hazardous medium and reduced consumption of inhibitors. 4 cl, 4 dwg

Description

 The invention relates to the field of fire extinguishing and, in particular, to means of preventing or eliminating fires and explosions in a fire hazardous environment. The proposal may find application to maintain the required temperature range with a possible intensive increase in heat transfer of the medium, for example, in confined spaces of space objects, submarines, in elevators for grain storage, etc.

 In some cases, with a certain degree of moisture, for example, grain, a chemical reaction may occur under conditions of progressive self-acceleration, associated with the accumulation of heat in the medium. Subsequently, as the heat is released, the rate of the chemical reaction increases sharply, ignition of the elements of the medium and subsequent explosion of gaseous reaction products occurs.

 Under these conditions, the existing ventilation and fire extinguishing systems, for example, elevators or other product storages, are ineffective. Therefore, it is very urgent to develop methods and systems for effective thermal control and means of timely active exposure to a fire hazardous environment to prevent fires and subsequent explosions.

At present, fire extinguishing agents based on, in particular, activated inhibitory aerosol, which should be formed during combustion with the release of active radicals, are spreading. Thus, the aerosol must have a high temperature, at the level of 1500 ÷ 1700 ^o C.

At the same time, in order to ensure operational safety, the temperature in many cases should not exceed 250 ÷ 300 ^o С. In this case, in order to reduce the toxicity of the aerosol, it is necessary to ensure that the products of combustion of the aerosol-generating composition (CO, N), which are unoxidized due to the low oxygen balance, must be burned out in air , NO) with the formation of the least toxic oxides. However, high-heat oxidation of carbon monoxide and hydrogen leads to an increase in the temperature of the resulting aerosol.

Thus, when developing fire extinguishing means in the form of aerosol fire extinguishers, it is necessary to solve three main problems:
- to provide high extinguishing efficiency at the most extinguishing concentration of inhibitor in aerosol;
- minimize the temperature of the aerosol to a safe level of 250 ÷ 300 ^o C at the outlet of the generator;
- reduce the toxicity of combustion products to a level that is safe for humans (Yu.M. Milekhin, EF Zharov. New highly effective universal high-speed fire extinguishing agents. In the collection "Conversion in mechanical engineering." M., 6, 2001).

 A known method of ventilating quarries (USSR, AS 1245713, E 21 F 1/00, 1984), including the removal of contaminated air from the stagnant zone of the quarry by means of a fan and the regulation of the zone of supply of contaminated air to the fan. In order to increase the efficiency of ventilating the quarry by increasing the amount of contaminated suction air from the stagnant zone, a fan is installed between the ventilation trenches, and a guide board is placed above the stagnant zone at an acute negative angle to the plane of rotation of the helicopter rotor.

 This method is quite complicated and is applicable exclusively for ventilation of mountain quarries.

 A known method of preventing the explosion of gas mixtures (USSR, AS 1245714, E 21 F 5/00, 1977), which consists in supplying an inhibitor to an explosive atmosphere. In order to increase the efficiency of neutralization of an explosive atmosphere and reduce the consumption of an inhibitor by increasing the accuracy of determining the time of administration of an inhibitor before the formation of an explosive situation, the concentration of the gas-air mixture is preliminarily recorded. When approaching the maximum permissible explosive concentrations, an inhibitor is fed into the zone of the alleged accumulation of explosive gases until an explosive concentration is formed in it.

 However, this method does not take into account the dynamics of the temperature of the explosive atmosphere.

 A known method of extinguishing and localizing fires in solid fossil fuels is a prototype (USSR, AS 1245717, E 21 F 5/00, 1985), including two-stage injection of flame retardant mixtures to the fire source. In order to increase the efficiency of extinguishing, localizing and preventing relapse of fires by creating heat-insulating and gas-tight layers, a mixture of flame retardants consisting of sulfite-alcohol mud, diammonium phosphate and a surfactant is injected in the first stage. In the second stage, a mixture of flame retardants, consisting of water glass, surfactant and glycerin, is injected.

 This method is applicable exclusively in mining conditions and, due to the use of toxic components in it, it is not applicable, for example, for storages of grain and other food products. It also does not take into account the dynamics of heat generation in a fire hazardous environment.

 The aim of the proposed method is to increase the efficiency of neutralization of explosive atmospheres and reduce the consumption of inhibitors due to the formation of fans oriented in space flows of gaseous inhibitors, increase the accuracy of determining the time of introduction and dosage of inhibitors to the formation of an explosive situation.

 This goal is achieved by the fact that for a timely impact on the source of ignition, for example, in the bulk of bulk materials, a predetermined amount of fire-extinguishing ingredients is pumped through a perforated pipeline through a perforated pipe and the system is regulated and controlled using an electronic system.

If the temperature in the zone of possible ignition is higher than the specified limits, for example, by 40 ÷ 60 ^o С, a peripheral gas supply stream is formed in the form of a high-speed supply stream of cooled nitrogen at a temperature of 40 ÷ 60 ^° С below the ambient temperature and the through flow is vented cavities. With a further increase in temperature in the medium at the beginning of ignition, a regulated supply of liquefied carbon dioxide is carried out at an initial pressure of 60 ÷ 70 atm to the central zone of the supply laminar nitrogen flow to reduce the temperature in the zone of possible ignition to ambient temperature.

где G_т - расход сжиженной двуокиси углерода при температуре Т^oК среды, кг/с;
G_max - максимальный расход сжиженной двуокиси углерода при максимальном нагреве среды, кг/с;
T - температура нагревающейся среды, Т^oК;
Т_окр - температура окружающей среды, Т^oК.In this case, the regulation of the supply of liquefied carbon dioxide is carried out so that the condition

where G _t - the flow of liquefied carbon dioxide at a temperature T ^o To the environment, kg / s;
G _max - the maximum consumption of liquefied carbon dioxide at maximum heating of the medium, kg / s;
T is the temperature of the heating medium, T ^o K;
T _okr - ambient temperature, T ^o K.

 A device for implementing the method of preventing fire and explosion of a fire hazardous environment is based on the operation of the supply system of fire extinguishing components and controlling their arrival rate depending on the temperature in the environment of a possible fire.

 A device for feeding foam is known (USSR, AS 1245319, A 62 C 31/12, 1984). The device is designed to neutralize the source of ignition and contains a foam generator, on the outlet of which a nozzle is installed, made in the form of a hollow cylinder, inside of which a deflector is installed. In order to increase the range of foam supply while maintaining the area of its loss, the deflector is made in the form of an open truncated hollow cone, the smaller base of which is located on the side of the outlet of the foam generator.

 This device provides only the possibility of fire fighting and is not intended to respond to ambient temperature.

 Known air dryer (USSR, AS 1245809, F 24 F 3/14, 1984), comprising a housing with inlet and outlet nozzles, mounted in the housing with the possibility of periodic rotation around its axis, a rotor with four flow cavities, a drainable blower air connected to the inlet of the housing. In order to increase the efficiency of air drying, it is equipped with a heater and a humidity sensor, and the rotor is installed along one of the walls of the housing.

 This device is designed exclusively for drying air and cannot be used for fire fighting.

 A device for humidification of air is known, which contains an electric motor, a fan with a hub and blades, equipped with a shell of microporous material with internal channels that communicate with the inner space of the hub (USSR, AS 307251, 05 V 3/10, 1971).

 Water is supplied through the water supply to the inner space of the hub, which, under the action of centrifugal forces, enters the body of the blade and evaporates into the air driven by the fan.

 The main disadvantages of this device are its unsightness for fighting a fire, an almost constant amount of sprayed water at different fan speeds, and the lack of dependence of its operation on the ambient temperature.

 A known aerosol generator, prototype (USSR, AS 1245296, A 01 M 7/00, 1985), comprising a fan and a disk atomizer mounted on one drive shaft, air and liquid supply channels to the atomizer and a droplet eliminator with a conical nozzle at the outlet aerosol torch from a generator. In order to improve the quality of spraying by preventing the formation of condensate on the nozzle and its release into the environment, the air supply channel has a conical shape.

 This device does not have sufficient efficiency to deal with fire, and also in its work does not take into account the dynamics of changes in ambient temperature.

 The aim of the proposed device is to increase the efficiency of neutralization of explosive atmospheres and reduce the consumption of inhibitors due to the formation of fans oriented in space flows of gaseous inhibitors, increase the accuracy of determining the time of introduction and dosage of inhibitors to the formation of an explosive situation.

 This goal is achieved by the fact that for a timely impact on the source of ignition, for example, in the bulk of bulk materials, a predetermined amount of fire-extinguishing ingredients is pumped through a perforated pipeline through a perforated pipe and the system is regulated and controlled using an electronic system. The invention is characterized by all the features of claims 1 to 4 of the claims.

 The invention explains the following graphic material.

Figure 1 presents a General view of the device. Figure 2 presents the design of the disk atomizer. Figure 3 presents the circuit diagram of the device. Figure 4 presents the dependence of the flow rate (G _T ) CO ₂ from the rotation speed (N _{r / c} ) of the atomizer and the number (n) of openings in the disks.

 A device that implements the inventive method contains an outer cylindrical casing 1, longitudinal plates 2 are fixed on the inside of the casing, and a nitrogen supply diffuser 3, a fan 4 with an electric drive 5, a disk atomizer 6 with a hub 7 and an electric drive 8 are coaxially located in the inner cavity conical fairing 9. The internal cavity of the casing 1 is hydraulically connected to the inlet openings of the pipelines 10 for supplying fire-extinguishing ingredients to the ignition zone through the through openings on the periphery of the pipelines.

 Disk sprayer 6 includes a housing of a sealed hub 7 (Fig. 2), on which perforated nozzles 11 are mounted with hollow disks 12 rigidly fixed to them with holes made in them from the axis of rotation of the hub. The inner cavity of the hub 7 is hydraulically connected to the nozzles 11, disks 12 and the liquefied carbon dioxide supply pipe 13.

In each of the nozzles, a movable piston 14, spring-loaded with a coil spring 15, mounted on the other side of the nozzle, is placed on the side of the axis of rotation. Between the disks 12, fragments of the blade 16 are fixed on each nozzle 11 to initiate the supply of CO ₂ towards the outlet openings of the casing.

 The electric drives of the fan 4 and the disk atomizer 6 are made in the form of DC motors 17 with an adjustable rotation speed by changing the excitation current in the winding using an adjustment rheostat 18 and a starting rheostat 19 (Piotrovsky L.M. Electric machines. L.-M., 1960) .

 The current collectors of rheostats are mechanically connected with micromotors 20, electrically connected through the first output of a multi-pole electric relay 21, a current amplifier 22 with a temperature sensor 23, made, for example, on pyro piezoelectric elements.

In turn, the second output of the electric relay 21 is electrically connected to the electro-pneumatic valve 24 of the cylinder 25 with compressed CO ₂ at a pressure of, for example, 60–70 atm, and the third output is connected to the electro-pneumatic valve 26 of the cylinder 27 with nitrogen, under pressure, for example, 2-3 atm and a temperature of minus (20 ÷ 30) ^o С, and tanks 24 and 27 are hydraulically connected, respectively, with the internal cavity of the atomizer sleeve and the nitrogen supply diffuser. To manually turn on the device control system, an electric switch 28 is inserted into it.

 This method is implemented as follows (Figure 1).

The use of nitrogen in the first stage, cooled to a temperature of 40 ÷ 60 ^o C below the ambient air, is due to the fact that nitrogen is chemically very inert and does not support combustion, and the low temperature of the gas entering in the form of a laminar flow into the zone of the beginning of intense heat environment, can extinguish a possible source of ignition.

 In this case, the movement through the pipelines of nitrogen in the form of a laminar, rather than turbulent, flow reduces its heating in thickness from the outer walls.

In the case of continued heating of the medium, for example, wet grain, which is recorded by temperature sensors, the system of controlled supply of liquefied carbon dioxide to the fire fighting zone is activated. At a pressure of about 60 atm, carbon dioxide is stored in the form of a liquid at ordinary temperature in steel cylinders. Entering the disk atomizer, this liquid with rapid expansion is rapidly sublimated with decreasing temperature to minus 78.5 ^o C.

Carbon dioxide enters the ignition zone inside the laminar stream of nitrogen, which acts as a thermal insulator. Moreover, CO ₂ also has the property of not burning and not sustaining combustion, which makes it possible to accelerate the elimination of the source of ignition.

 The control of the carbon dioxide supply intensity in this method is carried out automatically by changing the rotational speed of the disk atomizer in accordance with the above temperature dependence obtained empirically.

 The device operates as follows.

When the temperature of the medium rises above normal, the signal from the temperature sensors automatically turns on all the elements of the device (Figure 3). This involves the supply of nitrogen and liquefied CO ₂ and the electric current of electric motors 5 and 8. With a slow increase in electric current in the circuit, the shaft of the electric motor 5 together with the fan starts accelerated rotation. And nitrogen through the diffuser 3, expanding and further cooling, is pumped by the laminar flow formed by the plates 2 at the outlet of the casing 1 through pipelines 10 and ventilation cavities into the zone of elevated ambient temperatures. At the first stage of the device’s operation, only cooled nitrogen is supplied to the temperature rise zone, under the influence of which a temperature decrease to predetermined limits is initiated. At the signal of the temperature sensors, the entire system is automatically turned off. In case of continued rise in temperature, the second stage of operation of the entire device begins. The signal from the temperature sensors increases the current in the circuit of the electric motors, and their rotation speed increases. At the same time, with a continuing supply of nitrogen, the CO2 liquefaction injection system is switched _on . In this case, the pistons 14 in the nozzles 11 under the action of centrifugal force, compressing the springs 15, begin to move along the nozzles, giving CO ₂ access to the holes in the nozzles and disks.

With the acceleration of rotation of the disk atomizer, the pistons 14 are more and more squeezed out to the ends of the nozzles, and the liquefied СО ₂ with intensive expansion is cooled to a temperature of ~ (-78 ^o С) and injected through the hole in the disks towards the axis of rotation of the atomizer. At the same time, blades 16 installed along the nozzles, the cooled gas is ejected into the Central zone of the laminar flow of nitrogen and then sent to the zone of ignition of the medium.

 The implementation of the control action of function (I) is carried out by uneven distribution of holes in the disks of the atomizer 6 in accordance with the schedule (Figure 4).

При этом скорость вращения вентилятора и распылителя определяет зависимость:
N_об/с=К₁J=К₂ΔТ,
где J - сила тока от датчиков температуры;
ΔТ - рост температуры;
К₁, К₂ - коэффициенты пропорциональности.If we take into account that the air temperature T _okr varies relatively insignificantly compared with fire hazardous heating of the medium (usually), then
TT _ocp = ΔT
depends only on the degree of heating of the medium. Then

In this case, the rotation speed of the fan and atomizer determines the relationship:
N _{r / s} = K ₁ J = K ₂ ΔT,
where J is the current strength from temperature sensors;
ΔТ - temperature increase;
K ₁ , K ₂ - proportionality coefficients.

 Then, for example, with a monotonous increase in the temperature of the medium and, accordingly, the fan speed per unit time, an opening of a larger number of holes occurs compared to the previous period. In this case, the maximum consumption of carbon dioxide (all openings in the atomizer are open) is calculated from the maximum allowable heat transfer of the medium.

The advantages of this method are:
- the possibility of changing the mass of the supplied ingredients over a wide range depending on the application;
- the possibility of changing the volumetric feed rate of the ingredients (m ³ / s) depending on the requirements of fire fighting;
- regulation of both the linear speed of the outflow of ingredients and the direction of the outgoing flow (one-sided, two-sided, radial - comprehensive);
- the possibility of stationary fixing the device to the protected object.

 At the same time, as mentioned above, the number of protected objects by the proposed method can include both economic objects (warehouses, vegetable and grain storages, shops, etc.), and many special objects, for example, space manned ships, submarines, heavy aircraft, etc. In these cases, through ventilation cavities in the form of perforated pipelines can be laid between bulkheads, flooring or wall coverings.

 Thus, the effectiveness of this method and device as a whole is due to the relative simplicity and reliability, the possibility of its multipurpose use, as well as the reduction of labor costs, energy resources and time to manufacture the system.

Claims (4)

1. A method of preventing ignition and explosion of a fire hazardous environment, comprising two-stage injection of gaseous inhibitors to a possible fire source, characterized in that through fire cavities form through ventilation cavities in which dynamics of temperature changes are monitored and at the first stage of temperature increase in the medium before ignition forming a peripheral speed laminar flow supply feed to possible flashpoint cooled nitrogen with temperature at 40 ÷ 60 ^o C below the temperature Ambient of air and the second stage at the beginning of ignition, is injected into the central zone of the laminar stream of nitrogen, liquefied carbon dioxide at an initial pressure of 60 ÷ 70 atm, and supply of carbon dioxide is carried out so as to satisfy the condition

where G _t - the flow of liquefied carbon dioxide at a temperature T ^o To the environment, kg / s;
G _max - the maximum consumption of liquefied carbon dioxide at maximum heating of the medium, kg / s;
T is the temperature of the heating medium, T ^o K;
T _okr - the initial equilibrium temperature of the medium, T ^o K.  2. A device for preventing ignition and explosion of a fire hazardous environment, comprising a fan and a disk atomizer with electric drives, pipelines for supplying ingredients to the fan and atomizer, characterized in that a compressed nitrogen supply diffuser, a conical gas flow divider and reinforced are mounted coaxially in the common casing on the inner side of the casing are longitudinal plates, and the disk atomizer is made in the form of perforated hollow disks mounted on perforated rigidly interconnected nozzles and blades that are mounted on a hollow sealed hub hydraulically connected to perforated nozzles, discs and a supply pipe to the atomizer of liquefied carbon dioxide.  3. The device according to claim 2, characterized in that each of the nozzles installed on the hub is equipped with a spring-loaded movable working piston, and the holes on the spray disks are made from the side of the spray axis of rotation.  4. The device according to claim 2, characterized in that the electric drives of the fan and the disk atomizer are made in the form of direct current motors electrically connected to temperature sensors and electro-pneumatic valves of cylinders with compressed nitrogen and liquefied carbon dioxide.

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