I. Basic concepts
1, solid particle aerosol extinguishing agent -PGAS (aerosol generated by fireworks).
2. Aerosol is a kind of sol formed by liquid or solid particles suspended in gas dispersion medium.
3. Aerosol fire extinguishing agents can be divided into two types: one is that before the release of aerosol fire extinguishing agent, the gas dispersion medium and the dispersed medium exist stably, and the release of aerosol fire extinguishing agent is the process of gas dispersing liquid or solid fire extinguishing agent to form aerosol; The other is that the release of aerosol fire extinguishing agent undergoes combustion reaction, and the reaction products are both solid and gas, and the gas disperses solid particles to form aerosol, which can also be called aerosol generator.
4. According to the temperature when aerosol is produced, it can be divided into cold aerosol and hot aerosol. When the reaction temperature is greater than 300℃ (? ) is called a hot aerosol, while it is a cold aerosol.
5. Aerosol generator is an energetic material, which belongs to a kind of pyrotechnics. Explosives can be divided into three categories: explosives, gunpowder and pyrotechnics. The selection, manufacture, performance parameters and processing technology of aerosol products are all guided by pyrotechnic technology.
6. In order to reduce the temperature when aerosol is generated, there are two ways to use coolant. One is to mix the coolant evenly in the medicine, which is called internal cooling; Another cooling method is to put the coolant in the gas channel of the gas generator, which can be called external cooling.
Two. Fire extinguishing mechanism
1. Taking metal K as an example, the fire extinguishing mechanism of aerosol fire extinguishing agent is introduced.
(1) Influence of endothermic decomposition on cooling and fire extinguishing. K2O will decompose when the temperature is higher than 350℃, and the melting point of K2CO3 is 89 1℃, and it will decompose when it exceeds this temperature. These are all strong endothermic reactions: K2O+C? 2K+CO； 2K2O+C4K+CO2；
(2) Gas phase chemical inhibition. Under the action of heat, K dissociated from solid particles in aerosol may exist in the form of vapor or cation, and may have many chain reactions with active groups H, OH and O in combustion in an instant. : K+ oh? KOHK+O？ KO； KOH+OH？ KO+H2O； KOH+H？ K+H2O consumes active groups and inhibits the exothermic reaction among active groups H, OH and O, thus inhibiting the combustion reaction.
(3) inhibition of chain reaction by the surface of solid particles (solid phase chemical inhibition). The solid particles in aerosol are extremely small, with large surface area and surface energy. It takes some time for them to be pyrolyzed by heat in fire, and they cannot be completely pyrolyzed or gasified. After entering the fire, solid particles are impacted by the pyrolysis products of combustible materials. Their size is much larger than that of active groups H, OH and O. These active groups collide with the surface of solid particles, are instantly adsorbed and undergo chemical reactions. The following reactions may occur: K2O+2h? 2KOHKOH+OH？ KO+H2O； KO+H？ chhirp
This is repeated in order to consume combustion active groups.
2. Adsorption
The solid particles in the product are mainly metal oxides, carbonates or bicarbonates, most of which are less than 1? M, accounting for more than 90%. The gas is mainly nitrogen, a small amount of carbon dioxide gas and water vapor.
The aerosol produced by combustion reaction is a strong exothermic reaction, which will produce gaseous metal salts. When cooled and condensed, aerosol particles are extremely fine and have a very large specific surface area, so they become particularly excellent fire extinguishing agents. Its fire extinguishing efficiency is 4 ~ 6 times that of alkyl halide 130 1.
Step 3 know about aerosols
List some related things to help understand the fire extinguishing effect of aerosol.
1, flame retardant
Adding potassium chloride to gunpowder can effectively reduce the size of explosion flame.
In military application, the flame should be minimized when the weapon is launched to avoid exposing its shooting position. In the mine where blasting coal mining is used, blasting with explosives containing flame suppressant will not cause fire and gas explosion in the working face where the gas concentration exceeds the explosion limit.
It is mainly the function of K to capture the free radicals of combustion chain reaction and reduce the explosion temperature. It effectively collides with free radicals in the gas phase, absorbs energy and decays it.
In heterogeneous catalysis, the atomic groups on the surface of the flame arrester crystal show strong unsaturation and adsorption, which can adsorb and attach to the free groups in the fuel gas and make them reach a stable state through interaction.
2, potassium bicarbonate dry powder
It is a black powder, which consists of 66% potassium bicarbonate, 0/5.5% potassium nitrate, 7.8% melamine, 3.75% charcoal, 0.9% sulfur, 3.5% talcum powder, 0/0.5% mica powder and 0/0.4% magnesium stearate. Among them, potassium nitrate, sulfur and charcoal are the components of black powder.
Dry powder is sprayed to the combustion area to extinguish the fire under the impetus of power gas (nitrogen or carbon dioxide). Potassium salt decomposes at high temperature in the combustion zone, which plays the role of chemical fire extinguishing, but the dry powder particles are large, the adsorption is greatly reduced, and the fire extinguishing efficiency is average.
3. Influence of particle size
The new mechanism of dry powder fire extinguishing and the optimization of formula design are ministerial projects completed by tianjin fire Research Institute of the Ministry of Public Security. In the experiment, potassium carbonate with different particle sizes was used to disperse gas with pressurized nitrogen as the power to put out the gasoline fire in the 0.6 cubic meter experimental container. The experimental conclusion is that the particle size is 20? Dry powder below m has higher fire extinguishing efficiency, when the particle size is greater than 20? The efficiency of fire fighting decreased sharply.
Russians also did the same experiment when studying cold aerosols, and reached a similar conclusion. Even an industrial production device of aerosol ultrafine particles based on nanotechnology was designed.
Four. Various aerosol preparations
1. Formula developed by the Soviet Union in the mid-1960s: contains about 35-50% oxidant, and the oxidant is potassium chlorate, potassium nitrate, sodium nitrate or ammonium nitrate; The fuel (nitrogenous organic matter) containing 15 ~ 40% can be dicyandiamide, nitroguanidine or urea; About 22-35% of ammonium, sodium, potassium, calcium and magnesium carbonate and Aidoo sugar alcohol.
2. The fire extinguishing agent invented by Americans contains carbon halide compound, oxidant (potassium perchlorate, potassium chlorate and potassium nitrate), component dispersant and binder fuel, and adopts casting solidification molding process.
3. The Russian formula is potassium nitrate 6 1.2%, potassium ferricyanide 4.8%, diphenylamine 0.5%, carbon 8.4%, lubricating oil 0.5%, fluoroplastics 1.5%, sodium stearate 0. 1%, plasticized nitrocellulose 23.0%, etc. The fire extinguishing efficiency is high (about 20.
4. Another Russian formula can be cast and pressed, with potassium perchlorate 10%, potassium nitrate 60% and * * * as oxidants, epoxy resin+anhydrite 29.95%, carbon 0.025%, sulfonated ricinoleate 0.025%, etc.
5. The components disclosed in the German patent are potassium nitrate 56-63%, linear phenolic resin 12.5- 15%, basic magnesium carbonate 23-29%, and processing aid10.5% (the processing aid can be fluoroplastics, zinc stearate, calcium stearate, magnesium stearate, etc.). ), which can be press-molded.
6. The Canadian patent contains 40-70% potassium nitrate, 5- 15% carbon and plasticized nitrocellulose as combustion binders. Another patent also uses aerosol generated by the combustion of oxygen-containing solid fuel to extinguish fire.
7. Japanese patent JP03 03,126,472 uses propellant components to drive a mixture of octafluoropentane and difluoroethane in an aerosol fire extinguisher.
8. Pyrogen fire extinguishing agent: solid chemical composition: potassium nitrate 62.3%, nitrocellulose 22.4%, carbon 9%, process mixture 6.3%.
Application of verb (abbreviation of verb) aerosol fire extinguishing agent
1. Automatic accident prevention device "Karpas" and small fire extinguisher "Mangust" of Moscow Institute of Chemical Mechanics. Automatic accident prevention device "Karpas" mainly eliminates the explosion of gas and dust mixture in coal mine. Once a fire is detected, the electric starting device will act immediately; Karpas can put out the deflagration of methane-air mixture gas, and the flame front speed is 320m/s ... The "Mangoste" fire extinguisher is only 1.5Kg, which is put in the engine room of a car to put out gasoline fires.
2. There are some articles about aerosol in domestic professional fire periodicals, which are about Russian Gabal device, and the aerosol it produces can put out all kinds of fires, including smoldering material fires; While the temperature of aerosol does not exceed 60℃.
3. The Gabal device in Russia is filled with TTK, and the combustion temperature is 1500℃. Take technical measures to solve the problems of high aerosol temperature and open flame;
(1) The method of adding liquid coolant to the aerosol flow, adding water to the injector, successfully protected 10 ~ 1000 cubic meters of petroleum product storage tanks and liquefied gas storage tanks, the outlet aerosol temperature of the injector was lower than 60℃, and the open flame was completely eliminated. The device can protect 5000 cubic meters of storage tanks.
(2) Aerosol bubbles through the liquid layer. The generated aerosol enters from the bottom of the storage tank and passes through the liquid to extinguish the fire on the liquid surface, which is suitable for small-capacity storage tanks.
(3) Use ablative materials to absorb heat. A special generator is made, and a cylindrical container is made of thin steel plate, and TTK agent and coolant are filled in the container according to a certain proportion.
Research and development direction of intransitive verb aerosol fire extinguishing agent
1. Aerosol is an energetic substance, which needs to undergo a combustion reaction during its release, resulting in a high-temperature flame. Reducing the reaction temperature can make aerosol fire extinguishing agents more widely used. Some fire extinguishing agent formulas mentioned above have considered the problem of reducing the flame temperature.
2.2 formula. TTK is constantly improving, and the latest TTK8 particles can effectively put out wood fires.
3. In recent years, the US Army, Navy and Air Force and Spectronix Limited have been conducting aerosol research and developing SFE/EMAA fire extinguishing agent. Initially, SFE had three formulas: A, B and C. Recently, formula D appeared, which can put out class A deep fire.
Seven. Foreign aerosol fire protection products
1. Aerosol fire extinguishing technology developed from the military technology of the former Soviet Union has a history of more than 25 years, and has formed a series of products in Russia, which are widely used in various places to extinguish fires.
2. Protect relatively closed spaces such as cabins, warehouses and engine rooms, petrochemical product storage tanks, ships, airplanes, automobiles, diesel locomotives, cable trenches, cable shafts, pipe interlayers and other closed semi-closed spaces. Aerosol fire extinguishing agents are also used in open air.
3. It can be used in all kinds of fire fighting equipment: hand-held fire extinguishers; Hand-thrown fire extinguisher, lit and put into the fire; Vehicle-mounted projectiles are thrown into the fire by special tools on fire engines; The vehicle-mounted launcher, like the rocket mine-laying vehicle, carries the launcher and can launch fire-fighting bombs to a distance of1500 m. UPG-92 fire-extinguishing propulsion device was successfully developed by Morozov Machinery Manufacturing and Design Bureau in Kharkov, Russia. The fire extinguishing device was installed on a combat tank manufactured by Marishev Industrial Company, and the combat weapon was replaced by five salvo barrels, each containing 200 kilograms of special powder (aerosol fire extinguishing agent). 1 ton of gunpowder volley can cover the whole fire area and put out the fire. This former combat weapon has reliable three-prevention functions (fire prevention, radiation prevention and chemical weapons prevention), so it can enter the center of the fire zone 50 meters. This kind of fire extinguishing device is used to put out oil and gas fires, which can put out the fire of 100 square meter in a few seconds.
4. International industrial facilities for installing aerosol fire extinguishing systems include: nuclear power plant control room, military facilities, ship engine room, telecommunication/electronic equipment room and aircraft engine room.
Comprehensive evaluation
First, the choice of haloalkane fire extinguishing agent substitutes
1. At present, the main substitutes for haloalkane fire extinguishing agents used in China are FM200, "substitutes", carbon dioxide, smoke burnout, water mist and aerosol.
2. In the past, people praised 130 1 and naturally compared it. Clean gas fire extinguishing agent can be compared from 10.
(1) The release process has no damage to the protected object (clean);
(2) The ozone depletion potential value is very small and zero;
(3) Good fire extinguishing efficiency;
(4) low toxicity or non-toxicity;
(5) The composition has a short shelf life (ALT) in the atmosphere;
(6) The greenhouse effect potential (GWP) is very small or nonexistent;
(7) Good gas phase electrical insulation;
(8) Good storability and stability;
(9) The volume ratio of applications to 130 1 is small;
(10) Economically reasonable and acceptable market price.
Second, the sub-project evaluation
1.FM200
(1)FM200 fire extinguishing system is almost the same as 130 1 in equipment, pipeline and configuration.
(2) Although the DOP value of FM200 is 0, the GWP is 2900 and the atmospheric residence time is 3 1 year. The United States, Britain and other countries have included HFC in the control use plan, so it is not suitable to consider as a long-term substitute.
(The toxicity and carcinogenicity of FM200 are controversial in international academic circles.
(4)FM200 will decompose hydrofluoric acid during fire extinguishing, and the amount of acid gas produced is 8 ~ 1 3010 times of that of1. The actual amount of acid gas produced is about 300ppm, which is far greater than the international standard of dangerous concentration of 50ppm hydrofluoric acid exposed for a short time.
(5) The price of FM 200 is 30% higher than that of 130 1.
2. "Special iodine substitution"
The minimum design concentration of "alternative" extinguishing agent is 2 1.4 times NOAEL (when no adverse reaction is observed), so it is impossible to carry out fire fighting in crowded places.
3. Carbon dioxide
(1) The application volume is too high. The minimum design concentration of fire extinguishing is 34.0%, and the use amount is large.
(2) The minimum fire extinguishing design concentration exceeds the lethal concentration of people, which is very dangerous.
(3) The high-pressure carbon dioxide container has high pressure and the filling density is 60-68%. When the extinguishing agent is released, it is easy to damage the envelope and the protected object.
(4) It cannot be used to extinguish the fire of charged objects.
(5) The routine maintenance of low-voltage system is complicated.
Burn out smoke
(1) Tobacco branding is a "green" medium with full marks due to environmental factors, which is non-toxic and harmless.
(2) The relative volume ratio of application amount is too high. The minimum design concentration of fire extinguishing is 37.5%, and the use amount is large.
(3) The pressure of the container is as high as 15Mpa. When the extinguishing agent is released, it is easy to damage the envelope and the protected object.
(4) expensive.
5. Water mist
(1) system is very complex, which requires special high-pressure water mist nozzle.
(2) The scope of application is small, and it is limited to the pre-action system of individual occasions. Only directional injection can be used, and it cannot be used for all-round and full-filled fire fighting.
(3) The application cases are few, the cognition is insufficient, and the technology application is difficult. 1997 code for fire protection design of high-rise civil buildings (GB50045) stipulates in article 7.6.6 that water spray fire extinguishing systems should be installed in oil-fired and gas-fired boiler rooms and self-contained generator rooms. However, there is no corresponding regulation in Code for Design of Water Spray Fire Extinguishing System (GB502 19-95), which brings difficulties to the design. According to the investigation, the fire extinguishing systems used in oil-fired and gas-fired boiler rooms and self-contained generator rooms are as follows: light water (low power) foam fire extinguishing systems are mostly used in Shanghai and other places; However, gas fire extinguishing systems are widely used in most areas of China, such as Beijing and Guangzhou.
6.aerosol
(1) Aerosol fire extinguishing agent relies on the aerosol generated by its own combustion reaction to extinguish the fire.
(2) Aerosol aerosol fire extinguishing products are simple in system, low in price, non-corrosive, pollution-free, non-toxic, harmless, non-ozone-depleting, less in residue, high in speed, high in efficiency, totally submerged, and fire extinguishing in all directions. They are ideal halon substitutes and have good market prospects.
(3) portability, usability, robustness, reliability and low cost.
(4) Smoke will be formed after aerosol release, and the visibility is less than 1 m, which will affect people's escape (fire visibility
Three. Research and development direction of aerosol fire extinguishing agent
1. Aerosol is an energetic substance, which needs to undergo a combustion reaction during its release, resulting in a high-temperature flame. Reducing the reaction temperature can make aerosol fire extinguishing agents more widely used. Some fire extinguishing agent formulas mentioned above have considered the problem of reducing the flame temperature.
2.2 formula. TTK is constantly improving, and the latest TTK8 particles can effectively put out wood fires.
3. A lot of research work has been done on cold aerosol abroad, and many explorations have been made on the preparation, storage and use of cold aerosol.
4. In recent years, the US Army, Navy and Air Force and Spectronix Limited have been conducting aerosol research and developing SFE/EMAA fire extinguishing agent. Initially, SFE had three formulas: A, B and C. Recently, formula D appeared, which can put out class A deep fire.
Four. Hot issues in aerosol application
Problems encountered: flame spraying, surface heating, corrosiveness of aerosol, generation of toxic gas, buoyancy of aerosol and user's feeling.
1. is not a clean fire extinguishing agent.
(1)FM200 injection reduces the ambient temperature at the nozzle and condenses the moisture in the air into water mist. In the process of fire extinguishing, FM200 will decompose hydrofluoric acid, and the amount of acid gas produced is 8 ~ 1 3010 times that of1,and the actual amount of acid gas produced is about 300ppm. Acidic substances are more harmful than alkaline substances; Although hydrofluoric acid is weakly acidic, it has specific corrosiveness and will cause great harm to specific objects.
(2) High and low pressure carbon dioxide injection greatly reduces the ambient temperature and condenses the moisture in the air into extremely thick water mist. Carbon dioxide, that is, carbonic acid, is soluble in water enough to damage magnetic media.
(3) The commonly used aerosol is a kind of sol formed by solid particles suspended in the air. Most solid particles in the product are less than 1? M, accounting for more than 90%. These dust particles are electrically neutral and easy to remove. The metal oxide, carbonate or bicarbonate contained in the residual fine dust is weakly alkaline when wet, which will only cause certain harm to specific equipment.
2. Acid-base balance and safety are considered in the formulation of corrosive and toxic aerosol, which can be stored for ten years. Aerosol formula comes with oxidant, which is designed as oxygen balance and will not be corrosive; The reaction does not depend on the consumption of oxygen in the air, and the oxygen concentration in the air is unchanged, which is harmless to people.
3. High temperature will cause secondary hazards. The high temperature generated by aerosol can be controlled in several ways:
(1) Extend the reaction time to release heat evenly. The current national standard reaction time of aerosol is 150s, which greatly reduces the temperature when aerosol is released.
(2) Adjust the aerosol formula to reduce the reaction heat.
(3) Take heat insulation measures to control the surface temperature of the fire extinguisher not to exceed 80℃. Avoid causing harm.
(4) Adopt internal and external cooling technical measures, such as "Gabal" device in Russia.
4. There is an open flame when it is released, which is not suitable for flammable and explosive places. Because the aerosol contains flame suppressant, the size of explosion flame can be effectively reduced. When the concentration of combustible substances in inflammable and explosive dangerous places exceeds the explosion limit, the burning aerosol particles will not cause fire and explosion. The electronic ignition device in aerosol fire extinguishing equipment should be specially protected to prevent the open flame from overflowing during ignition. Will not ignite dangerous goods. Special aerosol fire extinguishing equipment can be used to protect flammable and explosive places, such as the automatic accident prevention device "Karpas" of Moscow Institute of Chemical Mechanics.
5. Poor visibility after release. There is smoke after aerosol release, which affects people's escape. This is the biggest defect of aerosol fire extinguishing agent.
6. Can't extinguish Class A smoldering fire water is a cooling fire extinguishing agent, which can be used for various fires (using its own ability to absorb sensible heat and latent heat to cool the combustion). Aerosol and gas have no cooling effect, and their ability to extinguish Class A smoldering fire is poor. Continuously improve the aerosol formula, the latest TTK8 particles and the D formula of SFE in the United States can put out wood fires.
7. Aerosol fire extinguishing system is only suitable for small systems, which is different from prefabricated fire extinguishing devices in gas fire extinguishing. The aerosol fire extinguishing device has simple composition and high reliability, and can be purchased to meet the requirements of a larger protected area.
8. After aerosol is released, it does not have the ability of joint distribution and should not be transported through long pipelines. Aerosol particles are extremely fine, with very large specific surface area and strong adsorption. Therefore, pipeline transportation and combined distribution of aerosol will cause great losses, so it is not suitable for application. Aerosol fire extinguishing system is simple in composition and low in price, and does not need to consider joint distribution.
9. The experimental device that can realize cold aerosol is similar to the dry powder fire extinguisher, but the difference lies in the particle size. Very fine particles can be made in industry, but the strong adsorption between particles will make them stick together and cannot be stored.
10. The biggest difficulty is the pressure and high heat when aerosol can't be used in portable appliances, but the experiment proves that it can be realized.
Verb (abbreviation of verb) conclusion
Gas fire fighting is expensive and complicated, and its substitutes also have their own weaknesses.
Aerosol fire extinguishing products have the advantages of high fire extinguishing efficiency, simple system, low price, innocuity, no loss of ozone layer, less residue and so on. They are excellent halon substitutes and have good market prospects. But there is still some work to be done.
(1) To adapt to the new standard, we should make full use of the loose technical requirements of the new standard.
The requirements of the new standard are too low to reflect the advantages of aerosol. For example, the injection time is as long as 150s, the dosage is as high as 200g/m3, and there are many residues.
(2) Break through the old standards
Gas fire fighting has been used for a long time, and the standard is perfect; The introduction of new aerosol products will inevitably be subject to the traditional gas fire protection concept. Now the aerosol products on the market are all developed according to the concept of prefabricated fire fighting system in gas fire fighting. The protection area is not large, and the single fire extinguishing area is not large 100m2. Therefore, carbon dioxide is used in larger systems.
(3) Give full play to the technical advantages of aerosol.
Aerosol fire extinguishing products have the advantages of high fire extinguishing efficiency, simple system, low price, innocuity and harmlessness, no loss of ozone layer and less residue. Give full play to the advantages of aerosol technology.