On the design of automatic fire extinguishing syst

  • Detail

Talking about the design of automatic fire extinguishing system of cable interlayer

I. preface

article 5.8.6 of code for fire protection design of thermal power plants and substations stipulates that the cable interlayer of unit control room and electrical control building should be equipped with linear temperature sensing and smoke sensing combination and automatic sprinkler system. The author believes that gas fire extinguishing system and ultra-fine dry powder automatic fire extinguishing system can be added, so that they can be selected and applied according to the actual situation

for this protection area, water spray, gas and ultra-fine dry powder fire extinguishing systems have their own characteristics:

Second, water spray fire extinguishing system

water spray fire extinguishing system is a device that uses the cooling of water mist, the suffocation of water vapor volatilized by water mist, the impact of water dance and the water film formed by water mist on the surface of combustors to extinguish the fire

the principle is as follows:

1. The cooling effect of water mist. Water spray fire extinguishing equipment is characterized by small particle size of atomized water and small area of spray. Give full play to the effect of water on the surface temperature of the burning object. When the temperature of the burning object reaches below the ignition point, the flame goes out and the combustion stops

2. Asphyxiating effect of water mist. After the water mist is sprayed into the combustion area, because the temperature of the water mist increases instantly, the mist like water with small particle size will vaporize rapidly, absorb the heat of measurement in the vaporization process, and further greatly reduce the temperature of the combustion area. At the same time, a large amount of water vapor fills the combustion space, causing the oxygen concentration to drop, causing serious hypoxia in the combustion space, and the flame is extinguished due to asphyxiation

3. Covering effect of water film. The spray jet has a large diffusion area, which forms a water film on the surface of the combustor in a short time, and plays the role of isolating air and cooling objects. Make it difficult for combustible objects to continue to burn

according to the actual application, the water spray fire extinguishing system can also effectively control and extinguish the fire of charged objects and ensure personal safety. However, the fire extinguishing cycle is long, the integrity rate of pipelines and equipment failures directly affect the fire extinguishing efficiency. The water fire-fighting system is simple, but because the cable interlayer is usually a power distribution device room or other electrical equipment room, there are special requirements for waterproof, so it is necessary to waterproof the floor and make drainage design while making the water fire-fighting system. In addition, after the fire is extinguished, the damaged part of the cable needs to be replaced because of its reduced insulation performance, which will increase the cost

III. gas fire extinguishing system

the gas fire extinguishing system adopts the total flooding combination distribution mode, and the consumption is designed with the largest fire extinguishing area to meet the fire extinguishing requirements. At present, CO2 fire extinguishing system is commonly used

fire extinguishing principle:

co2 is non-conductive at room temperature, or it is a neutral, non corrosive inert gas. The liquid CO2 is stored in the rigid bottle. When extinguishing the fire, the liquid CO2 is ejected from the nozzle through the pipeline and vaporized immediately, taking away a large amount of vaporization heat, reducing the content of oxygen in the air, reducing the volume composition of oxygen in the protection area to less than 10%, so as to asphyxiate the combustion area and extinguish the fire

the gas has no damage to the cable, and it can be used only by locally replacing the burnt out part after a fire. However, the initial investment of the gas fire extinguishing system is large, and the storage facilities may have problems and affect the test results. The coal group in Xiangli will welcome ldquo; Seek acquaintance and cooperation rdquo; The indiscriminate bombardment of red envelopes is of great importance

III. superfine dry powder fire extinguishing system

the superfine dry powder fire extinguishing device is filled with superfine dry powder fire extinguishing agent. Its fire extinguishing mechanism:

1. Effective suppression of flaming combustion: after the release of the fire extinguishing agent, driven by atmospheric nitrogen, the fire extinguishing agent is fully mixed with the flame, and the fire extinguishing components quickly capture the combustion free radicals, so that the consumption rate of free radicals produced by the combustion reaction is greater than the production rate. Due to the lack of active free radicals necessary for combustion, the combustion chain reaction process is terminated, and the flame is extinguished rapidly

2. Strong suffocation effect on surface combustion: when ultra-fine dry powder contacts the surface of high-temperature combustibles, a series of chemical reactions occur, which are melted under the high temperature of the solid surface and form a glassy covering layer to separate the solid surface from the surrounding air, so as to suffocate the combustion

3. Block the thermal radiation of the flame and cool the protected objects: the high concentration powder generated when the fire extinguishing agent is released is mixed with the flame, and the decomposition endothermic reaction generated effectively absorbs part of the heat of the flame, while some by-products produced in the decomposition reaction, such as carbon dioxide, steam, etc., also have a partial dilution effect on the oxygen concentration in the combustion area, weakening the combustion reaction of the fire

the sliding surface of the ultra-fine dry powder tubeless inlaid steel plate in contact with the lining plate and the dovetail groove surface on the lining plate should adhere to the clean automatic fire extinguishing system, which adopts the suspension structure and is driven by nitrogen. Only by hanging the equipment above the protected object, it can realize full flooding and local protection, and the equipment can be filled repeatedly

III. conclusion

as a designer, we should consider the characteristics of the cable tunnel and choose the most suitable fire extinguishing device for how to select and use the cement pressure testing machine. In the face of various types of fire-extinguishing systems, it is also necessary to conduct in-depth investigation and comprehensive comparison in combination with practice. (end)

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