The dry powder fire extinguishing system is a fire extinguishing system in which the dry powder ** source is connected to a fixed nozzle through the conveying pipeline, and the dry powder is sprayed through the nozzle. The dry chemical fire extinguishing system is one of the four traditional fixed fire extinguishing systems and is widely used.
1. System fire extinguishing mechanism.
Although the types of fire extinguishing agents in powder fire extinguishing systems are different, the fire extinguishing mechanism is nothing more than chemical inhibition, isolation cooling and suffocation. This section focuses on the types of extinguishing agents and their extinguishing mechanisms for dry chemical fire extinguishing systems.
1) Dry powder fire extinguishing agent.
Dry powder fire extinguishing agent is a solid powder fire extinguishing agent made by grinding and mixing fire extinguishing base materials (such as baking soda, ammonium phosphate, etc.) and appropriate flow additives (magnesium stearate, mica powder, talcum powder, etc.) and moisture-proof agents (silicone oil) under certain process conditions.
2) Types of dry powder fire extinguishing agents.
1) Ordinary 1,000 powder fire extinguishing agent.
This type of fire extinguishing agent can extinguish Class B, Class C, and E fires, so it is also known as BC dry powder fire extinguishing agent. Dry powder fire extinguishing agents that belong to this category are:
1) Sodium salt dry powder fire extinguishing agent (baking soda dry powder) with sodium bicarbonate as the base material
2) Purple potassium dry powder fire extinguishing agent with potassium bicarbonate as the base material.
3) Super potassium salt dry powder fire extinguishing agent based on potassium chloride.
4) Potassium salt dry powder fire extinguishing agent with potassium sulfate as the base material.
5) Mixed dry powder fire extinguishing agent based on sodium bicarbonate and potassium salt.
6) Amino dry powder fire extinguishing agent (Maunex monnex dry powder) based on the reactants of urea and sodium bicarbonate (potassium bicarbonate).
2) Multi-purpose dry powder fire extinguishing agent.
This type of fire extinguishing agent can extinguish Class A, Class B, Class C, and Class E fires, so it is also known as ABC dry powder fire extinguishing agent. Dry powder fire extinguishing agents that belong to this category are:
1) Dry powder fire extinguishing agent with phosphate as the base material.
2) Dry powder fire extinguishing agent based on ammonium phosphate and ammonium sulfate mixture.
3) Dry powder fire extinguishing agent with ammonium polyphosphate as the base material.
3) Special dry powder fire extinguishing agent.
This kind of fire extinguishing agent can extinguish Class D fires, so it is also called Class D special dry powder fire extinguishing agent. The 1,000-powder fire extinguishing agents that belong to this category are:
1) Graphite: Add flow promoter to graphite.
2) Sodium chloride: Sodium chloride is widely used in the production of Class D dry powder fire extinguishing agent, and different additives are selected for different fire extinguishing objects.
3) Sodium bicarbonate: Sodium bicarbonate is the main raw material for making BC dry powder fire extinguishing agent, and some crust materials can also be added to make Class D dry powder fire extinguishing agent.
3) Precautions.
1) BC and ABC dry powder are not compatible.
2) BC dry powder is not compatible with protein foam or chemical foam, because dry powder has a greater destructive effect on protein foam and general synthetic foam.
3) For some gases with strong diffusion, such as hydrogen and acetylene gas, it is difficult to dilute the gas of the whole space after dry powder injection, and it will leave residue for precision instruments and meters, and it is not suitable to extinguish the fire with dry powder.
4) Fire extinguishing mechanism of dry powder.
The dry powder is driven by power gases (nitrogen, carbon dioxide) and fired into the flame to extinguish the fire. In the process of extinguishing the fire, the powder mist contacts and mixes with the flame, and a series of physical and chemical effects occur, and the fire extinguishing mechanism is introduced.
1) Chemical inhibition.
The combustion process is a chain reaction process, and the "·" in 0h· and h· They are the key free radicals to maintain the combustion chain reaction, they have high energy, very lively, but the service life is very short, once generated, immediately trigger the next step of the reaction, the generation of more free radicals, so that the combustion process can continue and expand. When the dry powder fire extinguishing agent is added to the combustion zone and mixed with the flame, when the dry powder powder is in contact with the free radicals in the flame, the OH· and H· are captured, and the free radicals are instantaneously adsorbed on the surface of the powder. When a large amount of powder is sprayed into the flame in the form of a mist, the free radicals in the flame are adsorbed and converted in large quantities, so that the number of free radicals is sharply reduced, resulting in the interruption of the combustion reaction chain, and finally the flame is extinguished.
2) Isolation.
The solid powder ejected by the dry chemical extinguishing system covers the surface of the combustible material and constitutes an insulating layer that hinders combustion. Especially when the powder cover reaches a certain thickness, it can also play a role in preventing re-ignition.
3) Cooling and asphyxiation.
When the dry powder fire extinguishing agent is sprayed to the combustion area under the impetus of the power gas to extinguish the fire, the base material of the dry powder fire extinguishing agent will undergo a series of decomposition reactions under the action of the flame high temperature, and the sodium salt and potassium salt dry powder absorb part of the heat in the combustion zone and release water vapor and carbon dioxide gas, which plays the role of cooling and diluting the combustible gas. Compounds such as phosphate have the effect of causing charring, it attaches to the surface of the igniting solid and can be charred, and the carbide is a poor conductor of heat that can slow down the combustion process and reduce the temperature of the flame.
2. System composition and classification.
According to the different fire extinguishing methods, protection conditions, driving gas storage methods, etc., dry powder fire extinguishing systems can be divided into more than ten types, and this section mainly introduces the system composition and classification.
1) The composition of the dry powder fire extinguishing system.
Dry chemical extinguishing systems are similar in composition to gas extinguishing systems. The dry powder fire extinguishing system consists of two parts: dry powder fire extinguishing equipment and automatic control. The former is composed of a dry powder storage container, a driving gas cylinder group, a starting gas cylinder group, a reducing valve, a pipeline and a nozzle. The latter consists of a fire detector, a signal feedback device, an alarm controller, etc.
2) Classification of dry powder fire extinguishing system.
1) Classification according to the mode of application.
1.Fully submerged dry chemical fire extinguishing system.
The total submerged dry powder fire extinguishing system refers to the system form of releasing the dry powder fire extinguishing agent to the entire protection area and implementing fire extinguishing by establishing a fire extinguishing concentration in the protection area space. The system is characterized by the overall protection of the protection area, which is suitable for small enclosed spaces, where the fire burning surface is not easy to determine and will not re-ignite, such as oil pump room and other occasions.
2.Dry chemical extinguishing system for local application.
Topical dry chemical extinguishing systems refer to systems that extinguish fire by spraying fire extinguishing agents directly onto the flame or burning surface through nozzles. When it is not advisable to establish a fire extinguishing concentration in the whole room or only protect a certain local range, a certain equipment, outdoor fire hazard places, etc., a dry powder fire extinguishing system can be applied locally, such as an open-top tank or tank for protecting Class A, B and C liquids, electrical equipment and other places that are not afraid of powder pollution.
2) Classification according to the design situation.
1.Designed dry chemical fire extinguishing system.
The designed dry powder fire extinguishing system refers to the system form determined by design calculation according to the specific situation of the protected object. All parameters in the system are determined by design and the individual component equipment models are selected as required. Generally, large protection places or places with special requirements should adopt a design-type system.
2.Prefabricated dry chemical extinguishing system.
Prefabricated dry powder fire extinguishing system refers to a series of complete sets of dry powder fire extinguishing equipment produced by the factory, the specifications of the system are pre-designed after the fire extinguishing test of the protected object, that is, all the design parameters have been determined, and only need to be selected when used, without complex design calculations. For places where the object of protection is not very large and there are no special requirements, prefabricated systems are generally selected.
3) Classification according to the protection of the system.
1.Combined dispensing system.
When there are several protected objects in an area and each protected object does not spread after a fire, a combined distribution system can be used, that is, multiple protected objects can be protected at the same time with one system.
2.Unit independent system.
If the spread of the fire cannot be improved, a separate set of system protection should be set up for each protection object, that is, a unit independent system.
4) Classification according to the storage mode of driving gas.
1.Gas storage dry chemical fire extinguishing system.
The gas storage dry powder fire extinguishing system refers to the driving gas (nitrogen, carbon dioxide) is stored separately in the gas storage cylinder for fire extinguishing, and then the driving gas is filled into the dry powder storage tank, and then the dry powder spray is driven to extinguish the fire. Dry chemical fire extinguishing systems mostly use this system form.
2.Pressure storage dry powder fire extinguishing system.
The storage pressure dry powder fire extinguishing system refers to storing the driving gas and the dry powder fire extinguishing agent in the same container, and directly starting the dry powder storage tank when extinguishing the fire. This system structure is simpler than that of a gas storage system, but requires that the drive gas must not leak.
The gas-fired dry powder fire extinguishing system means that the driving gas does not use compressed gas, but ignites the solid fuel in the gas generator in the event of a fire, and drives the dry powder injection to extinguish the fire through the gas pressure generated by combustion.
3.Gas-fired dry chemical extinguishing system.
3. The working principle and scope of application of the system.
The starting mode of dry powder fire extinguishing system can be divided into automatic control and manual control, and this section mainly introduces the working principle and scope of application of various control methods.
1) The working principle of the system.
1) Automatic control mode.
After the protection object is on fire, the temperature rises to the specified value, the detector sends a fire signal to the controller and then the controller opens the corresponding alarm equipment (such as sound and light and alarm bell), when the starting mechanism receives the start signal of the controller, the starting bottle is opened, the nitrogen in the starting bottle is opened through the pipeline to the bottle head valve of the high-pressure driven gas cylinder group, the high-pressure driving gas in the bottle enters the gas collector pipe, enters the pressure reducing valve through the high-pressure valve, and after the pressure is reduced to the specified pressure, it enters the dry powder storage tank through the inlet valve and stirs the dry powder fire extinguishing agent in the tankWhen the pressure in the dry powder tank rises to the specified pressure value, the constant pressure action mechanism starts to act, opens the ball valve at the outlet of the dry powder tank, and the dry powder fire extinguishing agent is sprayed to the fire object through the main door, the selection valve, the powder pipe and the nozzle, or the surface of the fire object is shot through the spray gun to extinguish the fire.
In practical applications, no matter what type of detector, due to its own quality and environmental influence, there is inevitably the possibility of false alarms in long-term operation. In order to improve the reliability of the system and avoid the malfunction of the fire extinguishing system caused by the false alarm of the detector to the greatest extent, which brings unnecessary economic losses, two different types or two groups of detectors of the same type are usually set up in the protection place for composite detection. The fire extinguishing system can only be activated if two different types or two sets of fire detectors of the same type detect the presence of a fire in the protected area.
2) Manual control mode.
Manual activation is a means of activating the fire extinguishing system when a person in the protection area or near the protected object discovers a fire danger. Therefore, it is required that the manual actuator be installed close to the protective area or the object to be protected, and at the same time in a position that can ensure the safety of the operator. In order to prevent the operator from pressing other buttons by mistake in an emergency, it is required that all manual actuation devices should be clearly marked with the name of the corresponding protection zone or protection object.
Manual emergency stop is a means of stopping the system when it is found that the sprinkler is not needed or cannot be applied during the delay period after the system is activated. There are many reasons for this, such as someone pressing the start button by mistake; If the fire situation does not reach the point where it is necessary to activate the fire extinguishing system, other simple fire extinguishing methods can be used instead; There are still people in the area who have not yet been completely evacuated. As soon as the system starts spraying the extinguishing agent, the manual emergency stop device is ineffective. After the emergency stop device is activated, although the system control device stops the follow-up action, the pressurization of the dry powder storage tank still continues, and the system is in a state of readiness, at this time, it is still necessary to restart the system and release the fire extinguishing agent, for example, someone has pressed the emergency stop button by mistake, and the person trapped in the protection area is required to start the manual start device again after using the manual emergency stop device.
Depending on the object and occasion, the fire extinguishing system can also be linked with temperature and smoke detectors. Semi-automatic operation can also be used in places where people are often occupied, that is, the fire is manually confirmed, and all the powder spraying and extinguishing actions are completed by activating the manual button.
2) Scope of application.
The dry chemical fire extinguishing system is fast and reliable, and is suitable for flammable liquids where the flame spreads rapidly; It has low cost, small footprint, and no freezing, which is especially suitable for the north of our country where there is no water and cold.
1) Scope of application of the system.
1) Gas fire that can cut off the gas source before extinguishing the fire.
2) Flammable, flammable liquids and meltable solid fires.
3) Combustible solid surface fires.
4) Fire of live equipment.
2) Scope of application of the system.
1) Nitrocellulose, explosives, and other chemicals that can oxidize rapidly without air and strong oxidants.
2) Potassium, sodium, magnesium, titanium, zirconium and other reactive metals and their hydrides.
Fourth, the system design parameters.
The dry powder fire extinguishing system relies on the driving gas (inert gas) to drive the dry powder, and the volume of the dry powder solids is much smaller than that of the driving gas, which is macroscopically similar to that of a gas fire extinguishing system, so the carbon dioxide fire extinguishing system design data can be used. The enclosure structure of the protection zone has a certain fire resistance limit and strength, which is the basic condition to ensure fire extinguishing.
a) General provisions.
1) Dry powder fire extinguishing system can be divided into total submerged fire extinguishing system and local application fire extinguishing system according to the application method. A total submerged fire extinguishing system should be used to rescue a fire in a closed space, and a local fire extinguishing system should be used to extinguish a fire with a specific protected object. The protective area with a total submerged fire extinguishing system shall comply with the following provisions:
1) The total area of the opening of the protection zone that cannot be automatically closed when spraying dry powder shall not be greater than 15% of the total inner surface area of the protection zone, and the opening shall not be located on the bottom surface.
2) The fire resistance limit of the enclosure structure and doors and windows of the protection area shall not be less than 050h, the fire resistance limit of the ceiling should not be less than 025 h;The allowable pressure of the envelope structure, doors and windows should not be less than 1200 pa.
2) The protection object of the local application fire extinguishing system shall comply with the following provisions:
1) The air flow speed around the protected object should not be greater than 2m s, and wind blocking measures should be taken if necessary.
2) Between the nozzle and the protected object, there should be no obstruction within the spray angle of the nozzle.
3) When the object of protection is a flammable liquid, the distance from the liquid level to the edge of the container shall not be less than 150 mm. When there are combustible gases and flammable and combustible liquid sources in the protection area or protection objects, the source of gas and liquid must be cut off before or at the same time when the dry powder fire extinguishing system is started.
Combustible gas, flammable, flammable liquid and meltable solid fire extinguishing agent should be used for sodium bicarbonate dry powder fire extinguishing agent; Ammonium phosphate dry powder fire extinguishing agent should be used for combustible solid surface fires.
The storage capacity of the extinguishing agent of the combined distribution system shall not be less than the storage capacity of the protection area or object of protection with the largest required storage capacity.
The sum of the protection zones and protection objects protected by the combined distribution system shall not exceed 8. When the sum of the protection area and the protected object exceeds 5, or when it cannot be restored to normal working state within 48 hours after spraying, the fire extinguishing agent should have a reserve amount. The reserve amount should not be less than the storage capacity for which the system is designed.
The standby dry powder storage container should be connected to the system pipe network and can be switched with the main dry powder storage container.
2) Total submerged fire extinguishing system.
The design concentration of fire extinguishing agent for a fully submerged fire extinguishing system shall not be less than 065kgm。The dry powder spraying time of the fully submerged fire extinguishing system should not be greater than 30s. The sprinkler head of the fully submerged fire extinguishing system should be arranged so that the fire extinguishing agent in the protection area should be evenly distributed. The protection area should be provided with a pressure relief port, and should be located on the outer wall, and its height should be greater than the net height of the protection area 2 3.
3) Local application of fire extinguishing system.
Topical fire extinguishing systems can be designed using either the area method or the volumetric method. When the ignition part of the protected object is flat, the area method should be used; When it is not possible to completely cover all surfaces using the area method, the volume method should be used.
The dry powder spraying time of indoor local fire extinguishing systems should not be less than 30s, and the dry powder spraying time of outdoor or indoor local fire extinguishing systems with a risk of re-ignition should not be less than 60s.
1) When the area method is adopted, the following provisions should be met:
1) The calculated area of the protected object shall be taken as the vertical projection area of the protected surface.
2) The dry powder conveying rate and the corresponding protection area of the overhead nozzle shall be determined by the distance from the outlet of the nozzle to the surface of the protected object, and the protective area of the grooved nozzle shall be determined by the dry powder conveying rate selected by the design.
2) When the volume method is adopted, the following provisions should be met:
1) The calculated volume of the object of protection shall be the volume of the hypothetical enclosure. The underside of the enclosure should be the actual underside; The sides and tops of the enclosure should not be less than 15 m
4) Prefabricated fire extinguishing devices.
1) Prefabricated fire extinguishing devices shall comply with the following requirements.
1) The storage capacity of fire extinguishing agent shall not be greater than 150 kg.
2) The length of the pipe shall not be greater than 20 m.
3) The working pressure shall not be greater than 25 mpa。
2) A protective area or protection object should be protected by a set of prefabricated fire extinguishing devices.
3) The prefabricated fire extinguishing devices used in a protection area or protection object shall not exceed 4 sets, and shall be activated at the same time, and the difference in action response time shall not be greater than 2s.
4) Pipe network calculation:
1) The pressure at the beginning of the pipe network (the outlet of the outlet of the dry powder storage container) should not be greater than 25 MPa, the working pressure of the sprinkler at the most unfavorable point of the pipe network should not be less than 01 mpa。
5. System components and setting requirements.
1) System components.
The storage device is composed of a dry powder storage container, a container valve, a safety pressure relief device, a driven gas storage bottle, a bottle head valve manifold, a pressure reducing valve, a pressure alarm and control device, etc., and shall comply with the following requirements:
1) The dry powder storage container shall comply with the relevant provisions of the "Regulations for the Safety and Technical Supervision of Fixed Pressure Vessels" (TSG21-2016), and the driving gas storage cylinder and its filling coefficient shall comply with the provisions of the "Regulations for the Safety and Technical Supervision of Gas Cylinders (TSG RO006-2014)".
2) The design pressure of the dry powder storage container can be taken 16MPa or 25 MPa pressure level; The loading factor of its dry powder fire extinguishing agent should not be greater than 085, and its pressurization time should not be greater than 30s.
3) The operating pressure and rated discharge of the safety pressure relief device shall be implemented in accordance with the General Technical Conditions for Dry Powder Fire Extinguishing Systems and Components (GB 16668-2010).
4) The dry powder storage container should meet the requirements of driving gas coefficient, dry powder storage capacity, dry powder conveying rate and pressure at the outlet of the output container valve.
The driving gas should be inert gas, and nitrogen should be selected; The moisture content of carbon dioxide should not be greater than 0015% (m m), the moisture content of other gases shall not be greater than 0006%(m/m);The driving pressure must not be greater than the maximum working pressure of the dry powder storage container.
Storage units should be arranged in such a way as to facilitate inspection and maintenance, and should be protected from direct sunlight, and their ambient temperature should be -20 50.
Storage devices should be located in dedicated storage rooms. The setting of the room of the dedicated storage device shall comply with the following requirements: It should be close to the protection area, and the exit should lead directly to the outside or evacuation route; The fire resistance grade should not be lower than the grade; It is advisable to keep it dry and well ventilated, and emergency lighting should be provided.
When measures such as moisture-proof, anti-freezing, and fire-proof are taken, the storage device for the local application of the fire extinguishing system can be set up in a fixed safety fence.
2) System setting requirements.
The connection of the drive gas pipeline must be firm, and each section of the pipeline installed should be purged to ensure that the pipe is clean before the pressure reducing valve and through the filter.
Dry powder fire extinguishing agent must be filled according to the specified variety and quantity, filling is best operated in sunny days, avoid operating in rainy days, and should be filled at one time, immediately sealed.
The working pressure of the nozzle should meet the product performance requirements, generally (0.).5~7)x10*pa。The sprinklers of the full submersion system should be evenly distributed, and the spacing of the sprinklers should not be greater than 225 m, the distance between the sprinkler head and the wall is not more than 1m, and the protection volume of each sprinkler is not more than 14m.
Note: 10* is to the 4th power of 10
