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Gas fire extinguishing system for LNG terminal: prefabricated non-pipe network heptafluoropropane total flooding fire extinguishing system


2015-11-30


Selection of gas fire extinguishing system for LNG terminal :

In GB 50370-2005 "Code for Design of Gas Fire Extinguishing System", three kinds of gas fire extinguishing systems are listed, namely: heptafluoropropane fire extinguishing system, IG541 mixed gas fire extinguishing system and hot aerosol prefabricated fire extinguishing system. According to the actual characteristics and specification requirements of the large number of protected areas and the small area of ​​each protected area in this project, a prefabricated non-pipe network heptafluoropropane total flooding fire extinguishing system is selected. The fire extinguishing system is a prefabricated, fully submerged fire extinguishing system, which is an independent complete set. Compared with the fire extinguishing system with pipe network, it has the advantages of flexible and convenient installation, beautiful appearance, no loss of fire extinguishing agent in the pipe network, high fire extinguishing efficiency, fast speed, and no fire extinguishing system. Pollution and other characteristics, it is a fire-fighting equipment without pipe network, portable, movable, and automatic fire extinguishing, which can protect a small area. The non-pipe network fire extinguishing system does not have a storage tank room, and the gas storage tanks and the entire system are set in the protected area. When a fire occurs, the system sprays the fire extinguishing agent directly into the protected area, which is convenient and quick. Suitable for protection areas in smaller spaces such as computer rooms, archives, valuables warehouses, and telecommunication centers.

Prefabricated ductless heptafluoropropane total flooding fire extinguishing system: fire extinguishing mechanism of heptafluoropropane

① Cool down the protected area

The heptafluoropropane fire extinguishing agent is stored in the container in the form of liquid under high pressure. When it is sprayed out of the nozzle, the liquid fire extinguishing agent quickly turns into a gaseous state, which needs to absorb a large amount of heat, which reduces the temperature in the protection zone and around the flame.

②Extinguishing agent inhibits combustion reaction

Heptafluoropropane fire extinguishing agent is composed of macromolecules. The molecular chains in the molecules are broken at high temperature, and its decomposition products can interrupt the chain transfer of chemical chain reactions in the combustion process, thereby inhibiting the chemical reactions in the combustion process and implementing fire extinguishing.

③Consumption of oxygen

The spraying of fire extinguishing agent in the protected area reduces the concentration of oxygen, thereby reducing the speed of combustion.

Prefabricated non-pipe network heptafluoropropane total flooding fire extinguishing system: fire extinguishing system setup

The design protection objects are transformer room, low-voltage power distribution room, control room, equipment room and UPS room, a total of 5 protection areas, and 5 sets of prefabricated non-pipe network heptafluoropropane fire extinguishing devices are used for protection. The design filling pressure of the system is 2.5MPa, and the design temperature of the fire extinguishing system is 20°C. The fire resistance rating of the enclosure structure of the protection zone and doors and windows should not be lower than 0.5h, and the fire resistance rating of the suspended ceiling should not be lower than 0.25h. The allowable pressure of internal pressure should not be lower than 1200Pa. The door of the protected area should be opened in the direction of evacuation and can be closed by itself, and the door used for evacuation must be able to be opened from the protected area. The unit volume of fire extinguishing agent in the system should not be greater than 1120kg/m3. The protection area should be provided with a pressure relief port, which should be located on the outer wall, and its height should be more than 2/3 of the net height of the protection area. Before the fire extinguishing agent is sprayed, other openings in the protected area except the pressure relief port should be able to close by themselves.

The evacuation passages and exits in the protected area should be equipped with emergency lighting and evacuation signs. At the entrance of the protection area, there are sound and light alarms and fire extinguishing agent discharge indicator lights, as well as permanent signs of the corresponding gas fire extinguishing system used in the protection area.

Prefabricated non-pipe network heptafluoropropane total flooding fire extinguishing system control method:

The fire extinguishing system has two control methods, automatic and manual, and the work flow of the fire extinguishing system is shown in Figure 1.

Fire extinguishing system workflow

①Automatic control

When there is no one in the protected area, turn the control mode switch in the automatic fire extinguishing controller to the "automatic" position, and the fire extinguishing system is in the automatic control state. Each protection area is equipped with two independent detection circuits. When the first detector in the protection area sends out a fire signal, an alarm will be issued to indicate the location of the fire. When the second detector also sends out a fire signal, the automatic fire extinguishing controller starts to enter the delay stage, and at the same time sends out a linkage command to turn off the linkage equipment and all power supplies in the protected area except emergency lighting. After an automatic delay of 30s (adjustable from 0 to 30s, this stage is used to turn off ventilation, air conditioning, doors and windows and all power supplies in the protected area except emergency lighting), send a fire extinguishing command to the electromagnetic starter controlling the fire area, and open the container valve , Open the heptafluoropropane gas storage cylinder, and carry out fire extinguishing operations to the protected area. At the same time, the alarm detector receives the feedback signal from the pressure signal generator, and the spray indicator light on the control panel is on.

② Electric manual control

When someone is working or on duty in the protected area, turn the control mode switch in the automatic fire extinguishing controller to the "manual" position, and the fire extinguishing system is in the manual control state. When the fire detector is in the manual state, when a fire occurs in the protection area, the fire detector only sends out an alarm signal and does not output an action signal. After the person on duty confirms the fire alarm, he can press the manual start button in the automatic fire extinguishing controller, or start the device. The emergency start button outside the door of the protected area can activate the fire extinguishing system according to the above procedures to implement fire extinguishing. In the automatic control state, electric manual control can still be realized. All personnel in the protection zone must be evacuated before the implementation of electrical manual control. When a fire alarm occurs and it is found that the fire extinguishing system does not need to be activated within the delay time, the emergency stop button on the automatic fire extinguishing controller or in the manual control box can be pressed to stop the fire extinguishing command and stop the system fire extinguishing program.

The composition of the fire extinguishing device of the prefabricated non-pipe network heptafluoropropane total flooding fire extinguishing system :

It is mainly composed of gas storage cylinder group, electromagnetic starter, pressure signal generator, connecting hose, box and nozzle, etc. The structure of the heptafluoropropane fire extinguishing device without pipe network is shown in Figure 2

The structure of heptafluoropropane fire extinguishing device without pipe network

①Gas cylinder group

The gas storage cylinder group is the main part of the automatic fire extinguishing system for storing and releasing fire extinguishing agent, and it is filled with heptafluoropropane and pressurized nitrogen according to the design requirements. When a fire breaks out, the fire extinguishing agent is released to extinguish the fire. The gas storage cylinder group consists of gas storage containers (heptafluoropropane gas storage cylinders, pressurized nitrogen gas storage cylinders), container valves, siphon tubes, protective caps, etc. The storage container is a steel seamless gas storage cylinder, and heptafluoropropane is stored in the container in a liquid state under high pressure. When a fire occurs, the container valve is opened by the electromagnetic starter, and heptafluoropropane is sprayed to the protection area through the container valve outlet.

In an emergency, you can use your fingers to hold the handle of the safety buckle, pull out the safety buckle, tap the manual button to open the container valve, and release the heptafluoropropane gas directly.

② Electromagnetic starter

It consists of an electromagnet, a release mechanism and an action mechanism. When a fire occurs, the fire alarm controller outputs a DC current to activate the electromagnet, which activates the release mechanism to make the action mechanism move, and the knife pierces the sealing diaphragm of the container valve to release the heptafluoropropane fire extinguishing agent.

③Pressure signal generator

It is composed of body, jog switch, spring, piston and so on. The contact of the pressure signal generator is usually open. When the gas fire extinguishing agent is released, the pipeline pressure pushes the piston of the pressure signal generator, turns on the switch, and sends a working signal to the fire extinguishing control system, indicating that the system has started.

④ Connect the hose

It is mainly composed of high-pressure rubber hose and spherical joint, and the connecting hose is the connecting pipeline between the container valve and the liquid one-way valve.

⑤Box and nozzle

The nozzle is a fully submerged nozzle, which is installed on the upper end of the box and is used to spray fire extinguishing agent. The box body is made of Q235 cold-rolled steel plate, and the surface is electrostatically sprayed. It is used to install storage bottle groups, high-pressure hoses, starters, nozzles and other components. Wire hole for connecting external equipment.

Main technical parameters of prefabricated non-pipe network heptafluoropropane total flooding fire extinguishing system

Article 3.3.4 of GB 50370-2005 "Code for Design of Gas Fire Extinguishing System": The fire extinguishing design concentration should be 9% for protection areas such as oil-immersed transformer room, power distribution room with oil switch and self-contained generator room. Article 3.3.5: The design concentration for fire extinguishing in protective areas such as communication room and electronic computer room should be 8%. Article 3.3.7: In protection areas such as communication machine room and electronic computer room, the design discharge time should not be greater than 8s; in other protection areas, the design discharge time should not be greater than 10s. Article 3.3.8: The impregnation time for fire extinguishing shall meet the following requirements: 5 minutes for electrical equipment fires in the communication room and electronic computer room; 10 minutes for other solid surface fires. The design parameters of the fire extinguishing system in each protection area are shown in Table 1.

3.7 Design calculation of fire extinguishing device

① Calculation of fire extinguishing design dosage

In the formula, m——the design amount of fire extinguishing or inertization, kg

K——altitude correction factor

V——net volume of protection zone, m3

n—mass volume of superheated steam of fire extinguishing agent at 101kPa and the lowest ambient temperature in the protection zone, m3/kg

c1——fire extinguishing design concentration or inactivation design concentration, %

q - the minimum ambient temperature in the protection zone, ℃

② System off! Calculation of sufficient dose storage

m0=m+Dm1+Dm2       (3)

In the formula, m0——system fire extinguishing agent storage capacity, kg

Dm1——the remaining amount of fire extinguishing agent in the storage container, kg

Dm2——the remaining amount of fire extinguishing agent in the pipeline, kg

③ Calculation of the area of ​​the pressure relief port in the protection zone

In the formula, A—area of ​​pressure relief port, m2

qm——the average discharge rate of fire extinguishing agent in the protected area, kg/s

p——The allowable pressure of the internal pressure of the enclosure structure, Pa

t——Designed discharge time of fire extinguishing agent, s

④Calculation example

Taking the control room as an example, the control room is manned, and q=20°C is set. The Dm1 of each protection area is calculated as 3kg, and the Dm2 is calculated as 0kg. The allowable pressure of the control room enclosure structure to withstand the internal pressure is 1200Pa.

From formulas (1) to (5), we can get:

Except for the control room, the rest of the protection areas are unattended, and it is calculated as q=5°C; the volume, fire extinguishing design concentration and design discharge time parameters of other protection areas are shown in Table 1. The design and calculation results of each protection zone are shown in Table 2.

 

Prefabricated non-pipe network heptafluoropropane total flooding fire extinguishing system precautions

①The products and components used in the design of the gas fire extinguishing system must meet the requirements of relevant national standards and regulations.

②The protected area after fire extinguishing should be ventilated, and the number of ventilation should not be less than 5 times/h.

③ Air respirators should be equipped in the manned control room.