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Application of Foam Spray Fire Extinguishing System in Power System


2012-11-22


Abstract: The foam spray fire extinguishing system uses high-efficiency synthetic foam liquid as a fire extinguishing agent , and sprays it onto the fire extinguishing object under a certain pressure through a special atomizing nozzle to quickly extinguish the fire. It is a fire extinguishing system especially suitable for power transformers. This paper mainly makes a brief description of the structure, working principle and design application of the system.

Key words: foam spray; system structure; principle; design

1 System overview

The foam spray fire extinguishing system absorbs the advantages of water mist fire extinguishing and foam fire extinguishing, and is a "efficient, economical, safe and environmentally friendly" fire extinguishing system. In terms of structural composition, it adopts the principle of pressure storage and driving, and in terms of design and application, it is similar to the water spray fire extinguishing system.

The characteristics of the foam spray fire extinguishing system are: it adopts advanced and efficient fire extinguishing agent, which can be used to extinguish Class A, B, and C fires; it is especially suitable for extinguishing fires such as hot oil flowing and power transformers; the amount of fire extinguishing agent used is small, biodegradable, and does not pollute The environment has good insulation performance and has no impact on the equipment; the gas storage pressure type power source is adopted, and no fire pool and water supply equipment are required; the fire extinguishing efficiency is high, safe and reliable, and the installation, operation and maintenance are simple.

Foam spray fire extinguishing system can be widely used in the following places: oil-immersed power transformers; oil-fired boiler rooms; oil-fired generator rooms; small oil depots; small oil storage tanks;

2 System structure composition and working principle

2.1 Structural Composition

The foam spray fire extinguishing system uses high-efficiency synthetic foam fire extinguishing agent to achieve the purpose of fire extinguishing through pneumatic spraying. The fire extinguishing system consists of a liquid storage tank, a synthetic foam fire extinguishing agent, a starting device, a nitrogen drive device, an electromagnetic control valve, a water mist nozzle and a pipe network. and so on.

 

 2.2 Working principle

The foam spray fire extinguishing system uses high-efficiency synthetic foam fire extinguishing agent stored in the liquid storage tank. When a fire occurs, it is controlled by automatic fire alarm linkage control or manual control; driven by high-pressure nitrogen, the synthetic foam fire extinguishing agent in the liquid storage tank is pushed; after passing through the pipeline and water mist nozzle, the foam fire extinguishing agent is sprayed on the protected object A fire extinguishing system that rapidly cools the surface of the protected object and produces a layer of flame-retardant film to isolate the protected object and the air to quickly extinguish the fire. The fire extinguishing system absorbs the characteristics of the water spray fire extinguishing system and the foam fire extinguishing system. In fact, it is similar to the water mist fire extinguishing system, but the fire extinguishing agent used is different. Since the foam spray fire extinguishing system uses the nitrogen stored in the steel cylinder to directly start the fire extinguishing agent in the liquid storage tank, and sprays out through the pipe and nozzle to extinguish the fire, it has the cooling, suffocation and emulsification functions of the water mist fire extinguishing system and the foam fire extinguishing system at the same time. , isolation and other fire extinguishing mechanisms. The whole fire extinguishing system has simple equipment and compact arrangement.

 

 2.3 Control method

Generally, the foam spray fire extinguishing system should be equipped with three control modes: automatic, manual and emergency operation. The bottle head valve of the high-pressure nitrogen drive device can be opened by linkage control of the fire alarm controller or manual control. The high-pressure nitrogen reaches the predetermined working pressure through decompression, and the nitrogen is delivered to the liquid storage tank. When the pressure in the tank increases to the working pressure, the solenoid valve at the outlet of the liquid storage tank is opened immediately, and the fire extinguishing agent is sprayed to the protected object through the pipeline and the water mist nozzle. In addition, a mechanical emergency start operation mode should be set up in the equipment room.

 3 design application

3.1 General provisions

3.1.1 The design dosage of synthetic foam fire extinguishing agent required by the foam spray fire extinguishing system to put out a fire should be calculated according to the following formula:

M=S×W×T

In the formula: M—the design dosage of synthetic foam fire extinguishing agent required by the fire extinguishing system to extinguish a fire (L);

S——horizontal projected area of ​​the protected object (m2);

W——the supply strength of the synthetic foam fire extinguishing agent of the fire extinguishing system (L/min m2);

T——Continuous supply time (min) of the synthetic foam fire extinguishing agent of the fire extinguishing system.

3.1.2 The supply intensity and continuous supply time of foam fire extinguishing agent in the fire extinguishing system should not be less than those specified in Table 1.

Table 1 Supply intensity and continuous supply time of foam fire extinguishing agent

 

protection object Water mist nozzle setting height (m) Synthetic foam fire extinguishing agent supply strength (L/min·m 2 ) Continuous supply time (min)
Oil-immersed power transformer oil-fired boiler room, oil-fired generator room, small oil depot, small oil storage tank, small car garage, small repair, garage, ship engine room and engine room ≤10 4 10

 

When the height of the water mist nozzle is higher than 10m, the minimum supply intensity of foam fire extinguishing agent shall be determined by experiment.

3.2 Water mist nozzle and its arrangement

3.2.1 The protection area and spacing of the water mist nozzles of the fire extinguishing system shall meet the requirements in Table 2.

Table 2 Protection area and spacing of water mist nozzles

 

name Water mist nozzle setting height (m) The maximum protection area of ​​a single water mist nozzle (m 2 ) Maximum horizontal distance of water mist nozzle (m) Working pressure (Mpa)
Water mist nozzle ≤10 12.5 3.6 ≥0.35

 

When the installation height of the water mist nozzle is greater than 10m, the maximum protection area of ​​a single water mist nozzle and the maximum horizontal distance of the water mist nozzle shall be determined by the test.

3.2.2 The arrangement of water mist nozzles of the fire extinguishing system shall meet the following requirements

(1) The layout of the water mist nozzles shall be determined according to the design supply strength of the synthetic foam fire extinguishing agent, the protection area and the characteristics of the water mist nozzles;

(2) The synthetic foam fire extinguishing agent should be sprayed directly on the protected object;

(3) The safe net distance between water mist nozzles, pipelines and live (exposed) parts of electrical equipment shall comply with the relevant current national standards.

3.3 Other regulations

3.3.1 The fire extinguishing system shall be equipped with automatic, manual and mechanical emergency operation modes. Under automatic control status, the response time of the fire extinguishing system should not exceed 60s.

3.3.2 The water head loss per unit length of the fire extinguishing system pipeline can be calculated according to the following formula:

Unit length of fire extinguishing system piping

 

In the formula: i——the head loss per unit length of the pipeline (KPa/m);

dj—the calculated inner diameter of the pipe (m);

qg - water supply design flow rate (m3 s);

Ch——Haicheng-Williams coefficient. 130 for copper pipes and stainless steel pipes, 100 for ordinary steel pipes and cast iron pipes.

3.3.3 The flow rate of a single water mist nozzle should be calculated according to the following formula:

 

In the formula: q—the flow rate of a single water mist nozzle (L min);

P - the working pressure of the water mist nozzle (MPa);

K——The flow coefficient of the water mist nozzle.

3.3.4 The calculated number of water mist nozzles required for the protection object shall be determined according to the following formula:

 

In the formula: n—the calculated number of water mist nozzles required to protect the object.

3.3.5 The liquid storage tank, starting device and nitrogen driving device of the fire extinguishing system shall be installed in the special equipment room. The indoor temperature of the equipment room should be kept above 0°C; its fire safety should meet the relevant requirements of the current national standards.

3.3.6 For the selection of pipe materials for liquid supply pipelines, stainless steel pipes should be used for wet parts, and hot-dip galvanized steel pipes should be used for dry parts.

3.3.7 The live insulation performance inspection of the fire extinguishing system shall comply with the provisions of the current national standard GB/T12113 on the measurement of contact current and protective conductor current.

3.3.8 The design of the automatic fire alarm system linked with the fire extinguishing system shall comply with the relevant provisions of the current national standard GB50116 for the design of automatic fire alarm systems.

4 foam fire extinguishing agent

4.0.1 The high-efficiency synthetic foam fire extinguishing agent selected by the foam spray fire extinguishing system should meet the requirements in Table 3 for its physical and chemical properties.

Table 3 Physical and chemical properties of foam fire extinguishing agents

project Require
Freeze-thaw resistance (synthetic foam fire extinguishing agent not affected by freeze-thaw) No visible layered heterogeneity or precipitate
pH value 6.0~9.5
Sediment (volume%) before aging ≤0.25; sediment can pass through 180μm sieve
after aging ≤1.0; sediment can pass through 180μm sieve
fluidity Flow rate greater than standard reference liquid
Foam coefficient ≥5.0
25% solution time min ≥3.5
Fire extinguishing time (min) petrol fire ≤5.0
25% anti-burning time (min) petrol fire ≥10.0

 

4.0.2 The service life of synthetic foam fire extinguishing agent should not be less than 5 years.

5 review

The foam spray fire extinguishing system is a new generation of fire protection products designed and produced by absorbing the working characteristics and technical principles of water spray fire extinguishing, water spray fire extinguishing, gas fire extinguishing and foam fire extinguishing systems. Its biggest advantage lies in its flexible combination and simple structure. Users can flexibly choose corresponding liquid storage tanks and nozzles according to the fire type and protection range of the protected body, and combine them into different fire extinguishing systems. It is a water system with a wide range of choices and flexibility. Fire suppression system. At present, the domestic foam spray fire extinguishing system has been widely used in the protection of large transformers in substations, nuclear power plants, power plants, etc.

The wide application of foam spray fire extinguishing system will provide the society with more perfect fire extinguishing equipment, which will have a huge impetus to my country's fire protection cause. The system is safe and reliable, easy to install and operate; high fire extinguishing efficiency; low cost, low daily maintenance cost, and obvious social and economic benefits.

references:

[1] CECS1562004. Application technical specification for synthetic foam spray fire extinguishing system.

[2] Zhao Yongdai. Discussion on the Application of SP Synthetic Foam Spray Fire Extinguishing System. Water Supply and Drainage, 2001, (3).

(This article is excerpted from HC Fire Network)