Dry fire arresters are protective devices on pipelines that freely allow the flow of gases through a solid fire retardant nozzle, but retard (extinguish) the flame. Their protective effect is based on the phenomenon of flame extinguishing in narrow channels.
The effect of extinguishing flames in narrow channels has been known since 1815, when it was discovered by Humphry Davy, the inventor of the safe mine lamp. Davy found that the flame of a methane-air mixture did not pass through a tube with a diameter of 3.63 mm and that a metal tube was more efficient than a glass one. Later (in 1883), French scientists Möllard and Le Chatelier established the independence of the extinguishing process from the material of the fire retardant.
Reducing the size (diameter) of the channel in which the combustion of the gas mixture occurs leads to an increase in specific heat losses in comparison with the heat release per volume of the burning mixture, a decrease in the combustion temperature in the reaction zone, a decrease in the reaction rate and a decrease in the speed of flame propagation. When heat loss from the combustion zone reaches a certain critical value, the combustion temperature and reaction rate decrease so much that further propagation of combustion of the mixture in a narrow channel becomes impossible. These are the conditions that are created in the fire arrester.
Fire arresters can be in the form of nets or nozzles (Fig. 8.1). Nozzles made of granular bodies (balls, rings, gravel, etc.) or fibers (glass wool, asbestos fibers, etc.) form curved channels. Nozzles in the form of plates made of corrugated foil, spirally rolled tapes, etc. form channels of triangular, rectangular or other cross-sectional shape. Nozzles in the form of plates made of metal ceramics and metal fiber have capillary channels.
The diameter of the nozzle channel or the opening of the fire arrester mesh, at which the heat release from the burning mixture will be equal to the heat loss, is called the critical diameter d Kp . Protection against flame propagation is achieved in a channel whose diameter is less than the critical one
Rice. 8.1. Fire arrester diagrams: A- with horizontal grids; b- with vertical grids;
V- with a nozzle made of gravel, balls, rings; G- with a tape cassette with straight corrugations; d- with a tape cassette with inclined corrugations; e- with a metal-ceramic nozzle; / - frame; 2 - flame retardant element
This size (diameter) of the channel is called quenching d. The calculation of a fire arrester consists of determining the critical and then extinguishing size of the channel. The relationship between the critical and extinguishing dimensions, as well as the design features of the fire arrester, are selected taking into account the relevant experimental data.
Various principles and methods for calculating fire arresters are known, based on various assumptions about the mechanism of heat loss from the flame zone and flame extinguishing.
Method of Ya. B. Zeldovich in domestic practice is generally accepted, but does not apply to special conditions combustion, when there is no heat removal into the heated walls of the channel.
Russian Federation Order of the GUGPS EMERCOM of Russia
NPB 254-99 Fire arresters and spark arresters. General technical requirements. Test methods
set bookmark
set bookmark
FIRE SAFETY STANDARDS
FIRE ARRESTERS AND SPARK ARRESTERS. ARE COMMON
TECHNICAL REQUIREMENTS. TEST METHODS
Flame arrestors and spark arrestors. Fire safety.
General technical requirements. Test methods.
Date of introduction 1999-11-01
DEVELOPED by the All-Russian Research Institute of Fire Defense of the Ministry of Internal Affairs of Russia (Yu.N. Shebeko, V.Yu. Navtsenya, A.K. Kostyukhin, O.V. Vasina), Moscow Institute fire safety Ministry of Internal Affairs of Russia (A.P. Petrov, S.A. Goryachev, V.S. Kluban), department of organization of state fire supervision of the Main Directorate of the State Fire Service (GUGPS) of the Ministry of Internal Affairs of Russia (V.V. Stavnov, V.V. Lepesiy), Gosgortekhnadzor of Russia (A.A. Shatalov).
INTRODUCED AND PREPARED FOR APPROVAL by the department of organization of state fire supervision of the Main Directorate for Fire Safety of the Ministry of Internal Affairs of Russia.
I. SCOPE OF APPLICATION
1. These standards apply to dry-type fire arresters (spark arrestors), and also establish general technical requirements for these devices and methods of their testing.
2. These standards do not apply to:
liquid safety valves;
fire arresters installed on technological equipment, which is associated with the circulation of flammable substances prone to explosive decomposition without an oxidizer.
3. These standards should be applied when designing and manufacturing fire arresters and spark arresters, as well as when conducting certification tests in the field of fire safety and other types of tests established by current standards and regulatory and technical documentation.
II. DEFINITIONS
4. The standards use the following terms with corresponding definitions.
Dry type fire arrestor - device fire protection, which is installed on a fire-hazardous technological apparatus or pipeline, freely passing the flow of a gas-vapor-air mixture or liquid through the flame-extinguishing element and contributing to the localization of the flame.
Dry type spark arrestor is a device installed on exhaust manifolds of various Vehicle, power units and ensuring the capture and extinguishing of sparks in combustion products generated during the operation of furnaces and engines internal combustion.
The time to maintain operability when exposed to flame is the time during which the fire arrester (spark arrestor) is able to maintain operability when heated by a stabilized flame on the flame extinguishing element.
Critical diameter of the flame retardant element - minimum diameter channel of the flame-extinguishing element through which the flame of a stationary vapor-gas mixture can spread.
The safe diameter of the flame-extinguishing element channel is the design diameter of the flame-extinguishing element channel, selected taking into account the safety factor, taken to be at least 2.
III. CLASSIFICATION OF FIRE ARRESTERS AND SPARK ARRESTERS
5. Fire arresters are classified according to the following criteria: type of flame-extinguishing element, installation location, time of maintaining operability when exposed to flame.
5.1. Based on the type of flame extinguishing element, fire arresters are divided into:
mesh;
cassette;
with a flame retardant element made of granular material;
with a flame retardant element made of porous material.
5.2. According to the place of installation, fire arresters are divided into:
tank or end (the length of the pipeline intended for communication with the atmosphere does not exceed three of its internal diameters);
communication (built-in).
5.3. Based on the time they remain operational when exposed to flame, fire arresters are divided into two classes:
Class I - time not less than 1 hour;
Class II - time less than 1 hour.
6. Spark arresters are classified according to the method of extinguishing sparks and are divided into:
dynamic (exhaust gases are cleared of sparks under the influence of gravity and inertia);
filtration (exhaust gases are purified by filtration through porous partitions).
IV. GENERAL TECHNICAL REQUIREMENTS
7. Fire arresters and spark arresters must comply with the requirements of these standards, GOST 12.2.047, GOST 14249, GOST 15150, as well as others regulatory documents, approved in accordance with the established procedure.
V. REQUIREMENTS FOR BASIC CHARACTERISTICS
8. The body of the fire arrester (spark arrestor) and the flame extinguishing element must be free of dents, scratches and defects in the anti-corrosion coating.
9. The weight and size characteristics of the fire arrester (spark arrestor) must correspond to the values specified in the technical documentation.
10. The technical documentation for the fire arrester (spark arrestor) must indicate the types (kind) of combustible mixtures for which they are used to protect, and the conditions of use (pressure, temperature).
Structural elements fire arrester (spark arrestor) must withstand the force loads that occur during the spread of flame, with the pressure for which the product is designed.
11. The design of the fire arrester (spark arrestor) must ensure the operability of its elements throughout the entire period of operation in the temperature range given in the technical documentation.
The design of the fire arrester (spark arrestor) must exclude the possibility of freezing of water (moisture) in the flame-extinguishing element.
12. The design of the fire arrester must provide for the possibility of its periodic cleaning if the device is intended to operate in the presence of mechanical impurities or liquid vapors prone to crystallization or polymerization in the gas flow or liquid.
13. The body of the fire arrester (spark arrestor), as well as detachable and permanent connections must be sealed (should not allow flames, sparks and combustion products to pass through).
14. In the design of a fire arrester (spark arrestor), the size of the slot gaps between the wall of its body and the flame-extinguishing element should not exceed the safe diameter of the channel.
15. Fire arresters (spark arrestors) must be resistant to external and internal corrosive effects of the environments in which they are intended to operate.
16. The design of the fire arrester (spark arrestor) must provide for the possibility of internal inspection, replacement of the flame retardant element, and ease of installation.
17. Structural elements of the fire arrester (spark arrestor) should not be deformed when flaming combustion is localized for a time equal to the time it remains operational when exposed to flame.
18. In fire arresters (spark arrestors) that use granular material as a flame extinguishing element, the granules must have a spherical or similar shape.
Granules must be made of heat-resistant and corrosion-resistant materials.
19. The structural (safe) diameter of the flame-extinguishing element of the fire arrester (spark arrestor) must be no more than 50% of its critical diameter.
20. The design of the fire arrester (spark arrestor) must ensure its reliable fixed mounting on the process equipment or exhaust manifold, taking into account vibration loads acting during the entire period of operation.
21. The following technical documentation must be attached to the manufactured fire arrester (spark arrestor):
technical passport for the product;
manual.
22. The maximum surface temperature of the spark arrester body placed in a flammable environment (flammable gases, vapors, aerosols, dust) must be at least 20% lower than the self-ignition temperature of the specified combustible substances.
23. The time for maintaining the functionality of the communication fire arrester when exposed to flame must comply with the requirements specified in the technical documentation for the product, but not less than 10 minutes.
24. The design of the fire arrester (spark arrestor) must provide for the possibility of sealing detachable connections (except for fastening ones) in order to control its integrity.
25. The fire arrester (spark arrestor) must remain operational:
under vibration influences arising during operation. The limits of their change must be established by the manufacturer and indicated in the technical documentation for the product;
within the operating and storage temperature ranges that must be set by the manufacturer and specified in the technical documentation for the product.
After the fire arrester has been triggered, its flame extinguishing element must be replaced with a new one.
27. The fire arrester (spark arrestor) must be replaced if the flame-extinguishing element is damaged, as well as if cracks or dents appear on the body.
28. The technical documentation for the fire arrester (spark arrestor) must reflect the following information:
information about functional purpose(type of flame retardant element, recommended installation location and product class);
types of flammable mixtures for which the product is intended to protect;
nominal diameter of the outlet;
operating temperature;
time to maintain operability when exposed to flame;
date of manufacture;
trademark or name of the manufacturer;
TU number.
VI. TEST METHODS
29. To control the compliance of the fire arrester (spark arrestor) with the requirements of these standards, tests are carried out: acceptance, periodic, certification and standard.
All tests, unless otherwise specified by these standards, must be carried out under normal climatic conditions established by GOST 15150.
30. Acceptance tests of fire arresters (spark arrestors) are carried out in accordance with GOST 15.001 on samples of a pilot batch according to a program developed by the manufacturer and developer.
A batch is defined as the number of products accompanied by one document.
31. Periodic tests are carried out in order to monitor the stability of product quality indicators and the possibility of continuing production of the product. Selection of samples for testing is carried out in accordance with GOST 18321. 2% of the quantity of produced fire arresters (spark arrestors) are subjected to periodic testing every month. At least four samples of each standard size are selected for testing.
32. Type tests are carried out when design or other changes are made (manufacturing technology, material, etc.) that can affect the main parameters ensuring the operability of the fire arrester (spark arrestor). The test program is planned depending on the nature of the changes and is agreed upon with the developer.
For standard tests, at least five samples of fire arresters (spark arrestors) of each type are selected.
33. Certification tests are carried out in order to establish compliance of the characteristics of the fire arrester (spark arrestor) with these standards, as well as to issue a fire safety certificate. For certification tests, three samples of fire arresters (spark arrestors) of each type are selected.
34. The scope of acceptance, periodic and certification tests is given in the table.
Scope of acceptance, periodic and certification tests
List of indicators | Clauses of these standards containing | Type of test |
|||
technical requirements | test methods | Reception | Periodically | Certificate |
|
The ability of a fire arrester to localize a flame and a spark arrestor to prevent ignition | |||||
The tightness of the fire arrester (spark arrestor) housing | |||||
Maximum surface temperature of spark arrestor housing | |||||
Performance of a fire arrester (spark arrestor) under vibration loads | |||||
Time to maintain the operability of a fire arrester (communication) when exposed to flame | |||||
Equipment, appearance fire arrester (spark arrestor), product compliance with design documentation | |||||
Weight and dimensions of the product |
35. If negative results are obtained for any type of test, the number of samples tested is doubled and the tests are repeated again in in full. If negative results are received again, further testing should be stopped until the causes are identified and the detected defects are eliminated.
36. Compliance of the fire arrester (spark arrestor) with the requirements of paragraphs 8 and 9 is established by external inspection using the appropriate measuring tool. The accuracy class of the measuring instrument is determined according to the technical documentation.
37. The mass of the fire arrester (spark arrestor) and the mass of the flame extinguishing element are determined by weighing on a scale with an error not exceeding 2%. To do this, first weigh the fully equipped fire arrester (spark arrestor), after which it is disassembled and the flame-extinguishing element is weighed. If the product, in accordance with the requirements of technical documentation, is not subject to disassembly, then only the mass of the fire arrester (spark arrestor) with the flame extinguishing element is determined.
38. Determination of the ability of a fire arrester to localize a flame and a spark arrestor to prevent ignition.
For testing use:
a) a test bench consisting of two cylindrical chambers (combustion and control). The equipment of the stand must withstand the pressure generated during testing.
The combustion chamber must be equipped with fittings for supplying a flammable gas-vapour-air mixture, placing a pressure sensor, an ignition source and have a diameter of at least 50 mm. The ratio of the length of the chamber to its diameter must be at least 30.
The control chamber must be equipped with fittings to accommodate a pressure sensor and an ignition source. The capacity of the control chamber must exceed the capacity of the combustion chamber by at least 5 times;
b) system technical devices, ensuring the production of a gas-vapor-air mixture based on the partial pressures of the components with an error of no more than 0.5% (vol.). The system should include the following equipment:
mixing chamber;
evaporator;
container with flammable liquid, flammable liquid or flammable gas;
air compressor;
pipelines with valves.
Partial pressure gas component determined by the formula
where is the volume concentration of the th gas component, % (vol.); - total pressure in the mixing chamber, kPa.
The mixing chamber must have a capacity that ensures that the combustion chamber and control chamber are filled with the required gas-vapor-air mixture at the pressure and temperature values specified for testing;
c) an ignition source, which is a nichrome wire with a diameter of 0.3 mm and a length of 2 to 4 mm, burnt out electric shock when applying voltage (40±5) V;
d) a pressure recording system consisting of primary transducers and secondary devices and providing recording of signals from primary converters over time in the frequency range from 0.1 to 1 kHz.
The ability of a fire arrester to localize a flame and a spark arrestor to prevent ignition is determined using the types of combustible mixtures they are intended to protect. It is allowed to carry out tests on model combustible mixtures, which in terms of normal burning rate are close to the specified mixtures for which the product is intended.
A fire arrester (spark arrestor) is installed and secured on the stand in accordance with the requirements of technical documentation in such a way as to ensure the tightness of the tested product and fire chambers.
The chambers are evacuated test bench to a residual pressure of no more than 5 kPa and supplying the gas-steam-air mixture from the mixer to the required pressure. The gas mixture is maintained for at least 5 minutes.
The devices for measuring and recording pressure over time are started and the ignition source in the combustion chamber is turned on.
The criterion for ignition of the gas-vapor-air mixture in the control chamber is considered to be an increase in overpressure no less than 2 times the initial pressure.
If there is no ignition of the gas-vapor-air mixture in the control chamber, it is considered that the fire arrester (spark arrestor) has passed the test.
The test results are considered positive if, in three consecutive tests, no breakthrough of a flame (spark) through the flame arrester element or a spark through the spark arrester filter element is recorded.
39. If the fire arrester is designed to operate at atmospheric pressure, it is allowed to carry out tests to determine the ability of a fire arrester to localize a flame and a spark arrester to prevent ignition without a control combustion chamber. The process of the flame (spark) breaking through the flame arrester element of the fire arrester is recorded visually, using as an indicator the ignition of gasoline poured into a pan, which is located directly at the outlet of the fire arrester (spark arrestor) at the flame arrester element.
40. Tests of the fire arrester (spark arrestor) for tightness are carried out in accordance with the “Rules for the design and safe operation of pressure vessels”.
41. Determination of the maximum surface temperature of the spark arrester housing.
Tests are carried out on the exhaust manifolds of vehicles and power units, on which spark arresters are installed, or on equipment that simulates the operating conditions of furnaces and internal combustion engines, at the rated power of the power unit.
For testing use:
electrical thermal converters TXA in accordance with GOST R 50431 with a diameter of no less than 0.5 and no more than 1.5 mm. Three electrical thermal converters are installed on each spark arrester: two at the input and output of the spark arrester; the third - in the central part of the spark arrestor body;
Testing:
the spark arrester is placed on the exhaust manifold of the power unit;
turn on the power unit and bring it to the operating mode corresponding to the rated power;
record the temperature readings of each electrical thermal converter for one hour during continuous operation of the power unit in a mode corresponding to the rated power.
Based on the measurement results, the maximum temperature value is determined from the readings of three electrical thermal converters, which is taken as the maximum temperature of the surface of the spark arrester body.
42. Tests for the vibration strength of a fire arrester (spark arrestor) are carried out on a vibration stand of the VEDS-200 (400) type or another type with similar characteristics.
Fire arresters (spark arrestors) are attached to the movable platform of the vibration stand. Tests are carried out along each of the three coordinate axes with a frequency of 40 Hz and an amplitude of 1 mm, the test duration in each direction is 40 minutes.
After vibration impacts on all three axes, the ability of fire arresters to localize flames and spark arrestors to prevent ignition is determined in accordance with clause 38.
43. Determination of the time for maintaining the functionality of a fire arrester (communication) when exposed to flame.
The essence of the method is to determine the time interval during which the communication fire arrester retains the ability to localize the flame.
The time to maintain operability when exposed to flame is determined for fire arresters that have passed tests for the ability to localize a flame.
For testing use:
test bench, the description of which is given in paragraph 38. Two fire arresters are attached to the ends of the combustion chamber: one at the inlet, the other at the outlet. The fire arrester placed at the exit of the combustion chamber is being tested. A fire arrester placed at the inlet prevents the spread of flame from the combustion chamber to the mixer. The fire arrester, located at the entrance to the control chamber, is supplied with a flammable mixture from the mixing chamber. The mixing chamber must be of a flow type and ensure combustion of the combustible mixture on the surface of the flame arrester element attached at the outlet of the combustion chamber. The supply of the combustible mixture must be continuous and equal to 10, 40, 70 and 100% of the nominal throughput of the product. The number of tests carried out at each of the specified feed values is assumed to be 2;
electrical thermal converters TXA in accordance with GOST R 50431 with a diameter of no less than 0.5 and no more than 1.5 mm. Two electric thermal converters are placed on the tested fire arrester, installed at the exit of the combustion chamber: at the input and output directly in the central part of the flame arresting element;
secondary instruments for measuring temperature in the range from 0 to 1300 °C, having an accuracy class of 0.5.
Testing:
the combustible mixture is supplied from the mixing chamber to the fire arrester being tested (the supply corresponds to 10% of the nominal capacity of the product) and it is ignited at the outlet of the flame arrester element;
record the temperature readings of each electrical thermal converter.
Based on the results of measuring the readings of electrical thermal converters, the time interval during which the spread of flame throughout the product is not observed is determined. The criteria for flame propagation along a fire arrester are:
a) the appearance of a flame at the outer surface of the fire arrester body, as well as the formation of cracks, burnouts and other through holes not specified in the design documentation;
b) simultaneous appearance of the following symptoms during continuous supply of a combustible mixture:
disappearance of the flame at the surface of the flame extinguishing element, which is recorded visually and using a signal from an electrical thermal converter located at the output of the fire arrester;
the occurrence of a flame at the entrance to the fire arrester under test, detected using a signal from an electrical thermal converter located at the entrance to the flame extinguishing nozzle.
The tests are repeated with a continuous supply of the combustible mixture at a flow rate of 10, 40, 70 and 100% of the nominal throughput of the fire arrester, and the minimum time for the entire test cycle is determined during which no flame spread throughout the product is observed.
GOST 12.4.009-83. SSBT. Fire fighting equipment for the protection of objects. Main types. Accommodation and service.
GOST 15.001-88. System for developing and putting products into production. Products for industrial and technical purposes.
GOST 5632-72. High-alloy steels and alloys, corrosion-resistant, heat-resistant and heat-resistant. Stamps.
GOST 12766.1-90. Wire made of precision alloys with high electrical resistance. Technical conditions.
GOST 14249-89. Vessels and devices. Norms and methods of strength calculations.
GOST 15150-69. Machines, instruments and other technical products. Versions for different climatic regions. Categories, conditions of operation, storage and transportation in terms of the impact of environmental climatic factors.
GOST 18321-73. Statistical quality control. Methods for random selection of samples of piece goods.
GOST 18322-78. Equipment maintenance and repair system. Terms and Definitions.
GOST 19433-88. Dangerous cargo. Classification and labeling.
GOST 22520-85 E Pressure, vacuum and pressure difference sensors with electrical analog output signals GSP. General technical conditions.
GOST 24054-80. Mechanical engineering and instrument making products. Leak testing methods. General requirements.
GOST R 50431-92. Thermocouples. Part 1. Nominal statistical characteristics of the transformation.
The text of the document is verified according to:
official publication
M.: VNIIPO Ministry of Internal Affairs of Russia, 1999
Purpose
The fire arrester OP (AAN) is installed between the vertical tank and the safety or breathing valve. The fire arrester OP is designed to protect a vertical tank from the penetration of fire (flame or spark) into the gas space through breathing valves (vent pipes or safety valves), thereby protecting oil from a flash or explosion.
Specifications
TU 3689-014-10524112-2002 corresponds to:
- AOMZ TU 63-RSFSR68-75;
- NGM Group 3689-016-79167039-2006.
Design and principle of operation
The principle of operation of the fire arrester OP is based on flame retardation by a cassette placed inside the housing. The cassette consists of a package of alternating corrugated and flat plates, forming small-diameter channels. The flame, entering the channels of small cross-section, is split into separate small streams. The contact surface of the flame with the fire arrester OP increases, heat transfer to the channel walls increases, and the flame goes out. The design of the fire arrester OP is collapsible, which allows you to periodically remove the cassettes for inspection and monitoring their condition.
The basis of the design is a fire-retarding element 2, placed between two halves of the body 1, pulled together by four pins 3. The fire-retardant element consists of flat and corrugated tapes wound on an axis, which also protects the element from falling out.
The extinguishing effect of the fire arrester OP, installed on the roof of an RVS-type tank, is based on the principles of intense heat exchange that occurs between the walls of the narrow channels of the fire-retardant element and the gas-air flow passing through it. This achieves a reduction in the temperature of the gas-air flow to safe limits.
1 - body consisting of two halves; 2 - fire-retarding element; 3 - four connecting pins.
Specifications
| Parameter name | OP-50AAN* | OP-80AAN* | OP-100AAN | OP-150AAN | OP-200AAN | OP-250AAN | OP-300AAN | OP-350AAN | OP-500AAN |
|---|---|---|---|---|---|---|---|---|---|
| Nominal size DN | 50 | 80 | 100 | 150 | 200 | 250 | 300 | 350 | 500 |
| Throughput at air flow resistance 118 Pa, m³/hour, no more | 100 | 150 | 200 | 215 | 380 | 600 | 700 | 900 | 2950 |
| Overall dimensions, mm, no more | |||||||||
| D n | 160 | 214 | 230 | 303 | 375 | 450 | 527 | 635 | 858 |
| H | 172 | 200 | 200 | 250 | 275 | 263 | 295 | 440 | 337 |
| Connecting dimensions, mm | |||||||||
| D | 141 | 184 | 205 | 260 | 315 | 370 | 440 | 485 | 640 |
| D 1 | 110 | 150 | 170 | 225 | 280 | 335 | 395 | 445 | 600 |
| d | 14 | 18 | 18 | 18 | 18 | 18 | 22 | 22 | 22 |
| n | 4 | 4 | 4 | 4 | 4 | 6 | 6 | 6 | 16 |
| Weight, kg, no more | 3 | 5 | 6,1 | 10 | 16 | 20 | 30 | 45 | 70 |
* OP products with a nominal bore of DN 50 (DN 80), at the customer’s request, can be manufactured for a tongue-and-groove flange connection. A groove is made in the flange(s) of the products. At the customer's request, the product can be equipped with mating flanges in accordance with GOST 12815. Sealing gaskets are not supplied.
the essence of the protective action;
determination of the critical diameter of the channel;
fire arrester design diagrams;
requirements for placement and operation.
features of their use on gas and liquid lines.
Dry fire retardants.
Dry fire arresters are used to protect pipelines without a liquid phase, in which, during certain periods of operation, a flammable concentration of vapors or gases with air can form, as well as to protect lines with substances that can decompose under the influence of pressure, temperature and other factors.
The essence of the protective action of dry fire retardants.
The essence of the protective effect of dry fire arrestors is to extinguish the flame in narrow channels, which is caused by an increase in the intensity of heat loss compared to heat release as a result of an increase in the specific surface area of the flame front.
When the rate of heat loss compared to the rate of heat release reaches a critical value, the combustion temperature, and hence the rate of chemical reactions in the combustion zone, decreases so much that the propagation of combustion (flame front) through the combustible mixture in a narrow channel becomes impossible.
These are exactly the conditions that are created in dry fire retardants.
The flame, spreading through the combustible mixture, enters the fire arrester nozzle, consisting of a large number of narrow channels, where it breaks up into many small flames, which cannot spread in narrow channels.
Diagrams of fire arresters .
To divide the live (flow) section of the protected pipeline into a family of narrow channels in fire arresters, various nozzles are used in the form of a bundle of tubes, meshes, granules, rings, fibers (metal, glass, asbestos), metal ceramics, etc. The nozzles are located in the fire arrester body.
To reduce hydraulic resistance, the diameter of the fire arrester body is increased in size compared to the diameter of the protected pipeline.
For reliable connection of the fire arrester body with the pipeline, there are flanges on both sides of it, the diameter of which corresponds to the diameter of the protected pipeline.
Diagrams of the main types of fire arresters are presented in Figure 1.
Fig.1. Diagrams of the main types of fire arresters
A – with horizontal grids; b – with vertical grids; V – with gravel; G – with corrugated and flat tapes spirally rolled together; d – with a metal nozzle.
1 - frame; 2 - flame-retardant nozzle; 3 - grate; 4 – support rings
The critical diameter of the fire arrester nozzle channel.
The diameter of the fire arrester nozzle channel, at which a thermal balance (equality) between heat release and heat loss is established in the combustion zone, is called the critical diameter d cr .
This diameter is determined by calculation. It depends on the properties of the combustible mixture, concentration, initial temperature and pressure. You can see the calculation of the critical diameter in.
The actual (extinguishing) diameter of the fire arrester nozzle channel is taken smaller and, taking into account the safety factor, is 0.5-0.8 d cr .
You can get acquainted with other types of fire arrester designs.
Requirements for placement and operation.
So, dry fire arresters most often protect gas and steam-air lines in which, due to technology conditions or in case of disruption of normal operating conditions, flammable concentrations can form (breathing lines of tanks, measuring tanks, intermediate tanks, pressure tanks and similar devices with flammable liquids, as well as with flammable liquids heated to flash point or higher).
Dry fire arresters protect bleed lines and purge lines of recovery units; lines running from devices and containers to the torch; lines gas piping tanks with flammable liquids, etc.
Dry fire retardants also protect lines containing substances that can decompose under the influence of pressure, temperature and other factors.
Liquid fire arresters (hydraulic seals).
The essence of protective action.
Flame extinguishing in water seals occurs at the moment of passage (bubbling) of the burning gas-vapour-air mixture through the barrier layer of liquid as a result of its fragmentation into thin streams and individual bubbles, in which the flame front appears dismembered.
The total heat-transfer surface of the flame increases.
As a result, just as in dry fire retardants, conditions are created in the reaction zone for the intensity of heat loss to exceed the intensity of heat release.
For steam-gas lines, water is used as a barrier liquid, and in liquid lines, the transported liquid is used.
To increase the effectiveness of the fire extinguishing effect of liquid fire arresters, the height of the barrier layer of liquid at normal pressure is taken from 10 to 50 cm.
In addition, to reduce the size of bubbling bubbles of the flammable mixture, special slots are provided at the end of the pipe immersed in the hydraulic seal liquid.
Scope of application of liquid fire arresters (hydraulic valves).
To protect liquid and gas pipeline lines, trays, industrial sewers, etc., in which operating conditions may create a danger of flame propagation in kinetic and diffusion combustion modes, liquid fire arresters (hydraulic valves) are used.
Let's remember a little in which cases kinetic combustion occurs and in which diffusion combustion occurs.
When flame propagation occurs in the kinetic combustion mode, the reaction occurs with an explosion.
Slow propagation of the flame over the surface of the liquid is observed in the diffusion combustion mode.
The schematic diagram of low pressure hydraulic seals on the gas line is shown in Fig. 2. :
1- body; 2- water; 3- water supply line; 4- supply pipe; 5- outlet pipe; 6 - line for removing excess water; 7-disc; 8-slots.
Fig.2. Low pressure hydraulic valve diagram
Features of the use of fire arresters on gas and liquid lines.
Water seals are widely used to protect filling lines of devices with bottom liquid supply, drain lines on unloading racks, overflow lines of tank devices, industrial sewage systems at enterprises with flammable liquids and gas liquids, pump room trays, etc.
To protect medium and high pressure gas lines, special water seals are used, which, unlike low-pressure liquid fire arresters, have a small amount of locking fluid, equipped with a check valve and a safety diaphragm.
The operating principle of such hydraulic seals is similar to a low-pressure hydraulic seal.
Liquid fire arresters must strictly comply with the technical conditions for their manufacture in terms of design and completeness.
When using water as a shut-off liquid, it is advisable to place fire arresters in heated rooms.
If this is not possible, additives are added to the water to lower its freezing point (ethylene glycol, glycerin, etc.)
Hydraulic valves.
