RU2717066C1 - Powdered fire extinguishing compound for sodium and alkali metals quenching - Google Patents

Abstract

FIELD: fire-fighting equipment.

SUBSTANCE: invention relates to powdered means for quenching of alkali metals, particularly sodium. Essence of the proposed fire-extinguishing composition is determined by its formula, formed by results of laboratory and large-scale (polygon) tests for sodium quenching. Base of this composition is potassium chloride with additives allowing to provide conditions of storage, transportation and uniform distribution when supplied from a fire extinguisher (anti-caking additive and fluidity additive) – fine silicon dioxide and aminoplast, additive to reduce hygroscopicity – graphite, as well as an additive of fine powder of aluminum, which, as shown by calculated data and results of tests, increases heat removal from combustion source and accelerates achievement of quenching of sodium and alkali metals.

EFFECT: reduced consumption of powdered fire-extinguishing composition is reduced by (20–25 %).

1 cl, 1 tbl

Description

The invention relates to powder extinguishing agents for alkali metals, in particular sodium.

In nuclear energy with fast neutron reactors (BN), in which molten sodium is the coolant, the means and methods of extinguishing sodium have gained particular importance. When spilling sodium from its circulation system at nuclear power plants, immediate firefighting measures are required, as sodium in contact with water and oxygen is self-igniting.

Large-scale sodium leaks are collected in the so-called self-extinguishing pallets (Patent RU No. 2419472 MPK А62С 3/06 (2006.01), B65D 90/22 (2006.01) “Device for self-extinguishing liquids burning during an accident during spill”, published on 05.27.2011 .), where sodium is in an atmosphere of nitrogen or argon. Small-scale sodium leaks (50-200 kg) must be extinguished with special-purpose fire-extinguishing powder composition (OPS SN) using manual or automatic fire extinguishing means in accordance with current regulatory documents (GOST R 53280.5-2009, class D2 fire (burning of alkali metals) .

Currently, a number of OPS SN are known as powder formulations for the extinguishing of sodium and other alkali metals. In one of the inventions (AS No. 698630 IPC A62D 1/00 "Powder for extinguishing alkali metals", published on November 26, 1979), an OPS composition based on sodium bicarbonate with the addition of bitumen, metal stearates, talc is proposed. At the same time, bitumen is used as a component that increases fire extinguishing efficiency due to its melting on the surface of burning sodium, mixing with sodium bicarbonate. However, such mixing cannot be uniform and requires additional mechanical mixing.

In another invention (AC No. 919684 IPC A62D 1/00 "Means for extinguishing light metals", publ. 04/15/1982) proposed composition for extinguishing metals based on zinc powder. The rate of metal quenching (powder consumption kg / m ^{2 of the} burning surface) was compared with the results of metal quenching using alumina. Fine zinc powder as a quenching agent turned out to be much more effective than alumina, which is probably due to the fact that fine zinc powder removes heat from the burning metal surface coated with it, cooling it to a complete cessation of combustion. A similar method of accelerating the extinguishing of a burning metal due to the intensive removal of heat from the burning surface of the metal is of considerable interest from the point of view of increasing the efficiency of fire extinguishing, which we used to develop a new fire extinguishing composition. At the same time, this composition, when used in standard fire fighting equipment (fire extinguishers, etc.), requires the development of a special design fire extinguisher.

The invention (AC No. 724146 IPC A62D 1/00 "Composition for the extinguishing of metals", publ. March 30, 1980) proposes a composition based on a liquid ester of boric acid. The composition contains a mixture of boron esters of ethylene bromohydrin and β-dibromohydrin. In this composition, bromine atoms contained in hydrocarbon radicals have the ability to inhibit the combustion process and cannot evaporate from the liquid during storage. Inhibition of flame occurs with the help of bromine released from ethers during their thermal decomposition in a flame. However, the constituent substances are expensive in production.

Closest to the claimed invention is a composition for extinguishing a fire (Patent RU No. 2108126 C1 IPC A62D 1/00 (1995.01) "Composition for extinguishing fires", published on 04/10/1998). This composition contains potassium chloride, graphite, an anti-caking additive and an aminoplast (additive for fluidity). This powder composition is currently produced and used to extinguish alkali metals, including sodium. This composition is adopted as a prototype.

The objective of the invention is to provide a fire extinguishing powder composition for special purposes with high fire extinguishing efficiency for fires of classes D1 and D2 in accordance with GOST R 53280.5-2009, which has low caking and hygroscopicity when stored in bags and other containers. Also, to improve the operational properties of the OPS, additives should be present in their composition to improve the fluidity during its use.

The solution to the problem is achieved by the fact that the composition includes components that allow combining these conditions, including finely divided aluminum powder, which, having a high heat capacity, on the one hand provides heat intake from the combustion zone, and on the other hand, is an additional source of heat removal to the environment, in the following ratio of components of the composition,% (mass.):

- anti-caking additive: finely divided silica: 2-4;

- graphite 2-7;

- additive for fluidity: aminoplast: 4-6;

- aluminum powder PA-4: 10-15;

- potassium chloride: 68-82

In the process of developing the inventive composition, computational and experimental studies were carried out. As a result of thermophysical calculation, the following dependence of the consumption of OPS on quenching on the proportion of the metal additive in its composition was revealed:

j _SM - consumption of OPS with a metal additive, kg / m ² ;

j _P - consumption of OPS for extinguishing without metal additives, kg / m ² ;

with _M is the heat capacity of the metal in the mixture, J / kg K;

with _P - the heat capacity of the extinguishing powder, J / kg K;

β is the relative proportion of the metal additive in the composition.

The conclusions from the thermophysical calculation are as follows:

- the larger the proportion of the metal additive in the powder, the lower the rate of extinguishing the mixture, compared with pure powder;

- the rate of quenching with a mixture of powder with metal decreases with increasing heat capacity of the metal.

The quenching tests of alkali metals were carried out in 2 stages. At the first stage, the tests were carried out in laboratory conditions, at the second - at the test site. Aluminum metal powder PA-4 (GOST 6058-73) and copper electrolytic powder (GOST 4960-2009) were used as a metal additive in the composition of OPS.

The results of laboratory tests showed that in the case of the introduction of metal powder as an additive into the composition of the OPS, the specific extinguishing powder consumption decreases. The composition with the addition of aluminum powder PA-4 showed greater efficiency compared to the addition of copper powder, as was revealed as a result of thermophysical calculation. As a sample for comparison, we used a fire extinguishing composition [5], which we took as a prototype. The results of laboratory tests were confirmed during field tests.

The test results of the fire extinguishing composition with the addition of metal powders of copper and aluminum during sodium quenching are shown in the table.

The data obtained are summarized in the article: "Improving the fire extinguishing efficiency of special-purpose powders" // ISSN 2411-3778. Fire Safety Magazine, Moscow: VNIIPO, 2018, No. 3, p. 78-81.

The composition with the addition of copper powder of 10% (mass.) Showed similar results with the prototype, with a slight improvement. The lower efficiency of the composition of the powder with the addition of copper, compared with the addition of aluminum, is apparently due to the fact that, despite the increased heat dissipation, due to the heavier weight, the addition of copper “fell” into sodium having a low density and formed “relatively large "agglomerates, which influenced the flow characteristic.

A fire extinguishing composition with the addition of fine aluminum powder PA-4 showed the best result from the tested compositions. Obtained in the tests, the flow rate characteristic was ~ 15 kg / m ² , which is approximately 25% more effective than the powder that was chosen for the prototype. The higher extinguishing efficiency, apparently, is associated with a higher rate of heat capacity of aluminum, which provides heat intake from the combustion zone and at the same time more intense heat removal due to the physicochemical properties of the metal.

Adding more than 15% (mass.) Of a finely dispersed metal component to the composition is impractical due to the deterioration of the performance characteristics of the composition, such as an increase in caking properties, due to the appearance of agglomerations of the heavier component in the lower part of the container during transportation and operation.

Claims (2)

A powder extinguishing composition for extinguishing sodium and alkali metals, containing potassium chloride and additives, which provide high flow rates and low caking and hygroscopic properties, characterized in that finely dispersed aluminum powder PA-4 is included as an additive in the following ratio of components (% mass.): Anti-caking additive: fine silica 2-4 Graphite 2-7 Additive for fluidity: aminoplast 4-6 PA-4 aluminum powder 10-15 Potassium chloride 68-82