Foam extinguishing agents mainly use the foam covering, suffocation and the cooling effect of precipitated water to achieve extinguishing. Therefore, the stability of the foam structure is a very important factor affecting its extinguishing and anti-refiring performance. However, the higher foam stability will make it possible for a large number of residual foams to accumulate on the fire scene and in the surrounding environment after the fire extinguishing, which will seriously affect the fire-fighting activities of the fire-fighting forces, making it impossible for the fire officers and soldiers to remove the hidden fire points effectively and in time. The investigation and identification of the causes brought great difficulties. In practice, the firefighting force uses water to flush away the foam. Although this method will have a certain effect, the impact of water flow will cause the surfactant contained in the foam to re-expand, consume large amounts of water and defoam Not obvious. At the same time, a large number of fire-fighting foams will enter the sewage treatment plant along with the urban drainage system, which will cause the sludge in the aeration tank to float up, and it will be impossible to achieve effective separation of sludge and water, which will cause great problems for the normal operation of the sewage treatment plant. Therefore, the rapid and effective cleaning of residual foam after fire extinguishing is a real problem that needs urgent solution.

Studies have confirmed that, compared with traditional fire-fighting systems, compressed air foam systems combined with special Class A foam fire extinguishing agents can effectively extinguish vehicle fires with Class A and B mixed fire characteristics, and have the advantages and potential for application in road tunnels. . However, due to the fine and uniform foam state produced by the system, the foam structure is stable, and it can be stable for a day or two in the natural environment. In addition, the space of the highway tunnel is narrow and closed, and the foam generated by the system will accumulate in large amounts in the tunnel, which will greatly affect the evacuation of people and vehicles in the tunnel and the cleanup after the disaster, which limits its practical application in the tunnel. Therefore, solving the problem of rapid defoaming of compressed air foam in road tunnels becomes even more urgent and urgent.

At present, there are no effective methods and pharmaceutical products that specifically address the residual foam cleanup after firefighting. Defoamers on the market are mainly used to suppress and eliminate foams produced during mixing and mixing of liquid products such as paints, lubricating oils, and inks. The types of commonly used defoamers can be divided into silicones, polyethers and non-silicons ( mineral oils, amides, lower alcohols, etc. ) . The author determined the defoaming and defoaming effects of various commercially available defoamer products through laboratory tests, provided solutions for the rapid defoaming of fire-fighting foams, and promoted the application of compressed air foam fire-extinguishing technology in highway tunnels.

1 test materials and devices

1 . 1 test material

The test agents are known Class A foam made with the unit, model MJABP, product performance in line GB 27897-2011 "A Class A foam extinguishing agent" standards.

The three defoamer products selected for the test are shown in Table 1 .

Table 1 Defoamer samples

1 . 2 test apparatus and method

The small laboratory compressed air foam system used in the test is shown in Figure 1 . The system foam solution flow can be 0 . 26 to 2 . Fine control within the range of 6 L / min , flexibility to adjust different foam conditions to meet the needs of different test conditions. Foam analysis rate measuring device, as shown in Figure 2 .

Figure 1 Schematic diagram of a small compressed air foam system

Figure 2 liquid rate measurement device does not provoke

The foam fire extinguishing agent of type A was mixed with water in a proportion of 1 % and was added to a pressure-resistant storage tank of a small compressed air foam system as shown in FIG. 1 . The pressure and flow rate of the compressed air and foam solution were adjusted so that the flow rate of the foam solution was 1 L / min , and the gas-liquid ratio was fixed at 20 : 1 . According to the relevant requirements in GB 27897-2011 " Class A foam extinguishing agent" standard, the foaming foam generation times and the time of 25 % liquid analysis are determined.

The defoamer's defoaming ability was examined using the foam decanting rate measuring device of FIG. 2 . The foam receiving tank is used to receive the foam and determine its quality. The defoamer is applied on the surface foam of the foam receiving tank in proportion with a hand-held spray device. Afterwards , the decanting tank is placed on the electronic balance as shown in FIG. 2 . Receiving tank placed on the iron ring, continuously record the quality of the liquid change.

After adding the defoamer, the precipitated liquid was allowed to stand at room temperature for 1 h , then 10 mL of the precipitated liquid was added to a 100 mL glass graduated cylinder, and the re-foaming of the precipitated liquid was observed after vigorous shaking for 30 days and the height of the foam layer was recorded.

2 test results and discussion

2 . 1 Comparison of defoaming effects of different defoamers

The defoaming effect of three defoamers at a 5 % foam quality was investigated . Using the same amount of water as the blank control, the time for the 25 % foaming time of the foam after adding three kinds of antifoaming agents was determined as shown in Table 2 , and the curve of the fluid quality with time was shown in FIG. 3 .

Table 2 Addition of 25 % of liquids to different defoamer samples

LC analysis Division I always set different curves in FIG. 3 defoamer

The 25 % time for liquid analysis refers to the time required for the foam to produce 25 % of its own weight, and it is an important indicator of the stability of foam extinguishing agents. I chose this parameter to quantify and compare different antifoams. As for the defoaming effect, the shorter the time for the 25 % liquid release after the addition of the defoamer, the more pronounced the defoaming effect of the defoamer. The time for testing the foaming time of Class A foam extinguishing agent in the compressed air foam system was 14 34 , which was basically the same as the time of liquid analysis of the blank control group in Table 2 , which showed that 5 % was applied to the generated foam surface layer . The weight of water does not play a defoaming effect. After adding three kinds of antifoaming agents, the time for liquid separation was shortened to varying degrees, of which 5 % of organic silicon antifoams had the worst defoaming effect, and 25 % of the 5 % general antifoams had only 25 % of liquid time. 5 46 , compared with the blank control of water shortened by 60 . 51 % , the most effective defoaming effect. From the experimental phenomenon, it can be seen that after applying a general-purpose defoamer to the foam surface with a watering can, the original delicate, uniform surface foam quickly disappears and breaks and sounds, continuously bulging out large bubbles, and the degree of unevenness of the foam layer increases. As the defoamer flows downwards into the foam, the foam layer begins to collapse and the rate of liquid evolution increases.

From Fig. 3 , the curve of the quality of the liquid evolved over time shows that the foam added with 5 % polyether first started the rapid fluid analysis, followed by the silicone and the general-purpose defoamer, while the blank control group added with water was basically not in the first 300 s. The liquid precipitated. The universal defoamer has a significantly faster liquid release rate from 200 S , and maintains a high rate of liquid release for a long period of time. The collapse of the foam layer is also most noticeable during the liquid separation. The effectiveness of polyether antifoams is second only to general purpose defoamers. At the end of the observation period of 1 470 S , the amount of liquids released from the general purpose defoamer, polyether, silicone defoamer, and blank control group was 80 . 28 %, 73 . 16 %, 59 . 78 % and 53 . The 60% indicates that the defoaming ability of general purpose and polyether defoamers is significant, while the defoaming effect of silicone defoamers on Class A foams is not obvious.

Defoamer mechanism of action is mainly reflected in the liquid film invading the bubble in the form of particles, by displacing the solvent on the surface of the liquid film to reduce the surface tension at the place, so that the internal force of the liquid film is uneven, to promote liquid film rupture. Some defoamers also achieve defoaming by destroying the elasticity of the film and causing the liquid film to lose its self-repairing effect. In practical use, different defoamers have their most suitable defoaming system, and a single type of defoamer is only effective for one or several systems. From the above test results, polyethers and silicone defoamers all have a defoaming effect on compressed air A foams, but the defoaming effect is the most common one. The main components of this general purpose defoamer are metal soaps and mineral oils. Usually, the use of several antifoaming agents has a synergistic effect and can increase the defoaming efficiency. In comparison, general purpose defoamers are more suitable for compression. Defoaming of Air A foam.

2 . 2 Antifoaming effect of defoamers at different concentrations

To further investigate the defoaming effect of defoamers at different concentrations, a general purpose and polyether defoamer with good defoaming effect was selected to compare the defoaming ability at 5 % and 1 % concentrations. After adding different concentrations of antifoaming agent, the foaming time of 25 % is shown in Table 3 , and the curve of the quality of the extracted fluid over time is shown in Figure 4 .

As can be seen from the data in Table 3 , 25 % of the time for the addition of 1 % of the general purpose defoamer and the polyether defoamer foam was 9 20 and 10 44 , respectively , which is much higher than the time for the liquefaction at 5 %, indicating that After the concentration of defoamer was reduced from 5 % to 1 %, the defoaming effect was significantly reduced. During the test, it was also observed that when the defoamer concentration was 1 %, the rate of depression of the foam layer was significantly slowed down, and the rate of liquid deposition decreased.

Table 3 Addition of 25 % liquid release time for different defoamer samples

Fig. 4 Curve of the quality of the liquid under different concentrations of general purpose ( upper ) and polyether defoamer ( lower )

It can be seen from the curves of the quality changes of the two defoamers at two concentrations of 1 % and 5 % in Fig. 4. For a general-purpose defoamer, the rate of the foam's liquid is slowed down after the concentration is reduced, but Overall, it still maintains a high rate of liquid release. And at the end of the observation period of 1 470 S , the foam added with 1 % general-purpose defoamer precipitated 75 . 88% foam quality, higher than the liquid mass polyether defoaming agent at a concentration of 5% precipitate (73.16%). For the polyether defoamer, the rate of the liquor is slowed down when the concentration is decreased, and the rate of the liquor is only slightly higher than that of the blank control group in the early period, but the rate of the foam liquid in the latter period is slow, which is basically the same as that of the blank control group. At the end of the observation period, the 1% defoamer polyether foam 59 only precipitated. 34% by mass, slightly higher than the control group (53.06%), which indicates that the polyether defoamer at this concentration effect is not obvious.

The defoaming effect of the two defoamers showed that the defoamer showed a good defoaming effect at 1 % and 5 % concentrations, and the concentration of the defoamer had no significant effect on the defoaming effect. However , the defoaming effect of polyether defoamer at 5 % concentration is acceptable, but the defoaming ability decreases with the decrease of the concentration. The defoaming effect is basically not exhibited at 1 % concentration, and the defoaming ability is affected by the decrease in concentration. More significant.

2 . 3 Defoamer's ability to inhibit foaming

Defoamers with excellent properties must take into account both defoaming and defoaming functions. After application, they can not only rapidly defoam, but also have a high ability to inhibit foaming and prevent the re-formation of foam for a relatively long period of time. The vibration suppression capability of different types and concentrations of defoamers was investigated using the shaking and shaking method. The foam volume data formed after shaking was shown in Table 4 .

Table 4 Add foam volume after foam defoaming of different defoamers

As can be seen from the data in Table 4 , the bubble volume of the blank control group added with water after shaking and shaking was 50 mL , indicating that the foam without adding any defoamer still has strong re-foaming ability after being analyzed. Under the right conditions, it will still foam again. However, when the concentration is decreased to 1% antifoaming agent; added 5% -i ~ lh after standing defoaming agent dialysate no foam generating three defoamers have very good antifoam effect at this concentration , Foam volume produced by general-purpose defoamer and polyether defoamer were 15 mL and 20 mL , respectively, and the foam suppression capability was weakened. This shows that reducing the concentration of defoamer will not only affect its defoaming effect, but also result in a decrease in its foam suppression capability.

Considering the defoaming and defoaming effects of the three defoamers, the 5 % defoamer has obvious advantages in terms of defoaming speed, defoaming effect, and foam suppression ability. It can be considered in road tunnels, etc. Narrow sites are used for rapid defoaming of compressed air foam and other types of fire fighting foam. In addition, in order to meet the needs of practical engineering applications, it is necessary to conduct studies on the application of defoamers in the future, clarify the optimal particle size and spray pattern of defoamers, and achieve uniform and rapid application of defoamers to fully enhance defoaming. The defoaming effect of the agent.

3 Conclusion

The defoaming and anti-foaming effects of three types of commercially available defoamers, polyether, silicone, and general-purpose foams on compressed air foams, were compared using the method of determination of liquid rate and shaking and shaking. The following conclusions were obtained:

(1) At the use concentration of 5 %, the defoaming capacity of the three defoamers is in the order of general-purpose defoamer > polyether defoamer > silicone defoamer, and the general defoamer has the most defoaming effect. Obviously, the defoaming rate is the fastest, and the time for 25 % of the defoaming time is 6O shorter than that of the blank control . 51 % , which is related to the synergistic effect of multi-component defoamers.

(2) When the use concentration of defoamer is reduced from 5 % to 1 %, the defoaming effects of general-purpose defoamers and polyether defoamers are all reduced, but the defoaming ability of general-purpose defoamers is reduced when the concentration is decreased. The effect is relatively small, and the defoaming ability of the polyether is more significant, and the polyether shows only a very weak defoaming ability at a 1 o5 concentration.

(3) The three defoamers can inhibit the foam no longer foaming at 5 % concentration, and have very good defoaming effect; but at a concentration of 1 %, general defoamers and polyethers are used for defoaming The agents all have different degrees of foaming, and the ability to inhibit foaming is reduced.

(4) Comprehensively consider the defoaming and defoaming effects of the three defoamers. It is recommended that 5 % of general-purpose defoamers be used in highway tunnels to rapidly defoam foams that are difficult to eliminate, such as compressed air foam, but in the future, The relevant dispensing equipment needs to be studied to ensure the defoamer's rapid defoaming effect.

The information in this article comes from the Internet and was reorganized and edited by China Rescue Equipment Network.