Production Process and Performance of Foam Extinguishing Agent

 

1. protein foam fire extinguishing agent

 

The foaming agent of protein foam fire extinguishing agent is hydrolyzed protein of animal (mainly pig) hair and hooves. At present, there are two hydrolysis processes for protein foam, one is to hydrolyze with caustic soda (NaOH), and then add hydrochloric acid (HCl solution) to neutralize; the other is to hydrolyze with lime [Ca(OH)2], and then add NH4HCO3 Ca2 and OH-ions. Due to the relatively complex production process of protein foam, there are fewer producers, especially fewer producers in the lime hydrolysis process. The former contains strong acid and alkali salt, the foam quality is slightly inferior, the sediment is more, the validity period is shorter, but the process is simpler, the quality requirements of raw materials are slightly lower, the production cost is low, the price is low, and it is basically used for domestic sales. The latter process is more complex and has waste residue discharge in the production process, high quality requirements for raw materials, low output rate, good foam quality and high price, and is basically sold to developed countries and regions.

Protein-based foam fire extinguishing agents include protein foam (P), fluorine protein foam (FP), and film-forming fluorine protein foam (FFFP). Protein foam is made by adding the required additives after the above hydrolysis and neutralization, and its foam fluidity and oil repellency are poor, and the fire extinguishing efficiency is low. Fluoroprotein foam is made by adding a small amount of fluorocarbon surfactant on the basis of protein foam, the surface and interfacial tension is reduced, the foam fluidity and oleophobicity are improved, and the fire extinguishing performance is also significantly improved. The film-forming fluorine protein foam is formed by adding a large amount of fluorocarbon surfactant on the basis of protein foam, and has the film-forming property of aqueous film-forming foam on the surface of oil products, and the fire-extinguishing performance is higher than that of fluorine protein foam. However, the addition amount of the foam fluorocarbon surfactant is not less than that of the aqueous film-forming foam, and the added types may be more, and the environmental protection is poor.

 

 

 

Production Process and Performance of 2. Synthetic Foam-like Fire Extinguishing Agent

 

The so-called synthetic foam fire extinguishing agent means that the main raw materials in its formulation are synthetic, and the production process is basically a physical process. At present, the synthetic foam extinguishing agents used in fixed fire extinguishing systems are mainly aqueous film-forming foam extinguishing agents and high-multiple and medium-multiple foam extinguishing agents. The basic components of foam extinguishing agents have been introduced in the second section of this chapter, and the formulations of various manufacturers vary due to the wide variety of hydrocarbon surfactants. But it is made by dissolving, mixing and stirring the components in the formula in a certain order.

Because the production process of the water film foam extinguishing agent is simple, the dosage is large. Due to price competition, some companies reduce the amount of fluorocarbon surfactants, etc., making many commercially available products may be unqualified. In order to curb the spread of this phenomenon, the national standard "Code for Construction and Acceptance of Foam Fire Extinguishing System" (GB 50281-2006) stipulates that the dosage of 6% low-multiple foam liquid shall not be less than 7.0t and that of 3% low-multiple foam liquid shall not be less than 3.5t, and shall be sent to a testing unit with corresponding qualifications for testing. But the implementation effect is not ideal.

The application range of high-multiplier foam fire extinguishing agent is narrow, and it is difficult to further expand the application site, so the amount is small, the producer is also small, and the relevant manufacturers do not take it as the main product. In addition, as a relatively mature technology, high-multiplier foam fire extinguishing technology is difficult to make new breakthroughs. Some developed countries basically completed the main research and development work before the 1980 s, and my country basically stopped the main research and development after the 1990 s. jobs. Therefore, the current high-multiplier foam fire extinguishing agent basically stays at the technical level of the 1980 s and 1990 s.

 

 

 

3. anti-dissolving foam extinguishing agent

 

Anti-dissolving foam (anti-alcohol foam) is made by adding anti-alcohol and other high molecular polysaccharide compounds (xanthan gum) to ordinary foam. At present, anti-soluble foam has anti-soluble protein, anti-soluble fluorine protein, anti-soluble film fluorine protein, anti-soluble water film, anti-soluble synthetic foam. The mixing ratio is 6% and 3%.

Before the 1980 s, China used a KR-765 of metal soap-type anti-dissolving foam fire extinguishing agents, which were made by adding metal soap complex salt to the hydrolyzed protein solution. The fire extinguishing effect is not ideal, and the length of the foam mixture pipeline is limited to 200m. If it is too long, the metal soap complex will precipitate and settle, and lose its anti-dissolving effect. For this reason, it was later eliminated. In the same era, the Tianjin Fire Research Institute of the Ministry of Public Security developed gel-type anti-dissolving foam extinguishing agent, anti-dissolving fluorine protein foam extinguishing agent and anti-dissolving water film foam extinguishing agent with xanthan gum as anti-alcohol agent. At present, there is a rare application of anti-soluble protein fire extinguishing agent is also added xanthan gum.

At present, a domestic enterprise has also developed and produced a 3% low viscosity anti-fluorine-soluble protein foam extinguishing agent (FP/AR-D) consisting of protein liquid hydrolyzed by calcium hydroxide, 6-carbon composite fluorocarbon surface active agent, foam stabilizer, preservative, etc., with a viscosity of <10 mPa.s at 20 ℃. In the 2015 test of the Ministry of Public Security's special project "Research on Foam Extinguishing Mechanism and Technology of Water-soluble Combustible Liquid Storage Tank", the selectivity of fire extinguishing liquid and how to use it need to be further discussed when relevant specifications are revised.

Due to the addition of xanthan gum in the anti-soluble foam liquid, its viscosity is relatively high. For example, AFFF/AR produced by an enterprise, at 20 ℃, the dynamic viscosity of 6% type is 550mpa.s, and that of 3% type is 1000mpa.s, I .e. 3% type is about twice that of 6% type. Under low temperature conditions, it is difficult to mix the 3% anti-soluble protein, anti-soluble fluorine protein and anti-soluble film fluorine protein foam extinguishing agent into foam mixture according to the rated ratio by the proportional mixing device. If the viscosity is reduced, the amount of polymer compounds such as xanthan gum is usually reduced, and ethylene glycol is added, but this will affect the stability and fire extinguishing performance of the foam.

 

 

Performance of 4. foam fire extinguishing agent

 

In order to ensure the quality, most countries have formulated the technical standards of foam fire extinguishing agent and stipulated the performance of foam fire extinguishing agent. In terms of engineering applications, the main focus is on the main performance indicators of foam such as foam multiple, liquid separation time, fire extinguishing time, and anti-burning time. Low multiple foam and medium and high multiple foam are different in detection test methods, detection items and indicators, see the relevant standards.

The internationally recognized testing standard for foam extinguishing agent is the ISO7203 "Fire Extinguishing Agent Foam Liquid" series of standards, which currently includes three parts. ISO 7203-1 "Fire Extinguishing Agent Foam Liquid is Suitable for Low-fold Foam Liquid Applied on Top of Non-water-soluble Liquid Fuel", ISO 7203-2 "Fire Extinguishing Agent Foam Liquid is Suitable for Low-fold Foam Liquid Applied on Top of Water-soluble Foam Liquid In 1994, China issued the national standard "General Technical Conditions for Foam Extinguishing Agents" GB 15308-94, which is intended to cover all air foam extinguishing agents and replaces the the People's Republic of China Ministry of Public Security standard "Technical Conditions and Test Methods for Protein Foam Extinguishing Agents and Fluoroprotein Foam Extinguishing Agents" (GN13 ~ 14-82). This standard actually draws on the above international standards, but does not use n-heptane used by ISO 7203-1, instead, 90# vehicle gasoline is used, resulting in most products that cannot pass the fire extinguishing test. For this reason, China has separately formulated the national standard "Aqueous Film Forming Foam Extinguishing Agent" GB 17427-1998. The fire extinguishing test fuel adopts solvent oil for rubber industry (120# solvent gasoline). Since then, the national standard "General Technical Conditions for Foam Extinguishing Agents" GB 15308 has been comprehensively revised. In 2006, the renamed national standard "Foam Extinguishing Agents" GB 15308-2006 has been issued. Since then, a complete and unified foam extinguishing agent testing standard has been formed, and local revision provisions have been issued in 2009. Due to the difficulty of obtaining n-heptane, the standard fire extinguishing test fuel uses solvent oil for rubber industry.

The short extinguishing time and long anti-burning time indicate that the foam has good fire extinguishing performance. See Table 4-1 for the relevant provisions of the national standard Foam Extinguishing Agent GB 15308-2006.

 

As far as the fire extinguishing difficulty of the test fuel is concerned, n-heptane has a single component, boiling range of 98.2 ℃ ~ 98.6 ℃, and the combustion state is stable, while the boiling range of 120# solvent gasoline is 80~120 ℃, and the latter is slightly more difficult than the former.

 

Table 4-1 Fire Extinguishing Performance Level and Burning Resistance Level of Low Expansion Foam

 

 

With regard to the storage period (validity period) of foam extinguishing agents, most manufacturers promise to store protein foam and anti-dissolving foam extinguishing agents for 2 years under the required conditions, aqueous film foam extinguishing agents for 8 years, and high-multiplier foam extinguishing agents for three years. However, under the actual engineering storage conditions, there will be differences due to the influence of environmental temperature, humidity, sealing conditions and other factors. However, for good quality proteinaceous foam extinguishing agents, the 2-year effective storage period may be conservative; under adverse conditions, the 8-year effective storage period of aqueous film foam extinguishing agents may be of concern. Therefore, should be timely inspection and testing.