Discussion on fire fighting of the largest liquefi

With the development of social economy and the gradual deepening of the commercialization of LPG Industry, LPG, as an important industrial and domestic energy, has spread all over major and medium-sized cities. In order to save costs, reduce land occupation and operating expenses, modern liquefied gas production, storage, transfer and sales enterprises are developing towards large-scale and intensive. Large and oversized gas tanks of 2000m3 ~ 100000m3 are not uncommon. Since compressed liquefied gas is a liquid at room temperature, with high output pressure and fast flow speed, there is great danger to improve product quality. Once leakage or fire occurs, the consequences are unimaginable. It is of great practical significance to study, be familiar with and master the characteristics of liquefied gas fire, leakage characteristics and the technology and tactics of disposal. This article talks about some superficial views

I. fire risk analysis of liquefied gas leakage

most of the current liquefied petroleum gas materials are propane and butane, which belong to class a dangerous chemicals, with high combustion calorific value and low explosion limit. In addition, there are many spherical tanks, many pipelines, large volume and large capacity in large storage tank areas, which together constitute the high risk of large storage tank areas. First, the lower explosion limit is low. Once it leaks, it is very easy to form explosive mixture in the air, which can explode and cause explosion in case of open fire or static electricity. The explosion limit of liquefied petroleum gas is usually between 1.5% and 10%. The air mass formed by leakage is very easy to reach the explosion limit in the air, and the dead progress prospect of the building is very decadent and low-lying. When encountering strong winds or strong airflow, its drift distance can reach 1500m, forming explosive mixed gas in a large range, and will cause explosion and large-area combustion when encountering fire sources, The strong shock wave of 2000 ~ 3000m/s generated is enough to destroy the gas transmission pipeline within the scope of explosion, thus causing new secondary disasters such as leakage, combustion, deflagration, etc. Second, the combustion heat value is high, the flame temperature is high, and the strong thermal radiation will seriously threaten the safety of this tank, adjacent tanks and nearby gas transmission pipelines. The leakage combustion of liquefied petroleum gas is characterized by fast combustion speed, large over fire area and three-dimensional combustion. The combustion temperature in the gas with slight chemical change on the surface of empty PCU can reach 1800 ℃, and the strong radiant heat directly bakes the safety of adjacent tanks or nearby filling areas and their gas transmission pipelines, which is very easy to cause multi-point leakage and multi-point combustion. Third, large liquefied gas storage tanks have large capacity, large heating area, long leakage and combustion time, and it is difficult to guide the tank technology. For the heated adjacent tanks, due to their large capacity (usually more than 2000m3) and large volume (the diameter of the inner tank is usually 30 ~ 40m), the compressed LPG in the tank changes from liquid to gaseous after heating, and the volume expands rapidly (the expansion rate of the liquid LPG is about 10 ~ 14 times greater than that of water), resulting in a sudden increase in the pressure in the tank, causing local overpressure and prone to biological rational explosion. At the same time, compared with the liquid LPG, the liquefied gas that changes to gaseous state, When guiding the tank, the gas output speed is fast, and it is easy to accumulate a large amount of static electricity. If the air tightness of the gas transmission pipeline is slightly poor, a new leakage combustion point will be formed, resulting in the expansion of the fire

II. Difficulties in fire suppression of large liquefied gas tank leakage

first, the tank is large and difficult to cool. Under normal circumstances, the fire sprinkler facilities at the scene of explosion and fire caused by leakage are generally damaged and lose the cooling function. High power fire engines are often difficult to approach due to the complexity of roads, pipelines and site conditions. The on-board water cannon cannot effectively cool directly from the upper part of the tank. Even if close combat cooling is carried out at risk, it is often inadequate due to insufficient pressure, insufficient range and small flow. Second, the radiation is strong and it is difficult to extinguish the fire and stop the leakage. Once the liquefied gas tank causes leakage and combustion, a blowout flare will be formed at the leakage, causing thousands of degrees of temperature around. In addition, the inlet and outlet valves on the top of the tank may be damaged, so that the rescuers cannot start the automatic control system shut-off valve, let alone climb on the top of the tank to manually shut-off the valve. However, it is not only difficult and risky to carry out fire fighting directly from the leakage port and do a good job in epidemic prevention and control in an all-round way, but also difficult for the personal protection of combatants to meet the fire-fighting requirements. Third, the leakage is fast and easy to cause secondary explosion. In the process of extinguishing the liquefied gas leakage fire, when the water is sprayed directly to the leakage part, it will accelerate the evaporation of liquefied gas, make the combustion flame hotter, and release more heat energy. If an explosion is formed, a "vapor cloud" of liquefied petroleum gas will be generated. Once the air invades and generates an explosive mixture of gas, it can produce "secondary explosion", "tertiary explosion" and even continuous multiple explosions when encountering fire, So as to produce unimaginable malignant consequences