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液化石油气主要知识简介 Section 1 Introduction to the main knowledge of LPG
First, the main ingredients
Liquefied petroleum gas is a by-product obtained from the production process of petroleum extraction, cracking and refining. C3H8 ）、丙烯（ C3H6 ）、丁烷（ C4H10 ）、丁烯（ C4H8 ）和丁二稀（ C4H6 ），同时还含有少量的甲烷（ CH4 ）、乙烷（ C2H6 ）、戊烷（ C5H12 ）及硫化氢（ H2S ）等成分。 Liquefied petroleum gas is a mixture of hydrocarbons. Its main components include: propane ( C3H8 ), propylene ( C3H6 ), butane ( C4H10 ), butene ( C4H8 ), and butadiene ( C4H6 ). It also contains a small amount of methane. ( CH4 ), ethane ( C2H6 ), pentane ( C5H12 ) and hydrogen sulfide ( H2S ). Liquefied petroleum gas is obtained from different production processes, and its composition is different. C3H8。 The chemical formula of LPG is C3H8.
C3 、 C4 成分的沸点都低于常温，容易汽化为气体，由于 C5 以上成分的沸点较高，在 C3 、 C4 等汽化之后仍以液态残留在容器之中，因此称为残液。 Under normal pressure conditions, the boiling points of the C3 and C4 components of the liquefied petroleum gas are lower than normal temperature, and they are easy to vaporize into gas. Due to the higher boiling points of the components above C5 , they still remain in the container in liquid state after vaporization of C3 , C4, etc. It is therefore called residual fluid. The content of residual liquid liquefied petroleum gas in our country is relatively high.
Second, the main physical properties
． 1 . Relative density
Liquefied petroleum gas is a mixture whose relative density changes with composition. 1.2~2.0 倍；液态相对密度大约 0.51 。 Generally speaking, the relative density of liquefied petroleum gas is 1.2 to 2.0 times the relative density of air; the relative density of liquid is about 0.51 .
． 2 ． Liquid volume expansion coefficient
10-16 倍。 The volume expansion coefficient of liquid liquefied petroleum gas is about 10-16 times the volume expansion coefficient of water at the same temperature . Therefore, when the container is filled with liquefied petroleum gas, the liquid phase must not be filled, but a certain gap must be left for occupation by the heated volume expansion.
． 3 ． Solubility
Solubility refers to the water content of liquefied petroleum gas. It is characterized by increasing solubility with increasing temperature. Because liquefied petroleum gas has a certain solubility in water, a certain amount of water is often deposited on the bottom of the liquefied petroleum gas container such as a storage tank, a steel bottle and the like, and it needs to be discharged regularly.
． 4 . Concentration explosion limit, minimum ignition energy, combustion heat value
Liquefied petroleum gas is a mixture of hydrocarbons, and its concentration explosion limit, minimum ignition energy, and combustion heat value change with the composition. 1.5%~9.5% ，最小点火能量低于 0.3 毫焦耳，燃烧热值为 92092~12139 千焦 / 立方米。 However, it is generally believed that the explosion limit of the volume concentration of liquefied petroleum gas in the air is about 1.5% to 9.5% , the minimum ignition energy is less than 0.3 millijoules, and the heat of combustion is 92092 to 12139 kilojoules per cubic meter.
． 5 . Resistivity
1011~1014 欧 * 厘米。 The resistivity of liquefied petroleum gas is about 1011 ~ 1014 ohm * cm. 9000 伏。 It is determined that the electrostatic potential generated when liquefied petroleum gas is ejected from containers, equipment and pipelines can reach 9000 volts.
Third, the fire danger of liquefied petroleum gas
． 1 . Explosive
When liquid petroleum gas is mixed with air to a certain ratio (or concentration), it can cause a fire and explosion when it encounters a fire source. % ）来表示。 The concentration range at which this fire source can explode (ignite) is called the explosive (ignition) concentration limit (referred to as the explosive limit), which is usually expressed by volume percentage ( % ). 1.5%~9.5% 。 The explosion limit of LPG is about 1.5% ~ 9.5% . 1.5%~9.5% 这个范围时，混合气体遇火源就能着火爆炸；当液化石油在空气中的浓度低于 1.5% 时，因可燃气体不足，混合气体不燃烧、不爆炸， 1.5% 叫做液化石油气的爆炸下限；当液化石油气在空气中的浓度高于 9.5% 时，因氧气不足，混合气体也不燃烧、不爆炸， 9.5% 叫做液化石油气的爆炸上限。 That is to say, when the concentration of liquefied petroleum gas in the air reaches the range of 1.5% to 9.5% , the mixed gas can explode when it encounters a fire source; when the concentration of liquefied petroleum gas in the air is less than 1.5% , Insufficient, the mixed gas does not burn or explode. 1.5% is called the lower explosion limit of LPG; when the concentration of LPG in the air is higher than 9.5% , the mixed gas does not burn or explode due to insufficient oxygen, 9.5% It is called the upper explosion limit of LPG.
When the concentration of liquefied petroleum gas in the air is at the lower explosive limit or the upper explosive limit, the mixed gas generally only deflagrates when encountering a fire source. 405 千帕（ 4 个大气压）。 Deflagration pressures generally do not exceed 405 kPa ( 4 atmospheres). 4.0% ），则发生威力最大的爆炸。 However, when the concentration of liquefied petroleum gas in the air exceeds the lower explosive limit, especially when the reaction equivalent concentration (about 4.0% ) is reached , the most powerful explosion occurs. 709 千帕（ 7 个大气压），爆炸后压力还会不断激增，并伴有震耳的声响。 The pressure generated during the explosion can reach 709 kPa ( 7 atmospheres). After the explosion, the pressure will continue to increase, accompanied by a loud noise.
Because the lower explosion limit of liquefied petroleum gas is low, as long as a small amount of gas leaks, it will quickly form an explosive mixed gas with air within a certain range, so it is said that liquefied petroleum gas is extremely flammable.
． 2 ． Easy to burn
LPG is a first-grade combustible gas and is more flammable than gas (carbon monoxide), gasoline and other substances.
LPG is not only flammable, but also the heat (calorific value) and flame temperature emitted when burning. 15605.5 千焦 / 公斤（ 91272 千焦 / 立方米 ) ，火焰温度高达 2120 ℃ 。 Its calorific value is more than 15605.5 kJ / kg ( 91272 kJ / m3 ) , and the flame temperature is as high as 2120 ℃ . When the fire is on, the heat radiation is very strong, and it is easy to ignite and detonate the surrounding flammable and explosive materials, which will cause the fire to expand.
． 3 ． Easy to swell
The liquefied petroleum gas stored in the container is in an equilibrium state of gas-liquid coexistence at a certain temperature and saturated vapor pressure. As the temperature increases, the volume of the liquid will continue to expand, and the gaseous pressure will continue to increase. 1℃ ，体积膨胀 0.3~0.4% ，气压增大约 19.6~29.4 千帕。 For every 1 ° C increase in temperature , the volume expands by 0.3 to 0.4% , and the air pressure increases by approximately 19.6 to 29.4 kPa. The higher the temperature, the greater the volume expansion, and the greater the air pressure.
48℃ 时的饱和蒸气压确定钢瓶的设计压力为 1568 千帕，按照液态纯丙烷在 60 ℃ 时刚好充满整个钢瓶来设计钢瓶的内容积。 According to this physical property of liquefied petroleum gas, the state stipulates that the design pressure of the cylinder should be 1568 kPa according to the saturated vapor pressure of pure propane at 48 ° C , and the interior of the cylinder should be designed according to the pure pure propane at 60 ° C to fill the entire cylinder. Volume. 0.42 公斤。 And stipulated that the filling volume of the steel bottle is not more than 0.42 kg per liter . 85% ，还留有 15% 的气态空间供液态受热膨胀。 If it is filled according to the prescribed filling volume, at normal temperature, the liquid volume occupies only about 85% of the inner volume of the cylinder , and 15% of the gaseous space is left for the liquid to expand when heated. 48 ℃ ，钢瓶是不可能爆炸的，但是，如果让钢瓶接触热源，那就很危险了。 Under normal circumstances, the ambient temperature does not exceed 48 ℃ , and it is impossible for a cylinder to explode. However, if the cylinder is exposed to a heat source, it is very dangerous.
． 4 . Easy to gasify
Liquefied petroleum gas is gaseous at normal temperature and pressure. It is compressed and liquefied to a liquid state under low temperature or high pressure conditions and stored in a pressure-resistant container. 1 个大气压）下的沸点为－ 42.1~0.5 ℃ 即液体开始沸腾气化时的温度。 The boiling point of liquid liquefied petroleum gas at atmospheric pressure ( 1 atmosphere) is -42.1 ~ 0.5 ℃ , which is the temperature at which the liquid begins to boil and vaporize. Therefore, liquid liquefied petroleum gas is easily vaporized at normal temperature and pressure. 升液体可气化为 250~300 升气体。 1 liter of liquid can be gasified into 250 ~ 300 liters of gas. 1.5 倍 ~2.0 倍。 The relative density of gaseous liquefied petroleum gas is 1.5 to 2.0 times that of air . Because it is heavier than air, it is not easy to spread out, and can float on the ground for a long time or accumulate in low places. Therefore, in the process of storage, filling, transportation, and use of liquefied petroleum gas, once a liquid leak occurs, it will easily cause a large-scale fire or explosion accident.
． 5 . Easy to generate static electricity
The liquefied petroleum gas can generate static electricity when it is ejected from a nozzle, a nozzle or a broken place at high speed. According to tests, the electrostatic voltage generated when liquefied petroleum gas is ejected can reach thousands or even tens of thousands of volts. The main reason is that liquefied petroleum gas is a multi-component mixed gas. The gas contains liquid or solid impurities, which causes strong friction with nozzles, nozzles or broken places during high-speed ejection. The more liquid or solid impurities contained in the liquefied petroleum gas, the more electrostatic charges it generates; the faster the gas flow rate, the more electrostatic charges it generates. 350~450 伏时，所产生的放电火花就能引起可燃气体燃烧或爆炸。 According to measurements, when the electrostatic voltage is between 350 and 450 volts, the generated sparks can cause a combustible gas to burn or explode. Because the liquefied petroleum gas is ejected from the nozzle, nozzle or damaged place at high speed, it is easy to generate high potential static electricity, so its discharge spark is enough to cause fire or explosion accident.
． 6 . Corrosive
Most of the liquefied petroleum gas contains different amounts of hydrogen sulfide. 作用；硫化氢的含量越高，对容器的内壁腐蚀越快。 Hydrogen sulfide has a corrosive effect on the inner wall of the container ; the higher the content of hydrogen sulfide, the faster the inner wall of the container corrodes. 0.1 毫米 / 年。 According to some measurements, the corrosion rate of the inner wall of the cylinder by hydrogen sulfide is as high as 0.1 mm / year. As a liquefied petroleum gas container is a pressure container, internal corrosion can continuously thin the container wall, reduce the compressive strength of the container, shorten the service life of the container, cause leakage or burst of the container perforation, and cause fire and explosion accidents. FeS ）粉末，附着在器壁上或沉积于容器底部。 At the same time, the inner wall of the container is corroded by hydrogen sulfide, and it also generates black-brown ferrous sulfide ( FeS ) powder, which is attached to the container wall or deposited on the bottom of the container. Fe3O4 ）和二氧化硫（ SO2 ）。 If this kind of ferrous sulfide powder is poured out with the residual liquid, or a large amount of air enters the container for evacuating the liquid, the ferrous sulfide powder will oxidize with the oxygen in the air, exotherm and spontaneously ignite to form iron oxide ( Fe3O4 ) And sulfur dioxide ( SO2 ). This spontaneous combustion phenomenon is also easy to cause fire and explosion accidents.
10% 时，就会使人头昏，以至窒息死亡。 In addition, liquefied petroleum gas is narcotic to the central nervous system of the human body. When the concentration of liquefied petroleum gas in the air is higher than 10% , it will make people dizzy and even suffocate to death. 10~15 毫克 / 米 3 时，会使人中毒，另外，液化石油气在不完全燃烧时会产生一氧化碳毒气。 In addition, hydrogen sulfide in liquefied petroleum gas is toxic. When the content of hydrogen sulfide in the air is higher than 10-15 mg / m3 , it will cause people to be poisoned. In addition, liquefied petroleum gas will be produced when incomplete combustion Carbon monoxide poison gas. Therefore, there must be good ventilation when storing, filling and using liquefied petroleum gas, and care must be taken when extinguishing fires.
Fourth, the combustion conditions of liquefied petroleum gas
LPG is flammable and explosive, but there are certain conditions for combustion and explosion. For LPG to burn or explode, the following three conditions must be met at the same time:
First, there must be a certain amount of combustible gas. Only when the concentration of liquefied petroleum gas in the air reaches the explosive limit range can it burn or explode. 9.5% ，如重新遇到空气，就仍有燃烧或爆炸的危险。 If the concentration of liquefied petroleum gas in the air is higher than 9.5% , if it encounters air again, there is still the danger of burning or explosion.
Second, there must be sufficient air, and for LPG to burn or explode, sufficient air must be mixed with it. If there is not enough air, the combustion will gradually weaken until it goes out. 21% ，氮气约占 79% 。 In the air, oxygen accounts for approximately 21% and nitrogen accounts for approximately 79% . 11.5% 时，液化石油气就不会燃烧或爆炸。 When the oxygen content in the air is lower than 11.5% , the LPG will not burn or explode.
1 立方米的液化石油气完全燃烧大约需要 30 立方米的空气。 In general, about 30 cubic meters of air is required to fully burn 1 cubic meter of liquefied petroleum gas .
Third, there must be a source of fire. Any thermal energy source that can cause LPG to burn or explode is called a source of ignition. Such as flames, red hot metals, Mars and electric sparks. For LPG to burn or explode, the ignition source must have a certain temperature and heat. 430~460℃ ，最小点火能量约为 0.31~0.38 毫焦耳，引爆的最小电流强度为 0.36~0.48 安。 It is generally believed that the liquefied petroleum gas composed of various components has an ignition temperature of about 430 to 460 ° C , a minimum ignition energy of about 0.31 to 0.38 millijoules, and a minimum current intensity of detonation of 0.36 to 0.48 amps. Tiny flames are enough to cause the combustion or explosion of liquefied petroleum gas.
In summary, only when the above three conditions are met at the same time and interact with each other can the LPG be burned or exploded.
Here, it should be noted that although both combustion and explosion are phenomena that are manifested by a violent chemical reaction between liquefied petroleum gas and oxygen in the air under the action of a heat source, there is a difference between the two. 处高压喷出，受磨擦或其他着火源作用，则发生喷流式的扩散燃烧；如果液化石油气与空气的混合是在燃烧之前进行的，如气体泄漏到空间与空气混合达到着火（爆炸）浓度极限后，遇火源则发生瞬间燃烧，同时生成大量的热和气体，并以很大的压力向四周扩散，这种瞬间燃烧现象就是爆炸。 From the point of view of fire protection, if the mixing of liquefied petroleum gas and air is carried out during the combustion process, such as gas cooking, welding, etc., stable diffusion combustion occurs; if the liquefied petroleum gas is from the container nozzle, nozzle Or high-pressure spray from the damaged area, friction or other sources of ignition, jet-type diffusion combustion occurs; if the mixture of liquefied petroleum gas and air is performed before combustion, such as gas leaking into space and mixing with air to catch fire (Explosion) After the concentration limit, instantaneous combustion occurs when encountering a fire source, and a large amount of heat and gas are generated at the same time, and it spreads to the surrounding area with a large pressure. This instantaneous combustion phenomenon is an explosion.
V. Basic measures for fire and explosion prevention of LPG
According to the three conditions of LPG combustion or explosion, corresponding preventive measures can be targeted to prevent these three conditions from coexisting and interacting. The basic measures for fire and explosion protection are:
． 1 . Manage the gas source to prevent leakage
In the process of storage, filling, transportation, and use of liquefied petroleum gas, it is prohibited to use unqualified containers and equipment, and overfilling is prohibited to prevent equipment from leaking or bursting. Attention should be paid to ventilation to prevent deposition after gas leakage; Residual fluids are forbidden to be stored or used in underground buildings.
． 2 ． Cut off from the air
For liquefied petroleum gas, it is mainly to prevent air from entering the container. Because air enters the container, it can form explosive mixed gas in the container, which is very dangerous. Therefore, the newly manufactured liquefied petroleum gas storage tanks, tank cars, and cylinders must be evacuated before filling; the liquefied petroleum gas in the storage tanks, tank cars, and cylinders cannot be completely discharged or used up, and the residual pressure should be left, and The valve should be closed tightly so that the remaining air does not escape, etc.
． 3 ． Eliminate ignition sources
Liquefied petroleum gas cylinders are not allowed to be near high heat sources and are not allowed to be used in the same room with coal stoves. When equipment leaks, all nearby fires must be banned immediately. LPG storage and supply stations must be designated for fire ban areas and all fire sources; Tractor, battery cart and carriage are strictly prohibited from entering the fire banned area. The entrance of cars and tank cars must be equipped with a fireproof cover on the exhaust pipe; workers entering the station must wear anti-static shoes and anti-static clothing. Lighters and matches are strictly prohibited. Tools that can catch fire; electrical equipment in the station must be explosion-proof, storage tanks and pipelines must have good static discharge facilities, and reliable lightning protection facilities must be installed in the storage tank area; hot-fire welding and cutting operations in the depot are strictly prohibited.
． 4 . Implement fire separation and fire blocking facilities
Build firewalls between LPG buildings and other buildings, set fire prevention distances and fire exits; build protective walls in storage tank areas; set pressure relief doors and windows, and light roofs in factory warehouses that can form explosive mixed gases And ventilation facilities; install safety valves, emergency shut-off valves on container pipes; safety water seals on drainage pipes, etc.