Complete Analysis of Liquefied Petroleum Gas Knowledge: Source, Composition, Usage, Characteristics, and Hazards

1、 Source and composition of liquefied petroleum gas

Source of liquefied petroleum gas
Liquefied petroleum gas, mainly composed of propane and butane, is produced as a byproduct in the process of oil and gas extraction and refining. These hydrocarbons are gases at room temperature and pressure, but can be converted into liquids by pressurization or cooling, hence the name liquefied petroleum gas. These gases are colorless and odorless at room temperature, lighter than water, and insoluble in water. For the convenience of leak detection, thiols and ethers are intentionally added during transportation and storage to give it a pungent odor.

Composition of liquefied petroleum gas
The main components of liquefied petroleum gas include propane (C3H8) and butane (C4H10), while also containing small amounts of methane, ethane, propylene, butene, and other components. In addition, the remaining trace liquid in the steel cylinder is called residual liquid, which is mainly composed of pentane and hydrocarbons above pentane. According to national standards, the residual liquid content should be controlled within 3%.

2、 The widespread application of liquefied petroleum gas
Civil gas: Liquefied petroleum gas is an important energy source for household cooking, boiling water, heating, etc.
Industrial use: It is widely used in processes such as drying, shaping, foaming, melting metals, and baking.
Agricultural production: Liquefied petroleum gas is also suitable for baking, heating, and ripening in agricultural production.
3、 Physical and chemical properties of liquefied petroleum gas
Density: Density is a measure of the mass of a substance per unit volume. The density of liquefied petroleum gas varies depending on its state, with a density of approximately 2.01 to 2.50 Kg/Nm3 in the gaseous state and a density ranging from 0.5297 to 0.6165 KG/liter in the liquid state.
Specific gravity: Specific gravity represents the ratio of the density of a substance to the density of a standard substance. The gas density of liquefied petroleum gas is 1.52 times that of air, which means it will sink in the air and flow towards low-lying areas. And liquid liquefied petroleum gas is lighter than water, with a specific gravity range between 0.50.6.
Volume expansion coefficient: The volume expansion coefficient is a parameter that measures the change in volume of a substance with temperature. However, the original text did not provide detailed information regarding the specific value of this parameter.
Liquids usually expand when heated, and the higher the temperature, the more significant the expansion. The expansion coefficient of liquefied petroleum gas is approximately 16 times that of water, so sufficient space must be reserved when filling containers. At the same time, the filling coefficient of liquefied petroleum gas should be controlled within 85% at normal temperature and pressure to ensure safety.

In addition, the saturated vapor pressure of liquefied petroleum gas is also a key parameter. At a certain temperature, the gaseous and liquid states of liquefied petroleum gas will reach an equilibrium state, at which point the vapor pressure is the saturated vapor pressure. It should be noted that as the temperature increases, the saturated vapor pressure also increases accordingly. The design temperature range for civilian liquefied petroleum gas cylinders is+60 ℃ to -40 ℃, and the saturated vapor pressure at+60 ℃ is used as the design basis, with a design pressure of 1.57MPa.

In addition, the latent heat of vaporization of liquefied petroleum gas is also an important physical quantity. When a liquid vaporizes, it absorbs a large amount of heat, which is called latent heat of vaporization. When a large amount of gas is supplied from a steel cylinder, the temperature of the cylinder will decrease due to the large amount of heat required for liquid evaporation. If the ambient temperature is low and the required heat cannot be provided in a timely manner, the temperature of the steel cylinder will further decrease, causing the surrounding water vapor to condense into dew or frost. At this time, the indoor temperature should be appropriately increased or the amount of liquefied petroleum gas used should be reduced to prevent the pressure of liquefied petroleum gas from decreasing due to low room temperature, which affects normal gas supply.

In addition, the flash point and ignition point of liquefied petroleum gas are also important indicators for evaluating its hazard. Flash point refers to the lowest temperature at which a gas can ignite instantly when mixed with air. The main components of liquefied petroleum gas have a low flash point, which means that its danger is relatively high. Therefore, extra caution must be taken when handling and using liquefied petroleum gas.
After mixing gaseous liquefied petroleum gas with air, it will undergo continuous combustion once it comes into contact with an open flame. The lowest temperature of this combustion is called its ignition point or ignition temperature. Under normal pressure, the ignition point range of liquefied petroleum gas is approximately between 470 ℃ and 510 ℃.

Next, let's talk about boiling point. As the temperature of the liquid increases, its vapor pressure will gradually rise until it reaches equilibrium with the external pressure. When the temperature of a liquid reaches a specific value, internal gasification occurs, which is called boiling. The temperature at which boiling occurs is called the boiling point. It is worth noting that the boiling point will adjust with changes in external pressure. For example, if the air is thin on a high mountain and the pressure is below 1 atmosphere, the boiling point of water will be below 100 ℃. By contrast, at one standard atmospheric pressure, the boiling point of water is 100 ℃, while the boiling point of propane in liquefied petroleum gas is -42 ℃ at standard atmospheric pressure, but when the pressure increases to 8 atmospheres, its boiling point rises to+20 ℃.

In addition, gaseous liquefied petroleum gas condenses into dew point when cooled or pressurized, and the temperature at this point is called dew point. For example, at 1 atmosphere, the dew point of propane is -42 ℃, while at 8 atmospheres, the dew point value is+20 ℃. This means that below this dew point temperature, liquefied petroleum gas will transition from a gaseous state to a liquid state. It is worth noting that the boiling point and dew point of liquid liquefied petroleum gas are the same at the same pressure, which actually represents the saturation temperature at the saturation pressure of liquefied petroleum gas.

In addition, liquefied petroleum gas also has explosive properties. When it mixes with air and reaches a certain concentration, it will explode when exposed to an open flame. The concentration range of gas that can trigger an explosion is called the explosion limit, usually expressed as a volume percentage. Within this range, the lower limit of gas concentration is called the lower explosive limit, and the upper limit is called the upper explosive limit. For liquefied petroleum gas, its explosive limit range is 1.5% to 9.5%.

In summary, liquefied petroleum gas has the characteristics of being volatile, flammable, and explosive, so extra caution must be taken when using and handling it. Understanding its physical properties and hazards helps us use this energy more safely.
The flash point range of liquefied petroleum gas is -140 ℃ to -40 ℃, which makes it highly flammable and therefore highly dangerous. When liquefied petroleum gas comes into contact with air, even tiny Mars can ignite it, and its combustion value is quite high, reaching 2.10 × 104 to 2.90 × 104 Kcal/m3, which is even higher than the combustion value of natural gas. In addition, the combustion speed of liquefied petroleum gas is also quite fast, reaching 0.38 to 0.5 meters per second.

On the other hand, although liquefied petroleum gas has a low sulfur content and is generally not corrosive, it has a softening effect on rubber and can dissolve certain oil-based paints and pastes. Therefore, when dealing with liquefied petroleum gas, it is necessary to use specialized high-pressure hoses to prevent such chemical reactions.

Meanwhile, liquefied petroleum gas also has certain toxicity. When the concentration in the air is below 1%, it is harmless to the human body; However, prolonged exposure to high concentrations of liquefied petroleum gas may have adverse effects on the nervous system. It is worth noting that when the concentration of liquefied petroleum gas in the air exceeds 10%, it can cause suffocation.

In addition, liquefied petroleum gas also has the characteristics of thermal expansion and contraction, with an expansion coefficient of about 16 times that of water. This means that even small changes in temperature can lead to a significant increase in pressure when a steel cylinder is filled with liquefied petroleum gas. Therefore, strictly prohibiting overloading is an important regulation for the safe operation of liquefied petroleum gas.

The danger of liquefied petroleum gas cannot be ignored. Due to its low flash point, it poses a great risk of fire, especially in hot summers or cold winters, where it can ignite upon contact with fire without the need for heating. In addition, the explosion range of liquefied petroleum gas is wide, and once it encounters a fire source, there is a risk of combustion or even explosion. Its explosion speed can reach 2000 to 3000 meters per second, the flame temperature can reach up to 2000 ℃, and its destructive power is extremely high. Therefore, when storing and using liquefied petroleum gas, safety regulations must be strictly followed to ensure good ventilation and prevent accidents from occurring.
Liquefied petroleum gas has a low boiling point range and is usually in a liquid state under low temperature or pressure conditions, stored in specialized storage tanks or steel cylinders. Once a leak occurs, these liquefied gases will quickly transform from liquid to gas, while absorbing a large amount of heat from the surrounding environment, resulting in local low temperatures. Especially when there is a leakage at the valve of the pipeline, a low-temperature environment may form there, and even ice may form, which may seriously affect the normal closing of the valve. During the maintenance process, there is a risk of a large amount of liquid liquefied petroleum gas splashing, which can cause frostbite if it splashes onto the human body. In addition, when exposed to liquid liquefied petroleum gas, one may feel extremely cold. Failure to change clothes in a timely manner and encounter a fire source may lead to serious accidents. Therefore, immediate action should be taken, such as using a damp cloth or water to extinguish the fire, to prevent the accident from further escalating.

In addition, liquefied petroleum gas also has a certain risk of poisoning. After high concentrations of liquefied petroleum gas are inhaled by the human body, it can have an anesthetic effect on the central nervous system, leading to symptoms such as coma, vomiting, and even suffocation and death in severe cases. Meanwhile, the combustion process of liquefied petroleum gas requires a large amount of air, and incomplete combustion under oxygen deficient conditions can produce toxic gases such as carbon monoxide, further increasing the risk of poisoning.