Difference Between Compressed Gas and Liquefied Gas
1. Definition of compressed gas and liquefied gas.
1) Compressed or liquefied gas with a critical temperature lower than 50, or a vapor pressure greater than 294kPa at 50;
2) Compressed gas with an absolute pressure greater than 275 kPa at a temperature of 21 1 or a compressed gas with an absolute pressure greater than 715 kPa at 54 4; Or at 37 8, the red vapor pressure is greater than 275kPa liquefied gas or pressurized dissolved gas.
In order to facilitate storage, transportation and use, the gas is often compressed or liquefied by cooling and pressurization method and stored in cylinders. Due to the different properties of various gases, some gases will not become liquid at room temperature, no matter how much pressure is added to it, and the temperature must be reduced to a certain value at the same time as pressure to liquefy it (the temperature is called critical temperature), and at the critical temperature, the minimum pressure necessary to liquefy the gas is called critical pressure. Some gases are easier to liquefy, and at room temperature, simple pressure can make them liquid, such as chlorine, ammonia, and carbon dioxide. Some gases are more difficult to liquefy, such as helium, hydrogen, nitrogen, and oxygen. Therefore, some gases are easily pressurized into a liquid state, and some are still in a gaseous state, and those in a gaseous state in a cylinder are called compressed gases, and those in a liquid state are called liquefied gases. In addition, this class includes dissolved gases under pressure, such as acetylene.
2. Hazardous characteristics of compressed gases and liquefied gases.
1) More than half of compressed gases and liquefied gases are flammable and explosive. Once the flammable gas is ignited, it can all be burned out in a very short time, which is very dangerous and difficult to extinguish.
2) Strong flow diffusion. Compressed and liquefied gases can spontaneously fill any container and diffuse very easily. For example, most flammable gases are heavier than air, can spread quite far, drift on the surface, ditches, tunnels, dead corners of factories, etc., gather for a long time, and burn or ** in case of fire source, which is easy to cause the fire to expand.
3) Expansion by heat and increase of air pressure. Both compressed and liquefied gases stored in cylinders usually have high air pressures. Excessive heating will cause the air pressure to rise sharply, and once the air pressure exceeds the compressive strength of the container, it will cause the container to rupture and cause accidents, such as fire or poisoning.
4) It is easy to generate or accumulate static electricity. When compressed and liquefied gases are ejected at high velocity from the nozzle or from a broken area, static electricity is generated due to strong friction.
5) It is corrosive and toxic. In addition to oxygen and compressed air, most compressed gases and liquefied gases are toxic and corrosive.
6) Asphyxiating. Compressed gas and liquefied gas have a certain degree of suffocation, once a leak occurs, if the corresponding ventilation measures are not taken, people can suffocate to death.
7) It is oxidizing. There are two kinds of hazards of compressed gas and liquefied gas: one is combustible gas, such as oxygen; The second is toxic gas, which is not flammable, but has strong oxidation, and can be burned or ** after mixing with combustible gas, such as chlorine and acetylene.