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Advantages of using cryogenic cylinders for storing and transporting liquid oxygen, ammonia, and argon, as well as questions regarding cylinder packaging and safety in use: From the perspectives of efficiency and cost, what are the advantages of using cryogenic cylinders for storing and transporting liquid oxygen, ammonia, and argon compared to using steel cylinders for this purpose? Answer: Gaseous oxygen, nitrogen, and argon are stored, usually in steel seamless gas cylinders with a capacity of 40L. The weight of this type of gas cylinder is approximately 60 kg, and at a filling pressure of 14.7 Mpa, the standard volume of oxygen, nitrogen, or argon that can be stored in it is 6 m3. Since the standard densities of oxygen, nitrogen, and argon are 1.429 kg/m3, 1.251 kg/m3, and 1.784 kg/m3 respectively, the weights of oxygen, nitrogen, and argon filled in are 8.574 kg, 7.506 kg, and 10.704 kg respectively. The ratios of the cylinder’s net weight to the weight of the gas are 6.998, 7.994, and 5.605, respectively. It can be seen that for every 1 kg of gas transported, 5.6 to 8 kg of steel must be transported as well, resulting in extremely low transportation efficiency. When storing and transporting liquid oxygen, nitrogen, and argon in low-temperature cylinders, since at standard conditions their densities are 1140 kg/m3 for liquid oxygen, 810 kg/m3 for liquid nitrogen, and 1410 kg/m3 for liquid argon, these values are respectively 797.76 times, 647.48 times, and 790.36 times the densities of their gaseous forms under standard conditions; or they are respectively 142.81 times that of gaseous oxygen at 20°C and 14.7 Mpa, 115.91 times that of gaseous nitrogen, and 141.49 times that of gaseous argon. The ratio of the weight of cryogenic cylinders used to transport liquid oxygen, nitrogen, and argon to the weight of the liquid gases being transported is much smaller. For example, the cryogenic cylinders produced by Sichuan Air Separation Equipment Factory, which can store and transport 147 L or 168 kg of liquid oxygen, weigh only 110 kg. The ratio of their weight to the weight of the liquid gas they carry is 0.655. If steel seamless cylinders are used to transport 168 kg of gaseous oxygen, 20 cylinders with a capacity of 40 L each would be required, giving a total weight of 1200 kg. The ratio of the weight of these cylinders to the weight of the gas inside them is 7.14, which is 10.9 times higher than the previous ratio. In terms of saving transportation fuel, a cryogenic cylinder with a capacity of 175 L is equivalent to 20 steel cylinders used for transporting gaseous substances. When transported using 4-ton trucks, each truck can carry 6 to 8 cryogenic cylinders. If calculated based on 6 units per load, this means 120 steel gas cylinders per truck. This is equivalent to 2.4 times the transportation efficiency when transporting bottled gaseous gases (50 per vehicle). If the distance traveled is the same, 50% less fuel oil can be saved. Question: The nominal working pressure of a carbon dioxide cylinder is 15 Mpa, yet the pressure after filling is only 7–8 Mpa, which is far below the nominal working pressure. Why is it emphasized that overfilling is strictly prohibited, and must filling be carried out according to a standard of 0.6 kg/L? Answer: It is a high-pressure liquefied gas among bottled gases, with a critical temperature of 31°C. When the temperature is below 31°C, it can be liquefied by applying pressure; when the temperature is equal to or above 31°C, the liquid carbon dioxide in the bottle turns into gaseous carbon dioxide. When carbon dioxide is filled at a standard rate of 0.6 kg/L, at a temperature of around 31°C, the pressure inside the bottle corresponds to a gas-liquid coexistence state, with the saturated vapor pressure at the liquid interface being 7.39 Mpa. When the temperature reaches or exceeds 31°C, a phase change from liquid to gas occurs; the pressure inside the bottle is no longer determined by the saturated vapor pressure of carbon dioxide, but rather by the sudden increase in pressure resulting from the massive vaporization of liquid carbon dioxide. At this point, the pressure condition inside the bottle is essentially the same as that of a perfect gas. As the temperature continues to rise to 54°C, the pressure inside the bottle increases to about 15 Mpa, which is equivalent to the nominal operating pressure of the gas cylinder. Due to these characteristics of carbon dioxide in the cylinder, to ensure the safety of the gas cylinder during filling, storage, transportation, and use, it must be filled strictly in accordance with the specified filling coefficient. A gas cylinder is a separate, thin-walled, insulated container; the pressure of carbon dioxide inside it depends not only on temperature but also on the amount of gas filled in it. The nominal working pressure of a gas cylinder refers, for cylinders containing permanent gases, to the specified filling pressure of the gas at 20°C; the amount of gas filled is measured in terms of pressure ； For cylinders containing high-pressure liquefied gases such as carbon dioxide, the specified value refers to the gas pressure inside the cylinder at a temperature of 60°C, and the filling amount is measured in terms of weight. If the filling is not done at a rate of 0.6 kg/L but instead overfilled, the gas space inside the bottle decreases accordingly. As the temperature rises, the volume of liquid carbon dioxide expands, further reducing the gas space, until eventually the bottle becomes completely filled with liquid and no gas space remains. The bottle becomes filled with liquid, and the pressure is no longer the saturated vapor pressure; instead, it is the expansion force resulting from the volume increase of liquid carbon dioxide. This expansion force is much greater than the saturated vapor pressure. Liquid carbon dioxide has a high coefficient of volume expansion; within the range of -5 to 35°C, for every 1°C increase in temperature, the pressure inside the container rises by 0.314 to 0.834 Mpa. Therefore, overfilling can easily lead to overpressure and explosion of the gas cylinder. Question: The color coding for gas cylinders specified in the UK, Japan, and South Korea is simpler than that in other countries – what is the reason for this? Answer: This simple regulation originated in the UK; Japan followed the British approach, while South Korea followed the Japanese approach, although the colors specified in each case are different. This simple rule is based on the following considerations: 1. There are hundreds of known gases and gas mixtures, and attempting to use a single color or combination of colors to identify each one would lead to confusion and misjudgments ； 2. Repeated use of gas cylinders can cause the painted color markings to wear out, change color, or get covered over ； 3. Some people are color-blind and are unable to distinguish all colors in the spectrum ； 4. Under the light of certain light sources, such as fluorescent lamps and mercury (gas) lamps, colors appear differently ； 5. The colors used among different gas supply companies are often inconsistent. Question: What emergency measures must be taken when a gas cylinder is threatened by an external flame? Answer: When a gas cylinder is threatened by an external flame, emergency measures must be determined based on the degree of threat posed by the flame to the cylinder. If the flame has not yet reached the gas cylinder, every effort should be made to extinguish the fire source ； If the flame has reached the gas cylinder or the cylinder is already in flames, to prevent it from exploding due to overheating, it is necessary to quickly move the cylinder to a safe location before it gets too hot. The time available to rescue the gas cylinders from the fire is very limited, at around 10 minutes only. If the conditions at that time did not permit it, then, while ensuring a safe distance, a large amount of water should be sprayed for cooling using hoses or other methods. Afterward, the method suitable for the properties of the gas inside the cylinder is used to release the gas from the burned cylinder, and then the cylinder is sent to a cylinder inspection facility for testing and evaluation to determine whether it can be used again. If the flame is coming from the cylinder valve, a pipeline joint, or a pipe valve, quickly close the cylinder valve or the flow control valve on the pipeline to cut off the gas supply, being careful not to get burned. If conditions do not permit it, it is necessary to ensure that the gas cylinders burn in an open area, to prevent the flames from spreading and damaging other cylinders or facilities. Question: What does the tare weight of a dissolved gas cylinder refer to? Answer: The tare weight of a dissolved acetylene gas cylinder refers to the sum of the mass of the cylinder, filler, and accessories (cylinder valve, fixed special cylinder cap, fusible alloy plug, and inspection mark ring) and the filling volume specified in the regulations. Question: If a gas cylinder has been partially or completely burned, how should it be inspected and evaluated? Answer: In cases where a gas cylinder is partially or completely burned by fire, it can be roughly divided into 4 types: (1) The paint coating is scorched or burned off ； (2) Metal sintering ； (3) Cylinder deformation ； (4) Melting of the bottle valve components. If conditions (2) and (3) mentioned above are found on the bottle under inspection, it should be classified as scrap. If the paint coating on the bottle under inspection is only scorched or bulged but has not fallen off, it indicates that the metal has not been damaged, and it should be rated as qualified. During the regular inspection of gas cylinders, two other types of localized thermal damage can also be encountered: (1) arc scars on the cylinder body caused by starting welding arcs on the cylinder” ； (2) Reinforce loose or detached collars and bases using welding or gas welding, and weld up any cracks or holes that allow air to leak through. During inspections, any cylinder showing such thermal damage is identified, regardless of the size, depth, or height of the scar ； Regardless of the size of the solder joints used for reinforcement or leak sealing, as well as the length and width of the welds, they should all be deemed unserviceable.