Thread Content
【Principles of Chemical Safety Design】Pressure vessels refer to closed devices that hold gases or liquids and are subject to certain pressures. Its scope is defined as gases and liquefied gases with a maximum operating pressure of 0.1 MPa (gauge pressure) or higher, liquids with a maximum operating temperature equal to or higher than their standard boiling point, as well as fixed and mobile containers with a volume of 30 L or more and an inner diameter (for non-circular cross-sections, this refers to the largest geometric dimension of the cross-sectional boundaries) of 150 mm or more ； Gas cylinders designed for gases, liquefied gases, and liquids with a standard boiling point of 60°C or lower, whose nominal working pressure is 0.2 MPa (gauge pressure) or higher, and whose product of pressure and volume is 1.0 MPa·L or higher ； Oxygen chamber. Usually, only fixed pressure vessels are considered, that is, pressure vessels used in fixed locations. The main risks of pressure vessels such as towers and tanks are that they can have a large capacity and operate under high pressure, posing a risk of fire or explosion due to material leakage. (1) The greatest risk factor for pressure vessels containing flammable materials is the flammable materials themselves inside the vessel; the liquid materials in the tower are usually transferred to downstream equipment via pumps. If it is discussed that the pump poses a risk of leakage leading to fires or explosions, it is necessary to isolate the source of fire and the material by using emergency shut-off valves. When designing pressure vessels, the liquid level should be set at its minimum value as long as it still meets the requirements of the process operation, thereby reducing the risk of fires caused by excessive storage volume. (2) Vacuum design: Ordinary pressure vessels generally cannot withstand negative pressure, especially large-scale vessels. The design must take into account situations that cause negative pressure operation of the pressure vessel (such as reboiler failures in distillation towers, changes in the composition of the feedstock, etc.). For example, during a shutdown when the reboiler stops heating, the liquid cools below its boiling point, creating a vacuum in the container.