What is the safe discharge capacity of a pressure vessel? What is the displacement of a safety valve?

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What is the safe discharge capacity of a pressure vessel? What is the displacement of a safety valve? The safe discharge volume of a pressure vessel refers to the amount of gas that must be discharged per unit time when the vessel is under overpressure, in order to prevent its pressure from rising any further. The discharge capacity of a safety valve refers to the amount of fluid discharged per unit time under the discharge pressure when the valve is in its fully open position. For boilers, it is required that the total discharge capacity of the safety valves must be greater than the boiler’s maximum continuous evaporation rate, and that the steam pressure inside the drum shall not exceed 1.1 times the design pressure once all safety valves on the drum and superheater are opened. For pressure vessels, it is required that the discharge capacity of the safety valve must be greater than or equal to the safe venting capacity of the pressure vessel. When selecting a safety valve, the following aspects should be considered: (1) The type of structure – the choice of safety valve type is primarily determined by the process conditions of the equipment and the properties of the working medium. Under normal circumstances, spring-type safety valves are commonly used for boilers and pressure vessels. If the working medium in the container is toxic, flammable, or explosive, a closed-type safety valve should be used. For boilers and high-pressure vessels, as well as medium and low-pressure vessels with a large safety discharge volume and relatively thin wall thicknesses, full-disc safety valves are the best choice. (2) Pressure range safety valves are designed and manufactured according to nominal pressure standard series, with each type of safety valve having a specific operating pressure range. When selecting, an appropriate safety valve should be chosen based on the maximum allowable operating pressure of the boiler and pressure vessel. (3) The discharge capacity of the safety valve used for emission control must be greater than the safe discharge capacity of the equipment; this ensures that when the boiler or pressure vessel is under overpressure, the safety valve can open to allow some of the fluid to be discharged promptly, thereby preventing the pressure inside from rising further. Source: China Safety Instrument Network (Responsible Editor: Lu Haibiao)