How is the pressure vessel vented?

In the petrochemical industry, asme pressure vessels are used to store and transport compressed gas. Under working conditions, the gas in the pressure vessel needs to be vented to ensure the safety of equipment and pipelines. Based on the laws of thermodynamics, the conservation of mass and the equation of state AGA8, the dynamic model of the pressure vessel discharge process is established. The changes in parameters such as temperature, pressure, heat insulation index, and compressibility are analyzed, and the gas in the vessel is analyzed and given The influence factors of gas composition, external temperature, orifice area on time, the diameter of the orifice can be calculated.

With the development of natural gas extraction technology and the continuous growth of market demand for natural gas, high-pressure energy storage systems have attracted more and more attention in the fields of gas gathering and transportation stations and petrochemical machinery manufacturing. Generally, pressure vessels are used as high-pressure storage systems. Due to their good storage performance and Flexible structure is widely used. Under certain working conditions, such as natural gas leakage or fire in the station, the pressure vessel needs to be vented quickly to ensure the safety of the collection station or mechanical equipment and prevent further loss and damage.

In pressure vessels, gas composition and physical parameters directly affect the discharge process, which has become an important aspect of research. The AGA8 equation of state is an equation proposed by the American Natural Gas Association to calculate the compressibility of natural gas. This equation has a wide range of applications and high calculation accuracy. It is a common method for calculating physical parameters of natural gas. There are relatively few studies on the influence of physical parameters on the discharge process and gas composition of pressure vessels, so further analysis is needed.

As time increases, the air pressure gradually becomes lower. The greater the pressure, the faster the pressure drop per unit time. When the time is less than 2.5 minutes, it can be found that the gas temperature gradually decreases with the increase of time when the gas temperature changes. When the time is greater than 2.5min, the gas temperature gradually increases with the increase of time, and slightly appears with the increase of time. There are two reasons for this phenomenon: 1. The gas in the container during the gas release process The internal temperature of the gas becomes lower and the energy becomes lower; the second gas conducts heat transfer with the surrounding environment. At the beginning, the heat is transferred from the gas to the surrounding environment. The gas temperature is higher than the outside temperature, and the gas temperature drops. When the gas temperature is lower than the ambient temperature, the gas absorbs heat from the environment. When the absorbed heat is greater than the reduced internal energy released, the temperature of the gas in the container will increase.

The gas compressibility and thermal insulation index are not fixed values, but continuously change with the release time. The compressibility first decreases and then increases with the increase of time. The change trend of the thermal insulation index is exactly the opposite of the compressibility. Therefore, the influence of the compressibility and thermal insulation index cannot be ignored.

The mass flow rate of the gas flowing through the orifice is related to factors such as the gas pressure in the container, the compressibility factor, and the thermal insulation index. In addition, through observation, it is found that the mass flow rate is approximately linear with time, and the change trend of the gas flow rate is the same as the change trend of the mass flow rate.

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