Purging prior to putting liquid hydrocarbon storage tanks into service; requirements or specifications for water content indicators
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For example: A factory requires that prior to putting an ethylene storage tank into service, the dew point of gas samples taken from the upper, middle, and lower portions of the tank must not exceed -60°C, and the water content must be less than 10 ppm. Process Management Group
Thank you for your question. Based on your description, a certain plant requires a pre-purging of the ethylene storage tank prior to its commissioning. It also stipulates that the dew point of gas samples taken from the upper, middle, and lower parts of the tank must not exceed -60°C, and the water content must be less than 10 ppm. This is a common requirement for tank pretreatment; its purpose is to ensure that the humidity and moisture content of the gas inside the tank remain within acceptable limits, thereby preserving the quality of the ethylene stored in the tank. The specific operating methods and standards may vary depending on different process flows and enterprise requirements. .
Based on your question, my understanding is that it should be determined according to the required water content in the medium stored in the tank. For example, for propylene, if the required water content in the product is 10 ppm, then the mass ‘m’ of water after drying can be calculated. Subsequently, we can determine how much propylene should be stored in the tank. After accounting for the existing moisture in the propylene, we find the appropriate value for ‘m’, add some margin, and then work backwards to determine what the dew point should be. I’ve done it before – -20 is fine.