Ethylene oxide and propylene oxide storage tanks
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When selecting the material and design pressure for ethylene oxide and propylene oxide storage tanks (horizontal tanks), should the saturated vapor pressure at the highest ambient temperature be used, or the highest operating pressure under nitrogen sealing? What other considerations should be taken into account in the design?
Speaking one by one: Ethylene oxide has a boiling point of 10.73°C and is classified as a Class A fire hazard. Its storage can be done either at normal temperature under saturated pressure or at low temperatures. For storage at normal temperature under saturated pressure, stainless steel 304 is sufficient; the pressure rating of the storage tank can be determined using the standards for liquefied gas tanks. Stainless steel is chosen because ethylene oxide can undergo self-polymerization at temperatures above room temperature in the presence of metal oxides, which can lead to explosions. If stored at low temperatures (–15°C or lower), carbon steel storage tanks can be used, but stainless steel tanks are preferred. Choosing normal-temperature storage means that, in addition to safety considerations in the design aspect, there are many other aspects related to storage safety as well; I won’t go into detail here because your question does not cover these. Propylene oxide: Boiling point 34°C, fire hazard classification is Class A-B. It can be stored at normal temperature under saturated pressure; a design pressure of no more than 0.5 MPa is sufficient. The material of choice is stainless steel 304, with carbon steel being an alternative as well.
For the design of propylene oxide tanks, it should be carried out in accordance with API620 or domestic standards for the design of large low-pressure storage tanks; the design pressure can be set at 0.07 MPa, and the design temperature is approximately 25 degrees, for reference only.