Is nitrogen or liquefied gas after vaporization used to pressurize the new tank when it is put into operation?
Thread Content
Recently, I was discussing a question with my colleagues: should a new spherical tank be pressurized with nitrogen or with liquefied gas after it has been vaporized? A colleague believed that pressurization with gasified liquefied gas should be used. His reasoning was as follows: 1) When pressurized with nitrogen, the partial pressure of oil and gas inside the spherical tank is 0; as a result, the liquid liquefied gas will vaporize in large quantities, absorbing heat and causing the temperature inside the tank to drop. 2) Nitrogen is incompressible, and the feeding process can cause overpressure in the spherical tank. I fully agree with point 2), but I’m not sure about point 1): if point 2) is not taken into account, I think it’s okay to use nitrogen for pressurization, as it won’t cause a large amount of the liquid liquefied gas to vaporize. None of us two can convince the other; please give us some advice! !
Are you going to conduct a leak test on the new sphere tank? Can flammable gases be used for leak testing? What if there’s a leak and flammable gas spreads everywhere? Compressed air or nitrogen is used for airtightness testing.
Before putting it into use, it is necessary to ensure that the oxygen content in the spherical tank is within acceptable limits before introducing liquefied gas. This requires filling the tank with nitrogen to reduce the oxygen content to 0.5% or less, thereby creating conditions suitable for liquefied gas.
Let’s talk about these two points you mentioned. First, why does liquefied gas vaporize in large quantities once it enters, and under what conditions can it vaporize? If the pressure inside your tank is the same as that of the liquefied petroleum gas entering it, it is already at its saturated vapor pressure; then why would it vaporize? Secondly, continuous feeding will certainly reduce the pressure increase in the gas space of the spherical tank. But don’t you have a flare? I’m not sure about venting – at the beginning of feeding, nitrogen can definitely be vented into the atmosphere.
Just to ask further, what is the size of the tank? And what exactly is the liquefied gas – is it liquefied petroleum gas, liquefied ammonia, liquefied chlorine, or something else?
It’s not a gas-tightness test; it’s done when feeding material, after all the startup procedures have been completed
It’s not nitrogen displacement; it’s the feeding process that takes place after all the startup procedures are completed
My colleague believes that when nitrogen is used for pressurization, the partial pressure of oil and gas is 0, which results in extensive vaporization. 2) Let’s not discuss that for now; let’s just talk about point 1). 3000 m3 spherical tank, liquefied petroleum gas.
Well, now it’s clear: a liquefied petroleum gas cylinder tank with a capacity of 3,000 liters. It is a flammable and explosive gas; therefore, it is necessary to ensure that the oxygen level inside the spherical tank is within acceptable limits before feeding it. You manage your pressure well, so it doesn’t cause excessive vaporization. Liquefied petroleum gas vaporizes under reduced pressure; there are no conditions for it to vaporize at sufficient nitrogen pressure. Think about it the other way around: in our manufacturing processes, nitrogen is generally used to maintain or replenish pressure. After pressure is replenished, the partial pressure of oil and gas decreases; therefore, the oil and gas will not vaporize to replenish that pressure.
When a new ball tank is put into use, I believe it’s necessary to have some nitrogen under pressure; it doesn’t need to be very high – around 3 kilograms is sufficient. Control the feeding speed during feeding to avoid excessive gasification. If there is no pressure before feeding the spherical tank, the amount of gasification will be very high. As for what the original poster said about nitrogen not compressing easily and causing overpressure, when there is a certain amount of material inside the sphere tank, proper venting through a flare allows nitrogen to be discharged easily. As long as the nitrogen content in the gas phase is kept below 10%, there should be no major problems. I have personally tested its effectiveness; the same method is used for 5,000 m3 of propane and 3,000 m3 of propylene.