LNG cryogenic tank J-T valve
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I have only been working with LNG liquefaction for a short time; what is the reason why the temperature in front of the J-T valve in our cryogenic tank is lower than the temperature behind the valve? Isn’t the J-T valve used for throttling and cooling? How can the temperature before the valve be lower than the temperature after the valve? I hope the experts can give me some advice... Thank you! !
It’s likely the throttle valve that comes out of the cryogenic tank is the problem; there is nitrogen and helium inside it, so it’s not a pure substance
JT valves have positive and negative effects
The inversion is mainly due to an issue with the refrigerant ratio; it seems that there is too little of the heavy components in the refrigerant, which results in an excessively high temperature in the pre-cooling section
The J-T effect has both positive and negative directions; not all refrigerant components experience temperature reduction upon throttling, and those that do not necessarily maintain this cooling effect. For example, methane experiences temperature reduction upon throttling at temperatures above -140 degrees, but at -145 degrees it instead experiences temperature increase upon throttling. Only nitrogen consistently shows a temperature reduction upon throttling. In summary, the situation of increased temperature due to throttling you mentioned must be caused by an excessively low nitrogen content, while the proportion of refrigerant components above C2 is too high, thereby counteracting the cooling effect of nitrogen.
When designing a throttle valve, there is a specific operating range – it cannot be fully open. The design team determines the appropriate opening degree for the J-T valve based on your factory’s production volume; when the valve is opened to a degree lower than this value, throttling and cooling effects occur, while when it is opened further, only pressure reduction takes place (usually around 60% or less of the maximum opening degree, more or less). When your factory operates at full capacity, this valve should reach its designed upper limit! It’s possible that the opening degree is set too high or that there is damage inside the valve; it’s better not to buy domestic versions of such core valves!
I’ve never heard of that before; I’ve been wondering why LNG product valves don’t have a throttling and cooling function. Is there any basis for what you’re saying? Where can I find relevant literature? ? Thank you!
It is caused by an excessive ratio of refrigerant.
What effect does nitrogen have on it? Please advise
Not all gases produce a throttling cooling effect; hydrogen and helium actually cause heating (an inverse effect), while most gases exhibit a throttling cooling effect (a positive effect). Ideal gases have no such effect. It is explained quite clearly in the J-T principle.