Has the nitrogen in the mixed refrigerant been liquefied in the cryogenic heat exchanger?
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The critical temperature of nitrogen is over -146 degrees; before the throttle valve in the cryogenic heat exchanger it is over -157 degrees, and after throttling it is over -160 degrees. So the question is, does nitrogen liquefy before or after throttling? Newbies hope that expert can clarify things for them.
It’s also related to pressure; after throttling, as the temperature decreases, the pressure also drops. There’s a temperature-pressure saturation curve that can be referred to for this purpose
In my case, it’s LNG liquefaction. The mixed refrigerant exits the cryogenic heat exchanger, undergoes throttling, and then flows back into the intercooler and precooler. From there, it enters the cold box and finally reaches the compressor. What I’m asking is: when nitrogen comes out of cryogenic conditions and is throttled, does it liquefy?
It was liquefied before throttling, and then vaporized at low pressure after throttling
Pressurization and cooling may cause nitrogen and methane to liquefy before throttling. After throttling, as pressure and temperature drop, nitrogen is no longer in a liquid state at these conditions. The liquefied methane remains supercooled after throttling. The heat generated by this throttling process is exchanged with the hot fluid on the other side of the heat exchanger; as a result, the methane and nitrogen gradually evaporate upward, resulting in different temperature distributions across various layers of the cryogenic tank. If the flow rate and pressure on the refrigerant side remain unchanged during operation, but the flow rate or temperature of the fluid on the other side of the heat exchanger decreases, then the cold box will become undercooled, and liquid accumulation may occur on the refrigerant side. The above views are for reference only. :time::victory:
Some of it is liquefied; for our natural gas project, the refrigerant consists of nitrogen along with three other components. After throttling, the temperature reaches around -165 degrees, and the pressure is three to four hundred kilopascals – roughly a quarter of the nitrogen is liquefied in this process. The gas phase is almost entirely nitrogen. You can just do a HYSYS simulation and you’ll get the result
The refrigerant partially condenses; it isn’t entirely in liquid form, and the gas pushes the liquid along
Nitrogen is the driving force behind the refrigerant system; nitrogen does not liquefy