Questions regarding supercooled LNG
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This post was last edited by shaodf77 on 2015-12-24 at 16:48. I used HYSYS for the simulations; the LNG was subcooled (assumed to be pure methane). In one case, the pressure was 0.5 MPAG at -180°C, and after throttling it dropped to 0.1 MPAG at -179.8°C. The other one is 0.5 MPAG at -170°C; after throttling, it becomes 0.1 MPAG at -169.8°C. Both are liquids, and the two streams enter separate storage tanks. Assuming the tanks are empty initially, what will be the outcome? What will be the pressures in each case? The bubble point of LNG at 0.1 MPAG is -152.6°C. I guess both tanks are under negative pressure, but the degree of vacuum differs, which in turn results in different temperatures. This is what should happen when considering the storage conditions of LNG. But now, let’s assume that both types of material are present, along with a throttle valve and the pipeline downstream of it. I will take a section of the LNG pipeline downstream of the throttle valve as the subject of study – the pipeline is filled with LNG, which is in liquid form, at a pressure of 0.1 MPAG; however, the temperature varies. If we consider that section of pipeline as a storage tank, then what happens? What exactly is the problem? I would be very grateful if experts could help me understand this
Can’t anyone give an answer? . . . . .
It’s not that I don’t want to answer; I really didn’t understand it
It was my fault for not expressing myself clearly; let me rephrase the question. For LNG, the pressure before the valve is 0.5 MPAG at -180°C, and after throttling it drops to 0.1 MPAG at -179.8°C. The gas then enters a sealed tank at atmospheric pressure. So what are the final pressure and temperature in that tank? Assume that the storage tank is relatively large,
Change the inlet flow rate so that the outlet volume equals the tank volume.
I’m stupid and don’t understand what it means. . .
In other words, that’s the volume of material that can end up inside the tank; at this point, all you need to do is check the temperature and pressure.
For LNG, the pressure is 0.5 MPAG before the valve, at -180°C; after throttling, it drops to 0.1 MPAG at -179.8°C. It then enters a sealed tank at atmospheric pressure. So what are the final pressure and temperature in that tank? Assume that the storage tank is relatively large. What I want to ask and know is about pressure and temperature. . . .
No matter how large the storage tank is, its volume still needs to be determined; since the volume of the tank varies, the final temperature will also vary
In other words, change the inlet flow rate so that the outlet volume equals the tank volume. The outlet temperature and pressure at this point are the values you need.
Well then, our LNG storage tank has a capacity of 10,000 cubic meters, and the amount of LNG entering the tank is 10 cubic meters per hour