During forward flow expansion, both the expander and the air compressor are oversized; how can the condition of air entering the tower be ensured?
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Small air separation unit, single tower, producing only liquid nitrogen; forward expansion mode, with the expanded gas exiting directly from the cryogenic tank without entering the tower. The air compressor is oversized, so not all of the air can enter the cold box. Due to the inaccurate platinum resistor before the distillation tower, the inlet temperature is around -154 degrees, resulting in a liquid level forming at the bottom of the distillation tower. It seems that the expander is producing too much cooling capacity; the inlet temperature reached -160 degrees within half an hour, and it is likely to continue dropping further. The liquid level reached around 17% within 5 minutes, and then stopped rising. The pressure also decreased from 0.6 MPa to 0.5 MPa (absolute pressure). If the liquid-air throttle valve (leading to the condenser) was adjusted to a setting of around 2 turns, the pressure increased, but the liquid level gradually decreased until it eventually disappeared. What’s going on here? Is it possible that the air entering the bottom of the distillation tower is all supercooled liquid? How can the flow of air into the distillation tower be controlled when the platinum resistor fails? First, thank you all, experts.
Additionally, the distillation tower has only an air inlet and a liquid-air outlet, both located at the bottom of the tower. During startup, the liquid nitrogen outlet valve is closed. How is the pressure inside the distillation tower controlled, and how is purification achieved?
I’ll give it another try to see if there are any experts out there
-At 160 degrees and low pressure, air cannot be supercooled; it is merely humid air. Could it be that there is too much cooling capacity? If liquid nitrogen is not used, the degree of expansion can be reduced appropriately. Producing liquid requires more cooling energy than producing gas, in my humble opinion
Is there a throttle valve before the air enters the lower tower? If it has one, turn it up. Based on your description, should it be only this stream that goes into the lower tower? I’m not quite clear about the process. What is the exhaust pressure of the air compressor in kilograms? Are there low-temperature ice machines? Was the main cooling nitrogen gas from the reflux not taken for expansion?