After parking in winter and starting the air separation unit, the temperature coming out of the main heat exchanger is too low
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RT is a factory in the north where the ambient temperature in winter drops below -20°C. Carbon steel pipes are used for transporting low-pressure nitrogen and contaminated nitrogen after they pass through the heat exchangers. During startup in winter, there is often a problem of the temperature coming out of the main heat exchanger being too low (sometimes it can drop below -30°C), especially after the expansion engine starts up, as the temperature of the contaminated nitrogen drops sharply. The cold-crack protection level is -15°C; at this temperature, the chain must be removed to allow free movement, which carries a high risk. I would like to ask those with experience in this area how to reduce the risk of cold brittleness Thank you!
If it is only the temperature of the contaminated nitrogen pipeline that is low, then increase the flow rates of oxygen, nitrogen withdrawal, and venting during gas introduction to control the amount of contaminated nitrogen that is vented.
I’ve seen on-site the temperature of nitrogen-carbon steel pipelines drop to -126 degrees; lucky enough. By controlling the hot and cold flows properly and making adjustments in a timely manner, there should be no major issues.
This is because the hot air cannot flow in, resulting in insufficient reheating; additionally, heat conduction is to blame (sometimes the valves are not open, which also causes the temperature to drop rapidly). . . At this point, it should be discharged from the low-temperature pipes, such as liquid oxygen and liquid nitrogen, as well as the gaseous nitrogen from the upper tower (that has not entered the main exchanger). . .