Liquid level control of the ammonia cooler in low-temperature methanol washing
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I would like to ask everyone: in the Lurgi low-temperature methanol wash process, how are the liquid level alarms for the ammonia coolers set? In the Luchi process package, the normal liquid level is set at 40% of the shell side diameter, the low liquid level alarm is set at 5% of the shell side diameter, and the high liquid level alarm is set at 60% of the shell side diameter. I would like to ask that, according to the settings of the process package control, it is impossible for the liquid ammonia in the shell side to flood the tube side; as a result, some of the gas in the tube side cannot come into contact with the liquid ammonia. Is there any problem with the process package being set up in this way?
I really think I’ve seen somewhere that ammonia coolers generally don’t have a liquid level indicator. When it was in Weihua, their ammonia coolers were still discharging liquid. The tube bank should mainly exchange heat with gaseous ammonia!
When the ammonia cooler is started up, the temperature of the entire system is still relatively high; there may be no liquid level. But is there also no liquid level during normal operation? If there is no liquid level, I think it indicates that the amount of cooling capacity provided by the ammonia is not sufficient, which is why the ammonia turns into a gas as soon as it enters the heat exchanger
The function of the ammonia cooler is to utilize phase-change cooling, taking advantage of the heat removed during the phase change from liquid to gas phase; therefore, the control of the liquid level is not fixed
This post was last edited by poatmc on 2009-11-6 at 15:56. 4# chengangzi: I want to ask why the high liquid level alarm and the normal value are set so low, as a result of which some parts of the pipe network are not submerged in liquid ammonia.
We generally do not set a specific level for the ammonia cooler liquid level; of course, it is also possible to maintain a certain level. We adjust the amount of ammonia supplied by monitoring temperature changes.
In the normal operation of ammonia coolers, the liquid level is kept low in order to create more evaporation space, which in turn helps to generate more cooling capacity. The level at which the liquid level is set determines the amount of cooling that can be achieved; operators need to keep experimenting and drawing conclusions in order to determine an appropriate value based on experience.
Whether to establish a liquid level control is related to the amount of cooling capacity in the system. If the system has sufficient cooling capacity (especially in processes that involve liquid nitrogen cooling), then there is generally enough cooling available, and some factories opt not to implement liquid level control, relying instead on the latent heat to provide cooling. Conversely, sensible heat is utilized; a certain level of liquid ammonia can deliver more cooling capacity
The liquid level in the ammonia cooler should generally not be set too high; this is mainly to provide space for evaporation, so that heat can be absorbed during phase change and cooling can take place. If the liquid level is too high, gaseous ammonia will contain liquid droplets. The control of the general liquid level is mainly based on temperature to adjust the amount of ammonia added. There is a discharge valve at the bottom of the ammonia cooler; it should be opened if the temperature of the ammonia vapor at the outlet is high or if the ammonia contains liquid.