【Weekly Topic】Week 30 of 2011——How to speed up warm-up driving?

Provided that sufficient preparation is done.

1. The programmatic activation time of the molecular sieve allows for the purging of the distillation column to be carried out even when the gas dew point is not within acceptable limits at the start-up stage. The molecular sieve is activated during the purging process. 2. Reduce the startup time of the systems outside the tower; some companies are able to get the molecular sieve system ready in 4 hours (excluding the unit components). 3. Improve operators’ understanding and control of the system. 4. As for inside the tower, you are experts.

I think starting up in hot conditions is simpler than doing it in cold conditions, as the reactions aren’t as intense; however, accelerating the process still requires some skill. After the purging is complete, do not rush to close the purge valve; instead, start the expander first and wait until frost forms on the purge valve before closing it. This allows hot gas to be expelled more quickly, although some believe it results in a loss of cooling capacity. For the temperature drop after starting the expander, is it better to have ten, fifteen, or twenty degrees per hour? Is it better for the throttle valve to be fully open or not fully open? Does the pre-liquidation expander require a low temperature or a certain cooling capacity? Has anyone looked for the boiling zone of the main cooler? When should one of the two expanders be shut down? Is the cooling capacity distributed in the argon tower? Can all the liquid air from the lower tower be sent to the upper tower? When should the liquid nitrogen reflux valve be opened? What is the ratio of processed air volume to gas venting?

The topics set recently might be too broad; those with high skill levels are not interested in them, while those with lower skill levels don’t know how to respond. It is suggested that moderators come up with more specific questions, as these overly general questions are difficult to address.

Reply to 5# Tianxia Di Ji: Thank you for your suggestion, but it’s hard to satisfy everyone’s tastes. I’ll try to follow what you suggested. If you have any good ideas, please feel free to share them

Take the expander as an example! Some say that maintaining a low temperature helps the liquid to remain in a liquefied state, while others argue that a higher temperature is beneficial for the expansion machine to fully utilize its cooling capabilities. I believe that when liquid is present, it is best to keep the temperature low enough so that the expansion machine does not operate with liquid inside it; therefore, it is advisable to keep the expansion machine running at a higher temperature before liquid accumulates

Is the poster referring to a steam turbine? Air separation unit?

1. Before starting the operation, blow out the pipes of the air separation unit thoroughly. During startup, do not close the blowing valve right away; use cold air to clean the pipes. Close the valve only once a slight amount of frost forms on it. Although this results in some loss of cooling capacity, it is beneficial for removing accumulated liquid, thereby speeding up the startup process. 2. Once the temperature of the liquid in the main cooler drops to a certain level and liquid appears, it is possible, if conditions permit, to use the method of pouring liquid oxygen in order to ensure that there is liquid in the main cooler; this helps to accelerate the process of distillation and thus speeds up the startup process.

There is no need to discuss the activation and heating processes of the molecular sieve mentioned earlier; the time for these processes is fixed, and the operation of the air separation unit begins when the expansion machine is started. There are three stages in total: cooling ； fluid accumulation ； Purify. As for the purification process, there’s no need to elaborate – it’s not difficult and doesn’t take long either. Therefore, the duration of the entire process depends mainly on the cooling and liquid accumulation stages. I believe that during the cooling phase, what air separation units need most is cooling capacity, and this cooling capacity is provided by expanders; therefore, the key to proper operation is to maintain the maximum refrigeration capacity of the expanders. “\"High temperature and high enthalpy drop\" – just operate according to this principle. During the liquid accumulation phase, what air separation units need most is not cooling capacity, but rather an adequate supply of air and low temperatures. Since the material that needs to be liquefied first is air, it is necessary to ensure an adequate amount of air in order to facilitate the liquefaction process. This answers the question of when to shut down one of the expanders: during the liquid accumulation phase, while all other parameters remain unchanged, the rate at which the level of the main cooling fluid rises slows down significantly. This indicates a lack of air supply, and it is then necessary to shut down one of the expanders. Furthermore, during the liquidation phase, low temperature is required rather than a high cooling capacity, as liquefaction is only possible when the temperature reaches the liquefaction point; therefore, the outlet temperature of the expander must be adjusted to be as low as possible (of course, no liquid should be present after the machine). As for the throttle valves, there is no dispute over keeping the valve from liquid air to the upper tower fully open; however, there is significant controversy regarding the valve from liquid nitrogen to the upper tower. The after-sales adjustment experts at Hangyang have differing opinions – some advocate keeping this valve fully open while others suggest keeping it fully closed, and neither side can convince the other. Tests have shown that fully opening or fully closing the liquid nitrogen throttle valve has little impact on the liquid accumulation time, allowing for satisfactory results in both cases.

【Weekly Topic】Week 30 of 2011——How to speed up warm-up driving? I’d like to say a few words too. I won’t go into the preliminary steps; the most important aspects of driving a vehicle are cooling, fluid management, and purification. Firstly, when measuring the dew point, it is possible to start the expanders at temperatures above -40 degrees. After starting two expanders, it is advisable to open the blow-off valve on the upper tower as wide as possible during cooling, in order to reduce the pressure in that tower. This helps to lower the pressure after the expanders, thereby increasing their refrigeration capacity per unit. When fluid accumulation occurs, close the upper column purge valve to increase the pressure in the upper column and raise the liquefaction temperature. Pay attention to adjusting the temperature difference of the main heat exchanger to reduce heat loss. Of course, in some units, when liquid appears, the method of backfilling liquid oxygen can be used to accelerate the startup process. During the purification stage, pre-purification is carried out when the liquid level in the main cooler is at around 70% of its normal level. Of course, many operations still depend on practical experience.