【JST-005】One-on-one Assistance Office for Air Separation Process Technology
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This post was last edited by Firefly on 2015-4-10 08:17. Specialization: Air separation process and control. My expertise lies in the operation of air separation processes as well as the methods used for their control. I have 5 years of experience in this field. Everyone is welcome to discuss issues related to the operation and control of air separation processes; I will do my best to provide answers. If you are not satisfied with the responses, please post your questions in the Air Separation Technology section or other relevant forums to seek further solutions. I have the right to refuse to answer posts containing aggressive remarks, and I reserve the right to request that the moderators ban such users.
To support my post, I would like to raise a question – a simple one for everyone to discuss: regarding the return water control valve at the bottom of the air-cooled tower, should it be of the air-open type or air-close type? And why?
Could the original poster provide a simulation of an air separation process that includes argon production, preferably using Aspen for the simulation?
Hehe, well, that’s okay. Please leave your email address, hehe
The return water valve at the bottom of the air-cooled tower is usually a gas-operated valve, ensuring that it remains open in emergency situations so as to prevent the water level in the air-cooled tower from rising too high and compromising the safety of the molecular sieve system.
I’m not sure if there are any other answers, so I’d like to hear everyone’s thoughts after we discuss this. I hope everyone will speak up actively!
If a gas-open valve is installed at the return water inlet of the air-cooled tower, an accident could pose a serious threat to the air compressor and the molecular sieve. However, if a gas-close valve is used, approximately 5 kilograms of air will be forced into the return water pipeline in the event of an accident, which can damage the water supply equipment and may also affect the heat exchange efficiency of all heat exchangers that use circulating water. However, for the protection of the unit and the molecular sieve, a gas shut-off valve is still installed. :)
Personal opinion: I think an air-operated valve should be installed on the air-cooled condenser return water valve, to close it in case of an accident. The backflow pressure in ordinary companies is usually above 2 kilograms. Although there is a check valve for backflow, this valve has a risk of leakage. After the system is shut down, the pressure in the air-cooling tower drops rapidly, which can lead to an increase in the liquid level in that tower, thereby causing damage to the air pressure system and the molecular sieve. It is set as a gas shut-off valve to prevent an increase in liquid level in the event of an accident; this increase in liquid level is caused by water accumulated in the packing of the air cooling tower flowing downward. The rise in liquid level is limited and will not cause damage to the air compressor or the molecular sieve. I wonder if this item is included in everyone’s emergency response plan for air separation unit shutdowns: after the air separation unit stops operating, the manual isolation valves located before and after the inlet and outlet valves of the low-temperature water pumps in the pre-cooling system, as well as those of the air cooling tower return water. The manual stop valves before and after the automatic water supply control valve of the water cooling tower are closed. It is to prevent water from the pipeline network from entering the air-cooling tower! Please give me lots of advice, everyone!
What you said makes sense; I’ve learned something from it. I’m a beginner, and after checking, I indeed found that the return water valve at the bottom of the air-cooled tower in my unit is a pneumatic-operated valve
1. May I ask, when starting the machine in cold conditions, are the liquid air throttle valve and the liquid nitrogen throttle valve fully closed, or are they kept at their positions from before shutdown? I’ve heard that in some places, when driving in cold conditions, the liquid nitrogen throttle valve and the liquid air throttle valve are left in their positions from when the system is shut down, allowing gas to flow directly. In our facility, however, both the liquid air throttle valve and the liquid nitrogen throttle valve are fully closed before gas is allowed to flow; they only start to open when the pressure in the lower tower reaches 0.4 MPa! ! 2. In our situation, how should the liquid air throttle valve and the liquid nitrogen throttle valve be operated? Which one should be opened first? What criteria are used to determine the gradual opening of these valves, and what determines the speed at which they open? 3. Should the liquid-air throttle valve be opened first, or the liquid nitrogen throttle valve first? Or should the liquid-air throttle valve be opened gradually as the liquid level rises, once there is liquid in the lower tower (after we shut down the system, all the liquid air is transferred to the upper tower, so there is no liquid level in the lower tower)? 4. During hot startup and gas guiding, under what conditions are the liquid air and liquid nitrogen throttle valves opened, and under what conditions are they adjusted to be opened further during this process? Please answer each of these questions, thank you! ~
Same request; the original poster, my email address is rlw25@sina.com