What is the reason for a rapid increase in pressure in the high-pressure circuit when the liquid level in the synthesis tower drops during normal CO2 stripping operation?
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Our plant is equipped with a 300,000-ton CO2 stripping urea production unit; during normal operation, when the CO2 flow rate is between 45,000 and 46,000 and the NH3 level is between 32.5 and 33, the liquid level in the synthesis tower is at its maximum while the pressure remains normal. However, once the liquid level in the synthesis tower starts to drop, it inevitably leads to a rapid increase in the pressure in the high-pressure section. Please ask an expert to solve it
This post was last edited by Xieshui on 2010-1-10 at 22:26. Dear poster: You have a CO2 stripping production unit with a urea production capacity of 1,000 tons per day, right? The CO2 flow rate is 45,000–46,000 – what is the unit here? This phenomenon may be caused by an overly high liquid level indication in the synthesis tower; when the liquid level drops slightly, it leads to evacuation of the synthesis tower, resulting in CO2 backflow and a rapid increase in pressure in the high-pressure system. To determine whether the synthesis tower has indeed been evacuated, check the steam consumption in the stripping tower as well as the opening degree of the outlet valve of the stripping tower. If time permits, monitor the outlet temperature of the high-pressure ammonium methanate condenser as well – this will help confirm whether there is CO2 backflow. The solution is to quickly close the outlet valve of the synthesis tower; the tower can only be operated with a high liquid level temporarily. It is recommended that the instrumentation engineer recalibrate the liquid level measurement in the synthesis tower.
The water conservation analysis is good; it’s possible that CO2 backflow is the cause
For a urea production plant that uses 300,000 tons of CO2 for gas stripping, the CO2 flow rate ranges from 45,000 to 46,000; regardless of the unit of measurement, this is a relatively high CO2 flow rate. I guess that’s why the display value is too high? The water conservation expert’s analysis is excellent; I support his views!
The flow rate, in standard cubic units, should be 21,000
The analysis on the 2nd floor is very professional. Additionally, I also recommend hiring someone with expertise in instrumentation to calibrate the carbon dioxide flow meter; the cost is indeed quite high.
I wonder what value the high-pressure level reaches in the phenomenon you described? What are the indications in the stripping tower? And what are the changes in the temperature indication on the liquid outlet line of the synthesis tower? The apparent characteristics of the phenomenon you mentioned are incomplete; therefore, relying solely on two factors (a drop in liquid level and an increase in pressure) to conclude that instrument malfunction has led to a vacuum in the synthesis tower and resulting gas leakage warrants caution. If there is a process of material interruption in the stripping tower before the pressure in the synthesis tower rises, accompanied by significant changes in the temperature in the liquid outlet line of the synthesis tower, it clearly indicates that a malfunction in the level gauge of the synthesis tower has led to a drop in the liquid level there, resulting in gas intrusion – which can interrupt production. If the pressure you mentioned is only increasing, but there is no material interruption in the stripping tower and no significant changes in the temperature of the liquid outlet line of the synthesis tower, please visit http://bbs.hcbbs.com/viewthread.php?tid=597185&page=1#pid3404712
Friend Haina, your analysis makes sense. But in my opinion, the original poster explained very clearly: when the synthesis tower is at full liquid level, the pressure remains normal; however, once the liquid level in the synthesis tower starts to drop, it inevitably causes the pressure in the high-pressure section to rise rapidly. Maintaining normal production at a full liquid level indicates that the level is probably too low; this situation can lead to air intrusion, causing the pressure in the high-pressure section to rise rapidly. Neither of us knows the exact dimensions of the owner’s synthesis tower; if the zero point is too close to the flare tip, or even below it, gas leakage is almost inevitable. It is recommended that the poster recalibrate the liquid level, or check for any traces left by urine when there is an opportunity to open the synthesis tower; that way they will know.
Cherish water, embrace friends – your two analyses make sense. But in my opinion, the original poster explained very clearly: when the synthesis tower is at full liquid level, the pressure remains normal; however, once the liquid level in the synthesis tower starts to drop, it inevitably causes the pressure in the high-pressure section to rise rapidly. Maintaining normal production at a full liquid level indicates that the level is probably too low; this situation can lead to air intrusion, causing the pressure in the high-pressure section to rise rapidly. Neither of us knows the exact dimensions of the owner’s synthesis tower; if the zero point is too close to the flare tip, or even below it, gas leakage is almost inevitable. It is recommended that the poster recalibrate the liquid level, or check for any traces left by urine when there is an opportunity to open the synthesis tower; that way they will know. When parking, fill the synthesis tower with deionized water to check whether the liquid level gauge of the synthesis tower is accurate.
8# Cherish Water: First of all, I would like to thank friend Cherish Water for praising my argument. But I think the original poster didn’t describe the first characteristic of the accident clearly. Therefore, be cautious. I believe that CO2 leakage during normal production (referred to as CO2 backflow) is not the primary characteristic of an accident. It is a consequent phenomenon resulting from the evacuation of the liquid level in the outlet line of the synthesis tower, which leads to the loss of the liquid seal and thus causes CO2 to take a shortcut, resulting in a sudden rise in pressure in the high-pressure system; it is not a direct phenomenon. The interruption of feed to the stripping tower is the primary characteristic that occurs prior to this sudden rise in pressure. A malfunction in the level indicator of the synthesis tower caused the liquid level in the outlet pipeline of the synthesis tower to drop to zero, resulting in a lack of feed to the stripping tower. The most serious consequence was backflow of CO2, which led to a sudden increase in pressure in the high-pressure system and forced shutdown of the CO2 handling system or an overall plant shutdown. Therefore, the view I presented on the 7th floor is that the description given by the original poster in the topic is incomplete. A specific judgment can only be made after the original poster provides a complete version of the question. It entirely depends on whether the poster provides a response regarding the material breakage in the stripper.
2# Water conservation: We produce 1,350 tons per day. I have observed the phenomena related to the stripping tower that you mentioned, but they are not significant. Our current control method involves closing the outlet valve of the synthesis tower in a timely manner; as long as this is done promptly, the liquid level will not drop too low and gas mixing will not occur (provided the level gauge is accurate)