Why must there be at least a 4-meter height difference between the lowest point of the pipeline and the inlet before urine enters the stripping tower?
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During my studies, I noticed that the urine pipeline coming from the synthesis tower in my plant entered the stripping tower in a reverse “V” shape. It was only by examining the design drawings that I saw a note stating that \"the lowest point of the urine pipeline entering the stripping tower should be at least 4 meters above the inlet of the stripping tower.\" My understanding is that the urine flows out of the synthesis tower through the overflow pipe at its upper part; according to Bernoulli’s equation, its static pressure energy (i.e., the energy due to gravity) is converted into kinetic energy (i.e., the flow velocity of the urine) upon reaching the inlet of the stripping tower. Although resistance will reduce this velocity, it should still be quite high. If the pipeline were straight, it would cause impact on the tower wall opposite the inlet, and urine with such high flow velocity would have difficulty being distributed evenly through the liquid distributor； If a nozzle is used, the urine flow rate is high, resulting in reduced contact with the stripping gas CO2, which affects the stripping efficiency. Under the influence of the resistance caused by the inverted \"few\"-shaped urine tube, the flow rate of the urine decreases as it enters the stripping tower; it enters the tower in an overflow manner, which allows for good distribution across the liquid distributor. With a low flow rate, the urine descends due to its own gravity, resulting in better contact with CO2, and thus the stripping effect should be improved. But after reading a post by a member of the forum, “Why are butterfly valves used as the outlet valve in the CO2 stripping synthesis tower?” ”As discussed earlier, \"Between the four high-pressure devices, material flow is achieved by overcoming resistance through height differences. Considering construction costs, these differences cannot be too large. High-pressure washers cannot rely on injectors; the height difference between the synthesis tower and the stripping tower is 9 meters. With this amount of static pressure, it’s not easy to overcome the resistance posed by valves such as angle valves and ball valves. Therefore, butterfly valves are used, as they present very little resistance. The above points are well understood by those who are familiar with this topic...\" Posted by Xishui on 2010-1-4 18:09. images/common/back.gif Learn from friend Xishui* – what was said above is completely correct. The materials in the high-pressure system circulate automatically due to gravity. Butterfly valves are used for the liquid outlet valve in the synthesis tower, mainly due to their low resistance. If other valves are used, the height from the synthesis tower to the stripping tower must be more than 9 meters. "After that, I was a bit confused. If what the person above said is true, then what is the purpose behind the design institute’s decision to design it in this way?
This area is a U-shaped tube that contains urine, serving as a liquid seal to prevent gas leakage between the synthesis tower and the stripping tower. When performing heating passivation while driving, the liquid seal must be maintained to ensure the process required for heating passivation. It’s not about reducing resistance.
Hello, sir. I really admire your eagerness to learn; I believe you will soon become an expert in this field. However, your understanding of this issue is open to discussion. In any CO2 stripping urine process, regardless of its capacity, it differs from previous water-based urine processing methods – 80% of the unconverted material returns through a high-pressure system. The flow of materials between the four devices occurs due to gravity (the difference in height), which overcomes resistance. This is also the principle of the process as explained by your instructors. There are two key points in this flow: 1. the high-pressure ejector, and 2. the discharge valve of the synthesis tower. The use of butterfly valves was mentioned earlier to reduce resistance (by minimizing the height difference). But then, if a “U”-shaped tube is used, it’s said that it increases resistance through liquid sealing – isn’t that contradictory? It’s difficult for those new to this topic to understand. In fact, there’s no contradiction: the purpose of butterfly valves is to reduce the kinetic energy of the urine as it flows out (if the valve resistance is too high, it could cause problems with urine discharge under high load conditions). Among the four devices, the stripping tower has the highest pressure, and urine must overcome this resistance to flow in. However, this pressure difference is quite small; any slight fluctuation might allow the stripping gas (CO2 gas) to pass through the butterfly valve and reach the top of the synthesis tower (when the resistance for the stripping gas to reach the high-pressure ammonium methoxide condenser or the bottom of the synthesis tower is greater than that of the butterfly valve). To address this, designers used 4-meter “U”-shaped tubes to increase resistance on this side, making it greater than that on the other side, thereby ensuring that the materials flow as desired. As you said, a Bernoulli equation can be applied to describe the flow between these four devices; instructors often use equations to explain this, though their explanations can be somewhat confusing. Regarding the liquid distributor at the top of the stripping tower, there is a liquid level of 300–450 units on the pipe sheet. Urine flows into three small holes under the effect of static pressure, at a very slow speed, forming a uniform liquid film on the surface of the stripping tubes. When the load is high, the liquid level rises slightly to overcome the resistance of the small holes and ensure proper flow, and vice versa. Of course, if the small holes get blocked, the liquid level will also rise.
It serves as a liquid seal to facilitate driving and prevent gas from passing between the synthesis tower and the stripping tower; the residence time of the fluid in this path is approximately one minute.
I still have some questions regarding the statement that \"among the four units, the stripper has the highest pressure.\" In a document on the operation of the high-pressure refrigeration unit and the synthesis tower, there is a passage about pressure control that reads: \"The entire high-pressure system, which includes 4 high-pressure units, consists of interconnected devices without any valves for regulation; therefore, only one pressure measurement point is needed to determine the pressure of the high-pressure system.\" It can be seen that during normal operation, the pressure throughout the high-pressure system remains relatively constant; there is no such thing as a maximum or minimum pressure, only slight variations may occur. It’s just my personal understanding; I hope everyone will continue to discuss it
It can be seen that during normal operation, the pressure throughout the high-pressure system remains relatively constant; there is no such thing as a maximum or minimum pressure, only slight variations may occur. It’s just my personal understanding; I hope everyone will continue to discuss it. Friends, you haven’t started production yet, right? In the future, pay attention to the CO2 pressure at the bottom of the stripping tower – it is different from the pressure in the high-pressure system. If there is no difference between these pressures, how can the materials flow from one place to another?
The liquid seal function mainly prevents backflow of gas.
Friend of the poster, the pressure in the air lift towers of the four units is the highest; if there’s a short shutdown, it will be necessary to drain the liquid.
After reviewing information on the startup of high-pressure synthesis processes as well as various materials, I finally understood that the U-tube for the synthesis liquid before it enters the tower serves to create a liquid seal during startup and to balance the pressure on both sides of the U-tube during operation, thereby preventing the backflow of CO2. Additionally, regarding the issue of the impact of the synthesis liquid entering the stripping tower that I mentioned, it was incorrect of me to not be familiar with the structure of the stripping tower; I would like to apologize to all of you here. The impact of the feed solution on the tower and its effect on liquid level fluctuations are controlled through the semi-circular baffles in the liquid distributor. The principle is that after entering the tower, the synthetic liquid encounters a semi-circular baffle; it then splits into two streams and flows in a circular direction along the groove formed by the baffle and the inner wall, entering the upper deck through the open end to form a liquid level layer.
CO2 stripping presents the issue of this liquid seal, which is also a challenge in operation. It’s also something that sets it apart from ammonia stripping!
Tianze Yongfeng, Jincheng, Shanxi. The factory started operating early, but there aren’t many experienced workers there; it’s mostly young people who only know how to operate the equipment. I’ve just arrived as well, and I have to learn many things on my own*