Scaling in the two-stage condenser of a centrifugal CO2 compressor
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This post was last edited by Fan Zhou Wu Hu on 2009-6-22 at 18:58. Scaling on the tube side of the two-stage condenser in centrifugal CO2 compressors: Design values: Pressure: 2.3 Mpa; Temperature: 190°C at the inlet of the two-stage condenser, and 42°C at the outlet. Two-way heat exchanger: CO2 flows on the tube side, while circulating water flows on the shell side. The U-tube side using CO2 is currently suffering from severe scaling; the scale layer is relatively loose, making it easy to clean with a water gun. The shell side is very clean; the U-shaped tubes are made of 304 stainless steel, while the shell is made of carbon steel. The scale layer reached a thickness of up to 4 mm, resulting in an outlet temperature of 65°C and a pressure excess of 2.45 Mpa. What is unclear now is why CO2, which is originally a clean gas, causes such scaling inside the tube bundles The synthetic decarburization is carried out using the low-temperature methanol washing process, achieving a purity of over 98%, with the sulfur content also kept within the specified limits. I wonder if anyone has encountered such a phenomenon? Please, friends, help to clarify this!
I would like to ask the general moderators: What is the production capacity of your urea plants? Based on the data you provided, the binary CO2 temperature is as high as 190°C, which is a bit high. At such high temperatures, scaling on the circulating water side is inevitable. Therefore, it is recommended to find a way to lower the temperature of the binary or row first, as that is the fundamental solution.
It should have been brought in by the upstream pipeline; this kind of issue occurs frequently when the pipelines are made of carbon steel.
For large nitrogen fertilizers, our inlet temperature is 42°C; 190°C is the inlet temperature of the inter-stage condenser, which is also the temperature at the outlet of that stage. Moderator lxq700918 might have a misunderstanding: our circulating water side is very clean, with the stainless steel tubes shining brightly. It is the CO2 side inside the tube that gets scaled, so why is that confusing?
Let’s discuss this further with the general moderators: What processes do you use for decarbonization? Is scaling occurring on the CO2 side inside the tubes of the inter-stage condenser, indicating that there is a liquid carryover in the decarburization and regeneration system? For example, in the hot potassium alkali process, if there is liquid carryover, the alkaline solution will end up in the CO2 compressor.
5# lxq700918 Haha, I already mentioned in the main post that decarburization is achieved through low-temperature methanol washing.
Friend of the poster: How long has the unit been in operation? Has this happened before? Is it a low-temperature methanol wash unit that has just started operating? We are also starting to use a low-temperature methanol wash unit; we really need to be careful with the second-stage cooler of the CO2 unit. I’ve never seen this before… It’s just a guess. It can’t be some powder resulting from a conversion process, right? Is desulfurization being carried out? It can’t be ZNO2 powder, can it? Were any samples kept? If they are sent for qualitative analysis, there’s no need for guessing anymore.
Thank you for your interest. We have been using these old units for over a decade; our second stage is equipped with desulfurization equipment, but it is located after the cooler. The results of the scale analysis that was sent for testing have not yet come back.
Once the results of the scale analysis are available, please have the moderator announce them so that everyone can be informed and learn from the experience.
This post was last edited by Fan Zhou Wu Hu on 2009-6-26 00:12. We use the same setup, and currently it is Lowjia that supplies CO2. However, scaling on the tube side has never occurred; in the past, when the methane level was low, CO2 carried a large amount of methanol, which was recovered in various separators. During the maintenance and cleaning of C2/C3 in April this year, a small amount of white crystalline substances were found on the tube side; they could be easily washed away. In this situation, our analysis indicates that when the compressor experiences surging or an emergency shutdown, leakage occurs in the check valves at the compressor outlet and the air lift tower inlet, causing the process material to flow back into the compressor. Last year, at low speeds, our compressor unit experienced the backflow of process material into the compressor due to various reasons (such as leaks in check valves and shut-off valves). Substances similar to those described by the original poster were found in vessel 101-F (the inlet separation tank); as a result, we were forced to shut down the unit and subject each separator section to water washing, as well as clean vessel 101-F by opening it and flushing it. I’m not sure if this will be helpful to the original poster. . .
Poster: Everyone is paying attention to the results of the scale inspection; please provide updates promptly so that various factories can learn from them, reduce energy consumption, and enhance social benefits.