Operation issues in low-temperature methanol washing
Thread Content
The methanol exiting the middle section of the upper tower of the low-temperature methanol wash absorption tower is cooled by a deep cooler, resulting in a temperature of -15°C; the design value is -35°C. The methanol at the outlet of the lower section of the upper tower, which goes to the H2S absorption section in the lower tower, has a temperature of -6°C, while the design value is -9°C. What is the reason for this situation? How should it be adjusted?
System cooling imbalance； The circulation volume is too high ； The system’s cold loss is too high!
Could you provide a simple process to facilitate analysis?
The original poster only mentioned that the temperature did not meet the design requirements, without providing any detailed explanations, so it’s difficult to determine the exact situation. As for the temperature difference in the lower tower, it’s not significant, so it’s not a major issue. Regarding the upper tower, you can first check whether there is a problem with the deep cooler by examining the temperature difference before and after it; if there is no problem, then it indicates that the upward movement of the sulfur dioxide tower is the cause
The temperature of methanol leaving the upper tower is -10 degrees; after passing through the cryocooler, it is cooled to -35 degrees, with no issues. Overall, it seems that CO2 is rising to the upper layers significantly. I would like to ask how adjustments should be made in this situation?
You never mentioned anything about adjusting carbon dioxide; your process must be for ammonia synthesis, right? Regarding the cryocooler on the upper tower, the load is already high enough; the temperature difference between the front and back is 15 degrees, and it’s not good for this level to persist. I’m not familiar with your manufacturing processes. My suggestion is that you first find a way to reduce the temperature in the lower tower; this will result in less carbon dioxide in the upper tower, and as a consequence, the temperature of methanol in the lower tower will be appropriately lower. This will balance out quickly. Another reason is also the low circulation volume of your poor methanol; you can increase this circulation volume appropriately and see if that makes a difference – it should improve the situation. A significant upward movement of the dioxide tower is detrimental to the operation of the process gas, as it easily leads to exceedance of limits.
1. I think it’s the rise in temperature that causes CO2 to rise, rather than CO2 rising causing the temperature to increase (it’s just a guess of mine)； 2. If the temperature increase is caused by the upward movement of CO2, is it because you haven’t adjusted the H/C ratio properly in the process of variation & vaporization? ； Is it because less methanol is being recycled at the lower stage? ； 3. Is the methanol temperature entering the tower in line with the design? Is the overheating caused by the methanol temperature entering the tower not being at the required level? ； 4. Is the load a bit high?
Check whether the operation of the ammonia cooler (such as evaporation pressure, liquid level control, etc.) is normal At the same time, it is necessary to check whether there are issues such as air blockages in the heat exchanger after cooling with ammonia; if there is an air blockage in such a heat exchanger, the temperature of methanol flowing through its shell side should be lower
It’s stated in too general terms; it’s impossible to make any determination. Everyone is just guessing. It is believed that the upward movement of CO2 mentioned above is a phenomenon resulting from poor absorption by the tower, coupled with the use of a high circulation rate, which leads to insufficient cooling capacity in the system. Since a large amount of CO2 gets absorbed in the upper part of the tower, methanol absorption in the lower part of the tower becomes poor, thus causing the CO2 to move upward. Meanwhile, in order to prevent CO2 levels from exceeding limits, a high circulation rate has to be used, and this excessive circulation rate results in insufficient cooling capacity. Therefore, it is recommended to monitor the temperature difference; check whether it is within normal ranges, especially the temperature differences in the middle and lower sections of the tower. There should be changes and indications in these values. At the same time, the load should be reduced, as well as the circulation rate, so as to bring them as close as possible to the design values. Only after stability is achieved can the load be increased. This is just my opinion
I’m a bit confused. Sometimes you say the temperature is -15 degrees after passing through the cryocooler, and other times it’s -35 degrees; it’s a bit confusing. Comrade Li #1
I think the problem mentioned by the original poster lies with the cryocooler; it should be checked to see if there are any issues with that device.