Regarding the flooding phenomenon in the solvent regeneration tower, how can it be resolved?
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This post was last edited by liaifeng on 2018-9-10 at 19:21. Recently, the solvent regeneration tower in the company’s sulfur recovery unit has been experiencing problems where the liquid on the tray fails to drain properly. The liquid control valve at the bottom of the tower gradually closes, and in severe cases it shuts off completely. This results in a decrease in the temperature of the amine-rich liquid entering the solvent regeneration tower, as well as a drop in the pressure at the top of the tower. When the pressure control valve leading to the sulfur production furnace is closed, the reflux tank at the top of the regeneration tower fills up within 2 minutes. If the acidic gas generated during regeneration is not removed in time, this acidic liquid can end up in the sulfur production furnace, easily causing the SO2 levels in the exhaust gases to exceed permissible limits. Dear sea friends, have you ever encountered such a situation? How to solve it? Is the circulation volume too high? (The designed circulation rate is 66.8 t/h, with a steam volume of 6 t/h). The specific process is shown in the figure below: Note: 1. The MDEA concentration measured through sampling and analysis in the unit is around 22% (slightly low), but the degree of depletion remains slightly high, at around 1.4 mg/L. 2. At that time, the volume of acidic gas was around 2000 Nm3/h (the design value was 3320 Nm3/h), and almost no acidic gas containing amino acids entered the sulfurization furnace. 3. Both the rich-ammonia solution and the lean-ammonia solution obtained are not dirty; the lean-ammonia solution is bright yellow in color, while the rich-ammonia solution is slightly darker in color.
Based on the phenomena you described, it seems that there is poor flow within the tower, and the pressure difference between the upper and lower parts of the tower is also quite high. It is recommended to try the following approaches: 1. Check the control valves for material inflow and outflow, as well as the flow meters and instruments for measuring pressure and temperature, to rule out issues related to measurement or control problems. 2. If the steam volume at the bottom of the tower is too high, the vapor load inside the tower becomes excessive, which prevents smooth flow of the liquid phase; in such cases, the steam volume can be reduced appropriately. 3. If the amount of liquid phase entering the tower is too large, try reducing the circulation volume of the rich liquid ； Additionally, depending on the sulfur content in the lean liquid, the steam volume should be appropriately reduced, thereby decreasing the flow rate of acidic water at the top of the tower. 4. Impurities clogging the trays in the regeneration tower can cause poor flow of the liquid phase; this is a likely possibility. If this is confirmed to be the cause, the amine solution can be drained, and the system can be washed with deoxygenated water or demineralized water. At the same time, an appropriate amine filtration system should be used to remove the impurities.
Additional suggestions: 1. Conduct an amine solution foaming test to observe the foaming behavior. 2. Manually control the feed flow rate of the rich amine solution and adjust it in conjunction with the steam flow rate to see if the situation improves. 3. Further reduce the load (both the amount of amine solution and steam) to check for any improvement. 4. If similar problems persist at reduced loads, consider the possibility of tray inversion or blockage, especially after the system has just been started up or if there have been sudden fluctuations in operation, such as an excessive increase in steam flow. In such cases, it is advisable to use more manual controls, as fully automatic operation may hinder fault diagnosis
Based on observations over these past few days, it is suspected that several of the lower trays in the tower have turned upside down, as there is a difference of 6–7°C between the temperature at the top of the tower and that at the bottom; the temperature at the bottom is 120–122°C, while it is 114–116°C at the top.