Regarding the issue of the liquid level at the bottom of the solvent regeneration tower.
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As a new recruit in the sulfur department, I have a question I’d like to discuss with everyone. During normal operation, the liquid level in the regeneration tower should rise gradually, as the moisture contained in the gas phase at the top of the quench tower enters the subsequent absorption and regeneration systems. If all other liquid levels are under automatic control circuits, and the bottom of the regeneration tower serves as a buffer volume, then the liquid level rises slowly. Indeed, within just over a month after our plant began operating normally, the liquid level at the bottom of the regeneration tower showed a gradual rise. However, recently the trend has been the opposite: the liquid level has been dropping gradually, and at a fairly fast pace – nearly 10% of the liquid level disappears each day. The relevant processes have also been checked, and all the valves that need to be closed have been turned off. When the liquid level is low, only water and solvent need to be added. There are no major changes in the operation procedures. I would like to ask other users whether they have encountered similar issues – what is the reason for the drop in liquid level in your areas? How to handle it? As an additional piece of information, the solvent concentration in our lean solution is on a downward trend. . . . . . .
The last edit to this post was made by ylb913 on 2016-4-6 at 22:34. 1. The solvent concentration in the lean solution shows a downward trend; this is the most common scenario, otherwise no amine solution would be consumed. 2. Usually, the level of the amine solution in the system keeps dropping, so it is necessary to add water regularly. For this reason, in 1994 we added an amine solution circulation tank; since the capacity at the bottom of the regeneration tower is very limited, the circulation tank has a much larger capacity, which allows water to be added less frequently. The effect of this in dealing with sudden tower flooding is of course more noticeable. 3. The concentration of the amine solution will not decrease. Let me mention a special case for us: in 2012, an independent regeneration unit was built for a sulfur plant; after it came online, the amount of amine stored in the system kept increasing. We tried to address this by adjusting the temperature at the outlet of the quench tower (by lowering it), but this didn’t work. The temperature in the absorption tower also couldn’t be too high, so the problem wasn’t resolved. Fortunately, we had a process that allowed acidic water to be directly sent to the wastewater stripping unit. During the plant’s major overhaul in April 2013, it was discovered that one of the tube bundles in the amine solution cooler was leaking and blocked, and as a result, the amount of amine stored in the system continued to increase even after the unit came back online. However, the amine concentration has not decreased for over two years, and not a single drop of amine has been added to the system. However, both the exhaust gas absorption tower and the amine solution absorption tower often experience flooding. As a workaround, we can transfer the amine solution to the old centralized amine regeneration system and then replenish it with new amine solution. In March of this year, we carried out shutdown maintenance on the amine liquid regeneration tower and the reboiler (the exhaust gas absorption could be switched to be handled by centralized amine liquid regeneration). It was found that there were some manufacturing defects in the small floating head partitions of the reboiler, which were addressed; after restarting the system, its storage capacity continued to increase. It can be said that the amine solution concentration will not decrease; it is likely related to the amount of gas carried.
Yu Gong’s analysis is quite detailed, but please allow me some time to process it! :)
I would like to report to Engineer Yu on the reasons why the level of our liquid was first increasing before starting to decrease: 1. The rich liquid pump was repaired at one point, and after the repair, one of the vent valves was not closed properly, which led to direct leakage of the solvent. 2. During this period, in order to address the issue of uneven air cooling in the quench tower, an additional air cooler was added, which reduced the temperature at the top of the quench tower by nearly 5°C. The temperature difference between the top of the absorption tower and the top of the quench tower also decreased by about 5°C. Preliminary analysis suggests that the amount of liquid components carried away by the gas phase at the top of the quench tower has decreased, resulting in a gradual decline in the liquid level in the rear section. After restoring the previous operating condition, the liquid level basically returned to its previous slow rising pattern. PS: For this excess water, is it better to discharge the acidic water from the bottom of the quench tower or from the top of the regeneration tower?