Seeking advice on the issue of tower flooding in catalytic absorption towers
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Since the maintenance last year, when the absorber’s packing was replaced with Sulzer trays, accidents of flooding in the absorber have occurred frequently since it came back online. In particular, after another minor maintenance session this year (with no changes made to the absorption and stabilization sections), such flooding incidents have happened regularly, almost on a daily basis. The technical department is currently unable to determine what exactly causes these incidents. Below is a brief description of the situation regarding the tower overflow. When an overflow occurs, the rich absorbent solution that is absorbed cannot flow to the bottom of the tower; Pump 2 becomes empty, while Pump 1 operates normally ； The liquid levels in the absorption tower, condensate oil tank, stripping tower, and stabilizer were all emptied, while the liquid level in the reabsorption tower rose to full capacity. Meanwhile, condensate oil was also introduced into the desulfurization system from the reabsorption tower, causing the secondary buffer tank for dry gas to become filled as well. This is basically how it works: once the gas-liquid equilibrium in the absorption tower is disrupted, it’s very difficult to restore it. Has anyone encountered this phenomenon before? I urgently need a solution; thank you so much! ! ! ! ! ! ! !
Before and after the maintenance, the feed material changed from residue oil to wax oil; due to raw material constraints, the feed volume became even lower than before the modification. Before the modification, the feed volume was 170 t/h (residue oil + wax oil), while after the modification it remained between 130–160 t/h. Therefore, the amount of rich gas should be less than before. Additionally, the rich gas is condensed in oil tanks and then used to reprocess the reforming gas. One theory is that the instability of the reforming gas leads to a vapor-liquid imbalance, which in turn causes flooding of the tower; another theory is that the reforming gas contains ammonia, which causes salt formation on the trays of the absorption tower, blocking the sieve pores and preventing proper flow of the absorbent (however, in previous cases where reforming gas was reused, no such salt formation was observed). It’s not clear whether these two theories are valid! This post was last edited by chengkang on 2009-4-8 19:49]
It’s very likely that salt deposition has occurred, which has interrupted the internal recirculation, led to the evacuation of the secondary system, and caused a series of imbalances thereafter
It is necessary to analyze the composition of the reformed gas to determine whether changes in the raw materials are causing variations in the gas composition There is a high possibility of tray blockage. Also, it is necessary to check the requirements of Sulzer trays for vapor-liquid equilibrium. This post was last edited by qlasd on 2009-4-8 19:43]
What is the change in the gas richness compared to before the modification – an increase or a decrease? Are there any malfunctions with the instruments? The main issues are the temperature at the bottom of the desorption tower and the flow rate of the supplementary absorbent. Measures: 1. Appropriately reduce the heat taken from the bottom of the desorption tower. 2. Appropriately reduce the amount of absorbent added. 3. Ensure that the temperature of the absorption tower remains around 40 degrees; it should not be too low. 4. If possible, temporarily stop the supply of reforming gas to observe any changes. If that doesn’t work, there is a high likelihood that there is a problem with the equipment inside the tower.
According to the original poster: the absorber’s packing was replaced with Sulzer trays – that’s the only reason for this change. Now there are frequent tower cleaning operations, whereas this used to happen less often. It is recommended to use CTST trays; we installed these new type of high-efficiency jetted three-dimensional mass transfer trays during our last maintenance work. I also think that the feed temperature and the liquid-to-gas ratio of the feed are very important; making appropriate adjustments might lead to improvements.
Note: It’s not just the absorption tower that is under pressure, but also the reabsorption tower; the situation is already quite serious. What needs to be considered in the process is that the properties of the raw material feed have changed compared to before, and experimental analysis of the enriched gas fractionation is very important. On the equipment: effect of the absorption tower trays, effect of the feed cooler, salt deposition at the top of the distillation tower==
1) The reformed gas contains ammonia, and ammonia is likely to form salts in the absorption tower, as the operating temperature of the absorption tower is much lower than the crystallization temperature of ammonia. 2) Is there frequent fluctuation in the flow rate of the reforming gas? Since, according to you, the purge of the tower does not occur continuously but intermittently, it’s necessary to check the flow rate during such purges. Generally, plants are equipped with flow meters, so the flow rate can be determined by checking those meters.
The key issue is that the rich absorption liquid cannot flow to the bottom of the absorption tower, which leads to chaos in the operation of the four towers. It is recommended to reduce the amount of absorption fluid supplied first; meanwhile, before the phenomenon of tower flooding occurs – which surely happens when the flow rate of lean gas and dry gas increases – it is necessary to reduce the gas feed into the absorption tower. If needed, the overall feed volume to the unit as well as the amount of external gas should be reduced to restore balance. Based on the observed symptoms, there may be a problem with the downcomer; if salt deposition is the cause, there will be a significant pressure difference between the upper and lower parts of that area.
The tray is blocked; at this stage, the only option is to reduce the supplementary absorption dose in order to maintain operations