Problems with water content and appearance in refined diesel products
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The diesel hydrofining unit was put back into operation in September after maintenance, with a feed rate of about 120 tons per hour, and a feed ratio of catalyzed diesel to straight diesel of approximately 2:1. It has been observed that the diesel product is turbid, with greater turbidity the closer to the outlet of the unit. At the end of the product pipeline are the flow control valve, the aggregation dehydrator, and the mass flow meter at the outlet of the unit; the distance between these components along the pipeline is approximately 45 meters. Due to the turbidity issue, the dehydrator has been removed. The microwater analysis in these three samples was approximately 150PPM, 200PPM, and 1400PPM. Over time, diesel products gradually become clearer in appearance when stored for a long period. The unit process consists of a stripping tower, a feed heater for the distillation tower, and the distillation tower itself; both the stripping tower and the distillation tower are supplied with stripping steam. Currently, the amount of stripping steam used has been reduced to the minimum level, and the temperature of the feed to the distillation tower is being increased. The other process conditions have remained relatively unchanged compared to before the major overhaul. I would like to ask my colleagues: what are the reasons behind changes in the form of water in diesel products, and are there any effective methods to address issues related to the appearance of diesel?
Is it possible that water remained in the pipelines during the major repair?
This post was last edited by uyouu1 on 2019-10-23 08:43. In the steam stripping process using a distillation tower, diesel produced often contains free water. When the coalescer works properly, there is only a trace of such water; once the coalescer fails, the presence of free water becomes very noticeable (visually). This is also why diesel becomes clear after being left to stand for some time. This problem generally does not occur when a heating furnace is used in the distillation tower process. Suggestions: First, modify the coalescer, such as by increasing its volume; additionally, it would be beneficial to have an additional set of coalescers available for online switching. Hope this helps!
Reason for the change in water morphology: I’m not sure if you replaced the catalyst, as this change in the composition of the product has prevented water from being effectively removed in the coalescer. Another issue is the coalescer. Our facility uses a vacuum dehydration tower, and the results are quite good.
It’s likely that the residence time in the coalescer was too long, which prevented the free water in the diesel from being removed. We encountered a similar problem of water in the diesel during previous diesel hydrogenation processes; by reducing the amount of stripping steam and increasing the temperature at the top of the tower, the amount of water in the diesel was significantly reduced. Now, free water still appears occasionally
The stripping steam is the superheated steam used to heat the reaction feed furnace; due to the large amount of heat released during the reaction, all the main burners in the reaction furnace are shut off. The only adjustment possible is to increase the temperature at the outlet of the feed heater for the fractionation tower and reduce the amount of stripping steam used.
Work started in early September, and the situation has persisted to this day. The water storage should have been brought in long ago. :handshake
This post was last edited by Podilroga on 2019-10-24 09:17
This post was last edited by Podilroga on 2019-10-24 09:18
:The handshake catalyst has not been replaced, and the overall operating conditions remain largely unchanged. After identifying the appearance issues, repeated attempts by the collector to shut down, restart, and replace the filter elements yielded unsatisfactory results