Control of dry point in diesel reformate naphtha
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Firstly, the feed oil consists of straight-run diesel along with catalyzed diesel; the specific gravity of this mixed feed is around 850–860. The inlet temperature of the reforming reactor varies between 290–325°C, and it is currently around 300°C. Under normal conditions, the inlet temperature of the reforming reactor, the feed temperature to the distillation tower, and the bottom temperature of the distillation tower remain constant. Adjustments are made in response to changes in the specific gravity of the feed oil. Generally, we control the top temperature of the tower by adjusting the reflux rate. But how exactly should these adjustments be made? How should factors such as the top temperature, reflux rate, and the amount of naphtha produced be adjusted?
Personally, I think it’s caused by changes in the raw material composition; secondly, could it be that the temperature control at the top of your tower is also unstable?
Yes, the tower top temperature is very unstable. . .
Let’s take a look at the control parameters for the dry point of naphtha; tests and analyses are carried out on a daily basis. The density of our raw material is around 860, and the inlet temperature is 303. The dry point is kept below 170; if it exceeds this value, reflux is used to lower the temperature at the top of the tower, with the temperature there generally staying around 120. With a heavier crude oil composition and a high feed temperature, the dry point is generally high. The main method is still backflow temperature control.
It’s just a temperature issue; the recirculation pump is connected in cascade with the temperature at the top of the tower, so the temperature remains very stable, and there’s little change when it gets drier. Speaking of changes in the raw material composition, why does the feed temperature to the distillation tower, as mentioned by the poster, remain unchanged? Logically, it should also change, right? Changes in the composition lead to changes in the reaction depth, as well as changes in the feed temperature of the hot fraction; these in turn affect the temperature in the distillation zone.
We have low temperature differentials; the feed temperature does not change significantly, while the temperature at the top of the tower varies quite a lot. The main method used to address this is by implementing reflux, with automatic control of the reflux rate being based on the amount of reflux flow. There is no cascade control, and constantly changing the reflux rate still does not result in stability, as well as fluctuations in the dry point temperature. . .