Regarding mid-section reflux
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In normal operation, the temperature at the top of the vacuum distillation tower is high, and increasing the reflux at the tower top does not yield any effect; it becomes necessary to use reflux from the middle section. Is it better to use reflux from the first middle section or from the second middle section?
Whether to reduce the temperature at Stage 1 or Stage 2 needs to be determined based on the overall thermal balance of the tower and the heat exchange network system; factors such as whether sufficient heat is extracted from each section of the tower, whether the final temperature after heat exchange is too low, and the quality of the product from the side streams all play a role in this decision. Also, is the degas reflux temperature too high?
One should start with the atmospheric tower; provided that the requirements are met, efforts should be made to increase the yield of light products, which will naturally reduce the load on the top of the vacuum tower. Fuel-type pressure reduction starts more directly from stage 1, while lubricant-type is adjusted according to the quality of the side-product.