Reissue of 【One Question per Day】1.16 Short-answer question: What is the impact of high reflux rates in the first and second stages of an atmospheric pressure tower on the product?

What is the impact of high reflux rates in the first and second stages of the atmospheric pressure column on the product? Due to the different properties of crude oil, variations in the amount of reflux at each stage, differences in the extraction temperature for each reflux stream, variations in the amount of product extracted from each side stream, as well as the influence of human operational factors, all these contribute to differences in the temperature differences between the various reflux streams. Taking the second intermediate stage as an example: the temperature of the vapor phase is 295°C while that of the liquid phase is 200°C; in another case, the vapor phase temperature is 299°C with a liquid phase temperature of 195°C; and yet another case shows a vapor phase temperature of 301°C alongside a liquid phase temperature of 192°C. These three sets of values demonstrate the existence of temperature differences as well as variations in the amount of reflux. If an unchanged reflux amount is used across these different temperature conditions, it will either result in a lower yield of light oil or lead to energy waste. In other words, changes in the temperature difference of the intermediate stage reflux inevitably lead to changes in the amount of reflux. Finding an optimal temperature difference for intermediate stage reflux, along with an appropriate amount of reflux, is what we refer to as optimized operation.

Returning from Stage 1 with a large volume results in lighter tower top product and a reduced yield. The high backflow rate in Line 2 significantly affects the separation performance of other lines.

In the first and second distillation columns, the reflux rate is high; as a result, the dry points of the naphtha at the top of the tower as well as the jet fuel from the first distillation line decrease. The composition becomes lighter and the boiling range shortens, but the yield also decreases accordingly. The initial boiling point of the diesel from the second and third distillation lines drops, along with its freezing point; thus, the properties of the diesel improve. Overall, the yield of light products from the atmospheric distillation column decreases

A high reflux rate in Column 1 has a significant impact on the gasoline produced in Column 1 and the oil obtained from it; this leads to a reduction in the density of the product and a decrease in yield. A high reflux rate in Column 2 mainly affects the distillation efficiency of the oil produced in Columns 2 and 3

The dry point and initial boiling point of the side-stream products will decrease appropriately.

A large reflux flow in Unit 1 has a significant impact on regular top gasoline and the products from Line 1; this leads to lighter product compositions and reduced yields. A large reflux flow in Unit 2 affects the distillation efficiency of the products from Line 2 and Line 3.

Normal and light fractions have low flash points, low boiling ranges, and low top temperatures, which affect the dry point of the normal distillate

The crude oil from our plant’s first distillation stage is generally used as aviation fuel; the key parameters to control are flash point and freezing point. The high reflux rate in this stage results in an excessively low flash point, which affects the quality of the product. For the second and third tiers, focus mainly on the 95% level. Excessive backflow can cause the 95% point to be too low, affecting product quality