The impact of side-line production on tower operation
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I would like to ask everyone about the impact of increasing the side-line recovery rate and recovery temperature on the top temperature and pressure of the tower. I hope an explanation of the principle can be provided; thank you!
I’ll start by offering my own insights. I believe that when too much liquid is removed from the side lines, the liquid phase inside the tower decreases, which means fewer heavy components reach the bottom of the tower. As a result, there is an increase in heavy components at the top of the tower, leading to an rise in temperature. Moreover, the increase in heavy components results in an increase in the upward-flowing gas phase inside the tower, thereby raising the tower pressure. This is my understanding; I hope experts can provide further guidance
With all other conditions unchanged, increasing the side-stream recovery rate leads to an increase in the heavy components, and consequently the recovery temperature must rise as well； The heat taken from the lower section decreases, while the heat taken from the upper section increases. This results in an increase in the gas-liquid load in the upper section, an increase in the liquid-to-gas ratio, and an increase in the operating line slope; as a result, the system moves further away from the equilibrium line. The number of theoretical plates required to achieve the same separation requirements decreases. With the number of plates in the upper section remaining unchanged, the purity of the product at the top of the tower improves. When the tower pressure remains constant, the temperature at the top of the tower decreases.
Excuse me, on the 3rd floor, when the slope of the operating line increases, shouldn’t it be adjusted using the **balance line? In that case, the Reorganization fraction of the product at the top of the tower should increase, which would then raise the temperature at the top of the tower
I’ve learned a lot more, thank you all.
Side-line extraction is of two types: one is liquid-phase extraction, and the other is gas-phase side-line extraction. For liquid-phase side extraction, since the liquid is relatively stable, it has little impact on tower pressure and temperature. In contrast, gas-phase extraction has a significant effect on the pressure at the top of the tower; when more liquid is extracted, the tower pressure drops, which increases the volatility of the liquid in the lower parts of the tower and leads to an increase in temperature in the upper parts of the tower. In such cases, it is necessary to increase the reflux rate in order to control the temperature. The larger the amount extracted, the greater the corresponding increase in backflow.
In my opinion, the amount of material drawn off through the side line takes some of the material from the tower, resulting in a decrease in heat content within the tower as a whole. However, for the section below the extraction port, there should be a reduction in internal heat reflux, which leads to an increase in the gas-phase load in the lower part, and as a result the tower pressure increases slightly. Furthermore, if the side-stream flow rate is increased, the material load in the tower as a whole becomes greater than before, so the temperature will also rise. It’s just my personal opinion; I’m also open to advice from experts so that I can make progress in my learning.