Under the condition of steam injection at the bottom of the tower, the temperature at the bottom of the tower is generally lower than the temperature in the feed section.

I don’t quite understand this sentence either. In the stripping towers I encounter in practice, superheated steam is used, with a temperature that is higher than that of the material; moreover, the temperature at the bottom of the tower is also higher than the temperature in the feed section.

Under bottom-blowing conditions, the material at the bottom of the tower partially evaporates and vaporizes; the latent heat of vaporization is high, resulting in a temperature that is generally lower than that in the feed section.

What you are referring to is a distillation column in which no reboiler is used at the bottom, but instead steam is employed for stripping. Such columns are generally used in situations where the material contains many impurities that could easily clog a reboiler; petroleum distillation is an example of this. In such cases, the heat required for vaporization comes from two sources: the flashing gas generated when the heated material enters the column, and the steam introduced at the bottom of the column for stripping purposes. In this setup, the stripping section of the column functions as a stripping zone, and separation is achieved by the volatilization of the light components in the material into the stripping gas – this differs from the traditional principles of distillation. However, since the temperature of the steam introduced at the bottom of the tower is usually lower than the feed temperature, the temperature at the bottom of the tower is often lower than that in the feed section, but this does not affect the occurrence of stripping. In principle, as long as the temperature of the steam injected at the bottom of the tower is sufficient to maintain good fluidity of the material there, it is fine; of course, the higher the temperature, the better. Therefore, the steam injected at the bottom of the tower is usually superheated steam. For information on this topic, one can refer to books on petroleum refining; we can also continue to discuss it!

The main function of bottom steam injection is to reduce the partial pressure of the oil and gas at the bottom of the tower; this means that as the feed enters the tower, it undergoes flashing. Flashing is equivalent to a pressure reduction, so the feed liquid vaporizes under low pressure, and low pressure corresponds to a lower phase equilibrium temperature. The temperature of the steam used has little actual impact; the specific heat of gases is very low. Of course, a higher temperature is better. The temperature should not be lower than that at the bottom of the tower, so that the gas does not condense – otherwise, there will be no gas available for flashing.