The problem with the siphon reboiler has recurred

The normal liquid level in the tower bottom is at the same level as the height of the upper tube sheet of the reboiler

The liquid level in the tower bottom should not be too high relative to that of the reboiler; a high liquid level causes the tubes in the reboiler to be filled with liquid, leaving no space for evaporation. This results in bubbling noises and insufficient evaporation volume. It is advisable to consult books on the design of such reboilers

Thermal siphon reboilers utilize the density difference between the gas-liquid mixture in the reboiler and the liquid at the bottom of the tower as a driving force. In my opinion, if the reboiler is completely filled, this driving force decreases or even disappears almost entirely, resulting in a reduced heat exchange efficiency that fails to meet the process requirements; hence this approach is not advisable

Can the liquid level in the distillation column bottom be set to be higher than the lowest point of the inlet to the siphon reboiler? The liquid level in the distillation column bottom should indeed be higher than the lowest point of the siphon reboiler inlet, as the material at the bottom of the column needs to be heated by the reboiler

The poster asked, “If the partition in the distillation column bottom is removed by making holes in it, can the liquid level in the distillation column bottom be set higher than the lowest point of the inlet to the siphon reboiler, so that the tubes remain filled with liquid?” ” The “liquid level height in the distillation column bottom” here refers to the liquid level during normal operation of the column. It certainly “can be set higher than the lowest point of the inlet to the siphon reboiler,” as it is necessary to ensure proper operation of the vertical siphon reboiler (to provide sufficient heat exchange area). The height of the upper tube sheet of the reboiler should ideally be at the same level as the lowest liquid level in the column bottom; therefore, the lowest point of the reboiler inlet is definitely below the upper tube sheet, that is, below the lowest liquid level in the column bottom, not to mention below the liquid level during normal operation. As for keeping the tubes filled with liquid, that is certainly the case; however, due to heating, the density of the liquid in the tubes decreases from bottom to top, and at certain points near the top it partially vaporizes, resulting in a two-phase flow of liquid and gas. The density difference between the liquid in the bottom of the tower and the liquid in the tubes is precisely what drives the proper operation of the thermal siphon reboiler.

Reply to 1# zybrong: The siphon reboiler in a distillation tower generally does not have a controlled liquid level; if the temperature is to be controlled by regulating the reboiler’s liquid level, then the column cannot be filled to capacity.

Personally, I think it’s fine as long as it doesn’t affect the normal operation of the reboiler. If certain media are prone to structural issues and severe coking, it is detrimental to the proper operation of the reboiler, requiring frequent maintenance.

Generally, the reboiler level is not controlled; instead, the distillation column level is controlled by regulating the draw at the bottom of the tower. The liquid level in the distillation tower determines the liquid level in the reboiler as well.

The reboiler tube bundle can operate at a full liquid level; in this condition, the reboiler is fully capable of functioning properly. The design of the reboiler takes into account operation at full liquid level