What are the factors that affect the top and bottom temperatures of a distillation tower? How to adjust it?
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The temperatures at the top and bottom of the tower reflect the boiling points of the mixed components. For example, when distilling a mixture of water and ethanol, if the alcohol content in the vapor coming from the top of the tower is close to 100%, then the temperature at the top of the tower is close to the boiling point of ethanol. If the alcohol content at the bottom of the tower is 50%, then that is the boiling point of this alcohol; treating the two components as a single substance, it’s roughly the average of 78 and 100. But this temperature and component content are not that precise either. Overheating in the reboiler at the bottom of the tower, undercooling in the condenser at the top of the tower, or poor heat transfer can all affect the temperatures at the bottom and top of the tower. Excessive steam heating in the reboiler can raise the temperature at the bottom of the tower, which directly affects the bottom temperature of the tower; this bottom temperature is the temperature of the gas above the liquid in the tower bottom. This causes the temperature to be a bit higher. Subcooling of the top condenser also lowers the top temperature, resulting in a reduced amount of evaporation. All of these are abnormal; the heat supplied by the reboiler should be equal to the cooling capacity provided by the condenser, so as to keep the amount of vaporization during distillation stable. In that case, the temperatures at the bottom and top of the tower will also be stable, approaching the boiling points of their respective mixtures. Pressure affects the temperatures at the top and bottom of the tower, just as it affects the boiling point.
The temperature distribution of the tray reflects the proportions of the various components. Under stable pressure conditions, the feed rate, steam volume, circulation water flow and pressure in the top condenser, reflux rate, and product recovery rate all influence the temperature distribution across the tray. During regulation, certain quantities generally remain constant, such as the feed rate and the water volume and pressure in the top condenser; operation is stabilized by controlling other parameters. Such as reflux or steam. In short, once stable operation is achieved inside the tower, if certain temperatures are not appropriate, it is sufficient to adjust just one of them; making too many adjustments will only lead to greater confusion.
It is mainly influenced by the internal pressure and the composition of the material.