Heat balance refers to the balance between the heat entering and exiting the column, specifically reflected in the top temperature. Heat balance is the foundation for achieving material balance and gas-liquid phase balance, and in turn, depends on them. Without a hot gas phase and a cold reflux, the entire distillation process cannot be achieved; changes in the column's operating pressure and temperature (i.e., changes in the gas-liquid phase balance composition) will alter the heat released by gas condensation and the heat absorbed by liquid vaporization on each tray, reflected in changes in feed heating and top heat extraction.
Mastering material balance, gas-liquid phase balance, and heat balance is crucial for distillation operation. These three balances influence and constrain each other. In operation, the focus is usually on controlling material balance, with corresponding adjustments to heat balance to ultimately achieve gas-liquid phase balance.
(1) To maintain a stable liquid level balance at the bottom of the column, the following must be stable: ① feed rate and feed temperature; ② top, side stream, and bottom extraction rates; ③ top pressure.
(2) To maintain a stable top temperature, the following must be stable: ① feed rate and feed temperature; ② reflux flow rate and temperature in each section of the top reflux and circulating reflux; ③ top pressure; ④ stripping steam flow rate; ⑤ free of water in the feed and reflux.
By closely monitoring the top temperature and bottom liquid level, analyzing the causes of fluctuations, and making timely adjustments, the three balances of the column can be maintained, ensuring normal operation of the column.
