On the use of intermediate reboilers in the rectifying section and condensers in the stripping section of a distillation column

Advantages of an intermediate reboiler in the stripping section of a distillation column and an intermediate condenser in the rectifying section are well-known. For highly nonideal mixtures the distillation process can be improved by placing an intermediate reboiler in the rectifying section of the column or an intermediate condenser in the stripping section, which is counterintuitive. In consequence the more expensive heating utility used in the bottom reboiler can be partially replaced with a less expensive heating medium (at a lower temperature) used in the intermediate reboiler. Similarly, a portion of the condensing duty from the top condenser can be replaced with the less expensive condensing duty (at a higher temperature) in the intermediate condenser. This placement of reboilers (condensers) can be used to reduce the total number of stages in the distillation column with a lower (higher) level of utility. Operating and capital costs of the distillation process with an intermediate heat exchanger can be lower than those for a classic column. A simple method providing valuable insights on the possible placement of intermediate heat exchangers along the column is proposed. It is based on calculations of the vapor flow along the height of a reversible, binary distillation column performing the equivalent separation task.