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 d istillation column and an intermediate condenser in the rectifying sec tion are well-known. For highly nonideal mixtures the distillation pro cess can be improved by placing an intermediate reboiler in the rectif ying section of the column or an intermediate condenser in the strippi ng section, which is counterintuitive. In consequence the more expensi ve heating utility used in the bottom reboiler can be partially replac ed with a less expensive heating medium (at a lower temperature) used in the intermediate reboiler. Similarly, a portion of the condensing d uty from the top condenser can be replaced with the less expensive con densing duty (at a higher temperature) in the intermediate condenser. This placement of reboilers (condensers) can be used to reduce the tot al number of stages in the distillation column with a lower (higher) l evel of utility. Operating and capital costs of the distillation proce ss with an intermediate heat exchanger can be lower than those for a c lassic column. A simple method providing valuable insights on the poss ible placement of intermediate heat exchangers along the column is pro posed. It is based on calculations of the vapor flow along the height of a reversible, binary distillation column performing the equivalent separation task.