Similarly, let us think of the number of vapor recompression schemes for distillation columns that have been considered in the past without knowledge of the pinch phenomenon. The appropriate placement concept shows that these schemes can never have a chance of producing net energy savings (compared to a properly integrated process), if the distillation column reboiler and condenser lie on the same side of the pinch. Also, for technical and economic reasons concerned with the heat pumping equipment itself, the temperature difference between boiler and condenser needs to be small. And even if these two criteria are met, the "need" for vapor recompression can be designed out of the system by altering column pressure appropriately, so as to eliminate the problem at source (Dunford and Linnhoff, 1981). Hence, future possibilities for vapor recompression viable in otherwise well-integrated processes seem to be rare.
ACKNOWLEDGMENTThe authors acknowledge the many contributions of all members of the Process Synthesis Team in the ICI New Science Group, and thank ICI Ltd. for permission to publish the paper. NOTATION CP F = heat flow, MW AH Z j ( A H ) , Z+Zj(AH),,j = enthalpy balance over all temperature intervals i of all streams j existing within intervals i, MW = heat quantity or flow, MJ or MW = minimum hot utility requirement for heat recov-Q QIN QOUT = minimum cold utility requirement for heat re-= heat capacity-flowrate, MW /" C = difference of enthalpy flow, MW = enthalpy balance over all streams j , MW ery problem, MW covery problem, MW 9
9E= temperature, K = interval boundary temperature, "C = temperature difference, "C = minimum approach temperature difference, "C = Work or power, MJ or MW = heat engine or heat pump temperature efficiency, = total heat engine or heat pump efficiency, di-