Processes with Indirect Thermal Column Coupling

3 Processes with Indirect (Thermal) Column Coupling 

A further meastrre for process intensification is the indirect (or thermal) coupling of columns. In principle, waste heat of the process is internally used to cover the heat demand elsewhere. The prerequisites of this heat matching are appropriate amoimt and temperature level of the heats. In evaporators and condensers, the temperature level can be adjusted by variations of operating pressures. However, as the vapor pressure is, in a first approximation, an exponential function of temperature, rather large pressure changes are necessary for adjusting temperature levels. 

In processes for fractionating multicomponent mixtures, several colirmns are arranged in hne. The energy demand of such processes can be drastically reduced by utilizing the waste heat from a condenser for heating the reboiler of another col-trrtm. 

The process structiue and energy demand of the thermally coupled c-path are illustrated in Fig. 11.2-16. Here, the colurrm C-1 is operated at a higher pressitre and the waste heat of this colurrm is supplied to the reboiler of colitrrm C-2. As can be seen from the parameter lines in the triangrrlar diagram, the fractiorration of the ternary mixture (characterized by norrlinear parameter Mnes, see Chap. 5) in colimm C-1 is decisive for the energy demand of the integrated process at low values of (see Fig. 5.2-32). 

Thermal coupling of columns is often used in industrial processes since it effectively reduces the energy demand by multiple use of the external heat supplied. An interesting example is the Linde Process for air separation (Fig. 11.2-18). In this 

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