*2.3. Advanced Exergy Analysis*

In order to obtain the real potential of improvement of each component, the avoidable and unavoidable parts of the exergy destruction were calculated. The unavoidable part of the exergy destruction ( . *E UN D*,*k* ) would be the exergy that will inevitably be destroyed, due to technological limitations, no matter how much capital is invested, and can be calculated by using Equation (19) [29], where ( . *ED*/ . *EP*)*UNk* is the relationship between the exergy destruction and exergy product rates estimated using the unavoidable conditions for each component.

$$
\dot{E}\_{D,k}^{LIN} = \dot{E}\_{P,k} \left(\frac{\dot{E}\_D}{\dot{E}\_P}\right)\_k^{LIN} \tag{19}
$$

Values of the unavoidable and real operation conditions of the components are summarized in Table 3, and were assumed according to previous studies [14,30]. For the spray dryer, the minimum air flow required to supply the energy for water evaporation was calculated as an avoidable condition [31].

**Table 3.** Assumptions that are considered for real conditions (RC), unavoidable thermodynamic inefficiency conditions (RTI), and unavoidable investment cost conditions (UIC).


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