Pinch Point principle

From the above example we learned that the Pinch separates the space of heat recovery into distinct regions, as represented in Fig. 10.15. The original problem is decomposed in two sub-problems, above and below the Pinch. Consequently, a Pinch Point principle can be formulated as follows (Linnhoff and Hindmarsh, 1982) ... 

Remark 1 For (i) and (ii) we assumed a values of HRAT. For (iii) and (iv) we can have H RAT = TIAT since we decompose into subnetworks based on the location of the pinch point(s). We can also have in (iii) and (i v)EM AT = TIAT < HRAT for each subnetwork which may result in less units, less total area, and less investment cost. By relaxing EM AT — TIAT, that is, being strictly less than H RAT, more opportunities to make matches are introduced in the heat cascade. Note, however, that for the network derivation we may have EM AT < HRAT of EM AT = HRAT depending on which criterion of feasible heat exchange is considered. In principle, if EM AT < H RAT, EM AT can take any small value e close to zero. Also note that EM AT is not a true optimization variable but simply a requirement for feasible heat exchange that can even be relaxed (i.e., may be e from zero). If EM AT - TIAT = e > 0, then the only specification in the above problem statement is that of HRAT based upon which (i) and (ii) are obtained. We will discuss later on how such a specification can be overcome. 

Pinch Point Analysis (PPA) is an extension of the second principle of Thermodynamics to the energy management of the whole plant. PPA deals with the optimal structure of the heat exchange between the process streams, as well as the optimal use of utilities. Among benefits we mention ... 

After the theoretical principles of Pinch Point Analysis this chapter continues with some major applications. We will develop the idea that the energetic performance of a unit operation in a process depends not only on its performance as stand-alone piece of equipment, but also upon the interactions with the other units. 

In the next chapter, an equivalent node-shifting principle will be shown for continuous distillation column sections at the appropriate operating conditions, pinch points can be shifted. Some pinch points move from real space (within the MET) to negative space (outside the MET), and vice versa. Thus, the mode of operation of the piece of equipment can be used to shift unwanted topological features outside the MET. 

---