Stream Population

Conversely, immediately below the pinch, each lean stream has to be brought to its pinch composition. At this composition, any lean stream can only operate against a waste stream at its pinch composition or higher. Since a MOC design does not permit the transfer of mass across the pinch, each lean stream immediately below the pinch will require the existence of at least one waste stream (or branch) at the pinch composition. 

Therefore, immediately below the pinch, the following criteria must be satisfied  

---

Interval Temperature Stream Population INTERVAL ICPc ICPh INTERVAL Surplus/ Deficit... 

Figure 7.6 The enthalpy interval stream population for Example 7.2.

Figure 7.6 now shows the stream population for each enthalpy interval together with the hot and cold stream temperatures. Now set up a table to compute Eq. (7.6). This is shown in Table 7.2. Thus the network area target for this problem for = 10°C is 7410 m. ... 

Figure E.2. Stream population for targeting the munber of shells for the data from Table 7.1.

The stream population is shown in Figure 16.16 with a vertical temperature scale. The interval temperatures... 

Figure 16.16 The stream population for the data from Figure 16.2.

Interval Temperature Stream Population INTERNAL (°C) 1CP -XCPH MW K-1 INTERNAL (MW) Surplus/ Defict... 

A type of problem called class 2 is not amenable to straightforward linear analysis. In this type of problem, the form of the energy recovery constraint changes when the stream population at the pinch changes somewhere in the uncertainty range. This section defines and describes the differences betweeen class 1 and class 2 problems. 

In HEN synthesis, the pinch occurs at a stream supply, dew point, or bubble point (Saboo and Morari, 1984). A HEN resilience analysis problem is class 1 if the uncertainties are small enough that the stream population at the pinch is constant throughout the uncertainty range. If the uncertainties are too large, then the stream population at the pinch changes and the problem is class 2. 

Fig. 7. Class 2 problem—stream population at pinch changes when 7 2 changes (a) 7h2 = 480 K, (b) Tl2 = 460 K.

Fig. 9 The stream population for the data in Table 2. (View this art in color at www.dekker.com.)...

Interval Temperature Stream Population TintERVAL (°C) 2CPc- ZCPh (MW/°C) interval (MW) Surplus/ Deficit... 

CPj s are the heat capacities of the active streams in the temperature interval AT). The value TTo can shift the position of the composite curve. The partition in temperature intervals is based on the analysis of stream population. For the streams in Table 10.1, there are three intervals for the hot streams, and three for the cold streams (Fig. 10.6). 

In the first step we examine the possibility of heat integration of streams around the reactor. In a first approach we may disregard the quench. Table 17.5 presents the stream population for an operating point at a conversion of about 77 %. 

Table 17.5 Stream population for heat integration around the reactor...

The overall balance gives an excess of 1500 kW, so the problem does not require hot utility. There is need only for cold utility (cooling water). Thus, feed preheating may be covered exclusively by the exothermic reaction and save a significant amount of energy. However, a furnace is necessary before reactor to ensure constant temperature. The reactor outlet is quenched at 620 °C. Assume that the furnace has to preheat the reaction mixture from 520 °C to a reaction temperature of 630 °C. By simulation we find a duty of 3800 kW. The new stream population for heat integration becomes ... 

---