Heat Integration

Heat integration is a technique used to integrate heat duties of the process. Also, it is applied to heat exchanger network (HEN) to find if there are possibilities of reducing utilities, and as a result of reducing utilities, the cost of utility’s stream will be reduced. For heat integration, a useful technique used to integrate heat is called pinch analysis.

Pinch analysis is a technique used to find minimum cooling utility (Qc), and minimum heating utility (Qh) that are needed in the process.

Figure 140: Temperature vs Enthalpy for hot and cold composite curve.

Figure 1 shows temperature vs enthalpy for both hot and cold composite curve. This figure is being plotted by first tabulating all inlet and outlet temperatures for hot and cold stream which will allow finally to find the energy targeted value.

When pinch analysis method is used, there are some rules that must be obeyed which are:

1. No external heating below the pinch point. 2. No external cooling above the pinch point. 3. No heat transfer across the pinch point.

Figure 141: Cost vs ∆Tmin .

Minimum temperature difference (∆Tmin) can be found by plotting energy, total cost and capital cost. For total cost curve, it is being found by adding energy cost curve to capital cost curve, where ∆Tmin is the lowest value on total cost curve. In petrochemical processes, ∆Tmin is ranging between 10 oC to 15 oC. In propane dehydrogenation process (PDH) a value of 10 oC is assumed for ∆Tmin .

Table 145: Hot and cold streams.

Stream Name

Supply Temperature

Target Temperature

Heat Capacity Flowrate Heat Flow Stream Type Supply Shift Target Shift

K K kW/K kW °C °C

C-101 316.4 324.7 173.001 1435.9058 COLD 48.3 56.6 C-102 259.4 339.4 76.717 6137.3587 COLD -8.8 71.3 C-103 499.4 573.1 94.230 6944.7598 COLD 231.3 305.0 C-104 339.4 419.4 70.795 5663.593 COLD 71.3 151.3 C-105 419.4 499.4 82.723 6617.8733 COLD 151.3 231.3 H-106 867.7 750.1 137.668 16189.7803 HOT 589.6 472.0 H-107 750.1 633.1 126.830 14839.11 HOT 472.0 355.0 H-108 633.1 516.1 114.297 13372.7361 HOT 355.0 238.0 H-109 516.1 401.1 99.954 11494.6606 HOT 238.0 123.0 H-110 401.1 333.1 84.330 5734.4686 HOT 123.0 55.0 H-111 428.7 297.2 90.199 11861.1935 HOT 150.6 19.1 H-112 391.6 286.9 102.951 10779.0084 HOT 113.5 8.8

In table 7, hot and cold stream have been listed with their supply and targeted temperatures. Heat flow also has been calculated for each stream, and streams have been classified as hot or cold stream.

Figure 142: Composite curve.

Table 146: Grid diagram.

Grid diagram shows information of each component such as supply and targeted temperatures which are presented by arrows. Also, stream classification as hot or cold stream is mentioned for each stream. Finally, heat flow (Kw) is measured for each steam