Plus and Minus — Principle

Following this general principle, several ideas for changes to this process can be proposed. For example, raising the temperature of reactor 2 could increase the heat load for the effluent from reactor 2, a hot stream above the pinch, which could reduce the heater duty for reactor 1. On the other hand, if the reactor 1 temperature could be reduced, the heat load of the reactor 1 feed stream, a cold stream above the pinch, could be decreased and thus the heater duty would be reduced as a result. For the separation column, if the top temperature of the column could be reduced via reducing the column pressure, the duty of the overhead condenser (a hot stream below the pinch) could be reduced. Of course, the effects of these changes have to be evaluated in the overall context of yields, product quality, energy use, and equipment cost. 

the plus and minus (+/—) principle (Linnhoff and Vredeveld, 1984) can be 

(+) Increase the heat duty of hot streams above pinch 

(—) Decrease the heat duty of eold streams above pinch 

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