Heat exchanger network synthesis considering different minimum approach temperature

Abstract

The minimum approach temperature (∆Tmin) has been used in the design of heat exchanger networks (HEN) and in energy targeting based on Pinch Analysis. It refers to the minimum allowable temperature difference between a heat source and a heat sink for designing an energy-efficient HEN. Smaller ∆Tmin can improve process heat recovery but require large heat transfer area and may result in a higher capital cost. Capital-energy trade-off is typically performed to determine the cost-optimum ∆Tmin during HEN synthesis (HENs). Conventionally, an entire process is analysed to obtain the optimum value of ∆Tmin. In this work, the capital-energy trade-off is performed using the individual stream temperature versus enthalpy plot (STEP) to obtain an optimum ∆Tmin for each identified STEP. First, simultaneous area and utility targeting of HEN is performed using the established STEP HEN targeting procedure. The capital-energy trade-off is then analysed separately for every identified STEP. The different values of ∆Tmin obtained are then applied for the grassroots synthesis of HEN. Application of the proposed procedure on a literature case study shows that the total annualised cost is reduced by 7.03 % when the capital-energy trade-off is performed separately for every STEP as compared to trading-off ∆Tmin for an entire process.