Targeting for process HENs design in the context of total sites

Abstract

The paper presents a targeting method for process heat exchanger networks (HENs) design in the context of total sites. The method is based on a simultaneous optimization framework for the HENs utility cost and utility systems operating cost. Instead of the standalone HEN capital-energy costs trade-off, the method utilizes the trade-off between the HEN capital cost and the total utility systems operating cost. The total utility systems include steam and non-steam utility systems within the site. The energy cost of the HEN is replaced by the total utility systems operating cost to avoid explicit calculations of steam costs when targeting for HENs design. This enables handling the variability of steam costs with the steam utility loads and the minimum approach temperature, ΔT <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> , of the HEN without assuming fixed steam costs as in the existing methods. The optimum ΔT <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> is that corresponds to the minimum total cost which involves the HEN capital cost and total utility systems operating cost. The simultaneous optimization framework combines the optimization of utility systems using Mixed-Integer Linear Programming (MILP) with targeting for the HENs design using Pinch Analysis. The method was demonstrated using an example total site.