Energy integration of industrial sites with heat exchange restrictions

Process integration methods aim at identifying options for heat recovery and optimal energy conversion in industrial processes. By applying pinch analysis methods, the first step is to calculate the maximum heat recovery between cold and hot streams. The second step consists in designing the corresponding heat recovery exchanger network, based on a fixed list of streams. For the heat cascade, it is assumed that any heat exchange between cold and hot streams is possible, but due to industrial constraints, in many cases, this assumption cannot be accepted in practice and it is necessary to impose restricted matches. This introduces energy penalties, which could be reduced by using intermediate heat transfer systems. This paper introduces a targeting method including industrial constraints to ensure feasible solutions for the heat exchanger network. Intermediate heat transfer systems are integrated so that restricted heat exchanges become possible and heat recovery penalties, created by those constraints, can be reduced. The problem is formulated as a MILP (mixed integer linear programming) problem, which considers not only restricted matches but also the optimal integration of the energy conversion system, like heat pumping and combined heat and power production. The application of the method will be illustrated by an industrial example from the pulp and paper industry. The extension of the method to study the heat integration of semi batch processes will be discussed.