Mathematical programming synthesis of non-isothermal water networks by using a compact/reduced superstructure and an MINLP model

Synthesis of single and interplant non-isothermal water networks

“…Fig.1 shows a conceptual superstructure of an interplant heat-integrated water network involving two plants. A recently proposed compact superstructure (Ibrić et al, 2016) for individual plants has been modified in order to account for location of heating and cooling stages required for piping cost calculation as well as to represent connections between units within different plants.…”

“…3 shows the overall model consisting of three sub-models, namely, the water network model (M1), the simultaneous optimisation and heat integration model (M2) (Duran and Grossmann, 1986) and the heat exchanger network model (M3) (Yee and Grossmann, 1990). These models were combined within a two-step iterative solution strategy (Ibrić et al, 2016) consisting of initialisation and design steps ( Fig. 3).…”

“…Steps 1 and 2 are solved within the iterative procedure in which the heat recovery approach temperature (HRAT) required for solving M1-M2 is changed within the each iteration providing different bound for 7 water and utilities consumption and consequently different initialisation for the model M1-M3. A detailed explanation of the iterative procedure related to obtaining multiple locally optimal solutions can be found in our recent publication (Ibrić et al, 2016). Iterative procedure requires subsequent solution of multiple first NLPs/MINLPs and second MINLPs requiring additional time for obtaining the solution.…”

“…The bound can be obtained using known temperature levels, maximum inlet/outlet contaminants concentrations and maximum water flow rates within process water-using units. The reader is referred to recent paper (Ibrić et al, 2016) for the further details about deriving the generalized variables bounds.…”

“…The aim of this paper is to present a Mathematical Programming (MP) approach for the synthesis of single and interplant non-isothermal water networks. A recently proposed MINLP model (Ibrić et al, 2016) was modified by introducing binary parameters for identifying process units, wastewater treatment units and hot/cold streams within different plants and removing restricted connection between the units within different plants. This modified model enables the synthesis of interplant water networks, simultaneously exploring different water and heat integration opportunities.…”