MINLP model and two-stage algorithm for the simultaneous synthesis of heat exchanger networks, utility systems and heat recovery cycles

Abstract

This work proposes a novel approach for the simultaneous synthesis of Heat Exchanger Networks (HEN) and Utility Systems of chemical processes and energy systems. Given a set of hot and cold process streams and a set of available utility systems, the method determines the optimal selection, arrangement and design of utility systems and the heat exchanger network aiming to rigorously consider the trade-off between efficiency and capital costs. The mathematical formulation uses the SYNHEAT superstructure for the HEN, and ad hoc superstructures and nonlinear models to represent the utility systems. The challenging nonconvex MINLP is solved with a two-stage algorithm. A sequential synthesis algorithm is specifically developed to generate a good starting solution. The algorithm is tested on a literature test problem and two industrial problems, the optimization of the Heat Recovery Steam Cycle of a Natural Gas Combined Cycle and the heat recovery system of an Integrated Gasification Combined Cycle.

Design of a Pilot SOFC System for the Combined Production of Hydrogen and Electricity under Refueling Station Requirements

“…The SYNHEAT superstructure stands for the type of streams connections and layout, originally proposed in . The SYNHEAT algorithm from , is modified here to take into account the multi‐period optimization strategy from . The core of the MOO methodology is the QMOO algorithm developed at EPFL for energy system optimizations.…”

“…The ad hoc SYNHEAT superstructure for the optimization of the proposed CH2P plant has the following characteristics [30,24]: (i) constant h values for each stream, along the different periods (calculated from the steady state simulations); (ii) the minimum temperature (ΔT min ) is given as an input, thus, not considered for optimization; (iii) each HEX is assigned to the same pair of hot and cold streams at all the periods; (iv) countercurrent HEX configuration; (v) a fix number of stages established by the user (below the maximum number of either the hot and cold streams), as defined in the SYNHEAT superstructure [24]; (vi) for each stage, streams are split to cover all hot and cold streams matches; (vii) the outlet temperatures of each stage, for each stream, are treated as variables; (viii) in order to simplify the model formulation, utilities are placed at the outlet of the superstructure and streams are mixed isothermally; (ix) the approach from [31] is used to model condensers, evaporators and isothermal reactors; (x) consideration of one hot and one cold utility; (xi) the hot utility load is treated as a decision variable of the master (upper) level optimization, and therefore, it is treated as a process stream; (xii) the cold utility is considered a cold end, reducing the size of the combinatorial (superstructure) problem; (xiii) the HEN design can restrict stream splitting, can forbid matches and restrict/oblige other matches (e.g., avoid the contact of a combustible stream with an O 2 -rich stream); parallel and in-series configurations are allowed; (xiv) the dynamics when changing flow rates or temperatures between periods, e.g., residence times and thermal inertia, are neglected; (xv) the SYNHEAT approach does not deal with streams' temperatures change, but these are modified by the MOO algorithm.…”

Optimization of Organic Rankine Cycles for Waste Heat Recovery From Aluminum Production Plants

“…The well-known energy targeting model proposed by Duran and Grossmann (1986) is used to address the heat integration, and then a suboptimal HEN is derived heuristically. Martelli et al (2016Martelli et al ( , 2017, and Elsido et al (2017a,b) proposed a simultaneous method for the combined synthesis of HENs and utility systems for one or more available heat sources, including heat recovery cycles, and the selection and design of the latter ones, while considering all the possible integration options between process heat sources/sinks and utility systems. Compared to sequential or separated approaches, the advantage of the simultaneous approach is that it allows one to systematically optimize not only the cycle configuration but also the heat integration and HEN while rigorously taking into account the trade-off between energy efficiency and costs.…”

“…Compared to sequential or separated approaches, the advantage of the simultaneous approach is that it allows one to systematically optimize not only the cycle configuration but also the heat integration and HEN while rigorously taking into account the trade-off between energy efficiency and costs. For this reason, the methodology proposed by Martelli et al (2017) has been selected for this work.…”

“…The main peculiarity of the plant is the availability of two hot streams with different temperatures, which calls for the use of heat integration methodologies. For this reason, working fluid and cycle pressure and temperatures are optimized with the systematic optimization approaches recently proposed by Scaccabarozzi et al (2018), while the ORC design, mass flow rates, and HEN are optimized with the approach developed by Martelli et al (2017) and Elsido et al (2018). Both approaches can handle the optimization of Rankine cycles integrated with multiple hot and cold streams.…”