An extended superstructure modeling method for simultaneous synthesis of direct work exchanger networks

Generalized simultaneous optimization model for synthesis of heat and work exchange networks

Synthesis of heat exchanger network considering pressure drop and layout of equipment exchanging heat

MINLP model for work and heat exchange networks synthesis considering unclassified streams

Solution of MEN synthesis problems using MINLP: Formulations of the Kremser equation

Costs and environmental impacts multi-objective heat exchanger networks synthesis using a meta-heuristic approach

Multi-objective optimization of a solid oxide fuel cell-based integrated system to select the optimal closed thermodynamic cycle and heat coupling scheme simultaneously

Total annualized cost optimality properties of state space models for mass and heat exchanger networks

Simultaneous optimization approach for integrated water-allocation and heat-exchange networks

Fouling and aging are the main causes for the degradation of heat exchanger performance from a well-behaved heat-transfer performance. They result in extra capital and energy costs for heat exchanger networks (HENs) to compensate for the gap in target temperatures. To reduce the negative effect of deposition, this paper presents a novel methodology for managing the cleaning schedule problem in the design of HENs. The method consists of three steps. First, obtain an original HEN using pseudotemperature enthalpy diagram approach. Then, simplify the structure of the original HEN through loop-breaking and small size unit eliminating strategies. Finally, optimize heat-transfer areas and cleaning schedules by considering the growth of deposits via a mixed integer nonlinear programming model. Therefore, the model is capable of weighing the capital cost for exchangers and the operation cost for both utility consumption and cleaning activities. In this study, two off-line cleaning alternatives with distinct cleaning efficiencies are provided for deposition removal; therefore, the problem of which method should be selected for each exchanger will also be investigated in the model. At the end of the study, an illustrative example is presented to demonstrate the proposed method. The results have indicated the potential for cost savings when good cleaning schedules are planned with the design of HENs.

The simultaneous heat exchanger network (HEN) synthesis problem is generally formulated as a mixed integer non-linear programming (MINLP) problem by using superstructures, which embed several possible stream matches and various alternative HEN designs. The superstructures proposed by Yee et al. [1] and by Floudas et al. [2] are used for this purpose. In the present work, the graph theoretic principles used by Shivakumar and Narasimhan [3] to develop an efficient nonlinear program (NLP) formulation for Yee superstructure has been extended to the Floudas superstructure. A comparison of the NLP formulations based on the two superstructures, in terms of efficiency, scalability, convergence and quality of solution has been carried out using several test problems available in the literature. It has been shown that the Floudas superstructure is superior in terms of these performance metrics, and appears to be the best suited for optimisation based HEN synthesis.

Heat exchanger network synthesis using genetic algorithm and differential evolution

A typical heat-integrated water network (HIWN) synthesis problem aims to minimise freshwater and utility consumption while establishing trade-offs between operating and investment costs by exploring different water and heat integration opportunities. Heat integration between hot and cold water streams is performed to save external heating and cooling utilities required to achieve the target temperatures of these streams. This paper proposes a mathematical programming approach to integrate water-to-water heat pumps into the HIWNs. A simple cascade heat pump system with isobutane as a natural working fluid enables a larger temperature lift between the heat pump source and the sink. The objective function of the proposed mixed-integer nonlinear programming (MINLP) model is to minimise the total annualised cost (TAC). The TAC includes operating costs for freshwater, heating/cooling utilities, electricity, and investment in heat exchangers and heat pumps. A sensitivity analysis is performed to evaluate the economic feasibility of the system by varying the heating/electricity cost ratio and depreciation period for the capital investment. The results show that additional utility savings can be obtained by integrating heat pumps into the HIWNs. For threshold problems, a heat pump is feasible for heating/electricity price ratios from 1.175, and heating utility is replaced by electricity for a 1:1 ratio. However, for pinched problems, the feasibility of the heat pump is shifted to lower heating/electricity price ratios, from 0.3 to 0.5, depending on the annualisation factor for the investment.

A simultaneous optimization approach for the design of wastewater and heat exchange networks based on cost estimation

A master–slave solving method with adaptive model reformulation technique for water network synthesis using MINLP

This paper introduces a mathematical programming approach for synthesising heat-integrated water networks (HIWNs) with a detailed heat exchanger design. A common assumption of constant heat capacities of water streams is relaxed. The specific heat capacity of water is now considered as a nonlinear function of temperature to avoid errors in calculating energy balances. In addition, most previous works have assumed constant individual heat transfer coefficients for water streams and utilities when estimating heat transfer areas. This assumption can lead to significant over- or under-estimation of heat transfer areas. In this research, individual and overall heat transfer coefficients for heat exchangers are calculated based on the detailed design of plate heat exchangers for heat recovery. The objective function of the proposed mixed integer nonlinear programming (MINLP) model is to minimise the total annualised cost (TAC). The TAC includes operating costs for freshwater and utilities, pumping costs for overcoming pressure drops in heat exchangers, and investment costs for heat exchangers. Three examples are solved in this work to verify the proposed model.