Multi-period Heat Exchanger Network Synthesis Research Articles

Synthesis of multiperiod heat exchanger networks: Minimum utility consumption in each period

Heat exchanger networks in real industrial processes often have to be designed for varying parameters of the process streams that renders multiperiod heat exchanger network synthesis essential in industrial realization. However, three standing issues must be considered in the synthesis procedure. (1) The generated network should be efficient in all periods, preferably consuming minimum utility. (2) This network should also be structurally as simple as possible for minimizing the investment cost and making the process controllable. Furthermore, (3) all or the n-best networks that fulfilled the first two principles must be considered for the selection of the most preferred industrial realization. The method proposed in the current work satisfies all three requirements simultaneously; it has been the only known method with these properties. The method primarily relies on the formerly developed P-graph-based heat exchanger network synthesis procedure. Three case studies demonstrate the application of the proposed method.

Multi-period Heat Exchanger Network Synthesis with Temperature Intervals and Uncertain Disturbances

High energy consumption is a major challenge currently threatening many industrial processes. This has made industrial processes such as absorptive CO2 capture expensive and energy intensive. However, research has shown that the application of Heat Exchanger Networks has the potential of minimizing energy demands in many industrial processes due to its energy recovery advantage. In this study, a sequential procedure is presented for the synthesis of heat exchanger network for multi-period operations with specified uncertainties in flow rates and variations in inlet and outlet temperatures of process streams. The synthesis task in this study was sequentially decomposed into three stages. Temperature interval method was used to determine the loads and minimum utilities required by the network in the first stage. Determination of the minimum number of units was considered in the second stage while the third stage was dedicated to the derivation of a network configuration and sizing of heat exchangers to determine the capital cost using area targeting technique. Efficacy of the proposed methodology was tested using an example from literature. A new heuristic rule was established and the network topologies obtained using the proposed approach testifies to the applicability of HENs for energy minimization during absorptive CO2 capture.

Efficient multiperiod heat exchanger network synthesis using a meta-heuristic approach

Multiperiod heat exchanger networks (HEN) are required in plants with seasonal alterations to operating conditions. Like for single-period HEN, the synthesis of multiperiod HEN can be formulated as a mathematical programming optimization problem. However, since the network needs to feasibly perform heat integration under different process conditions, additional constraints are required and problem complexity is increased. Studies on the subject based on mathematical programming often use deterministic approaches and rely on commercial solvers. In this work, a meta-heuristic two-level method based on Simulated Annealing and Rocket Fireworks Optimization (SA-RFO), originally developed for single-period HEN synthesis, is adapted to handle multiperiod HEN optimization. A new post-optimization (PO) strategy is coupled with the main method in order to improve the results. Four case studies are investigated and results are compared to the literature. The solutions achieved presented lower total annual costs (TAC) than those obtained by other methods and the new PO scheme was able to significantly improve the results.

Integrating renewables into multi-period heat exchanger network synthesis considering economics and environmental impact

Abstract This paper presents a further development of synthesis methods that considers economics and environmental impact in the integration of renewable energy into the optimisation of heat exchanger networks involving multiple periods of operations and multiple options of utilities. The multi-period process stream parameters, and those of the utility sources are integrated in a systematic approach using an expanded version of the simplified stage-wise superstructure multi-period model. Two examples were used to demonstrate the benefits of the expanded synthesis method and the quality of solutions obtained were judged by representation on a Pareto curve and by the use of a modified goal solution method. It was found that various combinations of utility sources were selected for use at various periods/seasons of operations, while utilities from solar photovoltaic were not selected for use at any of the periods/season of operation due to its relatively high cost and limited periods of availability.

Optimal synthesis of multiperiod heat exchanger networks: A sequential approach

Heat exchanger network (HEN) synthesis is an important research field in industrial processes. It is possible to minimize utilities usage as well as pollutant emissions by an optimal HEN synthesis. In multiperiod HENs, the same heat transfer devices must be able to operate under different operating conditions. The synthesis of multiperiod HEN can be formulated as an optimization problem. In the present paper it is used a sequential approach to solve the problem of synthesizing multiperiod HEN, considering heat capacities and stream temperatures variations into different operation periods. In this approach, multiperiod HEN synthesis is decomposed into three sequential steps, considering three optimization models. The novelties of the proposed approach are a modification in a well-known superstructure from the literature, with the inclusion of new by-pass streams, and an improvement in the NLP model of the third step. Two benchmark literature examples are studied and the obtained results prove the approach applicability, showing better values and network topologies.

Two-step hybrid approach for the synthesis of multi-period heat exchanger networks with detailed exchanger design

In this study a novel methodology for multi-period heat exchanger network synthesis is presented. The new synthesis method aims to systematically generate many candidate networks and, through the use of more detailed individual heat exchanger designs and their evaluation over all periods, guide the network optimisation to more realistic designs. This is done by using the multi-period mixed integer non-linear programming (MINLP) stage-wise superstructure (SWS) model and modifying it to include correction factors. These correction factors enable the MINLP optimisation of the overall cost of the designed network, which uses only shortcut models of the individual exchangers, to be guided by more detailed models of the individual heat exchangers that comprise the network. The designs obtained at the topology optimisation stage thus more accurately represent an actual network. The correction factors take into account aspects of the real design, such as TEMA standards, FT correction factors, number of shells, and changes in overall heat transfer coefficients. Each exchanger is designed to function over all periods of operation, and if this is not possible, extra exchangers are designed for the periods that cannot be satisfied. The methodology is applied to a case study that demonstrates the benefits of the proposed approach.

A heuristic Lagrangean approach for the synthesis of multiperiod heat exchanger networks

In this work, we apply a decomposition technique to address the multiperiod heat exchanger network synthesis. Each period corresponds to changes in operating conditions, i.e. inlet temperatures and heat capacity flowrates. The problem size grows quickly with the number of streams and the number of periods resulting in a large scale problem to solve. In order to reduce the problem to a manageable size, we propose a specialized heuristic algorithm that relies on the concept of Lagrangean decomposition. We present an iterative scheme where feasible solutions are postulated from the Lagrangean decomposition subproblems, and the Lagrangean multipliers are updated through a subgradient method. Numerical examples are used to illustrate the proposed approach and the solutions are compared with the full space solutions with no decomposition. In general, slightly better solutions are found but in the terms of computational effort, its use is only justified as the problem size is increased.