Synthesis Of Flexible Heat Exchanger Networks Research Articles

A Flexible Heat Exchanger Network Synthesis Method Adapted to Multi-Operation Conditions

This paper presents a flexible HEN (heat exchanger network) synthesis methodology for designing a multiperiod HEN with streams involving phase changes. The methodology is based on an MINLP (mixed integer nonlinear programming) model, identification of critical points, and flexibility index analysis considering phase changes. A nominal multiperiod HEN topology is constructed in the first step. Then each process operating condition’s critical points and flexibility index are calculated to verify the feasibility of the designed HEN under multiple operating conditions. To verify the validity of the method, the proposed methodology will be applied to a case study on an ammonia synthesis process heat transfer network design based on renewable energy. The results show that the method can obtain a flexible heat transfer network that is cost-effective and adaptable to multi-condition production for green ammonia synthesis.

A Sequential Integration between Optimal Flexible Heat Exchanger Network Synthesis and Control Structure Design

In this work, the optimal synthesis and control structure design (CSD) problems for flexible heat exchanger networks (HENs) are integrated into a new sequential methodology. The proposed approach r...

Synthesis of flexible heat exchanger networks considering fouling resistance

The conventional synthesis of heat exchanger network (HEN) is performed under nominal conditions with fixed operating parameters. However, it is inevitable for the network configuration to be disturbed by uncertain operating conditions (for example, feed temperatures, heat capacity flow rates, etc.). At the same time, fouling is a non-negligible factor, which will cause sustained decrease to the overall heat transfer coefficient due to the growth of deposit over the heat transfer surface of the heat exchange units. In practice, the fouling resistance is often fixed to its maximum value instead of considering its dynamic growth. In order to make the synthesis more controllable and operable, this paper presents a flexible synthesis method, in which uncertain operating conditions and the growth of the fouling resistances are considered simultaneously. The methodology is sequentially implemented in two steps: the flexibility analysis and the flexible synthesis. By searching the critical directions, the improved flexibility analysis method for evaluating the flexibility index is proposed, which can reflect the simultaneous influence of uncertain operating conditions and fouling resistances. Then, the flexible HEN synthesis method based on the critical operating points identified by the aforementioned flexibility analysis method is presented, with the target of decreasing the complexity of the HEN to avoid over-synthesis and minimizing the total annual cost (TAC) simultaneously. The effectiveness of the methodology is demonstrated by a case study.

Structure and Area Optimization of Flexible Heat Exchanger Networks

A novel method is outlined for flexible heat exchanger network synthesis including nonconvex problems. The presented method is sequentially implemented by two main steps: structure synthesis and area optimization; nevertheless, the optimization of heat exchanger areas can still react on the structure to gain the global optimal solution. The structure is initially synthesized at the nominal operating point and renewed by the topological union with the structure of the critical point and the improved heat transfer loops disconnection strategy. For area optimization, an iterative approach with strong robustness is proposed based on the influences of heat exchanger areas on flexibility index and total annual cost, respectively. The direction matrix method is employed to provide the operational flexibility of the network and the critical operating point. Two examples with nonconvex feasible regions have been studied, and the results well demonstrate the effectiveness of the proposed approach.

A Method for Flexible Heat Exchanger Network Design under Severe Operation Uncertainty

AbstractMost investigations on heat exchanger network (HEN) synthesis which plays an important role in improving the efficiency of industrial plants, focus on deterministic conditions whereas operational flexibility and feasibility are less concerned. In the real industrial world, each system experiences various disturbances due to changes in stream temperature, flow rate, and other uncertain factors. An approach for flexible HEN synthesis under severe operation uncertainty is proposed, which is represented by the Probability bounds analysis (PBA) theory and is sampled by a double‐loop sampling method. A case study, which generates a better solution with less total annual cost and good flexibility under severe uncertainty, demonstrates the capability of this simplified approach.

Simultaneous Optimization of Synthesis and Scheduling of Cleaning in Flexible Heat Exchanger Networks

A novel methodology is presented for simultaneously optimizing synthesis and cleaning schedule of flexible heat exchanger network (HEN) by genetic/simulated annealing algorithms (GA/SA). Through taking into account the effect of fouling process on optimal network topology, a preliminary network structure possessing twofold oversynthesis is obtained by means of pseudo-temperature enthalpy ( T- H) diagram approach prior to simultaneous optimization. Thus, the computational complexity of this problem classified as NP (Non-deterministic Polynomial)-complete can be significantly reduced. The promising matches resulting from preliminary synthesis stage are further optimized in parallel with their heat exchange areas and cleaning schedule. In addition, a novel continuous time representation is introduced to subdivide the given time horizon into several variable-size intervals according to operating periods of heat exchangers, and then flexible HEN synthesis can be implemented in dynamic manner. A numerical example is provided to demonstrate that the presented strategy is feasible to decrease the total annual cost (TAC) and further improve network flexibility, but even more important, it may be applied to solve large-scale flexible HEN synthesis problems.

Multicriteria synthesis of flexible heat-exchanger networks with uncertain source-stream temperatures

A multi-criteria synthesis strategy for heat-exchanger networks (HENs) simultaneously considering minimum utility consumption, maximum source-stream temperature flexibility, and even minimum number of matches is proposed. The flexible HEN synthesis problem is formulated as a multi-objective mixed-integer linear programming (MO-MILP). For handling the multiple conflict design targets, a two-phase fuzzy multi-criteria decision-making method is presented to attain a best compromised solution. Two numerical examples with flexibility preferences in source-stream temperatures are supplied, demonstrating that the proposed strategy can provide definite and feasible compensatory solutions for multi-criteria HEN synthesis problems.