Abstract

We provide a new method to represent all potential flowsheet configurations for the superstructure-based simultaneous synthesis of work and heat exchanger networks (WHENS). The new representation is based on only two fundamental elements of abstract building blocks. The first design element is the block interior that is used to represent splitting, mixing, utility cooling, and utility heating of individual streams. The second design element is the shared boundaries between adjacent blocks that permit inter-stream heat and work transfer and integration. A semi-restricted boundary represents expansion/compression of streams connected to either common (integrated) or dedicated (utility) shafts. A completely restricted boundary with a temperature gradient across it represents inter-stream heat integration. The blocks interact with each other via mass and energy flows through the boundaries when assembled in a two-dimensional grid-like superstructure. Through observation and examples from literature, we illustrate that our building block-based WHENS superstructure contains numerous candidate flowsheet configurations for simultaneous heat and work integration. This approach does not require the specification of work and heat integration stages. Intensified designs, such as multi-stream heat exchangers with varying pressures, are also included. We formulate a mixed-integer non-linear (MINLP) optimization model for WHENS with minimum total annual cost and demonstrate the capability of the proposed synthesis approach through a case study on liquefied energy chain. The concept of building blocks is found to be general enough to be used in possible discovery of non-intuitive process flowsheets involving heat and work exchangers.

Highlights

  • Heat and work are used as the primary energy utilities in most chemical process plants

  • Based on the representation approach, we develop the corresponding MINLP model for work and heat exchanger network synthesis (WHENS), which is discussed

  • We presented a method to automatically generate numerous alternative configurations for the synthesis of integrated work and heat exchange networks using building blocks

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Summary

Introduction

Heat and work are used as the primary energy utilities in most chemical process plants. Though significant progress has been made in terms of theoretical development [17,18] and methodological advances [19,20], there are several limitations of pinch analysis This approach is time-consuming when applied to systems involving many process streams [2]. Superstructure provides an excellent means to automatically generate many network configurations, but the traditional superstructures could still miss innovative solutions due to a lack of representation To this end, Hasan and co-workers have recently put forward a novel superstructure representation using abstract building blocks for systematic process synthesis and intensification [37,38,39,40]. Combination of pinch analysis, exergy analysis, and optimization to find heat exchanger network (HEN) with minimal irreversibility by varying pressure levels of process streams. Integration of process streams with the same supply and target temperatures (2016c) [12]

Graphical methodology using thermodynamic insights for WHENS
A Building Block Representation of WHENS
Elements of Building Block Representation
Equipment Representation
Flowsheet Representation
Block Superstructure for WHENS
MINLP Model for WHENS
Block Material Balance
Flow Directions
Block Energy Balance
Product Stream Assignments and Logical Constraints
Boundary Assignment
Phase Relation and Stream Enthalpies
Heat Transfer Boundary Modeling
Work Calculation
Objective Function
Conclusions
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