# Building Block-Based Synthesis and Intensification of Work-Heat Exchanger Networks (WHENS)

^{*}

## Abstract

**:**

## 1. Introduction

## 2. A Building Block Representation of WHENS

#### 2.1. Elements of Building Block Representation

#### 2.2. Equipment Representation

#### 2.3. Flowsheet Representation

#### 2.4. Block Superstructure for WHENS

## 3. MINLP Model for WHENS

#### 3.1. Block Material Balance

#### 3.2. Flow Directions

#### 3.3. Block Energy Balance

#### 3.4. Product Stream Assignments and Logical Constraints

#### 3.5. Boundary Assignment

#### 3.6. Phase Relation and Stream Enthalpies

#### 3.7. Heat Transfer Boundary Modeling

#### 3.8. Work Calculation

#### 3.9. Objective Function

## 4. WHENS Case Study on Liquefied Natural Gas (LNG)-Based Cryogenic Energy Chain

## 5. Conclusions

## Author Contributions

## Funding

## Conflicts of Interest

## References

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**Figure 2.**Equipment representations using building blocks for work and heat exchanger network: (

**a**) Expander/compressor; (

**b**) Work-exchanger shafts for work integration; (

**c**) Two-stream exchanger for heat integration; (

**d**) Multi-stream heat exchanger (MHEX).

**Figure 3.**Various flowsheets and networks representations for work and heat integration in WHENS: (

**a**) Work and heat exchange network for a separation system. (

**b**) Work and heat exchange network for liquefied energy chain. (

**c**) Work and heat exchange network with three hot streams and two cold streams. (

**d**) Work and heat exchange network for single mixed refrigerant (SMR) process.

**Figure 4.**A general superstructure representation using building blocks for work and heat integration in WHENS: (

**a**) General block representation; (

**b**) Interaction of blocks through boundaries and connecting flows.

**Figure 7.**Resultant integrated work and heat exchanger network for the liquefied energy chain (case 1): (

**a**) Bock representation; (

**b**) Equivalent WHEN structure.

**Figure 8.**Manifestation of a refrigeration cycle using building blocks for cryogenic liquefaction process: (

**a**) block representation, and (

**b**) equivalent WHEN structure.

Reference | Approach | Application/Case Studies |
---|---|---|

Wechsung, Aspelund, Gundersen, Barton (2011) [29] | Combination of pinch analysis, exergy analysis, and optimization to find heat exchanger network (HEN) with minimal irreversibility by varying pressure levels of process streams | An offshore natural gas liquefaction process |

Razib, Hasan, Karimi (2012) [7] | First formalization of an optimization-based systematic work exchange network (WEN) synthesis problem | Integration among high-pressure and low-pressure streams |

Dong, Yu, Zhang (2014) [21] | Superstructure optimization for heat, mass and pressure exchange networks with exergoeconomic analysis | Wastewater distribution network in a petroleum refining process |

Onishi, Ravagnani, Caballero (2014a) [41] | Superstructure optimization for HEN design with pressure recovery | Cryogenic process design |

Onishi, Ravagnani, Caballero (2014b) [22] | MINLP-based WHENS using a multi-stage superstructure for optimal pressure recovery of process gaseous streams | Integration among high-pressure and low-pressure streams |

Fu and Gundersen (2015a,b,c,d) [14,15,16,42] | Graphical methodology for HEN design including compressors or expanders to minimize exergy consumption above or below ambient temperature | Integration of process streams with supply and target states |

Huang and Karimi (2016) [3] | MINLP-based approach to synthesize WHENS for optimized selection of end-heaters and end-coolers to meet the desired temperature targets | Integration among high-pressure and low-pressure streams and a transport chain for stranded natural gas |

Fu, Gundersen (2016) [13] | Correct integration of both compressors and expanders in HEN to minimize exergy consumption | Integration of process streams with the same supply and target temperatures |

Fu, Gundersen (2016c) [12] | Graphical methodology using thermodynamic insights for WHENS | CO${}_{2}$ capture processes |

Onishi, Ravagnani, Caballero (2017) [43] | Multi-objective optimization of WHENS using a multi-stage superstructure | Integration among process streams based on economic and environmental criteria |

Zhuang, Liu, Liu, Du (2017) [44] | Synthesis of direct work exchange network (WEN) in adiabatic process involving heat integration based on transshipment model | Integration of high-pressure and low-pressure streams in a chemical plant |

Nair, Rao, Karimi (2018) [24] | MINLP-based general WHENS framework considering stream temperature, pressure and/or phase changes without a $priori$ classification of stream identity | C3 splitting and offshore liquefied natural gas (LNG) processes |

Specification/Parameter | ${\mathit{S}}_{1}$ | ${\mathit{S}}_{2}$ | ${\mathit{S}}_{3}$ | ${\mathit{S}}_{4}$ | HU | CU |
---|---|---|---|---|---|---|

Feed pressure, ${P}_{f}^{feed}$ (MPa) | 10 | 10 | 6 | - | - | - |

Feed temperature, ${T}_{f}^{feed}$ (K) | 103.45 | 319.80 (298.15) | 221.12 | - | 383.15 | 93.15 |

Target pressure, ${P}_{p}^{min}={P}_{p}^{max}$ (MPa) | 0.1 | 10 | 6 | - | - | - |

Target pressure range, ${T}_{p}^{min}={T}_{p}^{max}$ (K) | - | 104.75 (113.15) | 293.15 | - | 383.15 | 93.15 |

Flowrate, ${F}_{f}^{feed}$ (kg/s) | 1.2 | 1 | 2.46 | - | - | - |

Molecular weight, $MW$ (kg/kmol) | 28 | 19 | 44 | 23.82 | 28 | 18 |

Stream | ${\mathit{a}}_{\mathit{k}}^{\mathit{b}}$ | ${\mathit{b}}_{\mathit{k}}^{\mathit{b}}$ | ${\mathit{a}}_{\mathit{k}}^{\mathit{d}}$ | ${\mathit{b}}_{\mathit{k}}^{\mathit{d}}$ | ${\mathit{a}}_{\mathit{k}}^{\mathit{l}}$ | ${\mathit{b}}_{\mathit{k}}^{\mathit{l}}$ | ${\mathit{c}}_{\mathit{k}}^{\mathit{l}}$ | ${\mathit{a}}_{\mathit{k}}^{\mathit{v}}$ | ${\mathit{b}}_{\mathit{k}}^{\mathit{v}}$ | ${\mathit{c}}_{\mathit{k}}^{\mathit{v}}$ |
---|---|---|---|---|---|---|---|---|---|---|

Nitrogen | 10.284 | 93.947 | 10.284 | 93.948 | 2.495 | −0.57 | −625.05 | 1.15 | −2.38 | −342.2 |

Natural gas | 0 | 197.35 | 0 | 265.15 | 3.51 | 0 | 0 | 3.46 | 0 | 123.77 |

Carbon dioxide | - | - | - | - | 2.318 | 0 | 0 | - | - | - |

**Table 4.**Cost coefficients for equipment and utilities ($CF$: fixed cost for different equipment; $CP$: appropriate cost coefficient for associated equipment; $CC$: unit cost for utilities).

Capital Cost (K $) | Operating Cost | ||||
---|---|---|---|---|---|

$\mathit{CF}$ | $\mathit{CP}$ | $\mathit{\beta}$ | $\mathit{\alpha}$ | $\mathit{CC}$$\mathit{or}$$\mathit{Rev}$ | |

Compressor | 184.12 | 2.4 $\times \phantom{\rule{3.33333pt}{0ex}}{10}^{-5}$ | 2.988 | 2.5 | - |

Expander | 29.20 | 0.4872 | 1 | 2.5 | - |

Motor | −1.1 | 2.1 | 0.6 | 4 | 455.04 ($/(KW·a)) |

Generator | −1.1 | 2.1 | 0.6 | 4 | 455.04 ($/(KW·a)) |

Heat exchanger | 27.05 | 0.5027 | 0.8003 | 3.5 | 337 ($/(KW·a)) |

HU | - | - | - | - | 337 ($/(KW·a)) |

CU | - | - | - | - | 1000 ($/(KW·a)) |

${\gamma}_{a}=0.18$, $\gamma =1.51$, $d{t}^{min}=4\phantom{\rule{3.33333pt}{0ex}}$K, ${U}^{L}={U}^{V}={U}^{LV}=0.1\phantom{\rule{3.33333pt}{0ex}}$m${}^{2}$K/KW, ${U}^{HU}={U}^{CU}=1\phantom{\rule{3.33333pt}{0ex}}$m${}^{2}$K/KW |

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).

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**MDPI and ACS Style**

Li, J.; Demirel, S.E.; Hasan, M.M.F.
Building Block-Based Synthesis and Intensification of Work-Heat Exchanger Networks (WHENS). *Processes* **2019**, *7*, 23.
https://doi.org/10.3390/pr7010023

**AMA Style**

Li J, Demirel SE, Hasan MMF.
Building Block-Based Synthesis and Intensification of Work-Heat Exchanger Networks (WHENS). *Processes*. 2019; 7(1):23.
https://doi.org/10.3390/pr7010023

**Chicago/Turabian Style**

Li, Jianping, Salih Emre Demirel, and M. M. Faruque Hasan.
2019. "Building Block-Based Synthesis and Intensification of Work-Heat Exchanger Networks (WHENS)" *Processes* 7, no. 1: 23.
https://doi.org/10.3390/pr7010023