The document discusses options for retrofitting a heat exchanger network (HEN) to improve its efficiency. It analyzes three main retrofit options - resequencing, adding new heat exchangers, and stream splitting. For each option, it examines the effects on the network structure and pinch points. Case studies are presented to demonstrate how each option can eliminate pinch points and improve performance. The overall goal is to help users decide where to make effective structural changes to optimize a HEN.

1. Heat Exchanger Network Retrofit
by Djasmine Mastisya Saharudin (Supervisor: Professor Robin Smith)
Aim: To provide a conceptual understanding behind heat
exchanger network (HEN) retrofit options.
Objectives:
• To provide justifications behind HEN structural changes.
• To evaluate on the effect of the changes to the network pinch.
• To compare the list of suggested modifications for each
retrofit option.
Motivation: Limited availability of research papers focusing on
understanding behind HEN structural changes.
The base cases are incorporated into SPRINT
software with retrofit objective set to minimum utility.
Each retrofit option is applied to all cases.
- Up to the best four suggestions per
search are recorded.
The main focus is the analysis of HEN structural changes
suggested using three retrofit options; resequencing, addition
of new heat exchanger and stream splitting. Three retrofit
problems are presented to support the findings.
Degrees of freedom in the network are identified and their
changes after each modification are justified, leading to the
analysis of heat load shifting within network loops and paths.
All retrofit options attempt to overcome as many network
pinches as possible in one step.
Resequencing option tends to move heat exchangers with highest
∆Tmin first. Addition of new HE option involves creating new loop
or path and more flexible. Stream splitting option usually relaxes
temperature restrictions.
The project will help user in deciding where the most effective
HEN structural changes could be made.
Base Case
Resequencing
Resequencing
Addition of
new HE
Stream
Splitting
Addition of
new HE
Resequencing
Addition of
new HE
Stream
Splitting
Stream
Spitting
Resequencing
Addition of
new HE
Stream
Splitting
- Parallel search tree
is used to search for
the best retrofit
combination.
All suggested modifications generated are analysed
in depth to achieve the aim of the project.
An example of HEN Retrofit Problem (Adapted from Jiang et. al., 2014)
Resequencing
1st modification: Moving HE7
to the outlet of HE4 (Stream 6)
saves 5.70% of duty. Network
pinches in HE4 and HE6 are
overcame.
2nd modification: Moving HE3
to the outlet of HE6 (Stream 6)
saves 3.88% duty. Network
pinch in HE6 is eliminated.
Network Pinches are at HE2, HE4 and HE6 (∆Tmin of 15°C)
Addition of New HE
Adding HE13: Network
loop (HE6,HE13) is
created, reducing HE11 to
0 kW.
Adding HE14: New loop
(HE4,HE14) is created.
Network pinch in HE4 is
eliminated.
Stream Splitting
2875 kW duty is
transferred from HE3 to
HE2. Temperature
restrictions are reduced.
Best Retrofit Combination
24% overall energy saving.
i. 1st resequencing modification.
ii. Add HE13 at the outlets of HE2 (Stream 1) and HE4 (Stream 6).
iii. Add HE12 at the outlet of HE5 and the start of stream 2.
Base Case
Resequencing Resequencing
Addition of New
Heat Exchanger
Addition of New
Heat Exchanger
Stream Splitting Stream Splitting
Adding HE15: Another loop is created
between stream 2 and 6. Network
pinch in HE5 is relaxed.