Bing Shen How
56523047700
Publications - 21
Exhaustive enumeration of heat exchanger networks with minimum utility consumption using graph-theoretic approach
Publication Name: Energy
Publication Date: 2025-10-30
Volume: 335
Issue: Unknown
Page Range: Unknown
Description:
Enhancement in energy recovery is always an essential element that requires academic spotlights to ensure its capability to contribute towards carbon neutrality. Recent works have extended to cover multi-solution heat exchanger networks (HEN) synthesis instead of generating a single best solution, which is not guaranteed to be practical. Nevertheless, owing to the technical challenges of synthesising all feasible networks, none of the existing works attempts to comprehensively elucidate how network topologies affect the network cost. To address this gap, P-HENS, a graph theoretic-based HEN synthesis tool, was utilised to generate the set of all heat exchanger networks with minimum utility consumption. Its effectiveness is demonstrated through an illustrative case study, which eventually generates more than 45,000 HENs. The impacts of structural variables on the cost, including the number of exchangers and the stream pairings, were analysed. The cost range of the networks was identified, revealing cost differences of 30 % despite minimum utility consumption or 15 % despite the minimum number of exchangers. Key stream pairs required to meet maximum energy recovery and influence cost were identified, leading to recommendations for improving solution searches. The solution set and the insight from this work are available to the research community for further analysis, offering valuable insights to enhance energy integration in the industry.
Open Access: Yes
Multi-Solution Heat Exchanger Network Synthesis for Turbo-Expander-Based Cryogenic CO2 Capture Technology
Publication Name: Industrial and Engineering Chemistry Research
Publication Date: 2025-01-22
Volume: 64
Issue: 3
Page Range: 1664-1679
Description:
Cryogenic separation of CO2 is a potential technology that can benefit from energy efficiency improvements. However, the current conventional and emerging cryogenic technologies face challenges in terms of high utility consumption. The high utility requirement leads to increasing operational costs and emissions due to the production of required utilities from external energy sources. This issue can be solved if the heat recovery potential of the technology can be realized. Heat recovery enables further improvement in energy efficiency that is required to elevate the feasibility of cryogenic separation. This paper explores heat recovery opportunities between hot and cold streams in a novel cryogenic CO2 capture technology known as Turbo-Expander-based Cryogenic Distillation (CryoDT). This is achieved using P-HENS, a P-graph-based heat exchanger network synthesis tool where multiple feasible heat exchanger network configurations are generated to determine the options that effectively recover process heat to reduce utility consumption. Moreover, the solutions generated by P-HENS are benchmarked with other tools like Aspen Energy Analyzer, by comparing the number of required heat exchangers, along with the associated capital and operating costs. For the predefined hot and cold process streams of the novel technology, the total number of heat exchangers present in the network was lower in the recommended design using P-HENS (i.e., 9 heat exchangers) as opposed to Aspen Energy Analyzer (16 heat exchangers) while maintaining similar energy consumption levels. This indicates that there is a further opportunity to reduce capital costs as a result of less heat exchangers. The CryoDT configuration that is integrated with a heat exchanger network offers significant economic advantages as opposed to other existing cryogenic processes in the market such as the Ryan Holmes and Controlled Freeze Zone (CFZ) processes. Despite its high capital cost, the CryoDT process demonstrates significantly lower operating cost relative to the other two processes. Hence, while the initial investment is substantial, the CryoDT process is much more cost efficient to operate. The low operating cost is attributed to its higher energy efficiency and minimal energy penalties, with only 0.26 GJ/tonne of CO2 compared with 0.82 GJ/tonne of CO2 for the CFZ process and 2.33 GJ/tonne of CO2 for Ryan Holmes. In contrast, the Ryan Holmes process, despite its low capital cost, incurs extremely high annual operational costs, rendering it less economic in the long term. The CFZ process, with its moderate operating cost, presents a balance between capital cost and operational efficiency.
Open Access: Yes
The P-graph application extension in multi-period P2P energy trading
Publication Name: Renewable and Sustainable Energy Reviews
Publication Date: 2024-08-01
Volume: 200
Issue: Unknown
Page Range: Unknown
Description:
An optimization model that incorporates all combinatorically feasible inter-plant collaboration networks is developed using P-graph. It has been theoretically proven that time-sliced-based energy planning optimization has positive impacts and is capable of achieving carbon emissions reduction goals and minimizing costs simultaneously. However, as the number of entities increased, an exponential growth in possible combinatorial feasible coalitions is anticipated. Therefore, an extension of the P-graph optimization tool that is capable of generating all possible outcomes in multi-period P2P energy trading – PEP (P-graph for energy planning) is developed. The PEP software can be effectively used in modelling complex process networks graphically and solving optimization problems with the combined advantages of combinatorial algorithms and mathematical programming. In this paper, a systematic framework for implementing P2P energy trading using PEP software is proposed and demonstrated using a real-life case study.
Open Access: Yes
Electrification of oil refineries through multi-objective multi-period graph-theoretical planning: A crude distillation unit case study
Publication Name: Journal of Cleaner Production
Publication Date: 2024-01-01
Volume: 434
Issue: Unknown
Page Range: Unknown
Description:
Electrification using renewable energy sources is the key to paving a sustainable and cleaner future for the oil and gas sector, which is known to be a significant carbon dioxide emitter. Nevertheless, the suitability of the electrification designs heavily depends on the seasonal availability of renewable energy sources. This work proposes to use a multi-period graph-theoretical (P-graph) approach to determine the optimal retrofit strategy to achieve electrification with consideration of economic and environmental factors. Both single-period and multi-period models are considered via a graph-theoretical approach to rank and evaluate all the combinatorically feasible electrification pathways based on the overall performance. The effectiveness of the proposed method is developed using a crude distillation unit (CDU) case study adopted from a multinational company. The effectiveness of the proposed method is illustrated using a crude distillation unit (CDU) case study shown in three different scenarios that include prioritizing economic aspect (Scenario 1), prioritizing environmental aspect (Scenario 2), and considering equal importance of both aspects (Scenario 3). For single-period operation, the results showed a mix of natural gas and hydropower energy, exclusive use of onshore wind energy, and a mix of onshore wind energy and biogas cogeneration energy for Scenario 1, Scenario 2, and Scenario 3, respectively. In contrast, the multi-period model also utilized nuclear energy for Scenario 2 and Scenario 3 given the seasonal availability constraint. Following that, a sensitivity analysis is conducted to see the effect of the absence of the most influential energy sources on the optimal solution of each scenario and the top solutions under budget and CO2 emission constraints. Pareto analysis is outlined to offer an understanding of tradeoffs between differently prioritized solutions that decision-makers can select. The combination of the proposed analysis provides a systemic approach towards transforming traditional industries towards a cleaner future via electrification.
Open Access: Yes
Synthesis of N-best Heat Recovery Networks with Consideration of Dynamic Control Performance
Publication Name: Chemical Engineering Transactions
Publication Date: 2024-01-01
Volume: 114
Issue: Unknown
Page Range: 73-78
Description:
Recently, graph-theoretic methods have increasingly been employed to generate near-best (n-best) heat recovery networks, aiming to maximize energy recovery efficiency. The exploration of these n-best networks has proven pivotal for making informed decisions. Nevertheless, existing studies in this domain have not attempted to study the favourability of these generated networks based on their respective dynamic control performance. This performance metric reflects the network's ability to maintain target temperature even under disturbances. The network topologies play important role in both economic (i.e., total annual cost (TAC)) and dynamic control aspects. To address this gap, this work introduces a hybrid approach. First, all combinatorically feasible heat recovery networks are generated using P-HENS. Thereafter, each network undergoes dynamic control performance evaluation through Aspen Plus simulations. The final step involves optimization of the network structures based on fuzzy method which avoids over-prioritization. To illustrate the efficacy of the proposed methodology, it is applied to solve a 5-stream problem. Results showed that Network A with the least TAC ($122,249) is not necessarily associated with the greatest dynamic performance (with failure rate of 15 %). Network C which offers the balance performance (with TAC of $122,666 and failure rate of 0 %) is chosen.
Open Access: Yes
DOI: 10.3303/CET24114013
Retrofit heat exchanger network optimization via graph-theoretical approach: Pinch-bounded N-best solutions allows positional swapping
Publication Name: Energy
Publication Date: 2023-11-15
Volume: 283
Issue: Unknown
Page Range: Unknown
Description:
Retrofit heat exchanger network (HEN) optimization is a fundamentally unique problem which requires the consideration of existing structures, compared to grassroots design problems. The optimization of retrofit HENs is particularly difficult due to the integration of both existing and newly acquired equipment. The re-routing of existing equipment can lead to various network topologies, increasing the complexity of considerations. In this work, we exploit the P-graph framework to solve retrofit HEN problems, guaranteeing to find the topology of optimal solutions within the constrained space of the HEN retrofit problem. The P-graph framework has additional advantages that allows topologically-efficient search space, simplifies additional unit placement, considers unit positional swapping (re-sequencing and re-piping within search constraints), considers stream splitting, and n-best solution visualization. The pinch minimum utility constraint also provides a bound for the maximum number of modifications in the HEN, significantly reducing search space. The proposed P-graph-based approach is demonstrated using a real refinery case study to show its capability in obtaining the topology of the optimal HEN, highlighting the economic and energy benefits. Further extensions to other retrofit process integration problems (e.g. retrofit water network, hydrogen network etc.) will be enabled via the proposed P-graph approach.
Open Access: Yes
Synthesis of multiperiod heat exchanger networks: n-best networks with variable approach temperature
Publication Name: Thermal Science and Engineering Progress
Publication Date: 2023-07-01
Volume: 42
Issue: Unknown
Page Range: Unknown
Description:
In industrial processes, the stream parameters of the heat exchanger network (HEN) synthesis problem can vary during different periods. As a result of the change in inlet and outlet temperatures and the flow rates of the streams, the optimal HEN and the optimal heat transfer areas of the heat exchangers can be different in each period. In our previous work, the standard HEN synthesis for minimum utility consumption was extended to consider varying stream parameters, where bypasses at the heat exchangers are used to ensure the exit streams meet the expected outlet temperatures. This requires optimization of the total annualized cost based on the maximal heat transfer areas of the heat exchangers for each period. Minimum approach temperature is applied to ensure that the areas of the heat exchangers stay within reasonable limits in the solution network. Since minimum approach temperature affects both the structure of the HEN and the total annualized cost, its value needs to be determined during the optimization procedure. The current work proposes a procedure for HEN synthesis which determines the best, n-best, or all feasible HENs for all periods considering variable approach temperature. The proposed method extends the P-graph-based HEN synthesis method for determining all feasible networks in all periods. Three case studies are used to demonstrate the application of the proposed method. The case studies show that while the commonly applied minimum approach temperature of 10 °C does indeed gives near-optimal results, some problems need different values, such as 25 °C or 30 °C.
Open Access: Yes
Enabling in-depth analysis in heat exchanger network synthesis via graph-theoretic tool: Experiences in Swinburne University of Technology Sarawak Campus
Publication Name: Education for Chemical Engineers
Publication Date: 2023-04-01
Volume: 43
Issue: Unknown
Page Range: 100-112
Description:
The ability and capability to analyze and benchmark alternative designs on top of the optimal network are deemed valuable competencies for current and future chemical engineers. In this context, a process graph (P-graph)-inspired tool – P-HENS is introduced to an integrated plant design unit in an undergraduate chemical engineering degree program at Swinburne University of Technology Sarawak Campus in Malaysia. The energy recovery aspect is one of the key design elements in the integrated plant design unit. The introduction of P-HENS, which is capable of mathematically determining multiple optimal and sub-optimal solutions is considered useful for the students to (i) identify plausible heat exchanger networks (HENs) structures that may be overlooked using conventional approaches and (ii) enable a more in-depth analysis to justify the selected design. Overall, the implementation of P-HENS shows positive outcomes, where this free-of-charge software complements the learning of conventional manual approaches used in HENs synthesis. Furthermore, recommendations suggested by the users (students) are collected and compiled for potential future software development. This work serves as an essential reference for other chemical engineering educators who are teaching pinch analysis or heat integration-related courses.
Open Access: Yes
Exploring N-best solution space for heat integrated hydrogen regeneration network using sequential graph-theoretic approach
Publication Name: International Journal of Hydrogen Energy
Publication Date: 2023-02-12
Volume: 48
Issue: 13
Page Range: 4943-4959
Description:
To achieve the ever-stringent sustainable goals, this paper aims to synthesize a heat integrated hydrogen regeneration network (HIHRN) using a graph-theoretic-based sequential method. Firstly, the optimal and near-optimal structures for a hydrogen regeneration networks (HRN) are determined using P-graph model with consideration of both impurity and pressure constraints. These networks are then used as inputs in P-HENS software to generate a list of optimal and near-optimal heat exchanger network (HEN) structures. An eight source and sink problem is used to demonstrate the effectiveness of the proposed method. There are 199,677 feasible HIHRN structures identified, while the 6 near-optimal solutions which are within 0.05% tolerance of the optimal network cost (i.e., less than 33.04 M$/y) are presented together with the top four HEN designs that can offer comparable costs (∼115,500 $/y). In addition, the impacts of pressure swing adsorber (PSA) pressure drop consideration and minimum temperature difference on the optimal design are also presented.
Open Access: Yes
Framework to embed machine learning algorithms in P-graph: Communication from the chemical process perspectives
Publication Name: Chemical Engineering Research and Design
Publication Date: 2022-12-01
Volume: 188
Issue: Unknown
Page Range: 265-270
Description:
P-graph is a popularly used framework for process network synthesis (PNS) and network topological optimization. This short communication introduces a Python interface for P-graph to serve as a linkage to modern programming ecosystems. This allows for a wider application of the fast and efficient P-graph solver, to provide structural and topological enumeration in numerous fields. The proposed framework allows for more integrative usage in Artificial Intelligence (AI), machine learning, process system engineering, chemical engineering and chemometrics. Large and repetitive topologies can also be automated using the new programming interface, saving time and effort in modelling. This short communication serves as a demonstration of the newly developed open-sourced P-graph interface.
Open Access: Yes
Synthesis of multiperiod heat exchanger networks: Minimum utility consumption in each period
Publication Name: Computers and Chemical Engineering
Publication Date: 2022-10-01
Volume: 166
Issue: Unknown
Page Range: Unknown
Description:
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.
Open Access: Yes
Multiple-solution heat exchanger network synthesis using P-HENS solver
Publication Name: Journal of the Taiwan Institute of Chemical Engineers
Publication Date: 2022-01-01
Volume: 130
Issue: Unknown
Page Range: Unknown
Description:
Analysis on the alternative designs on top of the optimal network has proven valuable and meaningful for the decision-makers in determining the most suitable options which fulfill a wide range of objective functions. On the basis of an extension of the P-graph framework, a procedure was developed previously for multiple-solution heat exchanger network (HEN) synthesis. This procedure is capable of generating the n-best HENs depending on predefined structural constraints, for example, the maximum number of heat exchangers used for the entire system, the maximum number of sequential heat exchangers on each stream, the maximum number of stream splittings per stream. Since the choice of a parameter influences the effect of other parameters on the result, it is difficult to find the proper set of parameters for the solver that result in all plausible solutions to the original problem. Naturally, this issue emerges in any HEN synthesis problem, its systematic treatment is essential. The purpose of the current work was to develop a heuristic framework for determining the most reasonable parameters of the HEN generation algorithm and guiding the designer through the optimization process. The outcome of this study not only benefits the researchers and industrial practitioners of this field but may also be extended for educational purposes.
Open Access: Yes
Reliability incorporated optimal process pathway selection for sustainable microalgae-based biorefinery system: P-graph approach
Publication Name: Computer Aided Chemical Engineering
Publication Date: 2022-01-01
Volume: 49
Issue: Unknown
Page Range: 217-222
Description:
Biofuel from microalgae is one of the promising solutions on addressing climate change by its possibility of reducing the fossil fuel dependency. Till-date, the overall competitiveness of microalgae based biorefinery is the major concern due to its unique operational mechanism, especially the biological growth of microalgae that fluctuates towards the surrounding. Therefore, a novel graph-theoretic approach has been proposed to provide an optimization approach for identifying optimal process design with the consideration of three aspects that includes: economic, environmental, and reliability. The optimization is conducted using P-graph (a powerful graph-theoretic tool) which is capable to determine optimal and near-optimal solutions based on three objective functions: (i) minimizing annual operating cost, (ii) minimizing potential environmental impact, and (iii) maximizing reliability of process. The pool of feasible solutions (optimal and near-optimal) is obtained by satisfying the constraints on both greenhouse gas emissions and its respective reliability along. Thereupon, a further analysis was carried out with the aid of TOPSIS considering three of the assessment aspects to identify the optimal microalgae biorefinery configuration
Open Access: Yes
Heat Integrated Water Regeneration Network Synthesis via Graph-Theoretic Sequential Method
Publication Name: Chemical Engineering Transactions
Publication Date: 2021-01-01
Volume: 88
Issue: Unknown
Page Range: 49-54
Description:
The integration of multiple resources conservation networks is necessary to attain the ever-stringent sustainable goals. This work takes initiatives to develop a heat integrated water network via a proposed P-graph-based sequential methodology. In the first step, a set of feasible water regeneration networks is generated using the conventional P-graph framework. Then, the obtained feasible networks will be used as the inputs in the second stage which aims to generate various sets of feasible heat exchanger networks. It is worth noting that the second model is solved by an extended P-graph framework (P-HENS) for combinatorial process network optimization. The solutions are then ranked based on the total network cost. To demonstrate the effectiveness of the proposed method, a typical water regeneration network (three sources and three sinks) with multi-contaminants is used. The results show a total of 103 feasible water network structures (water network cost ranging from 0.76 M$/y to 1.18 M$/y). Thereafter, a list of feasible HIWRN can be determined using P-HENS. The top four HIWRNs which offer similar total network cost (~1.639 M$/y) are demonstrated. This proposed method provides valuable insights that allow decision-makers to further select the optimal solution which may be more beneficial as compared to the one obtained via conventional methods.
Open Access: Yes
DOI: 10.3303/CET2188008
Pathway Optimization for Low-Carbon Plastic Waste-to-Hydrogen Production with Flexible Feed Composition Using a Regression Model
Publication Name: Chemical Engineering Transactions
Publication Date: 2025-01-01
Volume: 120
Issue: Unknown
Page Range: 169-174
Description:
Conversion of plastic waste into hydrogen is a potential solution to address the issues of growing demand for hydrogen and the massive accumulation of plastic waste simultaneously. However, most studies on plastic-to-hydrogen technology selection were based on predetermined plastic waste composition, limiting their applicability to dynamic real-life operations. To address this, this work introduces a flexible optimisation model capable of accommodating varying compositions of plastic waste. With the aid of regression models, the optimisation model can optimise the plastic-to-hydrogen production pathways, considering economic and environmental performances, without the constraints of specific plastic waste types or mixture compositions. Regression models are developed based on the ultimate analysis data (carbon, hydrogen, nitrogen, oxygen, and sulphur content) to estimate hydrogen yield and purity across various pathways. Thereafter, fuzzy optimisation is employed to identify the trade-off between cost and environmental impact. In addition to the selection of optimal plastic waste-to-hydrogen pathways, the model also considers different purification technologies that can improve the hydrogen purity to various extents. The model demonstrated that pyrolysis-steam reforming combined with PSA is capable of achieving hydrogen purity of 99.999 % with a highest overall satisfaction of 0.7141 (equivalent to total cost of 3.43 M$ and emissions of 528,647 kg CO2 /y) while pyrolysis-catalytic decomposition is more suitable to produce hydrogen with lower purity (55 %).
Open Access: Yes
DOI: 10.3303/CET25120029
Enhanced Heat Recovery Network with Integrated Sensible Heat Storage Facilities for Energy Intensive Industry
Publication Name: Chemical Engineering Transactions
Publication Date: 2025-01-01
Volume: 120
Issue: Unknown
Page Range: 19-24
Description:
Energy-intensive industries contribute large amounts of greenhouse gas emissions. An effective strategy to decarbonise these industries is by applying process integration tools to enhance energy efficiency and reduce overall energy consumption. Recent studies showed that thermal energy storage offers significant benefits in energy efficiency enhancement, as it can amplify the energy recovery potential. Despite its potential, studies that applied process integration tools to address heat recovery problems with consideration of heat storage remain limited. This work develops an optimisation framework that aims to determine optimal heat storage type and size based on the total annualised cost (i.e., costs associated with storage facilities and utilities) to form a feasible heat recovery network between plants. The proposed framework is demonstrated through a case study that focuses on optimising the sensible heat storage selection for indirect heat integration between a mixed plastic waste treatment plant and a steel mill. By analysing the performance and effectiveness of the storage media studied, nitrate salt storage medium is selected due to its greatest energy and cost savings of 12.7 % and 20.7 %, when compared to direct Heat Integration. Insights from this provide information on the feasibility of implementing a storage-supported heat recovery network in the energy-intensive industry.
Open Access: Yes
DOI: 10.3303/CET25120004
Enabling Energy-Efficient and Sustainable Green Glycerol-Derived 1,3-Propanediol Production via a Graph-Theoretical-Based Approach
Publication Name: ACS Sustainable Chemistry and Engineering
Publication Date: 2025-07-28
Volume: 13
Issue: 29
Page Range: 11178-11189
Description:
The rise in biodiesel production results in an excess of crude glycerol, which further leads to environmental concerns. Consequently, transforming crude glycerol into valuable products is deemed an effective way to address this issue. Process Integration techniques are introduced to enhance the overall economic viability by maximizing the energy recovery in the biodiesel plant. However, most of the existing studies merely focused on a single optimal heat exchanger network (HEN) generated. In this study, P-HENS software is utilized to generate viable HENs for a glycerol-derived 1,3-propanediol plant. Subsequently, piping costs of each HEN are estimated to determine the optimal HEN by assuming the respective heat exchanger is placed at the centroid. Finally, the optimal HEN is identified based on the total annualized costs (TAC) (which include the capital cost of the heat exchanger, utility cost, and piping costs) and energy-related carbon emissions of the network. The results show that, among the 4,188 feasible networks generated, network #623 possesses the best overall performance when both cost and environmental aspects are considered. The carbon emissions of network #623 is 16.7% lower than that of the case without heat recovery. This work demonstrates the usefulness of the generated near-best HENs in enabling a more comprehensive HEN optimization. By application of the proposed methodology, the most economical and environmentally friendly HEN can be determined. This contributes to both cost savings and sustainability in HEN design.
Open Access: Yes
Systematic generation of flexible heat exchanger networks with minimum utility consumption
Publication Name: Thermal Science and Engineering Progress
Publication Date: 2026-02-01
Volume: 70
Issue: Unknown
Page Range: Unknown
Description:
Heat exchanger network (HEN) synthesis is a topic of high importance, encompassing several solution approaches and problem aspects. One such aspect crucial to industrial applications is flexibility, since real systems often experience variations of certain parameters, e.g., inlet temperatures or flowrates. Decades of research have revealed numerous methods for analyzing the flexibility of a given heat exchanger network. Meanwhile, the synthesis of flexible HENs continued to prove to be a severely difficult task, especially since handling the parameter deviations should not compromise the high level of heat integration. This work introduces a novel direction for synthesizing flexible HENs by combining flexibility analysis methods with P-graph-based, exhaustive, combinatorial network generation. The method generates all feasible networks that satisfy both the structural criteria and the maximum energy recovery over the entire variation region, and presents them ordered by capital cost. This first iteration of the work focuses on variations in inlet stream temperatures. This allows proving the validity of the underlying concepts by generating HENs that achieve minimum utility consumption for the entire range of temperature variations. The capability to generate multiple suitable networks is demonstrated through a case study, where 429 feasible networks were generated, which are all capable of achieving maximum heat integration within the parameter variation region. For the best generated design options, a 4–6% increase in capital cost compared to the base case is sufficient to satisfy the flexibility requirements.
Open Access: Yes
How to design a dynamically-feasible heat exchanger network? Insights gained from experience
Publication Name: Energy
Publication Date: 2026-02-01
Volume: 344
Issue: Unknown
Page Range: Unknown
Description:
This paper aims to share the challenges encountered by the authors while exploring the significance of controllability in the early stage of heat exchanger network (HEN) design, particularly through the use of P-HENS – a graph theoretic-based HEN synthesis tool for multi-solution HEN synthesis. Presently, no existing studies have leveraged P-HENS-derived networks to reveal insight on how network topology affects its dynamic performance. This work began with a 5-stream problem as a base case, where P-HENS was used to generate four feasible HENs that meets the minimum energy requirement (MER). A preliminary screening narrowed these options to two configurations, which were then simulated in Aspen Plus. Bypass are added to the two selected HENs for further control studies in Aspen Plus Dynamics. The results indicated that both HENs could handle only some disturbances and return the outlet temperature to its nominal value, with some cases showing marginal deviations. Then, different bypass values (e.g., 0.1 and 0.5) were explored to analyze its impact on control performance but it reveals that even with a larger bypass value of 0.5, the HEN struggled to adequately adjust during disturbances. The findings from this work showed that the controllability of the HEN is collectively influenced by the bypass value, the temperature difference of the “direct inlet and outlet of the heat exchanger”, and the temperature difference of the “inlet streams of both hot and cold streams placed in the heat exchanger”. A generic workflow that would help future researchers avoid similar pitfalls has been presented.
Open Access: Yes
Navigating Cost-Efficient Circular Integration of Plastic Waste-to-X Pathways into Oil Refinery Using the Graph-Theoretic Approach
Publication Name: Industrial and Engineering Chemistry Research
Publication Date: 2026-04-01
Volume: 65
Issue: 12
Page Range: 6587-6604
Description:
Plastic waste conversion has been widely recognized as a promising strategy to address growing waste management challenges. However, the feasibility of its integration into existing industrial systems remains uncertain. This paper explores a plastic waste-to-X strategy aimed at reintegrating plastic waste into its original supply chain, in alignment with circular economy principles. A graph-theoretic optimization model is developed using P-graph to identify the optimal and near-optimal pathway configurations under multiple scenarios. Under a cost minimization scenario, the optimal solution achieves a 0.013–0.19% lower cost compared with alternative pathways; however, related to the higher opportunity cost of up to 24,364 USD/y from forgone utility savings and carbon tax reductions. Incorporating carbon credits shifts the focus toward balancing cost efficiency and emission reduction. Under budget constraints, the benefit-cost analysis reveals that emission reduction does not increase linearly with budget expansion. These findings guide decision-makers in setting realistic emission reduction targets and allocating budget efficiently, while helping policymakers to develop a financial scheme that promotes greater emission reductions without excessive expenditure.
Open Access: Yes
Enabling industry symbiosis between energy-intensive industries via optimal integration of thermal energy storage
Publication Name: Thermal Science and Engineering Progress
Publication Date: 2026-06-01
Volume: 74
Issue: Unknown
Page Range: Unknown
Description:
Energy-based industrial symbiosis is a potential decarbonisation strategy for energy-intensive industries, which contribute significantly to carbon emissions. Thermal energy storage (TES) can be integrated to enhance energy efficiency and operational flexibility, while addressing issues related to supply–demand fluctuations. Nonetheless, the economic feasibility of TES-supported interplant heat recovery depends on the costs and properties of the storage media incorporated. Therefore, this work presents a systematic framework for optimising TES selection across a spectrum of storage options for interplant indirect heat integration. The objective is to minimise the total annualised cost (TAC), comprising energy and storage capital costs. The optimal TES option can then be identified based on its respective TAC ranking. A case study that compares the effectiveness of the indirect method against the intraplant and direct methods is conducted. The results show that among the 33 TES options evaluated, silica fire brick offers the lowest TAC and energy-related carbon emissions, leading to a reduction of 21.60% and 13.16%, respectively, as compared to the intraplant method. Subsequently, a sensitivity analysis is performed to explore the impacts of varying stream flowrates and storage capacity redundancy allocation on the TES selection. This provides insights into the performance of various TES options under intraplant, direct, and indirect heat integration methods. Finally, the threshold (i.e., stream flowrate required to provide economic gain under a given redundant allocation scenario) aligned with the strategic planning can be determined. This work demonstrates that TES integration can improve the economic feasibility and sustainability of industrial symbiosis in energy-intensive industries.
Open Access: Yes
