Ákos Orosz

55320568500

Publications - 29

Exhaustive enumeration of heat exchanger networks with minimum utility consumption using graph-theoretic approach

Ákos Orosz Dhanaraj Turunawarasu Viknesh Andiappan Bing Shen How Jean Pimentel Sin Yong Teng Lip Siang Yeo Ferenc Friedler

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

DOI: 10.1016/j.energy.2025.137898

Towards the synthesis of reliable and resilient complex networks

Ákos Orosz Kirti M. Yenkie Jean Pimentel Andres Castellar-Freile

Publication Name: Current Opinion in Chemical Engineering

Publication Date: 2025-09-01

Volume: 49

Issue: Unknown

Page Range: Unknown

Description:

Process synthesis methodologies have traditionally focused on optimizing the economic criteria. However, owing to the complexity of real systems, external factors, such as expected or unexpected events or disturbances, negatively affect the performance of optimal networks. In this context, it becomes essential to consider the effect of such events on the performance of the network in the early design stages. This work presents a comprehensive review of the contributions related to this relevant topic, focusing on two widely utilized indicators: reliability and resilience. Reliability focuses on the probability of system failures due to disturbances, and resilience analyzes the behavior of the system after disturbances and its capacity to recover over time. Relevant contributions are reviewed, which present deterministic and stochastic methods to estimate these indicators, with a special focus on the design phase. Moreover, this work also presents a perspective on using machine learning methods on complex systems datasets as an emerging direction for enhancing the estimation of these properties. This contribution highlights recent advancements in this field and emphasizes the relevance of resilience and reliability as key metrics for developing safer processes with improved operability.

Open Access: Yes

DOI: 10.1016/j.coche.2025.101172

Multi-Solution Heat Exchanger Network Synthesis for Turbo-Expander-Based Cryogenic CO2 Capture Technology

Ákos Orosz Jaka Sunarso Dhanaraj Turunawarasu Viknesh Andiappan Bing Shen How Yat Choy Wong Ferenc Friedler

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

DOI: 10.1021/acs.iecr.4c03469

The P-graph application extension in multi-period P2P energy trading

Ákos Orosz Jaka Sunarso Bing Shen How Wei Dong Leong Sin Yong Teng Karen Gah Hie Kong Alvin Guo Jian Lee Ferenc Friedler

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

DOI: 10.1016/j.rser.2024.114544

Systematic Method of Retrofitting Wastewater Transportation Systems for Enhanced Reliability

Ákos Orosz Kirti M. Yenkie Jean Pimentel Andres Castellar-Freile

Publication Name: Chemical Engineering Transactions

Publication Date: 2024-01-01

Volume: 114

Issue: Unknown

Page Range: 1075-1080

Description:

While the treatment of wastewater is an important issue that received significant attention in the past decades, improving the related technologies is only one part of a more complex task. Domestic wastewater is usually transported via the city's sewer system, and in many places, it is combined with rainwater. This means that disturbances, such as heavy rainfall or failures in the pipeline system, can lead to floods of polluted wastewater. Thus, it is important to design such transportation systems to be reliable. This work presents a methodology for generating several potential extensions to retrofit an existing water transportation network and increase its reliability. Reliability and feasibility evaluation is performed via the P-graph framework, after which the nondominated networks are collected. Results of the presented case study show that reliability can be increased 3 times by adding only some of the possible extensions to the network. The methodology proposed analysed 512 plausible retrofitting alternatives, from which 20 are non-dominated networks. This range of alternatives provides designers with insightful information to decrease water pollution and the vulnerability of wastewater systems.

Open Access: Yes

DOI: 10.3303/CET24114180

Electrification of oil refineries through multi-objective multi-period graph-theoretical planning: A crude distillation unit case study

Ákos Orosz Bing Shen How Sin Yong Teng Abdulqader Bin Sahl Ferenc Friedler

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

DOI: 10.1016/j.jclepro.2023.140179

Synthesis of N-best Heat Recovery Networks with Consideration of Dynamic Control Performance

Hao Yeh Lee Ákos Orosz Bing Shen How Zong Yang Kong Tiffany Ang Ferenc Friedler

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

Ákos Orosz Bing Shen How Sin Yong Teng Ferenc Friedler Jeroen J. Jansen

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

DOI: 10.1016/j.energy.2023.129029

Process synthesis considering sustainability for both normal and non-normal operations: P-graph approach

Ákos Orosz Jiří Jaromír Klemeš Petar Sabev Varbanov Ferenc Friedler

Publication Name: Journal of Cleaner Production

Publication Date: 2023-08-15

Volume: 414

Issue: Unknown

Page Range: Unknown

Description:

Process synthesis usually determines the normal operation of the process. In addition to the cost, recently, sustainability has also become essential in selecting the process. In case of failures of some redundant operating units of the process, it may still be operational as a non-normal operation. This work shows that the sustainability performance of a process in non-normal operation can be much worse than that of the normal case. Consequently, during process synthesis, it is essential to consider the sustainability of a process for both normal and non-normal operations. The current work is the first in offering synthesis of a process network taking into account a pre-specified limit of the process sustainability indicator for both normal and non-normal modes. This synthesis procedure is formulated in a general way, to interface with any sustainability indicator, expressed as a scalar, here Sustainable Process Index has been used in the case studies. The presented method is illustrated on two case studies to showcase the capability of synthesizing processes for multiple operation. The obtained results indicate that it is possible to simultaneously reduce environmental impact and process cost by more than 20%, by appropriate modification of the operating modes.

Open Access: Yes

DOI: 10.1016/j.jclepro.2023.137696

Synthesis of multiperiod heat exchanger networks: n-best networks with variable approach temperature

Ákos Orosz Rozália Lakner Bing Shen How Ferenc Friedler

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

DOI: 10.1016/j.tsep.2023.101912

Enabling in-depth analysis in heat exchanger network synthesis via graph-theoretic tool: Experiences in Swinburne University of Technology Sarawak Campus

Ákos Orosz Jaka Sunarso Bing Shen How Sin Yong Teng Ferenc Friedler

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

DOI: 10.1016/j.ece.2022.12.003

Exploring N-best solution space for heat integrated hydrogen regeneration network using sequential graph-theoretic approach

Ákos Orosz Bing Shen How Adrian Chun Minh Loy Juin Yau Lim Abdulqader Bin Sahl Ferenc Friedler

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

DOI: 10.1016/j.ijhydene.2022.10.196

Framework to embed machine learning algorithms in P-graph: Communication from the chemical process perspectives

Ákos Orosz Bing Shen How Jean Pimentel Sin Yong Teng Ferenc Friedler Jeroen J. Jansen

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

DOI: 10.1016/j.cherd.2022.09.043

Enabling technology models with nonlinearities in the synthesis of wastewater treatment networks based on the P-graph framework

Ákos Orosz Kirti M. Yenkie Jean Pimentel Emmanuel A. Aboagye Mihály Csaba Markót Heriberto Cabezas Ferenc Friedler

Publication Name: Computers and Chemical Engineering

Publication Date: 2022-11-01

Volume: 167

Issue: Unknown

Page Range: Unknown

Description:

Designing effective wastewater treatment networks is challenging because of the large number of treatment options available for performing similar tasks. Each treatment option has variability in cost and contaminant removal efficiency. Moreover, their mathematical models are highly nonlinear, thus rendering them computationally intensive. Such systems yield mixed-integer nonlinear programming models which cannot be solved properly with contemporary optimization tools that may result in local optima or may fail to converge. Herein, the P-graph framework is employed, thus generating all potentially feasible process structures, which results in simpler, smaller mathematical models. All potentially feasible process networks are evaluated by nonlinear programming resulting in guaranteed global optimum; furthermore, the ranked list of the n-best networks is also available. With the proposed tool, better facilities can be designed handling complex waste streams with minimal cost and reasonable environmental impact. The novel method is illustrated with two case studies showing its computational effectiveness.

Open Access: Yes

DOI: 10.1016/j.compchemeng.2022.108034

Synthesis of multiperiod heat exchanger networks: Minimum utility consumption in each period

Ákos Orosz Rozália Lakner Bing Shen How Ferenc Friedler

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

DOI: 10.1016/j.compchemeng.2022.107949

General formulation of resilience for designing process networks

Ákos Orosz Jean Pimentel Ferenc Friedler Andres Argoti

Publication Name: Computers and Chemical Engineering

Publication Date: 2022-09-01

Volume: 165

Issue: Unknown

Page Range: Unknown

Description:

Herein, the formula proposed for quantifying the resilience of engineering systems, including processing systems, is general in several aspects. The structure of a system can be highly complex where the numbers of loops, raw materials, and products are not limited. The mathematical models of the operating units can be either linear or nonlinear for simulating the effect of the failures. The damage caused by an unexpected event can result in various levels of operation for the operating units. The proposed formula is also general in the sense that all possible combinations of failures are considered. The problem formulation, the related structure representation, the enumeration and evaluation of possible failures are based on the P-graph framework and its algorithms. The proposed formula for resilience is applicable to any complex engineering system whose behavior is primarily determined by its structure, including supply chains, information systems, municipal infrastructures, and electrical transmission networks.

Open Access: Yes

DOI: 10.1016/j.compchemeng.2022.107932

P-graphs for process systems engineering: Mathematical models and algorithms

Ákos Orosz Jean Pimentel Losada Ferenc Friedler

Publication Name: P Graphs for Process Systems Engineering Mathematical Models and Algorithms

Publication Date: 2022-02-03

Volume: Unknown

Issue: Unknown

Page Range: 1-261

Description:

This book discusses the P-graph framework for developing and understanding effective design tools for process systems engineering, and addresses the current state of its theory and applications. The book details the new philosophy of the axioms-based mathematical modelling of processing systems, the basic algorithms, areas of application, future directions, and the proofs of theorems and algorithms. Because of the rigorous foundation of the theory, the framework provides a firm basis for future research in mathematical modelling, optimization, and design of complex engineering systems. The various P-graph applications discussed include process network synthesis, reliability engineering, and systems resilience. The framework opens new avenues for research in complex systems including redundant operations for critical infrastructure, systems sustainability, and modelling tools for disaster engineering. Demonstration software is provided to facilitate the understanding of the theory. The book will be of interest to institutions, companies, and individuals performing research and R&D in process systems engineering.

Open Access: Yes

DOI: 10.1007/978-3-030-92216-0

Multiple-solution heat exchanger network synthesis using P-HENS solver

Ákos Orosz Bing Shen How Ferenc Friedler

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

DOI: 10.1016/j.jtice.2021.05.006

Reliability incorporated optimal process pathway selection for sustainable microalgae-based biorefinery system: P-graph approach

Ákos Orosz Bing Shen How Juin Yau Lim Ferenc Friedler Chang Kyoo Yoo

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

DOI: 10.1016/B978-0-323-85159-6.50036-1

The P-graph approach for systematic synthesis of wastewater treatment networks

Ákos Orosz Kirti M. Yenkie Jean Pimentel Heriberto Cabezas Ferenc Friedler

Publication Name: Aiche Journal

Publication Date: 2021-07-01

Volume: 67

Issue: 7

Page Range: Unknown

Description:

Wastewater treatment consists of three or four sequential stages: preliminary, primary, secondary, and tertiary. Each stage can comprise multiple alternative technologies that can perform the same tasks with different efficiencies, operating times, and costs. Thus, we propose a systematic approach for designing wastewater treatment networks by utilizing principles of mathematical modeling and generating an exhaustive enumeration of all the possible technologies and their connections during the early stages of designing a treatment facility. Some of these structures are nonintuitive and include recycling, reprocessing, bypasses, and multiple technologies in parallel or series to remove the same contaminant. The nonintuitive structures with multiple technologies may provide a measure of resilience compared to typical heuristic designs. Thus, the combination of P-graph methodology and the sequence of treatment technologies predicted via the optimization algorithm from the maximal structure is based on holistic considerations and does not lead to suboptimal solutions.

Open Access: Yes

DOI: 10.1002/aic.17253

Conceptual design of a negative emissions polygeneration plant for multiperiod operations using P-graph

Kathleen B. Aviso Ákos Orosz Raymond R. Tan Jean Pimentel Ferenc Friedler

Publication Name: Processes

Publication Date: 2021-02-01

Volume: 9

Issue: 2

Page Range: 1-19

Description:

Reduction of CO2 emissions from industrial facilities is of utmost importance for sustainable development. Novel process systems with the capability to remove CO2 will be useful for carbon management in the future. It is well-known that major determinants of performance in process systems are established during the design stage. Thus, it is important to employ a systematic tool for process synthesis. This work approaches the design of polygeneration plants with negative emission technologies (NETs) by means of the graph-theoretic approach known as the P-graph framework. As a case study, a polygeneration plant is synthesized for multiperiod operations. Optimal and alternative near-optimal designs in terms of profit are identified, and the influence of network structure on CO2 emissions is assessed for five scenarios. The integration of NETs is considered during synthesis to further reduce carbon footprint. For the scenario without constraint on CO2 emissions, 200 structures with profit differences up to 1.5% compared to the optimal design were generated. The best structures and some alternative designs are evaluated and compared for each case. Alternative solutions prove to have additional practical features that can make them more desirable than the nominal optimum, thus demonstrating the benefits of the analysis of near-optimal solutions in process design.

Open Access: Yes

DOI: 10.3390/pr9020233

Processing systems design considering resilience

Ákos Orosz Jean Pimentel Ferenc Friedler

Publication Name: Computer Aided Chemical Engineering

Publication Date: 2021-01-01

Volume: 50

Issue: Unknown

Page Range: 807-812

Description:

The resilience of a system is defined as the system's capability of recovering from failures. Traditionally, only predictable aspects are considered when designing processing systems. Evaluation of these aspects is performed via assessment of exact indicators and enumeration of all cause-effect options. However, such evaluation is not appropriate for determining the resilience of processing systems, since resilience is based on unexpected events in addition to the expected ones. Consequently, the cause part of the cause-effect relation is not known or not effective. In the current work, the general formula for determining resilience of a system is embedded into a P-graph based process synthesis algorithm. Thus, the resilience can be considered when selecting the most preferred process during its synthesis. The result is illustrated by synthesizing a process of adipic acid production by nitric acid oxidation of KA oil.

Open Access: Yes

DOI: 10.1016/B978-0-323-88506-5.50126-1

Retrofit Synthesis of Industrial Heat Exchanger Networks with Different Types of Heat Exchangers

Olga Arsenyeva Ákos Orosz Ferenc Friedler

Publication Name: Chemical Engineering Transactions

Publication Date: 2021-01-01

Volume: 88

Issue: Unknown

Page Range: 613-618

Description:

Heat Exchanger Network (HEN) synthesis is a powerful tool for the development of more efficient processes with high utilization of mass and energy resources. The implementation of compact heat exchangers with enhanced heat transfer into the industrial flowsheets can provide more efficient and economically feasible solutions. Plate Heat Exchanger (PHE) is one of established types of enhanced HEs. To estimate possible benefits of that kind of heat transfer enhancement, a mathematical model of PHE, which accounts for different plate types and corresponding corrugations geometry, is used. The integration of this model with the P-graph-based HEN synthesis approach allowed to create the method, which considers different types of heat exchangers. This approach enables to integrate not only conventional shell-and-tube heat exchangers, but also PHEs, which overall heat transfer coefficient is in average 2-3 times higher, during the optimization process of a new or existing HEN. The capabilities of the proposed method are presented via a case study for oil preheat train, where an existing network is retrofitted; first with shell-and-tube heat exchangers only, then with the consideration of both shell-and-tube and plate heat exchangers.

Open Access: Yes

DOI: 10.3303/CET2188102

Heat Integrated Water Regeneration Network Synthesis via Graph-Theoretic Sequential Method

Ákos Orosz Bing Shen How Sin Yong Teng Juin Yau Lim Ferenc Friedler

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

Efficient Design and Sustainability Assessment of Wastewater Treatment Networks using the P-graph Approach: A Tannery Waste Case Study

Ákos Orosz Kirti M. Yenkie Jean Pimentel Emmanuel A. Aboagye Heriberto Cabezas Ferenc Friedler

Publication Name: Chemical Engineering Transactions

Publication Date: 2021-01-01

Volume: 88

Issue: Unknown

Page Range: 493-498

Description:

In the tannery industry approximately, 30 - 35 m3 of wastewater (WW) is generated per ton of rawhide processed. The WW comprises high concentrations of salts, ammonia, dye, solvents, and chromium. Of particular interest is chromium, which has been proven to cause dermatological, developmental, and reproductive issues on exposure. Thus, there is a need for appropriate treatment of the tannery WW before it is discharged for natural remediation. However, designing a treatment process is multifaceted due to the availability of multiple technologies that can perform similar tasks and the complex composition of waste streams. This necessitates the treatment to be performed in stages namely, primary, secondary, and tertiary. In some cases, pretreatment is required to enhance the recovery in the following stages. Due to the combinatorial nature of this problem, the P-graph approach, which uses principles from graph theory, can be used to synthesize a treatment pathway by selecting appropriate technologies at each stage, while meeting required purity specifications. Furthermore, the P-graph approach can provide alternate feasible treatment structures ranked based on Economics as well as Sustainability indicators, such as the Sustainable Process Index (SPI). In this work, a tannery WW case study is investigated with multiple stages and treatment technologies. A complex maximal structure is generated comprising all possible technologies, flows, connections, bypasses, mixers, and splitters. The models for each technology involve capital and operating costs, efficiency, and SPI at each stage of the treatment process. This problem is formulated in P-graph and solved using the Accelerated Branch-and-Bound algorithm.

Open Access: Yes

DOI: 10.3303/CET2188082

Multiple-solution heat exchanger network synthesis for enabling the best industrial implementation

Ákos Orosz Ferenc Friedler

Publication Name: Energy

Publication Date: 2020-10-01

Volume: 208

Issue: Unknown

Page Range: Unknown

Description:

The synthesis of heat recovery networks traditionally results in an optimal or suboptimal solution for the supplied set of streams and simplifying assumptions. In the current work, the assumption of a single optimal solution is replaced by the goal of generating an ordered set of optimal or quasi-optimal networks. This enables industrial engineers to further select the solution most suitable for detailed design and practical implementation. The problem is formulated for and solved by an extension of the P-graph framework for combinatorial process network optimization. The presented method for HEN synthesis generates a list of solutions ranked by the Total Annualized Cost. In addition to the feasibility, all list elements also feature a degree of heat recovery ranging from the thermodynamic maximum, down to a specified margin allowing accounting for the energy-capital trade-off. The current method is illustrated with three case studies. The obtained results demonstrate optimal solutions that cannot be generated by the Pinch-based methods or the stage-wise superstructure approaches. The proposed parameters, an upper limit on the number of heat exchangers per process stream and a maximum relaxation of utility demand compared to the Pinch targets, allow performing parametric evaluations of the resulting solutions.

Open Access: Yes

DOI: 10.1016/j.energy.2020.118330

Socio-ecological network structures from process graphs

Angelyn Lao Ákos Orosz Raymond R. Tan Heriberto Cabezas Ferenc Friedler

Publication Name: Plos One

Publication Date: 2020-08-01

Volume: 15

Issue: 8 August

Page Range: Unknown

Description:

We propose a process graph (P-graph) approach to develop ecosystem networks from knowledge of the properties of the component species. Originally developed as a process engineering tool for designing industrial plants, the P-graph framework has key advantages over conventional ecological network analysis techniques based on input-output models. A P-graph is a bipartite graph consisting of two types of nodes, which we propose to represent components of an ecosystem. Compartments within ecosystems (e.g., organism species) are represented by one class of nodes, while the roles or functions that they play relative to other compartments are represented by a second class of nodes. This bipartite graph representation enables a powerful, unambiguous representation of relationships among ecosystem compartments, which can come in tangible (e.g., mass flow in predation) or intangible form (e.g., symbiosis). For example, within a P-graph, the distinct roles of bees as pollinators for some plants and as prey for some animals can be explicitly represented, which would not otherwise be possible using conventional ecological network analysis. After a discussion of the mapping of ecosystems into P-graph, we also discuss how this framework can be used to guide understanding of complex networks that exist in nature. Two component algorithms of P-graph, namely maximal structure generation (MSG) and solution structure generation (SSG), are shown to be particularly useful for ecological network analysis. These algorithms enable candidate ecosystem networks to be deduced based on current scientific knowledge on the individual ecosystem components. This method can be used to determine the (a) effects of loss of specific ecosystem compartments due to extinction, (b) potential efficacy of ecosystem reconstruction efforts, and (c) maximum sustainable exploitation of human ecosystem services by humans. We illustrate the use of P-graph for the analysis of ecosystem compartment loss using a small-scale stylized case study, and further propose a new criticality index that can be easily derived from SSG results.

Open Access: Yes

DOI: 10.1371/journal.pone.0232384

General formulation for the resilience of processing systems

Ákos Orosz Jean Pimentel Ferenc Friedler

Publication Name: Chemical Engineering Transactions

Publication Date: 2020-01-01

Volume: 81

Issue: Unknown

Page Range: 859-864

Description:

Resilience is one of the key indicators of processing systems, it expresses the behaviour of the system as a result of expected or unexpected failures. This indicator can be essential during systems design and operation, especially, when the system is part of or related to a critical infrastructure. The numerous contributions on systems resilience are related to a wide range of applications, however, there is no general uniform framework for resilience evaluation. For instance, most studies examine resilience as a function of the continuous parameters of the system, usually avoiding the influence of its structure. In the current work, a general framework for determining the structural resilience of processing systems is presented. This framework derives on formulas that satisfy the requirements of the original definition of resilience. The formerly developed P-graph framework is the mathematical basis of the procedure for determining the indicator. The resilience of the system is calculated as a function of the operative subprocesses for all possible failures and is a normalized indicator on [0, 1]. The examination of two industrial case studies shows that the proposed resilience can be an appropriate indicator to be considered in process design.

Open Access: Yes

DOI: 10.3303/CET2081144

Automated synthesis of process-networks by the integration of P-graph with process simulation

Ákos Orosz Raymond R. Tan Jean Pimentel Ferenc Friedler

Publication Name: Chemical Engineering Transactions

Publication Date: 2020-01-01

Volume: 81

Issue: Unknown

Page Range: 1171-1176

Description:

Chemical process simulation has become one of the most important tools for the analysis of process networks. The simulation software currently available are not capable of automatically generating the process structure, the designer must provide it as an input for the simulation. This limits the contribution of simulation to the latter stages of design after the structure has been clearly defined. Since the P-graph methodology was originally conceived to generate process structures systematically, it can be used to produce the topology of the problem automatically based on rigorous combinatorial axioms and algorithms. In this work, the properties of two P-graph algorithms are exploited to automatically generate alternative structures in a commercial simulator, conferring the latter an improved capacity to assist during the early stage of design. Initially, the maximal structure generation (MSG) algorithm is employed to identify a rigorous superstructure from the initial set of plausible operating units. The solution structure generation (SSG) algorithm is then used to enumerate all combinatorially feasible processes included in the superstructure. Each process structure is individually exported to Aspen Plus®, where rigorous models are used to simulate its performance. A set of alternative processes ranked by their economic performance can be generated. This integrated methodology is employed in a case study for producing methyl lactate from methanol and lactic acid. This work demonstrates that integration of P-graph with rigorous simulation constitutes an enhanced tool for process synthesis that automates the generation of process alternatives, providing useful information and additional insight of the synthesis problem.

Open Access: Yes

DOI: 10.3303/CET2081196