A novel two-step approach for multi-plant indirect HENs design

Design of optimum flexible heat exchanger networks for multiperiod process

Multi-period design of heat exchanger networks

Modeling and optimization of inter-plant indirect heat exchanger networks by a difference evolutionary algorithm

kamaruddin@cheme.utm.my Heat exchanger network (HEN) is very important to optimise energy usage in process industry. Heat exchanger network synthesis is an important process synthesis problem where different tools and methods have been presented to solve this synthesis problem. In HEN synthesis, the feasibility of the HEN design is not taken into consideration. The HEN design may not be able to be implemented in industrial applications. It is essential to check the feasibility of a design before it is being implemented in the industry. The objective of this paper is to present the application of a new flexible and operable heat exchanger network (FNO HEN) methodology in synthesising a feasible HEN using a simple case study. The novelty of this work is to determine an optimal ΔTmin value that gives minimum external energy requirement (EER) and heat exchanger area (HEA) as well as simultaneously analyse the feasibility of the HEN design in an easy, systematic and efficient manner. Using the new developed FNO HEN methodology framework, HEN design target, which is the value of ΔTmin is determined to obtain the feasible HEN design. From process design point of view, ΔTmin value determines the size of heat exchanger in the network as well as energy saving. A process simulator is used to check the process feasibility of the HEN designs. With the use of the feasible HEN trade-off plot, which is a plot of EER and HEA at different value of ΔTmin with additional of feasibility area, the optimal feasible HEN design which satisfies external energy requirement (operability), heat exchanger area (capital) and process feasibility has been successfully determined.

Process integration via pinch technology is widely regarded as an effective approach to boost industrial sustainability and competitiveness by reducing process-related energy and material consumption and environmental impacts. So far, such approach has been mainly applied to energy-intensive processes. As a result, industrial sectors like the food industry still offer wide margins for energy efficiency improvement via pinch analysis. As well known, food manufacturing requires many process operations, such as pasteurization, sterilization, and drying, which involve the heat transfer between products and heating/cooling media. Therefore, the design and optimization of heat exchanger network is crucial to minimize external heating and cooling requirements and improve the recovery of waste heat streams. In this paper, a flexible open-source model is proposed for the design or retrofit of industrial heat exchanger networks (HENs) via pinch-analysis. The model is used to investigate a real dairy process for cream production with the aim to identify the energy saving opportunities and assess the potential techno-economic and environmental benefits. The study found out that the design of the heat exchangers network under conditions of maximum energy recovery results in a significant reduction of 95.8 kW in the thermal power exchanged with external utilities. This improvement provides a reduction in the thermal power of hot and cold utilities by 48.5% and 44.9% respectively compared to the reference case.

Heat recovery is considered as the key to improve energy efficiency in the process design. An appropriate heat exchanger network (HEN) design is an effective tool to maximize heat recovery from the process streams and to minimize energy consumption. The objectives of this study were arranging optimum HEN based on the annual cost in the power industry. HEN in the Paiton Steam Power Plant, East Java, Indonesia, was designed using spreadsheet and Aspen Energy Analyzer with Peng-Robinson equation. Pinch analysis was conducted by comparing Tmin (10°C - 19°C) to obtain Maximum Energy Recovery (MER) and Heat Exchanger Area (HEA). The HEN design was optimized using grid diagram. Simulation in this study succeeded to reduce the annual cost the most effectively at ∆Tmin 16°C. This design optimized the process integration and contributed to the capital, operation, and total annual cost reduction of 14.3%. The maximum energy recovery was 286,706 kW and HEA 138.790 m2. This result is a solution for Steam Power Plant as an effort for enhancing energy efficiency and the company competitiveness.

Heat Exchanger Network (HEN) optimization by mathematical programming has been developed for half of century. Stage-wise superstructure by Yee and Grossmann (1990) is one of the most popular HEN design models dividing process temperature into stages under assumption of constant specific heat capacity (Cp). To make model more realistic, the model is developed under temperature-dependent Cp which is a cubic equation of temperature. To simplify this circumstance, non-linearity of Cp is linearized by applying partitions of linear equations of Cp at different temperature intervals. HEN from the modified stage-wise superstructure model with variable Cp by GAMS software version 24.2 is validated with crude preheat train case from commercial simulation program (Pro/II software version 9.1). The Cp from Pro/II software as a function of temperature is divided into three linear equations of Cp at three temperature intervals. A case study of crude preheat train without HEN consists of five hot product streams and one cold crude oil stream, consuming hot and cold utilities of 175,353.53 kW and 107,945.89 kW, respectively. The new model synthesizes HEN for the crude preheat train, consuming less hot and cold utilities of 82,100.93 kW and 14,654.38 kW. The synthesized HEN is validated by Pro/II software, giving duties of hot and cold utilities of 81,835.30 kW and 14,417.20 kW. Percent error of hot and cold utilities of HEN from GAMS model are only 0.31 % and 1.65 %, compared to ones from Pro/II software. Compared to Pro/II results, percent error of process HEN area and utility HEN area from new model are 1.22 % and 2.91 %, respectively. New model with variable Cp assumption gives a good agreement with validated HEN by Pro/II. Compared to examples from other publications, the model shows that it generates HEN design with less TAC and less computational time.

The problem of interaction between economic design and controller design of heat exchanger network (HEN) is addressed in this work. The feasibility and sensitivity issues are incorporated in the classical design of HEN. HENs in industry seem to be very efficiently operated. The network that may have operated efficiently perhaps is the one that is not fully optimised in term of flexibility and sensitivity. It is important to do synthesis and sensitivity analyses of the designed network. The objective of this paper is to investigate and compare the sensitivity criteria of the originally designed HEN of the fatty acid fractionation process (FAFP) and the new HEN design. In this study, the HEN designs are already fixed at the value of ?Tmin = 40 °C. A new suggested HEN is redesigned from the original HEN of FAFP plant by obeying Pinch Analysis (PA) rules. The new HEN was redesigned by applying the PA stream splitting compared to the original HEN (that has been used in the industry), in which the design is not have stream splitting. The aim of this work is to determine the best optimised design whether the one that not followed Pinch Analysis rules or the other one. Using the new developed FNO HEN methodology framework, sensitivity analysis was applied which consists of two tests: 1) Flexibility Analysis and 2) Sensitivity Analysis. According to the results, the best candidate that satisfies the sensitivity and economy criteria is the new HEN design. It can be concluded that it is important to do stream splitting in order to obtain not only the best HEN in terms of design and economy criteria, but also in the matter of sensitivity criteria.

The paper presents a targeting method for process heat exchanger networks (HENs) design in the context of total sites. The method is based on a simultaneous optimization framework for the HENs utility cost and utility systems operating cost. Instead of the standalone HEN capital-energy costs trade-off, the method utilizes the trade-off between the HEN capital cost and the total utility systems operating cost. The total utility systems include steam and non-steam utility systems within the site. The energy cost of the HEN is replaced by the total utility systems operating cost to avoid explicit calculations of steam costs when targeting for HENs design. This enables handling the variability of steam costs with the steam utility loads and the minimum approach temperature, ΔT <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> , of the HEN without assuming fixed steam costs as in the existing methods. The optimum ΔT <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">min</sub> is that corresponds to the minimum total cost which involves the HEN capital cost and total utility systems operating cost. The simultaneous optimization framework combines the optimization of utility systems using Mixed-Integer Linear Programming (MILP) with targeting for the HENs design using Pinch Analysis. The method was demonstrated using an example total site.

This comprehensive study delves into the field of energy optimization in biodiesel production, specifically focusing on the utilization of waste cooking oil (WCO). The study employs the integration of pinch analysis and heat exchanger network (HEN) design, two powerful tools in process engineering. Pinch analysis is a thermodynamic technique used for reducing energy usage in processes by calculating thermodynamically feasible energy targets. On the other hand, HEN design involves the strategic arrangement of heat exchangers to maximize energy recovery. This approach not only reduces the overall production costs but also mitigates the environmental impact, making the process more sustainable. The research methodology involves the use of Aspen Plus and Aspen Energy Analyzer software. Aspen Plus is used to simulate the biodiesel production process, providing a detailed understanding of the process dynamics. The Aspen Energy Analyzer is then used to perform pinch analysis, which helps identify the pinch temperatures and calculate the minimum heating and cooling energy requirements. These findings are crucial in determining the optimal design of the HEN. The pinch analysis identified key pinch temperatures at 177°C, 165°C, 125°C, 115°C, 50°C, and 40°C. The analysis also determined that the minimum hot utility demand (Qhmin) was 1.04E+07 kJ/hr, while the minimum cold utility requirement (Qcmin) was 7.96E+06 kJ/hr, highlighting opportunities for improved energy efficiency. Hence the proposed HEN design showed promising results as it demonstrated significant energy savings, reducing hot utility energy by 3,203,188.31 Watts and cold utility energy by 3,306,114.41 Watts. This translates to an estimated annual cost saving of USD 295,146 for hot utilities and USD 23,808 for cold utilities. In conclusion, the study demonstrates the potential of integrating pinch analysis and HEN design in enhancing energy efficiency and reducing production costs in biodiesel production from WCO.

Economic and system reliability optimization of heat exchanger networks using NSGA-II algorithm

Chemical processes are energy intensive industries; the majority of energy consumed in industrial processes is mainly used for heating and cooling requirements. This results in increasing the interest in obtaining the optimum design of the heat exchanger networks to reduce the energy consumption and face the growing energy crises. Most of the published literature over the last fifty years promotes the process integration technology as a main part of the process system engineering science. Graphical Pinch Analysis method normally includes two key steps, firstly obtaining the energy targets which include the minimum energy required for the HEN design, then designing the heat exchanger network (HEN). This paper introduces a new graphical approach for the design of new heat exchanger networks (HENs) based on pinch analysis rules. The HEN is represented on a simple graph, where the cold stream temperatures are plotted on the X-axis while the driving forces for each exchanger are plotted on the Y-axis. This graphical technique can describe the energy analysis problems in term of temperature driving force inside the heat exchanger, which is an important factor in the design process as the differences in these driving forces are involved in calculating the area of heat exchangers, and consequently affecting the cost.

SePTA—A new numerical tool for simultaneous targeting and design of heat exchanger networks

This paper presents the application of the proposed model-based methodology in solving integrated process design and control (IPDC ) of heat exchanger networks ( HENs ). Many methods for HENs synthesis have been developed over the past decades, which aim to provide HENs designs that yield a reasonable trade-off between capital and operating costs. However, in most of HENs synthesis activities, the sole consideration in solution derivation is about design cost. Process operational issue especially controllability is frequently not a concern in the process design. As a result, the controllability of a designed HEN may be questionable. Industrial practice has made it clear that process controllability should be considered during process synthesis. The HENs design can be further improved to ensure that the design is more cost efficient and controllable. This can be achieved by developing a new model-based integrated process design and control methodology, which includes cost optimality and controllability aspects at the early HEN design stage. The IPDC for HEN problem is decomposed into four hierarchical sequential stages: (i) target selection, (ii) HEN design analysis, (iii) controllability analysis, and (iv) optimal selection and verification. The set of constraint equations in the IPDC problem for HEN design is decomposed into four sub-problems which correspond to four hierarchical stages. The capability of the proposed methodology in solving IPDC of HEN problem was tested using biomethanol production plant. The results show that the proposed methodology was able to find the best solution which satisfied design, control and economic criteria in easy, efficient and systematic manner.

This paper explains about the controllability effect on delta temperature minimum (ΔTmin) in order to get flexible and operable heat exchanger network (HEN). There are many researches based on design and cost effect to ΔTmincontribution. However, there are lacks of study on how the ΔTmineffect to controllability of HENs. Therefore, this paper focuses on controllability analysis of different HENs design based on ΔTmincontribution. There are six HEN designs were obtained from different ΔTminvalues such as 20°C, 25°C, 30°C, 35°C, 40°C and 50°C and has been analyzed. The analysis consists of three different controllability tests which are feasibility, flexibility and sensitivity. Feasibility test is used to check either the HEN design is feasible or not. Next, the feasible HEN design is then analyzed in terms of flexibility. The flexibility test is used to calculate the design flexibility in terms of how much the percentage the design can handle under uncertainties. Lastly is to test the process sensitivity with respect to disturbance changes. Throughout the controllability tests, several options for control structure were built and analyzed. A simple HEN case study was used to analyze the controllability.