Industrial Heat Exchanger Network Research Articles

A Sustainable Retrofit of an Industrial Heat Exchanger Network — A Case Study of a Gas Separation Plant in Thailand (HEN Retrofit on GSP)

A Sustainable Retrofit of an Industrial Heat Exchanger Network — A Case Study of a Gas Separation Plant in Thailand (HEN Retrofit on GSP)

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

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.

Estimation of thermal effects of fouling growth for application in the scheduling of heat exchangers cleaning

Energy-saving heat recovery in an industrial heat exchanger network may by impaired by fouling build-up on heat transfer surfaces of the exchangers. During longer periods of network operation, monitoring of fouling growth based on measurement data makes it possible to schedule and perform exchanger cleaning if needed for the mitigation of adverse effects of fouling. Three different methods of measurement-aided fouling monitoring are outlined: two simple methods known from literature and a least-squares based method introduced by the authors. A case study is performed on their hypothetical application in a real-life network of shell-and-tube heat exchangers used for heat recovery in crude distillation unit. Using historical measurement data recorded during three-year continuous operation of the network, the different methods are first employed to estimate the thermal effects of fouling and then used in the simulation of attainable energy and economic savings resulting from two alternative options of cleaning interventions in the network. The least-squares based method of measurement-aided fouling monitoring is identified as best suited for the evaluation of effectiveness of cleaning interventions in heat exchanger networks.

A robust design method for retrofit of industrial heat exchanger networks using modified stage-wise model

For over 20 years, various heat exchanger network (HEN) retrofit methods based on mathematical programming have been studied and proposed. However, determining suitable heat exchanger network retrofit designs for industries still remains a challenge. Most retrofit methods have limitations in terms of computational time and feasibility, and their proposed solutions involve mostly heat exchanger modifications and relocations which could be impractical and uneconomical. To overcome these limitations, this paper presents a robust heat exchanger network retrofit method for industrial applications which relies on mathematical programming under specific retrofit concepts and an effective solving strategy. The retrofit concepts reduce mathematical difficulties and provide heat exchanger networks that are practical for industries. The solving strategy provides a sustainable systematic solving method which guarantees good feasible solutions within a reasonable computational time. Finally, the performance of the proposed heat exchanger network retrofit method is illustrated and compared throughout three various scale examples.

A computational tool for guiding retrofit projects of industrial heat recovery systems subject to variation in operating conditions

Heat exchanger networks (HEN) in industrial heat recovery systems often consist of large and complex subsystems. Usually, such HENs are subject to variation in operating conditions, such as varying inlet conditions or changing heat capacity flow rates. Additionally, complexities such as stream splits and recycle loops are commonly present in industrial HENs. Therefore, extensive modelling and/or analytical calculations may be necessary when analyzing different retrofit proposals. Furthermore, retrofit opportunities in industrial heat recovery systems are often constrained by operability considerations, i.e. retrofit actions are supposed to have as little impact as possible on the production process to maintain the quality of the core product. In this work, a computational analysis tool is proposed for effective screening of HEN retrofit design proposals at an early stage in the design process. The proposed tool enables fast evaluation of the network’s response, i.e. temperatures and heat loads, when operating conditions change and/or operational settings are manipulated, and it is applicable for a wide range of HEN structures. The practical use of the analysis tool is demonstrated in a case study on the HENs of a large modern Kraft pulp mill.

Solving complex retrofit problems using constraints and bridge analysis

The aim of this paper is to conduct retrofit analysis of large, complex industrial Heat Exchanger Networks using an automated Bridge Analysis. Large, complex networks have many different possible retrofit designs, or Retrofit Bridges, which requires both computational effort and user effort to evaluate. In this paper, constraints relating to the thermodynamic and economic performance of a retrofit design are proposed and applied to significantly reduce Retrofit Bridge options to a smaller, manageable number of design options. These constraints relate to capital costs, payback period, piping, and plant layout. The method is demonstrated with a Kraft pulp mill case study. The Kraft pulp mill currently has 54 heat exchangers and 73 hot and cold streams. Without constraints, the number of possible Retrofit Bridges is 1 x 1020. After applying the constraints, this number is reduced to 15. The remaining Retrofit Bridges are considered to provide high thermodynamic and economic benefit and can be more easily assessed for the best projects. The use of constraints has allowed the complex case study to be solved quickly, and a single design can be selected for further development. The suggested design reduces the utility consumption by 9.2 MW and has an annual Total Retrofit Profit of NZD 2,140,000, requiring a single new exchanger.

An improved design method for retrofitting industrial heat exchanger networks based on Pinch Analysis

Energy integration relies on matching process hot streams with process cold streams, and utilities are only introduced to balance the deficit in energy consumption. A systematic but simple Pinch Analysis (PA)-based retrofit approach is proposed to lessen the utility consumption of any industrial heat exchanger network (HEN) under new minimum temperature approach (ΔTms) at the cost of minor capital investment. This work is an extended and improved version of our previous work (Li and Chang, 2010). Elaborate visualized tool of T–H diagram for identification of cross-pinch heat load is proposed to fully address the case that phases change in the cross-pinch heat exchanger. Main characters of industrial HENs which are large scale, varied heat capacity flow rate and multiple pinches are fully addressed. Specifically, each cross-pinch exchanger or match is identified and those matches with large cross-pinch loads are disconnected first, and then their heat loads on the hot and cold stream side are split according to pinch temperatures. Next, at either side of or between the pinches, the divided heat loads on each stream are combined and matched according to a systematic Pinch Analysis (PA) based procedure. Retrofit modifications are focused on those cross-pinch matches and utility exchangers, so the retrofit procedure of an industrial HEN is obviously simplified. An industrial case of Crude oil preheat train (COPT) is retrofitted to demonstrate the effectiveness of the proposed approach.

Effect of Flow Distribution in Parallel Heat Exchanger Networks: Use of Thermo-Hydraulic Channeling Model in Refinery Operation

Parallel branches are commonly observed in industrial heat exchanger networks (HENs). Despite the important relationship between flow distribution and network efficiency, not all parallel branches comprise of flow controllers or not least, flow measurements. When the network is subject to fouling, uncontrolled flow branches can introduce undesired phenomenon such as thermo-hydraulic channeling (THC) [presented at the 2007 HEFC conference; Ishiyama et al., Effect of fouling on heat transfer, pressure drop and throughput in refinery preheat trains]. Recent analysis of crude preheat train heat exchangers has shown the need to use THC models, in particular, for situations where there is insufficient flow measurement data, especially in nonsymmetric branches. This paper revisits the THC model and highlight practical importance of the THC phenomenon through analysis of plant data. The hydraulic aspect of the analysis is strongly linked to the knowledge of deposit thermal conductivity. A case study of a section of a crude refinery HEN is used to illustrate the use of thermo-hydraulic models in data reconciliation to understand flow imbalances caused due to differences in operating conditions and fouling of heat exchangers in each branch of a parallel network.

Robust model predictive control and PID control of shell-and-tube heat exchangers

Robust model predictive control (MPC) with integral action is designed for the shell-and-tube heat exchangers that are a part of an industrial heat-exchanger network. The advanced control strategy is used for optimizing the control performance as fouling influences operation of the heat exchangers and causes changes of the heat exchangers' parameters. The time-varying parameters of the heat exchangers are considered as parametric uncertainties and robust MPC is used as it is able to handle processes with uncertainties. Integral action is implemented in the robust MPC to assure offset-free control responses. The extensive simulation case study of the robust MPC and proportional-integral-derivative (PID) control of the shell-and-tube heat exchangers confirms significantly improved control performance and energy savings when the newly designed robust MPC with integral action is used.

Development of a Semi-Empirical Fouling Model to Accommodate Characteristics Linear, Exponential and Sigmoid on Heat Exchanger

Fouling is the formation of a layer of deposits on heat transfer surfaces of undesirable materials or compounds. It is influenced by fluid property that is the presence of flow rate and fluid temperature. Fouling on heat exchanger is a very complex phenomenon in such a way that difficult to analyze analytically. So it takes a mathematical fouling model to predict fouling rate in order to increase the efficiency of the heat exchanger caused by the existence of fouling. The model was developed based on the first principal model with the advantage that the model has more detailed potential phenomena regarding the occurance of fouling, nonetheless the data that this research used is difficult to find. As broadly known, the advantages of an empirical model was able to get fouling rate with ease and it agree with the form of fouling that occurs in the plant, but it could not describe the phenomenon that occurs. Therefore it takes a developed fouling model by combining the first principal models and empirical equations to become a semi-empirical model on heat excanger which could describe the phenomenon and also follow the pattern to accommodate the linear, exponential and sigmoid characteristics. The Boltzmann-sigmoidal function captures the fouling initiation period which is the major advantage of this model over the other type of models used by previous researchers. This paper presents the development of empirical models for an industrial HEN (Heat Exchanger Network) using the plant operating data. The fouling models are developed and shown to describe the fouling resistance over time in a crude preheat train with reasonable accuracy.

Integrated approach for sustainable development of energy, water and environment systems

The Conferences on Sustainable Development of Energy, Water and Environment Systems (SDEWES) at the beginning of the 21st century have become a significant venue for researchers to meet, and initiate, discuss, share, and disseminate new ideas in various disciplines of sustainable development. In 2002, the first conference was organised in Dubrovnik, Croatia and since then, 10 more successful conferences were realised. Following the success of international conferences in Dubrovnik, the organizing committees decided to organize the main conference and regional conferences all over the world in even years. In 2016, the second regional SDEWES conference, namely the 2nd South East European Conference on Sustainable Development of Energy, Water and Environment Systems, was held June 15–18 in Piran/Portorose, Slovenia while the 11th SDEWES conference was organised in Lisbon, Portugal on September 4–8. There were 10 special sessions dedicated to various sustainability topics organised in both conferences.This special issue is based primarily upon a collection of 35 papers selected from among 538 scientific contributions presented at the 2nd SEE and 11th SDEWES Conferences. Moreover, this editorial summarises SDEWES published articles that have addressed and identified problems or provided the background for the research that is reported in the current special issue. The main topics of the selected papers address sustainable combustion technologies, renewable energy sources and sector integration, including the integration of renewable technologies in the urban environment, the integration of heat, cold, electricity and fuel production in buildings and industrial applications, heat exchangers and heat exchanger networks, the development and integration of energy storage for concentrated solar power plants, and sectorial integration of bioenergy resources and biorefineries with a particular focus on system integration for efficient and low-carbon systems.

Sensitivity analysis of industrial heat exchanger network design

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.

Thermal and hydraulic impacts consideration in refinery crude preheat train cleaning scheduling using recent stochastic optimization methods

Fouling in heat exchanger network (HEN) in a refinery has been identified as a major obstacle for efficient energy recovery. Fouling causes loss in efficiency over the time, additional pumping cost and loss of production due to additional downtime. A complex crude preheat train (CPT) in a petroleum refinery was chosen in this study to represent an industrial HEN experiencing severe fouling and huge economic losses due to fouling issues. The objective of this study was to develop a realistic cleaning schedule optimization problem. An improved optimization problem for the cleaning schedule of the heat exchangers in the CPT was developed which takes into account the hydraulic impact of fouling through the additional pressure drops. The problem fall into the MINLP class, which is very complex and finding the global optimum is a challenging task. Hence, the recent stochastic methods are proposed and used to solve the MINLP problem without introducing any approximations or simplifying assumptions. Optimizations were performed over an operating period of 44months following crude slate variations and operating conditions of the refinery. The solution provided by recent stochastic algorithms is global optimum solution. The results show that ignoring the additional pumping cost in the objective function resulted in an optimal cleaning schedule that provides a less savings (18.09% of maximum potential savings) in the net loss compared to the optimal cleaning schedule that utilizes the additional pumping cost in the objective function, which increases about 19.34% of maximum potential savings.

Efficient Retrofitting Approach for Improving Heat Recovery in Heat Exchanger Networks with Heat Transfer Intensification

In this paper, an efficient design method is presented to implement heat transfer intensification technologies for increasing energy saving in industrial scale heat exchanger networks (HENs). First of all, the detailed models of shell-and-tube heat exchangers are utilized to estimate exchanger performances under normal and intensified conditions, and an optimization method based on simulated annealing is proposed to find appropriate retrofitting options in the existing HENs. Then, a novel retrofit approach based on the exchanger models and optimization method is introduced to retrofit HENs with several possible retrofit strategies, including exchanger relocations, heat transfer intensification, additional area, and stream repiping. Moreover, a new efficient software package (int-HEAT) is developed for the addressed retrofit problems. The interface of int-HEAT is designed to focus on a clear presentation of HEN retrofit procedure, which allows users to easily control all the retrofit stages. An industrial ...

Margin design, online optimization, and control approach of a heat exchanger network with bypasses

During the life cycle operation of a heat exchanger network (HEN), factors such as equipment aging, gradually decrease heat transfer performance and increase energy consumption. Industrial HEN design currently fails to effectively solve these problems. To resolve this problem, we present an online optimization and control approach method for an HEN with bypasses. The approach is based on the principles of sustainable energy conservation during the life cycle. The area margin of the heat exchanger is gradually released via bypass adjustment, thereby resulting in energy conservation. First, bypasses are set on the HEN to enhance HEN control and enable optimal manipulation of the equipment. Then, the total cumulative cost increment of the HEN, including the increment of utility costs and equipment investment costs, is regarded as the objective function. The effects of the heat transfer efficiency of the heat exchanger and the effects of bypass adjustment are also taken into account. We solve the optimal design margin of the HEN, thereby providing an operational space for optimal control. Finally, using the margin optimization design of the HEN with bypasses as basis, we treat the cumulative costs of the HEN in a certain cycle as the objective function to solve the optimal opening dynamically. While, we present an optimal control structure, which is combined with existing conventional control loops. The HEN of a given crude distillation unit in a refinery is chosen as the research object. And, results illustrate the effectiveness and application prospects of the proposed method.

Hypertargets: a Conceptual Programming approach for the optimisation of industrial heat exchanger networks—Part III. Industrial applications

The fundamentals of the grassroots and retrofit technology have been presented in Parts I and II. This part emphasises on common complications associated with deviations from the counter-current heat transfer, and the integration of streams with properties that face significant variations over the perceived range of energy recovery. A number of propositions are made with simple and straightforward modifications to the conceptual models. The modifications save the need to revert to elaborate, simulation-type models that can mire the benefits of the systematic approach. The paper further discusses the application of the technology to problems of special importance such as debottlenecking projects. It explains its potential as an analysis and a decision making tool with an example from the pulp and paper industry. A final test of its potential to remain systematic, rigorous, and fully automated, even against large scale, complicated problems, is illustrated with two Crude Oil distillation applications.

Hypertargets: a Conceptual Programming approach for the optimisation of industrial heat exchanger networks — II. Retrofit design

The paper extends the Conceptual Programming technology of Part I for retrofit design problems. Similar to the grassroots designs, the methodology includes a targeting and an optimisation stage and accounts for the simultaneous use of thermodynamic principles and mathematical programming. It discusses the development of two conceptual models which enable an automated auditing of the existing network (HEAT model), and a screening of its most promising modifications (TAME model). Both models are formulated and optimised as Mixed Integer Linear Programming problems whose sizes, unlike previous mathematical programming developments, remain very manageable even for large scale industrial problems. The optimisation of these models gives rise to the retrofit Hypertargets which involve, in addition to the energy, all other costing information available. The new methodology reports improvement of up to 40% against the established techniques and its application is illustrated in several examples.

Hypertargets: a Conceptual Programming approach for the optimisation of industrial heat exchanger networks—I. Grassroots design and network complexity

The paper proposes a new design approach for the optimal synthesis of heat exchanger networks. The approach combines thermodynamics, engineering knowledge, and mathematical programming and leads to Conceptual Programming methodology with a clear potential to address industrial applications from a systematic and rigorous perspective. The methodology employs a Conceptual Programming model, the Area Target Model, to screen and scope the solution space for primal, promising options. The model embeds targeting terms from the pinch analysis and supports the development of Hypertargets, a graphical targeting tool with functions similar but much more general and rigorous than Supertargets. Following the targeting stage, a network optimisation stage is facilitated with an extended mathematical formulation that handles complexity issues, and accounts for the development of functional layouts without the need for evolution.

Retrofit and optimisation of industrial heat exchanger networks: A complete benchmark problem

With the significant increase in fuel price, energy conservation projects should be reviewed and analyzed properly. Retrofit of heat exchanger networks (HENs) is among the common projects to reduce the plant operational cost. This paper introduced a new procedure using the path analysis approach for HEN retrofit. The developed procedure attempts at generating options for retrofit solution. These options are created by combining the available utility paths in HEN systematically. Instead of relying on a single path, the heat load could be shifted from HEN utilities using a set of paths simultaneously. To ensure feasible heat transfer between the hot and cold streams throughout, Exchanger Minimum Approach Temperature (EMAT) is maintained while shifting the heat load. The available exchangers’ pressure drop is considered in calculating the heat transfer coefficients. HEN devices are subjected to some additional area without any topological modification. In addition, the investment of such area could be recovered in a short span of time. The calculation of this approach encountered some iteration which has been overcome by mathematical programming. Demonstration example showed some options to be reasonable retrofit solutions. Energy savings ranged between $150 K and $450 K per year with payback time of less than 2 years were possible.

Retrofit and optimisation of industrial heat exchanger networks: A complete benchmark problem

Retrofit and optimisation of industrial heat exchanger networks: A complete benchmark problem