Heat Exchanger Network Retrofit Research Articles

Graphical pinch analysis-based method for heat exchanger networks retrofit of a residuum hydrogenation process

Sustainable energy systems are crucial for reducing carbon emissions because renewable energy sources leave a footprint. The petrochemical industry often suffers from inefficient heat exchange network (HEN) systems, leading to substantial energy wastage. In the current work, a real case study of the residue hydrogenation process was analyzed to identify potential energy savings. A new method combining Pinch Analysis and Thot–Tcold diagram analysis methods was proposed. This graphical analysis method plots the cold-flow temperature of each heat exchanger unit on the x-axis and the hot-flow temperature on the y-axis. By applying the Thot–Tcold diagram to a practical case of residue hydrogenation in Zhejiang, the existing process energy state was evaluated, and HEN was retrofitted to achieve energy savings and carbon emission reduction. Following optimization, the energy recovery amounted to 202.71 GJ/h with an energy recovery rate of 14.3 %. The proposed method saves approximately 4.058 × 105 GJ/y compared to current operations, resulting in an annual cost saving of approximately $ 2.76 M/y, with an investment payback period of less than 0.36 y. This study offers a solution to the energy challenges of industrial residue hydrogenation by enhancing the economic and environmental sustainability of existing process flows.

Total Site Targeting Approach for Heat Recovery at a Paper Factory

The total Site heat integration approach has been used extensively in the industry, including process services and heat exchanger network design integrated with the site service system. This work aims to propose a design for the heat recovery network in the paper factory through Total Site targeting. A procedure that includes the energy analysis and Pinch Analysis methodologies, with the use of Aspen Energy Analyzer is applied. The heat exchanger network design through total site heat integration shows that the rehabilitation of the heat recovery system of the paper machine and boiler blowdown is feasible, with a potential annual saving of 259 t of fuel oil and 116 000 m3 of water, which make it feasible to invest in the factory’s heat recovery system, whose project budget is estimated to recover in a year. Heat exchanger network retrofit design allows to recover 46.2% of the maximum energy recovery.

A heuristic method to introduce hot feed into chemical process for energy saving with minor structure modification

Hot feed is a relatively inexpensive strategy to improve the energy utilization in chemical plants. Since hot feed is often an afterthought, retrofitting the heat exchanger network (HEN) with hot feed becomes a key step to decide the energy saving. This paper proposes a heuristic method to introduce hot feed into the existing HEN with minor structure modifications. The concept of heat flow path is extended to fit the hot feed problem. The possible changes of heat exchangers in a path are analyzed in details referring to the heat flow direction. Based on this, the bottleneck and the maximum shift capability of each path can be determined quantitatively. Rules for the creation and selection of new paths are presented to achieve more hot utility saving. A wax oil hydrogenation unit is analyzed to illustrate the proposed method, where heat carried by hot feed can be fully used to save the hot utility. The proposed method obtains more hot utility reduction (3349.0 kW versus 783.8 kW) by the hot feed strategy and a simpler retrofitting scheme than a previous method based on the grand composite curve. Besides, this method can show clear insights in the HEN retrofit with hot feed and it is easy for industrial application.

Retrofit heat exchanger network optimization via graph-theoretical approach: Pinch-bounded N-best solutions allows positional swapping

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.

Synthesis and Retrofit of Multiperiod Heat Exchanger Networks Considering Heat Transfer Enhancement and Environmental Impact

Heat transfer enhancement has been used to achieve lower heat transfer area and reduced utility requirements in heat exchanger network synthesis problems involving retrofit. This paper presents a technique for implementing heat transfer enhancements in both grassroot and retrofit heat exchanger network synthesis problems involving multiperiod operations. For the grassroot scenario, the approach adopted involves extending the stage-wise superstructure model for multiperiod heat exchanger network synthesis to accommodate various options of tube-side and shell-side heat transfer enhancement techniques. The extended model is then applied to a retrofit scenario using the reduced superstructure synthesis approach. The results obtained demonstrate the benefits of heat transfer enhancement through reduced operating costs in the grassroot and retrofit scenarios. For the grassroot scenario, the operating and capital costs obtained in this paper are 12.3% and 20% lower than solutions obtained using conventional non-enhanced synthesis methods, while for the retrofit scenario, solutions which compare favourably with literature solutions, and which has the potential to be more environment friendly by virtue of lower energy utilisation, are obtained.

Multi-objective evolutionary optimization for multi-period heat exchanger network retrofit

Increase in energy efficiency and reduction in greenhouse gas (GHG) emissions in industry are important steps towards a more sustainable economy. Due to the growing share of high value-added industries multi-period operation becomes more common in process industry. Therefore, retrofit of existing multi-period production plants is a key aspect towards more sustainable production processes. Hence, in this work, an existing two-level evolutionary algorithm using a genetic algorithm and a differential evolution for multi-period heat exchanger network retrofit is extended to consider GHG emissions as a second objective to the total annual cost (TAC). The multi-objective problem is addressed by incorporating a non-dominated sorting genetic algorithm (NSGA-II) and hypervolume indicators into the algorithm. By analyzing an industrial case study of a potato chips production, the results of the multi-objective optimization shows that GHG emissions can be reduced by 50%. However, compared to the single-objective optimization, TAC is increased by 27%. By selecting capital costs and operating costs as objectives instead, similar results to the single-objective optimization are achieved showing that the results are highly dependent on the selection of the objectives. Further, changes in utility costs and caused emissions have a high impact on the results.

Improved energy recovery from the condensed steam as part of HEN retrofit

The conventional approach to heat exchanger network (HEN) retrofit involving design techniques based on Pinch Technology (PT) is extended to include minimization of energy losses resulting from steam-condensate expansion. The authors proposed a new approach to minimize energy losses in utility system, thermally coupled with the combined heat and power (CHP) plant, using condensate subcooling phenomena. Moreover, applying condensate subcooling can counteract the drawbacks of commonly used multi-stage condensate expansion which increase operability and reduces investment and maintenance costs. A case study illustrates the suitability of improved condensate management as a HEN retrofit measure. The study object is a Methyl-Tert-Butyl Ether (MTBE) plant processing 18 t/h isobutylene and consuming 4386 kW of hot utility (steam) in the HEN. A study of the maximum possible heat recovery using PT indicates that the combined heat recovery from hot process streams and condensate can be increased by 510 kW compared to the existing state. At the same time, it is possible to generate additional power of 120 kW in the CHP plant that supplies energy to the MTBE plant. The locations of heat exchangers are accounted for in HEN reconfiguring. A new scheme of steam and condensate system is presented.

Energy Integration of Crude Distillation Unit of a Refining and Petrochemical Company in Northern Nigeria

Most Nigerian refineries were constructed before pinch technology was developed, hence, the design were not optimal, leading to high energy loss. The objective of this work is to evaluate energy integration of crude distillation unit (CDU) of a refining and petrochemical company in Northern Nigeria using pinch analysis by utilising HINT software. Minimum heating and cooling demand of 32251.1 kW and 29637.9 kW at the pinch point of 506.5 K was evaluated from the composite curve, grand composite curve and the cascade diagram. The region of overlap in the composite curve indicates a total of 108,945 kW as the possible energy that can be recovered in the process. Existing utility demand of the unit was 96,873.5 kW, after heat integration it reduces to 61,889 kW, this showed 36.11 % energy saving with a total operating cost of US$4,560,766.5 that could be saved (annually). Minimum approach temperature (DTmin) analysis results showed an optimum DTmin of 15 K which resulted in a total annual cost of US$6,715,700. Furthermore, the analysis showed the effect of DTmin on energy, area, minimum number of units and cost targets. The design objective of the retrofit heat exchanger network (HEN) was set toward maximum energy recovery. A total of twenty (20) heat exchangers made up the new network, which comprises of twelve (12) process to process heat exchangers, two (2) heaters and six (6) coolers.

A novel relatively linear hybrid Three-Level strategy for retrofitting heat exchanger networks

This paper proposes a three-level straightforward retrofitting approach for heat exchanger networks (HENs) using a genetic algorithm (GA) coupled with linear programming (LP) and integer linear programming (ILP) formulations. At the first level, the GA produces HEN structures. The local total annual cost (TAC) of these HENs is computed at the second level, consisting of LP, ILP, and an external search loop. LP model is formulated based on the minimum utility consumption, whereas ILP determines the minimum investment cost of implementing potential changes to the existing network to turn it into a GA-generated network. The external search loop is also used to handle the stream splitting ratios. Eventually, the final optimal TAC of the retrofitted network is determined by applying a correction procedure at the third level to the second level results. The results demonstrate that this approach could reduce the retrofitted network's TAC by about 0.5%-20% compared to others.

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)

Environmental and economic assessment of the efficiency of heat exchanger network retrofit options based on the experience of society and energy price records

Retrofit of the heat exchanger network is one of the vehicles of energy efficiency and emission reduction in the process industry. For further implementation, several alternative retrofit options exist, and better economic indicators provide the selection of the best one. Usually, the analysis is made using a forecasting model of energy prices, but the last pandemic and political crises demonstrate unpredictable changes. This paper proposed an approach for the economic and environmental assessment of retrofit options based on the experience of society from 1861 to 2021 and the corresponding energy price trends. Essential financial, e.g. NPV, IRR, DPP, and environmental criteria of retrofit options of heat exchanger network, are analysed considering different trends of energy prices. The most effective project is selected, providing the decision-makers with all data on overdetermined or lost benefits in all possible conditions. The case study analyses three alternative retrofit options for crude oil distillation. Two scenarios presume implementation after 1 and 3 years after project acceptance. The analysis shows IRR is on average 28, 99 and 61% for retrofit options 1, 2 and 3 when a preparatory period is 3 years and low energy prices. NPV is on average 21, 15 and 9 million USD, respectively. The DPPs are 3.8, 2.3, and 2.6 years and the reduction of carbon footprint is by 152, 71 and 45 ktCO2/year. It was also found that the retrofit option with the most extensive energy and emission saving is the most effective for periods with high energy prices regardless of a project implementation period. The retrofit option with the minor network changes is better for low and average energy prices regardless of a project implementation period. The method allows decision-makers to assess the alternative retrofit project in different economic conditions and could be applied in other process industries.

A Novel Step-by-Step Automated Heat Exchanger Network Retrofit Methodology Considering Different Heat Transfer Equipment

Improving the energy efficiency in heat exchanger networks (HENs) remains a significant industrial problem, specifically in energy-intensive operations. A particular method for such an objective is the modification of HENs at the equipment-use level, where structural changes take place and units within the network are moved, replaced and/or removed. This practice is usually known as retrofit. The objective of a retrofit is to maximize the heat recovery using the minimum modifications possible and minimum retrofit cost. Traditional retrofit techniques would normally consider one type of heat exchanger (based on the original network) with no additional design features (i.e., heat transfer enhancement technologies). The expansion of such alternatives is limited by practical use and availability of theoretical methods. In this context, the inclusion of high-performance heat exchangers such as plate heat exchangers (PHEs) has not been widely explored, even when their design and operational advantages are known. In this work, a new step-by-step automated HENs retrofit approach based on Pinch Analysis is proposed. The approach is possible to identify the best modification, its location within the network, and its cost simultaneously. Moreover, to increase energy savings, this work presents a strategy that seeks to utilize high efficiency heat exchangers such as plate heat exchangers for retrofit. A distinctive feature of this new method is the ability to handle different minimum approach temperatures, given the different types of exchangers, within the optimization of HENs. Three cases are studied using this methodology to quantify the potential benefits of including PHEs in HEN retrofits, via the analysis of the retrofit cost. Results are compared with a baseline consisting in the same network, where only Shell-and-Tube-Heat-Exchangers (STHXs) are used. In addition, the results demonstrate that this methodology is flexible enough to be applied in a wide range of retrofit problems.

Applied heat exchanger network retrofit for multi-period processes in industry: A hybrid evolutionary algorithm

In Swiss process industry, process integration is often applied to retrofit existing plants with multi-period operation. Such periods may experience a high degree of variation in temperature or mass flow. Some process streams may not exist in every period or are soft streams. The resulting retrofitted network needs to be able to ensure feasible heat transfer in each period by the integration of mixer configurations to control the temperature. These attributes increase the complexity of the solution space. Hence, this work proposes an evolutionary two-level algorithm for heat exchanger network retrofit. Genetic algorithm is used for topology optimization and a differential evolution algorithm handles the heat loads. The algorithm is extended with practical constraints such as a maximum number of heat exchangers. Explicit mixer temperature calculations are implemented using the Lambert W-function. The algorithm was successfully applied to an industrial case study, reducing its total annual cost by approximately 66%.

An advanced Grid Diagram for heat exchanger network retrofit with detailed plate heat exchanger design

This paper presents a method for heat exchanger network (HEN) optimisation considering plate heat exchangers (PHEs), incorporating detailed PHEs design. The developed method starts from a mathematical model based on the Advanced Grid Diagram, which can optimise the HEN structure. The model minimises the energy consumption cost with the constraints that enable a solution thermodynamically feasible. Then comes the heat exchanger type selection part, which is provided by a graphical tool helping to identify which types of the heat exchanger are feasible. The feasible temperature range can be easily visualised to avoid the temperature violation of PHEs. This selection part integrates the area calculation and cost calculation with the detailed heat exchanger design. The method has been tested by a case study of crude oil distillation system illustrating that the application of brazed plate heat exchangers (BHEs) of CB series manufactured by Alfa Laval can save 6.6% of the investment cost for new heat exchangers compared with the retrofit plan that only shell-and-tube and double pipe heat exchangers are used.

An engineering target-oriented multi-scenario heat exchanger network retrofit methodology with consideration of exergoeconomic assessment

An engineering target-oriented multi-scenario heat exchanger network retrofit methodology with consideration of exergoeconomic assessment

A parallelized hybrid genetic algorithm with differential evolution for heat exchanger network retrofit

The challenge of heat exchanger network retrofit is often addressed using deterministic algorithms. However, the complexity of the retrofit problems, combined with multi-period operation, makes it very difficult to find any feasible solution. In contrast, stochastic algorithms are more likely to find feasible solutions in complex solution spaces. This work presents a customized evolutionary based optimization algorithm to address this challenge. The algorithm has two levels, whereby, a genetic algorithm optimizes the topology of the heat exchanger network on the top level. Based on the resulting topology, a differential evolution algorithm optimizes the heat loads of the heat exchangers in each operating period. The following bullet points highlight the customization of the algorithm:•The advantage of using both algorithms: the genetic algorithm is used for the topology optimization (discrete variables) and the differential evolution for the heat load optimization (continuous variables).•Penalizing and preserving strategies are used for constraint handling•The evaluation of the genetic algorithm is parallelized, meaning the differential evolution algorithm is performed on each chromosome parallel on multiple cores.

A parallelized hybrid genetic algorithm with differential evolution for heat exchanger network retrofit

A parallelized hybrid genetic algorithm with differential evolution for heat exchanger network retrofit

A New Technique for Heat Exchanger Network Retrofit Using Individual Stream Heat Cascade Analysis

A New Technique for Heat Exchanger Network Retrofit Using Individual Stream Heat Cascade Analysis

Simultaneously Retrofit of Heat Exchanger Networks and Towers for a Natural Gas Purification Plant

As an essential part of Heat Integration, the heat exchanger network (HEN) plays a vital role in large-scale industrial fields. The optimisation of HEN can increase energy efficiency and considerably save the operating and investment cost of the project. This study presents a novel approach for simultaneous optimisation of plant operating variables and the HEN structure of an existing natural gas purification process. The objective function is the total energy consumption of the studied process. A two-stage method is developed for optimisation. In the first stage, a particle swarm optimisation (PSO) algorithm is developed to optimise variables including tower top pressure, tower bottom pressure, and reflux ratio on the HEN, thereby changing the initial temperatures of cold and hot streams in the HEN. In the second stage, a shifted retrofit thermodynamic grid diagram (SRTGD)-based model and the corresponding solving algorithm was applied to retrofit the HEN. The case study shows that the optimal operating conditions of towers and temperature spans of heat exchangers can be solved by the proposed method to reduce the total energy consumption. The case study shows that the total energy consumption is reduced by 41.5 %.

Economic Assessment of Heat Exchanger Network Retrofit Options Based on Historical Data of Energy Price Trends

Energy-saving retrofit of industrial plants is one of the vehicles of decarbonisation and the goal of modern society. The retrofit of the heat exchanger network allows saving a large amount of primary energy across units and industrial clusters. Usually, selecting suitable retrofit options is a big challenge for decision-makers that impacts future plant profit and environmental issues. This research proposes assessing different retrofit options of crude oil distillation unit based on historical data of energy prices. Periods with different energy price trends were analysed, accounting for the retrofitted unit start-up after the first and third year. The impact of energy price dynamics on economic and environmental benefits of different retrofit option was analysed. The sustainability of the most economically beneficial option was assessed across different energy price trends. The overdetermined/lost benefits of all options were calculated, allowing the decision-maker to proceed with the most appropriate one.