Existing Heat Exchanger Network Research Articles

Application of pinch analysis to improve the heat integration efficiency in a crude distillation unit

In this paper, the thermal efficiency of the heat exchanger network of an existing crude distillation unit (CDU) was evaluated. The main goal is to determine how much energy savings can be achieved by network retrofitting. Energy losses are inevitable especially in process where equipment and heat integration network design are outdated. Pinch analysis method can help in minimizing the energy losses by retrofitting the heat exchanger grid and it is proven to be successful in many applications to predict more efficient heat exchanger networks. A base scenario case study was suggested to determine the maximum possible energy savings that can be achieved. In this scenario, the energy analyzer model in Aspen HYSYS was used to determine the optimum energy network that can accomplish maximum energy recovery with minimum capital cost. Another alternative was also evaluated using pinch analyzer tools in Aspen HYSYS. In this scenario, the existing heat exchanger network was optimized to determine how much energy can be recovered. All analysis conducted were based on the existing cooling and heating utilities in the plant. The results obtained indicate that around 67.5 MW of maximum cooling and heating utility can possibly be recovered compared to the existing utility load of 148.6 MW. This represents around 45% reduction in heat utility requirements. There is also an indication of substantial positive environmental impact in terms of how much reduction in the CO 2 emissions that can be achieved reaches up to 1079 kg CO 2 /h for a practical and feasible option, and up to 7840 kg CO 2 /h for grass rooting retrofitting scenario.

Application of entransy method in heat exchanger networkoptimization for low-grade waste heat utilization

<p indent="0mm">Efficient utilization of low-grade industrial waste heat is of great significance to improve the efficiency of energy utilization and to reduce CO₂ emission. Energy system integration and corresponding heat exchanger network optimization are effective solutions. The entransy method is suitable for quantifying the irreversibility of the heat exchange process and guiding and evaluating heat exchanger network optimization. However, there are relatively few cases in which the entransy method is applied to the heat exchanger network optimization for waste heat utilization. In this study, the waste heat utilization of steam condensate in an industrial park through a heat exchanger network was analyzed based on the entransy method. By reducing the entransy dissipation of the heat exchange process of the condensate, the existing heat exchanger network was optimized, and the high-grade waste heat was utilized by an absorption chiller for local air conditioning demands. As a result, the discharge of high-grade waste heat was converted to the discharge of low-grade waste heat. The optimized heat exchanger network guided the redesign of the actual heat exchanger network. The testing results showed that the cooling effect of the developed seawater cooled absorption chiller reached <sc>3430 kW</sc>, with a coefficient of performance of 0.76. The entransy dissipation of the heat exchange process of the condensate was reduced by 57.3%. The thermal efficiency and exergy efficiency of the heat exchanger network were increased by 55.8% and 81.1%, respectively. These results demonstrate that the entransy method is valid in the application of low-grade waste heat utilization through heat exchanger network optimization.

Heat Integration of an Industrial Unit for the Ethylbenzene Production

This paper presents both the results of a study of the existing heat exchanger network (HEN) of an industrial unit for ethylbenzene (EB) production by the alkylation of benzene with ethylene, and an analysis of four different HEN retrofit projects carried out using process integration methods. The project of modernization of HEN was carried out using classical methods of Pinch analysis. For this case, the value of ΔTmin is determined, which is limited by the technological conditions of the process. Additionally, two different heat pump (HP) integration options and the joint retrofit Pinch project with HP integration are under consideration. The economic analysis of each of the projects was carried out. It is shown that the best results will be obtained when implementing the joint project. As a result, steam consumption will be reduced by 34% and carbon dioxide emissions will be decreased by the same amount.

Heat Exchanger Network Retrofit of an Oleochemical Plant through a Cost and Energy Efficiency Approach

Limited research of heat integration has been conducted in the oleochemical field. This paper attempts to evaluate the performance of an existing heat exchanger network (HEN) of an oleochemical plant at 600 tonnes per day (TPD) in Malaysia, in which the emphases are placed on the annual saving and reduction in energy consumption. Using commercial HEN numerical software, ASPEN Energy Analyzer v10.0, it was found that the performance of the current HEN in place is excellent, saving over 80% in annual costs and reducing energy consumption by 1,882,711 gigajoule per year (GJ/year). Further analysis of the performance of the HEN was performed to identify the potential optimisation of untapped heating/cooling process streams. Two cases, which are the most cost-effective and energy efficient, were proposed with positive results. However, the second case performed better than the first case, at a lower payback time (0.83 year) and higher annual savings (0.20 million USD/year) with the addition of one heat exchanger at a capital cost of USD 134,620. The first case had a higher payback time (4.64 years), a lower annual saving (0.05 million USD/year) and three additional heaters at a capital cost of USD 193,480. This research has provided a new insight into the oleochemical industry in which retrofitting the HEN can further reduce energy consumption, which in return will reduce the overall production cost of oleochemical commodities. This is particularly crucial in making the product more competitive in its pricing in the global market.

RETROFITTING DESIGN OF HEAT EXCHANGER NETWORKS USING ASPEN-HYSYS: A CASE STUDY OF CRUDE OIL REFINING PROCESS

Energy integration is an important request in many chemical industries, particularly in petroleum refinery, because the cost of energy used in operation represents a significant percentage of the total energy. Retrofit of heat exchanger networks (HENs) is a magical solution for energy saving and minimizing external consumption of cold and hot facilities through several mathematical and graphical methods in recent years, but many of these methods are complementary complex and uneconomic. Redesign approach is developed for the existing heat exchanger network using the ASPEN-HYSYS. Simulation of Middle East Petroleum Refinery has been done then, linked to energy analyzer program to make the necessary retrofit which shows reduction of 28.46 (MW) 29.55%, 14.23 (MW) 37.6% and 14.23 (MW) 24.34% in total utilities, hot utility and cold utility, respectively with 29.55% reduction of CO2 emissions.

Heat flow diagram as an extension of bridge retrofit method to save energy in heat exchanger networks

Retrofitting or reducing heat consumption in existing Heat Exchanger Networks can be done by set of modifications which is termed “bridge”. A bridge links heat outlets to hot utility users. The most complicated step in identification of the economical bridges, is the determination of the optimum routes. The “Energy Transfer Diagram” and a few modifications on bridge method are among the recent efforts for the better identification of the bridges. Though the internal exchangers in the initial network participate as the “transferring interface or chain rings along the bridges”, the role and the characteristics of their participation has not dealt with clearly and quantitatively in any of previous works. This paper presents “Heat Flow Diagram” as a new graphical tool and also an analyzing algorithm, to improve bridges identification in retrofit analysis method. The role of internal exchangers as the transferring interface and the limiting factors affects its transferring capacity is conceptually and quantitatively analyzed for the first time. Subsequently several illustrative examples ‘covering different situations and clarifying concepts of new retrofitting method’ were illustrated. Heat integration of a Methanol plant analyzed with three different method to compare with our new suggestion; resulted in 18.8%, 79.2% and 98.9% heat recovery.

Utility Paths Combination in HEN for Energy Saving and CO2 Emission Reduction

Energy demand and flue gas emissions, namely carbon dioxide (CO2) associated with the industrial revolution have exhibited a continuous rise. Several approaches were introduced recently to mitigate energy consumption and CO2 emissions by either grass root design or retrofit of existing heat exchanger networks (HEN) in chemical process plants. In this work, a combinatorial approach of path combination is used to generate several options for heat recovery enhancement in HEN. The options are applied to successively shift heat load from HEN utilities using combined utility paths at different heat recovery approach temperature (HRAT) considering exchangers pressure drop. Industrial case study for HEN of the preheat train in crude oil distillation unit from the literature is used to demonstrate the approach. The obtained results have been studied economically using the cost targeting of Pinch Technology. As a result, both external energy usage and CO2 emissions have been reduced from a heater device in HEN by 20% and 17%, respectively, with a payback of less than one year.

Analysis of an Operating Tmp Mill Using Advanced Composite Curves and Heat Load Model for Pulp and Paper

In this study an operating thermo mechanical pulp and paper mill (TMP) is analyzed using advanced composite curves. The use of advanced composite curves is a relatively novel method developed in Chalmers University by Nordman and Berntsson. It is a graphical pinch based approach that takes into account the existing heat exchanger network and the utilities used. With this information provided it is possible to predict order of magnitude of the cost associated to retrofit certain part of the heat exchanger network. The method also reveals the possibilities to integrate heat pumps into the system. The mill is modelled using the Heat Load Model for Pulp and Paper (HLMPP). The mill used as an example in this study is a European mill, producing paper on three paper machines. The mill has three pulp lines; two TMP lines and one DIP line. The study also covers debarking and waste water treatment plants. The analysis shows a potential for improvement. The technical economical possibilities of achieving this potential are discussed.

Approaches for retrofitting heat exchanger networks within processes and Total Sites

This study presents developed approaches that could be used for retrofitting of existing heat exchanger networks (HENs) within individual processes and industrial sites to achieve lower energy consumption, cost savings and emission reduction. Successful industrial applications are further presented, and future challenges are identified. Approaches used for retrofitting of existing HENs are based on heuristics, on thermodynamic analysis and insights – Pinch Analysis and recently developed Bridge Analysis, on numerical optimisation - Mathematical Programming, and on hybrid or combined approaches which are based on a combination of heuristics, physical insights and/or numerical optimisation. Optimisation-based approaches could be further divided into deterministic and stochastic (probabilistic) methods. Those systematic approaches (all approaches except pure heuristics) use either sequential (divided into sub-problems) or simultaneous synthesis methods.

Energy optimization of integrated atmospheric and vacuum crude distillation units in oil refinery with light crude

The heat integration and retrofit analysis of Arabian light crude distillation units was carried out to identify opportunity for energy savings using different design options, to achieve optimum heat exchanger network. Data used were extracted from an existing and operating crude oil refining plant. The pinch analysis of existing plant using process integration software (Heat-Int) Process Integration Limited, Cheshire, United Kingdom revealed that the hot and cold utilities consumptions at the prevailing ΔTmin of 77 °F in the plant were 680.23 and 521 MMBtu/h, respectively. Economic evaluation of existing plant revealed total operating cost of $4 829 625/year. Retrofit of existing plant using different design options generated an optimal network comprised four additional heat exchangers with reduction in ΔTmin from 77 °F to 57 °F. The hot and cold utilities consumptions also reduced to 623.23 and 464.44 MMBtu/h, respectively. Economic evaluation of the new design showed energy savings of $259 860/year. The trade-off between energy and capital costs in terms of the costs procurement and installation new heat exchangers gives overall cost savings of $32 800/year with payback period of 11 months. The study concluded that retrofitting of existing heat exchanger network to correct those exchangers that are transferring heat across the pinch could result in enormous energy savings. © 2013 Curtin University of Technology and John Wiley & Sons, Ltd.

An Enhanced Tool for Heat Exchanger Network Retrofit Towards Cleaner Processes

The individual stream temperature versus enthalpy plot (STEP) is a graphical tool that can be used to simultaneously diagnose and retrofit existing heat exchanger networks (HEN). The Modified Energy Transfer Diagram (ETD) utilises the Grand Composite Curve (GCC) to provide insights on the scope for HEN retrofit and to pinpoint retrofit alternatives based on the Bridge Analysis method. Both the STEP and the Modified ETD methods are based on graphical representation of individual process streams that enable users to visually identify the potential scope for improvement in an existing HEN. It is found that, using the distance of the horizontal gap between the stream pairs of the STEP diagram can simplify the construction of the Modified ETD. The Modified ETD can help monitor the progress of HEN retrofit. This paper shows through a case study that, combining the use of STEP-ETD methods can simplify, facilitate and enhance the simultaneous targeting, diagnosis and retrofit of a HEN toward achieving cleaner processes, while yielding the same final retrofitted structure like those produced by using only the Modified ETD.

Revamp of Feed Preheat Network Using Aspen Hysys in a Kero Hydro-Desulphurization Unit

Abstract The paper is based on the revamp of feed preheat network in a Kero hydro-desulphurization unit. This revamp is beneficial as it does not require additional equipment to raise the feed temperature. Desulphurization of crude is a catalytic process used in oil and gas refining industry to remove sulphur content from refined petroleum products. Previously, feed was charged from the crude distillation unit at 103 ° C. Due to envisaged changes, the feed is now charged from storage tanks at a temperature of 40 ° C. This requires a higher feed heater duty or decrease in feed rate. This potential underutilization of the unit could impact the product supply from the refinery with negative financial implications. The aim is to preheat the feed at a temperature of 40 ° C to a temperature of 150 ° C prior to entering the feed heater. The methodology was to configure the feed preheat network of the unit in Aspen-Hysys as existing to validate the exchanger design with present operating condition and to reconfigure the same feed preheat network to maximise the feed temperature, whilst ensuring sufficient temperature availability at the fractionator inlet for the required performance. Based on the simulation study, it can be concluded that feed could be preheated to the optimum level by reconfiguring the existing heat exchanger network. This configuration would reduce the charge heater duty along with maintaining the required fractionator feed temperature at an optimum level. This approach requires the reconfiguration of the existing streams, without having to involve additional equipment . This paper would give insight on ways in which reconfiguration of existing preheat networks can be carried out without the use of additional equipment and also provide knowledge on methods to utilize energy sources present within the process which would lead to financial savings. Keywords: Heat exchanger, hydro-desulphurization , Aspen Hysys , preheat network, reconfiguration Cite this Article Natasha Vincent, Patil Kiran D, Mahesh Kumar B. Revamp of Feed Preheat Network Using Aspen Hysys in a Kero Hydro-Desulphurization Unit. Journal of Petroleum Engineering and Technology . 2017; 7(2):

Analysis and revamping of heat exchanger networks for crude oil refineries using temperature driving force graphical technique

The refining industry is an energy-intensive industry; most of the energy is consumed in heating and cooling requirements. Revamping or retrofitting of existing chemical engineering plants is an appropriate opportunity for improving and enhancing the existing heat exchanger network’s (HEN) design and performance. Revamping is commonly used to modify the existing process for many objectives, such as saving energy, reducing the environmental emissions and increasing the productivity of the plant. This paper presents a new graphical approach for the analysis and revamping of existing 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 temperature driving forces for each exchanger are plotted on the Y-axis. This graphical technique describes the energy analysis problems in terms of temperature driving force (TDF) inside the heat exchanger, which is an important factor in the revamping process as the difference in that temperature driving force is involved in the calculation of the area of heat exchangers, consequently affecting the cost. Also, each exchanger is represented in this graph as a straight line whose slope is related to the heat capacities and length is related to the heat flow. The TDF graphical approach is applied to an existing HEN in an Egyptian crude oil refinery. The detailed steps for the graphical analysis and revamping are applied on the HEN for the objective of energy savings, and obtained results showed savings of approximately 10.5% in the energy demand with minor structural modifications and equivalent energy cost savings of 360,000 $/year.

Revamping of Heat Exchanger Network of an Egyptian Refinery Plant Using New Temperature Driving Force (tdf) Graphical Technique

This paper introduces a new graphical approach for revamping of existing 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 against the driving forces for each exchanger 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 revamping process as the differences in these driving forces are involved in calculating the area of heat exchangers, and consequently affecting the revamping cost. Also, each exchanger is represented in this graph as a straight line with a slope related to the heat capacity flows and length as function of the heat duty. An algorithm for revamping is also proposed.The temperature driving force new representation is applied on an existing HEN in an Egyptian refinery (EORU) to boost its energy efficiency. The graphical revamping in application on the HEN shows savings of approximately 10 % in the energy demand with minor structural modifications.

A systematic method to customize an efficient organic Rankine cycle (ORC) to recover waste heat in refineries

Organic Rankine cycles (ORCs) convert low temperature waste heat into power. When there are multiple waste heat sources in a refinery, operability and safety considerations may make it more practical to use hot water as the medium to recover waste heat. The hot water stream can then release the heat to the organic working fluid in an ORC system. In this paper, how to customize an efficient ORC for a heat exchanger network (HEN) to optimally recover multiple strands of waste heat is investigated. Because the heat exchanger network structure, the hot water loop, and ORC system interact with each other, the coordination and synthesis of these systems ought to be considered simultaneously to maximize the energy performance. A methodology is proposed using the waste heat composite curve (WHCC) and grand composite curve (GCC) to diagnose inefficiencies in an existing heat exchanger network. In addition, the WHCC can be used to solve the problem of the tradeoff between waste heat quality and quantity recovered with an intermediate stream. WHCCs are classified into two types, and procedures for designing the recovery network for each type are presented while considering the interaction with working fluid selection. The methods proposed in this paper can help engineers diagnose problems with the original heat exchanger network, and determine the flowrate of hot water, the structure of the waste heat recovery network, the best working fluid and the operating conditions of ORC system in an integrated manner. The ideas are applied to an illustrative case study in collaboration with Sinopec. The case study shows the effectiveness of this method and compares different extents of heat exchanger network modification.

Model based approach to synthesize spare-supported cleaning schedules for existing heat exchanger networks

Almost every modern chemical process is equipped with a heat-exchanger network (HEN) for optimal energy recovery. However, as time goes on after startup, fouling on the heat-transfer surface in an industrial environment is unavoidable. If the heat exchangers in an operating plant are not cleaned regularly, the targeted thermal efficiency of HEN can only be sustained for a short period of time. To address this practical issue, several mathematical programming models have already been developed to synthesize online cleaning schedules. Although the total utility cost of a HEN could be effectively reduced accordingly, any defouling operation still results in unnecessary energy loss due to the obvious need to temporarily take the unit to be cleaned out of service. The objective of the present study is thus to modify the available model so as to appropriately assign spares to replace them. Specifically, two binary variables are adopted to respectively represent distinct decisions concerning each online exchanger in a particular time interval, i.e., whether it should be cleaned and, if so, whether it should be substituted with a spare. The optimal solution thus includes not only the cleaning schedule but also the total number of spares, their capacities and the substitution schedule. Finally, the optimization results of a series of case studies are also presented to verify the feasibility of the proposed approach.

SAGD 법을 이용한 오일샌드 플랜트 열교환기망 최적화를 위한 사례연구

Oil sands are a mixture of sand, clay, and a high-viscosity petroleum called bitumen. Steam-Assisted Gravity Drainage (SAGD) is the most viable and environmentally safe recovery technology for extracting bitumen. It extracts the viscosity-lowered bitumen by high pressure, high temperature steam injected into the bitumen reservoir. The steam is produced at the Central Processing Facility (CPF). Typically, more than 90% of the energy consumed in producing bitumen are used to generate the steam. Fuels are employed in the process, which cause economic and environmental problems. This paper explores the retrofit of heat exchanger network to reduce the usage of hot and cold utilities. The hot and cold utilities are reduced respectively 6% and 37.3% which in turn resulted in 5.3% saving of total annual cost by improving the existing heat exchanger network of the CPF.

Feasible heat recovery of interplant heat integration between two plants via an intermediate medium analyzed by Interplant Shifted Composite Curves

Interplant heat integration brings more opportunity to utilize the surplus/waste heat in individual plants. In most previous studies on interplant heat integration, either Grand Composite Curves (GCCs) or waste heat source/sink in the existing heat exchanger networks (HENs) were used for analysis. However, for these two methods, the former may generate intricate HENs, while the latter may miss some possible heat recovery potential. This paper investigates a way to achieve almost maximum possible heat recovery for indirect heat integration between two plants without basically changing the existing HENs. The selection of appropriate hot/cold streams participated in integration is investigated. A novel concept named Interplant Shifted Composite Curve (ISCC) is proposed to determine the maximum feasible heat recovery potential via indirect interplant heat integration and the minimum flowrate of a single-circuit intermediate medium used. Compared to the waste heat source/sink in the existing HENs being used directly for integration, a case study shows 43.1% of energy saving with minimum flowrate of a single-circuit intermediate medium, which can be easily obtained in the ISCC. Meanwhile, compared to the GCCs being used for integration, a scheme relatively easy and practical to implement can be achieved with the proposed method.

Initial analysis on heat exchanger networks of fatty acid fractionation plant to optimize energy recovery and controllability

The objective of this paper is to present the initial analysis on the energy recovery and controllability of the existing heat integrated fatty acid fractionation plant. From this initial analysis, the existing heat integrated fatty acid fractionation plant is analysed to know the either the existing heat exchanger networks (HENs) satisfied the design criteria, or controllability criteria by using trade-off plot. According to the trade-off plot, if the existing HENs is better in terms of design criteria, then more efforts need to be invested to control the network. On the other hand, if the existing HENs is better in terms of controllability criteria, then more efforts need to be invested to reduce the energy consumption. In this study, the initial analysis means the value of the ?Tmin used for the current HENs is investigated and the controllability of the network is predicted by using trade-off plot. In order to investigate the value of the ?Tmin used for the current HENs, only the first two stages of the model-based flexible and operable HENs is used. In the Stage 1, the value of the ?Tmin is investigated by selecting the value of the ?Tmin ranging from 10 °C to 40 °C with the increment of 10 °C. Then, HEN is synthesized for the selected value of the ?Tmin. Once the networks have been synthesized, all candidates are transferred into a process simulator to test their process feasibility in Stage 2 where the unfeasible candidates will be eliminated. Then all feasible candidates will be predicted in terms of their controllability performance by using trade-off plot. Energy integrated fatty acid fractionation plant is used as a case study for this initial analysis. This paper only considers steady state controllability test without considering process dynamics.

Retrofit of heat exchanger networks without topology modifications and additional heat transfer area

Numerous design methods for the retrofit of heat exchanger networks have been proposed over the years, with most depending greatly on topology modification and additional heat transfer area. However, topology modifications and the installation of additional heat transfer area can lead to uneconomic retrofit in many cases, largely as a result of the expense of civil engineering work and pipework modifications. Retrofit of a heat exchanger network can be achieved without the need for topology modifications and additional heat transfer area by the use of heat transfer enhancement. This paper presents a methodology for heat exchanger network retrofit around a fixed network and without the need for additional heat transfer area and topology modifications. Heat transfer enhancement techniques are used to improve the energy performance of an existing heat exchanger network. A dominance ratio is explored to identify the best location to apply enhancement. Sensitivity analysis is used in finding the sequence of the most effective heat exchangers to enhance in order to improve the performance of the network. Sensitivity analysis introduced to study network flexibility is adapted to study heat transfer enhancement. Heat exchanger networks are complex systems with interactions between various components. A change in one component can have an effect on other downstream heat exchangers. Therefore, the proposed methodology presents a way of eliminating the need for additional heat transfer area after enhancement, while ensuring the stream target temperatures are met. This is based on a key optimisation strategy which depends on a trade-off between utility consumption and the need for additional heat transfer area.