Analysis Of Heat Exchanger Network Research Articles

Development of an efficient ammonia-water power cycle through heat exchanger network analysis and artificial neural network

• The heat integration of the reference Kalina cycle is studied. • Increasing the internal heat recovery can improve the thermal performance. • The improvement in COP can be as high as 8.5%. • A thermal relation embedded artificial neural network is proposed. • The generation performance can be increased by at least 25% at small training sets. This paper presents an efficient ammonia-water power cycle based on the basic Kalina cycle. The heat exchanger network analysis (HEN) is applied to identify all the possible heat-saving configurations. There are 13 different cycles proposed, and each is analyzed and optimized under the same working condition. The results show that there exists a saturation region between the cycle complexity and thermal performance. The thermal efficiency of the optimum cycle has been increased by 8.5% compared to that of the reference Kalina cycle under the heat source temperature of 550℃ and cooling temperature of 24.5℃. The artificial neural network (ANN) surrogate model is also provided to alternatively determine the maximum thermal efficiency under the condition that there is sufficient training data available. The results are compared with those obtained from the thermal model within 0.06% to 1.2% differences. The common practices of ANN in the thermal systems are treated as black-box. Ignorance of thermal principles can lead to a misleading result when using the black-box model, especially for the small size of the training set. In this paper, a thermally constrained ANN architecture is proposed by considering the first law of thermodynamics. The results indicate that, as compared to the black-box model, the generalization performance can be increased at least by 25% with the optimum network configuration of 15-6-3-3 for 50 instances in the training set.

Feasibility study on ammonia water absorption refrigeration cycle without distillation column

The water content in the refrigerant may undermine the cooling effect in ammonia water absorption refrigeration systems. Distillation column is normally implemented. The use of distillation columns, however, may increase system complexity, especially in practical operation. In fact, the distillation column can be eliminated under particular operating conditions. This paper presented an ammonia water absorption refrigeration cycle without distillation column, which is replaced by two separators and one heater. The resulting vapor is nearly pure with an ammonia mass fraction of 0.998. Heat exchanger network analysis is carried out for searching all the potential heating-saving possibilities. The thermal performance was improved by the combination of solution recirculation and absorption heat recovery, and the results indicated that the thermal performance has been increased by 42.6% than that of the basic cycle at certain working condition. The proposed cycle has limited ranges of working conditions operated under small temperature lifts,and the payback period is 4.28years.

Modeling and passivity properties of multi-producer district heating systems

We propose a comprehensive nonlinear ODE-based thermo-hydraulic model of a district heating system featuring several heat producers, consumers and storage devices which are interconnected through a distribution network of meshed topology whose temperature dynamics are explicitly considered. Moreover, we analyze the conditions under which the hydraulic and thermal subsystems of the model exhibit shifted passivity properties. For the hydraulic subsystem, our claims on passivity draw on the monotonicity of the vector field associated to the district heating system’s flow dynamics, which mainly codifies viscous friction effects on the system’s pressures. For the temperature dynamics, we propose a storage function based on the ectropy function of a thermodynamic system, recently used in the passivity analysis of heat exchanger networks.

Exergy analysis of multiple heat exchanger networks: An approach based on the irreversibility distribution ratio

This study presents a simple approach for the exergy analysis of heat exchanger networks (HENs). This approach is based on approximating the irreversibility distribution ratio (φ) and the exergy destruction of a HEN in a large natural gas refinery, without needing to design the individual heat exchangers. Only the thermodynamics properties and the temperatures of the hot and cold streams at the inlets and outlets of the heat exchangers, as well as a model assuming for temperature distributions along the exchangers, are required. The exergy efficiencies and destructions were calculated for the individual heat exchangers and therefore for the HEN by superposing them. Also, φ and Bejan number were obtained by approximating irreversibilities arising from the heat transfer and pressure drop due to fluid friction. The total φ (φtot) in the whole network was 0.188, with a Bejan number of 0.842. The results showed that the main source of the exergy destruction in the whole heat exchanger network of the plant is the irreversibility arising from heat transfer and the heat transfer irreversibility contribution to the total irreversibility in all the HENs was 84.2%. Moreover, the overall exergetic efficiency was 63.34%, which shows a great potential for improvement in the network system under consideration.

Preliminary plant design of thermochemical conversion for rice straw-based second-generation bioethanol production in West Java

Thermochemical conversion is selected in the design of a rice straw-based bioethanol production plant. This study examines the gasification and catalytic synthetic process technologies of rice straw into ethanol. The size of rice straw was reduced and dried before entering the gasification reactor to convert into syngas. The clean gas goes to the mixed alcohol synthesis process in a plug flow reactor with CuO/ZnO as a catalyst. The product is then purified through several separation methods, i.e., column distillation, stripping, and absorption. The controlled parameters for this plant are temperature, flow rate, pressure, level, and concentration. The paper describes the piping instrumentation diagram with a graphical representation of the equipment, piping, and instrumentation. A Heat Exchanger Network analysis achieves an efficiency of 34.4%. The electricity required is fulfilled by turbine expander for about 1,493 kW, and the rest of it is provided by PLN, besides an emergency generator sets. The capacity of this plant is 100,000 kL/year.

Industrial Energy Retrofit Planning Using Automated Retrofit Targeting

There is increasing pressure for industrial sites to minimise energy consumption. A long-term energy reduction strategy plays a critical role in realising energy savings. A key exchange mechanism of energy for sites is the heat exchanger network, which can be revamped and retrofitted to lift process energy efficiency. Retrofit analysis of heat exchanger networks commonly looks for a modified design that could provide significant energy savings for a comparatively modest investment but rarely does the analysis consider how retrofit projects can be sequenced as part of an energy retrofit plan while staying with capital investment constraints. The challenge in developing a long-term plan is the identification of projects and their ideal order out of the numerous possible combinations. This paper aims at developing an energy retrofit planning tool by performing a multi-stage retrofit analysis based on the automated retrofit targeting algorithm used to search for retrofit designs. The key output of the energy retrofit planning analysis is several sets of retrofit plans that can be further analysed for case-specific practicality (e.g., space, distance, and fluid compatibility) and developed into an energy retrofit plan, forming a part of a company’s overall energy strategy. The method is demonstrated using two industrial case studies with complex features and room for multiple sets of retrofit modifications. For the petrochemical complex case study, the study concludes that a 4-stage retrofit plan could be undertaken under a strategic investment plan that in total requires 11 modifications to the system, which generates 1.47 million EUR in annual profit with a payback of 1.75 years.

Advanced exergy analysis of heat exchanger network in a complex natural gas refinery

In this paper, the advanced exergy analysis was used to determine the avoidable and unavoidable exergy destructions of the heat exchanger networks (HENs) in a complex natural gas refinery in the South Pars gas field, focusing only on the improvement of the avoidable part. Exergy balances were evaluated for the HENs and the equations of advanced exergy destruction and exergetic efficiency for the HENs were developed. The total exergetic efficiency of the HEN in the plant was determined to be 62.8% that could be increased up to 84.2%, suggesting a high potential for improvement. Also, it was shown that the HEN1 had the most severe condition in the plant with the highest inefficiencies among the other networks. The avoidable and inevitable irreversibilities were calculated for all the heat exchangers running in the plant network. The advanced exergy analysis revealed that the exergy destruction had two major contributors. First, about 59% of the total irreversibility of the system was avoidable and could be eliminated by the well-known optimization techniques. Secondly, only 18 most inefficient heat exchangers (17% in numbers) contributed to more than 61% of the total exergy destruction in the plant network. Hence, there was a high potential for improvement of the operational cost in such a huge consuming energy system.

Design-Oriented Structural Controllability and Observability Analysis of Heat Exchanger Networks

The control-relevant design and analysis of Heat Exchanger Networks (HENs) is an essential issue in terms of the design and intensification of sustainable production systems. The structural controllability and observability of HENs should be studied based on their dynamical model. Recently, a maximum matching based algorithm was developed to determine the locations of the minimum number of actuators and sensors needed to ensure the controllability and observability of linear dynamical systems. In this paper, the ability of concentrated parameter state-space models of the heat exchanger units to serve as building blocks of the network of state variables in HENs, and the use of the resultant network of state variables to study the control of relevant topologies and properties of HENs is highlighted. Based on the results of the systematic analysis, the structural patterns that facilitate the control and observation of HENs with a relatively small number of actuators and sensors were determined. Two methods were proposed to define the sets of additional actuators and sensors which are required to improve the operability of the network by decreasing the order of the controlled system. The first method is based on the interpretation of the placement of the sensors and actuators as a set cover problem, while the second one uses two network science-based measures: closeness centrality and betweenness centrality. The proposed methodologies are demonstrated on a benchmark example that is well covered in the literature.

Heat integration of ammonia-water absorption refrigeration system through heat-exchanger network analysis

Abstract The heat integration of existing single-effect ammonia-water absorption system is studied. A set of possible heat modifications involving with absorption heat or rectification heat recovery are identified on energy transfer diagram, the performance of each heat modification is studied and compared, and the interaction of heat transfer in generator, absorber, rectifier and solution heat exchanger is investigated through different combinations of heat modifications. There are two approaches of increasing thermal performance, one is aimed to increase the feed temperature of the distillation column by isolating heat exchanger components. The purpose of the other approach is to reduce heat consumption through heat integration by using bridge analysis. The two approaches can both boost the thermal performance effectively. The results demonstrate 22% increases in Coefficient of Performance (COP) compared with traditional single-effect cycle under certain working conditions. In general, obtaining the maximum heat saving capacity in advance under different working conditions is necessary either for retrofit or in preliminary design stage. In this paper, the selection guidance of suitable cycle under different working conditions is provided.

Comparative feasibility study of CO2 capture in hollowfiber membrane processes based on process models and heat exchanger analysis

Carbon dioxide capture based on membrane separation process is one of the most promising methods to reduce greenhouse gases emissions. Many studies concerning economic competitiveness of membrane separation processes have been conducted. Heat exchangers can be effectively used to reduce the total energy consumption in the membrane separation process. The two-stage membrane separation processes considered in this work include heat exchangers with H2O sweep. The necessity of this work arose from the need to apply the heat exchanger network analysis in order to identify the optimal process configuration based on the process models. Typical multicomponent separation models for the counter-current flow pattern using hollowfiber membranes are validated with experimental data. Effects of the pressure ratio and membrane area to achieve a target CO2 purity (90%) and recovery (90%) are investigated. Energy analysis including heat recovery and utility power are performed using pinch technology. The results show that significant amount of total energy (1.31MJ/kg CO2) can be reduced by introducing heat exchangers compared to the two-stage separation process without heat exchangers.

Analysis of Heat Exchanger Network of Distillation Unit of Shiraz Oil Refinery

Analysis of Heat Exchanger Network of Distillation Unit of Shiraz Oil Refinery

Techno-economic Evaluation of Quality Improvement of Heavy Gas Oil with Different Processes

Abstract Nowadays, high quality diesel fuels can only be produced by the hydrotreatment of various refinery streams. Preparing catalytic experiments and process engineering calculations are inevitable for selecting the most technically and economically appropriate process. There is limited information in the free literature about the complex approach of hydrotreating processes that deal with both the catalytic and process issues. This paper summarizes the results of an engineering study to evaluate the techno-economic feasibility of different types of hydrotreating processes for producing high quality gas oil blending components from heavy gas oil fraction. Hydrotreatment of feed in one-stage on nickel(Ni) molybdenum(Mo)/alumina and in two-stage on NiMo/alumina followed by on platinum(Pt) palladium(Pd)/zeolite catalysts were investigated. In one stage hydroprocessing sulphur and polyaromatic contents of the products met the requirements of the standard only if strict process parameters were applied (temperature > 370 °C and Liquid Hourly Space Velocity −1 ) which resulted in operation problems and product loss, moreover the advantageous process parameters of hydrodesulphurization and hydrodearomatization did not coincide. In two-stage hydrotreating results showed that the advantageous process parameters for reduction of sulphur and aromatics coincided. Advantageous process parameters to produce gas oil of quality meeting the requirement of the standard were determined. Based on the experimental results model for both alternatives was prepared, and heat and material balances were determined. By applying two step hydrotreating, the yield of gas oil having low sulphur and aromatic content was 6.2% higher than that obtained in one step. Heat exchanger network analysis and sizing of main equipments were accomplished. Operating and investment costs were estimated for both processes, which showed that all the cost elements were higher for the two-stage process. But it provides the following advantages in comparison to one-stage process: higher yield of gas oil, better product quality allowing the application of low value hydrocarbon streams in higher quantity at the blending, the lower density of products would be the source of extra profit due to diesel fuels are sold on volume basis at the petrol stations. Estimation of emission potential of feed and products was prepared, too. This showed that the hydrotreating of heavy gas oil contributes to significant reduction in emission of particulate matter, hydrocarbons and carbon monoxide, but the effect on the emission of nitrogen oxides was scarce. Product of two-stage process provided considerably greater decrease in carbon monoxide and hydrocarbon emissions comparing to the one-stage alternative (52% vs. 14% and 54% vs. 14%). Consequently, the estimation of emission potential of hydrotreated products can be used as one of the parameters for selecting between various process alternatives.

Techno-economic evaluation of quality improvement of heavy gas oil with different processes

Nowadays, high quality diesel fuels can only be produced by the hydrotreatment of various refinery streams. Preparing catalytic experiments and process engineering calculations are inevitable for selecting the most technically and economically appropriate process. There is limited information in the free literature about the complex approach of hydrotreating processes that deal with both the catalytic and process issues. This paper summarizes the results of an engineering study to evaluate the techno-economic feasibility of different types of hydrotreating processes for producing high quality gas oil blending components from heavy gas oil fraction. Hydrotreatment of feed in one-stage on nickel(Ni) molybdenum(Mo)/alumina and in two-stage on NiMo/alumina followed by on platinum(Pt) palladium(Pd)/zeolite catalysts were investigated. In one stage hydroprocessing sulphur and polyaromatic contents of the products met the requirements of the standard only if strict process parameters were applied (temperature > 370 °C and Liquid Hourly Space Velocity < 1.5h−1) which resulted in operation problems and product loss, moreover the advantageous process parameters of hydrodesulphurization and hydrodearomatization did not coincide. In two-stage hydrotreating results showed that the advantageous process parameters for reduction of sulphur and aromatics coincided. Advantageous process parameters to produce gas oil of quality meeting the requirement of the standard were determined. Based on the experimental results model for both alternatives was prepared, and heat and material balances were determined. By applying two step hydrotreating, the yield of gas oil having low sulphur and aromatic content was 6.2% higher than that obtained in one step. Heat exchanger network analysis and sizing of main equipments were accomplished. Operating and investment costs were estimated for both processes, which showed that all the cost elements were higher for the two-stage process. But it provides the following advantages in comparison to one-stage process: higher yield of gas oil, better product quality allowing the application of low value hydrocarbon streams in higher quantity at the blending, the lower density of products would be the source of extra profit due to diesel fuels are sold on volume basis at the petrol stations. Estimation of emission potential of feed and products was prepared, too. This showed that the hydrotreating of heavy gas oil contributes to significant reduction in emission of particulate matter, hydrocarbons and carbon monoxide, but the effect on the emission of nitrogen oxides was scarce. Product of two-stage process provided considerably greater decrease in carbon monoxide and hydrocarbon emissions comparing to the one-stage alternative (52% vs. 14% and 54% vs. 14%). Consequently, the estimation of emission potential of hydrotreated products can be used as one of the parameters for selecting between various process alternatives.

Analysis of heat exchanger network for temperature fluctuation

Subject to temperature disturbance, exchangers in heat exchanger network will interact. It is necessary to evaluate the degree of temperature fluctuation in the network. There is inherently linear relationship between output and inlet temperatures of heat exchanger network. Based on this, the concept of temperature-change sensitivity coefficient was put forward. Quantitative influence of temperature fluctuation in the network was carried out in order to examine transmission character of temperature fluctuation in the system. And the information was obtained for improving the design quality of heat exchanger network. Favorable results were obtained by the introduced method compared with the experimental results. These results will assist engineers to distinguish primary and secondary influencing factors, which can be used in observing and controlling influencing factors accurately.

Design and analysis of heat exchanger networks for integrated Ca-looping systems

One of the main challenges of carbon capture and storage technologies deals with the energy penalty associated with CO2 separation and compression processes. Thus, heat integration plays an essential role in the improvement of these systems’ efficiencies. CO2 capture systems based on Ca-looping process present a great potential for residual heat integration with a new supercritical power plant. The pinch methodology is applied in this study to define the minimum energy requirements of the process and to design four configurations for the required heat exchanger network. The Second Law of Thermodynamics represents a powerful tool for reducing the energy demand since identifying the exergy losses of the system serves to allocate inefficiencies. In parallel, an economic analysis is required to asses the cost reduction achieved by each configuration. This work presents a combination of pinch methodology with economic and exergetic analyses to select the more appropriate configuration of heat exchanger network. The lower costs and minor destroyed exergy obtained for the best proposed network result in a of 0.91% global energy efficiency increase.

Entransy-dissipation-based thermal resistance analysis of heat exchanger networks

Heat exchanger network optimization has an important role in high-efficiency energy utilization and energy conservation. The thermal resistance of a heat exchanger network is defined based on its entransy dissipation. In two-stream heat exchanger networks, only heat exchanges between hot and cold fluids are considered. Thermal resistance analysis indicates that the maximum heat transfer rate between two fluids corresponds to the minimum entransy-dissipation-based thermal resistance; i.e. the minimum thermal resistance principle can be exploited in optimizing heat exchanger networks.

Thermohydraulic Simulation of Heat Exchanger Networks

This paper presents a simulation scheme of heat exchanger networks considering thermal and hydraulic effects simultaneously. The determination of network temperatures is carried out together with the evaluation of flow rates and pressures along the network, considering head losses in heat exchangers and associated piping. The model encompasses two systems of equations: a network hydraulic model, composed by a nonlinear system of mass balances and fluid flow equations, and an energy model, represented by a linear system of energy balances and heat exchanger equations. The mathematical structure is based on a matrix representation of the network. The proposed model allows a more realistic analysis of heat exchanger networks where flow rates are constrained by limitations of hydraulic facilities. The utilization of the simulation scheme is illustrated by the analysis of a cooling water system.

Applying process design software for capacity increase and revamp of distillation units

The paper presents the results of feasibility study for increase of crude processing capacity and improves of energy efficiency of crude oil distillation units. Results introduce that boosting up the distillation capacity was solved while keeping the flexibility of units for processing different type crude oils. Analysis of heat exchanger network resulted significant reduction in fuel consumption and in CO2 emission (93 × 106 GJ year−1 and 3,030 tCO2 year−1, respectively). Modification of furnace of one of the distillation units showed 63 GJ kt crude −1 saving in energy and 4.5 tCO2 kt crude −1 decrease in emission.

Exergoeconomic Analysis of Heat Exchanger Networks for Optimum Minimum Approach Temperature

AbstractHeat exchanger networks (HENs) design for optimum minimum approach temperature is presented using exergoeconomic analysis. Cold and hot utilities are integrated with process streams into T‐H plots, forming balanced composite curves, based on pinch technology. Exergy consumption of heat transfer in HENs is calculated using subsection integral on balanced composite curves. Exergy consumption expense substitutes utilities cost as operating cost. The objective function based on exergoeconomics is proposed, which determines the optimum minimum approach temperature of HENs. Numerical results in the cases demonstrate the validity of the proposed approach. Some measures of decreasing energy consumption are disclosed in the dealing process as well.

Fluid dynamical considerations on heat exchanger networks

The synthesis and analysis of heat exchanger networks are issues of great industrial interest due to the possibilities of decreasing plant costs, through the reduction of the utilities consumption and/or the number of equipments, in a grassroot design or retrofitting an existent network. The present paper explores a new design algorithm based on the Total Annual Cost (TAC) optimization for a thermal equipment, with mean tubeside and shellside flow velocities constraints, studying also the influence of pumping cost in the network’s final cost.