A combined numerical and visualization tool for utility targeting and heat exchanger network retrofitting

This paper addresses the problem of a heat exchanger network (HEN) retrofit considering process changes. Traditionally it is a common practice to fix process conditions before a HEN is retrofitted. However, it has been realized that there exists strong interactions between HENs and processes, and it should simultaneously consider the changes to process conditions (e.g. flow rates, temperatures) and the HEN retrofit. In this paper, new insights for process changes and their impacts on HEN retrofit have been developed and the T-H diagram is used to represent the interactions. On the basis of the newly developed understanding, a systematic method has been developed to deal with process changes and HEN topological changes in a simultaneous way. To demonstrate this, a short-cut crude distillation model has been built up that relates stream temperatures and flow rates to process conditions. This model has been combined with the model for HEN topological changes proposed by Zhu and Asante, which forms a complete model for optimizing the tradeoff between HEN retrofit and process changes. The case study shows significant cost savings by considering process changes and HEN modifications simultaneously.

A simultaneous optimization approach for the retrofit of heat exchanger networks (HENs) by Ma Kin Lung Ronald thesis 1999 xii, 124, 31 leaves : ill. ; 30 cm Retrofit design of Heat Exchanger Networks (HENs) is an increasingly significant industrial…Read more ›

In the situation of high prices and depletion of the world energy, one way for energy management is process heat integration. In Specific, pinch technology has demonstrated that good process integration pays off through simplicity of plant design and good use of energy and capital. The principle is to predict what should be achieved (targeting), and then to set out how to achieve it (design). For modification of existing plants, retrofitting is used with the same thermodynamic principles that area of an aromatics plant, retrofitting the heat exchanger network to obtain the best design which results in high degree of energy recovery. In this area of plant, nine heat exchangers can be found. The streams that involve in this pinch analysis can be grouped into two types; hot and cold streams, which are thirty and twenty on for hot and cold streams respectively. First of all, the target of energy savings will be conducted for the specified payback period. In this step the problem table analysis and composite curves have been done in order to find the area and energy target. The result of these targets shows the very low payback period. The retrofit procedure then can be done by constructing the grid diagram and finding the heat exchangers crossing pinch point. Eliminating these exchangers plus adding some area of heat exchangers result in energy saving about 10-20%.

Optimal assignment of multiple utilities in heat exchange networks

Chapter 10 Pinch point analysis

Minimizing investment cost for multi-period heat exchanger network retrofit by matching heat transfer areas with different strategies

A novel Heat Exchanger Network Bridge Retrofit method using the Modified Energy Transfer Diagram

The retrofit of heat exchanger networks (HENs) is very important to high-energy consumption enterprises for saving energy, protecting the environment, and improving their market competitiveness. It is also an important branch of heat integration research. The retrofit of HENs is more difficult than grassroots design because of the greater number of constraints. In this paper, the novel mathematical model for HEN retrofit is based on the stepwise superstructure model from Yee et al. The existing heat exchangers and structures are applied fully in the retrofitted HEN, and the modification cost is decreased with energy saving. The hybrid genetic algorithm is used to solve the mixed integer nonlinear program problem. Two examples are given to show the improved effect of the novel retrofit method with the minimum of the total cost of new heat exchangers and newly added areas of the existing heat exchangers and repiping and utilities.

Heat exchanger network (HEN) retrofitting improves heat recovery and thus reduces energy required in existing plants. This can be achieved by either increasing the heat transfer area and/or using heat transfer enhancements to increase heat transfer coefficients. There is an increasing interest in HEN retrofitting as can be seen from 20 journal papers since 2009 (about 5 years) compared to 15 in the 10-year period 1999–2008. In total, there are about 60 journal papers on HEN retrofitting since the year 1985; however, in the past 20 years, there has been no review paper summarizing HEN retrofitting methodologies and their applications. This provides the motivation for this review paper. HEN retrofitting methods can be classified into three broad categories, namely, mathematical programming based methods, pinch analysis based methods, and hybrid methods according to their underlying approach. Further, some HEN retrofitting methods include pressure drop considerations, and HEN retrofitting can be using heat t...

The natural gas separation process is an extremely high energy-consuming process. It consists of distillation units and cryogenic heat exchangers requiring refrigerant. This leads to high operating costs. This study focuses on the gas separation unit I which has three main distillation columns: a demethanizer, deethananizer, and depropanizer. A simulation model of the columns was created using the Pro/II software program and the pinch technology technique to determine the excess energy by modifying the existing process to reach high energy savings. The pinch analysis was divided into two parts: distillation column targeting and heat exchanger networks (HENS). The simulation model gave equilibrium and thermodynamics data used for generating column grand composite curves (CGCCs) and column composite curve (CCCs). The demethanizer was modeled as four conventional columns connected in the series and a pinch point was found on CGCC which meant that this column was energy efficient. The depropanizer had one pinch point found in CGCC, while pinch point was not found in CGCC of the deethanizer. The background process was studied using six hot streams and seven cold streams to generate a composite curve for the process.

Targeting the maximum heat recovery for systems with heat losses and heat gains

Ventilation heat loss is one of the most important factors contributing to energy performance of greenhouses. This paper suggests a systematic method based on dynamic pinch analysis (PA) to design an integrated heating, cooling, and ventilation system that uses ventilation waste heat in a cost-effective and energy efficient way. A heat recovery system including an air handling unit, borehole thermal storage, and a heat pump is proposed to investigate all heat integration scenarios for an entire year. In the first step, the heat integration scenarios are reduced to a few typical days using a clustering technique. Then, a generic methodology for designing a heat exchanger network (HEN) for a dynamic system, ensuring both direct and indirect heat recovery, is presented and a set of HENs are designed according to the conditions of typical days. Afterwards, the best HEN design is selected among all design alternatives using a techno-economic analysis. The whole procedure is applied to a commercial greenhouse and the best HEN configuration and required equipment sizes are calculated. It is shown that the best-performing design for the greenhouse under study produces primary energy savings of 57%, resulting in the shortest payback period of 9.5 years among all design alternatives.

In this chapter, a new methodology for heat exchanger networks synthesis, extending traditional pinch technology to include exergy-destruction cost, is described and employed for practical applications. In the proposed approach, the cost rate of exergy destruction substitutes the utility cost in a trade-off between the operating and capital costs in the conventional pinch analysis to determine the optimum minimum approach temperature, ΔT min, in the energy assessment of heat exchanger networks (HENs). It is demonstrated that the balanced composite curves can be used directly in the calculation of the exergy destruction, heat recovery, and heat-transfer area for a specified minimum approach temperature. Moreover, it is showed that the grand composite curve can be utilized for determination of the optimal external utility allocation. The inclusion of thermal exergy destruction into pinch analysis decreases the optimum value of network ΔT min, due to increase in the system operating costs by considering both the external utility requirements and internal exergy destruction. The results of this assessment provide a better and more realistic utilization of external utilities considers the required capital investment. Two case studies are presented to show how to apply the proposed methodology effectively and practically. Case studies are analyzed using Aspen energy analyzer software.

This paper presents a case study of heat exchanger network (HEN) retrofit with the objective to reduce the utilities consumption in a biodiesel production process. Pinch analysis studies allow determining the minimum duty utilities as well the maximum of heat recovery. The existence of heat exchangers for heat recovery already running in the process causes a serious restriction for the implementation of grassroot HEN design based on pinch studies. Maintaining the existing HEN, a set of alternatives with additional heat exchangers was created and analysed using some industrial advice and selection criteria. The final proposed solution allows to increase the actual 18 % of recovery heat of the all heating needs of the process to 23 %, with an estimated annual saving in hot utility of 35 k€/y.

On-line cleaning of heat exchangers operating in a heat exchanger network (HEN) is aimed at preventing unnecessary losses of energy that can be recovered in HEN. If time behaviour of fouling in each heat exchanger can be estimated on the basis of past experience, then the optimal schedule of cleaning interventions can be determined by maximizing the objective function expressing the economic value of avoidable reduction in the energy recovery [1]. The crucial assumption for the presented paper is that on-line measurements of the mass flow and inlet and outlet temperature are available for each process stream. That made possible to evaluate fouling-induced reduction in the recovered energy flow using neural network model of HEN based on the measurements. The neural network (NN) model of HEN was applied in diagnostics of deposits influence on heat recovery in HEN by taking into account the time behaviour of fouling approximated by NN. The application of a neural network to the evaluation of changes in the energy flow recovered in a HEN has been tested using a simulated heat exchanger network as a reference. The simulation of HEN (implemented in MATLAB software) was based on a dynamic HEN model employing heat exchanger decomposition into interconnected cells whose overall dynamic behaviour is described by an array of lumped-parameter models. Computational aspects of the approach outlined above were studied on the example of a HEN featuring 26 process streams and 31 heat exchangers, operating in a crude distillation unit of 440 t/h processing capacity. A diagnostics of deposits influence on heat recovery in HEN makes it possible to attain a saving of about 5% of recoverable energy with the annual value of about 0,86 million USD.