Retrofit Problems Research Articles

Retrofit of Heat Exchanger Networks for Multiperiod Operations by Matching Heat Transfer Areas in Reverse Order

This work presents a retrofitting approach for heat exchanger networks (HENs) for single-period and multiple-period operations, aiming at the improvement of operation flexibility of HENs. A two-step method is proposed to solve the problems of redundant heat transfer areas in multiperiod HENs and the incomplete utilization of existing heat-transfer areas in HEN retrofit. In this approach, a multiperiod HEN design model is first solved to target the retrofit. Then, the final HEN is obtained by matching the required heat exchangers with the existing ones in reverse order. The proposed matching procedure is provided in detail and mathematically proven. Three case studies are employed to illustrate the advantages of the proposed method for solving the problems in the multiperiod HEN retrofit. In addition, the proposed method is extended to solving single-period HEN retrofit problems. Results indicate that the proposed method makes full use of the existing heat exchangers to reduce retrofit costs and increases the energy utilization efficiency of the HEN in multiperiod operations. The proposed method is simple and easy to implement. It can reduce the computational load and the difficulties in solving practical industrial problems.

Systematic retrofit design with Response Surface Method and process integration techniques: A case study for the retrofit of a hydrocarbon fractionation plant

This paper demonstrates the Retrofit Design Approach (RDA) and Response Surface Methodology (RSM) for the retrofit of industrial plants in which assessment of design options for improving existing processes in a site-wide and integrated manner is not straightforward, due to complex design interactions in the process. The design methodology applied in this study is based on the systematic use of a process simulator which is used to identify promising variables through sensitivity analysis. Hence, the most important factors are determined and a reduced model is constructed based on RSM. An optimization framework is then built using the reduced model based on key selected variables, which is optimized to find optimal conditions and performance of the process. This design methodology provides strategic guidelines for determining the most cost-effective design options. The retrofit of a hydrocarbon fractionation plant is presented as an industrial case study. This includes a large number of design options with different process configurations and operating conditions due to the interconnection of distillation columns in sequence and the integrated heat recovery within the plant. The case study results demonstrate the applicability of the proposed approach which is able to effectively deal with a large retrofit problems. This is possible with the aid of process simulation and RSM producing a reduced model which requires considerably less computational effort to solve.

Improved heat exchanger network retrofitting using exchanger reassignment strategies and multi-objective optimization

HEN (heat exchanger network) retrofitting is useful to reduce energy consumption in the existing process industries. In this study, several ERS (exchanger reassignment strategies) for HEN retrofitting are proposed and tested by performing single objective optimization on retrofit problems using IDE (integrated differential evolution). A reassignment strategy which includes practical considerations is also developed and used in MOO (multi-objective optimization) on retrofit problems. Results of application problems show that ERS play an important role in obtaining better solutions, and that MOO provides many optimal solutions for HEN retrofitting to decision makers for choosing one of them for implementation.

Modelling and optimization of retrofitting residential energy systems at the urban scale

Local governments and property developers are increasingly seeking robust models for strategic planning of retrofitting residential energy systems. Strategic planning here infers making decisions on technology upgrades at the concept design stage. This represents a problem with many degrees of freedom. Optimization models offer a solution. The presentation of the tool RESCOM is the focus of this paper, a MILP (mixed integer linear program) that builds upon previous models of urban energy systems and extends these efforts by incorporating both demand side technologies, and explicit spatial and temporal resolution.A test case for a London borough describes the result of applying spatial optimization and demonstrates the accessibility of this program to decision makers. Results provide the optimal configuration of supply side and demand side technologies required to satisfy thermal energy requirements for a range of scenarios. The presented approach solves retrofit problems at urban scale in an efficient and thorough manner, providing an expandable framework towards providing solutions for the selection and operation of complex energy systems.

New MILP-based iterative approach for retrofitting heat exchanger networks with conventional network structure modifications

Conventional network structure modifications for retrofitting heat exchanger networks (HENs) usually require a large network superstructure, which might lead to very large scale retrofit models, and thus increases the computational difficulties of optimization, especially for industrial applications. This paper presents a novel optimization approach of retrofitting HENs for both small scale and industrial scale problems. To overcome the drawback of the existing retrofit research, a simple but efficient method is proposed to determine the network retrofit superstructure based on the concept of pinching match. Then two optimization stages (network structure optimization and investment optimization) are solved with the MILP-based iteration method that has been developed. The proposed approach has many benefits for solving HEN retrofit problems. First, smaller size of retrofit superstructure is provided based on the pinching match analysis. Second, the MILP-based iteration method developed converts conventional a mixed integer non-linear programming (MINLP) to a mixed integer linear programming (MILP), and significantly reduce the computational difficulties of nonlinear programming associated with configurational changes or structural modifications for existing heat exchanging arrangements, which is upgraded based on the MILP-based iterative method proposed by Pan et al. (2012a) for retrofitting HENs with heat transfer intensifications, as the earlier work was only applicable to the cases without network topology modification. In case studies, the new proposed approach is compared with the existing methods in two literature examples and one industrial problem, demonstrating that the new proposed approach is able to obtain better and more realistic solutions for HEN retrofitting considering the economic trade-offs between energy savings and investments.

Heat transfer intensified techniques for retrofitting heat exchanger networks in practical implementation

This paper addresses the implementation of heat transfer intensified techniques in practical heat exchanger networks (HENs). The issues considered in this paper not previously addressed include heat transfer intensification, changes in multiple tube passes and shell passes and temperature dependence of stream heat capacity (CP). These must be formulated into a new complex nonlinear model not reported previously in the existing literature. To solve such retrofit problems, an MILP-based iterative method has developed based on the work proposed by Pan et al. (2012a). A large scale example is presented to demonstrate the validity and efficiency of the proposed approach.

Retrofit of a Heat-Exchanger Network by Considering Heat-Transfer Enhancement and Fouling

Many design methods for the retrofit of heat-exchanger networks have been proposed during the last 3 decades. Conventional retrofit methods use additional area to accommodate the increasing heat duty. However, the implementation of additional area may prove difficult because of topology, safety, and downtime constraints. This problem can be mitigated through the use of heat-transfer enhancement. This Article investigates the influence of heat-transfer enhancement on fouling in heat-exchanger networks. A novel design approach is used to solve heat-exchanger network retrofit problems on the basis of heat-transfer enhancement by considering fouling. Simulated annealing is used to optimize the retrofit problem under fouling conditions. The results show that heat-transfer enhancement is a very attractive option for retrofitting when fouling is considered. The consideration of fouling in heat-transfer enhancement has the potential to make a significant impact on retrofit design and to make the design more cost-effective than conventional design approaches.

A novel optimization approach of improving energy recovery in retrofitting heat exchanger network with exchanger details

Improving energy recovery with retrofitting heat exchanger network has been widely studied in academic and industrial communities. Distinct from most of existing works on HEN retrofit neglecting exchanger geometry, this paper presents a novel optimization method for dealing with the main exchanger geometry details in HEN retrofit problems. The addressed details of shell and tube exchangers include tube passes, shell passes, heat transfer intensification, logarithmic mean temperature difference (LMTD), and LMTD correction factor (FT), which are systematically identified under given objective function and topological constraints in the existing heat recovery systems. Based on the recent works proposed by Pan et al. [1] on HEN retrofit scenarios addressing network topology modification, an efficient optimization framework, consisting of two optimization stages with the implementation of MILP-based iterative method [2], has been developed to deal with the computational difficulties associated with the nonlinearity of LMTD and FT. Case study from literature examples are carried out to demonstrate the validity and soundness of the proposed approach, showing that the new proposed approach is able to provide realistic and practical solutions for debottlenecking of HEN with systematic consideration of exchanger details.

A disjunctive programming model and a rolling horizon algorithm for optimal multiperiod capacity expansion in a multiproduct batch plant

This paper addresses a multiperiod mixed integer nonlinear programming problem for the capacity expansion of multiproduct batch plants. Given a certain batch plant with its current configuration, product recipes, and growing production targets, modular expansions are wanted so that new demand can be met. Unlike most work for the batch retrofit problem, a multiperiod disjunctive model is presented, such that long term investments and expansions can be planned out in advance. To solve the model we propose a rolling horizon algorithm that further exploits the advantages of a disjunctive programming model. Empirical work shows that the rolling horizon algorithm is very effective on finding near optimal solutions to large instances with a considerable number of time periods. Furthermore, the solution found by the proposed algorithm can be used as a starting solution for the direct method to the original problem delivering a global optimal solution.

Heat exchanger network retrofit optimization involving heat transfer enhancement

Heat exchanger network retrofit plays an important role in energy saving in process industry. Many design methods for the retrofit of heat exchanger networks have been proposed during the last three decades. Conventional retrofit methods rely heavily on topology modifications which often result in a long retrofit duration and high initial costs. Moreover, the addition of extra surface area to the heat exchanger can prove difficult due to topology, safety and downtime constraints. Both of these problems can be avoided through the use of heat transfer enhancement in heat exchanger network retrofit. This paper presents a novel design approach to solve heat exchanger network retrofit problems based on heat transfer enhancement. An optimisation method based on simulated annealing has been developed to find the appropriate heat exchangers to be enhanced and to calculate the level of enhancement required. The physical insight of enhanced exchangers is also analysed. The new methodology allows several possible retrofit strategies using different retrofit methods be determined. Comparison of these retrofit strategies demonstrates that retrofit modification duration and payback time are reduced when heat transfer enhancement is utilised. Heat transfer enhancement can be also used as a substitute for increased heat exchanger network surface area to reduce retrofit investment costs.

Application of intensified heat transfer for the retrofit of heat exchanger network

A number of design methods have been proposed for the retrofit of heat exchanger networks (HEN) during the last three decades. Although considerable potential for energy savings can be identified from conventional retrofit approaches, the proposed solutions have rarely been adopted in practice, due to significant topology modifications required and resulting engineering complexities during implementation. The intensification of heat transfer for conventional shell-and-tube heat exchangers can eliminate the difficulties of implementing retrofit in HEN which are commonly restricted by topology, safety and maintenance constraints, and includes high capital costs for replacing equipment and pipelines. This paper presents a novel design approach to solve HEN retrofit problems based on heat transfer enhancement. A mathematical model has been developed to evaluate shell-and-tube heat exchanger performances, with which heat-transfer coefficients and pressure drops for both fluids in tube and shell sides are obtained. The developed models have been compared with the Bell-Delaware, simplified Tinker and Wills–Johnston methods and tested with the HTRI® and HEXTRAN® software packages. This demonstrates that the new model is much simpler but can give reliable results in most cases. For the debottlenecking of HEN, four heuristic rules are proposed to identify the most appropriate heat exchangers requiring heat transfer enhancements in the HEN. The application of this new design approach allows a significant improvement in energy recovery without fundamental structural modifications to the network.

Heat Exchanger Network Retrofit Through Heat Transfer Enhancement

Many design methods for the retrofit of heat exchanger network (HEN) have been proposed during the last three decades. The conventional methods used to solve retrofit problems often involve too many topology modifications and are limited by the size and complexity of retrofit problems. Moreover, practical implementation of the additional area in retrofit problems can be difficult due to topology, safety and downtime constraints. Heat transfer enhancement (HTE) can increase heat transfer coefficient so as to make exchangers smaller. The application of HTE provides an opportunity to avoid high capital costs for replacing equipments and pipelines in topology modification and the difficulties of additional area implementation in retrofit design. This paper presents a novel design approach to solve HEN retrofit problems based on HTE. An optimisation method based on simulated annealing has been developed to find the appropriate heat exchangers to be enhanced and augmentation level of enhancement. The new methodology allows enhancement to be added to tube-side or shell-side or both, which depends on the heat transfer control side. The application of this new methodology can bring a significant energy saving in retrofit design without any topology modification, or investment reduction in retrofit design with topology modifications. Copyright ? 2011, AIDIC Servizi S.r.l.

Energy Requirement of a Distillation/Membrane Parallel Hybrid: A Thermodynamic Approach

This paper presents a new thermodynamic approach, based on the notion of power of separation, for the retrofit problem of finding the minimal energy requirement of an existing binary distillation column when coupling it in parallel with a membrane unit. A new geometric interpretation of this concept, which is supported by a rigorous mathematical proof, is introduced. From it results an efficient and accurate shortcut method to tackle the aforementioned problem. Numerical examples are considered for the energy intensive separation of olefins from paraffins, namely the retrofit of a C3-splitter and the retrofit of a C2-splitter through parallel hybridization with facilitated transport membranes. The results of the proposed shortcut method are compared to those obtained via the nonlinear programming optimization solvers GAMS-CONOPT and GAMS-CoinIpopt for a superstructure based problem formulation, which act as a reference. In both case studies, the shortcut method results in a significant reduction in proble...

A two-stage stochastic programming model for transportation network protection

Network protection against natural and human-caused hazards has become a topical research theme in engineering and social sciences. This paper focuses on the problem of allocating limited retrofit resources over multiple highway bridges to improve the resilience and robustness of the entire transportation system in question. The main modeling challenges in network retrofit problems are to capture the interdependencies among individual transportation facilities and to cope with the extremely high uncertainty in the decision environment. In this paper, we model the network retrofit problem as a two-stage stochastic programming problem that optimizes a mean-risk objective of the system loss. This formulation hedges well against uncertainty, but also imposes computational challenges due to involvement of integer decision variables and increased dimension of the problem. An efficient algorithm is developed, via extending the well-known L-shaped method using generalized benders decomposition, to efficiently handle the binary integer variables in the first stage and the nonlinear recourse in the second stage of the model formulation. The proposed modeling and solution methods are general and can be applied to other network design problems as well.

A PATTERN FRAMEWORK FOR SOFTWARE QUALITY ASSESSMENT AND TRADEOFF ANALYSIS

The earliest design decisions often have a significant impact on software quality and are the most costly to revoke. One of the challenges in architecture design is to reduce the frequency of retrofit problems in software designs; not being able to improve the quality of a system cost effectively, a problem which frequently occurs during late stages. Software architecture assessment is essential in the design of a high quality system. However, assessing the effect of individual design decisions with respect to quality is often complicated by the fact that it is hard to identify exactly how particular qualities and quality factors are improved or impaired by design decisions. In this paper we present a framework that formalizes some of the relationships between software architecture and software quality; it compiles existing design knowledge (quality improving patterns) in a format suitable for architecture assessment. This framework may prevent the retrofit problem and can assist in reasoning about intra- and inter- quality tradeoffs. We illustrate our framework by creating an instance for it for the qualities usability, security and safety.

Multiobjective supply chain design under uncertainty

In this article, the design and retrofit problem of a supply chain (SC) consisting of several production plants, warehouses and markets, and the associated distribution systems, is considered. The first problem formulation modifies and extends other previously presented models, in order to include several essential characteristics for realistically representing the consequences of design decisions on the SC performance. Then, in order to take into account the effects of the uncertainty in the production scenario, a two-stage stochastic model is constructed. The problem objective, i.e., SC performance, is assessed by taking into account not only the profit over the time horizon, but also the resulting demand satisfaction. This approach can be used to obtain different kinds of solutions, that may be valuable at different levels. On one hand, the SC configurations obtained by means of deterministic mathematical programming can be compared with those determined by different stochastic scenarios representing different approaches to face uncertainty. Additionally, this approach enables to consider and manage the financial risk associated to the different design options, resulting in a set of Pareto optimal solutions that can be used for decision-making.

Design and Retrofit of Reliable Sensor Networks

This work proposes an approach to sensor network design and retrofitting that combines quantitative process knowledge and fault tree analysis into a new methodology for evaluating the reliability of process variable estimation, taking into account both hardware and functional redundancy. The reliability of estimating process variables is used to determine the sensor network reliability, which, in turn, is used for the design and retrofit of the network. Thus, a reliable sensor network design and retrofit problem is formulated as a mathematical programming optimization problem and solved using genetic algorithms. The performance of this proposed methodology is compared with the current approaches using different case studies and handling several scenarios.

Synthesis of robust water reuse networks for single-component retrofit problems using symmetric fuzzy linear programming

Water integration techniques can be used to minimize the utility water consumption and effluent generation of process plants through the implementation of reuse or recycle networks. There are a number of graphical and mathematical programming techniques available for the synthesis of such water reuse networks. However, effective use of these methods requires the availability of reliable process data, which in reality might be difficult to acquire. This paper describes a procedure for the synthesis of robust water reuse networks from imprecise data using symmetric fuzzy linear programming (SFLP). Two model variants, one based on mass exchange units and the other on source/sink allocation, are presented. Each variant is illustrated with a numerical example.

Retrofit of multiproduct batch plants through generalized disjunctive programming

The retrofit problem for multiproduct batch plants deals with the modification of the original structure of the plant to meet new production conditions such as the introduction of new products, a new supply pattern, etc. For this problem, a disjunctive model is presented, which takes into consideration every usual alternative about the configuration of units and storage tanks. A disjunction is generated for that purpose. The selection of one of those alternatives sets up all the corresponding constraints, which are: operation time, unit size and cost, etc. Finally, the performance of this approach is analyzed through the resolution of a set of examples.

Retrofit design of multipurpose batch plants with multiple production routes

This work analyzes possible alterations of configuration of an existing multipurpose batch plant for which new production targets and selling profits have been specified. New equipment can be added to the batch plant in the form of a retrofit in order to become a more economical and optimal design. The retrofit problem is posed as a mixed-integer formulation (MILP). The application of the proposed model is illustrated using three examples where can be verified that the method is efficient and of easy application, when compared of the others strategies to solve the retrofit problem.