Retrofit of Total Site Heat Exchanger Networks by Mathematical Programming Approach

Abstract

Heat Integration and Total Site Integration can provide considerable energy savings and emission reduction within industrial plants and entire Total Sites. Several approaches have been developed, such as an approach based on physical insights—Pinch Analysis, an approach based on Mathematical Programming, and recently combined or hybrid approaches based on both Mathematical Programming and Pinch Analysis. There are two designs, grassroots design for new process plants and Total Sites and retrofit design for existing plants and Total Sites. Tools for grassroots designs usually differ from those for retrofits, and retrofit analysis is considerably more difficult as the existing layout should be taken into consideration. This chapter provides an overview of the recent developments in Total Site Integration focusing mainly on the retrofits of existing Total Sites by Mathematical Programming approach and hybrid approaches. First, the Total Site Integration, approaches for Total Site Integration and software tools for Total Site Integration are introduced, followed by the retrofitting of existing heat exchangers within Total Sites. Furthermore, two illustrative examples are shown. Finally, the concluding remarks and sources of further information are provided. Suggested citation Čuček L., Kravanja Z., 2016, Retrofit of Total Site Heat Exchanger Networks by Mathematical Programming Approach, In: M. Martín (Editor), Alternative Energy Sources and Technologies: Chapter 11, Springer International Publishing Switzerland, doi: 10.1007/978-3-319-28752-2_11

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Robert Alan Silverstein

Glossary

Grassroots design

It represents the design of a new plant or Total Site. It is also called minimum energy requirement design and has the widest freedom of choice.

Heat Integration

It means integrating different processes to achieve energy savings (Klemeš et al. 2010). It examines the potential for improving and optimising the heat exchange in order to reduce the amount of external utilities used and thus to reduce costs and emissions.

Mathematical Programming

It is also called ‘mathematical optimisation’, or ‘optimisation’. It stands for the use of specific methods for determining the best solutions to a problem, subject to given constraints. It is the act of obtaining the best result under given circumstances (Rao 2009). It is the key methodology used for sustainable process design and synthesis (Klemeš et al. 2010). The general form of the mathematical programming is the mixed integer nonlinear program (MINLP). The optimality, feasibility and integrality of the obtained solutions are the main capabilities of Mathematical Programming (Kravanja 2010).

Pinch Analysis or Pinch Technology

It is a systematic methodology for analysing and optimising energy savings in processes, plants and Total Sites. It sets the targets by determining the thermodynamic maximal possible rate of heat recovery (Nemet et al. 2015b).

Process Integration

It consists of a family of methodologies for reducing the consumption of resources and emissions within processes, plants and Total Sites (Klemeš et al. 2010). One of the definitions of Process Integration is that it represents (Gundersen 2000): ‘Systematic and General Methods for Designing Integrated Production Systems ranging from Individual Processes to Total Sites, with special emphasis on the Efficient Use of Energy and reducing Environmental Effects’. Methodologies of Process Integration are: Heat Integration, Total Site Integration, Mass Integration, Water Integration, Hydrogen Pinch, etc.

Retrofit design

It stands for the modification of the existing plant(s) or Total Site. It is also called revamp, reconstruction or redesign. The motivation to retrofit could be to increase capacity, allow for different feed or product specifications, reduce operating cost, improve safety, increase capacity, etc. (Smith 2005). The fewer there are modifications the better. There are many ways of improving the existing designs, such as changes in the usages of utilities, topological modifications, installing of additional areas, repiping of streams, reassignments of matches and heat transfer enhancement (Wang et al. 2012).

Code HENSYN

It is used for the final synthesis of the retrofitted heat exchanger network (HEN) for the identified more promising retrofitting modifications obtained from the software tool TransGen. It consideres in detail the trade-offs between investment and operating cost. It can be applied for the retrofitting of existing large-scale industrial plants and Total Sites under nominal and uncertain conditions (Čuček and Kravanja 2015a).

Software tool TransGen

Software tool for (i) targeting and comparing the target and existing designs for obtaining the potential for Heat and Total Site Integration and intermediate utility production, and (ii) identifications of alternatives for retrofitting modifications, and selections of modifications by forbidding unfeasible matches. It is an extension of an expanded transhipment model (Papoulias and Grossmann 1983) and is based on a combined Mathematical Programming/Pinch Analysis (MP/PA) approach. It is suitable for analysing energy targets and existing HEN designs, and especially for proposing optimal modifications for the retrofitting of each plant and Total Sites under nominal and uncertain conditions. Retrofitting of HENs could be performed for problems of any size (Čuček and Kravanja 2015b).

Total Site

It is a set of factories incorporating several processes, serviced by and linked through a central utility system (Dhole and Linnhoff 1993). The concept of Total Site has been extended by including processes from residential, business, service and agricultural sectors (Perry et al. 2008), renewable energy sources and storage systems for accommodating the variations (Varbanov and Klemeš 2011), surrounding of the Total Site by district heating and cooling (Gundersen 2013a) and to a regional level (Čuček et al. 2013).

Total Site Integration

It offers energy conservation opportunities across different individual processes and for designing and optimising the central utility system (Bandyopadhyay et al. 2010). There are two possibilities for Total Site Integration: indirect via intermediate utility and direct integration between process streams where either hot or cold process stream is transported between the processes.