Pinch analysis focused on secondary heat - How to include multi phase flows by using the advanced composite curves

Pekka Ruohonen

    Research output: ThesisDoctoral ThesisCollection of Articles

    Abstract

    The problem of how to design heat exchanger networks in an optimal way, or heat exchanger networks synthesis, was first studied in the 1960s. The development was fast and the spreading of the methods has caused significant changes in operation of many industrial fields. Traditionally, the work has been divided in pinch based methods and optimisation. This dissertation has focus on the pinch based methods that can be used for heat exchanger network retrofit. Special attention is given for industrial processes with significant possibilities to utilize secondary heat. The literature review shows that the latest developments in the field are the advanced composite curves. Therefore this method is chosen for closer consideration. A logical choice for comparison is the traditional pinch analysis. The objective of this dissertation is to find what advantages do the advanced composite curves have over traditional pinch analysis and identify improvement possibilities in the both methodologies. The study has been carried out by conducting industrial case studies and developing simplified examples when it comes to use of new methods developed in this study. It is shown in the studies that the advanced composite curves give a lot more information on the studied system than traditional pinch-based methods. The whole mill can be shown in two diagrams, one above and the other below the pinch, that show at a glance how the existing heat exchanger network is designed compared to theoretical possibilities. The real temperature levels of the utilities used at the mill and the theoretical upper and lower level for those temperatures, shown together in the curves, give guidance to the engineer as to where to look for improvement potential. Based on the experience from the case studies, the method should be widely implemented in the industry. A novel approach is presented that shows how to use the advanced composite curves to show the upper and lower limits for heat recovery in cases where some of the soft streams have phase changes at the temperature interval in question. The study shows that this can be done with a satisfactory precision. Technical limitations can be taken into the analysis and described graphically. This gives new ideas for saving possibilities not seen by the traditional analysis.
    Translated title of the contributionPinch-analyysi ja sekundäärilämpö - Miten ottaa monifaasivirtaukset huomioon kehittyneempiä yhdistelmäkäyriä käyttämällä
    Original languageEnglish
    QualificationDoctor's degree
    Awarding Institution
    • Aalto University
    Supervisors/Advisors
    • Ahtila, Pekka, Supervising Professor
    • Sivill, Leena, Thesis Advisor
    Publisher
    Print ISBNs978-952-60-6322-5
    Electronic ISBNs978-952-60-6323-2
    Publication statusPublished - 2015
    MoE publication typeG5 Doctoral dissertation (article)

    Keywords

    • pinch analysis
    • energy efficiency

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