Unlocking the Full Energy Potential of Sewage - Unlocking the full energy... · Unlocking the Full

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  • Unlocking the Full Energy Potential of Sewage Sludge

    Research Engineer - Nick Mills

    Doctor of Engineering

    2015

    Supervisors:

    Professor Rex Thorpe

    Jeff Farrow

    Pete Pearce

    The thesis and the work to which it refers are the results of my own efforts. Any ideas, data, images

    or text resulting from the work by others (whether published or unpublished) are fully identified as

    such within the work and attributed to their originator in the text, bibliography or in footnotes. The

    thesis has not been submitted in whole or in part for any other academic degree or professional

    qualification. I agree that the University has the right to submit my work to the plagiarism detection

    service TurnitinUK for originality checks. Whether or not drafts have been so-assessed, the

    University reserves the right to require an electronic version of the final documentation (as

    submitted) for assessment as above.

    Signed .. Nick Mills

  • Unlocking the Full Energy Potential of Sewage Sludge

    University of Surrey SEES Engineering Doctorate Thames Water

    Abstract

    The UK water industry has huge, but as yet under-developed, potential to generate

    sustainable energy from the main by-product created in the treatment of wastewater.

    Sewage sludge is an energy rich sustainable biomass resource with a similar calorific value

    to woodchip.

    Until recently, technologies and processes for further energy recovery have not been

    efficient or viable for large-scale use, but this research has shown that developments and

    innovations are now available and can realistically be brought into use. Using a combination

    of detailed techno-economic analysis and data from several large scale demonstration

    plants this research has shown that the renewable energy produced from sewage sludge in

    the UK could be significantly increased.

    A typical conventional AD site will achieve 15% electrical conversion efficiency; this can be

    improved to 20% with the Thermal Hydrolysis Process (THP). Second generation THP

    developed during the project could boost recovery to 23% with other benefits such as

    reduced support fuel requirements and sludge transport volumes. By combining THP,

    sustainable thermal drying and pyrolysis, gross conversion efficiencies of 34% to electricity

    are achievable. All of the scenarios developed by the project have been proven to

    environmentally & economically sustainable and have been demonstrated at a large scale

    as part of this project.

    A UK wide study in conjunction the Department of Energy & Climate Change showed that

    an economic deployment across the UK of second generation THP, followed by drying and

    pyrolysis, could generate to 2,216GWh or an additional 1,310GWh pa of renewable

    electricity from sewage sludge.

  • Unlocking the Full Energy potential of Sewage Sludge

    3

    Nick Mills May 2015

    Table of Contents

    Abstract .................................................................................................................................... 2

    Nomenclature .......................................................................................................................... 6

    Acknowledgements .................................................................................................................. 7

    Executive Summary .................................................................................................................. 8

    Background .......................................................................................................................... 8

    How sustainable are existing processes? ............................................................................. 9

    What does the future look like? ........................................................................................ 11

    What is the UK Potential? .................................................................................................. 16

    Contributions to Knowledge .............................................................................................. 16

    Conclusions ........................................................................................................................ 17

    Recommendations ............................................................................................................. 18

    1. Introduction ................................................................................................................... 20

    1.1 Objectives............................................................................................................... 20

    Project Lifecycle ............................................................................................................. 21

    1.2 Industry Background .............................................................................................. 21

    1.2.1 Wastewater Treatment .................................................................................. 21

    1.2.2 Sewage Sludge ............................................................................................... 23

    2. How sustainable are existing processes? ....................................................................... 25

    2.1 Anaerobic Digestion ............................................................................................... 25

    2.2 Advanced Anaerobic Digestion .............................................................................. 28

    2.3 Biogas Utilisation ................................................................................................... 31

    2.4 Incineration with energy recovery ......................................................................... 32

    2.5 Environmental Life Cycle Assessment .................................................................... 33

    2.6 Economic Analysis .................................................................................................. 39

    2.6.1 OpEx ...................................................................................................................... 39

    2.6.2 CapEx ..................................................................................................................... 41

    2.6.3 Analysis ................................................................................................................. 42

    2.7 Summary of existing processes .............................................................................. 45

    3. What does the future look like? .................................................................................... 46

    3.1 THP development................................................................................................... 46

    3.1.1 SAS only THP .................................................................................................. 46

  • Unlocking the Full Energy potential of Sewage Sludge

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    Nick Mills May 2015

    3.1.2 Steam Explosion ............................................................................................. 47

    3.1.3 I-THP ............................................................................................................... 56

    3.1.4 ITHP Pilot Plant ............................................................................................... 57

    3.1.5 Second Generation THP Assessment ............................................................. 64

    3.2 Sustainable Thermal Drying ................................................................................... 65

    3.2.1 Sold fuel production trial ............................................................................... 66

    3.2.2 End of Waste (EoW) ....................................................................................... 76

    3.2.3 Low temperature dryers ................................................................................ 80

    3.3 Advanced Energy Recovery .................................................................................... 84

    3.3.1 Pyrolysis ......................................................................................................... 85

    3.3.2 Gasification .................................................................................................... 86

    3.3.3 Pilot trials ....................................................................................................... 86

    3.3.4 Configuration and Analysis ............................................................................ 88

    3.4 Environmental Life Cycle Analysis .......................................................................... 90

    3.4.1 System Boundaries ................................................................................................ 91

    3.4.2 Inventory ............................................................................................................... 91

    3.4.3 Environmental Life Cycle Analysis Results ............................................................ 92

    3.5 Economic Analysis .................................................................................................. 94

    3.5.1 OpEx ...................................................................................................................... 94

    3.5.2 CapEx ..................................................................................................................... 97

    3.5.3 Analysis .........