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  • Syngas to Bio-ethanol

    Fermentation

    University of Groningen

    2018 Chemical Engineering Bachelor Design Project

    Supervisors

    Prof. ir. Jos Winkelman

    Ir. Wersse Leusman

    Kenny Zuur

    By:

    Remco Bos S2325926

    Patrick Bosch S2599953

    Caelan Randolph S2954222

    Jeff B. W. Wijaya S2935341

    Date of submission: July 3rd, 2018

  • 1

    Executive Summary

    Minimizing waste and environmental impact of industrial installations is a relevant concern in

    2018, and a modern engineer is more so than ever asked to solve environmental challenges

    pertaining to future and legacy technology. An area with large waste streams, and great

    potential for innovation is the steel industry, which produces large volumes of toxic and

    greenhouse gasses like carbon monoxide and carbon dioxide. Typically, said gasses are burned,

    but steel furnace exhaust gasses have a very low heating value, being ten times less productive

    than natural gas1 2. A possible alternative to burning said gas is to convert it into a useful

    product. As early as the 1990s, publications arose discussing the conversion of synthetic gas

    (syngas) using the wood-ljungdahl pathway, a metabolic pathway used by anaerobic microbes

    to convert carbon monoxide and carbon dioxide to products like acetic acid and ethanol, among

    other less prominent products3. One of the first microbes studied in this fermentation process

    was Closterium ljungdahlii (C.ljungdahlii)3. Despite the early discovery of the wood-Ljungdahl

    pathway and the possibilities C.ljungdahlii offered in syngas conversion, very few

    implementations of syngas bio-fermentation processes exist, and none at significant industrial

    scale. In order to assess the potential of syngas bio-fermentation in conjunction with steel gas

    waste streams, this paper examines the economic viability of said process by designing a syngas

    bio-fermentation plant using exhaust gasses of a TATA steel plant in southern Holland. This

    paper begins by introducing C.ljungdahlii, the microbe of choice, and the pathway used in the

    bioreactor. Next, reactor choice and design occur, followed by a syngas pretreatment design,

    then product purification design. The design process involves both theoretical design

    calculations, and process simulation using Aspen Plus. Lastly, the cost and turnover of said

    installation is examined to determine whether such a project is viable. Cost analysis was

    achieved using Aspen Plus Economic Analyzer, and process costing theory from Chemical

    Engineering Design by Towler and Sinnot53. Our findings estimate a near $8.64 billion-dollar

    project investment cost, with a $1.8 billion-dollar turnover on ethanol sales from the plant

    annually, the plants primary product. The process is found to be extremely energy intensive,

    with the plant under steady state operation estimated to consume nearly 5.93GW. Due to the

    large energy demands of product purification and syngas pretreatment, the project was found

    to be un-economical. This approach does however offer valuable information for future

    designs, as expensive aspects of syngas fermentation are highlighted, such as the syngas

    pretreatment, which is responsible for 85% of the initial $8.64 billion-dollar investment. With

    this in mind, future investigations should focus on minimizing syngas pretreatment and

    implementing energy saving measures to create a less energy intensive and laborious process,

    which may make syngas bio-fermentation profitable.

  • 2

    Contents

    Chapter I - INTRODUCTION ................................................................................................... 6

    Background ............................................................................................................................ 7

    Steel-mill off-gases ............................................................................................................. 7

    Ethanol supply and demand ................................................................................................ 8

    Chemical vs. biological catalysis........................................................................................ 9

    Wood-Ljungdahl pathway (WLP) based biocatalytic mechanism ................................... 11

    Design Parameters ................................................................................................................ 13

    Objectives ......................................................................................................................... 13

    Steel-mill off-gas stream specification ............................................................................. 13

    Biocatalyst specifications ................................................................................................. 14

    Chapter II - PROCESS DESIGN ............................................................................................. 16

    Reactor Design ..................................................................................................................... 17

    Reactor criteria and design ............................................................................................... 17

    Clostridium ljungdahlii ..................................................................................................... 17

    Previous applications ........................................................................................................ 18

    Reactor Choice ..................................................................................................................... 18

    Process Upscale and Optimization ....................................................................................... 21

    Syngas Optimization......................................................................................................... 27

    Auxiliary Calculations ...................................................................................................... 34

    Syngas processing ................................................................................................................ 36

    Carbon based solids .......................................................................................................... 36

    Tar removal....................................................................................................................... 37

    Hydrogen sulfide removal ................................................................................................ 38

    NO and SO2 removal ....................................................................................................... 39

    Nitrogen removal .............................................................................................................. 40

    Syngas process modeling ..................................................................................................... 41

    Raw gas feed ..................................................................................................................... 41

    Cyclone ............................................................................................................................. 42

  • 3

    Compressors ..................................................................................................................... 43

    Heat exchangers ................................................................................................................ 43

    Tar reformer ...................................................................................................................... 43

    Fixed bed reactors ............................................................................................................. 44

    CSTR ................................................................................................................................ 45

    Results .............................................................................................................................. 45

    Reactor Model ...................................................................................................................... 46

    Growth/acidogenesis reactor (R1) .................................................................................... 46

    Production/solventogenesis reactor (R2) .......................................................................... 49

    Product Work-up .................................................................................................................. 54

    Extractive distillation ........................................................................................................ 54

    Product work-up feed ....................................................................................................... 55

    Process design................................................................................................................... 56

    Feed preparation ............................................................................................................... 57

    Feed pre-heating ............................................................................................................... 62

    Chapter III -