[PDF] Adapting catalytic methanation to small- and mid-scale SNG

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der Friedrich-Alexander

Erlangen-Nürnberg

zur Erlangung des Doktorgrades

DOKTOR-INGENIEUR

vorgelegt von

Michael Franz Walter Neubert

aus München

Als Dissertation genehmigt

Tag der mündlichen Prüfung: 9. Dezember 2019

Gutachter: Prof. Dr.-Ing. Jürgen Karl

Prof. Dr.-Ing. Markus Lehner

III

Für meine Frau Franziska

und meine Tochter Emilia. IV

Abstract

The present thesis evaluated simulation-based and experimentally different approaches to adapt catalytic methanation to small- to mid-scale SNG production processes. Contrarily to state-of-the art technologies, a smaller plant size requires a reduced complexity of the overall SNG process to keep the specific CAPEX costs at a reasonable level. Simluations underlined that a two-stage methanation concept with intermediate water condensation and removal is capable for the production of grid-injectable SNG. This process design fits well to the thermo- chemical pathway via gasification of coal or biomass as well as to a power-to-gas process. The experimental evaluation of the process design and related issues comprises in total an experimental test duration under relevant conditions of more than 2000 h. A main conclusion from the experiments underlines that the low number of reaction stages requires mandatorily a non-adiabatic reactor. With the applied catalyst, the maximum temperature must not exceed

550°C whereas the outlet temperature should be as low as 260°C. One may expect that a

lower overall process complexity comes along with a worse syngas cleanliness. Experiments with a complete lab-scale coal-to-SNG process chain demonstrated how an integrated CO2 and sulfur removal raised deactivation of the methanation catalyst in comparison to adsorptive deep desulfurization. Further experiments have proven that the sulfur slip namely thiophene causes irreversible catalyst deactivation without showing a positive effect on possible carbon formation. The catalyst consumption relative to the sulfur concentration in the feed gas has been ranging from 0.5 to 5 gcat/mmolS in the conducted experiments. Additionally, the experimental results underlined that the C/H/O conditioning by CO2 removal or hydrogen addition upstream of the methanation step raises the maximum synthesis temperature. The last part of the present thesis proposes a new reactor concept that solves the conflict between a suitable C/H/O stoichiometry with respect to methanation for a low process complexity and the maximum tolerable synthesis temperature. The proposed non-adiabatic, structured reactor applies heat pipes to remove the heat of reaction from the main reaction zone inside a single reaction channel. The experimental results obtained with a 5 kW prototype have proven that the maximum synthesis temperature has been more than 100 K lower than the adiabatic one even with a maximum steam content of 4 vol.-% in the feed gas. The reactor allowed for a reliable control of the synthesis temperature below the catalyst limit. V

Kurzfassung

Die vorliegende Arbeit untersuchte simulationsbasiert und experimentell verschiedene um dem Skaleneffekt bei den spezifischen Investitionskosten entgegenzuwirken. Die durchgeführten Simulationen zeigten, dass ein zweistufiges Methanisierungskonzept mit zwischengeschalteter Wasserabtrennung eine sinnvolle Option ist, sowohl für die SNG Erzeugung mittels thermo-chemischer Konversion von Kohle oder Biomasse, als auch mittels Power-to-Gas Prozess. Die experimentelle Untesuchung dieses Prozessdesigns und der damit verbundenen Detailaspekte umfasst insgesamt Experimente mit einer Laufzeit von mehr als 2000 h unter relevanten Betriebsbedingungen. Eine wichtige Schlussfolgerung aus den Experimenten unterstreicht, dass für die angestrebte geringe Gesamtzahl an Reaktionsstufen würde aller Voraussicht nach auch mit einer verringerten Eduktgasreinheit einhergehen. Eine Verwendung einer vereinfachten Synthesegasaufbereitung mit kombinierter CO2- und Schwefelabtrennung im Vergleich zu adsorptiver Entschwefelung. Außerdem verdeutlichten weitere Experimente, dass die zu erwartenden schwefelhaltigen Spurenstoffe namentlich Thiophen zu irreversibler Katalysatordeaktivierung führen, ohne einen positiven Effekt auf durchgeführten Experimenten im Bereich von 0.5 bis 5 gKat/mmolS bezogen auf die Schwefelkonzentration im Eintritt. Des Weiteren verdeutlichten die Experimente, dass eine Zielkonflikt zwischen einem C/H/O-konditionierten Eduktgas für eine geringe der einzelnen, die maximale Synthesetemperatur bei einer Dampfzugabe von bis zu 4 vol.-% um mehr als

100 K unter die adiabate Synthestemperatur verringert werden konnte und das

VI VII

Danksagung

Schwerpunkte zu setzen. Das Vertrauen von Prof. Karl in meine Arbeit und auch in meine die dann manchmal auch (nicht) zum Ziel führten. Weiterhin gebührt mein Dank auch Prof. Markus Lehner zur Begutachtung meiner Dissertation. Des Weiteren waren meine KollegInnen für mein Promotionsvorhaben sicherlich genauso wichtig wie mein Doktorvater. erleichterte es mir die manchmal frustrierenden oder besonders fordernden Perioden durchzustehen. Besonders dankbar bin ich dafür, dass aus kollegialen teils auch auch die Hilfe der zahlreichen Studenten und Studentinnen, die mit mir zusammenarbeiteten.

Danke an Alle.

Verantwortung. Mit großer Demut und Dankbarkeit bin ich mir darüber bewusst, dass mir meine Gesundheit das Promovieren erlaubte. auf die Dinge, die neben einer gesunden Portion Selbstbewusstein auch ein hilfreiches Maß bewusst, dass diese gegen Ende ihrer Fertigstellung bereits hinter etwas noch Wichtigerem und Erfüllenderem zurückweichen würde. Die eigene Familiengründung lud erhebliche Verantwortung auf meine Schultern die ich mit großer Freude übernehme. Meine Frau Franziska und meine Tochter Emilia sind diejenigen Menschen in meinem Leben, die mir Danke Franzi und Emilia. Diese Arbeit widme ich euch Beiden. VIII

Content

Abstract ................................................................................................................................. IV

Kurzfassung ........................................................................................................................... V

Danksagung ......................................................................................................................... VII

Content ................................................................................................................................ VIII

List of figures ........................................................................................................................ XI

List of Tables ...................................................................................................................... XVI

List of Abbreviations and Symbols ................................................................................. XVII

The initial position ........................................................................................................... 1

1 Motivation for small- and mid-scale SNG production ................................................. 2

1.1 Objective and scope of the present thesis ................................................................ 5

2 Thermodynamics and heterogeneous catalysis of methanation ............................... 8

2.1 Reaction equations and process variables ............................................................... 8

2.2 Adiabatic synthesis temperature ............................................................................ 13

2.3 Heterogeneous catalysis of methanation ............................................................... 15

2.3.1 Catalytic active materials .............................................................. 16

2.3.2 Reaction kinetics and mechanism ................................................ 18

2.4 Catalyst deactivation in methanation process ........................................................ 21

2.4.1 Formation of nickel tetracarbonyl Ni(CO)4 .................................... 22

2.4.2 Catalyst sintering .......................................................................... 24

2.4.3 Formation of solid carbon ............................................................. 25

2.4.4 Sulfur poisoning ............................................................................ 28

3 Pathways for SNG production ..................................................................................... 33

3.1 Specifications of gas grid injectable SNG quality ................................................... 36

3.2 Industrial state-of-the art methanation concepts .................................................... 38

3.3 Innovative concepts for process intensification of methanation.............................. 42

3.3.1 Tube reactors ............................................................................... 42

3.3.2 Structured and micro-channel reactors ........................................ 43

3.3.3 Three-phase and biological methanation...................................... 46

3.3.4 Direct control of reaction kinetics through optimized temperature

profiles 50

3.4 Thermo-chemical SNG production ......................................................................... 51

3.4.1 Coal as feedstock ......................................................................... 53

3.4.2 Biomass as feedstock ................................................................... 55

3.4.3 Syngas cleaning ........................................................................... 60

3.5 Power-to-Gas ......................................................................................................... 62

3.5.1 Hydrogen sources for Power-to-Gas ............................................ 67

3.5.2 Carbon sources for Power-to-Gas ................................................ 70

IX

The challenging trilemma ........................................................................................... 75

4 The principle trilemma and a proposal for the process design ............................... 76

4.1 SNG production in equilibrium and ternary diagrams ............................................. 78

4.1.1 Basic process design to adapt C/H/O ratio ................................... 78

4.1.2 Quantification of gas quality, CO2 removal and H2 addition .......... 80

4.1.3 Equivalent steam content m and risk of carbon formation ............ 88

4.2 Kinetic based simulation of fixed-bed methanation ................................................ 89

4.2.1 Reaction rate expression and methodology ................................. 89

4.2.2 Operating maps of methanation and estimated heat release ....... 91

5 Experimental approach, methods and materials ....................................................... 96

5.1 Objectives and experimental approach .................................................................. 96

5.2 Experimental equipment ....................................................................................... 101

5.2.1 Methanation bench-scale test rig ................................................ 101

5.2.2 Nickel based catalyst .................................................................. 106

5.2.3 Simultaneous thermal analysis (STA)......................................... 107

5.2.4 Gas analytics for sulfur and hydrocarbon measurements .......... 109

6 Adapting syngas methanation for small-scale processes ...................................... 112

6.1 Supply of real synthesis gas and Benfield srubber ............................................... 112

6.2 Syngas conversion and temperature management .............................................. 117

6.2.1 Methanation of real lignite-derived syngas ................................. 117

6.2.2 Methanation of real biomass-derived syngas ............................. 122

6.2.3 Hydrogen intensified methanation of biomass-derived syngas .. 126

6.3 Catalyst deactivation resulting from syngas methanation..................................... 131

6.3.1 Integral relative activity loss in experiments with real-syngas .... 132

6.3.2 Solid carbon depositions in experiments with real-syngas (catalyst

batch No.4) ............................................................................................... 134

6.3.3 Deactivation due to impurities in synthetic gas mixtures ............ 139

6.3.4 Simultaneous thermal analysis (STA) of sulfur adsorption on Ni-

based catalyst ........................................................................................... 149

6.4 Conclusions from hydrogen intensification and combined syngas treatment ....... 158

The new reactor concept .......................................................................................... 165

7 Heat pipe cooled structured reactor for improved temperature control ............... 166

7.1 Concept for active temperature control ................................................................ 166

7.2 Proposed structured reactor concept ................................................................... 168

7.2.1 Heat pipes as cooling device ...................................................... 169

7.2.2 Diameter of a single reaction channel ........................................ 172

7.2.3 Manufactured 5 kW lab-scale reactor ......................................... 178

7.3 Experimental performance of the heat pipe cooled structured reactor ................. 182

7.3.1 Control of synthesis temperature ................................................ 183

7.3.2 Feed gas conversion and methane yield .................................... 186

7.4 Conclusions from experiments with heat pipe cooled structured reactor ............. 188

8 Transferring the reactor concept to industrial applications ................................... 190

X

8.1 Carbon and energy flow analysis ......................................................................... 190

8.2 Scale-up for industrial applications ....................................................................... 191

9 Summary and outlook ................................................................................................ 195

10 Sources ........................................................................................................................ 197

XI

List of figures

Figure 1-1 CO2 emissions per capita for selected countries in 2016 ...................................................................... 2

Figure 1-2 Historic GHG emissions and planned reduction for the main sectors (reproduced from [1]) ................. 3

Figure 1-3 Heating systems in newly constructed housing units in Germany (reproduced from [4]) ....................... 4

Figure 2-1 Equilibrium composition (incl. H2O) of reactions involved in methanation process CO methanation (a),

CO2 methanation (b), water-gas-shift reaction (c); (a)-(c) at 1 bar and 10 bar for a stoichiometric feed gas; yCH4

and yH2 in equilibrium for CO methanation reaction and CO2 methanation reaction (d); only species involved in

the specific reaction are considered for equilibrium ........................................................................................ 10

Figure 2-2 Equilibrium composition for reactions forming solid graphitic carbon for 1 bar (solid lines) and 10 bar

(dotted lines) methane cracking of 1 mole methane (left) and Boudouard reaction of 2 mole CO (right) ..... 11

Figure 2-3 Equilibrium composition for a stoichiometric feed of H2/CO = 3 (left) and H2/CO2 = 4 (right); p = 1 bar;

species in equilibrium: CH4, CO2, CO, H2, H2O, C .......................................................................................... 11

Figure 2-4 Yield YCH4,CO2 (a), YCH4,CO (c) and methane concentration in dry product gas yCH4,dry (b,d) in

thermodynamic equilibrium at 5 bar for two different reactants mixtures: 4 mol H2 and 1 mol CO2 (a,b), 3 mol

H2 and 1 mol CO (c,d) ..................................................................................................................................... 13

Figure 2-5 Equilibrium conversion XCO and XCO2 of a stoichiometric H2/CO (blue) and H2/CO2 (grey) mixture for

methanation; product gas temperature Tadiabatic (filled quadrats) for Tin = 300°C; p = 5 bar ............................ 15

Figure 2-6 Scheme of steps within heterogeneous catalysis ................................................................................. 16

Figure 2-7 Concentration of nickel tetracarbonyl Ni(CO)4 in thermodynamic equilibrium for two different reactant

mixtures; equilibrium calculated for four different combinations of species that are allowed for equilibrium; CO

partial pressure is set in all cases to 0.051 bar; Ni, C and NiO are considered as solid phases in equilibrium, all

other compounds are considered as gaseous species; calculations performed with FactSage 7.2 and FactPS

database ......................................................................................................................................................... 23

Figure 2-8 Scheme of different mechanisms causing thermal aging ..................................................................... 24

Figure 2-9 Rate of formation and hydrogenation of CĮ and Cȕ versus reciprocal temperature (Reproduced with

permission from [82]. Copyright (1982) Taylor & Francis.) .............................................................................. 26

Figure 2-10 Proposed mechanism for carbon whisker growth involving moving step sites, where a graphene layer

grows (Reproduced with permission from [87]. Copyright (2006) American Physical Society.) ...................... 27

Figure 2-11 Series of snapshots taken from in situ HRTEM analysis of a growing whisker carbon under CH4:H2 = 1:1

atmosphere at 536°C (Reproduced with permission from [85]. Copyright (2004) Springer Nature.) ............... 27

Figure 2-12 Predominant phase plot of Ni-S-O system at 1073 K (left) and 673 K (right) for varying gas pressure of

S2 and O2; calculations performed with FactSage

CO, H2, H2O, H2S, S2 and O2 present in equilibrium (1.013 bar); 4, H2,

H2O, H2S, S2 and O2 present in equilibrium (1.013 bar) .................................................................................. 29

Figure 2-13 Isobars for chemisorption of H2S on Ni based catalysts (Reproduced with permission from [103].

Copyright (1981) Elsevier.) ............................................................................................................................. 30

Figure 3-1 Basic process scheme for SNG production .......................................................................................... 33

Figure 3-2 Overview of general approaches for thermal management of methanation ......................................... 35

Figure 3-3 H-gas and L-gas quality according to German DVGW G260 technical rule ......................................... 37

Figure 3-4 Lurgi methanation process as installed in Great Plains Synfuels Plant, adapted from [142,143] ......... 38

Figure 3-5 TREMP process scheme - adapted from [30] ...................................................................................... 39

Figure 3-6 HICOM process scheme - adapted from [148] ..................................................................................... 40

Figure 3-7 VESTA process scheme - adapted from [150] ..................................................................................... 41

Figure 3-8 Process scheme of a Güssing-type Fast Internally Circulating Fluidized Bed (FICFB) gasifier

(Reproduced with permission from [203]. Copyright (2011) Springer Berlin Heidelberg.) ............................... 56

Figure 3-9 Flow scheme of the pilot SNG plant at the Güssing site in the BioSNG project (Reproduced with

permission from [215]. Copyright (2016) John Wiley and Sons.) .................................................................... 57

Figure 3-10 Scheme oft he GoBiGas plant 1) combustion section, 2) gasification section, 3) methanation section,

4) gas compression, 5) BTX removal (Reproduced from [204]. Source is published under Creative Commons

Attribution License (CC BY).) .......................................................................................................................... 58

Figure 3-11 Energy demand of water/steam electrolysis at different temepratures (1 bar) (Reproduced with

permission from [156]. Copyright (2018) Elsevier.) ......................................................................................... 67

Figure 3-12 Summary of efficiency and operational range of alkaline (AEL), PEM and solid oxide (SOE) electrolysis

(Reproduced with permission from [271]. Copyright (2018) Elsevier.) ............................................................ 69

XII Figure 3-2 separation at different conditions ............................................. 70

Figure 4-1 Trilemma of decentralized methanation ............................................................................................... 76

Figure 4-2 Scheme of a polytropic temperature profile .......................................................................................... 77

Figure 4-3 Equilibrium curve for methanation of different feedstock in a series of adiabatic reactors stoichiometric

H2/CO2 mixture (left), stoichiometric H2/biogas mixture with biogas containing 50 % CH4 and 50 % CO2 (middle),

modified, stoichiometric H2/syngas mixture according Table 4-1 with H2 addition to adapt the stoichiometry; 5

bara ................................................................................................................................................................. 77

Figure 4-4 Ternary C-H-O diagram with phase equilibrium (shown for 260°C and 550°C) of solid graphitic carbon

and methane concentration yCH4,dry in equilibrium (on dry basis at 260°C) for 90 vol.-% (light red) and for

95 vol.-% (dark red); pressure 5 bara .............................................................................................................. 78

Figure 4-5 Basic two step process layout for decentralized methanation .............................................................. 80

Figure 4-6 Change of gas composition in ternary atomic C,H,O plot for CO2 removal (left) and H2 addition (right) to

syngas with composition from Table 4-1 ......................................................................................................... 81

Figure 4-7 Atomic ternary diagram illustrating C/H/O ratio modification in two-stage SNG production with

intermediate water removal for different feedstock a) syngas with ideal CO2 removal and 20 vol.-% in 1st stage

b) syngas with ideal H2 addition c) biogas with ideal H2 addition d)power-to-gas with stoichiometric H2/CO2

-case bar; syngas and biogas composition as listed in Table

4-1 .................................................................................................................................................................. 85

Figure 4-8 Different pathways for SNG production according to the basic process design as shown in Figure 4-5;

iso-lines for 95 vol.-% CH4 (dark red) and 90 vol.-% CH4 (light red) ............................................................... 86

Figure 4-9 Gas composition for thermochemical production: via CO2 removal and constant steam content of 25 vol.-

% in feed to 1st stage (left) and via H2 addition without additional modification of steam content in feed to 1st

stage (right); water removal between 1st and 2nd stage takes place at 100°C condenser temperature ........... 87

Figure 4-10 Phase equilibrium of solid graphitic carbon for a CH4 - H2O mixture with equivalent steam content m

........................................................................................................................................................................ 88

Figure 4-11 T(z) and yCH4,dry for different kinetic models and experimental data as published in [65]; synthesis gas

as listed for atmospheric conditions in Table 5-1 and reactor geometry according to Table 5-

1; Tin = 282 °C, pin = 1.013 bar (Reprinted with permission from [65]. Copyright (2017)

American Chemical Society) ........................................................................................................................... 91

Figure 4-12 Adiabatic synthesis temperature in dependency of CO2 removal and H2O content for raw syngas

according to Table 4-1; p = 5 bar, Tin = 300°C (Reprinted with permission from [65]. Copyright (2017) American

Chemical Society) ........................................................................................................................................... 92

Figure 4-13 Adiabatic synthesis temperature in dependency of H2/CO2 ratio and H2O content; p = 5 bar, Tin = 300°C

........................................................................................................................................................................ 92

Figure 4-14 One dimensional rate-based simulation for pure H2 /CO2 = 4 mixture with kinetic rate expression of

adiabatic case (orange line) and two user-defined profiles with set maximum temperature Tsim,max (dashed

lines); cumulated heat release Q/V for the three temperature profiles (bottom left and right) for each inlet

temperature, whereby the necessary heat removal to obtain the temperature profile is highlighted as shaded

area for each profile; p = 5 bara (pressure loss neglected) ............................................................................. 95

Figure 5-1 Scheme of axial shift of temperature profile; activity loss activity is highlighted as blue-shaded area; the

brown area refers to initial temperature profile obtained with fresh catalyst .................................................... 97

Figure 5-2 Picture of the experimental bench- - Two-stage methanation with

intermediate water removal ........................................................................................................................... 102

Figure 5- ............................................................... 103

Figure 5-4 CAD drawing of the tubular reactor B for pressurized methanation (figure is turned 90° counter clockwise)

...................................................................................................................................................................... 103

Figure 5--stage methanation with structured reactor ........... 104

Figure 5-6 Cooled bubble column used as condenser for intermediate water removal ....................................... 105

Figure 5-7 a) Comparison of two axial temperature profiles with different forward speed of the automated

measurement device b) picture of the automated measurement device as installed .................................... 106

Figure 5-8 TGA sample holder (left) and DCS sample holder (right) used in the STA PT1750 device ................ 107

Figure 5-9 Piping and instrument scheme of the experimental setup with STA device and gas mixing station ... 108

Figure 5-10 T-shaped fitting (made from PTFE) for mixing thiophene (dosed by syringe pump) with carrier gas H2;

the whole mixing fitting was vertically placed in the batch of a chiller filled with glycol at -9°C ..................... 109

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