Cost evaluation and life cycle assessment of biogas upgrading technologies for an anaerobic

113 Pages·2017·3.29 MB·English

by  Marina Jennifer Hauser

Cost evaluation and life cycle assessment
of biogas upgrading technologies for an
anaerobic digestion case study in the
United States
Marina Jennifer Hauser
Master in Industrial Ecology
Submission date: June 2017
Supervisor: Helge Brattebø, EPT
Norwegian University of Science and Technology
Department of Energy and Process Engineering

Marina Jennifer Hauser

Cost evaluation and life cycle assessment of biogas

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Preface
This thesis is carried out as the final assignment for the Nordic Five Tech master program in
Residual Resources Engineering at the Norwegian University of Science and Technology (NTNU)
in Trondheim in collaboration with the Danish Technical University (DTU) in Copenhagen and
the company B&W Megtec from De Pere, Wi. The presented study counts for 30 ECTS and has
been written at the Department of Energy and Process Engineering at NTNU in the period from
January 2017 to June 2017. The thesis builds on the project work carried out in the Fall semester
2016 at NTNU called “Energy evaluation of biogas upgrading technologies for an anaerobic
digestion case study in the United States”.
From the project work done in the previous semester, knowledge regarding the anaerobic digestion
and the different biogas upgrading technologies was already available. Besides, also most data
needed for the life cycle assessment and cost evaluation was also already found in literature as no
plant specific data was available from the company. Due to time and data restrictions, it was only
possible to analyze a system for anaerobic digestion using mixed waste in the life cycle assessment
but not one for using wastewater sludge. For the cost evaluation, data was only available for plants
with gas flow ranges up to 2000 Nm3/h and not 15,000 Nm3/h as specified in the assignment text.
Therefore, these two points of the assignment text could not be evaluated.
First, I would like to thank Gerald Norz not only for providing me with a topic for this thesis and
letting me work with such a renowned company as B&W Megtec, but also for helping me
throughout the project with advice and inputs, and for giving me a tour of the company and
showing me around the office in De Pere. Then I would also like to thank Helge Brattebø for being
my supervisor and for guiding me through this project. I would also like to thank Marina Zabrodina
for giving me very detailed feedback on drafts of this thesis. Lastly, I would like to thank Anders
Damgaard for helping me with any problems or questions I had regarding the modelling and the
EASETECH software.

Trondheim, June 12th 2017

________________________
Marina Hauser

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Abstract
Globally, around one third of the food produced is lost or wasted. Instead of landfilling or
incinerating, organic municipal solid waste has increasingly been used in anaerobic digestion in
order to produce biogas. The produced biogas contains around 60-70% methane, 30-40% carbon
dioxide, and minor parts of impurities such as hydrogen sulfide, nitrogen, or water vapor. The
biogas can be cleaned of impurities and upgraded by removing the carbon dioxide to substitute
either natural gas in the national gas grid or liquid natural gas for vehicles. Different technologies
exist for the removal of the carbon dioxide. The most widely used technologies are pressure swing
adsorption, water scrubbing, amine scrubbing, membrane separation, and cryogenic separation.
These five technologies were assessed in this study using literature data.
The first purpose of this study is to evaluate the environmental impact of the anaerobic digestion
with following biogas upgrading in the geographical context of the United States. A life cycle
assessment considering all the impacts from the anaerobic digestion to the substitution of natural
gas including the biogas upgrading technology, gas compression and possible leakages along the
way was performed using the EASETECH software. The normalized results show that the largest
impacts occur in Freshwater Eutrophication and Global Warming. The largest savings are achieved
in Freshwater Ecotoxicity, followed by Marine Ecotoxicity, fossil Depletion and Human Toxicity.
Of the total 14 impact categories, cryogenic separation had the largest saving in eight impact
categories and the largest impact in only one. However, including the sensitivity analysis, it was
found that the uncertainty is so large that the error bars overlap for most impact categories and it
is therefore most of the time not possible to show clearly which category is best or worst. Only for
climate change, cryogenic separation clearly had the smallest impact, and for human toxicity and
marine ecotoxicity, cryogenic separation clearly had the largest saving. It was also found that for
the two impact categories with the largest environmental impact, the biogas production of the
anaerobic digestion was the major contributing process for three of the scenarios. For the four
impact categories with a negative impact, the substitution of natural gas was the major contributor.
This study also evaluates the costs and revenues associated with the anaerobic digestion and the
following biogas upgrading. The calculations included investment cost, yearly costs, as well as
income from tipping fees, the sale of biogas, and the sale of digestate. The net present value was
calculated for plants with three raw biogas flow rates to compare the profitability of anaerobic
digestion with following pressure swing adsorption, water scrubbing, and amine scrubbing. The
analysis showed that water scrubbing and amine scrubbing had similar net present values, whereas
the net present values for pressure swing adsorption was considerably lower. The sensitivity
analysis showed that the factors with the largest sensitivity are the tipping fee and the biogas yield
of the food waste which are both part of the anaerobic digestion. However, there is large
uncertainty in the data used. Only one set of data was available from literature. Also, this data is
from Europe and from 2008 adding additional uncertainty.
The conclusion was that depending on the goal of a project, such as low environmental impact,
high energy efficiency, low methane slip, etc., a different technology may be preferred. Also, in
order to get a complete picture, data from real plants need to be available.
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Terminology
AD Anaerobic Digester
AS Amine Scrubbing
CBG Compressed Biogas
CH Methane
4
CNG Compressed Natural Gas
CO Carbon Dioxide
2
C/N carbon/nitrogen
DMEA Dimethylethanol amine
EPA Environmental Protection Agency
GHG Greenhouse Gas
GWP Global Warming Potential
H S Hydrogen Sulfide
2
ISO International Standards Organization
LBG Liquefied Biogas
LCA Life Cycle Assessment
LCI Life Cycle Inventory
LCIA Life Cycle Impact Assessment
LHV Lower Heating Value
LNG Liquid Natural Gas
MEA Monoethanol Amine
MPa Megapascal (1 MPa = 0.1 bar)
MSW Municipal Solid Waste
NPV Net Present Value
N Nitrogen
2
OMSW Organic Municipal Solid Waste
O Oxygen
2
PSA Pressure Swing Adsorption
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RFS Renewable Fuel Standard
TS Total Solids
VFA Volatile Fatty Acids
VS Volatile Solids
WS Water Scrubbing
WW Wet Weight

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Table of Contents
1. Introduction .......................................................................................................................................... 1
1.1. Background ................................................................................................................................... 1
1.2. Research Question ........................................................................................................................ 3
1.3. Structure of the Thesis .................................................................................................................. 4
2. Literature & Theory ............................................................................................................................... 5
2.1. Biogas Systems from Waste .......................................................................................................... 5
2.2. Biogas Upgrading Technologies .................................................................................................... 7
2.2.1. Removal of Impurities ........................................................................................................... 8
2.2.2. Pressure Swing Adsorption ................................................................................................. 10
2.2.3. Water Scrubbing ................................................................................................................. 11
2.2.4. Amine Scrubbing ................................................................................................................. 13
2.2.5. Membrane Separation ........................................................................................................ 14
2.2.6. Cryogenic Separation .......................................................................................................... 16
3. Methods .............................................................................................................................................. 17
3.1. Case Study Description ............................................................................................................... 17
3.2. Life Cycle Assessment ................................................................................................................. 17
3.2.1. Methodology ....................................................................................................................... 17
3.2.2. The Model ........................................................................................................................... 22
3.2.3. Data Collection .................................................................................................................... 24
3.2.3.1. Anaerobic Digestion ........................................................................................................ 24
3.2.3.2. Pressure Swing Adsorption ............................................................................................. 27
3.2.3.3. Water Scrubbing ............................................................................................................. 29
3.2.3.4. Amine Scrubbing ............................................................................................................. 31
3.2.3.5. Membrane Separation .................................................................................................... 33
3.2.3.6. Cryogenic Separation ...................................................................................................... 34
3.3. Cost Evaluation ........................................................................................................................... 35
3.3.1. Methodology ....................................................................................................................... 35
3.3.2. The Model ........................................................................................................................... 36
3.3.3. Data Collection .................................................................................................................... 38
3.3.3.1. Anaerobic Digestion ........................................................................................................ 38
3.3.3.2. Pressure Swing Adsorption ............................................................................................. 40
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3.3.3.3. Water Scrubbing ............................................................................................................. 42
3.3.3.4. Amine Scrubbing ............................................................................................................. 43
4. Results ................................................................................................................................................. 45
4.1. Life Cycle Assessment ................................................................................................................. 45
4.1.1. Perturbation Analysis .......................................................................................................... 54
4.1.2. Uncertainty Propagation ..................................................................................................... 57
4.2. Cost Evaluation ........................................................................................................................... 63
4.2.1. Sensitivity Analysis .............................................................................................................. 65
5. Discussion ............................................................................................................................................ 68
5.1. Life Cycle Assessment ................................................................................................................. 68
5.1.1. Main Findings ...................................................................................................................... 68
5.1.2. Agreement with Literature ................................................................................................. 69
5.1.3. Strength and Weaknesses ................................................................................................... 70
5.2. Cost Evaluation ........................................................................................................................... 71
5.2.1. Main Findings ...................................................................................................................... 71
5.2.2. Agreement with Literature ................................................................................................. 74
5.2.3. Strength and Weaknesses ................................................................................................... 76
5.3. Implication of the Findings.......................................................................................................... 77
6. Conclusions ......................................................................................................................................... 80
7. List of References ................................................................................................................................ 82
Appendix I: Master Thesis Assignment Text ............................................................................................... 86
Appendix II: CO Transfer in Biogas Upgrading ........................................................................................... 89
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Appendix III: List of Geographies from Ecoinvent ....................................................................................... 91
Appendix IV: EASETECH Screenshots .......................................................................................................... 92
Appendix V: Sensitivity Ratio Calculations for LCA ..................................................................................... 95
Appendix VI: Normalized Sensitivity Ratios for P ...................................................................................... 98
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Appendix VII: Results from NPV calculations .............................................................................................. 99

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