PhD Defence by Jens Kristian Jørsboe

Principal supervisor
Associate professor Philip L. Fosbøl

Co-supervisors
Associate professor Ioannis Skiadas
DTU Chemical Engineering

Associate Professor Jens Abildskov
DTU Chemical Engineering

Examiners
Associate professor Martin Høj
DTU Chemical Engineering

Senior lecturer Helena Svensson
Department of Chemical Engineering, Lund University, Sweden

Lead Carbon Capture Consultant Jimmy Andersen
Rambøll, Denmark

Chairperson at Defence
Special Consultant Sebastian Nis Bay Villadsen

Popular summary

In recent times, the production of energy from fossil fuels is responsible for a large fraction of
human emissions of greenhouse gases [1]. To limit these greenhouse gas emissions, and also
satisfying the demand for energy, there has been great focus on the development of renewable
energy technologies including hydro, wind and solar power, and the production of biogas [2].
Biogas is a mixture of approximately 60 vol% methane (CH4) and 40 vol% carbon dioxide
(CO2), which is produced from anaerobic digestion of organic material such as food waste,
farm waste (manures, slurries) and residuals from waste water treatment.

The driver for biogas as renewable energy source is the reduction in fugitive emissions from a
do-nothing scenario where the digested organic waste is released to the atmosphere [3]. Biogas
has an energy potential of upwards 2300 PJ per year for the European Union in 2030 [4] and
can be utilized through three pathways: 1) Heat generation, 2) combined heating and power
and 3) biogas upgrading where impurities are removed from the raw biogas to produce
biomethane. Biomethane can replace natural gas and can be distributed in the European natural
gas when fulfilling certain requirements. The biomethane production in Europe has expanded
drastically in the recent years, and in a Danish context, the consumption of biogas is expected
to fully replace natural gas before 2035 [5].

The amine scrubbing technology for the purpose of biogas upgrading is a mature process
capable of simultaneous production of high purity biomethane (CH4) and high purity biogenic
carbon dioxide (CO2). Further, the amine scrubbing process can potentially achieve negative
carbon emissions when combined with storage of the CO2 product. The technology is, however,
limited by various operational problems and especially the high energy demand for
regeneration of the amine solvent.

This Ph.D. thesis investigates how the operational costs for an amine scrubbing plant be
minimized by selection of a suitable solvent for biogas upgrading, and by implementation of
advanced process configurations to minimize wasted heat or to improve the absorption of CO2.
In this Ph.D. thesis, a mobile pilot plant is utilized for biogas upgrading at two industrial biogas
providers. It is demonstrated that the mobile pilot plant can produce high purity biomethane at
a comparable energy consumption to industrial standards when using conventional 30 wt%
MEA. Various solvents are investigated, and it is proven that the specific reboiler duty (SRD)
can be reduced by 10% by utilizing a 45 wt% piperazine (PZ) + methyldiethanolamine (MDEA) solvent.

Four different advanced process configurations are tested: Intercooled
absorber, rich solvent recycle, cold solvent splitting, and lean vapor compression (LVC). It is
found that absorption enhancing process configurations greatly improves the amine scrubbing
process. By utilizing the combination of intercooling, cold solvent splitting and lean vapor
compression, an SRD of 2.8 MJ reboiler duty per kg CO2 was obtained, which is 24% lower
than state-of-the-art. This Ph.D. thesis thereby concludes that there is potential for optimization
of the amine scrubbing process, which can be obtained by both solvent selection and
modifications to the process flow sheet.

References
[1] “IEA Bioenergy - Task 37 - Plant List 2019.” [Online]. Available:
https://task37.ieabioenergy.com/plant-lists/ (accessed 14-12-2021)
[2] I. R. E. Agency, “Global Energy Transformation - A Roadmap to 2050 - 1.1 Mixed
Progress on the Energy Transition.,” 2019. [Online]. Available:
https://app.knovel.com/hotlink/pdf/id:kt0135AGZ1/global-energytransformation/
mixed-progress-energy accessed 24-09-2023
[3] I. E. A. B. Task and I. E. A. B. Task, “The role of biogas and biomethane in a net zero
world PERSPECTIVES OF BIOGAS AND BIOMETHANE Pathway to Net Zero
Position paper,” 2022.
[4] A. K. P. Meyer, E. A. Ehimen, and J. B. Holm-Nielsen, “Future European biogas: Animal
manure, straw and grass potentials for a sustainable European biogas production,”
Biomass and Bioenergy, vol. 111, pp. 154–164, 2018, doi:
10.1016/j.biombioe.2017.05.013.
[5] Energistyrelsen, “Green Gas Strategy - The role of gas in the green transition,” 2021.