Capture and utilization of carbon dioxide from the lime kilns of a kraft pulp mill for bio-methanol production: Case study at the market pulp mill Södra Cell Mönsterås
Typ
Examensarbete för masterexamen
Master's Thesis
Master's Thesis
Program
Innovative and sustainable chemical engineering (MPISC), MSc
Publicerad
2023
Författare
Lindström, Vendela
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Bio-methanol is a valuable product that can be used for a variety of applications.
Södra Cell Mönsterås, a pulp mill situated in southern Sweden, currently produces
bio-methanol as a byproduct from the pulping process. However, methanol could
also be produced through carbon capture and utilisation (CCU), i.e. by capturing
carbon dioxide from point emission sources at the plant site and reacting it with
hydrogen. This master thesis aims to investigate the potential integration of such
a CCU concept at Södra Cell Mönsterås, thus potentially increasing bio-methanol
production on site.
The carbon dioxide was assumed to be captured through post-combustion capture
using an amine-based absorption process. For energy-efficient carbon dioxide capture,
a high concentration of carbon dioxide in the flue gas is favorable. Consequently,
the lime kilns of the mill were selected as potential carbon dioxide sources,
since they have the highest concentration of carbon dioxide in the flue gases of the
emission sources at the pulp mill. A 90 % capture rate of carbon dioxide from the
flue gases of both kilns was assumed, corresponding to a total of approximately 230
kton/year of captured biogenic carbon dioxide, which could be used to produce 170
kton/year of bio-methanol, requiring 30 kton/year of hydrogen.
For the energy balances, two levels of specific heating demands for the carbon capture
process were evaluated. As a conservative estimate, a literature value for a
standard capture process using a mono-ethanolamine (MEA) absorption solvent applied
to typical combustion flue gases was considered, with a heating demand of
3600 kJ/kg carbon dioxide captured. To get an estimate of potential improvements
with a more optimized process design and better performing solvents, a lower specific
heating demand of 2900 kJ/kg carbon dioxide captured, which has been reported for
the solvent blend amino-2-methyl-1-propanol/piperazine (AMP/PZ), was also evaluated.
This resulted in a heating demands of 230 GWh/year and 186 GWh/year for
the higher and lower value, respectively, when capturing 90 % of the carbon dioxide
from the lime kilns.
The results also indicate that the heating demand for the whole CCU concept can
be covered by steam that could be made available from the mill, more specifically
by bypassing the condensing turbine. However, the electricity demand for the electrolyser
seems to be a more limiting factor. Production of 30 kton/year of hydrogen
requires an elctrolyser with a total capacity of 260 MW of electric power input,
corresponding to an electricity demand of 2.2 TWh/year. This can be compared to
the current electricity consumption of the whole pulp mill, which was 0.7 TWh in 2021. One possibility could be to size the capture plant for maximum (90%) capture
from both lime kilns, but only use part of the captured carbon dioxide for methanol
production and sell the surplus or send it to permanent storage. Thus lowering the
electricity demand for production of hydrogen at site.