Examensarbeten för masterexamen


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  • Post
    Electrified District Heating Plants using Thermochemical Energy Storage
    (2023) Cortés Romea, Javier; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Chalmers University of Technology / Department of Space, Earth and Environment; Pallarès, David; Martínez, Guillermo; Toktarova, Alla; Guío-Perez, Diana Carolina
    Carbon emissions, particularly from electricity and heat generation, remain a major cause of global warming, accounting for 40 % of global CO2 emissions in 2021. To decarbonize the electricity sector, the use of variable renewable energy (VRE) sources is being encouraged. At the same time, variation management strategies are required to maximize the value of VRE as its share increases and to reduce curtailing. Meanwhile, the heating sector is called to transit into an electrified scheme, which should also reduce the use of biomass, as it is becoming a limited resource. Thermochemical energy storage (TCES) systems, particularly high-temperature solid cycles, such as metal redox-looping, provide a solution for both the electricity and heating sectors. TCES systems have the potential to use non-dispatchable renewable electricity to reduce a metal oxide, which can be stored for long periods of time at ambient conditions and subsequently oxidized to release the stored energy in the form of high-temperature heat (700-1100 °C). This thesis presents an economic assessment of the retrofitting of biomass-firing DH plants by incorporating a TCES scheme based on metal-oxide redox cycles. The viability of the proposed system is analyzed through a case study. Sweden was selected for the study case owing to the existence of a metal extraction and processing infrastructure and the availability of DH plants based on fluidized bed (FB) boilers. The cost of the retrofit was estimated and used as an input in a linear cost optimization model to investigate the impact of the electricity price variability on the cost-optimal size and operation of an electrified DH plant. Today’s typical capacity of biomass-firing DH plants was selected as a reference. The results of the study indicate that as a consequence of including storage the operation of the plant can be adapted to respond to electricity price variations. The proposed process can cover the heat demand at a cost of 55-70 €/MWh. The proposed main scheme proved profitable for the investigated scenarios of electricity price variation, while the economic viability of using solid oxide electrolyzer cells (SOEC) instead of alkaline ones or adding hydrogen storage depends on the potential cost reductions in these technologies in the future.
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    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
    (2023) Lindström, Vendela; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Chalmers University of Technology / Department of Space, Earth and Environment; Harvey, Simon; Svensson, Elin; Larfeldt, Jenny
    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.
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    Modelling the transition from animal to human culture
    (2022) Cvetkovic Destouni, Sofia; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Chalmers University of Technology / Department of Space, Earth and Environment; Andersson, Claes; Andersson, Claes
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    Characterisation of solid flux in packed-fluidized bed: Mixing response of a pulse input during fluidization
    (2022) Bengtsson, Mårten; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Chalmers University of Technology / Department of Space, Earth and Environment; Rydén, Magnus; Nemati, Nasrin
    Fluidized beds have been around for more than 100 years and new applications are constantly developed. One of them, chemical looping combustion technique(CLC), works by letting the fuel react with fluidized solid oxygen carrier instead of air. Previous work have shown that CLC can produce combustion conditions with pure CO2 flue gas stream [1], which would be more cost effective to pressurize and store compared to flue gas stream from air-combustion. One of the drawbacks of CLC is poor gas-mass transfer and the fluidized bed inability to achieve counter-current flow[1]. One approach that has shown improvement on the mass transfer is to introduce packing material to the fluidized bed to facilitate counter-current flow. Earlier work has shown packing material in the fluidized bed greatly increased the conversion of fuel to CO2 in CLC applications. This study investigated the potential of generating counter-current flow patterns for packed-fluidized bed, which can allow for reactor designs with better performance than thermodynamic equilibrium. To investigate the mixing response, a laboratoryscale cylindrical tubular reactor with dimensions 1 m high and 12 cm in diameter was used. Olivin sand with a diameter of 250-300 μm was used as bed material. The bed was fluidized with no packing material as a reference and the experiment were done with ASB 25.4 mm and ASB 6.35 mm as packing materials, at a 2-2.5:1 ratio packing to bed height, with a bed height of 20 cm. A magnetic tracer, magnetite of size 180-212 μm, together with magnetic sensors placed 13(outlet) and 47(inlet) cm from the the distributor plate were used to investigate the degree of plug flow using a pulse input method. Pressure drop over the reactor was measured with 4 sensors, 13.2, 7.6 and 2.1 cm from the bottom. One was placed in the windbox before the distribution plate as reference. The bed was fluidized at superficial gas velocity of 0.1 and 0.3 m/s. Experiments were repeated three times per setup expect for when superficial gas velocity was 0.1 m/s and there was no packing in the bed. This due to insufficient fluidization. Introducing packing material ASB 2.54 mm increased the degree of plug flow for both velocities, high velocity of 0.3 m/s showed higher degree of plug flow compared to 0.1 for the packing material ASB 25.4 mm. ASB 6.35 mm was too small and blocked the outlet yielding no plug flow or meaningful results. Using packed-fluidized bed increase the potential for plug flow and potential for efficient counter-current flow for fluidized bed. More work has to be done to further investigate the effect of confined beds on counter-current flow patterns.
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    Direct air capture for flue gas stream with low CO₂ concentration: Feasibility assessment of direct air capture for removing CO₂ from low CO₂ concentration flue gas streams
    (2022) Vishwanatha, Rishabh; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Chalmers University of Technology / Department of Space, Earth and Environment; Pallarès, David; Hoseinpoori, Sina; Roshan Kumar, Tharun
    Direct air capture (DAC) and storage is a technology that helps yielding negative CO2 emissions. This technology’s main objective is to reach the UN climate goals. The advantage of DAC over other traditional post combustion carbon capture technology is that it can capture CO2 from a stream where the CO2 concentration is very low (0.04%, atmospheric concentration). The aim of this thesis to assess if DAC technology can be used to capture CO2 from a manufacturing plant with very low(1%) CO2 concentration. Two promising technologies of DAC are explored in this thesis: High temperature absorption and Low temperature adsorption. First, a process model is developed for both the technologies to evaluate system for the required concentration. Then a techno-economic comparative analysis is conducted. From the results of this thesis, it is seen that the absorption process consumed more energy when compared to adsorption process. The absorption process also has a higher total levelized cost of CO2 captured when compared to adsorption process.