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    3D Radiative Transfer Modeling of the Red Supergiant NML Cyg
    (2021) Hirvonen, Per; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Chalmers University of Technology / Department of Space, Earth and Environment; De Beck, Elvire; De Beck, Elvire; Andrews, Holly
    Red supergiants are bright but cool massive stars that have depleted their core hydrogen supply and have started fusing heavier elements. These evolved stars ex perience a strong mass loss through a slow moving stellar wind that results in an extended circumstellar envelope with a rich chemistry. The circumstellar envelopes of red supergiants will eventually enrich the interstellar medium, influencing the formation and evolution of the next generation of stars and planets. Understanding the mass loss of massive evolved stars is a key component in understanding both the evolution of individual stars and the chemical evolution of the universe. We analyze carbon monoxide emission around the red supergiant NML Cyg ob served with the ground based JCMT 15 meter and Onsala 20 meter telescopes, as well as the HIFI instrument aboard the Herschel Space Observatory. The line pro files have complex shapes, suggestive of multiple components in the stellar outflow. 3D radiative transfer modeling is used to recreate the observed line profiles. We con clude that it is possible to recreate the observed line profiles by using one spherical component and three directed outflows.
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    Development of A drone based Hydro carbon sensor for gas flux measurements from oil and gas production
    (2022) Bandodkar, Sumedh; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Chalmers University of Technology / Department of Space, Earth and Environment; Mellqvist, Johan; Conde, Vladimir; Mellqvist, Johan
    Air pollution is considered the single largest environmental health risk worldwide due to its enormous impact on climate change and human health. It takes an adverse toll not only on human morbidity and mortality, but also affects the geographical distribution of many infectious diseases and natural disasters due to the result ing climate change. Corrective actions to reduce air pollution and its impact on the ecosystem thus require a good understanding of its sources, concentration of the pol lutants and their interaction with the atmosphere. A light weight, Unmanned Aerial Vehicle (UAV)-borne system has been developed to measure emissions of harmful trace gases like Sulphur Dioxide (SO2), Nitrogen Dioxide (NO2), a wide range of Volatile Organic Compounds (VOCs), and Particulate Matter (PM2.5, PM10), with the main application areas being ship emissions and oil refineries. The device is also equipped with auxiliary sensors to detect wind intensity and direction as well as am bient parameters such as temperature, humidity, altitude, positional co-ordinates; all in real-time. The data is relayed to the controller location by means of a ra dio transceiver to enable on-site analysis and logging of measured parameters. The objective of the work was to: a) Characterize effect of EMI on the small sensor outputs and implement corrective measures for diminishing it, b) Calibrate the sen sors for different gas concentrations in a controlled environment so as to obtain a linear relationship and determine the cross-sensitivity for SO2 and NO2 at different concentrations, c) Calibrate the Photo-ionization detector (PID) sensor against a reference and obtain the concentration curve in terms of sensor sensitivity, and d) Design an efficient, light-weight system with carefully weighed trade-offs between sensors used, their size, dimensions, power consumption and overall performance. A remarkable mitigation of EMI is achieved after implementing the corrective measures. The calibrated system was tested in a field campaign where more than a hundred ships were measured over a span of seven days. The results were used to calculate fuel sulfur content (FSC) and fuel NOx content, which is discussed in detail in the results section.
  • Post
    Chemical looping gasification for production of aviation fuel with negative emissions: Full chain process modeling and techno-economic analysis
    (2022) Saeed, Muhammad Nauman; Shahrivar, Mohammad; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Mattisson, Tobias; Soleimani, Amir
    The greenhouse gases from the conversion of fossil fuels are the main culprits for the increase in the planet's temperature which is reflected in the global warming context. The aviation sector is more dependent on fossil fuels as there is less possibility to find a viable alternative for fuel requirements for this sector. Chemical Looping Gasification with biomass as a fuel combined with downstream Fischer-Tropsch (FT) synthesis for aviation fuel production is a possible way to decarbonize transportation sectors like aviation. Chemical Looping Gasification (CLG) is like indirect gasification in a circulating fluidized bed, except that instead of inert bed material, particles containing metal-oxides, called oxygen carriers (OCs) are used as the bed material. CLG process has advantage of unnecessary use of an expensive and energy-intensive air separation unit (ASU). Also, due to the presence of a more oxidizing environment in CLG and the catalysing property of OC, the tar yield drops substantially resulting in improved syngas yield and better biomass to syngas conversion compared to the conventional gasification processes. Moreover, all produced CO2 is concentrated in the fuel reactor, with no or limited emissions from the air reactor. This means that it could be a very good process for combined fuel production and capture of CO2, something which would result in net-negative emissions. The study is based on modeling the full chain process of biomass to liquid fuel (BtL) using Aspen Plus software. The model is designed for a gasifier load of around 80 MWth and includes drying of biomass followed by a CLG unit using different oxygen carriers (LD slag and Ilmenite). The circulation rate of an oxygen carrier is adjusted to achieve the desired autothermal CLG operation with temperature of 935oC in the fuel reactor (FR). The resulting syngas from CLG goes through syngas cleaning and conditioning units to meet the requirements for FT synthesis. The steam to biomass ratio is adjusted to 0.7 to achieve an H2/CO ratio of 2.1 before the FT reactor. In the FT reactor with cobalt as a catalyst and at temperature of 220oC, the syngas gets converted into hydrocarbons with carbon numbers ranging from 1 to 40 using the Anderson-Schulz-Flory distribution. Since the aim of the model is to produce aviation fuel, the FT synthesis process combined with a reformer in the recycle loop is adjusted for maximizing the yield of paraffin with carbon numbers ranging from 8 to 16. Based on the optimized model, the clean syngas after syngas cleaning units has an energy content of 8.68 MJ/Nm3 (LHV basis) with a cold-gas efficiency of 77.86 %. FT synthesis model with a reformer estimates an FT crude production of around 647 bbl/day with 154 kilo-tonne of CO2 captured every year and conversion efficiency of biomass to FT-crude of 38.98 %. The calculated levelized cost of fuel (LCOF) is 35.19 $ per GJ of FT crude, with an annual plant profit (cash inflow) of 11.09 M$ and a payback period of 11.56 years for the initial investment.
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    Foreign aid and energy: Analyzing energy aid’s impact on sub-Saharan African countries’ electrification development
    (2022) Zhang, Handan; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Savvidou, Georgia; Hartvigsson, Elias
    Despite the continued flows of foreign aid on energy development to the sub-Saharan African region, more than half of the population lacks access to electricity. Achieving Sustainable Development Goal 7 and providing clean energy requires further development aid in the region. However, aid’s role in development has so far been inconclusive. Research on the impact that finance flows in different energy sectors, such as energy generation and energy policy, hasn’t gained much attention, mainly due to the lack of disaggregated data available until now. This research thus tries to look into energy aid’s impact on electrification rate through energy sub-sectoral aid data. This study uses two regression models to study aid’s impact on energy development in sub-Saharan African regions. An ordinary least squares model was built to analyze energy aid’s impact on the electrification rate with other macroeconomic factors such as economic growth, inflation, and trade openness, as well as countries’ governance scores. An autoregressive distributed lag model is used to study sector-specific aid’s impact on electrification rate in different country groups based on income. Results from the ordinary least squares model confirm aid’s inconclusive role in energy development but prove that an increase in inflation rate is correlated with higher electrification rate changes. Trade openness showed no significance, while governance changes indicate a positive relationship with changes in the electrification rate. The panel autoregressive distributed lag model found that aid’s impact differs among country groups. The electrification rate in the two lower income groups correlated with different energy aid. In comparison, only the electrification rate in the past period correlated with electrification in higher-income country groups. This study calls for future research to look into countries that receive large blocks of energy aid but shows little development, as well as countries that, despite receiving low amounts of energy aid, they have increased electrification rates, to understand what other factors influence the increase in electrification rate in SSA countries.
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    The utilization of cold storage through solar PV mini-grids to reduce spoilage in fisheries in Tanzania
    (2022) Carlsson, Ofelia; Johansson, Madeleine; Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap; Ahlgren, Erik; Hartvigsson, Elias
    The lack of electricity is a major problem in Sub-Saharan Africa, and a majority of the population live in rural areas where it might be difficult to extend the main grid. Mini-grids are a possible solution, and new mini-grids are continuously built to supply villages with electricity. The access of electricity might in turn be a part of a solution to another major problem, spoilage of fish due to the lack of cold storage. This thesis intents to add to the information of how electricity from a solar PV mini-grid can decrease the spoilage of fish. It also aims to investigate the economical possibility to implement a communal cold storage unit connected to a solar PV mini-grid and what technical requirements it puts on the operation of the mini-grid. The information required were gathered through a literature study and by performing a field study in Tanzania. The thesis is based on a case on the island Ukara in Lake Victoria. The data is used in a techno-economic analysis that simulates a walk-in cold storage room connected to a solar PV mini-grid on the island Ukara in Tanzania. The thesis also consists of a qualitative analysis, where a causal loop diagram illustrates the interlinkages between the variables in the system to identify the effects of electricity on the spoilage of fish. The findings indicates that it is economically feasible to implement a communal cold storage unit if an investor makes the initial investment and allow the fishermen to have a pay-back period of at least one year. Another finding is that the capacity of the mini-grid may need to increase to be able to cover the demand during the periods of low production of the solar PVs, where investments in increase capacity in solar PV and battery. The causal loop diagram indicates that access to electricity can be an important solution to reduce the spoilage by enabling the use of cold storage. In conclusion, access to electricity is important to small scale fisheries in rural areas, and it can help them to increase their income and decrease food insecurity.