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Politecnico di Milano (2020)

Direct air capture by large scale reforestation of Sahara desert

Blanco Hernandez, Ana

Titre : Direct air capture by large scale reforestation of Sahara desert

Auteur : Blanco Hernandez, Ana

Université de soutenance : Politecnico di Milano

Grade : Laurea Magistrale Master of Science Degree in Energy Engineering– Renewables and Environmental Sustainability 2020

The scope of this project is the study of how reforestation can contribute to limiting the climate change by capturing CO2. In this case, a reforestation has been simulated in the Sahara Desert, since it is a good representative of large-scale but challenging and complicated reforestation scenario, because of its mainly arid desert climate and its water scarcity. The following topics have been developed along the project in the same order :  In the first three chapters, a descriptive framework of the ecological aspects of the study area is established. Therefore, an analysis of the soil types, climate and water resources is carried out. The study area is also classified according to its ecoregions.  In the fourth chapter, a simulation of the reforestation is made by selecting the most suitable trees for the areas in question, their allometric equations for estimating biomass and their carbon content, calculating the CO2 that could capture, as well as the irrigation needs and hence, the water needs of the project. Moreover, three specific regions of 10.000 km2 surface are selected as a representative of three very different and contrasted scenarios of the study area, such as : desert coastal, desert interior and cropland currently suffering deforestation due to climate change.  In the fifth chapter, since it is an area with scarcity of water resources, two of the most commonly used desalination technologies have been studied : one using membranes, such as desalination plants based on Reverse Osmosis technology ; and another through thermal system processes, such as desalination plants based on Multi Stage Flash (MSF). Reference is made to the description of both components and processes, including thermodynamic analyzes of said processes, operational and efficiency parameters. In addition, the energy needs of both desalination technologies, their CO2 emission, their possible energy sources and the future trends for reducing energy consumption have been analyzed.  In the sixth chapter, a technical approach of the project is developed to design and calculate the most suitable desalination plants and infrastructure, such as power plants and water distribution networks.  In the seventh chapter, an environmental approach has been considered to calculate the CO2 balances, between sequestration and emissions.  In the eighth and last chapter, the cost analysis of the project has been developed. The overall cost of the project includes desalination costs, water distribution network costs as well as the forestry running costs. With all, a price per kilogram of CO2 sequestered has been achieved.


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