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In recent years, Grenada, a country in the West Indies, has been heavily impacted by the increased growth of macroalgae, specifically Sargassum. As of today, the country has a significant need for imported goods, resulting in high prices in the community. The country's electricity production currently relies on imported diesel, significantly affecting electricity prices. Research is underway on Sargassum's anaerobic digestion to produce biogas andfertilizer. AlgaeFuel Sweden AB is a startup striving to implement a combined heat and power plant in Grenada powered by biogas produced from Sargassum. This initiative will provide Grenada with local renewable energy, reducing its dependence on imported diesel and mitigating the impact of imported fuel prices. Currently, there are no similar facilities in Grenada, and the use of Sargassum for anaerobic digestion is new. To create an optimal production facility, an investigation is needed concerning the required components and how they need to be adapted to Grenada's climate. Therefore, components need to be selected and sized correctly to create a resource-efficient production. The purpose of this study was to examine and gather technical information about the current technology for a biogas plant and a combined heat and power plant. The investigation was conducted to recommend suitable technology for a future production facility in Grenada. AlgaeFuel Sweden AB requested a plant capacity to produce 150 kW of electricity from Sargassum. The goal was to determine if a plant with this capacity could be built and operatedefficiently in Grenada. An extensive literature review was conducted to collect data on various techniques for anaerobic decomposition and combined heat and power plants. Local conditions were investigated through field studies in Grenada, conducted within the framework of the KTH Field Studies program. The study resulted in the identification of the most suitable technology for biogas and electricity producti, Under de senaste åren har Grenada, ett land i Västindien, påverkats mycket av den ökade tillväxten av makroalgen Sargassum. Idag är landets behov av importerade varor stort vilket orsakar höga priser i samhället. Ett exempel är elektricitetsproduktionen i landet som idag är beroende av importerad diesel. Just nu pågår forskning om anaerob nedbrytning av makroalgen Sargassum för att tillverka biogas och biogödsel. AlgaeFuel Sweden AB är ett start-up företag som strävar efter att kunna implementera ett kraftvärmeverk på Grenada drivet av biogas, producerat av Sargassum. Detta för att skapa en lokal produktion av elektricitet och minska beroendet av priset på importerad diesel. Idag finns ingen liknande anläggning på Grenada och användningen av Sargassum för anaerob nedbrytning är ny. För att skapa en optimal produktionsanläggning krävs således en undersökning om vilka komponenter som behövs och hur dessa behöver anpassas till klimatet på Grenada. Komponenterna behöver därmed väljas och dimensioneras korrekt för att skapa en resurseffektiv produktion. Syftet med denna studie var att undersöka och samla teknisk information om den aktuella tekniken för en biogasanläggning och ett kraftvärmeverk. Undersökningen gjordes för att kunna rekommendera lämplig teknik för en framtida produktionsanläggning på Grenada. AlgaeFuel Sweden AB efterfrågade en anläggningskapacitet för att kunna producera 150 kW elektricitet från Sargassum. Målet var att undersöka om en anläggning med en elektrisk kapacitet på 150 kW går att bygga och driva på ett resurseffektivt sätt på Grenada. En omfattande litteraturstudie har genomförts med datainsamling om olika tekniker för anaerob nedbrytning och kraftvärmeverk. De lokala förutsättningarna har undersökts genom fältstudier på Grenada som har gjorts inom ramen för stipendieprogrammet KTH Field Studies. Studien resulterade i att den mest lämpliga tekniken för en resurseffektiv biogas och elektricitetsproduktion är en kolvmotor och en CSTR för AD. För

The overall purpose of this thesis is to investigate the feasibility of producing electrofuels from CO2 and H2 in connection to a CHP plant equipped with carbon capture technology. This is done by investigating the production of e-methane, e-methanol and e-kerosene from captured CO2 and H2 produced from electrolysis. Each of the processes is designed and analyzed in Aspen HYSYS. From this, the energy and product requirements for each process are obtained. With these results, a production model including the electrofuel and hydrogen production, integrated with the CHP plant Filbornaverket, were modelled in the software Energy Optima 3. Both a smaller system using only part of the captured CO2 and a system at full scale using all the captured CO2 are developed. Furthermore, the simulations were done for spot prices in SE4, for both 2021 and 2022. Average energy demands for the e-fuels were 28.8 kWh/kg for e-methane, 9.97 kWh/kg for e-methanol and 37.6 kWh/kg for e-kerosene. This includes the manufacturing process and hydrogen production. Production costs were lowest for the base case 2021, where e-methane, e-methanol and e-kerosene had production costs of 8.9, 2.2 and 16.4 SEK/kgfuel respectively. The highest production costs were for the full case 2022, where the costs were 31.8, 10.8 and 49.9 SEK/kgfuel, following the same order. For both 2021 and 2022, the production costs were higher for the full scale case than the base case. The main reason for this is that the CHP plant could not supply the processes with as much electricity, meaning the electricity costs for production quickly became high. The findings showed that integration of e-fuel production with a CHP plant could result in a lower production cost and energy demand. However, there are still many aspects of this project that needs to be further investigated to be able to say to which extent. The main factor affecting the production cost was electricity prices. And, the main factor affecting the energy dema, What if it is possible to produce fuels that generate no emissions, with the same characteristics as fossil fuels? High production costs are seen today but there are possibilities in reducing the costs and energy demand by having the production in direct connection with a CHP plant. Climate change is upon us, and actions are needed to decrease emissions of dangerous greenhouse gases. There are many proposed solutions and many cries for help to reach the 1.5 °C goal of the Paris Agreement. The transport sector is the sector that depends most on fossil fuels. It stands for almost 25 % of the world’s greenhouse gas emissions. Solutions for decreasing the emissions in this sector are highly needed. E-fuels are an innovative alternative to fossil fuels. They are based on electricity, hydrogen (H2) and carbon dioxide (CO2), and still, they possess the same characteristics. The CO2 is obtained by different capturing techniques. This way, instead of releasing new emissions, the CO2 can be continuously reused. To be considered renewable, the CO2 needs to be captured directly from the air (or from exhaust gases from burning biomass). Whether the CO2 is renewable determines if it is classified as green, blue, gray or brown. Green is considered the best. For that, renewable CO2 is required, as well as green H2. Green H2 is obtained when it is produced with renewable electricity. Three more well-known e-fuels are e-methane, e-methanol and e-kerosene. E-methane can substitute natural gas which is used by industries and for heating. E-methanol can power large ships, meaning that your future Caribbean cruise can be considered green. E-kerosene can be used as jet fuel, thereby flying to a ski resort could also be completely environmentally friendly. More and more facilities that produce e-fuels are popping up. Production prices are, however, still higher than for other fuels. So, more research needs to be done to make e-fuels part of the market. A combined heat and power (CHP) plant

To achieve greater economic stability, CHP plant operators such as VEAB from Växjö are motivated to search for a new business model that are compatible with their existing facilities while also contribute to increasing the overall revenue of the company. These processes include hydrogen production and biochemical products such as biopolymer and biofuels. However, these processes also produce a substantial amount of heat that needs to be taken care of. Alternatively, the extra heat storage capacity could allow the plant to be more selective of when to produce those heat to maximize profit. Therefore, it is important to investigate different approaches to achieve that, both traditional approach (e,g, convective cooling) and alternative approaches (different large scale underground heat storages). Lake source cooling is also investigated to determine whether it can replace convective cooling as a method of cooling off waste heat from the plant. The technical analysis showed that the alternative approach is certainly promising albeit with more land use (BTES requiring 36 000 m2 against 750 m2 of convectional cooling system) with some limitations that must be addressed when deciding the appropriate approach. In addition, it is found that by increasing the scale of the BTES system, the amount of heat loss per heat capacity reduces while increasing the borehole depth decreases the overall heat loss of the system. The economic analysis showed that when used solely to deal with the waste heat, the alternative approach is costs magnitude more than convective cooling, the alternative costing almost 6 times more than the convective cooling. There are certainly opportunities in the future that can make the BTES system to be a much more feasible choice if additional utilization of the BTES system could be found or potential demand may make the BTES system a more attractive choice to deal with the excess heat that comes with expanding the business of a CHP plant operator.