A Study Into Pyrolysis Of Biomass In Combination With CO2 Reforming And Its Subsequent Effect On C/N-cycles

Sammanfattning

Anthropogenic activities, such as using fossil fuels for energy production, synthesizing carbon-based products, and employing nitrogen fertilizers to meet the ever-growing food demand, have drastically disrupted the planet's carbon and nitrogen cycles. These activities effectively lead to global warming, eutrophication, and NOx production. Hence, the world is in need of coming up with new sustainable technological advancements to meet the demands of fuel synthesis, carbon-based material manufacturing and food production without impacting the world's natural carbon and nitrogen cycles. One proposed solution is to utilize pyrolysis of sustainable biomass to produce biochar, bio-oil, and pyrolysis gas. The bio-oil obtained from this process can be used in a CO2 reforming step, effectively converting it into syngas with a suitable H2/CO ratio for chemical synthesis or fuel production. The produced biochar can, through a CO2 activation step and adsorption of nitrogen, be used as a fertilizer. Lastly, combustion of the produced pyrolysis gas generates energy for the other processes in the system. In this master thesis, the aim was to evaluate the impact of the process on carbon and nitrogen cycles, analyze energy and carbon flows throughout the process, and optimize operational conditions to maximize syngas production. In addition, the study also addressed several research questions. These included investigating whether the process necessitates the introduction of external sustainable energy, and assessing the overall environmental impact of the process. To answer these research questions and overall aim, a model of the process was made in Aspen Plus V.14 in combination with a literature study on the biochars effect on the nitrogen cycle. The results indicate that up to 70% of the carbon going into the process can be successfully sequestered through the optimization of pyrolysis for bio-oil production and subsequently of syngas yield in CO2 reforming. The study also saw that using a combined steam and CO2 reforming process could be beneficial for syngas yield and sequestration of carbon. Another conclusion was that sufficient energy was generated in the Mild combustion step for the other processes within the system, effectively eliminating the need for the introduction of renewable resources. Overall, the process will diminish the anthropogenic impact on the C-cycle by capturing CO2 from the atmosphere and sequestering it into the soil through the biochar and by processing the syngas into carbon-based products. The total sequestered amount will highly depend on the subsequent use and products of the syngas. For the system it was seen that mainly the produced biochar will have an impact on the N-cycle, effectively reducing the needed amount of added nitrogen fertilizer to the soil by reducing ammonia volatilization and increasing the nitrogen uptake by the plants.