To limit global warming to “well below 2°C” according to the Paris Agreement, a drastic reduction of greenhouse gas emissions is necessary, as well as removing large quantities of CO2 from the atmosphere. This thesis work evaluates through the Life Cycle Analysis methodology the effectiveness of a process to remove CO2 from the atmosphere that combines technologies already in use (biomass or coal gasification, calcium carbonate calcination) with technologies not yet commercially available such as the CO2 storage and the alkalinization of the oceans by the spreading of calcium hydroxide (ocean liming). In detail, the system includes the calcination of the limestone exploiting the heat of the syngas produced by the gasification of biomass or coal. From the calcium oxide produced in the calcination, calcium hydroxide is produced with the addition of water and spread in the ocean by means of ship. Furthermore, the process produces a fuel gas rich in hydrogen that is used to produce electricity. A part of the produced electricity fulfills system energy demand the remaining part is fed into the grid. This last quantity of energy replaces the production of the same quantity of electricity from fossil sources avoiding the impacts related to its production. The LCA study is applied to four system configurations, combinations of two types of fuels (biomass or coal) and two types of CO2 storage (geological and in glass capsules on the seabed). In the configuration with biomass gasification, the removal of CO2 from the atmosphere also occurs through the storage of CO2 absorbed by the biomass during its growth, while in the case of coal the removal is caused only by the ocean liming, which causes an increase in the uptake of atmospheric CO2 by the oceans and its storage in the form of bicarbonates. In this LCA study, the functional unit (FU) of the system is 1 kg of Ca(OH)2 produced and discharged into the ocean. Fifteen impact categories have been considered for the calculation of impacts, the one of main interest is Climate change impact category. The results show that the system in any configuration has a totally negative impact on the Climate change category, i.e. there is a benefit for the environment from the system. The system removes or avoids 3.02 kgCO2eq/FU in the biomass configuration with geological storage and 1.71 kgCO2eq/FU in the coal configuration with geological storage. Changing the type of storage, the benefit is reduced by only 0.02 kgCO2eq/FU. Furthermore, the biomass configuration with geological storage has a total negative impact, that is a benefit for the environment, in 12 impact categories (11 in the case of storage in capsules) while there are 7 categories with negative impact in both configurations with coal. A sensitivity analysis was, then, performed, considering 5 parameters (discharge rate of Ca(OH)2, distance to transport the biomass to the plant, distance to transport the calcium carbonate to the plant, distance to transport Ca(OH)2 from the plant to the port and fossil energy source that is avoided by the surplus energy produced by the system). Three different operating conditions were analysed ("best", "most likely" and "worst" for CO2 removal). In all operating conditions, all configurations have a benefit on Climate change, i.e. a total negative impact. Regarding CO2, the configurations with biomass always have better performances than those with coal excluding Land use category. Finally, thanks to the removal of CO2 through the ocean liming, the configurations with the coal allow to have a benefit on Climate change, even without considering the avoided impacts of electricity production.
Per limitare il riscaldamento globale “ben al di sotto dei 2°C”, come deciso nell’ambito dell’Accordo di Parigi, è necessaria una riduzione drastica delle emissioni di gas climalteranti, nonché rimuovere dall’atmosfera ingenti quantità di CO2. Questo lavoro di tesi valuta attraverso la metodologia dell’Analisi del ciclo di vita (LCA) l'efficacia di un processo per rimuovere la CO2 dall'atmosfera che combina tecnologie già in uso (gassificazione della biomassa o del carbone, calcinazione del carbonato di calcio) con tecnologie oggi in fase di ricerca e sviluppo ma non ancora disponibili a livello commerciale, come lo stoccaggio di CO2 e l’alcalinizzazione degli oceani grazie allo spargimento di idrossido di calcio (ocean liming). Più in dettaglio, il sistema include la calcinazione del carbonato di calcio sfruttando il calore prodotto durante la gasificazione della biomassa o del carbone. L’idrossido di calcio viene formato aggiungendo acqua all’ossido di calcio prodotto nella fase di calcinazione. L’idrossido di calcio viene poi scaricato in mare con delle navi. Il sistema produce inoltre un gas combustibile ricco di idrogeno che viene sfruttato per la produzione di elettricità, usata sia per gli autoconsumi che immessa in rete; quest’ultima quantità di energia sostituisce la produzione della stessa quantità di elettricità da fonti fossili evitando gli impatti legati alla sua produzione. Lo studio LCA è applicato a quattro configurazioni del sistema, combinazioni di due tipi di combustibili (biomassa o carbone) e due tipi di stoccaggio di CO2 (geologico e in capsule vetrose sul fondo del mare). Nella configurazione con la gassificazione di biomassa la rimozione di CO2 dall'atmosfera avviene anche attraverso lo stoccaggio della CO2 assorbita dalla biomassa durante la sua crescita, mentre nel caso del carbone la rimozione è causata solo dall’ocean liming, che determina un aumento dell’assorbimento di CO2 dall’atmosfera da parte degli oceani e il suo stoccaggio in forma di bicarbonati. La LCA è stata svolta considerando come unità funzionale (UF) del sistema è 1 kg di Ca(OH)2 prodotto e scaricato nell'oceano. Sono state considerate per il calcolo dei potenziali impatti 15 categorie di impatto, con un focus particolare rivolto ai Cambiamenti climatici. I risultati mostrano che il sistema in qualsiasi configurazione ha un impatto totale negativo nella categoria dei Cambiamenti climatici, ovvero dà un beneficio all’ambiente rimuovendo 3.02 kgCO2eq/UF nella configurazione biomassa con stoccaggio geologico e 1.71 kgCO2eq/FU nella configurazione carbone con stoccaggio geologico. Cambiando la tipologia di stoccaggio, il beneficio si reduce di soli 0.02 kgCO2eq/UF. Inoltre, la configurazione biomassa con stoccaggio geologico ha impatto totale negativo, cioè un beneficio per l’ambiente, in 12 categorie di impatto (11 in caso di stoccaggio in capsule) mentre sono 7 le categorie con impatto negativo in entrambe le configurazioni con carbone. È stata quindi effettuata un'analisi di sensitività, considerando cinque parametri (rateo di scarico di Ca(OH)2, distanza per trasportare la biomassa all’impianto, distanza per trasportare il carbonato di calcio all’impianto, distanza per trasportare Ca(OH)2 dall'impianto al porto e fonte fossile di energia elettrica che viene evitata dal surplus di energia prodotto dal sistema). Sono state analizzate tre diverse condizioni operative ("migliore", "molto probabile" e "peggiore" per la rimozione di CO2). In tutte le condizioni operative, tutte le configurazioni hanno un beneficio sui Cambiamenti climatici, cioè un impatto totale negativo. Per quanto riguarda la CO2, le configurazioni con la biomassa hanno sempre prestazioni migliori di quelle con il carbone, ad esclusione della categoria Trasformazione del terreno. Grazie alla rimozione di CO2 attraverso l’ocean liming, le configurazioni con il carbone permettono un beneficio per la categoria di impatto Cambiamenti climatici, anche senza considerare gli impatti evitati della produzione di energia elettrica.
Life cycle assessment of a carbon dioxide removal process
CAMPO, FRANCESCO PIETRO
2018/2019
Abstract
To limit global warming to “well below 2°C” according to the Paris Agreement, a drastic reduction of greenhouse gas emissions is necessary, as well as removing large quantities of CO2 from the atmosphere. This thesis work evaluates through the Life Cycle Analysis methodology the effectiveness of a process to remove CO2 from the atmosphere that combines technologies already in use (biomass or coal gasification, calcium carbonate calcination) with technologies not yet commercially available such as the CO2 storage and the alkalinization of the oceans by the spreading of calcium hydroxide (ocean liming). In detail, the system includes the calcination of the limestone exploiting the heat of the syngas produced by the gasification of biomass or coal. From the calcium oxide produced in the calcination, calcium hydroxide is produced with the addition of water and spread in the ocean by means of ship. Furthermore, the process produces a fuel gas rich in hydrogen that is used to produce electricity. A part of the produced electricity fulfills system energy demand the remaining part is fed into the grid. This last quantity of energy replaces the production of the same quantity of electricity from fossil sources avoiding the impacts related to its production. The LCA study is applied to four system configurations, combinations of two types of fuels (biomass or coal) and two types of CO2 storage (geological and in glass capsules on the seabed). In the configuration with biomass gasification, the removal of CO2 from the atmosphere also occurs through the storage of CO2 absorbed by the biomass during its growth, while in the case of coal the removal is caused only by the ocean liming, which causes an increase in the uptake of atmospheric CO2 by the oceans and its storage in the form of bicarbonates. In this LCA study, the functional unit (FU) of the system is 1 kg of Ca(OH)2 produced and discharged into the ocean. Fifteen impact categories have been considered for the calculation of impacts, the one of main interest is Climate change impact category. The results show that the system in any configuration has a totally negative impact on the Climate change category, i.e. there is a benefit for the environment from the system. The system removes or avoids 3.02 kgCO2eq/FU in the biomass configuration with geological storage and 1.71 kgCO2eq/FU in the coal configuration with geological storage. Changing the type of storage, the benefit is reduced by only 0.02 kgCO2eq/FU. Furthermore, the biomass configuration with geological storage has a total negative impact, that is a benefit for the environment, in 12 impact categories (11 in the case of storage in capsules) while there are 7 categories with negative impact in both configurations with coal. A sensitivity analysis was, then, performed, considering 5 parameters (discharge rate of Ca(OH)2, distance to transport the biomass to the plant, distance to transport the calcium carbonate to the plant, distance to transport Ca(OH)2 from the plant to the port and fossil energy source that is avoided by the surplus energy produced by the system). Three different operating conditions were analysed ("best", "most likely" and "worst" for CO2 removal). In all operating conditions, all configurations have a benefit on Climate change, i.e. a total negative impact. Regarding CO2, the configurations with biomass always have better performances than those with coal excluding Land use category. Finally, thanks to the removal of CO2 through the ocean liming, the configurations with the coal allow to have a benefit on Climate change, even without considering the avoided impacts of electricity production.| File | Dimensione | Formato | |
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2019_07_Campo.pdf
Open Access dal 12/07/2020
Descrizione: Testo della tesi
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https://hdl.handle.net/10589/148651