Anaerobic digestion of biomass and sludges is a technology that is able to produce a gas mixture composed by methane (50-70%) and carbon dioxide (30-50%). This technique exploits a set of microorganisms that, through the degradation of organic matter, such as organic waste or wastewater sludge, produces this methane-rich gas known as biogas. However, a gas with a higher methane content, and therefore a higher heating value, is required for this renewable energy source in order to be implemented in the natural gas grid or as vehicle fuel. A whole class of technologies has been developed in the oil & gas field to remove the excess the CO2, through an operation known as “biogas upgrading”. Methods currently available, however, cause an increase in the process cost and the loss of a part of the methane processed. For this reason, in recent years, new alternative techniques have been investigated. One of the most important ones, the biological biogas upgrading, is able to increase the final methane discharge and reduce the CO2 concentration through the injection of hydrogen (H2) and biogas in a specialized reactor. Biological biogas upgrading is achieved by a set of archaea known as hydrogenotrophic methanogens. These ones, through a reaction known as Sabatier reaction, can consume hydrogen and carbon dioxide to produce methane. This thesis describes the design and the construction of a pilot-scale biological biogas upgrading reactor in the ex-situ mode, that has been built with the cooperation of the European Union, the Regional Government of Lombardy, Polytechnic of Milan and Gruppo CAP. The reactor’s configuration is known as CSTR (Continuous Stirred Tank Reactor). In in this configuration biogas and hydrogen are injected in the main tank, where the reaction occurs, which is equipped with a recirculation section where gas and sludge are mixed in order to improve the hydrogen solubilization. Preliminary analyses have been carried out for evaluating the best choice concerning initial conditions and then the technology has been compared to the existing upgrading techniques in order to determine the best solution for its development.
Il biogas è un composto gassoso ottenuto attraverso la digestione anaerobica di fanghi o biomasse. Questa tecnica sfrutta la degradazione di sostanze organiche ad opera di diversi ceppi di microorganismi e permette di produrre una miscela composta da CH4 al 50-70%, da CO2 al 30-50% e da composti in traccia. Il tenore di metano, però, non permette la sua iniezione diretta nella linea del gas o il suo utilizzo in veicoli alimentati a metano. Sono quindi stati sviluppati diversi sistemi che, basandosi su tecniche di rimozione fisico-chimiche, consentono di eliminare la CO2 dal biogas. Essi causano però un incremento nel costo di produzione e in alcuni casi determinano la perdita di una parte del CH4. È pertanto oggetto di studio una nuova tecnologia, nota come upgrading biologico, che sfrutta il metabolismo di metanogenesi idrogenotrofa in cui la CO2 è convertita a biometano tramite l’immissione di H2 esogeno; ciò permette di associare l’upgrading ad un incremento del volume di CH4. L’oggetto di questo lavoro di tesi è la realizzazione di un reattore a scala pilota del processo di upgrading biologico in modalità ex-situ, attività inserita nell’ambito del progetto PerFORM WATER 2030. Se ne è seguita la progettazione e l’installazione presso la società di ingegneria SEAM Engineering. Si è provveduto alla definizione e allo svolgimento delle prove preliminari alla sperimentazione, quali quelle di commissioning, di misura dell’attività della biomassa e di caratterizzazione del reattore, volte a valutare tempi di residenza e capacità di trasferimento di gas poco solubili. Il pilota è composto da una vasca principale, da una sezione di ricircolo di fango e gas e da due zone in cui avvengono dosaggio di micronutrienti ed analisi dell’off-gas. L’idrogeno in ingresso al reattore proviene da un elettrolizzatore AEM che permette all’upgrading biologico di rientrare nell’ambito Power-to-gas sfruttando il surplus energetico proveniente da fonti rinnovabili per accumulare energia sotto forma di H2 e CH4. Si è, infine, valutata l’efficienza di conversione energetica in confronto alle tecniche di upgrading preesistenti e si sono determinate le problematiche associate al suo sviluppo.
Upgrading biologico del biogas con processo ex-situ a scala pilota
TRIONFINI, MIRKO
2018/2019
Abstract
Anaerobic digestion of biomass and sludges is a technology that is able to produce a gas mixture composed by methane (50-70%) and carbon dioxide (30-50%). This technique exploits a set of microorganisms that, through the degradation of organic matter, such as organic waste or wastewater sludge, produces this methane-rich gas known as biogas. However, a gas with a higher methane content, and therefore a higher heating value, is required for this renewable energy source in order to be implemented in the natural gas grid or as vehicle fuel. A whole class of technologies has been developed in the oil & gas field to remove the excess the CO2, through an operation known as “biogas upgrading”. Methods currently available, however, cause an increase in the process cost and the loss of a part of the methane processed. For this reason, in recent years, new alternative techniques have been investigated. One of the most important ones, the biological biogas upgrading, is able to increase the final methane discharge and reduce the CO2 concentration through the injection of hydrogen (H2) and biogas in a specialized reactor. Biological biogas upgrading is achieved by a set of archaea known as hydrogenotrophic methanogens. These ones, through a reaction known as Sabatier reaction, can consume hydrogen and carbon dioxide to produce methane. This thesis describes the design and the construction of a pilot-scale biological biogas upgrading reactor in the ex-situ mode, that has been built with the cooperation of the European Union, the Regional Government of Lombardy, Polytechnic of Milan and Gruppo CAP. The reactor’s configuration is known as CSTR (Continuous Stirred Tank Reactor). In in this configuration biogas and hydrogen are injected in the main tank, where the reaction occurs, which is equipped with a recirculation section where gas and sludge are mixed in order to improve the hydrogen solubilization. Preliminary analyses have been carried out for evaluating the best choice concerning initial conditions and then the technology has been compared to the existing upgrading techniques in order to determine the best solution for its development.File | Dimensione | Formato | |
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2019_12_Trionfini.pdf
Open Access dal 03/12/2020
Descrizione: Testo della tesi
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https://hdl.handle.net/10589/150914