The growing demand for compact technologies Gas-to-Liquid (GtL) directs the research towards the intensification of natural gas (methane) conversion into synthesis gas (mixture of carbon monoxide and hydrogen) through the steam reforming reaction and from synthesis gas into liquid fuels through the Fischer-Tropsch reaction. The high exothermicity of the Fischer-Tropsch process makes the temperature control a critical issue. In this work, the possibility to operate a tubular reactor with conductive structures packed with cobalt-based catalysts has been demonstrated experimentally, under industrially relevant LTFT conditions. This work compares the performance of a conventional bed-packed reactor with a reactor loaded with a conductive structure (periodic open cellular structure-POCS) packed with the same amount of catalyst. POCS was produced by 3D printing at the department of mechanic of Polytechnic of Milan, using an aluminium alloy (AlSi7Mg0.6). The results obtained with the latter configuration were also compared with those obtained in a reactor loaded with an aluminium foam (reference literature test). The structured POCS reactor achieved exceptional performance with an excellent thermal control of the system despite the classic configuration (absence of conductive structure) that, already at low operating temperatures, showed a thermal runaway. The structured POCS reactor has also exceeded the performance of the reference test in terms of heat exchange. The best performance has been attributed to the different geometric properties and to the best contact at the wall of the POCS respect to the foam. In order to gain more insights on the effect of the reactor structure/wall contact, the reactivity of a POCS 3D-printed with a metallic outer skin has been investigated. The presence of such skin has allowed to maximize the contact between the wall and the structure reaching high catalytic and heat exchange performance. Eventually, the possibility of loading the reactor by diluting the catalytic bed with a crushed conductive material has been investigated. The worst performance of the diluted bed with conductive material highlights the importance of employing a continuous structure to improve the reaction heat removal.
La crescente richiesta di tecnologie compatte Gas-to-Liquid (Gtl) spinge la ricerca verso l’intensificazione dei processi di conversione di gas naturale (metano) a gas di sintesi (miscela di monossido di carbonio e idrogeno) attraverso la reazione di steam reforming e da gas di sintesi a combustibili liquidi attraverso la reazione di Fischer-Tropsch. L’elevata esotermicità del processo Fischer-Tropsch fa sì che il controllo della temperatura sia un problema di primaria importanza. È qui dimostrato sperimentalmente la possibilità di operare con un reattore tubolare in condizioni industrialmente significative di LTFT (Low Temperature Fischer-Tropsch) con strutture conduttive impaccate con catalizzatori a base di cobalto. In questo elaborato sono state confrontate le prestazioni di un reattore convenzionale a letto impaccato con quelle di un reattore caricato con struttura conduttiva (periodic open cellular structure-POCS) impaccata con lo stesso quantitativo di catalizzatore. La POCS è stata prodotta tramite 3D printing presso il dipartimento di meccanica del Politecnico di Milano, utilizzando una lega di alluminio (AlSi7Mg0.6). I risultati ottenuti con quest’ultima configurazione sono stati inoltre confrontati con quelli ottenuti in un reattore caricato con una schiuma di alluminio (test di letteratura di riferimento). Il reattore strutturato POCS ha permesso di raggiungere prestazioni eccezionali con un ottimo controllo termico del sistema a dispetto della configurazione classica (assenza di struttura conduttiva) che, già a basse temperature operative, ha mostrato l’insorgere di un runaway termico. Il reattore strutturato POCS ha inoltre superato le prestazioni del test di riferimento in termini di scambio termico. Le migliori prestazioni sono state attribuite alle diverse proprietà geometriche e al miglior contatto in parete della POCS rispetto alla schiuma. Per valutare l’effetto del contatto struttura/parete del reattore, è stata infine investigata la reattività di una POCS stampata con una pelle esterna metallica. La presenza di tale pelle ha permesso di massimizzare il contatto in parete della struttura raggiungendo elevate prestazioni catalitiche e di scambio termico. Infine, è stata investigata la possibilità di caricare il reattore diluendo il letto catalitico con frammenti di materiale conduttivo invece di utilizzare una struttura impaccata. Le peggiori prestazioni del letto diluito con materiale conduttivo ha evidenziato l’importanza di impiegare una struttura continua per migliorare lo smaltimento del calore di reazione.
A novel reactor design for highly exothermic reactions : a case study on the Fischer-Tropsch synthesis
CASTANO, VINCENZO
2018/2019
Abstract
The growing demand for compact technologies Gas-to-Liquid (GtL) directs the research towards the intensification of natural gas (methane) conversion into synthesis gas (mixture of carbon monoxide and hydrogen) through the steam reforming reaction and from synthesis gas into liquid fuels through the Fischer-Tropsch reaction. The high exothermicity of the Fischer-Tropsch process makes the temperature control a critical issue. In this work, the possibility to operate a tubular reactor with conductive structures packed with cobalt-based catalysts has been demonstrated experimentally, under industrially relevant LTFT conditions. This work compares the performance of a conventional bed-packed reactor with a reactor loaded with a conductive structure (periodic open cellular structure-POCS) packed with the same amount of catalyst. POCS was produced by 3D printing at the department of mechanic of Polytechnic of Milan, using an aluminium alloy (AlSi7Mg0.6). The results obtained with the latter configuration were also compared with those obtained in a reactor loaded with an aluminium foam (reference literature test). The structured POCS reactor achieved exceptional performance with an excellent thermal control of the system despite the classic configuration (absence of conductive structure) that, already at low operating temperatures, showed a thermal runaway. The structured POCS reactor has also exceeded the performance of the reference test in terms of heat exchange. The best performance has been attributed to the different geometric properties and to the best contact at the wall of the POCS respect to the foam. In order to gain more insights on the effect of the reactor structure/wall contact, the reactivity of a POCS 3D-printed with a metallic outer skin has been investigated. The presence of such skin has allowed to maximize the contact between the wall and the structure reaching high catalytic and heat exchange performance. Eventually, the possibility of loading the reactor by diluting the catalytic bed with a crushed conductive material has been investigated. The worst performance of the diluted bed with conductive material highlights the importance of employing a continuous structure to improve the reaction heat removal.| File | Dimensione | Formato | |
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Descrizione: Testo della tesi Vincenzo Castano
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https://hdl.handle.net/10589/152440