Following the increase in power production from renewable power plants, it has been necessary to take action to make the behaviour of the electricity grid more reliable. In order to deal with the unpredictability of these sources, it is useful to exploit methods to store excess electric energy during off-peak periods (when the energy produced by the source is greater than that required by the network) and then be able to use it in moments of peak load (when the demand is greater than the production). A method that enables to store energy for long periods is Power-to-Gas: excess electricity is used to form hydrogen through an electrolysis reaction of water. At this point, however, the problem of managing this gas arises. In this work we will present the LOHCs, that are organic liquids used as hydrogen carriers. The use of these liquids allows the transport and storage of hydrogen in the form of liquid under ambient conditions. To do this, it is necessary to chemically bind the hydrogen molecules to those of the chosen LOHC through an exothermic hydrogenation reaction. This reaction takes place in a catalytic reactor at high temperatures and pressures. Once out of this process, the hydrogenated liquid is ready to be transported and stored without the need of special containment materials (as happens for example in the case of liquid hydrogen or compressed hydrogen). Once arrived at its destination, the liquid is dehydrogenated in a special reactor, catalytic also in this case, always at high temperatures but at pressures close to that of the environment. This second reaction is endothermic and therefore requires heat from the outside. If there are no processes from which this thermal power can be recovered, it will be necessary to use part of the transported hydrogen to make the reaction take place and therefore its release. This work presents some organic liquids that can act as LOHC divided into three main categories: cyclic hydrocarbons, N-heterocyclic compounds and circular hydrogen carriers. Each of these liquids is analyzed considering some properties necessary for the success of the entire process, including: reaction enthalpy, hydrogen storage capacity, dehydrogenation temperature, gas flow and energy density. Based on the end use of the LOHC, you can choose the best liquid. At this point it will be necessary to design the system, which can vary according to the choice of the liquid. In particular, this work presents the plant layout and some simulations carried out for the case of toluene, an organic liquid already used as LOHC by the Japanese company Chiyoda Corp. This new method for handling hydrogen is comparable, as for the energy consumption, to the liquefaction of hydrogen. Although less hydrogen can be transported with LOHCs, this alternative becomes interesting when the dehydrogenation reaction is coupled to a heat source from which it can recover what is necessary for the release of the gas.
A seguito dell’aumento degli impianti di potenza da fonti rinnovabili, è stato necessario prendere dei provvedimenti per rendere più affidabile il funzionamento della rete elettrica. Per far fronte all’imprevedibilità di queste fonti è utile sfruttare dei metodi per accumulare l’energia prodotta in eccesso durante i periodi di off-peak (cioè quando l’energia prodotta dalla fonte è maggiore di quella richiesta dalla rete) per poi poterla utilizzare nei momenti di peak load (quando la domanda in rete è maggiore della produzione). Un metodo che permette di stoccare energia per lunghi periodi è il Power-to-Gas: l’energia elettrica in eccesso viene sfruttata per formare idrogeno attraverso una reazione di elettrolisi dell’acqua. A questo punto si presenta però il problema della gestione di questo gas. In questo lavoro verranno presentati gli LOHC, ovvero i liquidi organici utilizzati come vettori di idrogeno. L’uso di questi liquidi permette di trasportare e stoccare l’idrogeno sottoforma di liquido in condizioni ambiente. Per fare ciò, è necessario legare chimicamente le molecole di idrogeno a quelle del LOHC scelto attraverso una reazione esotermica di idrogenazione del liquido, che avviene in un reattore catalitico ad elevate temperature e pressioni. Una volta uscito da questo processo, il liquido idrogenato è pronto per essere trasportato e stoccato senza bisogno di utilizzare speciali materiali di contenimento (come avviene ad esempio nel caso di idrogeno liquido o idrogeno compresso). Giunto a destinazione, il liquido viene de-idrogenato in un apposito reattore, anche in questo caso catalitico, sempre ad elevate temperature ma a pressioni prossime a quella ambiente. Questa seconda reazione è endotermica e necessita quindi di calore proveniente dall’esterno. In caso non ci fossero processi da cui poter recuperare questa potenza termica sarà necessario utilizzare parte dell’idrogeno trasportato per far avvenire la reazione e quindi il suo rilascio. In questo lavoro vengono presentati alcuni liquidi organici che possono fungere da LOHC, suddivisi in tre principali categorie: idrocarburi ciclici, composti N-eterociclici e circular hydrogen carriers. Ognuno di questi liquidi viene analizzato tenendo in considerazione alcune proprietà necessarie per una buona riuscita dell’intero processo, tra cui: entalpia di reazione, capacità di stoccaggio di idrogeno, temperatura di de-idrogenazione, flusso di gas e densità energetica. In base all’utilizzo finale del LOHC si potrà scegliere il liquido migliore. A questo punto sarà necessario progettare l’impianto, che può variare in base alla scelta del liquido. In questo lavoro è presentato lo schema di impianto e alcune simulazioni svolte per il caso del toluene, liquido organico già utilizzato dall’azienda giapponese Chiyoda Corp come LOHC. Questo nuovo metodo per il trattamento dell’idrogeno è comparabile, per quanto riguarda la spesa energetica, alla liquefazione dell’idrogeno. Nonostante con gli LOHC si riesca a trasportare una minor quantità di idrogeno, questa alternativa diventa interessante quando la reazione di de-idrogenazione è accoppiata ad una fonte di calore da cui recupera quanto necessario per il rilascio del gas.
LOHC : un metodo per il trasporto e lo stoccaggio di idrogeno attraverso liquidi organici
TURRI, SARA
2019/2020
Abstract
Following the increase in power production from renewable power plants, it has been necessary to take action to make the behaviour of the electricity grid more reliable. In order to deal with the unpredictability of these sources, it is useful to exploit methods to store excess electric energy during off-peak periods (when the energy produced by the source is greater than that required by the network) and then be able to use it in moments of peak load (when the demand is greater than the production). A method that enables to store energy for long periods is Power-to-Gas: excess electricity is used to form hydrogen through an electrolysis reaction of water. At this point, however, the problem of managing this gas arises. In this work we will present the LOHCs, that are organic liquids used as hydrogen carriers. The use of these liquids allows the transport and storage of hydrogen in the form of liquid under ambient conditions. To do this, it is necessary to chemically bind the hydrogen molecules to those of the chosen LOHC through an exothermic hydrogenation reaction. This reaction takes place in a catalytic reactor at high temperatures and pressures. Once out of this process, the hydrogenated liquid is ready to be transported and stored without the need of special containment materials (as happens for example in the case of liquid hydrogen or compressed hydrogen). Once arrived at its destination, the liquid is dehydrogenated in a special reactor, catalytic also in this case, always at high temperatures but at pressures close to that of the environment. This second reaction is endothermic and therefore requires heat from the outside. If there are no processes from which this thermal power can be recovered, it will be necessary to use part of the transported hydrogen to make the reaction take place and therefore its release. This work presents some organic liquids that can act as LOHC divided into three main categories: cyclic hydrocarbons, N-heterocyclic compounds and circular hydrogen carriers. Each of these liquids is analyzed considering some properties necessary for the success of the entire process, including: reaction enthalpy, hydrogen storage capacity, dehydrogenation temperature, gas flow and energy density. Based on the end use of the LOHC, you can choose the best liquid. At this point it will be necessary to design the system, which can vary according to the choice of the liquid. In particular, this work presents the plant layout and some simulations carried out for the case of toluene, an organic liquid already used as LOHC by the Japanese company Chiyoda Corp. This new method for handling hydrogen is comparable, as for the energy consumption, to the liquefaction of hydrogen. Although less hydrogen can be transported with LOHCs, this alternative becomes interesting when the dehydrogenation reaction is coupled to a heat source from which it can recover what is necessary for the release of the gas.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/153244