The low values of LCOE achieved recently by RES in remote location opens the possibility to use electricity-derived fuels as energy carriers to exploit such affordable energy source. The process for the synthesis of these fuels stays within the Power to Gas (PtG) technology, involving the conversion of water and carbon dioxide to methane by means of electric energy for the intermediate electrolysis process. The objective of this work is to design and evaluate the economic potential of a large PtG plant located in a region offering high RES potential while not being connected to the electric grid. In the analysis, photovoltaic is used as source of power, alkaline electrolyte (AEK) is used for electrolysis and adiabatic fixed bed reactors is the technology considered for methanation. As source of carbon dioxide, two alternatives are studied: capturing CO2 from the exhaust gases of nearby industrial facilities (CC) or capturing carbon dioxide directly form atmosphere (Direct Air Capture, DAC). The PtG plant is designed in three configurations, one using CC and the other two using DAC. The one using CC and one of the two DAC use Lithium-ion batteries for energy storage, the other uses a hydrogen-fed gas turbine to generate electric energy. These three configurations are evaluated in three cases: in the first (Full Load) the methanator always works at full load, requiring larger storage systems; in the second (Full Load and Recovery) the waste heat of the methanator is recovered and used; the third case (Partial Load with Recovery and Oversizing) oversizes the methanator and adds the possibility to operate at partial load. First, the analysis assesses the efficiency of each configuration as well as the corresponding Levelized Cost of Methane (LCOM), evidencing that the electric to gas efficiency goes from 31% (DAC with gas turbine) to 39% (CC). Then, it is calculated the breakeven price of carbon dioxide that aligns the LCOM of the three supply chains in Partial load case, as it revealed the most convenient. A sensitivity analysis has been performed on the CAPEX of the system components to evaluate the impact on the LCOM, showing that the most critical element is PV followed by AEK. The final cost of synthetic gas compared to a reference price of natural gas shows that the renewable gas costs more than ten times its fossil alternative.
I più recenti valori di LCOE rilevati da fonti rinnovabili situate in regioni remote aprono la possibilità di sfruttare tale energia anche per usi diversi, ad esempio produrre gas sintetico. Tale processo rientra nella tecnologia chiamata Power to Gas (PtG), che prevede la trasformazione di acqua e anidride carbonica in metano, consumando energia elettrica nel passaggio intermedio di elettrolisi. L’obiettivo di questo lavoro è stato il dimensionamento di un grande impianto PtG situato in una zona ad alto potenziale rinnovabile scollegata dalla rete elettrica e di valutarne i costi, in particolare il costo del gas prodotto. L’analisi ha considerato il fotovoltaico per la produzione di elettricità e la tecnologia Alkaline electrolyte (AEK) per il processo di elettrolisi, mentre per il processo di metanazione si è adottata la tecnologia dei reattori a letto fisso adiabatico. Come fonte di anidride carbonica sono state valutate due alternative: la prima prevede l’acquisto di CO2 catturata in un impianto industriale limitrofo (CC), la seconda integra la cattura direttamente della CO2 dall’atmosfera con la tecnologia Direct Air Capture (DAC). L’impianto è stato dimensionato in tre differenti configurazioni: una usa la CC e le altre due usano la DAC; quella che usa la CC e una delle due DAC, usano un pacco batterie agli ioni di litio mentre l’altra prevede una turbina a gas alimentata a idrogeno per produrre energia elettrica. Le tre configurazioni sono state valutate in tre casi: il primo (Full Load) prevede che il metanatore lavori sempre alla potenza nominale, richiedendo grandi accumuli per gestire l’intermittenza della fonte primaria; nel secondo caso (Full Load and Recovery) il calore disperso dal metanatore viene recuperato e utilizzato; nel terzo caso (Partial Load with Recovery and Oversizing) il metanatore viene sovradimensionato e viene aggiunta la possibilità di operare a carico parziale. Lo studio ha investigato l’efficienza energetica delle nove configurazioni insieme al costo del gas prodotto, evidenziando un’efficienza di conversione da energia elettrica a gas tra il 31% (DAC con turbina a gas) e il 39% (CC) .Poi sono stati calcolati i due prezzi breakeven della CO2 che facevano allineare LCOM del caso CC con quello delle altre due filiere DAC. Questa analisi è stata fatto solo per il caso migliore (Partial load). Un’analisi di sensibilità sul CAPEX dei componenti dell’impianto ha permesso di valutarne l’effetto sul costo finale del gas, mostrando che il maggior responsabile dei costi è il PV seguito dall’ AEK. Il costo finale del gas è stato confrontato con un prezzo di riferimento del gas naturale mostrando che il gas sintetico costa più di dieci volte l’equivalente fossile.
Synthetic methane production in high-RES remote regions : design and techno-economic evaluation of a large-scale PtG plant
Bosi, Emilio
2019/2020
Abstract
The low values of LCOE achieved recently by RES in remote location opens the possibility to use electricity-derived fuels as energy carriers to exploit such affordable energy source. The process for the synthesis of these fuels stays within the Power to Gas (PtG) technology, involving the conversion of water and carbon dioxide to methane by means of electric energy for the intermediate electrolysis process. The objective of this work is to design and evaluate the economic potential of a large PtG plant located in a region offering high RES potential while not being connected to the electric grid. In the analysis, photovoltaic is used as source of power, alkaline electrolyte (AEK) is used for electrolysis and adiabatic fixed bed reactors is the technology considered for methanation. As source of carbon dioxide, two alternatives are studied: capturing CO2 from the exhaust gases of nearby industrial facilities (CC) or capturing carbon dioxide directly form atmosphere (Direct Air Capture, DAC). The PtG plant is designed in three configurations, one using CC and the other two using DAC. The one using CC and one of the two DAC use Lithium-ion batteries for energy storage, the other uses a hydrogen-fed gas turbine to generate electric energy. These three configurations are evaluated in three cases: in the first (Full Load) the methanator always works at full load, requiring larger storage systems; in the second (Full Load and Recovery) the waste heat of the methanator is recovered and used; the third case (Partial Load with Recovery and Oversizing) oversizes the methanator and adds the possibility to operate at partial load. First, the analysis assesses the efficiency of each configuration as well as the corresponding Levelized Cost of Methane (LCOM), evidencing that the electric to gas efficiency goes from 31% (DAC with gas turbine) to 39% (CC). Then, it is calculated the breakeven price of carbon dioxide that aligns the LCOM of the three supply chains in Partial load case, as it revealed the most convenient. A sensitivity analysis has been performed on the CAPEX of the system components to evaluate the impact on the LCOM, showing that the most critical element is PV followed by AEK. The final cost of synthetic gas compared to a reference price of natural gas shows that the renewable gas costs more than ten times its fossil alternative.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/165095