The thesis aims at assessing the energy, environmental and economic performance of flexible biomass-to-X plants, based on biomass gasification. One of the investigated pathways is represented by power and biomass-to-X plants, where the bioenergy plant is integrated with water electrolysis which generates hydrogen to be combined with the syngas from biomass gasification. Such a plant design allows to increase the carbon utilization and product yield when the electrolysis unit is in operation (i.e. during low electricity price periods). The other investigated pathway corresponds to biomass-to-X plants with carbon capture and storage (CCS), where the bioenergy plant includes the capture of the excess CO2 generated in the conversion of the biomass into the final product. If the captured CO2 is permanently stored underground, such plants can produce negative emissions. The analysis includes different types of gasification technologies (direct, indirect and sorption-enhanced gasification) and different final products (methanol and hydrogen). Regarding power and biomass-to-X plants, since the investment in an electrolysis system is profitable only for capacity factors higher than 80%, the operational flexibility should be exploited by avoiding the consumption of high-price electricity rather than in the use low-price “excess” electricity that can only be available for a limited number of hours. Moreover, the attractiveness of operating power and biomass-to-X plants in a flexible way may increase significantly in future scenarios with very high penetration of intermittent renewables, leading to low average electricity prices but also longer periods of high peak prices. Conversely, current electricity price curves with limited number of very high price hours during the year would not justify plants conceived to operate flexibly. Credits lower than 80 €/tCO2 for CO2 storage are needed to make biomass-to-X plants with CCS competitive with the corresponding plants without CCS. CO2 credits of 130-160 €/tCO2 allow achieving competitive methanol and hydrogen production costs of 400 €/t and 2 €/kg respectively. In the future carbon-constrained world, the best bioenergy conversion pathway (electricity, H2, methanol, etc.) with/without CCS will depend on the relative value/price of the products and of CO2, that vary over time with different time scales. In this context, multi-product plants can operate flexibly to produce the good with the highest added value.
La tesi mira a valutare le prestazioni energetiche, ambientali ed economiche di impianti biomass-to-X flessibili, basati sulla gassificazione della biomassa. Uno dei percorsi indagati è rappresentato dagli impianti power and biomass-to-X, dove l'impianto a biomassa è integrato con elettrolisi che genera idrogeno che si combina con il syngas derivante dalla gassificazione della biomassa. Questo genere di impianti consentono di aumentare l'utilizzo del carbonio e la resa del prodotto quando l'unità di elettrolisi è in funzione (ovvero durante i periodi di basso prezzo dell'elettricità). L'altro percorso studiato corrisponde agli impianti biomass-to-X con cattura e stoccaggio del carbonio (CCS), in cui l'impianto a biomassa include la cattura dell'eccesso di CO2 generata nella conversione da biomassa a prodotto finale. Se la CO2 catturata viene immagazzinata permanentemente nel sottosuolo, tali impianti possono produrre emissioni negative. L'analisi include diversi tipi di tecnologie di gassificazione (gassificazione diretta, indiretta e sorption-enhanced) e diversi prodotti finali (metanolo e idrogeno). Per quanto riguarda gli impianti power and biomass-to-X, poiché l'investimento in un sistema di elettrolisi è redditizio solo per fattori di capacità superiori a 80%, la flessibilità operativa dovrebbe essere sfruttata evitando il consumo di energia elettrica a prezzo elevato piuttosto che l'utilizzo di energia elettrica "in eccesso" a basso prezzo che può essere disponibile solo per un numero limitato di ore. Inoltre, l'attrattiva per un funzionamento flessibile degli impianti power and biomass-to-X potrebbe aumentare in modo significativo in scenari futuri con una penetrazione molto elevata di rinnovabili intermittenti, che porterebbe a bassi prezzi medi dell'elettricità ma anche a periodi più lunghi di prezzi di picco elevati. Al contrario, le attuali curve dei prezzi dell'energia elettrica con un numero limitato di ore a prezzo molto elevato durante l'anno non giustificherebbero impianti concepiti per operare in modo flessibile. Sono necessari crediti inferiori a 80 €/tCO2 per lo stoccaggio di CO2 per rendere gli impianti biomass-to-X con CCS competitivi rispetto ai corrispondenti impianti senza CCS. Crediti di CO2 di 130-160 €/tCO2 consentono di ottenere costi competitivi di produzione di metanolo e di idrogeno rispettivamente di 400 €/t e 2 €/kg. In futuro, il miglior percorso di conversione della biomassa (elettricità, H2, metanolo, ecc.) con e senza CCS dipenderà dal valore/prezzo relativo dei prodotti e della CO2, che variano nel tempo con diverse scale temporali . In questo contesto, impianti multiprodotto possono operare in modo flessibile per produrre il bene con maggior valore aggiunto.
Flexible biomass-to-X plants for resilient renewable energy system
Poluzzi, Alessandro
2022/2023
Abstract
The thesis aims at assessing the energy, environmental and economic performance of flexible biomass-to-X plants, based on biomass gasification. One of the investigated pathways is represented by power and biomass-to-X plants, where the bioenergy plant is integrated with water electrolysis which generates hydrogen to be combined with the syngas from biomass gasification. Such a plant design allows to increase the carbon utilization and product yield when the electrolysis unit is in operation (i.e. during low electricity price periods). The other investigated pathway corresponds to biomass-to-X plants with carbon capture and storage (CCS), where the bioenergy plant includes the capture of the excess CO2 generated in the conversion of the biomass into the final product. If the captured CO2 is permanently stored underground, such plants can produce negative emissions. The analysis includes different types of gasification technologies (direct, indirect and sorption-enhanced gasification) and different final products (methanol and hydrogen). Regarding power and biomass-to-X plants, since the investment in an electrolysis system is profitable only for capacity factors higher than 80%, the operational flexibility should be exploited by avoiding the consumption of high-price electricity rather than in the use low-price “excess” electricity that can only be available for a limited number of hours. Moreover, the attractiveness of operating power and biomass-to-X plants in a flexible way may increase significantly in future scenarios with very high penetration of intermittent renewables, leading to low average electricity prices but also longer periods of high peak prices. Conversely, current electricity price curves with limited number of very high price hours during the year would not justify plants conceived to operate flexibly. Credits lower than 80 €/tCO2 for CO2 storage are needed to make biomass-to-X plants with CCS competitive with the corresponding plants without CCS. CO2 credits of 130-160 €/tCO2 allow achieving competitive methanol and hydrogen production costs of 400 €/t and 2 €/kg respectively. In the future carbon-constrained world, the best bioenergy conversion pathway (electricity, H2, methanol, etc.) with/without CCS will depend on the relative value/price of the products and of CO2, that vary over time with different time scales. In this context, multi-product plants can operate flexibly to produce the good with the highest added value.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/194922