This Thesis studies the performances and design parameters of a steam power plant burning solid biomass in a stoker boiler and investigates the possibility of adopting, for a similar plant, the Supercritical Carbon Dioxide (sCO2) closed Joule-Brayton thermodynamic cycles. First, an analysis on the current European biomass power production sector is proposed, with a focus on the plants operating in Italy. An existing steam power plant located in Piombino, presenting the typical characteristics of a power plant in the current biomass power sector in terms of cycle and boiler technologies, and plant size, is identified as reference. Therefore, a code is developed to simulate its design parameters, focusing on the thermodynamic performances and boiler sizing. For the Recuperated, Recompressed and Partial Cooling sCO2 cycles, an optimization of the design operating conditions that maximizes the plant electric efficiency is performed for the maximum cycle temperature (TIT) in a range going from 450°C to 570°C, which includes the design value of the reference plant. Therefore, a comparison in terms of plant efficiency and cost of electricity (COE) is performed between the reference steam plant and the three sCO2 cycles, considering the same TIT and electric power produced. For the sCO2 plants, also an evaluation of the first principle efficiency and Primary Energy Savings (PES) values reached when a heat recovery section is implemented is performed for the designs defined by the optimization. For the Recuperated cycle (the one with the lowest COE) also an analysis on the plant performances in partial load is proposed, considering both the electric-only and the cogeneration configuration. Results highlight how at a TIT=500°C the steam plant has an efficiency of 33.3%, while the Recompressed sCO2 cycle reaches an efficiency of 35.4%. The Recuperated cycle, instead, has COE=80 $/MWh, which is much lower than the COE=100 $/MWh of the steam plant.
Questa Tesi studia le prestazioni e i parametri di progetto di un impianto di produzione di potenza a vapore che brucia biomassa solida in una caldaia a grata e investiga la possibilità di adottare, per un impianto simile, i cicli di potenza di Joule-Brayton chiusi ad Anidride Carbonica Supercritica (sCO2). Innanzitutto, viene proposta un’analisi dell’attuale settore Europeo di produzione di potenza a biomassa, concentrandosi sugli impianti operanti in Italia. Presentando le caratteristiche tipiche di un impianto di potenza nell’odierno settore di produzione di potenza da biomassa, viene identificato come riferimento un impianto di potenza a vapore realmente esistente a Piombino. Conseguentemente, viene sviluppato un codice per simulare i parametri di progetto di questo impianto, concentrandosi sulle prestazioni termodinamiche e il dimensionamento della caldaia. Per i cicli sCO2 Recuperativo, Ricompresso e Partial Cooling, viene effettuata un’ottimizzazione delle condizioni operative di progetto che massimizza l’efficienza elettrica di impianto per una temperatura massima di ciclo (TIT) compresa in un intervallo tra 450°C e 570°C, il quale include il valore di progetto dell’impianto di riferimento. Dopodiché, viene effettuato un confronto in termini di efficienza di impianto e costo dell’elettricità (COE) tra l’impianto a vapore di riferimento e i tre cicli sCO2, considerando le stesse TIT e potenza elettrica prodotta. Per gli impianti sCO2, viene effettuata anche una valutazione dell’efficienza di primo principio e Indice di Risparmio Energetico (PES) raggiunti quando una sezione di recupero termico è implementata per i design definiti dall’ottimizzazione. Per il ciclo Recuperativo (quello con il più basso COE) viene proposta anche un’analisi delle prestazioni di impianto a carico parziale, considerando sia la configurazione di sola produzione elettrica, sia quella cogenerativa. I risultati mostrano come ad una TIT=500°C l’impianto a vapore abbia un’efficienza del 33.3%, mentre il ciclo sCO2 Ricompresso raggiunge un’efficienza del 35.4%. Il ciclo Recuperativo ha invece COE=80 $/MWh, molto più basso del COE=100 $/MWh dell’impianto a vapore.
Feasibility study on the application of supercritical carbon dioxide cycles to biomass-fired power plants. Design optimization and partial load analysis in electricity-only and cogeneration configurations
Zignani, Thomas
2019/2020
Abstract
This Thesis studies the performances and design parameters of a steam power plant burning solid biomass in a stoker boiler and investigates the possibility of adopting, for a similar plant, the Supercritical Carbon Dioxide (sCO2) closed Joule-Brayton thermodynamic cycles. First, an analysis on the current European biomass power production sector is proposed, with a focus on the plants operating in Italy. An existing steam power plant located in Piombino, presenting the typical characteristics of a power plant in the current biomass power sector in terms of cycle and boiler technologies, and plant size, is identified as reference. Therefore, a code is developed to simulate its design parameters, focusing on the thermodynamic performances and boiler sizing. For the Recuperated, Recompressed and Partial Cooling sCO2 cycles, an optimization of the design operating conditions that maximizes the plant electric efficiency is performed for the maximum cycle temperature (TIT) in a range going from 450°C to 570°C, which includes the design value of the reference plant. Therefore, a comparison in terms of plant efficiency and cost of electricity (COE) is performed between the reference steam plant and the three sCO2 cycles, considering the same TIT and electric power produced. For the sCO2 plants, also an evaluation of the first principle efficiency and Primary Energy Savings (PES) values reached when a heat recovery section is implemented is performed for the designs defined by the optimization. For the Recuperated cycle (the one with the lowest COE) also an analysis on the plant performances in partial load is proposed, considering both the electric-only and the cogeneration configuration. Results highlight how at a TIT=500°C the steam plant has an efficiency of 33.3%, while the Recompressed sCO2 cycle reaches an efficiency of 35.4%. The Recuperated cycle, instead, has COE=80 $/MWh, which is much lower than the COE=100 $/MWh of the steam plant.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/167404