The problem of global warming needs to be faced with clean technologies for power production and a more efficient utilization of fossil fuels. Fuel cells, although they are not commercially available like other technologies, offer strong potentialities with their high efficiency and low pollutant emissions. In this paper the integration of a SOFC stack is to be studied in a classical combined cycle with a GT-ST configuration with analysis of the benefits of integration on efficiency, pollutant emissions and better performance at partial load. At first a full load and partial load analysis is to be performed in the base case of GTCC. A plant size with 30 MWel power output is studied with a 21 MW gas turbine plus a one pressure level heat recovery steam cycle. The off-design condition is analysed at various partial loads: 80%, 60% and 40% of nominal power output. The integration of the SOFC stack in a direct hybrid system means that the cell stack is pressurized, and it partially substitutes the GT combustor heating up the air from the compressor and, additionally, already producing electricity. The power output more than triples itself up to 96.3 MW and the efficiency rises at any load with a peak at full load of 73.22% and staying over 50% at any load. Furthermore, a lower minimum load of 20% of nominal power is reached. The SOFC produces power with almost no pollutant emissions. Burning fuel, it oxidizes part of the oxygen from the compressor flow, thus reducing the amount of oxygen going to the GT combustor. In this way the flame temperature is strongly reduced, and the NOx emissions stay below 4 ppmvd@15%O2 at any load. The performance reached by the triple combined cycle give a relevant result. It demonstrates that, with a fuel cell integration in a GTCC combined cycle, can solve its problem of high emissions at partial load and its high minimum load that often forces the plant shut down due to emission limits. In addition, it gives benefits to the NOx emissions at any load.
A causa del riscaldamento globale in atto il mondo della produzione dell’energia elettrica sta cambiando a favore di impianti più efficienti e meno inquinanti. La tecnologia delle pile a combustibile, pur essendo ancora in fase di sviluppo, ha grandi potenzialità da offrire. La sua particlarità è la produzione di elettricità tramite reazione elettrochimica che riduce notevolmente gli inquinanti emessi con un’alta efficienza. Questa tesi propone l’integrazione di una pila SOFC in una centrale a ciclo combinato con turbina a gas e ciclo a vapore. Al principio una analisi a pieno carico e carico parziale viene effettuata sul ciclo combinato che viene scelto con una potenza nominale di 30 MW di cui 21 MW sono prodotti dalla turbina a gas. L’efficienza nominale si assesta sul 48.49% e scende fino al 38.50% al 40% di carico. In seguito viene integrata la pila SOFC per sostituire parzialmente il combustore. Il sistema ibrido così creato è diretto, la pila lavora in pressione e le sue performance migliorano. La potenza del nuovo ciclo a pieno carico cresce a 96.3 MW. Ai carichi parziali l’efficienza raggiunge un massimo a pieno carico di 73.22% e si mantiene sopra il 50% ad ogni carico. Inoltre, un minimo carico del 20% viene raggiunto. Avendo un inferiore carico minimo l’impianto può restare acceso con tutti i componenti in temperatura senza superare i limiti di emissioni e pronto ad alzare la potenza se richiesto dalla rete. Il numero di spegnimenti dell’impianto in un periodo sarebbero diminuiti e la sua effficienza globale nel tempo resterebbe più alta del caso base di ciclo combinato. Inoltre le emissioni di NOx vengono ridotte notevolmente. Dato che la pila a combustibile ossida parzialmente la portata d’aria in uscita dal compressore la frazione molare di ossigeno all’ingresso del combustore della turbina a gas è ridotta. Allo stesso modo si abbassa la temperatura di fiamma che riduce le emissioni di NOx sotto 4 ppmvd@15%O2 ad ogni carico.
Part-load analysis of a hybrid solid oxide fuel cell-gas turbine combined cycle
FASCIOLO, PIETRO
2016/2017
Abstract
The problem of global warming needs to be faced with clean technologies for power production and a more efficient utilization of fossil fuels. Fuel cells, although they are not commercially available like other technologies, offer strong potentialities with their high efficiency and low pollutant emissions. In this paper the integration of a SOFC stack is to be studied in a classical combined cycle with a GT-ST configuration with analysis of the benefits of integration on efficiency, pollutant emissions and better performance at partial load. At first a full load and partial load analysis is to be performed in the base case of GTCC. A plant size with 30 MWel power output is studied with a 21 MW gas turbine plus a one pressure level heat recovery steam cycle. The off-design condition is analysed at various partial loads: 80%, 60% and 40% of nominal power output. The integration of the SOFC stack in a direct hybrid system means that the cell stack is pressurized, and it partially substitutes the GT combustor heating up the air from the compressor and, additionally, already producing electricity. The power output more than triples itself up to 96.3 MW and the efficiency rises at any load with a peak at full load of 73.22% and staying over 50% at any load. Furthermore, a lower minimum load of 20% of nominal power is reached. The SOFC produces power with almost no pollutant emissions. Burning fuel, it oxidizes part of the oxygen from the compressor flow, thus reducing the amount of oxygen going to the GT combustor. In this way the flame temperature is strongly reduced, and the NOx emissions stay below 4 ppmvd@15%O2 at any load. The performance reached by the triple combined cycle give a relevant result. It demonstrates that, with a fuel cell integration in a GTCC combined cycle, can solve its problem of high emissions at partial load and its high minimum load that often forces the plant shut down due to emission limits. In addition, it gives benefits to the NOx emissions at any load.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/139894