ETD

Archivio digitale delle tesi discusse presso l'Università di Pisa

Tesi etd-04142014-115134


Tipo di tesi
Tesi di laurea magistrale
Autore
NIZZOLA, GIOVANNI
URN
etd-04142014-115134
Titolo
Soot and nitrogen chemistry in oxy-propane combustion: interactions and implications for NO reduction
Dipartimento
INGEGNERIA DELL'ENERGIA, DEI SISTEMI, DEL TERRITORIO E DELLE COSTRUZIONI
Corso di studi
INGEGNERIA ENERGETICA
Relatori
relatore Tognotti, Leonardo
tutor Andersson, Klas
Parole chiave
  • Oxy-fuel combustion
  • Combustion chemistry
  • Nitrogen oxides
  • Reburning
  • Soot
  • Soot-NO interactions
Data inizio appello
05/05/2014
Consultabilità
Completa
Riassunto
Oxy-fuel combustion is one of the most promising technologies to capture CO2 from power plants. The concept is to burn the fuel in a mixture of oxygen and recirculated flue gases instead of air. The resulting flue gases will then mainly be composed by CO2 and H2O. One interesting feature of oxy-fuel combustion is that the emission of NOx may be heavily reduced by reburning reactions due to the recycle of flue gases. In addition, experiments performed in Chalmers 100 kWth oxy-fuel unit with propane as a fuel showed a strongly increased reduction of NO when inlet oxygen concentration was increased above 35%. Under these conditions an increased soot formation was also observed. Therefore, could be inferred that soot formation could play some role in the reduction of NO and interactions between nitrogen and soot chemistry might take place. The aim of this work is to identify and describe possible interactions that could take place, of interest to explain the observed NO reduction trends. The investigation is based on combustion modeling, with focus on chemistry. Detailed reaction mechanisms from literature, relevant to nitrogen and soot chemistry were implemented and the sensitivity of results to combustion conditions was investigated. The modeling results showed that temperature, inlet oxygen concentration and mixing assumptions are important to radical pool and to determine the rates of key-reactions in both soot and nitrogen chemistry. In particular, an increasing soot formation was observed when local temperature and inlet oxygen concentration were increased in the model, with major importance of the former. In the same way, when the local stoichiometry was changed to a more oxygen-lean environment, the soot formation increased. On the other hand, nitrogen oxides showed characteristic trends in the reactor in all the simulations, with chemistry-based sections clearly detectable. The outlet NO concentration increased when the flame and post-flame temperature increased, whereas decreased when inlet oxygen concentration was increased. Stoichiometry acted on the local NO concentration and reburning, with low impact on outlet NO. However, the homogeneous NO reduction was not as high as in experiments, confirming the possible intervention of other phenomena, such as soot-NO interactions. The mechanisms that were identified in this work consisted essentially in homogeneous and heterogeneous ones. Homogeneous interactions that take place on a soot precursors’ level, mainly seen as competition for radicals between reburning and gas-phase soot chemistry. Heterogeneous interactions involving soot particles both as reactants and as catalyzers could be seen in flame and post flame regions. In conclusion, interactions could be a key-process to explain the enhanced NO reduction seen in the experiments at high inlet oxygen concentrations.
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