ETD

Digital archive of theses discussed at the University of Pisa

 

Tesi etd-04222020-114014


Thesis type
Tesi di laurea magistrale
Author
CERAGIOLI, FEDERICO
URN
etd-04222020-114014
Thesis title
Thermodynamic analysis of an inverted Brayton cycle coupled to an ORC in a Biogas plant with Biomethane upgrading
Department
INGEGNERIA DELL'ENERGIA, DEI SISTEMI, DEL TERRITORIO E DELLE COSTRUZIONI
Course of study
INGEGNERIA ENERGETICA
Supervisors
relatore Prof. Desideri, Umberto
relatore Prof. Lemort, Vincent
relatore Ing. Baccioli, Andrea
relatore Ing. Bischi, Aldo
Keywords
  • numerical simulation
  • ORC
  • biogas plant
  • inverted Brayton cycle
  • cogeneration
Graduation session start date
07/05/2020;
Consultabilità
Secretata d’ufficio
Release date
07/05/2090
Summary
In this thesis, a thermodynamic analysis under design conditions of the performance of a biogas-fuelled mGT based on inverted Brayton cycle is investigated. The case study is an existing biogas plant near Pisa which performs co-digestion of a mixture of civil sewage and organic waste. A preliminary study of potential biomethane production had been made. A remodelling of the cogeneration system has been considered in this work. The current plant consists of a gas turbine operating on the conventional Brayton cycle. This study aims to compare this system with one operating on the inverted Brayton cycle. The upgrading system reduces the size of the cogenerator and at the same time requires a large amount of heat for the separation of the carbon dioxide. Different configurations of the cogenerator for two sizes of the upgrading system have been considered. A steady-state simulation was performed by using the daily average conditions for the one-year long operation of the plant. The first comparison between the performance of an mGT in the case of traditional and inverted Brayton cycle shows that lower electricity production is achieved in the second case.
The opportunity to increase efficiency through the employment of an ORC as a bottoming cycle has been considered for both systems. The combination of the two cycles, as well as the selection of the organic fluid, depends on the thermal load of the plant.
The results show that the integration of an ORC produces better results in the case of the Brayton cycle for all plant sizes considered.
An increase in IBC performance alone and with ORC are obtained when a given percentage of flue gas is recirculated into the combustion chamber.
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