טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentChazan Idan
SubjectThermodynamic and Experimental Demonstration of Inverted
Brayton Cycle in Heat Recovery Applications
DepartmentDepartment of Energy
Supervisor Professor Beni Cukurel
Full Thesis textFull thesis text - English Version


Abstract

A deregulated electricity supply market, based on the implementation of renewable energy power plants, vastly promotes the emerging distributed power generation concept. Numerous small and efficient power units are progressively introduced to the market to satisfy the new demands and replace large outdated power plants. Significant potential lies in the further improvement of small-scale power production technologies such as micro gas turbines, especially in cogeneration systems.

The presented work deals with increasing the efficiency of energy generation in decentralized energy supply through utilizing waste heat. Waste heat typically contains one third of the total combustion energy and is largely unused in contemporary small- scale power units. The investigation into a new concept for the simultaneous production of hot water and electrical energy, based on the inverted Brayton cycle (IBC), is explored. The IBC utilizes hot exhaust gas at near-atmospheric pressure through expansion to sub-atmospheric conditions, followed by cooling in in a heat exchanger and recompression of the cooled gas back to atmospheric pressure. This heat recovery cycle generates power via expansion of the isobaric lines between the expansion and compression stages, resulting in net positive power output. This kinetic energy can be used to drive an electric generator, while the heated coolant can be used directly for combined heat and power generation.

When compared to contemporary solutions for heat recovery, the IBC has advantage in overall power output efficiency, simplicity in integration with existing technologies, and cost effectiveness.

The thesis addresses the thermodynamic cycle analysis and simulation of the inverted Brayton cycle for waste heat recovery applications, and the design and construction of a functional prototype where the inverted Brayton cycle is experimentally demonstrated. Experimental validation of the inverted Brayton cycle has been attempted by few other research teams, making the current effort presented in this work particularly relevant in developing the validation of mathematical models previously published regarding IBC in heat recovery.

The work includes development of full thermodynamic cycle analysis, providing essential tools to assess the viability of integrating IBC in a given application, guiding the industry application selection for the design of the experimental system.

The thermodynamic cycle simulation developed for real turbomachinery and heat exchanger data assists to advance the experimental facility design, providing real performance efficiencies under given operating points. The experimental facility design of the IBC was then developed with the components selected based on the simulated model. Key challenges of the design include:

-          High speed generator and shaft coupling, resolved with high-speed transmission to scale down the generator, and precision mounting, alignment and coupling of the shaft system;

-          Start-up of the system, resolved with pressurized gas for initial stages, and motor starter for full operation stage;

Successful demonstration of the IBC will prove the concept viability as an alternative heat recovery cycle to state-of-the-art solutions, providing new advantages and broadening the scope of future application.