Name: ALEXANDRE PERSUHN MORAWSKI
Type: PhD thesis
Publication date: 31/08/2021
Advisor:
Name |
Role |
|---|---|
| JOSÉ JOAQUIM CONCEIÇÃO SOARES SANTOS | Advisor * |
Examining board:
| Name |
Role |
|---|---|
| JOSÉ JOAQUIM CONCEIÇÃO SOARES SANTOS | Advisor * |
| ROGÉRIO RAMOS | Internal Examiner * |
Summary: The Brazilian thermal power plants were originally designed to serve as standby energy security for the grid, which is mainly supported by hydroelectric plants. The internal combustion engine (ICE) power plants eliminate copious amounts of residual heat through exhaust gases and cooling water. The current scenario has led to an increase in the operational times of these plants. An attractive solution for increasing power and efficiency in this situation is waste heat recovery (WHR). A variety of technologies and configurations can be used for WHR. The selection of the best WHR system is not a simple task, and the solution should not be generalized for different applications. In this context, optimization approach using mathematical programming has the advantage of providing a domain-independent systematic framework. In this thesis, a superstructure method is used for structural and parametric thermoeconomic optimization, selecting the best WHR for a Brazilian ICE power plant, considering UTE Viana as case study. The specificities and uncertainties of the Brazilian electricity scenario are taken into account through different operational and economic boundary conditions. The selection of the most suitable objective function that characterize the specificities of a Brazilian power plant is analyzed, as well as the influence of these objective functions on the optimization results. Moreover, is evaluated the influence of different heat carriers and economies of scale application. Four technologies are considered: conventional Rankine cycle (CRC), organic Rankine cycle (ORC), Kalina cycle (KC), and absorption chillers for intake air cooling (ChA). The adopted objective functions are: gross profit, net power, specific cost of investment, and specific cost of the generated power. The results demonstrate that the optimization responses are highly influenced by the objective functions, especially when different types of technologies are compared. The results analysis showed that the gross profit is the most suitable objective function to WHR of Brazilian power plants, accounting the uncertainties of the Brazilian scenario by means of annual dispatch hours and variable unit cost (VUC). The ORC alternative presented the best results when maximizing the gross profit, being indicated as the best alternative for WHR of Brazilian ICE power plants. The importance of a complete and simultaneous structural and parametric thermoeconomic optimization using the superstructure method was verified with the extensive variation of the optimum synthesis and parameters of the ORC. The optimization results showed that the influence of different objective functions, operational and economic boundary conditions, heat carries and economies of scale are present both in the variation of parametric variables, as in structural variables. For an optimistic scenario of dispatch and variable unit cost of electricity, the WHR using ORC systems can increase the power plant generation capacity up to 9.4%. For a more realistic scenario of boundary conditions, using an ORC system can increase the power plant generation capacity up to 5.4%.
