Thermal fluid modeling of small scale open Brayton cycle configurations
Lodewyckx, Jan Willem
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South Africa's high dependence on coal based power stations for the country's power demand as well as the increase in demand for energy, calls for the development of more efficient energy systems that are capable of utilising renewable energy sources to mitigate the emission of harmful gases produced by the combustion of fossil fuels, which adversely affects the environment and the health of the people. A solution to mitigate the aforementioned problems is utilising small scale open externally fired gas turbines (EFGTs). The EFGT, which is based on the working principle of a Brayton cycle, has grown in interest due to its capability to operate with renewable energy sources such as biomass, and it is drawing much attention now that there is a global trend in shifting towards "green" (environmentally friendly) power generation. The problem with EFGTs is that an efficient power generation system is required if biomass is to be used as a renewable fuel source due to its relatively low heating value compared to fossil fuels. The main objective is to thermodynamically evaluate different open EFGT configurations for small scale power generation in the range of 100 [kW]. The focus of this study is the development of thermal fluid simulation models for different configurations with a computer aided program known as Engineering Equation Solver (EES). In order to make a sensible comparison, the performance of each model was evaluated by generating efficiency graphs which are used to determine the best operating conditions to produce an electrical output of 100 [kW] under all constraints. The results obtained indicated that the regenerative EFGT cycle and the regenerative EFGT cycle with two turbines displayed the best performance with a net electrical efficiency of 0.1965 [-] and 0.2 [-] respectively, at a relatively low heat input to the combustion chamber. The regenerative cycle with reheat gained a third place with an efficiency of 0.1597 [-] while the simple EFGT cycle had the worst performance of all the configurations with a cycle efficiency of 0.1248 [-].
- Engineering