Cooling system design for 10MW sCO2 solar power plant

Renewable energy is the future of power generation in Australia, with fossil fuel powered generators slowly being phased out as part the energy mix. This Thesis examines one of the leading contenders to provide a large percentage of future energy generation; concentrated solar power (CST). However, the 10 MW system analysed here, operates with super critical carbon dioxide (sCO2) as the working fluid, rather than steam.To improve cycle efficiency, the cooling system design was optimised to more efficiently dissipate waste heat. Two systems were considered: a natural draft dry cooling tower (NDDCT) and a mechanical draft cooler (MDC). For a 10MW, sCO2, CST plant operating at a 45% efficiency, 12.22 MW of heat was required to be dissipated by the cooling system. An analysis methodology was followed similar to that provided by Kroger [1, 2]. For the NDDCT, an energy balance was used to compare the rate of heat transfer between the working fluid, air and heat exchanger. An iterative method was then completed using MATLAB to solve for exit air temperature, mass flow rate of air, tower height and heat exchanger size. A similar method was completed for the MDC, however, the velocity of air was provided at 2m/s. An economic analysis was then performed to compare the initial capital expenditure required to build a NDDCT to the ongoing costs of running 3 fans for the MDC. For the NDDCT, an existing model by a UQ researcher was utilised to estimate the cost inclusive of materials and labour. For the MDC, the discount rate was calculated using the capital asset pricing model (CAPM). The running costs were then calculated based on a high usage, rural tariff and discounted back to an NPV value for all future cash outflows. The results showed that a 28-meter high NDDCT was required to dissipate 12.22MW of waste heat energy. In comparison, the MDC required 3 axial fans, each 8.72 meters in diameter. This corresponded to a capital expenditure of 2.9 million dollars to build the NDDCT and a NPV of 8.1 million dollars to operate a MDC for the 20-year life of a CST power plant. Therefore, the optimum cooling system design for a 10 MW sCO2 solar power plant was a NDDCT.Recommendations for future research included: performing a sensitivity analysis on the results to account for changes in ambient temperature, updating the efficiency and material choice for the fans and NDDCT respectively, and completing a comparison of the results with the same system operating with steam as the working fluid.