Design of a Concentrated Solar Thermal Power Plant for Integration with coal-fired power stations

Abstract

There are problems of company closures, reduced standard of living for citizens, reduced capacity utilization of economic infrastructure and increased cost of doing business in Zimbabwe as a result of rampant and unprecedented blackouts caused by inadequate generation capacity. In addition, there are also climate goals setup by the United Nations COP 26 meeting which Zimbabwe with a lot of coal power stations must meet by reducing or eliminating carbon dioxide emissions from coal power plants. There are many generation technologies which Zimbabwe can tap into to solve the above problems including fossil fuel generation (coal, gas and oil), nuclear, hydro, geothermal, thermoelectric, photovoltaic, piezoelectric, tidal, wave, wind, thermionic, parabolic dish, Linear Fresnel, parabolic trough and Central Receiver tower power generation schemes also called solar tower. Literature review on conventional and other generation technologies will be briefly carried out in order to place Concentrated solar power generation in context of other options in terms of disadvantages and advantages. The thesis designed a 500 MW Power Tower power plant and demonstrated possible ways of integrating it with coal-fired power stations like Hwange, Munyati and Harare power stations in Zimbabwe. Yousef et.al. (2021) posits that integration of Central Receiver Tower (CRT) Power Plants with coal can reduce the cost of generated electricity by between 20-30 % that standard CRT power plants incur. Enkhbayar et.al. (2021) highlights that thermal to electricity conversion efficiencies of hybrid power plants i.e. solar-coal are greater than those of solar only generation at the same temperature. The Central Receiver Tower Power Plant is a type of a Concentrated Solar Thermal Power Plant. The Central tower was designed, solar absorber also designed followed by thermal energy storage tanks’ design. The heat exchanger was then designed and choice of an appropriate generator and turbine set followed. The control building was designed followed by step-up substation design. The site plan of the said substation if it was to be implemented in Kadoma area in Zimbabwe was designed and drawn. The thesis found out from literature that an average single tower Central Receiver Tower power plant has an overall plant efficiency of 20 %. Kayvani (2014) says that the following forces need to be considered in the design of tall buildings like the Central tower: - (1) gravity effects (2) likely earthquakes (3) wind (4) lateral earth pressures which are unbalanced that could be imposed onto the foundation pad in any given direction. It was found out that in order to increase the power tower plant efficiency, the following were crucial (1) Tracking which was dual-axis (2) An efficient receiver (3) The heat transfer fluid and working fluid paths had to be thermally insulated (4) The heat engine or power block had to be efficient and (5) Employment of highly reflective mirrors (96 % reflectivity). Alici and Turmay (2021) posits that the operation and maintenance costs for dual axis tracking is more compared to that for a single axis tracking system. Most data for this project were obtained from google and Meteorological office e.g. solar radiation map of Zimbabwe, wind speed at Kadoma at 4m high, average temperatures and soil strength in Kadoma. These where the values used in the calculations. The major findings were that (1) 500 MW Central Receiver Tower (CRT) power plant requires a lot of space 2.4 km by 2.4 km stand (2) multi-tower designs are more efficient but more expensive than single tower CRT power plants (3) coal-solar integration reduces intermittency and dispatchability of power generation in solar CRT power plants without enough heat storage or without storage. It was found out that solar-coal hybridization eliminates need for thermal storage.