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Solar Thermal Power
Published in D. Yogi Goswami, Principles of Solar Engineering, 2023
There are two basic approaches to solar electric power generation. One is by photovoltaic process, a direct energy conversion, which is described in detail in Chapter 9. The other approach is to convert sunlight to heat at high temperatures and then heat to mechanical energy by a thermodynamic power cycle and, finally, convert the mechanical energy to electricity. This indirect approach, called solar thermal power or CST, is based on well-established principles of thermal power. A vast majority of electricity in the world is produced by thermal power conversion. Most of the thermal power production in the world is based on Rankine cycle and, to a smaller extent, Brayton cycle. Both of these are applicable to solar thermal power conversion, with Rankine cycle being the most popular. Normally, water is the working fluid for the Rankine cycle. However, for lower-temperature solar collection systems (70°C to approximately 300°C), organic fluids are used, in which case the cycle is commonly referred to as the organic Rankine cycle (ORC). When a Rankine cycle is operated under supercritical conditions of the working fluid, the cycle is usually referred to as the supercritical Rankine cycle (SRC). The Stirling cycle has also shown great potential, and solar thermal power systems based on this cycle are under development. More recently, researchers have been developing modifications of these cycles or entirely new cycles or combined cycles to increase the conversion efficiencies and to make them more applicable to the solar collection systems.
Organic Rankine cycle integrated hybrid arrangement for power generation
Published in Anoop Kumar Shukla, Onkar Singh, Meeta Sharma, Rakesh Kumar Phanden, J. Paulo Davim, Hybrid Power Cycle Arrangements for Lower Emissions, 2022
Mohammad Bahrami, Fathollah Pourfayaz, Ali Gheibi
The main component of the basic Rankine cycle is boiler, pump, condenser, and turbine. Water is used as the working fluid in Rankine cycles. In the organic Rankine cycle, the working fluid is an organic fluid such as refrigerants and hydrocarbons. Organic working fluids are in the temperature range of 150–300ºC. A thermodynamic ORC is shown in Figure 12.5. As can be seen there are four main processes (Reddy et al. 2010). State 1: Isentropic expansion: Superheated steam enters the turbine and thermal energy converts to mechanical energy. A generator is connected to the turbine which converts mechanical energy into electricity. The pressure and temperature of the steam is reduced in the turbine exit.State 2: Isentropic heat rejection: The exit steam from the turbine enters the condenser and is condensed to liquid water.State 3: Isentropic compression: The working fluid enters the pump.State 4: Isentropic heat addition: Working fluid enters the boiler and by adding heat steam is generated and superheated within the boiler.
Improving Process Efficiency by Waste Heat Recuperation
Published in Sheila Devasahayam, Kim Dowling, Manoj K. Mahapatra, Sustainability in the Mineral and Energy Sectors, 2016
Ibrahim A. Sultan, Truong H. Phung, Ali Alhelal
A typical Rankine cycle has four main modules, a pump, a boiler, an expander (aka turbine) and a condenser, and utilises water as a working fluid. The working fluid within a Rankine cycle is used to transfer thermal energy from one component to another. With medium- and large-scale Rankine cycle plant, one of the three groups of working fluids is used: wet fluids, dry fluids and isentropic fluids. As shown in Figure 25.2, the fluid classification is based on the slope of the saturation vapour curve on the temperature, T, versus entropy, s (T–s) diagram. Small-scale Rankine cycle plant, on the other hand, makes use of organic fluids such as Honeywell synthetic refrigerants R123, R410a and R143a, which are largely categorised as isentropic fluid (Gao et al., 2012).
Modeling and thermodynamic analysis of gas-supercritical carbon dioxide combined cycle system
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2022
Jiayin Zhou, Diangui Huang, Yinke Qi
When the working fluid reaches the supercritical state, the gas can flow like liquid, and the liquid can be compressed like gas. The gas-liquid state at this moment is very similar. The supercritical liquid has better fluidity and thermal conductivity. Therefore, the supercritical state is used as the energy transmission working medium of the power generation system, which can greatly reduce the energy loss in the transmission process. The working fluid used in steam Rankine cycle power generation is supercritical water, whose temperature and pressure exceed 374.15s°C and 22.13Mpa separately. The use of supercritical water enables the unit to generate electricity efficiently, but it also brings great challenges to the unit materials. Because the supercritical state of water is oxidative and corrosive, it will cause damage to equipment materials, and the power generation system is required to have high strength and corrosion resistance. Using CO2 to generate electricity has many advantages over water. First of all, compared with water, CO2 is easier to reach the supercritical state (The critical temperature and pressure of CO2 are 30.98°C and 7.38 MPa). Secondly, the chemical properties of sCO2 are more stable than supercritical water, less corrosive to equipment, and have smaller frictional resistance, which can convert more heat source energy into mechanical energy (Schlosky 1989). Finally, the sCO2 Brayton cycle has more advantages such as its simple layout, high efficiency and compact equipment size compared to the traditional steam. Rankine cycle or Brayton cycle (Crespi, Gavagnin, and Sánchez et al. 2017; Liu, Wang, and Huang 2019). Therefore, gas-steam combined cycle power plants can use CO2 instead of steam to further improve their efficiency (Hada, Takata, and Iwasaki et al. 2015; Persichilli, Kacludis, and Zdankiewicz et al. 2012).