Abstract
To our knowledge, the potential use of CO2 as a heat-transmitting fluid for cooling applications in power plants has not been explored very extensively. In this paper, we conduct a theoretical analysis to explore the use of CO2 as the heat transmission fluid. We evaluate and compare the thermophysical properties of both dry air and CO2 and perform a simple analysis on a steam-condensing device where steam flows through one of the flow paths and the cooling fluid (CO2 or air) is expanded from a high-pressure container and flows through the other. Sample calculations are carried out for a saturated-vapor steam at 0.008 MPa and 41.5 °C with the mass flow rate of 0.01 kg/s. The pressure of the storage container ranges from 1 to 5 MPa, and its temperature is kept at 35 °C. The pressure of the cooling fluid (CO2 or dry air) is set at 0.1 MPa. With air as the heat-removing fluid, the steam exits the condensing device as a vapor-liquid steam of 53% to 10% vapor for the container pressure of 1 to 5 MPa. With CO2 as the heat-removing fluid, the steam exits the device still containing 44% and 7% vapor for the container pressure of 1 MPa and 2 MPa, respectively. For the container pressure of 3 MPa and higher, the steam exits the device as a single-phase saturated liquid. Thus, due to its excellent Joule–Thomson cooling effect and heat capacity, CO2 is a better fluid for power plant cooling applications. The condensing surface area is also estimated, and the results show that when CO2 is used, the condensing surface is 50% to 60% less than that when dry air is used. This leads to significant reductions in the condenser size and the capital costs. A rough estimate of the amount of CO2 that can be stored and utilized is also carried out for a steam power plant which operates with steam with a temperature of 540 °C (813 K) and a pressure of 10 MPa at the turbine inlet and saturated-vapor steam at 0.008 MPa at the turbine outlet. The results indicate that if CO2 is used as a cooling fluid, CO2 emitted from a 1000 MW power plant during a period of 250 days could be stored and utilized.
Highlights
Introduction iationsIn power plants, water is used to remove heat from a wide variety of sources
There are very few studies related to the power plant cooling using CO2 as the cooling fluid; in this paper, we propose that
To obtain a rough estimate for the amount of CO2 that can be stored and utilized, we hypothetically consider a steam power plant where the steam at 540 ◦ C (813 K) and 10 MPa expands through a turbine to become a saturated-vapor steam at 0.008 MPa (saturated temperature is 41.5 ◦ C (314.5 K))
Summary
The correlations reported by Span and Wagner [20] for calculating CO2 density and the correlations developed by Vesovic et al [21] and Fenghour et al [22]. In addition to the flow heat capacity, the cooling effectiveness of a fluid depends on its initial temperature when it enters a cooling device This temperature can be controlled by an important property called the Joule–Thomson coefficient. The values of μ of CO2 are 4.9 to 5.6 times higher than those of air as shown, and the temperature of the CO2 entering a cooling device, as given by Equation (2), depends on the storage tank temperature and the pressure, and it is 7 to 40 K lower than that of air. 5.0 after being expanded from a high-pressure container
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