Direct Vaporization of Organic Fluid in Parabolic Trough Collector for Solar Power Generation

Abstract

In this paper, an assessment of direct vaporization of organic fluid in a PTC field for power generation is conducted. The advantages of direct heating are simplicity of plants and about 15% less capital cost compared to plants with heat transfer fluids. Toluene has been selected for the organic Rankine cycle with its operating saturation temperature set at 300 °C, which is below its critical temperature. The assessment is based on numerically solving the governing equations using finite difference which is first-order temporally and second-order spatially accurate. The solution is obtained for the period that goes from 8:30AM to 3:30PM with solar conditions specific to June in a certain location, which corresponds to normal beam variation ~900 to ~1050 W/m2. The toluene flow rate has been constantly adjusted during the day so that it has remained saturated vapor when it has returned from the PTC field. The results show that the hourly actual scheme efficiency ranges from 20% to above 25%, averaging 22.6%, which suggest their competitiveness for large-scale solar power generation. Additional favorable attributes for use of PTCs include that they do not suffer from degradation at high solar beam intensities along with their long durability and ruggedness. In addition, results have revealed important information regarding temperature distributions in the absorber tube.