scholarly journals Energy and Exergy Assessment of S-CO2 Brayton Cycle Coupled with a Solar Tower System

Processes ◽  
2020 ◽  
Vol 8 (10) ◽  
pp. 1264
Author(s):  
Muhammad Ehtisham Siddiqui ◽  
Khalid H. Almitani
Keyword(s):  
Solar Energy ◽  
Power Input ◽  
Capital City ◽  
Brayton Cycle ◽  
Combustion Gases ◽  
Aspen Hysys ◽  
Central Receiver ◽  
Average Annual Loss ◽  
Energy And Exergy ◽  
Auxiliary Heater

In this research, we performed energy and exergy assessments of a solar driven power plant. Supercritical carbon dioxide (S-CO2) Brayton cycle is used for the conversion of heat to work. The plant runs on solar energy from 8 a.m. to 4 p.m. and to account for the fluctuations in the solar energy, the plant is equipped with an auxiliary heater operating on hot combustion gases from the combustion chamber. The capital city of Saudi Arabia (Riyadh) is chosen in this study and the solar insolation levels for this location are calculated using the ASHRAE clear-sky model. The solar collector (central receiver) receives solar energy reflected by the heliostats; therefore, a radially staggered heliostat field is generated for this purpose. A suite of code is developed to calculate various parameters of the heliostat field, such as optical efficiencies, intercept factors, attenuation factors and heliostat characteristic angles. S-CO2 Brayton cycle is simulated in commercial software, Aspen HYSYS V9 (Aspen Technology, Inc., Bedford, MA, USA). The cycle is mainly powered by solar energy but assisted by an auxiliary heater to maintain a constant net power input of 80 MW to the cycle. The heliostat field generated, composed of 1207 rows, provides 475 watts per unit heliostat’s area to the central receiver. Heat losses from the central receiver due to natural convection and radiation are significant, with an average annual loss of 10 percent in the heat absorbed by the receiver. Heat collection rate at the central receiver reveals that the maximum support of auxiliary heat is needed in December, at nearly 13% of the net input energy. Exergy analysis shows that the highest exergy loss takes place in the heliostat field that is nearly 42.5% of incident solar exergy.

SUNTRACKER

2015 ◽  
Author(s):  
Jon W. Teets ◽  
J. Michael Teets
Keyword(s):  
High Temperature ◽  
Solar Energy ◽  
Electric Power ◽  
Power Electronics ◽  
Turbine Rotor ◽  
Working Fluid ◽  
Brayton Cycle ◽  
Compressor Impeller ◽  
Temperature Application ◽  
Output Electric Power

A SUNTRACKER (illustrated in figure1), is a Concentrating Solar Power (CSP) unit, in the category of solar dish engines. The novel solar dish engine module (shown in figure 2) is designed to provide 10.1kW electric power (measured at the engine output electric power lugs), from a conversion of 21kW solar energy from the solar dish reflective sun light to the high temperature receiver focal point. Total electric power output from the solar dish engine module is attributed to combined cycles, closed brayton cycle (CBC) and a organic rankine cycle (ORC), both of which are hermetically sealed to atmosphere. The CBC engine receives 21kW solar energy from a solar dish, estimated to have 27 square meters (291 square feet) reflective surface area. However, unlike the photovoltaic (PV) units, the SUNTRACKER will provide increased use of available solar energy from sunlight. Concentrated sunlight from the dish will focus on the CBC engine receiver, which in turn heats the working fluid media to as much as 1600F, pending the ratio of solar dish to receiver areas. A specific gas mixture of xenon/helium, with excellent thermodynamic properties is used for the high temperature application. Turbomachinery in the CBC engine has one moving part / assembly (compressor impeller, alternator rotor and turbine rotor), mounted on compliant foil bearings. Reference figure 4 as an example. The engine operates with a compressor impeller stage pressure ratio 1.6, and is recuperated. Electric power, measured at the CBC engine electric power lugs, is 6.4kW. The CBC engine is not new, (a closed Brayton cycle, sealed to atmosphere) [1], [4], [8], [18], [19]. However, the application to extract thermal energy from the sunlight and provide electric power in commercial and residential use is (patented). In addition, to increase the efficiency of solar energy conversion to electric power, waste heat from the CBC engine provides thermal energy to an ORC engine, to generate an additional electrical output of 3.7kW (measured at the output electric power lugs). With use of an ORC system, the size of the radiator (CBC unit) for heat rejection is reduced significantly. Working fluid HFC-RC245fa [10] was selected for the ORC unit, based on the low temperature application. Also, as with the CBC turbomachinery, the ORC rotor assembly has one moving part, comprised of a pump impeller, alternator rotor and turbine rotor. With the two engines combined, total system thermal efficiency is 48% (10.1kW electric power out / 21kW solar energy in). However, power electronics are needed for conversion of high frequency voltage at the engine output electric power leads to 60/50 Hz power, for customer use. Power electronics losses for this machine, debits the power 0.5 kW. Thus total electric power to the customer, as measured at power electronics output terminals, is 9.6kW. With solar energy, from the reflective sunlight solar dish 21kW and measured output power from the power electronics 9.6kW, the conversion of solar energy to useful electric power an efficiency 46% (i.e. 9.6kW / 21kW). In addition, the design does not require external water / liquid for cooling.

Experimental Analysis of the Pool Boiling Phenomenon of Sugarcane Juice

2015 ◽  
Vol 789-790 ◽  
pp. 489-495 ◽  
Author(s):  
Daniel Marcelo ◽  
Paul Villar Yacila ◽  
Raúl La Madrid Olivares
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Experimental Analysis ◽  
Electrical Power ◽  
Power Input ◽  
Sugarcane Juice ◽  
Middle Level ◽  
Transfer Coefficients ◽  
Combustion Gases ◽  
Heat Transfer Coefficients

In Peru, jaggery making process has low energy efficiency and it is due to low heat transfer coefficients for natural convection linked to the sugar cane movement generated by the heat exchange between the sugarcane juice and the combustion gases. This low heat transfer coefficients are caused by improper heat exchangers designs. In this work, is performed an experimental analysis that consist in supplie heat to a pot containing sugarcane juice using a hot plate of constant electrical power. This study consist in identify boiling regimes and estimate the heat transfer coefficients linked to natural convection boiling, measuring: (i) the temperature at the bottom of the pot (ii) the temperature at the bottom level of sugarcane juice (iii) the temperature at middle level of sugarcane juice (iv) the temperature at free surface of sugarcane juice (v) rate of water evaporated. The method of linear regression and the correlation of Rohsenow were used for obtaining the values of the heat transfer coefficients ranging from 4088.6 W/m2°C to 12592.8 W/m2°C with power input ranging from 700W to 1300W.

Assessment of Photovoltaic Capabilities in Urban Environments: A Case Study of Islamabad, Pakistan

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Muhammad Zubair ◽  
Sajid Ghuffar ◽  
Muhammad Shoaib ◽  
Ahmed Bilal Awan ◽  
Abdul Rauf Bhatti
Keyword(s):  
Deep Learning ◽  
Solar Energy ◽  
Urban Areas ◽  
Capital City ◽  
Coefficient Of Performance ◽  
Energy Yield ◽  
Cooling Load ◽  
Zero Energy ◽  
Net Zero Energy ◽  
Net Zero

Abstract Photovoltaic (PV) estimation in an urban environment requires detection of rooftop area, design of PV system based on optimization on PV placement distance and the study of additional benefit of lower cooling load of building by shading provided by PV panels. The study is aimed at policymakers to introduce renewable energy policy toward net-zero energy buildings in urban areas. In this research, the capital city of Pakistan, Islamabad, is analyzed for rooftop PV capabilities using deep learning algorithms. The area of the rooftop is calculated by extracting buildings in high-resolution satellite imagery using a deep learning algorithm. The site location is analyzed for available solar energy resources. The distance between the rooftop-PV array is optimized based on self-shading losses, coefficient of performance, energy yield, net-zero energy analysis, and reduction of cooling load of the building provided by PV arrays as shading devices. The 40-km2 area of Islamabad considered in this research can generate 1038 GWh of solar energy annually from its 4.3-km2 rooftop area by installed capacity of 447 MW PV panels rows placed at 0.75 m apart. The electricity generated by Islamabad can curtail residential load from the national grid and form a near net-zero energy zone while the electrical energy from the grid can be provided to the industries to enhance the economy and reduce unemployment in Pakistan.

Effect of Pressure Drop and Reheating on Thermal and Exergetic Performance of Supercritical Carbon Dioxide Brayton Cycles Integrated With a Solar Central Receiver

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Ricardo Vasquez Padilla ◽  
Yen Chean Soo Too ◽  
Andrew Beath ◽  
Robbie McNaughton ◽  
Wes Stein
Keyword(s):  
Carbon Dioxide ◽  
Pressure Drop ◽  
Supercritical Carbon Dioxide ◽  
Surface Temperature ◽  
Brayton Cycle ◽  
Pressure Drops ◽  
Central Receiver ◽  
Maximum Value ◽  
Solar Receiver ◽  
Exergy Performance

Concentrated solar power using supercritical carbon dioxide (S-CO2) Brayton cycles offers advantages of similar or higher overall thermal efficiencies than conventional Rankine cycles using superheated or supercritical steam. The high efficiency and compactness of S-CO2, as compared with steam Rankine cycles operating at the same temperature, make this cycle attractive for solar central receiver applications. In this paper, S-CO2 Brayton cycle is integrated with a solar central receiver that provides heat input to the power cycle. Three configurations were analyzed: simple, recompression (RC), and recompression with main intercooling (MC). The effect of pressure drop in heat exchangers and solar receiver and solar receiver surface temperature on the thermal and exergetic performance of the CO2 Brayton cycle with and without reheat condition was studied. Energy, exergy, and mass balance were carried out for each component and the cycle first law and exergy efficiencies were calculated. In order to obtain optimal operating conditions, optimum pressure ratios were obtained by maximizing the cycle thermal efficiency under different pressure drops and solar receiver temperature conditions. Optimization of the cycle first law efficiency was carried out in python 2.7 by using sequential least squares programing (SLSQP). The results showed that under low pressure drops, adding reheat to the S-CO2 Brayton cycle has a favorable effect on the thermal and exergy efficiencies. Increasing pressure drop reduces the gap between efficiencies for reheat and no reheat configuration, and for pressure drop factors in the solar receiver above 2.5%, reheat has a negligible or detrimental effect on thermal and exergy performance of S-CO2 Brayton cycles. Additionally, the results showed that the overall exergy efficiency has a bell shape, reaching a maximum value between 18.3% and 25.1% at turbine inlet temperatures in the range of 666–827 °C for different configurations. This maximum value is highly dependent on the solar receiver surface temperature, the thermal performance of the solar receiver, and the solar field efficiency. As the solar receiver surface temperature increases, more exergy destruction associated with heat transfer losses to the environment takes place in the solar receiver and therefore the overall exergy efficiency decreases. Recompression with main intercooling (MC) showed the best thermal (ηI,cycle > 47% at Tin,turbine > 700 °C) and exergy performance followed by RC configuration.

Performance Evaluation of an Integrated Solar Combined Cycle

2012 ◽  
Author(s):  
Collins O. Ojo ◽  
Damien Pont ◽  
Enrico Conte ◽  
Richard Carroni
Keyword(s):  
Solar Energy ◽  
Capital Investment ◽  
Power Plants ◽  
Solar Power ◽  
Combined Cycle ◽  
Electricity Production ◽  
Water Steam ◽  
Plant Operator ◽  
Central Receiver ◽  
Solar Field

The integration of steam from a central-receiver solar field into a combined cycle power plant (CCPP) provides an option to convert solar energy into electricity at the highest possible efficiency, because of the high pressure and temperature conditions of the solar steam, and at the lowest capital investment, because the water-steam cycle of the CCPP is in shared use with the solar field. From the operational point of view, the plant operator has the option to compensate the variability of the solar energy with fossil fuel electricity production, to use the solar energy to save fuel and to boost the plant power output, while reducing the environmental footprint of the plant operation. Alstom is able to integrate very large amounts of solar energy in its new combined-cycle power plants, in the range of the largest solar field ever built (Ivanpah Solar Power Facility, California, 3 units, total 392 MWel). The performance potential of such integration is analyzed both at base load and at part load operation of the plant. Additionally, the potential for solar retrofit of existing combined-cycle power plants is assessed. In this case, other types of concentrating solar power technologies than central receiver (linear Fresnel and trough) may be best suited to the specific conditions. Alstom is able to integrate any of these technologies into existing combined-cycle power plants.

scholarly journals Use of the Brayton Cycle in Solar Electric Power Generation

1989 ◽  
Author(s):  
Dan Weiner ◽  
Giora Meron
Keyword(s):  
Gas Turbines ◽  
High Performance ◽  
Attractive Alternative ◽  
Brayton Cycle ◽  
Electric Generator ◽  
Central Receiver ◽  
System Components ◽  
Prime Movers ◽  
Turboshaft Engine ◽  
And Control

The utilization of gas turbines in a central receiver is an attractive alternative due to the ability of these prime movers to endure temperatures of about 2000°F while achieving high performance. In this paper the problems of modifying a 250 kW Allison Turboshaft Engine and its conversion into solar gas turbines are presented. The various solutions referring to the various system components, such as combustion chamber, hot pipeline, electric generator and control system are detailed.

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