Efficiency Enhancement of a Small Scale Closed Solar Thermal Brayton Cycle by a Combined Simple Organic Rankine Cycle

2012 ◽  
Author(s):  
H. Riazi ◽  
N. A. Ahmed
Keyword(s):  
Power Output ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Solar Thermal ◽  
Small Scale ◽  
Brayton Cycle ◽  
Efficiency Enhancement ◽  
Power Cycles ◽  
Micro Turbine ◽  
Net Power Output

In this paper efficiency enhancement of a small scale closed solar thermal Brayton cycle is investigated by combining it to a simple organic Rankine cycle. Brayton power cycles are generally known as the enabling technology for high temperature solar power towers due to their higher efficiencies compared to other power cycles. Unlike conventional solar-thermal plants, which concentrate the sun’s energy to generate steam for driving a turbine, the Brayton thermodynamic does not use water. Instead, the concentrated solar energy is used to heat compressed air, which then expands through a gas turbine to generate power. Irreversible loss in compressor and turbine, the operating temperature of solar collector and recuperator effectiveness are the main features that limit the net power output of the system which should be considered and analyzed. The exhaust of the gas turbine is still at high temperature that should be cooled down before entering the compressor. Thus, this heat can be utilized to operate a low temperature Rankine cycle and increase the system efficiency and power generation. Operating points of off the shelf micro-turbines and steam turbine with parabolic solar dish concentrator of various concentrating ratios are considered. Thermodynamic analysis is applied, by using the first and second law of thermodynamics, to obtain the optimum temperature of solar collector, minimum irreversibility rates to maximize the efficiency and net power output of the system at various steady-state conditions. Results show that for the closed solar thermal Brayton cycle the maximum overall first law efficiency of the system can be increased of more than 5% by combining a simple Rankine cycle to recover the exhaust heat and a significant 20% increase in the second law efficicency. The system efficiency is related to the solar concentration ratio with an optimum operating temperature and the choice of micro-turbine. On this basis, both the overall efficiency and the total output power may reach their maximum value by optimizing the pressure ratio. In a small scale closed solar thermal Brayton cycle combined by a Rankine cycle with a micro turbine operating at its highest compressor efficiency, the operating conditions can be optimized in such a way that the system produces maximum net power output or having the highest overall efficiency.

Maximum Net Power Output of the Recuperative Open and Direct Solar Thermal Brayton Cycle

2011 ◽  
Author(s):  
W. G. Le Roux ◽  
T. Bello-Ochende ◽  
J. P. Meyer
Keyword(s):  
Power Output ◽  
Trajectory Optimization ◽  
Optimization Method ◽  
Solar Thermal ◽  
Optimum Operating ◽  
Small Scale ◽  
Brayton Cycle ◽  
Steady State Condition ◽  
Micro Turbine ◽  
Net Power Output

The small-scale open and direct solar thermal Brayton cycle with recuperator has several advantages. These include low operation and maintenance costs and high recommendation. The main disadvantages of this cycle are the pressure losses in the recuperator and receiver, turbo-machine efficiencies and recuperator effectiveness, which limit the net power output of such a system. Thermodynamic optimization can be applied to address these disadvantages in order optimize the receiver and recuperator and to maximize the net power output of the system at any steady-state condition. The dynamic trajectory optimization method is applied to maximize the net power output of the system by optimizing the geometries of the receiver and recuperator, limited to various constraints. Standard micro-turbines and parabolic dish concentrator diameters of six to eighteen meters are considered. An optimum system geometry and maximum net power output can be generated for each operating condition of each micro-turbine and concentrator combination. The results show how the irreversibilities are spread throughout the system optimally, in order for the system to produce its maximum net power output. It indicates that the optimum operating point of a micro-turbine is at the point where the internal irreversibilities are approximately three times larger than the external irreversibilities.

Optimum Small-Scale Open and Direct Solar Thermal Brayton Cycle for Pretoria, South Africa

2012 ◽  
Author(s):  
W. G. Le Roux ◽  
T. Bello-Ochende ◽  
J. P. Meyer
Keyword(s):  
Power Output ◽  
Weather Conditions ◽  
Solar Thermal ◽  
Solar Irradiation ◽  
Operating Point ◽  
Optimum Operating ◽  
Small Scale ◽  
Brayton Cycle ◽  
Parabolic Dish ◽  
Net Power Output

The open and direct solar thermal Brayton cycle is exposed to various weather conditions like changing solar irradiation, wind and surrounding temperature. The geometries of the receiver and recuperator and the turbine operating point as parameter can be optimised in such a way that they accommodate these weather changes and allow for high net power output throughout a typical year. In this paper, a method of obtaining these parameters based on total entropy generation minimisation is presented. A parabolic dish concentrator with a diameter of 4.8 m is used as well as an off-the-shelf turbo-machine. Results show that the net absorbed power at the receiver and maximum allowed receiver surface temperature play important roles in determining the optimum operating point and maximum net power output.

Waste Heat Recovery in a Cruise Vessel in the Baltic Sea by Using an Organic Rankine Cycle: A Case Study

2015 ◽  
Author(s):  
Fredrik Ahlgren ◽  
Maria E. Mondejar ◽  
Magnus Genrup ◽  
Marcus Thern
Keyword(s):  
Power Output ◽  
Heat Recovery ◽  
Waste Heat Recovery ◽  
Waste Heat ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Operating Conditions ◽  
Maritime Transportation ◽  
Working Fluid ◽  
Net Power Output

Maritime transportation is a significant contributor to SOx, NOx and particle matter emissions, even though it has a quite low CO2 impact. New regulations are being enforced in special areas that limit the amount of emissions from the ships. This fact, together with the high fuel prices, is driving the marine industry towards the improvement of the energy efficiency of current ship engines and the reduction of their energy demand. Although more sophisticated and complex engine designs can improve significantly the efficiency of the energy systems in ships, waste heat recovery arises as the most influent technique for the reduction of the energy consumption. In this sense, it is estimated that around 50% of the total energy from the fuel consumed in a ship is wasted and rejected in fluid and exhaust gas streams. The primary heat sources for waste heat recovery are the engine exhaust and the engine coolant. In this work, we present a study on the integration of an organic Rankine cycle (ORC) in an existing ship, for the recovery of the main and auxiliary engines exhaust heat. Experimental data from the operating conditions of the engines on the M/S Birka Stockholm cruise ship were logged during a port-to-port cruise from Stockholm to Mariehamn over a period of time close to one month. The ship has four main engines Wärtsilä 5850 kW for propulsion, and four auxiliary engines 2760 kW used for electrical consumers. A number of six load conditions were identified depending on the vessel speed. The speed range from 12–14 knots was considered as the design condition, as it was present during more than 34% of the time. In this study, the average values of the engines exhaust temperatures and mass flow rates, for each load case, were used as inputs for a model of an ORC. The main parameters of the ORC, including working fluid and turbine configuration, were optimized based on the criteria of maximum net power output and compactness of the installation components. Results from the study showed that an ORC with internal regeneration using benzene would yield the greatest average net power output over the operating time. For this situation, the power production of the ORC would represent about 22% of the total electricity consumption on board. These data confirmed the ORC as a feasible and promising technology for the reduction of fuel consumption and CO2 emissions of existing ships.

Experimental characterization and comparison of an axial and a cantilever micro-turbine for small-scale Organic Rankine Cycle

2018 ◽  
Vol 140 ◽  
pp. 235-244 ◽  
Author(s):  
Andreas P. Weiß ◽  
Tobias Popp ◽  
Jonas Müller ◽  
Josef Hauer ◽  
Dieter Brüggemann ◽  
...  
Keyword(s):  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Small Scale ◽  
Experimental Characterization ◽  
Micro Turbine

Numerical Study of a Micro Gas Turbine Integrated With a Supercritical CO2 Brayton Cycle Turbine

2018 ◽  
Author(s):  
Fabrizio Reale ◽  
Vincenzo Iannotta ◽  
Raffaele Tuccillo
Keyword(s):  
Gas Turbines ◽  
Waste Heat ◽  
Numerical Study ◽  
Organic Rankine Cycle ◽  
Energy Systems ◽  
Rankine Cycle ◽  
Energy System ◽  
Small Scale ◽  
Brayton Cycle ◽  
Integrated Energy System

The primary need of reducing pollutant and greenhouse gas emissions has led to new energy scenarios. The interest of research community is mainly focused on the development of energy systems based on renewable resources and energy storage systems and smart energy grids. In the latter case small scale energy systems can become of interest as nodes of distributed energy systems. In this context micro gas turbines (MGT) can play a key role thanks to their flexibility and a strategy to increase their overall efficiency is to integrate gas turbines with a bottoming cycle. In this paper the authors analyze the possibility to integrate a MGT with a super critical CO2 Brayton cycle turbine (sCO2 GT) as a bottoming cycle (BC). A 0D thermodynamic analysis is used to highlight opportunities and critical aspects also by a comparison with another integrated energy system in which the waste heat recovery (WHR) is obtained by the adoption of an organic Rankine cycle (ORC). While ORC is widely used in case of middle and low temperature of the heat source, s-CO2 BC is a new method in this field of application. One of the aim of the analysis is to verify if this choice can be comparable with ORC for this operative range, with a medium-low value of exhaust gases and very small power values. The studied MGT is a Turbec T100P.

scholarly journals Comparative Analysis of Small-Scale Organic Rankine Cycle Systems for Solar Energy Utilisation

Energies ◽  
2019 ◽  
Vol 12 (5) ◽  
pp. 829 ◽  
Author(s):  
Ruiqi Wang ◽  
Long Jiang ◽  
Zhiwei Ma ◽  
Abigail Gonzalez-Diaz ◽  
Yaodong Wang ◽  
...  
Keyword(s):  
Solar Energy ◽  
Power Output ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Hot Water ◽  
Superior Performance ◽  
Small Scale ◽  
Water Storage Tank ◽  
Solar Thermal Collector ◽  
Cycle Systems

Small-scale organic Rankine cycle (ORC) systems driven by solar energy are compared in this paper, which aims to explore the potential of power generation for domestic utilisation. A solar thermal collector was used as the heat source for a hot water storage tank. Thermal performance was then evaluated in terms of both the conventional ORC and an ORC using thermal driven pump (TDP). It is established that the solar ORC using TDP has a superior performance to the conventional ORC under most working conditions. Results demonstrate that power output of the ORC using TDP ranges from 72 W to 82 W with the increase of evaporating temperature, which shows an improvement of up to 3.3% at a 100 °C evaporating temperature when compared with the power output of the conventional ORC. Energy and exergy efficiencies of the ORC using TDP increase from 11.3% to 12.6% and from 45.8% to 51.3% when the evaporating temperature increases from 75 °C to 100 °C. The efficiency of the ORC using TDP is improved by up to 3.27%. Additionally, the exergy destruction using TDP can be reduced in the evaporator and condenser. The highest exergy efficiency in the evaporator is 96.9%, an improvement of 62% in comparison with that of the conventional ORC, i.e., 59.9%. Thus, the small-scale solar ORC system using TDP is more promising for household application.

Dynamic Simulation and Optimization of an Experimental Micro-CSP Power Plant

2015 ◽  
Author(s):  
Matthias Mitterhofer ◽  
Matthew Orosz
Keyword(s):  
Control Strategy ◽  
Low Cost ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Economic Benefits ◽  
Solar Thermal ◽  
Small Scale ◽  
Pinch Point ◽  
Simulation And Optimization ◽  
Dynamic Representation

Small scale solar thermal systems are increasingly investigated in the context of decentralized energy supply, due to favorable costs of thermal energy storage (TES) in comparison with battery storage for otherwise economical PV generation. The present study provides the computational framework and results of a one year simulation of a low-cost pilot 3kWel micro-Concentrated Solar Power (micro-CSP) plant with TES. The modeling approach is based on a dynamic representation of the solar thermal loop and a steady state model of the Organic Rankine Cycle (ORC), and is validated to experimental data from a test site (Eckerd College, St. Petersburg, Florida). The simulation results predict an annual net electricity generation of 4.08 MWh/a. Based on the simulation, optimization studies focusing on the Organic Rankine Cycle (ORC) converter of the system are presented, including a control strategy allowing for a variable pinch point in the condenser that offers an annual improvement of 14.0% in comparison to a constant condensation pinch point. Absolute electricity output is increased to 4.65 MWh/a. Improvements are due to better matching to expander performance and lower condenser fan power because of higher pinch points. A method, incorporating this control strategy, is developed to economically optimize the ORC components. The process allows for optimization of the ORC subsystem in an arbitrary environment, e.g. as part of a micro-grid to minimize Levelized electricity costs (LEC). The air-cooled condenser is identified as the driving component for the ORC optimization as its influence on overall costs and performance is of major significance. Application of the optimization process to various locations in Africa illustrates economic benefits of the system in comparison to diesel generation.

A Finite-Time Thermodynamic Framework for Optimizing Solar-Thermal Power Plants

2007 ◽  
Vol 129 (4) ◽  
pp. 355-362 ◽  
Author(s):  
A. McMahan ◽  
S. A. Klein ◽  
D. T. Reindl
Keyword(s):  
Finite Time ◽  
Power Plants ◽  
Thermal Power ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Capital Cost ◽  
Solar Thermal ◽  
Thermal Power Plants ◽  
Power Cycles ◽  
Solar Thermal Power

Fundamental differences between the optimization strategies for power cycles used in “traditional” and solar-thermal power plants are identified using principles of finite-time thermodynamics. Optimal operating efficiencies for the power cycles in traditional and solar-thermal power plants are derived. In solar-thermal power plants, the added capital cost of a collector field shifts the optimum power cycle operating point to a higher-cycle efficiency when compared to a traditional plant. A model and method for optimizing the thermoeconomic performance of solar-thermal power plants based on the finite-time analysis is presented. The method is demonstrated by optimizing an existing organic Rankine cycle design for use with solar-thermal input. The net investment ratio (capital cost to net power) is improved by 17%, indicating the presence of opportunities for further optimization in some current solar-thermal designs.

Energy Recovery Improvement Using Organic Rankine Cycle at Covanta’s Haverhill Facility

2010 ◽  
Author(s):  
Heping Cui ◽  
Jim Lynch ◽  
David McQuillan ◽  
Joseph Becker ◽  
Tim Sundel
Keyword(s):  
Energy Efficiency ◽  
Power Output ◽  
Energy Recovery ◽  
Landfill Gas ◽  
Organic Rankine Cycle ◽  
Rankine Cycle ◽  
Low Grade ◽  
Waste Energy ◽  
City Water ◽  
Net Power Output

Covanta Energy, in cooperation with United Technologies Corporation (UTC), has evaluated, designed, and is in the process of installing an Organic Rankine Cycle (ORC) system at its Haverhill Energy from Waste (EfW) Facility to improve heat recovery and energy efficiency, and to generate more clean renewable energy. ORC systems have been applied in geothermal applications and some other industrial processes to recover low grade and waste energy to generate electricity. This paper describes the design and integration of the ORC system into the Haverhill EfW steam cycle, and the landfill gas engine system, which also operates at the facility. The anticipated energy efficiency improvements and increased net power output have been analyzed and simulated. The results show that the integration of the ORC system could lead to a potential increase in the net power output by as much as 305 kWe in the summer and by 210 kWe in normal weather. It is also anticipated that with the ORC system the facility has the potential to improve the overall plant energy efficiency, as well as save city water.

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