14:40
Session 5: Supercritical ORC
Chair: Dimitris Manolakos
14:40
20 mins
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DESIGN OF WASTE HEAT RECOVERY SYSTEMS BASED ON SUPERCRITICAL ORC FOR POWERFUL GAS AND DIESEL ENGINES
Oleksii Rudenko, Leonid Moroz, Maksym Burlaka, Clement Joly
Abstract: Nowadays the scientific world community is strongly concerned about problems of efficiency increase and emissions reduction of Internal Combustion Piston Engines (ICPE). The equipment of ICPE with Waste Heat Recovery Systems (WHRS) is an effective solution for the aforementioned problems. This paper focuses on finding the maximum possible heat recovery from the available high and low temperature waste heat flows of a powerful ICPE to produce the maximum amount of additional power while decreasing the load on the engine’s cooling system.
Having considered and analyzed existing works devoted to the development of WHRS the most effective ideas were combined to design several thermodynamic cycles for new WHRS of powerful piston engine (here a G3612 CAT gas petroleum engine is considered). The proposed WHRS is based on a Supercritical Organic Rankine Cycle (SORC) using R245fa as the working fluid where heat is extracted from the waste heat sources by a refrigerant at different pressure levels. Internal recuperation is used to further improve the cycle performances and increase the waste heat recovery. The thermodynamic analysis of the new WHRS showed that up to 19.5% of power boost for the internal combustion engine can be achieved without burning additional fuel which represents significant gains in terms of specific power.
In order to quantify the estimation of the performances for proposed cycles the design of a traditional, high efficiency, WHRS based on double pressure water steam cycle for the same engine's conditions was performed. This comparison of performances between the steam cycle and the SORC R245fa cycles confirmed a high potential for the designed cycles.
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15:00
20 mins
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PERFORMANCE ANALYSIS OF SUPERCRITICAL ORGANIC RANKINE CYCLES (ORCS) BASED ON THE VARIATIONS IN THERMAOPYSICAL PROPERTIES IN THE PSEUDOCRITICAL REGION
Ran Tian, Qingsong An, Lin Shi, Huixing Zhai, Xiaoye Dai
Abstract: Supercritical organic rankine cycles (ORCs) appear to be more attractive compared with subcritical ORCs in terms of lower exergy destruction and higher thermal efficiency and work output. However, the heat transfer mechanisms about supercritical cycle around the critical point is still less known due to the significant variations in thermophysical properties. The strong variations in thermophysical properties have great influence on the heat transfer and thus significantly affect the determination of ORCs operating parameters. The physical mathematical model considering supercritical pressure heat transfer is developed. The aim of this paper is to investigate the influence of the significant changes in thermophysical properties in the pseudocritical region on the ORC performance, providing guidelines for system design. Convection heat-transfer coefficient of the working fluid, pinch point location, heat exchanger area and work output are analyzed based on the changes of thermophysical properties in the pseudocritical region for different heat source temperature.
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15:20
20 mins
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INVESTIGATION AND OPTIMIZATION OF THE OPERATION AND DESIGN OF A SMALL SCALE EXPERIMENTAL TRIGENERATION SYSTEM POWERED BY A SUPERCRITICAL ORC
Tryfonas Roumpedakis, Konstantinos Braimakis, Sotirios Karellas
Abstract: In this work, the detailed investigation and the optimization of the operational parameters of an experimental, small scale trigeneration system encompassing a supercritical Organic Rankine Cycle (ORC) and a heat pump are presented. Both the ORC and the heat pump jointly operate with the same working fluid (R227ea). The heat input to the ORC is provided by a 75kWth biomass boiler. The electricity produced by the ORC, which has a nominal power output of 5 kWe, is used to power the heat pump, capable of covering a cooling load of 4 kWth, while any surplus electricity is exported to the grid. Meanwhile, the heat generated during the condensation of the working fluid (around 70 kWth) is utilized to produce hot water. The system has therefore the potential to produce combined cooling, heating and electricity, depending on the load requirements, by utilizing a renewable energy source with zero net CO2 emissions.
The investigation carried out includes the selection process of the working fluid of the system through the comparison of its performance with that of other typical working fluids and by taking into account environmental and safety factors. Furthermore the study presents the optimization procedure for selecting the working temperatures and pressures in order to maximize the cycle’s efficiency, given the technological limits of the elements of this system (heat exchangers, scroll expanders etc.). In addition, a supercritical plate heat exchanger model, used for the design of the heat exchanger of the unit, is presented.
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15:40
20 mins
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EXPERIMENTAL TESTING OF A SMALL-SCALE SUPERCRITICAL ORC AT LOW-TEMPERATURE AND VARIABLE CONDITIONS
George Kosmadakis, Dimitris Manolakos, George Papadakis
Abstract: The detailed experimental investigation of an organic Rankine cycle (ORC) is presented, which is designed to operate at supercritical conditions. The net capacity of this engine is almost 3 kW and the temperature of the hot water is always lower than 100 oC. The laboratory testing of the engine includes the variation of the heat input and of the hot water temperature. The maximum heat input is 48 kW, while the hot water temperature ranges from 65 up to 100 oC.
The tests are conducted at the laboratory and the heat source is a controllable electric heater, which can keep the hot water temperature constant, by switching on/off its electrical resistances. The expansion machine is a modified scroll compressor with major conversions, in order to be able to operate with safety at high pressure (max. pressure around 40 bar). The ORC engine is equipped with a dedicated heat exchanger of helical coil design, suitable for such applications. The speeds of the expander and ORC pump are regulated with frequency inverters, in order to control the cycle top pressure and heat input. The performance of all components is evaluated, while special attention is given on the supercritical heat exchanger and the scroll expander.
The performance tests examined here are the ones for hot water temperature of 95 oC, with the aim to examine the engine performance at the design conditions, as well as at off-design ones. Especially the latter are very important, since this engine will be coupled with solar collectors at the final configuration, where the available heat is varied to a great extent.
The engine has been measured at the laboratory, where a thermal efficiency of almost 6% has been achieved, while supercritical operation did not show superior performance as expected, due to the oversized expander. A smaller expander would allow operation at even higher pressures for higher speed with increased electric efficiency, which would probably reveal the full potential of the supercritical operation.
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