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organic rankine cycle

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Costante Mario Invernizzi
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Some historical notes, some technical details and some examples about the "low temperature" thermodynamic conversion of the solar energy. An update.
Costante Mario Invernizzi
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This study investigates the use of pure and hydrocarbons binary mixtures as potential alternatives working fluids in a usual biomass powered organic Rankine cycle (ORC). A typical biomass combined heat and power plant installed in Cremona (Italy) is considered as the benchmark. Eight pure hydrocarbons (linear and cyclic) and four binary mixtures of linear hydrocarbons were selected. The critical points of the binary mixtures at different composition were calculated using an in-house code developed in MATLAB c (R2018b) environment. Based on the critical point of a working fluid, supercritical and subcritical cycle configurations of ORC were analysed. A detailed thermodynamic comparison with benchmark cycle was carried out in view of cycle efficiency, maximum operating pressure, size of the turbine and heat exchangers. The supercritical cycles showed 0.02 to 0.03 points lower efficiency, whereas, subcritical cycles showed comparable efficiencies than that of the benchmark cycle. The cycles operating with hydrocarbons (pure and mixtures) exhibited considerably lower volume flow ratios in turbine which indicates lower turbine size. Also, size parameter of regenerator is comparatively lower due to the lower molecular complexity of the hydrocarbons. A noticeable increase in turbine power output was observed with change in composition of the iso-octane/n-octane binary mixture at the same thermodynamic efficiency.
Costante Mario Invernizzi
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This work explores the possibility to adopt in organic Rankine cycle (ORC) plants mixtures of water (acting as solvent) plus an organic compound (acting as solute) as the working fluid. Initially an evaluation of the thermodynamic properties of the mixtures is performed, in order to assess their properties, and to point out the molar fractions which entail a near-azeotropic behaviour. Four species from three different classes of chemical compounds are investigated: 2,2,2-trifluoroethanol and n-butanol for alcohols, where the first is fluorinated, acetonitrile for nitrile class and 2-methylpyrazine as a heterocyclic aromatic compound. Simultaneously, the thermal stability of the pure substances considered as the possible solute for the mixtures is experimentally investigated in order to estimate the temperature applicability range. The ORC plant performance, from a low-enthalpy geothermal heat source (hot water stream from 100 to 200 °C), adopting the selected mixtures as the working fluid is finally evaluated, and the analysis includes a preliminary discussion on the turbine design; results are compared with respect to the reference case of a hypothetical plant adopting water as the working fluid.
Ennio Macchi
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The thermal stability analysis of perfluorohexane (C6F14)is presented in this paper as a preliminary evaluation of the potential application of the binary mixture CO2 – C6F14 as innovative working fluid for transcritical-CO2 power cycles. After presentinga description of the experimental apparatus, saturation pressure models are compared and calibrated over measurementsof the virgin fluid (C6F14). Moreover, the methodologyapplied to attest the occurrence of a thermal decomposition is described. Finally, the paper presents a thermodynamic analysis of themeasurements obtained from the partially decomposed system,performed to investigate the nature ofthe partial thermal decomposition process.
Ennio Macchi
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In this paper, Titanium tetrachloride (TiCl4) is analyzed/assessed and proposed as a new potential working fluid in Rankine Cycles. Besides its good thermodynamic properties, TiCl4 is in fact a fairly low cost, non-carcinogenic fluid, with zero Global Warming Potential (GWP) and Ozone Depleting Potential (ODP) and it is currently employed in high temperature industrial processes. It is however very reactive with humid air and water. A preliminary thermodynamic analysis confirms its possible application in power plants with maximum temperature up to 500 C, considerably higher than the ORC state-of-the-art technology, performing electrical efficiencies as high as 35–40%. This suggests the potential use of TiCl4 as an alternative fluid in ORCs allowing the exploitation of high temperature sources (up to 500 C), typically used in steam cycles. To assess the possibility of operating the cycle in such high temperature conditions, we carried out an experimental thermal stress analysis, showing that the fluid is remarkably stable at temperatures up to 500 C, even in presence of P91 and Cupronickel, two materials typically employed in the high temperature section of power cycles.
Ennio Macchi
added 2 research items
The present work aims to investigate the potential advantages in using a novel wet and dry configuration for heat rejection units in ORC power plants. The reference case is a geothermal power plant that exploits a medium temperature brine and uses a closed loop of cooling water to release the condensation heat. In the calculations, the off-design operation of the whole plant is optimized by a techno-economic point of view with a realistic part-load behaviour for the ORC and the use of experimentally validated correlations for the heat rejection section. The performance attainable with the novel LU-VE Emeritus® unit equipped with a water spray system and adiabatic panels is compared with those achievable with the same unit in dry operation. Final results show a marked increase of revenues with Emeritus® units with respect to a dry unit.
This paper focuses on the design and the optimization of Organic Rankine Cycle (ORC) for LNG regasification plants. This technology is a promising solution with large benefits attainable in terms of primary energy savings compared to both Open Rack Vaporizer (ORV) and Submerged Combustion Vaporizer (SCV) technologies. Different cycle configurations are investigated including the option of multilevel condensation plants. The adoption of several working fluid candidates is analyzed and different design constraints are included to obtain a more reliable solution. The optimal combinations of cycle configuration and working fluid are presented with a preliminary design of the main components. Finally a dependency study on the seawater temperature is carried out.
Ennio Macchi
added 2 research items
The application of CO2 power cycles is advantageous to exploit high-temperature sources (500-800°C) in the case of available low-temperature heat sinks (15-25°C). However, their efficiency is strongly reduced for higher heat sink temperatures. At these temperatures, due to the low-critical temperature of CO2 (about 31°C), CO2 is in fact compressed in the supercritical vapor phase rather than in the liquid phase, thus increasing energetic demand for compression. One of the solutions envisaged to overcome this problem is the addition of one or more chemicals that allow having a mixture with a higher critical temperature than the one of pure CO2. This preserve the working fluid compression in its liquid phase, even in the case of heat sinks with temperatures greater than 25°C.
This paper, after a brief description of the radial outflow turbine and of its main features, discloses the field performances evaluation of two operating geothermal ORC (Organic Rankine Cycle) plants installed by Exergy Spa in Turkey. The work describes the test procedure, the measurements and calculation methods used to obtain the turbine efficiency as well as overall power cycle performance from the set of available experimental data.
Ennio Macchi
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Low-medium temperature heat sources in the range 5 - 50 MWth are made available by many industrial fields but they may also be of interest for biomass and solar energy applications. ORC has been proposed in the last 20 years as a reliable solution for the exploitation of these energy sources since the alternative represented by steam cycles leads to an inefficient conversion of such small available thermal powers. However, the use of organic fluids involves a number of safety and environmental issues, either related to fluid flammability (for hydrocarbons) or to their high-Global Warming Potential (for halogenated fluids), and of limitations to the achievable cycle maximum temperature, due to fluids thermal decomposition. To overcome these limitations, CO2-based transcritical and supercritical cycles have been proposed, in recent years, as a viable option for waste heat recovery applications. The present work aims to present a fair comparison between CO2 and ORC power plants for waste heat recovery applications.
Ennio Macchi
added 2 research items
The need for a simple method for predicting the efficiency of a turbine stage without carrying out a detailed aerodynamic design is enhanced. The results of an optimization study of a large number of turbine stages are presented. The turbine stage efficiency is found to be a function of three main parameters: the expansion ratio, defined as the specific volume variation across the turbine in an isentropic process; a given dimensional parameter which accounts for actual turbine dimensions, and the specific speed. The method is useful mainly for nonconventional turbine stages, the efficiency of which cannot be anticipated from previous machines experience.
Ennio Macchi
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Organic Rankine Cycle (ORC) Power Systems: Technologies and Applications provides a systematic and detailed description of organic Rankine cycle technologies and the way they are increasingly of interest for cost-effective sustainable energy generation. Popular applications include cogeneration from biomass and electricity generation from geothermal reservoirs and concentrating solar power installations, as well as waste heat recovery from gas turbines, internal combustion engines and medium- and low-temperature industrial processes. With hundreds of ORC power systems already in operation and the market growing at a fast pace, this is an active and engaging area of scientific research and technical development. The book is structured in three main parts: (i) Introduction to ORC Power Systems, Design and Optimization, (ii) ORC Plant Components, and (iii) Fields of Application. Provides a thorough introduction to ORC power systems Contains detailed chapters on ORC plant components Includes a section focusing on ORC design and optimization Reviews key applications of ORC technologies, including cogeneration from biomass, electricity generation from geothermal reservoirs and concentrating solar power installations, waste heat recovery from gas turbines, internal combustion engines and medium- and low-temperature industrial processes Various chapters are authored by well-known specialists from Academia and ORC manufacturers.
Ennio Macchi
added 2 research items
This chapter aims to define a set of general correlations for the estimation of axial-flow turbine efficiency in the Organic Rankine Cycle (ORC) field. A dedicated numerical tool is used for the optimization of several hundreds of turbines and the results are presented in terms of specific parameters (SP, Vr, and Ns) according to similarity rules. The analysis is carried out for single, two, and three stages turbines. For each case a correlation of efficiency at optimal rotational speed is calibrated in function of the equivalent single stage SP and the total isentropic Vr. Three sensitivity analyses are proposed in order to highlight the effects of each single parameter on stage efficiency. Finally, the effect of fluid choice on turbine performance and dimension is discussed with a numerical example.
This chapter aims to define a set of general correlations for the estimation of axial-flow turbine efficiency in the Organic Rankine Cycle (ORC) field. A dedicated numerical tool is used for the optimization of several hundreds of turbines and the results are presented in terms of specific parameters (SP, Vr, and Ns) according to similarity rules. The analysis is carried out for single, two, and three stages turbines. For each case a correlation of efficiency at optimal rotational speed is calibrated in function of the equivalent single stage SP and the total isentropic Vr. Three sensitivity analyses are proposed in order to highlight the effects of each single parameter on stage efficiency. Finally, the effect of fluid choice on turbine performance and dimension is discussed with a numerical example.