14:20
Session 7B: Miscellaneous
Chair: Matteo Pini
14:20
20 mins
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Application of finite-time thermodynamics for evaluation method of heat engines
Takeshi Yasunaga, Yasuyuki Ikegami
Abstract: The ORC is generally applied to generate the electricity from relatively low temperature difference heat sources. Typical low-grade heat sources utilized as the sensible heat are the discharged heat from the industrial plants, geothermal, hot-spring and ocean thermal gradient. In the design of the heat balance for the energy conversion systems, the maximization of available work per the heat source quantity is significantly important. The condition for maximized work output is determined by the balance of the donated heat duty from the heat source and the thermal efficiency of the heat engine. Since the thermal efficiency mainly depends on the available temperature difference of the heat source, the thermal efficiency itself does not present the performance of the energy conversion system. The alternative performance evaluation methods used as the exergy efficiency is generally complicated for the industrial and public use, then eventually the thermal efficiency is still applied to the evaluation of the system in spite of inherently irrelevance. Therefore, the alternative definition on thermal efficiency for performance evaluation of the systems are inevitably required. Firstly, this research clarify the potential energy of the heat sources using the dead state as the thermal equilibrium state of the finite heat sources instead of the infinite quantity of the environmental temperature, and secondly proposes the normalized thermal efficiency of energy conversion defined as ratio of the work over the potential energy. The normalized thermal efficiency coincides with a change in the work from heat engine. The result shows that the introduction of normalized thermal efficiency is significantly effective for the evaluation of energy conversion system based on two different temperature streams. In the stage of the design of the heat and mass balance in the ORC system, the optimization by the maximizing the normalized thermal efficiency will yield the effective power output in the limited heat sources.
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14:40
20 mins
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Using the forward movement of a container ship navigating in the artic to air-cool a marine Organic Rankine Cycle unit
Santiago Suárez de la Fuente, Ulrik Larsen, Rachel Pawling, Iván García Kerdan, Alistair Greig
Abstract: Ice coverage in the Arctic is declining, allowing for new shipping routes. Navigating Rotterdam-Yokohama through the Arctic instead of going through the Suez Canal reduces the travel distance by about 60% thus potentially reducing fuel consumption, CO2 emissions and other pollution factors. It is important to reduce the environmental impact further in the sensitive Artic, and this can be done with a waste heat recovery system (WHRS). Low heat sink temperatures increase the WHRS thermal efficiency substantially and the cold Arctic air presents an attractive opportunity at the cost of increased power consumption due to air moving through the condenser. This paper investigates the exploitation of the forward movement of a container ship navigating in the Arctic Circle and density-change induced flow as means of moving air through the condenser in an organic Rankine cycle (ORC) unit to reduce the fan power required. The ORC unit uses the available waste heat in the scavenge air system to produce electric power.
The paper uses a two-step optimisation method with the objective of minimising the ship’s annual CO2 emissions. The results suggest that using the supportive cooling could reduce the fan power by up to 60%, depending on the ambient air temperature.
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15:00
20 mins
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Experimental performance evaluation of a multi-diaphragm pump of a micro-ORC system
Gianluca Carraro, Platon Pallis, Aris-Dimitrios Leontaritis, Sotirios Karellas, Panagiotis Vourliotis, Sergio Rech, Andrea Lazzaretto
Abstract: The Organic Rankine Cycle (ORC) is a promising technology for recovering energy from low-temperature heat sources. In particular, small-size ORCs may heavily contribute to heat recovery from the high number of internal combustion engines (ICEs) existing in the market. The performance of micro-scale ORC systems strongly depend on the performance of their components: expander, pump and heat exchangers. While the heat exchangers and expander have been extensively investigated, the ORC pump has only received limited attention, regardless of its considerably low global efficiency in micro-scale applications and the impact of its operation on the stability of the whole system. In this context, the main purpose of this work is the experimental characterization of a multi-diaphragm positive displacement pump, integrated in an experimental ORC waste heat recovery system with a rated power output of 4kWel. The study focuses on the experimental evaluation of the pump performance as well as on stability issues like the occurrence of cavitation phenomena. A detailed presentation of the experimental procedure and results is supplied. In particular, a great effort has been put in calculating the global and volumetric efficiency of the pump for a wide range of operational conditions, which reach maximum values around 45 - 48% and 95%, respectively. As regards cavitation issues, the effect of the available Net Positive Suction Head (NPSHa) at the pump inlet at partial and full load has been investigated to obtain important guidelines for stable operation.
Finally, an extensive dataset of steady-state operating points has been used to calibrate an improved version of a semi-empirical model developed for positive displacement ORC pumps. Special attention has been given to the ability of the model to accurately predict the operational behaviour and performance of the pump at steady-state conditions, which are within its calibration range but have not been included in the calibration dataset. After the simulation, relative errors in between 0.5%, for the outlet temperature, and 10%, for the electric power consumption, have been achieved.
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15:20
20 mins
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Pumped heat electricity storage: potential analysis and ORC requirements
Dennis Roskosch, Burak Atakan
Abstract: The rising share of renewable energy sources in power generation leads to the need of energy storage capacities. In this context, also some interest in thermal energy storage, often called pumped heat electricity storage (PHES), arises. One possible design of such a PHES system consists of a compression heat pump, a thermal storage and an organic Rankine cycle (ORC). The present work analyses the general thermodynamic potential and limits of such a system and deals with the unusual requirements for the ORC. The potential analysis starts with the optimal case of combining two Carnot cycles with irreversible heat transfer. It is found that the efficiency of the entire process increases with increasing storage temperature and in general roundtrip efficiencies up to 70 % are predicted. Afterwards the cycles are transferred to cycles that are more realistic by considering technical aspects and a hypothetical working fluid which is optimized by an inverse engineering approach. This leads to lowered roundtrip efficiencies, which now, decrease with increasing storage temperatures. In a second step the specific ORC requirements as part of a PHES are considered, emphasizing the working fluid parameters. Especially, the use of a latent thermal energy storage leads to an ORC design differing from common (e.g. geothermal) applications. It is shown that the efficiency of the ORC and of the entire process strongly depends on the superheating at the expander inlet; here, the superheating must be held as small as possible, contrary to ORCs using common heat sources.
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15:40
20 mins
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A non-condensing thermal compression power generation system
Peter McGrail, Jeromy Jenks, Radha Motkuri, Nathan Phillips, Timothy Veldman, Ben Roberts
Abstract: Organic Rankine cycle (ORC) systems have attracted interest for more than three decades due to advantages in operation at lower working temperature, low maintenance requirements, and relative simplicity (fewer components). In theory, these advantages should make ORC technology economically attractive for the small and medium power scales the majority of geothermal, co-produced, and geo-pressured resources can provide. Unfortunately, the theoretical promise has been realized at only a tiny fraction of the estimated 100,000 MWe potentially obtainable in the U.S. alone from these resources. The low utilization is directly tied to the relatively low heat-to-power conversion efficiency (2 to 7% typically) and high cost of specially designed expander–generator equipment. The resulting high cost of the power generated just does not make economic sense except in very specialized situations. PNNL and its partners are developing and demonstrating a new type of harmonic adsorption recuperative power (HARP) generation system that offers potential for 40% more efficient power generation as compared with a standard ORC system. By introducing PNNL’s patented multibed adsorption architecture directly into the power generation cycle, a larger pressure and temperature drop across the expander is produced, thus generating more power. Moreover, the adsorption beds function as an efficient evaporator and condenser in the cycle, thus eliminating bulk vapor condensation and significant parasitic losses associated with pumping liquid refrigerant back to high pressure at the bottom of a standard ORC cycle. HARP takes advantage of new molecular engineered sorbent materials to reduce overall size and weight of the adsorption heat exchanger modules in the system. Testing has shown up to 8 times the compression power with the best sorbents relative to just heating the vapor alone. Finally, the HARP system uses the CraftEngine piston engine expander based on automotive components that allow straightforward mass production and maximum cost reductions. Capital and operating cost analysis for the HARP system show electric generation costs at very competitive rates below $0.10/kWh.
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