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Permanent URI for this collectionhttps://pepa.une.es/handle/123456789/68679

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COLD ENERGY RECOVERY IN LNG PLANTS WITH ORGANIC RANKINE CYCLE
Marchiori, Gabriele; Giudici, Marta; Ruffato, Giorgia; Astolfi, Marco
During the production phase, natural gas (NG) is compressed and chilled to liquid state (liquified natural gas, LNG) for sake of volume reduction, hence to ease transportation. Approximately, 500 kWh of electricity or mechanical power per ton of LNG is needed for LNG compression and refrigeration during the production phase, which makes cold energy exploitation interesting from a thermodynamics point of view. An effective way to harness the cold energy contained in LNG is through an Organic Rankine Cycle system. A Cold Energy Plant (CEP) is an efficient system based on ORC technology which regasifies liquified natural gas and converts the heat absorbed from sea water into electricity by recovering the valuable exergy content of LNG. This solution allows to produce electrical power onsite without any additional external fuel consumption and no emissions at stacks. The CEP is a lowmaintenance and cost-effective solution that can be efficiently applied in the LNG industry to increase energy efficiency and sustainability of operations. The CEP system designed by Exergy achieves high efficiency thanks to the use of the proprietary Exergy Radial Outflow Turbine combined with the Multilevel Condensation Cycle, maximizing the revenue from electricity production. This paper will outline the technical features of a CEP power plant and will present a case study based on a Liquified Natural Gas regassification system engineered to produce Nominal 4 MWe (4000 kWe) net electric power while simultaneously fulfilling the regasification of 180 ton/h (~1 MTPA) of LNG.
Pareto front analysis for the design and the working fluid selection in ORC-based pumped thermal energy storage technology in both pure electric and cogenerative applications
Astolfi, Marco; Alfani, Dario; Giostri, Andrea
Carnot Batteries are a sub-technology of Pumped Thermal Energy Storage concept where closed cycles are used in both charging and discharging phase. In charging mode, cheap off-peak electricity from the grid is used to store heat at a temperature different than the ambient one (generally higher) while in discharging mode the stored heat is exploited for power production. Carnot Batteries can be designed with different thermodynamic cycles (Brayton cycle, Steam Rankine cycle, Organic Rankine cycle) and can adopt different types of thermal energy storage technologies. For low duration storage (daily or weekly cycling) sensible or latent energy storage with phase change materials can be adopted, while for long duration storage (months, seasonal) the use of thermochemical reactions could be a valid option, as proposed by H2020 RESTORE project. Performance of Carnot Batteries is highly affected by the thermal storage temperature, the condensation temperature in discharging mode and the availability of residual heat at a temperature higher than the ambient one for boosting the heat pump coefficient of performance in charging cycle. This paper focuses on the optimal design of a reversible thermodynamic system working as a heat pump (HP) cycle in charging mode and as an organic Rankine cycle (ORC) in discharging mode. A dedicated numerical model developed in Python is employed to compare the techno-economic performances of different working fluids and select the most promising candidates. Main difficulty is related to the use of reversible heat exchangers which design impacts both on the charging and discharging operation, strongly affecting the system round trip efficiency, and requiring a discretized off-design modelling. A Pareto front of optimal round trip efficiency against total area of heat exchangers is obtained by varying the main design parameters, such as heat transfer temperature differences and heat exchangers pressure drops. Results show that for a given overall heat transfer area low critical temperature fluid are mainly penalized by poor HP performance due to high compressor specific work, while high critical temperature fluids are mostly penalized by high pressure drops caused by the low fluid density. The most eaching a RTE close to 35% for the pure electric configuration at its maximum RTE over total heat transfer area parameter
POTENTIAL OF TRIGENERATIVE WASTE HEAT RECOVERY CO2- MIXTURE TRANSCRITICAL POWER PLANTS FOR INCREASING THE SUSTAINABILITY OF DISTRICT HEATING AND COOLING NETWORKS
Baiguini, Mattia; Doninelli, Michele; Morosini, Ettore; Alfani, Dario; Di Marcoberardino, Gioele; Giulio Iora, Paolo; Manzolini, Giampaolo; Invernizzi, Costante Mario; Astolfi, Marco

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