1,721,230 research outputs found
Il ciclo a gas non solubile e liquido non volatile: modello termodinamico e banco sperimentale
No full textPROPOSAL OF AN INNOVATIVE, HIGHLY-EFFICIENT, LARGE-SCALE HYDROGEN LIQUEFIER
No full textAn innovative, efficient and large hydrogen liquefier is described. Innovations lie in the fact (i) the feed, 10 kg/s, is refrigerated in heat exchangers catalytically promoting the ortho-para conversion (ii) down to the low temperature of 20.5 K and at the high pressure of 60 bar at which it is available and (iii) lastly expanded to the storage conditions of 1.5 bar and 20 K through a liquid-phase turbomachine; (iv) refrigeration is via four helium recuperative Joule-Brayton cycles arranged so that the refrigerant follows the cooling curve of hydrogen and the volume flow rates in compression and expansion processes are typical of axial-flow high-efficiency turbomachines; (v) compression is accomplished in 15 intercooled 8-stage devices derived from gas turbine technology. Heat exchangers require specific surfaces comparable to current state-of-the-art liquefiers. Nevertheless, the predicted work of approximately 18 MJ/kg is half as much the requirement of those liquefiers and corresponds to a second-law efficiency of almost 48%
Constant-Volume Vapor-Liquid Equilibrium for Thermal Energy Storage: Proposal of a New Storage System for Concentrated Solar Power Plants
Full text linkThe development of thermal energy storage systems is key to increasing the deployability and reliability of concentrated solar power plants. Previous work from the authors studies the possibility of exploiting vapor-liquid phase change in closed and constant volumes as a thermal energy storage mechanism because of the higher heat transfer coefficients of the phenomenon with respect to solid-liquid phase change energy storage systems. The objective of this paper is to propose a new thermal energy storage condition based on vapor-liquid systems for concentrated solar power plants. The reference case of the Khi Solar One power plant in Upington, South Africa is taken. Results show that increasing the critical temperature of the storage fluid allows for increased temperature differences and higher volume-based energy storage, while the decrease of critical pressure allows lower mechanical stresses on the energy storage system. The use of high critical temperature fluids such as ethylene glycol allows for an increase of the volume-based energy storage of around 95% at same pressure conditions with respect to the base case. The use of low critical pressure siloxanes such as D6 results in a decrease of around 26% in the volume-based energy storage. The use of D6 on the other hand leads to a substantial decrease in the maximum pressure of the storage system, which drops from 8.2 MPa to 1 MPa, allowing the use of cheaper and less complex equipment. Both cases lead to a relevant increase in the maximum storage temperature, increased of 130 K and 55 K respectively
Hydrogen as a direct heat exchange fluid in room temperature hydride systems: Numerical study on the desorption process
Full text linkHydrogen, as an energy carrier, is a promising candidate to foster decarbonization. However, its storage poses significant challenges. Common methods, such as compressed gas and liquid hydrogen, have high energy consumption and safety concerns. Recently, solid hydrogen storage in materials like metal hydrides has gained attention for their ability to store hydrogen safely at low pressures and low temperatures. This study aims to develop a numerical model to simulate the performance of metal hydrides using hydrogen as a direct fluid heat exchanger during desorption. The model, formulated as a system of partial differential equations, is implemented in MATLAB with the ODE15s solver and applied to a disk-type lanthanum nickel reactor to minimize pressure drops. Performance is investigated by varying design parameters, including reactor length and diameter, bed porosity, hydride particle diameter, operating pressure and temperature, and hydrogen mass flow rate at the reactor inlet. Additionally, the energy consumption of auxiliary equipment, such as pumping and thermal power, is evaluated. Results show that the system energy requirement is about 8-9% of the hydrogen lower heating value, with most desorption occurring in less than 300 seconds. The reactor dimensions are crucial for fast desorption and low pressure drops, with pumping power under 1 W given the small thickness and flow rate. Particle diameter and porosity have minor impacts, while pressure, temperature, and flow rate are fundamental. High temperatures, low pressures, and high recirculating flow rates favor the reaction, though a trade-off between performance and energy consumption is necessary since all high temperatures high recirculated mass flow rate allows for high consumption
Impianto MCFC di Bicocca: sviluppo del sistema per la generazione di gas di sintesi a composizione variabile
No full textLiquid hydrogen: from clean coal to filling station. Part A: proposal on an innovative, highly-efficient, large-scale liquifier
No full textLiquid hydrogen: from clean coal to filling station. Part B: analysis of an advanced, highly-integrated, IGCC-liquefier infrastructure
No full text
Assessing well-to-wheel cost of avoided carbon dioxide of zero tailpipe-emission vehicles: A case study for a fleet in Valle Camonica
Full text linkThe road transportation significantly contributes to emissions. Battery electric vehicles (BEVs) and fuel cell electric vehicles (FCEVs) are potential zero tailpipe-emission solutions. This study presents a numerical model to minimize the annual cost of refueling infrastructure for a fleet of electric and hydrogen vehicles. The case study involves a fleet of 60 vehicles in Valle Camonica, Italy, covering 500,000 km annually and consuming 270,000 liters of diesel. The model evaluates the interaction between solar photovoltaic and the grid to understand the economics of carbon dioxide avoidance. It optimizes the design and operation of infrastructure components, considering variables such as vehicle tank energy content, energy sources, electricity prices, and the potential to sell electricity to the grid. Key findings indicate that, without logistical constraints, BEVs outperform FCEVs. However, FCEVs become necessary for longer missions. Grid-connected plants show superior economics, achieving 65%-90% emissions mitigation. The study also reveals that optimal economics are achieved by oversizing renewable energy sources and consistently selling electricity to the grid, resulting in a minimum cost of avoided CO2 of 35 €/ton. The optimal strategy for significant but not total decarbonization involves grid-connected plants, proving economically viable through electricity sales, requiring a shift in traditional logistics business model
- …
