Gianluca Valenti

Politecnico di Milano | Polimi · Department of Energy

The aim of this work is the implementation of an optimization model for a hydrogen production facility connected to a refuelling station for heavy-duty vehicles, operating in the field of waste management and transportation. The model is composed by two subsequent mixed integer linear programming problems. The first problem addresses the problem of...

International standards concerning hydrogen measurement in legal frameworks are still lacking. This study proposes a novel approach to instrument and procedure definition for the legal measurement of pure hydrogen volume and volumetric flow rate according to main international standards of metrology. A wet drum meter filled with water is chosen as...

Green hydrogen from electrolysis has become the most attractive energy carrier for making the transition from fossil fuels to carbon-free energy sources possible. Especially in the naval sector, hydrogen has the potential to address environmental targets due to the lack of low-carbon fuel options. This study aims at investigating an offshore liquef...

There are many industrial plants that use steam as an energy vector at different pressure levels, in which pressure reduction is commonly performed by a throttling valve, resulting a totally irreversible process. It is possible to recover this energy through an expander that generates mechanical or electric energy. This work is focused on the analy...

The 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 coefficie...

In this study, the thermal and electrical modeling of a photovoltaic panel is performed to evaluate its temperature profiles, electrical efficiency and the electrical power supplied. The energy balance equations under transient conditions of all the layers that make up the panel are discretized by the finite difference technique and solved with the...

Compressed air is crucial on an electric or electrified heavy-duty vehicle. The objective of this work was to experimentally determine the performance parameters of the first prototype of an electric-driven sliding-vane air compressor, specifically designed for electric and electrified heavy-duty vehicles, during the transient conditions of cold st...

The foreseen uptake of hydrogen mobility is a fundamental step towards the decarbonization of the transport sector. Under such premises, both refueling infrastructure and vehicles should be deployed together with improved refueling protocols. Several studies focus on refueling the light-duty vehicles with 10 kgH2 up to 700 bar, however less known e...

Microgrids represent a flexible way to integrate renewable energy sources with programmable generators and storage systems. In this regard, a synergic integration of those sources is crucial to minimize the operating cost of the microgrid by efficient storage management and generation scheduling. The forecasts of renewable generation can be used to...

Stirling units are a viable option for micro-cogeneration applications, but they operate often with multiple daily startups and shutdowns due to the variability of load profiles. This work focused on the experimental and numerical study of a small-size commercial Stirling unit when subjected to cycling operations. First, experimental data about ene...

The sector of thermal energy storage shows a number of alternatives that could have a relevant impact on the future of energy saving as well as renewable energy technologies. Among these, latent heat thermal energy storage technologies show promising results. Technologies that exploit solid-liquid phase change have already been widely proposed, but...

The decarbonization of the residential sector is fundamental for energy transition. In this context, it is promising the introduction of hydrogen in natural gas networks in specific hydrogen districts. Accordingly, hydrogen meters are needed for accounting the fuel consumptions. The topic of this work is the development and construction of an exper...

This work reports the measured and derived quantities of an experimental campaign conducted in an existing laundry to record the conditions of the exhaust air of a batch industrial natural gas-fired dryer for cotton flat fabrics, like bed linens or tablecloths. The load of fabrics is 85 kg, referred to the dry fabric. The measured quantities are te...

Waste heat recovery is one of the main strategies to reduce the use of primary resources. This work develops a cascade phase change regenerator to recover energy from exhaust air to fresh air of a natural gas-fired batch dryer in an existing industrial laundry, taken as a case study, where an experimental campaign is conducted. The regenerator comp...

Thermal energy storage is of great interest both for the industrial world and for the district heating and cooling sector. Available technologies present drawbacks that reduce the margin of application, such as low energy density, limited temperature range of work, and investment costs. Phase transition is one of the main phenomena that can be expl...

Waste heat recovery in the industrial sector plays a major role for reducing the use of primary energy. This work assesses a phase change regenerator for heat recovery from industrial dryers operating in a batch mode. The chosen architecture is a fixed bed type consisting of two vertical stoves with horizontal rod bundles, each rode being a hollow...

Ammonia is a promising solvent for the chemical absorption of carbon dioxide owing to its characteristics of low toxicity, low degradation, low cost, and low heat of desorption. The present work evaluates the energy and economic performances of the aqueous ammonia technology applied to a coal-fired power plant. First, the kinetics of absorption are...

Increasingly numerous are the experimental activities on low-grade ORC focused on expanders optimization, in order to increase the cycle net power and efficiency. In the range of small power ORCs, positive displacement expanders are more suitable than dynamic expanders thanks to lower speed, good off-design performance, high expansion ratio, low co...

Engine-driven reciprocating air compressors are employed on fuel-powered heavy vehicles to actuate a number of auxiliary systems, like brakes and suspensions. Electrically-driven sliding-vane air compressors turn particularly suited for electric heavy vehicles. Unlike in fuel-powered vehicles, the compressor is not heated up in the case of electric...

The industrial sector accounts for one third of the global energy use, mainly due to the energy-intensive industries. Waste heat recovery plays a major role among the advances that can lead to potential savings in these industries. The present work proposes an air compressor that generates industrial compressed air in a novel manner only by recover...

An innovative solvent based on the quaternary system CO2-NH3-K2CO3-H2O is reported and characterized in terms of its thermodynamic properties and rate of CO2 absorption. Thermodynamic properties of the solvent such as vapor-liquid equilibrium, solid-liquid equilibrium, and the heat of desorption were modelled with the Extended UNIQUAC thermodynamic...

Intercooling is a well-known practice in compression technology for reducing the discharge temperature and the power consumption of the process. Intracooling, a similar yet not identical concept, is the cooling of the compressed gas between two compression stages by way of spraying a liquid coolant in the gas flow without separating that liquid pri...

The absorption between aqueous NH3 and CO2 is studied using the Wetted Wall Column in order to show the effect of the solvent condition on the rate of reaction. A total of 27 different cases are investigated in the region defined by temperatures from 15 °C to 35 °C, NH3 concentrations from 5% to 15% and CO2 loadings from 0.2 to 0.6. The paper repor...

This work presents a novel type of positive-displacement expander, named the balanced rolling piston expander. It proposes also a design procedure and assesses the mechanical behavior of a virtual prototype. The expander is conceptually capable of operating at higher fluid temperatures than other positive-displacement expanders, such as scroll-or s...

The importance of water management in proton exchange membrane fuel cells is discussed in this paper. First part of research is dedicated to the characterization of a water-cooled 1kW PEMFC fuel cell stack at different operating conditions with calculation of net electric and thermal efficiencies. In the second part, the influence of inlet air humi...

Compressed air production is an energy–intensive sector, thus compressor manufacturers are constantly looking for enhancing the efficiency, by acting on several technological aspects. In an air compressor, about 80-90% of the input electric power used is wasted into the environment through the oil circuit, continuously cooled by ambient air blown v...

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...

Lube-oil injection is used in positive-displacement compressors and, among them, in sliding-vane machines to guarantee the correct lubrication of the moving parts and as sealing to prevent air leakage. Furthermore, lube-oil injection allows to exploit lubricant also as thermal ballast with a great thermal capacity to minimize the temperature increa...

Mixed-salt technology, a solvent-based technology for removing CO2 from flue gas streams offers a significant advantage over conventional amine-based CO2 removal technologies (e.g., Fluor Econamine FG PlusSM technology). SRI International (SRI) is currently investigating the application of mixed-salt technology for pulverized coal combustion (PCC)...

This paper focuses on carbon capture in an Ultra Super Critical power plant. The technology selected for CO2 capture is based on cooled ammonia scrubbing in post-combustion mode, as recently investigated by the authors in another work. Here, a rate-based approach is adopted. In detail, a specific primary energy consumption for CO2 avoided (SPECCA)...

Environmental and technical aspects of four supercritical (SC) pulverized-coal processes with post-combustion carbon capture and storage (CCS) are evaluated in the present work. The post-combustion CCS technologies (e.g. MDEA, aqueous ammonia and Calcium Looping (CaL) are compared to the benchmark case represented by the SC pulverized coal without...

In view of a vast hydrogen infrastructure, very large quantities of hydrogen may be distributed and stored as a liquid at about 20 K (− 253 °C). Today hydrogen liquefiers are a mature technology for capacities up to 30 ton day− 1 and with energy requirements of 30–40 MJ per kilogram of liquefied hydrogen, while the world's capacity today is around...

The aim of this paper is the evaluation of the influence of the kinetic of the NH3-CO2-H2O reactions in the absorber with respect to the electric power losses due to the steam bleeding from the turbine for the regeneration of the solvent. The results exposed conclude that there are few works about the kinetic of the aqueous reaction of the system N...

This work discusses the development of a benchmark comparison among hydrogen production technologies, focussing on the assessment of their operating conditions by the point of view of the potential impact on safety. The analysis focuses on state-of-the-art, fully industrialized and commercial technologies, or at least with established early-market...

A number of studies report the benefit of proper oil spraying in positive-displacement compressors. This work presents a thermodynamic model for simulating sliding-vane air compressors that employ an injection system for the lubricating oil based on both plain orifices and pressure-swirl nozzles to exploit the thermal effect of sprayed oil inside t...

The experimental activities, carried out at the Laboratory of Micro-Cogeneration (LMC) of the Department of Energy at Politecnico di Milano are hereby outlined in relation to the testing of four 2.5 kWel AC SOFC-based micro-CHP units developed by SOLIDpower S.p.a. The novelty of the work consists in carrying out a complete thermodynamic and environ...

In the future energy infrastructure there is a considerable potential for biogas and, in particular, for biomethane as a natural gas substitute. Among the alternatives of upgrading biogas to biomethane, this work focuses on membrane permeation. Taking cellulose acetate as membrane material and spiral-wound as membrane configuration, five layouts ar...

Post-combustion carbon capture technologies seem to be necessary to realize the CO2 mitigation policies internationally shared for the next future, despite none of them appears to be ready for full-scale applications. This work considers the aqueous ammonia-based process for a coal-fired Ultra Super Critical power plant. Two layouts are simulated w...

Stirling engines are a promising candidate for micro-cogeneration in residential and small-scale tertiary applications. Due to the variability of energy demand profiles and electricity tariffs, real applications often require to operate the cogeneration unit with multiple daily starts and stops, especially during summer and intermediate seasons. Th...

Positive-displacement compressors and, among them, sliding-vane rotary machines are widely used in the compressed air sector. As in many other industrial fields, the efficient utilization of energy has become a major goal also in this sector. The aim of the present activity is the experimental investigation on the influence of two vanes materials (...

Micro-cogeneration Stirling units are promising for residential applications because of high total efficiencies, favorable ratios of thermal to electrical powers and low CO as well as NOx emissions. This work focuses on the experimental and the numerical analysis of a commercial unit generating 8 kW of hot water (up to 15 kW with an auxiliary burne...

Micro-cogeneration Stirling engines are considered promising for residential applications. The present work covers the experimental and numerical analysis of a commercial Stirling unit capable of 8 kW of hot water and 1 kW of electricity. A previously concluded experimental campaign that focused on external measurements is extended here to include...

ScienceDirect 1876-6102 © 2014 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/). Peer-review under responsibility of the Organizing Committee of ICAE2014 Abstract Micro-cogeneration Stirling engines are promising for residential applications. Thi...

A way to increase the efficiency of positive-displacement air compressor is spraying the lube oil to exploit it not only as lubricating and sealing agent but also as thermal ballast. This work seeks the experimental evidence in sliding-vane compressors by measuring the air standard volume flow rate and the electrical power input of three diverse co...

This work discusses the design and the development of a Laboratory of Micro-Cogeneration (LMC) at Politecnico di Milano. The LMC laboratory is a unique structure devoted to small-scale power generation, with the main goals of testing and improving the performance of systems that produce or utilize electric and thermal (hot and/or cold) power in a v...

In industrial contexts, electrical energy for compressed air represents an important share of the global electricity consumption: this figure accounts for 4–5% of the total. Among the existing compressor technologies, rotary volumetric machines proved to be more suitable than other types (dynamic, reciprocating, etc.) in terms of pressure and flow...

Electrical energy for compressed air in industrial contexts represents an important share of the global consumption: this figure accounts for 4-5 %. Among the existing compressor technologies, rotary volumetric machines proved to be more suitable than other types (dynamic, reciprocating, etc.) in terms of pressure and flow rate delivered. Sliding V...

The isentropic efficiency of positive-displacement compressors may be improved in order to follow an increasing demand for energy savings. This work analyzes the thermal effect of the lubricating oil presence in the air during compression with the scope of exploiting it as a thermal ballast to mitigate both the gas temperature rise and its compress...

Many alternatives are being investigated for the carbon capture, but none appears to have been proved as the choice for full-scale applications. This work considers the Chilled Ammonia Process for coal-fired Ultra Super Critical power plants. Three layouts are simulated with Aspen Plus and the Extended UNIQUAC thermodynamic model. Compared to a tra...

In view of a possible hydrogen infrastructure a number of studies on large-scale hydrogen liquefiers state that conventional plant efficiencies may be substantially increased. Generally those studies consider different (i) working conditions, (ii) operational unit performances and (iii) thermodynamic models, making it difficult to compare their res...

Post-combustion carbon capture is attracting much attention due to the fact that it can be retrofitted on existing coal power plants. Among the most interesting technologies is the one that employs aqueous ammonia solutions to absorb the generated carbon dioxide. The evaluation of such process requires the modeling of electrolyte solutions. In this...

This paper presents new supercritical volumetric measurements on three binary mixtures mainly composed of carbon dioxide. The interest in the tested mixtures derives primarily from carbon capture and storage applications. In particular, CO2-rich streams with low amounts of nitrogen, oxygen and argon are representative of the flows that are treated...

As carbon dioxide anthropogenic generation and climate change appear to be correlated, carbon capture becomes necessary, in particular if applied to coal-fired power plants. The Chilled Ammonia Process (CAP) is a promising technology to be proved for the purpose. This work investigates the integration of Ultra Super Critical (USC) power plants with...

As carbon dioxide anthropogenic generation and climate change appear to be correlated, carbon capture becomes advisable, in particular if applied to coal-fired power plants. The Chilled Ammonia Process (CAP) is a promising technology to be proved for the purpose. Continuing an ongoing study, this work examines the integration of Ultra Super Critica...

Surface oil and gas treatment facilities in service for decades are likely to be oversized due to the natural depletion of their reservoirs. Despite these plants might have been designed modularly, meaning they comprise multiple identical units serving the same task, such units operate often in conditions far from the design point and inefficiently...

Post-combustion carbon capture in existing power plants is a strategic technology that can reduce emissions from power generation. The proven approach is scrubbing with amines. However, its drawbacks are energy requirement, 3 to 5 MJ per kg of captured CO2, as well as solution corrosion and solvent degradation. An alternative approach is scrubbing...

This paper presents a comprehensive analysis of three near-term plant configurations for CO2 capture from natural gas-fired power plants based on combined cycle: (i) amine post- combustion separation, (ii) syngas decarbonization, (iii) oxy-combustion. We address them as 'near-term' because they do not involve the development of components requiring...

An innovative, efficient and large hydrogen liquefier is described. Innovations lie in the fact that (i) the feed, 10 kg s−1, 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 sto...

We analyze the accuracy of three upwind discretization schemes (first order SPU, second order TVD and third or-der ENO) for the numerical simulation of one-dimensional three-phase multicomponent displacements. The solutions are stepped through time using Runge-Kutta methods with the same accuracy as the spatial discretization. The schemes are teste...

Thesis (M.S.)--University of Illinois at Chicago, 2001. Vita. Includes bibliographical references (leaves 281-284). Typescript (photocopy).