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Acoustic pyrometry is an interesting technique that may find several useful applications in turbomachinery. As the speed of sound is directly related a medium temperature, this measurement technique estimates the temperature of a gas by considering the time of flight of an acoustic wave moving through it. If only an acoustic emitter-receiver couple is used, only the average temperature along the acoustic path can be determined. If multiple emitter-receiver couples laying on the same plane are used, a reconstruction of the temperature map in the section is possible. This estimation is performed by considering that multiple acoustic paths travel across the same sub-portions of the section and, therefore, the temperature of each sub-portion affects the time of flight along several sound paths. Many parameters affect the accuracy of the measurement, and they are related to the physic of the phenomena involved in the measurement, the accuracy of the instrumentation used, the interaction between the acoustic wave and the flow velocity and the hardware set-up. In this study, the impact of some set-up parameters on the accuracy of the measurement was investigated and, in particular, the number of sound emitter-receiver couples and the number of investigation sub-portions in which the section is divided. A reference temperature map has been considered as a benchmark. This study, which is a preliminary investigation on this technique, was useful to assess the capability of this methodology to correctly describe a temperature distribution in an ideal condition. Therefore, it represents a first step in the set-up of an experimental investigation with an acoustic pyrometer..

A pervasive Renewable Energy Source (RES) exploitation poses a wide range of issues to electric grids, which the enhancement of the electric grid flexibility may mitigate. There are several approaches to improve grid flexibility, and a significant help will come from efficient, reliable, durable and cheap electric storage technologies. Inevitably, different storage technologies will be needed since different power and energy spectra characterise RES issues. In the category of high capacity-to-power ratio technologies, Pumped Thermal Electricity Storage (PTES) is becoming more and more popular. Such technology aims at replacing Pumped Hydro Energy Storage (PHES), and it is suited for daily cyclic operation (load shifting). In this paper, a Brayton PTES with liquid sensible heat storages is studied. Compared to the standard system equipped with packed beds, the liquid heat storage allows for a more straightforward state of charge estimation, control and, potentially, for a better usage of storage volume. Through a parametric analysis involving the main design specifications, the system performance is assessed under realistic assumptions. The resulting figures provide an exhaustive characterisation of the performance achievable by the system, which may be useful for a fair comparison between PTES and other competing storage technologies.

Small Mediterranean islands are typically served by mini-grids based on inefficient, polluting and costly diesel generators that provide electricity and freshwater through desalination plants. The study focuses on the case study of the Italian island of Ustica, for which the actual consumption and generation load profiles for 2018 have been used to simulate different scenarios through HOMER Pro software. The scenarios tested the possible integration of renewable energy sources (photovoltaic, small wind turbines) and electrochemical storage in the system, based on a techno-economic, financial, and environmental analysis. In addition to generation-side interventions, demand-side management strategies have been evaluated by considering the desalter as a deferrable load and by introducing energy efficiency measures. Finally, a sensitivity analysis on the most influential parameters (diesel price, discount rate) has been conducted on the base case scenario. The proposed technical solutions are compatible with the environmental and regulatory constraints of the island and lead to reduced emissions and long-term savings. The savings would enable a reduction in the cross-subsidy that the mainland electricity users pay to cover the higher costs incurred for diesel generation in non-interconnected small islands.

To reduce the pollutant emissions in the naval sector, the use of alternative fuels and new power generator systems are both promising solutions. In this study, the feasibility of replacing a pleasure boat Auxiliary Power Unit (APU) with a hybrid solution is studied from the economic and technical points of view. Several power generation technologies and layouts are considered. Many configurations were investigated, from hybrid battery/diesel generator to innovative layouts including fuel cell with onboard Liquified Natural Gas (LNG) reforming for hydrogen production. Since hybrid APUs may yield significant advantages in terms of both environmental and noise pollution, the opportunity of operating the system for several hours without powering up the traditional generators is also considered. For each configuration, CO2 and NOx emissions, purchasing and operating costs, as well as weight and volume, are estimated. Emissions may be reduced up to 20 % and 60 % for CO2 and NOx, respectively, and fuel cost reductions up to 35 % may be achieved.

Radical changes in production paradigms are affecting electric systems. This is due to Renewable Energy Sources (RES) introduction, which changed production from being centralized and dispatchable, to be more decentralized and unpredictable. Further transformations are expected as the RES share into electric grids will increase. RES further development will likely rely mostly on additional solar PV capacity, then relevant energy quantities will be needed to be shifted from day hours to evening and night hours. Such “Load Shifting” could be performed with Electric Energy Storage (EES) technologies. Few technologies suited for this are already commercially available, whereas others have been proposed. In this paper, the EES technologies suited for load shifting are reviewed with a focus on economic costs. After that, current and future EES economic feasibility are assessed by using Italian hourly energy prices from 2018. Since EES resulted to be currently uneconomic, the minimum price modification required to make EES feasible is calculated.

The pulp and paper industry is under increasing pressure to reduce its energy consumption and carbon footprint. This study examines the feasibility of integrating high-temperature heat pumps (HTHP) into tissue paper production to enhance energy efficiency and decarbonization. Focusing on the energy-intensive drying process, the study uses data from a typical tissue paper mill to simulate and optimize an HTHP system producing four tons per hour of nine-bar saturated steam. It also addresses necessary modifications for HTHP integration applicable across the sector. Various refrigerants were analyzed, achieving a maximum coefficient of performance (COP) of 2.01. Results showed that HTHP can reduce energy consumption and emissions by up to 17% and 40%, respectively, based on the European electricity mix. Although steam production costs increase by 55% compared to fossil fuel-based systems, HTHP is more cost-effective than direct electric resistance heating, which raises costs by 196%. With a CO2 price of EUR 100/t, HTHP offers a 12% cost reduction. However, without public funding, capital expenditures may be unsustainable in many regions, though viable in countries with favorable gas and electricity price differentials. The paper underscores the need for advancements in HTHP technology and cost reductions, emphasizing industry adaptation for seamless HTHP integration. [ABSTRACT FROM AUTHOR]

The waste heat recovery from the gas turbine (GT) exhaust is typical for increasing performance and reducing CO2 emissions in industrial facilities. Nowadays, numerous already operating gas turbine plants could be retrofitted and upgraded with a bottoming cycle powered by the exhaust gasses. In this case, the standard solution would be to use a water steam Rankine cycle. However, even if this technology usually yields the best efficiency, other alternatives are often preferred on the lower size scale. Organic Rankine cycles (ORCs) are the commercial alternatives to steam Rankine cycles, but many other alternative cycles exist or can be developed, with potential benefits from safety, technical or economic points of view. This study compares several alternative technologies suited to recover gas turbine waste heat, and a detailed cost analysis for each is presented. On this basis, a guideline is proposed for the technology choice considering a wide range of application sizes and temperature levels typical for waste heat recovery from gas turbines. The compared technologies are ORCs, Rankine cycles (RCs) with water and ammonia mixtures at constant composition, supercritical CO2 cycles (sCO2), sCO2 cycles with mixtures of CO2 and other gasses. As it resulted, ORCs can achieve the lowest levelized cost of energy (32 $/MWh-46 $/MWh) if flammable fluids can be employed. Otherwise, Rankine cycles with a constant composition mixture of water and ammonia are a promising alternative, reaching a levelized cost of energy (LCOE) of 36-58 $/MWh. [ABSTRACT FROM AUTHOR]

The growth of renewable energy source requires reliable, durable, and cheap storage technologies. In this field, the pumped thermal energy storage (PTES) is drawing some interest as it appears not to be affected by geographical limitations and use very cheap materials. PTES is less efficient than pumped hydro and batteries, but it could achieve satisfactory efficiencies, show better economic performance, and be characterized by negligible environmental impacts. A PTES stores the electric energy as thermal exergy in solid packed beds, by operating two closed Brayton cycles, one for charging and the other one for discharging. Although PTES thermodynamical behavior is well understood, the interaction between the components is rarely investigated. This study investigates the impact of packed-bed behavior on turbomachines operating conditions. In this way, PTES off-design and part-load performance are estimated. A control strategy especially suited for closed Brayton cycles, i.e., the inventory control (IC), is used to control the system. As it resulted, PTES is characterized by an excellent part-load performance, which might be a significant advantage over the competing technologies. However, the off-design operation induced by the packed-bed thermal behavior might significantly reduce the system performance and, in particular, that of the discharge phase. [ABSTRACT FROM AUTHOR]