Gianluca Valenti

Europe’s global liquid hydrogen production share remains limited at 7%, while research institutions face an inadequate supply chain for laboratory-scale procurement. The Department of Energy at Politecnico di Milano addresses this gap through the procurement of Italy’s first laboratory-scale LH₂ liquefaction system, designed with 70 L/day capacity, a 200 L ATEX-classified storage tank, and a 50 L mobile transport tank for investigations into heat transfer, cryogenic valve and sensor testing, superconducting electronics, and material compatibility. The absence of Italian standards and limited European precedents necessitated a comprehensive review of relevant European safety projects and industrial guidelines. Regulatory compliance is ongoing under ATEX directives, with safety consultants defining critical parameters via leakage simulations. The project requires around three years from conception to commissioning; this paper aims to accelerate similar implementations by sharing the experience at Politecnico di Milano for future laboratory-scale facilities. Systematic coordination among engineering design, safety consultation, and regulatory authorities remains essential for viable LH₂ infrastructure implementation.

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 experimental apparatus for testing safely hydrogen volume and flow meters up to 24 m3/h (referred to standard conditions) in controlled environmental conditions, between -25 and +55 °C (and beyond). The apparatus realized can test up to four volume and flow meters in a climatic chamber while processing air or pure hydrogen or methane. Methane-hydrogen mixtures can be tested connecting simply bottles with synthetic blends. The aim is to verify the measurement accuracy of the meters under test. A dedicated data analysis protocol featuring statistical process control is developed to monitor the stability of the system during the test. It exploits statistical indicators representing the autocorrelation, the normality of residuals of the mean value and the lag plot. The apparatus is realized, and it complies with the leakage limits set by indications in literature. A new ultrasonic domestic meter is tested in the apparatus. It has been developed by Pietro Fiorentini S.p.A. in the framework of the Hy4Heat project. Its error trends measured at all temperatures comply with the limit of 3.5% between 0.12 and 2 m3/h and 2% between 2 and 20 m3/h, as imposed by legislations.

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 analysis of a highly innovative steam expander based on sliding-vane technology. The design principles of the sliding-vane expander and two experimental campaigns are presented. The first experimental campaign allows to assess the reliability of the system with steam as working fluid, the second campaign leads to assess the stability during long-run and the performance of the system. A maximum expander mechanical power of 28 kW is measured. The pressure-Volume diagram of the expansion process is also measured and presented.

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 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.