G. Spazzafumo

Hydrogen energy storage: Hydrogen and oxygen storage subsystems

Abstract Hydrogen seems to possess all the characteristics to store the excess of electrical energy produced during off-peak periods. Hydrogen energy storage plants could be environmentally non-polluting, easy to place, not sensible to load variation, unbounded in size, efficient and safe. These last two features seem to contradict one another. An option that could give a reliable solution is the storage of hydrogen in metal hydride and the storage of oxygen as a liquid. Such a choice is probably the safest one to make and allows the achievement of efficiencies comparable to those obtainable with gaseous storage of both electrolytic products. The power consumption for H2 and O2 storage is only 3% of the total energy stored and the charging ratio approaches the values obtained with hydro-pumped storage plants.

Steam power-plants fed by high pressure electrolytic hydrogen

The possibility to obtain hydrogen and oxygen at high pressure directly from electrolysis was recently demonstrated at a laboratory scale. At the same time the working pressure of direct steam generator prototypes is increasing. The scaling-up of these devices will make very interesting the production of nuclear or renewable hydrogen (and oxygen) and its use in advanced steam power-plants fed with stoichiometric hydrogen/oxygen mixtures. This is a long-term view, but it is possible to find an interesting application even in the near term. It is the nightly and seasonal storage of energy by means of hydrogen and its use in attached steam power-plants. In this case the thermal energy required at low temperature can be supplied by regeneration and coal, while the combustion of hydrogen and oxygen is employed only in the steam super-heating phases. It results in high steam temperatures, increased specific work and improved thermodynamic efficiency. Moreover the availability of the reactants directly at high pressure, allows to save energy usually needed for storage and to avoid the installation of large compression units.

A steam cycle with an isothermal expansion: the effect of flowvariation

Abstract In the present paper the steam cycle proposed by Spazzafumo has been again taken into consideration and the effectof the flow variation on the cycle performances has been investigated. The isothermal expansion with increasingflow causes a decrease in cycle efficiency due to the greater condenser losses and, at high superheated temperatures,to the impossibility of full recovering of the available heat at the end of the expansion. However, using part of thisheat for preheating the required hydrogen and oxygen, yields a significant increase in efficiency.

A thermodynamic cycle with a quasi-isothermal expansion

Abstract The combustion of hydrogen and oxygen makes feasible a steam re-heating by mixing rather than by surface exchange. In such a way the use of several re-heaters is possible as well as the increase of re-heating temperature. The performances of steam power-plants with a large number of super-heaters (5–15) have been analyzed. Some theoretical considerations are also given in order to explain expectations, results and perspectives. Using so many super-heaters makes the expansion gradually approach isothermal conditions. A significant reduction of the efficiency gap with respect to the Carnot cycle was therefore expected. A thermal efficiency of 49.2% is achievable. Although this is far from the 61.6% of the Carnot cycle, the study points out some interesting aspects and suggests the basis for further development.

MHD plants: A comparison between two-level and three-level systems

The present paper aims to analyse a way to improve the performance of magnetohydrodynamic systems by introducing a third level in a classic MHD/steam plant. The task of this further level is to reduce the energy loss between the MHD outlet (T > 2000 K) and the steam turbine inlet. Two layouts have been considered: the first one with an air open cycle and the second one with an air closed cycle. This last layout shows the best current efficiency, close to 60%, having an improvement of about 10% with respect to the two-level system.

Parametric analysis of a steam cycle with a quasi-isothermal expansion

Using a hydrogen/oxygen steam generator it is possible to carry out many steam mixing re-heatings without increasing the complexity of a traditional steam power-plant: steam is not required to re-enter the boiler for each re-heating. An isothermal expansion could thus be approached by means of several adiabatic expansions and several steam mixing re-heatings. A theoretical investigation showed that an isothermal expansion could achieve high efficiency (up to 70% of HHV) when the waste heat at the turbine outlet is recovered for pre-heating water, hydrogen and oxygen. In a real plant the number of re-heatings that can be carried out, although high, is limited and we can therefore expect an efficiency drop which varies as a function of the number of re-heatings, the re-heating temperature and the maximum pressure. In order to evaluate real cycle performance, a numerical code, specifically created, was implemented.

Hydrogen energy storage: Preliminary analysis

Abstract A preliminary analysis of energy storage during off-peak periods by means of electrolytic hydrogen has been carried out. Electrolytic hydrogen and oxygen are produced during off-peak hours at a low cost and are then used to generate peak power. Hydrogen and oxygen are stored in gaseous or liquid phase. The reconversion to electric power is performed by means of traditional engines or fuel cells. The components considered are either already commercial or mid-term commercial, but they are not specifically designed for hydrogen energy storage plants. Performances achievable in the near future are very high when compared with current energy storage systems.

Fuel cell systems

In this chapter, the components of hydrogen fuel cell technologies are assembled into systems serving various sectors of societies, such as the transportation sector, the building sector, or the energy needs of individual devices such as smart phones or laptop computers. Also, the role of hydrogen and fuel cells in extended electricity networks supplying power to regions or nations is discussed. The applications for the transportation sector comprise passenger cars, buses, lorries, bicycles, and off-road vehicles such as forklifts or internal transportation in, for example, industries or airports, as well as energy systems for ships, trains, and airplanes. For energy needs in buildings, heat requirements may be provided by fuel cell devices replacing current natural gas or other fossil fuel systems, with the added advantage of cogenerating heat and power for the building and possibly export of power to the general grid. For portable energy requirements, the key issue for introducing fuel cells is the storage of the fuels needed, while the advantage, say over battery-operated equipment, is longer periods of autonomy. Because compressed hydrogen may be inconvenient for such devices, alternatives such as methanol may be preferred, either in direct methanol fuel cells or with a methanol-to-hydrogen converter added.

Pre-feasibility analysis of an energy supply system for Southern Europe: Technical aspects

Abstract Technical aspects of the feasibility of energy transmission from hydroelectric power plants in Zaire to southern Europe, and to Italy in particular, have been studied. Three alternatives were considered: electric power transmission, gaseous hydrogen pipeline, and methylcyclohexane/toluene loop cycle. The technical feasibility of each alternative, also for a mid-term prospect, and energy losses were examined and evaluated. A comparison, from an energetic point of view, was also carried out among the three systems by varying the ratio between hydrogen and electric power required by the users. The high values of the energy transmission factor make this energy supply system very attractive. Depending on the sharing of the energy required for final uses, a double transportation system, based on electric power together with hydrogen, could be convenient. Indeed, if a very high amount of hydrogen is required by the users, a system based on hydrogen would be preferable.

A Steam Cycle with Direct Combustion of Hydrogen and Oxygen and an Isothermal Expansion

A new thermodynamical cycle characterised from an isothermal expansion has been examined from a theoretical point of view. In the real cycle the isothermal expansion could be approached by means of mixing re-heatings. The high temperature steam for mixing is produced in a direct steam generator burning a stoichiometric mixture of hydrogen and oxygen. The theoretical analysis has shown that the reference cycle allows an efficiency very close to the efficiency of a Carnot cycle evolving between the same extreme temperatures. The ratio between the two efficiencies can approach 90%.