H2∕O2 Cycles: Thermodynamic Potentialities and Limits

Abstract

In this paper, the thermodynamic potentialities and limits of the H2∕O2 turbine cycles (afterward named only H2∕O2 cycles) are investigated. Starting from the conventional gas turbine and steam turbine technology, the paper qualitatively tackles problems related to a change of oxidizer and fuel: from these considerations, an internal combustion steam cycle is analyzed where steam, injected into the combustion chamber together with oxygen and hydrogen, is produced in a regenerative way and plays the important role of inert. A proper parametric analysis is then performed in order to evaluate the influence of the main working parameters on the overall performance of H2∕O2 cycles. All the results are carried out by neglecting the energy requirements for O2 and H2 production systems, but taking into account the work required by the O2 and H2 compression. This choice permits a great freedom in the definition of these thermodynamic cycles; moreover, it is possible to come to some general conclusions because the H2 and/or O2 production systems and their integrations with thermodynamic cycles do not have to be specified. Therefore, this paper can be framed in a context of centralized production of oxygen and hydrogen (by nuclear or renewable energy sources, for example) and their distribution as pure gases in the utilization place. By adopting some realistic assumptions, for example, a top temperature of 1350°C, the potentialities of H2∕O2 cycles are very limited: the net efficiency attains a value of about 50%. Instead, by adopting futurist assumptions, for example, a top temperature of 1700°C, a different H2∕O2 cycle scheme can be proposed and its performance becomes more interesting (the net efficiency is over 60%). The paper tackles the main thermodynamic and technological subjects of the H2∕O2 cycles: for example, it is underlined how the choice of the working parameters of these cycles strongly influences the attainable performance.