Thermodynamic comparison of two processes of hydrogen production: steam methane reforming-A solar thermochemical process

Hydrogen is mainly employed like primary product, for the synthesis of ammonia. The ammonia is synthesized by chemically combining hydrogen and nitrogen under pressure, in the presence of a catalyst. This ammonia is used, for the production of the nitrate fertilizers. Nowadays hydrogen gains more attention mainly because, it is regarded as a future significant fuel by much of experts. The widespread use of hydrogen as source of energy could help to reduce the concern concerning the safety of energy, the total change of climate and the quality of air. Hydrogen is presented then as an excellent alternate initially and as substitute thereafter. It can play a role even more significant than conventional energies. Indeed, it has the advantage of being nonpolluting and it can use the same means of transport as conventional energies. For Algeria, it proves of importance capital. It not only makes it possible to increase and diversify its energy reserves and its exports but also to provide for its energy needs which become increasingly significant. Although hydrogen can be produced starting from a large variety of resources using a range of various technologies, the natural gas is generally preferred and will remain in the near future the principal primary product for the manufacture of hydrogen. Currently the most effective means of production of hydrogen is the Steam Reforming of Natural Gas (SMR). This process is seen as a one of principal technologies for the production of hydrogen. The disadvantages of this process it's that it consumes a great quantity of primary energy and that it releases in the atmosphere the gases that contribute to the warming of the plane. Among the alternatives processes of hydrogen production one can quote solar thermochemical processes. In this study, an exergetic analysis of the process of hydrogen production based on Zn/ZnO redox reactions is presented. In the first part of this study, an exergetic analysis is made for a temperature of the receiver of 2300 K and a solar energy absorption efficiency of the receiver equal to 70%. It is also supposed that there is no formation of ZnO in quench by reverse reaction. In the second part of this study an exergetic analysis of the process while varying the solar energy absorption efficiency of the receiver and the rate of formation of ZnO in quench is made. The study of the variation of the rate of formation of ZnO in quench as well as the variation of the factor of absorption of the solar radiation made it possible to analyse, the variation of the exergy destroyed in quench and hydrolyser as well as the variation of exergetic efficiency of the process. The exergy destroyed in the receiver depends largely on the solar energy absorption efficiency of the receiver. The concentration-reception part is responsible for the greatest destroyed quantity of exergy. On the level of the solar concentration-reception in fact the losses by re-radiation are responsible for the greatest part of the destroyed exergy. Energetic and exergitic efficiencies of this solar thermochemical process are compared to those of conventional process of the hydrogen production by steam reforming of natural gas. This study made it possible to show the importance of solar thermochemical process for hydrogen production, which could be an alternative to conventional process of the hydrogen production by steam reforming of natural gas (SMR).(Author)