CC BY
15ADVANCED COMBUSTION SYNTHESIS FOR HIGH PERFORMANCE MATERIALS AND POWER SYSTEMS DEVELOPMENTS
O. Odawara
PROSAP Inc., Tokyo, 153-0064 Japan Professor Emeritus, Tokyo Institute of Technology e-mail: odawara@justsap-me.org
DOI: 10.24411/9999-0014A-2019-10111
Combustion synthesis has been successfully applied to geothermal energy developments [1] and in-situ resource utilization in space exploration [2] by establishing the optimum process control parameters under centrifugal force, low gravity, and high vacuum conditions. The potentials of the combustion synthesis technologies even in other extreme environments such as underwater and disaster-stricken areas are improved more flexibly and efficiently by combining the process characteristics with effective external additions and steep gradient in temperature and pressure formed during spontaneous propagation of exothermic reaction. In view of recent technological developments on energy storage, transport, and conversion, the combustion synthesis technologies to provide high performance materials and rapid high-temperature environments are widely expanded in practical approaches with much precise controllability.
The R&Ds on effective utilizations of resources, functional materials development and exergy loss minimization have advanced the combustion synthesis technologies as highly operable ones and made great progress toward the fields such as "AI-H2O" reactions, "catalytic recuperative coupling" reactions and "heat-to-electricity" conversions.
AKH2O reactions: Researches on Al-H2O reaction have been much attractive in the field of not only propellants and explosives but also H2 extraction/storage and ultra-low density transparent materials of AlOOH-based aerogels. With increasing the particle sizes of Al powders and lowering the reaction temperatures, the products synthesized by exothermic reactions of Al and H2O are in the order of AhOs (2Al + 3H2O = AhOs + 3H2), AlOOH (2Al + 4H2O = 2AlOOH + 3H2), and Al(OH> (2Al + 6H2O = 2Al(OH)s + 3H). Catalytic recuperative coupling reactions: The exothermic reaction of CO2 and H2 generates CH4 and H2O over efficient catalysts, which is called a "Sabatier reaction". Further utilizations of the CH4 are not only in the exothermic reaction of CH4-O2 but also for endothermic treatments of steam reforming, thermal pyrolysis and dry reforming. The recycle with self-supply of such as H2, H2O and syngas from CO2 can be systemized in the closed-loop of the catalytic recuperative coupling reactions formed by inducing these exothermic and endothermic processes adjacently.
Heat-to-electricity conversions: Concept of heat-to-electricity conversion has been proposed and developed in various fields aided with "waste-heat" of thermo-photovoltaic energy conversion, acoustic-to-electric power conversion, thermo-electric tube, etc. The combustion synthesis technologies can provide a high-temperature environment with simple processes, with which the system related with energy conversion of heat-to-electricity would be effectively combined.
In recent years, the developments of supercritical CO2 (s-CO2) cycle have been actively investigated for efficient power generation improvements. As the s-CO2 undergoes large changes in density with small changes in pressure or temperature, to use s-CO2 as the working fluid can reveal high efficiency for powering turbines and less work to convert heat to electricity regardless of the source of heat. The density of s-CO2 is about half of H2O, so the compressing
XV International Symposium on Self-Propagating High-Temperature Synthesis
is easier than steam. The energy saving feature of s-CO2 greatly contributes to the turbine's overall efficiency. With the s-CO2 as the working fluid, the generating plant can function with a smaller compressor and turbine, and the high fluid density of the s-CO2 can attain the compact and highly efficient system with simple single-casing body. The closed-loop geothermal power cycle with the s-CO2 has been also proposed to produce a few MWe with some existing nonproductive geothermal wells. If such a closed-loop system for single-well is established, it is possible to eliminate thermal fatigue and corrosion associated in the case of steam system.
The present work mainly focuses on a closed-loop s-CO2 geothermal power generation formed at the single-well with the downward and upward flowing lines set concentrically. As a principle, the system starts by injecting CO2 at supercritical conditions into an insulated pipe that is placed inside the well. The fluid then flows down until it reaches the heat exchanging part at the geothermal reservoir for absorbing the heat from the environment. Due to the fact that the higher the fluid temperature, the smaller the density, the temperature, and pressure of fluid are different at flowing lines downward and upward. The main principal of the system concerned with this power generation is the large variation of density with relatively small variations in pressure and temperature of the s-CO2, which results in a "thermo-siphoning effect" to the heat transport process of CO2. The flow of CO2 as a working fluid is ideally maintained in a supercritical state throughout the cycle. With decreasing the density of the s-CO2 with increasing the temperature where buoyancy forces come into play, the dense s-CO2 at high temperature pushes out the less dense hot s-CO2 to the surface. The pressure and temperature differences between the hot and cold sides of the cycle can then be exploited to generate electricity.
In the present work, the upward s-CO2 flow is amplified with the reduction of the density of upward s-CO2 flow with setting of the heat reservoir around the surface area of the concentric single-well as shown in Fig. 1. For keeping the temperature high around the surface area formedaround the heat reservoir, the combustion synthesis technologies are applied with the combinations of such as the AI-H2O reactions and catalytic recuperative coupling processes. The noticed approach of the present work is also in the utilization of dry ice as injection source. The downstream flow of dry ice is carried out undisturbed by the side wall of the pipe as the "Leidenfrost" effect which makes dry ice surface separate from the hot pipe wall. To inject CO2 source as dry ice to the geothermal well can make the maximum S-CO2 temperature difference with keeping S-CO2 in the high temperature and high pressure around the geothermal reservoir. Since the density of S-CO2 changes more drastically when increasing the temperature from its critical temperature than the case of the pressure changes from the critical pressure, the Fig. 1 Schematic of a closed-loop s-present approaches would play an important role in its CO2 geothermal energy system, thermosiphoning effect. The R&Ds of the combustion (1) turbine; (2) generator; synthesis technologies proceeded in consideration of the (3) compressor pump; effects involved in the phase change of C02 from dry (4) injection control; (5) heat storage.
ice to S-CO2, Leidenfrost levitation and catalytic combustion of recuperative coupling would be applicable in extreme environments utilizations toward improvements of sustainable human activities.
ROCK LAYERS O
GEOTHERMAL RESERVOIRE
308
O. Odawara
1. O. Odawara, T. Fujita, A.V. Gubarevich, H. Wada, Thermite-related technologies for developments in extreme geothermal environments, Int. J. Self-Propag. High-Temp. Synth., 2018, vol. 27, no. 4, pp. 228-235.
2. O. Odawara, Combustion synthesis technology for a sustainable settlement overnight, Eurasian Chem. Tech. J., 2018, vol. 20, no. 1, pp. 3-16.
