Harry Valentine writes:
Over the past several years dating back to 2005, the solar thermal power industry has seen fit to undertake research into large-scale thermal energy storage involving heat-of-fusion technology. While solar thermal power stations in desert regions can generate electric power while the sun shines, these power stations go dormant after sunset. Several solar thermal power companies have developed their own unique heat-of-fusion mixtures that can store sufficient thermal energy to generate superheated steam after sunset. While intended for stationary applications, the thermal energy storage material may also have mobile applications, such as fireless steam locomotives.
While the solar thermal power industry develops heat-of-fusion thermal storage technology, researchers connected to the nuclear thermal power industry such as Isentropic Energy of the UK, are developing large-scale, high-temperature seasonal geothermal energy storage technology. While such thermal energy storage installations are intended to produce steam that drives turbines to generate electric power at power stations, the same thermal energy storage installations may also provide the recharge for a variety of mobile fireless steam applications that includes modern fireless steam locomotives. A power company may own and operate a subsidiary short-line railway or tourist excursion railway.
Historically, the first heat-of-fusion fireless steam locomotives operated on a commuter passenger railway line in Denmark in 1924 and used caustic soda
(NaOH) as the medium of thermal energy storage. It melts at 320-deg C with a heat-of-fusion of 99-BTU/lb (230KJ/Kg). Some modern solar thermal power stations use a mixture of naturally occurring sodium nitrate and potassium nitrate that melts at over 500-deg C and holds about 40-BTU/lb (93KJ/Kg). Massive quantities of both materials are readily available at very low cost. For comparatively small-scale applications such as fireless steam locomotives, other materials that store more energy are available.
New Research (Post 2005):
Researchers connected to the solar thermal power industry have in recent years undertaken extensive testing of various metallic oxides and metallic oxide mixtures that melt at between 300-deg C and 500-deg C. A mixture of 80% lithium hydroxide
(LiOH) and 20% lithium fluoride (LiF) by molar weight, melted at 465-deg C with a heat-of-fusion of near 1150KJ/Kg or 500-BTU/lb. For mobile application, a conical container or one with a larger upper inner diameter than lower inner diameter and lined with a corrosion-resistant ceramic may hold the mixture, while the container may be encased in steel or iron.
It would be important to maintain the iron or steel at under 600-deg C, the temperature when steel undergoes significant changes in its molecular structure and changes in mechanical properties. A melting temperature of 465-deg C allows the storage system to receive a thermal recharge from an existing solar thermal power plant that includes thermal energy storage. There may be additional scope to thermally recharge the storage system from high-temperature geothermal storage installations of the power industry. A power utility that operates high-temperature thermal storage technology may own a railway division or through agreement, thermally recharge fireless steam locomotives.
High Temperature Material:
The development of new generation of ceramic compounds such as silicon carbide
(SiC) and silicon nitride (Si3N4) are corrosion resistant and maintain constant mechanical properties up to 1400-deg C. It could hold molten lithium hydride
(LiH) that melts at 688-deg C and provides a heat-of-fusion of 2900KJ/Kg (1250-BTU/lb). Due to the extremely high temperature, a casing of material such as sintered alumina
(Al2O3) may encase ceramic-lined containers of molten lithium hydride. A flow of fan-driven pressurized gas such as compressed carbon dioxide flowing inside a closed circuit may transfer heat from thermal storage into a boiler.
The material that encases the ceramic containers of lithium hydride may be encased by zirconium dioxide that is a superb thermal insulator. During thermal recharge from high-temperature geothermal energy storage installation, superheated air or steam would flow through a choke valve in order to force it to release massive amounts of thermal energy. The process of thermal conduction would transfer heat from the choke valve and into the thermal energy storage material. The development of high-temperature nuclear energy in China promises to create future grid-scale application for large-scale, high-temperature geothermal energy storage installations.
While electro-chemical batteries expire after a few hundred or a few thousand deep-cycle recharges and discharges, thermal energy storage technology offers greatly extended useful service lives. Over the long-term, thermal technology saves the cost of electro-chemical battery replacements. At the power station, a small amount of thermal energy that had earlier been transferred into storage may recharge fireless steam locomotives at very competitive costs, compared to the additional cost of having to generate electricity at the power station to recharge electro-chemical batteries. There is scope for modern fireless steam locomotives to be cost competitive to other locomotive types.
New research into thermal energy storage offers future potential to re-introduce fireless steam locomotives to selects railway services that may include shunting, tourist service and possibly commuter passenger service. Research related to the solar thermal power sector offers thermal energy storage materials that are competitive in thermal energy storage, useful life expectancy and long-term cost. There may actually be future application for a thermal rechargeable locomotive that may operate on steam, with an optional variant that may energize a closed-cycle air turbine.
Harry Valentine, email@example.com
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