Papers by Keyword: Molten Salt

Abstract: In this paper it is aimed to present the detailed design procedure of the first solar power system in Jeddah. A prototype of solar power tower system was built at King Abdulaziz University in Jeddah, Saudi Arabia where direct irradiation is very high. Heliostats were used to track the incident sun rays and focus the energy flow towards a solar receiver. The system consists of 10 heliostats directing incident solar rays to a tower of height about 7 meters. Two motors were used to control the heliostat rotational and elevation movements. A solar receiver made of alloy steel is installed at the top of the tower to collect solar energy reflected from the heliostats. A molten salt fluid consists of sodium and potassium nitrates (60/40) re-circulated in the receiver transfers the collected heat in the receiver to a storage tank. A cylindrical vessel with height of 1 m and diameter of 1.5 m was adopted for each of the cold and hot tanks. The design thermal power was 13 kW. The percentage error in the thermal power obtained is about 5.3%.

Abstract: Double perovskites, pyrochlores are having matching thermal expansion co-efficient with bond coat and may act as candidate materials for an intermediate layer between bond coat and top coat in Thermal Barrier Coatings. Hot corrosion stability of double perovskites and pyrochlores is also important for enhanced thermal cycle life. Based on these issues, systematic studies were conducted to find the hot corrosion stability of double perovskites and pyrochlores. The results revealed that, double perovskites and pyrochlores were undergone destabilization in the Na₂SO₄+50 wt.% V₂O₅ and Na₂SO₄+10 wt.% NaCl environments at 900 oC. The implications of these findings addresses the key issues related hot corrosion mechanisms and give a pathway to developing newer materials. This study clearly indicates the destabilization of both double perovskites and pyrochlores in vanadium and chloride environments at 900 oC.

Abstract: Single-crystalline BaTi₂O₅ nanowires were synthesized by a simple molten salt method, using BaC₂O₄•H₂O and TiO₂ powders as precursors. Electrical characterization was conducted with the as-synthesized BaTi₂O₅ nanowires. The current-time data of the nanowires obeyed the Curie-von Schweidler law. Steady-state I-V curve was obtained at room temperature from current-time data and it revealed that the leakage current of BaTi₂O₅ nanowires obeyed the ohmic law under low voltage, and obeyed the space-charge limited current (SCLC) law under higher voltage. The conductivity value of the BaTi₂O₅ nanowires is 2*10^-6 S/cm.

Abstract: The behavior of Fe-12Cr-2Mo stainless steel exposed isothermally in tube furnace at 700°C for 10 h had been studied in different environments; of mixed environment (Ar-20%O₂ with coated Na₂SO₄-50%NaCl salts), molten salt (Na₂SO₄-50%NaCl) and dry oxygen (Ar-20%O₂) atmospheres. The exposed samples were characterized by using optical microscopy (OM), scanning electron microscope (SEM), energy dispersive X-ray (EDX) and X-ray diffraction (XRD). The results indicated that, sample exposed in mixed environments undergoes highest corrosion rate compared with other samples. The main phase exists in all samples generally were iron-rich oxides which non-protective and thick. Conversely, EDX analysis on cross-sectional samples revealed the Cr-enrichment developed underneath the iron-rich oxide scales as the chromium concentration increases towards near the substrate. In presence of salt mixture, the oxide scales undergo spallation, however there is no crack observed. The catastrophic corrosion sample was occurred in combined environment due to the oxidation induced by the chloridation and sulfidation phenomena as well.

Abstract: The turbulent convective heat transfer in a transversely grooved tube of molten salt with natural convection effect has been numerically investigated. In general, the average Nusselt number with and without considering natural convection in transversely grooved tube was almost equal. According to the simulated results, the heat transfer coefficient of transversely grooved tube in upside region was lower than that of downside region. The effect of natural convection on unilateral heat transfer in transversely grooved tube was more obvious with lower Reynolds number and higher inlet temperature, and the effect of natural convection on unilateral heat transfer was lower with bigger groove deep.

Abstract: The CSIR-Ti process produces titanium metal powder through continuous stepwise metallothermic reduction of titanium tetrachloride (TiCl₄) in molten salt medium, and represents a cost-effective alternative to the standard Kroll process to produce titanium metal. Subsequent to proving the CSIR-Ti process at bench scale producing batches of ±2 kg titanium powder, the design, build and test of a continuous 2 kg/h Ti pilot plant was authorised. The scale-up process highlighted limited expertise in South Africa with regards to handling molten salt and molten reducing metals. Such gaps in knowledge are addressed in this study, which discusses a number of the engineering challenges faced and solutions developed around agitation of molten salt reactors, process pipe heating and insulation, molten salt flow measurement and also feeding of a highly reactive molten reducing metal. Scaling up the CSIR-Ti process, with requirements of continuous operation, compact size, effective agitation, pumping and maintaining salt in the molten state brought an unusual set of challenges requiring development of unique and prototype equipment. Further challenges were encountered in the handling and continuous feeding of molten reducing metal at the relatively small scale of the pilot plant. Solutions developed and discussed in this study include custom-modified agitators, custom-developed flow meters for measuring molten salt and molten metal flows, and a custom-designed molten metal feed system. Specialised materials such as, ultra-high temperature heating tape and ultra-low thermal conductivity insulation had to be imported as well as a special high-temperature pump that can pump a slurry consisting of molten salt containing a high weight percentage of suspended metal powder. The experience illustrates the technological difficulty of bridging the chasm between science and technology in that many unforeseen problems are encountered when developing and scaling up a new technology.

Abstract: One of the advantages of bubble columns is high heat transfer rates. High heat transfer is important in reactors when high thermal duties are required. An appropriate measurement of heat transfer coefficient is of primary importance for designing reactors that are highly exothermic or endothermic. This paper presents the design and operation of experimental setup used for measurement of the heat transfer coefficient in molten salt media. The experimental setup was operated with tap water, heat transfer oil 32, LiCl–KCl eutectic and argon gas. Tap water was operated at the temperature of 40^oC and heat transfer oil was operated at the temperature of 75^oC, 103^oC and 170^oC. There were some challenges when operating the bubble column with molten salt due to leakages on the welds and aggressive corrosion on the column. All the experiments were run at superficial gas velocities of 0.01–0.05 m/s. Three heating tapes, each connected to a corresponding variable AC voltage controller, were used to heat the column media. Heat transfer coefficients were measured by inducing a known heat flux through the column wall and measurement of the temperature difference between the wall and the contents. In order to balance the system, heat was removed by the cooling water flowing through a copper tube on the inside of the column. Temperature differences between the column wall and the liquid were measured at five axial locations. It was found that the heat transfer coefficient increases with superficial gas velocity. The values of heat transfer coefficient for argon–water system were higher than those of argon–heat transfer oil system. Heat transfer coefficient was also found to increase with an increase in temperature.

Abstract:

In the Kroll and Hunter processes to produce titanium from TiCl₄, magnesium and sodium are used respectively as reducing agents. These processes are slow and very energy intensive and consequently much work was done over the years to improve the economics of producing these metals. In this regard, more success has been achieved with improving the economics of magnesium electrowinning than with alkali metal electrowinning. Magnesium electrowinning cells generally have electrodes with a planar shape and alkali metal electrolysis cells have electrodes with a cylindrical shape. Furthermore, recent advances in magnesium electrolysis allowed the introduction of bipolar electrodes, whereas such electrodes have not been introduced in alkali metal electrowinning cells. It is conceptually possible to replicate the advances in the construction of magnesium electrowinning cells to improve sodium or other alkali metal electrowinning cells. However, there are underlying fundamental reasons why it would be difficult to do so.In this paper the technologies for magnesium and alkali metal electrowinning cells are briefly reviewed. The reasons why it would be difficult to copy the improvements made in magnesium electrowinning technology to alkali metal electrowinning technology are then explained in terms of the implications of the underlying chemical and physical properties of the chemicals involved in the processes.

Abstract: This article is about designing and building a small scale prototype tower system to gather solar energy and store it in a molten salt tank. The system consists of several heliostats directing incident solar rays to a receiver at the top of a tower. It is intended to establish highly reputable research and development facility in solar thermal energy systems. A thorough investigation in the field of building and utilizing solar tower system was conducted. The authors studied and presented the current state of art of the technological developments concerning the solar tower systems and an assessment of their advantages and disadvantages. The adaptability of CSP (Concentrating Solar Power) power systems to Saudi Arabia climate was closely investigated. A scheme for a pilot solar power plant that it most suited to the conditions of Saudi Arabia was proposed. The next stage will be building, fabrication, and constructing the various subsystems; heliostats, tower, receiver, and storage tank.

Abstract: The reaction mechanism of electrochemical extraction of Fe_xTi alloys direct from natural ilmenite in molten CaCl₂ has been investigated. The electrochemical deoxidation experiment process was carried out at 1000 °C and 3.8 V, and a solid oxide oxygen-ion-conducting membrane (SOM) filled with carbon-saturated liquid metal was served as the inert anode of the electrolytic cell. The macro-/micro-structure variations of the samples during electrolysis were investigated. The reaction routes from natural ilmenite to Fe_xTi alloys are proposed and discussed. It is found that element Fe is reduced firstly from ilmenite and thus serves as electronic conductor to accelerate subsequent deoxidation, Fe_xTi alloys can be produced directly from natural ilmenite by electrolysis in molten salt. It is suggested that Fe_xTi phase can be formed directly from Fe_xTiO_y compounds and/or from deoxidation-generated Ti and Fe through various reaction routes.