Papers by Keyword: Molten Salt

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Authors: Ming Li, Qing Qing Liu, Xiao Li Xi, Zuo Ren Nie
Abstract: In this study, a new green approach has been developed for the recovery of tungsten by using tungsten carbide (WC) scrap material as consumable anode in LiCl-KCl molten salts at 773 K to produce metallic tungsten. The feasibility of the direct electrochemical dissolution of WC anode into metallic tungsten was evaluated based on the experimental verifications and electrochemical methods. The effects of the main technical parameters, including the cell voltage, electrolysis time and electrolysis temperature, on the dissolved condition of anode were studied and the optimal anode parameters were obtained. It was found that a large electrolytic voltage, high electrolytic temperature and long electrolysis time would be favorable for the dissolved state of the tungsten carbide anode under the same conditions. The cathode product was analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the tungsten particles with a diameter of 100 nm could be prepared by this process in a molten salt bath. Linear sweep voltammetry was applied to investigate the dissolution of WC anode, and showed that the WC scrap material could be used as consumable anode to produce tungsten powder. Other electrochemical techniques including cyclic voltammetry , square-wave voltammetry and chronopotentiometry were employed to explore the electrochemical properties of tungsten ion derived from WC anode in LiCl-KCl melts. These results confirmed that electroreduction of tungsten ion in the melts proceeded in one step with four exchanged electrons.
Authors: Salomon Johannes Oosthuizen, Jaco Johannes Swanepoel, Dawid Steyn van Vuuren
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.
Authors: Emmanuel Rocca, Lionel Aranda, Michel Molière
Abstract: When ash-forming oils or contaminated distillate oils are used as fuels in land-based, marine or aero gas turbines, the hot gas path components, mainly the partition vanes and the blades of the expansion turbine are subjected to the deposition of slags that are corrosive at high temperature due to their low liquidus temperature. This hot corrosion process - if not properly inhibited - entails a dramatic life reduction of the hot gas path parts. MgO is a traditional, efficient inhibitor. Recently, it has been found that NiO also suppresses the corrosiveness of the (Na,S,V) melts by trapping vanadium in a refractory vanadate (Ni3V2O8); this compound is friable and does not tend to accumulate on turbine blades. The use of inhibitors entails losses in both machine performance and availability. Moreover, other metals can interfere with the inhibition process. In particular, zinc and iron are often inadvertently introduced in gas turbines fuels during their transportation or storage and they can significantly interact with nickel. This paper distinguishes the interactions between NiO on one hand and both ZnO and Fe2O3 on the other hand in the general complex chemistry of ash. The thermochemical study of (Na,S,V) melts in presence of Ni confirms that nickel is a good "trapper" of vanadium oxide at high temperature. However, they also show that nickel can react with iron to form the very stable ferrite NiFe2O4 and a low melting point vanadate phase. On the contrary, the presence of zinc affects to a lesser extent the reactivity of NiO versus V2O5 despite the formation of Ni1-xZnxO solid solutions.
Authors: Yeon Ki Hong, Byung Heung Park
Abstract: A pyroprocessing technology has been developed to process spent nuclear fuels with decreased waste and increased proliferation resistance. A main process of the pyroprocessing is an electrorefining which requires a post-treatment for recovered uranium. A distillation approach is adopted to remove an electrolyte salt residue on the uranium. In this work, the vapor composition of the distillation process and the total pressure were estimated to obtain basic data for process design and integration. Six chlorides including KCl, LiCl, UCl3, PuCl3, CeCl3, and YCl3 were considered to understand the behavior of the representative components of actinides and lanthanides. It was found that small amount of the actinides and lanthanides would be accompanied by the electrolyte salts (KCl and LiCl) during the distillation under high vacuum.
Authors: Nidal H. Abu-Hamdeh, Khaled A. Alnefaie
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%.
Authors: Deng Xiang Ji, Li Cui, Cheng Jie Huang, Ming Hui Gao, Feng Wen Yu, Ning Ai, Jian Bing Ji
Abstract: The objective of this study was to provide background date on rice straw pyrolysis in molten KCl(40mol%)-LiCl(60mol%). The effects of pyrolysis temperatures and sweep gas flow rates on the pyrolysis products yields and their chemical compositions were studied. The temperatures of pyrolysis and sweep gas flow rates were varied in the range of 380°C -540°C and 60L/h-260L/h, respectively. The compositions of gaseous products were analyzed by gas chromatography, and that of bio-oil obtained was investigated using gas chromatography-mass spectroscopic(GC-MS) technique. The yield of gaseous products increases with the increasing temperature, the char yield has demonstrated a downtrend, and the maximum yield of bio-oil is up to 15.43 wt.% at 460°C. The yield of char decreases with the sweep flow rate, the gaseous has a minimum yield at 100L/h, and the maximum yield of bio-oil is 15.43wt.% at 100L/h .The main gaseous products are CO, CO2 , H2 and CH4. Ketones and phenols are the main compounds in the bio-oil, the presence of molten inhabites their formation, and promotes the production of furfural. The bio-oil attained from pyrolysis is a potential source of renewable fuel and chemical feedstock.
Authors: Muhamad Izhar Sahri, Norinsan Kamil Othman, Abdul Razak Daud, Azman Jalar
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.
Authors: N. Arivazhagan, S Narayanan, Singh Surendra, Prakash Satya, G. M. Reddy
Abstract: In the present work hot corrosion studies were carried out on electron beam welded AISI 304 and AISI 4140 dissimilar weldment in molten salt (K2SO4-60% NaCl) environment at 800 °C for 50 cycles. The weight gain follows parabolic law in all the cases. It is observed that the scale formation was maximum on 4140 side as compared on 304 side. Moreover higher content of Fe2O3 and Cr2O3 on scale over weld zone may be due to enrichment of this zone with Fe and Cr. This could be attributed to diffusion of chromium towards AISI 4140 from the AISI 304 and diffusion of iron from AISI 4140 side towards AISI 304. Furthermore weld interface suffered accelerated corrosion behavior in the chloride and sulfate mixed molten salt environment in the form of intense spalling and sputtering of its scale. The cracking of oxide scale on the weldment might be attributed to different composition of base metals, weld metal and oxide formed.
Authors: J.-P. Millet, S. Chechirlian, X.Z. Chen, H. Mazille
Authors: Toshihide Takenaka, Masahiro Kawakami, Naoyuki Suda
Abstract: The ionic valence of Ti changed with electrorefining process of Ti in a bath equi-molar mixture of NaCl-KCl containing TiCln (n=2 or 3); The average valence was about 2.3 initially, and became about 2.1 after electrolysis. The cathodic current efficiency was getting better with electrolysis. It should be necessary to maintain the average ionic valence lower for efficient electrolysis in the molten salt. The dominant Ti ion and its electrode reaction changed with the addition of NaF-KF in the molten salt; The average valence shifted from about 2 to about 3, and the total amount of Ti in the bath decreased. The result indicates the disproportionation reaction: 3Ti2+ = Ti + 2Ti3+ is induced by the fluoride addition. The quantity of electricity for Ti deposition changed consequently, and the purity of the Ti deposit was also affected.
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