An evaluation of thermal plasmas in pyrometallurgy

The development of reliable, high powered plasma generators has resulted in many plasma processes being proposed as alternatives to existing pyrometallurgical technologies. This work evaluates the advantages and disadvantages of plasma systems by reviewing plasma generators, their integration with reactors and the process economics. Many plasma systems were shown to be technically and economically superior to existing technologies, but some of the plasma system advantages quoted in the literature were found to be impractical because of other system constraints. Process applications were limited by the power inputs available from plasma generators compared to AC electric furnaces. A series of trials were conducted where chromite and steelplant baghouse dusts were smelted in the Tetronics' 2.0 MW transferred arc/open bath reactor to confirm the operating characteristics of the plasma system and its economics. Chromite smelting was technical superior to submerged arc furnace technology, but the economics were unfavourable because of the limited power available from the water-cooled plasma torch and the high electrical energy consumption. A DC graphite electrode plasma furnace using preheated and prereduced chromite concentrates will compete economically with the submerged arc furnace. Ni, Cr and Mo were economically recovered from high alloy content steelplant dusts for recycling. Five Electric Arc Furnace dusts were smelted to produce a non-toxic residue and recover the contained zinc to an enriched zinc oxide product for recycling. It should be possible to condense the zinc vapour directly in a zinc splash condenser to increase the value of the product. Because of the limited power available from plasma generators, plasma processes will be most suitable for treating high and medium value materials such as Au, Pt, Mo, Ni, Ti, V, Cr etc at small production rates, heating metals in tundishes and ladles and remelting superalloy scrap. The treatment of environmentally hazardous waste materials is a particularly interesting application because of the additional financial incentives. Non-transferred arc plasma generators will be used for air and gas preheating in blast furnaces to reduce metallurgical coke consumptions.

UV-inscription, polarization-dependant loss characteristics and applications of 45° tilted fiber gratings

We have UV-inscribed and theoretically and experimentally analyzed fiber gratings with the structure tilted at 45° and implemented this type of devices as an in-fiber polarizer. A systematic investigation has been carried out on the characterization of 45° tilted fiber gratings (45° TFGs) in terms of the polarization-dependant loss (PDL) and thermal response. The detailed theoretical modeling has revealed a linear correlation between the grating length and the PDL, which has been proved by the experimental results. For the first time, we have examined the UV beam diffraction from a tilted phase mask and designed the UV-inscription system to suit the 45° TFG fabrication. Experimentally, a 24 mm long 45° TFG UV-inscribed in standard telecom single-mode fiber exhibited around 25 dB PDL at 1530 nm and an over ~300 nm bandwidth of PDL spectrum. By the concatenation method, a 44 mm long grating showed a PDL as high as 40 dB that is close to the high polarization extinction ratio of commercial products. Moreover, we have revealed that the PDL of 45° TFGs has low thermal influence, which is desirable for real application devices. Finally, we experimentally demonstrated an all-fiber twist sensor system based on a 45° and an 81° TFG.

UV-inscription, polarization-dependant loss characteristics and applications of 45° tilted fiber gratings

We have UV-inscribed and theoretically and experimentally analyzed fiber gratings with the structure tilted at 45° and implemented this type of devices as an in-fiber polarizer. A systematic investigation has been carried out on the characterization of 45° tilted fiber gratings (45° TFGs) in terms of the polarization-dependant loss (PDL) and thermal response. The detailed theoretical modeling has revealed a linear correlation between the grating length and the PDL, which has been proved by the experimental results. For the first time, we have examined the UV beam diffraction from a tilted phase mask and designed the UV-inscription system to suit the 45° TFG fabrication. Experimentally, a 24 mm long 45° TFG UV-inscribed in standard telecom single-mode fiber exhibited around 25 dB PDL at 1530 nm and an over ~300 nm bandwidth of PDL spectrum. By the concatenation method, a 44 mm long grating showed a PDL as high as 40 dB that is close to the high polarization extinction ratio of commercial products. Moreover, we have revealed that the PDL of 45° TFGs has low thermal influence, which is desirable for real application devices. Finally, we experimentally demonstrated an all-fiber twist sensor system based on a 45° and an 81° TFG.

Desalination of brackish water by a batch reverse osmosis desalink system for use with solar thermal energy

For remote, semi-arid areas, brackish groundwater (BW) desalination powered by solar energy may serve as the most technically and economically viable means to alleviate the water stresses. For such systems, high recovery ratio is desired because of the technical and economical difficulties of concentrate management. It has been demonstrated that the current, conventional solar reverse osmosis (RO) desalination can be improved by 40–200 times by eliminating unnecessary energy losses. In this work, a batch-RO system that can be powered by a thermal Rankine cycle has been developed. By directly recycling high pressure concentrates and by using a linkage connection to provide increasing feed pressures, the batch-RO has been shown to achieve a 70% saving in energy consumption compared to a continuous single-stage RO system. Theoretical investigations on the mass transfer phenomena, including dispersion and concentration polarization, have been carried out to complement and to guide experimental efforts. The performance evaluation of the batch-RO system, named DesaLink, has been based on extensive experimental tests performed upon it. Operating DesaLink using compressed air as power supply under laboratory conditions, a freshwater production of approximately 300 litres per day was recorded with a concentration of around 350 ppm, whilst the feed water had a concentration range of 2500–4500 ppm; the corresponding linkage efficiency was around 40%. In the computational aspect, simulation models have been developed and validated for each of the subsystems of DesaLink, upon which an integrated model has been realised for the whole system. The models, both the subsystem ones and the integrated one, have been demonstrated to predict accurately the system performance under specific operational conditions. A simulation case study has been performed using the developed model. Simulation results indicate that the system can be expected to achieve a water production of 200 m3 per year by using a widely available evacuated tube solar collector having an area of only 2 m2. This freshwater production would satisfy the drinking water needs of 163 habitants in the Rajasthan region, the area for which the case study was performed.

Thermal degradation of a brominated bisphenol a derivative

The thermal degradation of 2,6,2',6'-tetrabromo-4,4-pm-isoproylidene-di phenol (tetrabromobisphenol A) (TBBPA) has been investigated and a mechanism for its thermal degradation is suggested. TBBPA is a comonomer widely used in epoxy and in unsaturated polyester resins to impart fire retardance. These resins find a common use in electric and electronic equipment. The presence of bromine atoms is the key factor in fire retardant activity, while on the other hand it represents an ecological problem when pyrolytic recycling is programmed at the end of the useful life of such items. However, pyrolysis is the more advantageous recycling system for thermosetting resins and thus efforts should be made to control the pyrolysis in order to avoid or minimize the development of toxics. Homolytic scission of the aromatic bromine and condensation of aromatic bromine with phenolic hydroxyl are the main processes occuring in the range 270-340°C. A large amount of charred residue is left as a consequence of condensation reactions. HBr and brominated phenols and bisphenols are the main volatile products formed. Brominated dibenzodioxins structures are included in the charred residue and not evolved in the volatile phases.

Broadband tunable all-fiber polarization interference filter based on 45° tilted fiber gratings

We have theoretically and experimentally designed and demonstrated an all-fiber polarization interference filter (AFPIF), which is formed by a polarization-maintaining (PM) fiber cavity structure utilizing two 45° tilted fiber gratings (45°-TFGs) inscribed by UV laser on the PM fiber. Such a filter could generate modulated transmission of linear polarization status. It has been revealed that the modulation depth of the transmission depends on the coupling angle between the 45°-TFGs and the PM fiber cavity. When the two 45°-TFGs in PM fiber are oriented at 45° to the principal axis of the PM fiber cavity, the maximum modulation depth is achievable. Due to the thermal effect on birefringence of the PM fiber, the AFPIF can be tuned over a broad wavelength range just by simple thermal tuning of the cavity. The experiment results show that the temperature tuning sensitivity is proportional to the length ratio of the PM fiber cavity under heating. For 18 and 40 cm long cavities with 6 cm part under heating, the thermal tuning sensitivities are 0.616 and 0.31 nm/° C, respectively, which are almost two orders of magnitude higher than normal fiber Bragg gratings. © 1983-2012 IEEE.

Spectral characteristics and thermal evolution of long-period gratings in photonic crystal fibers fabricated with a near-IR radiation femtosecond laser using point-by-point inscription

The spectral properties of long-period gratings (LPGs) fabricated in photonic crystal fibers using femtosecond laser pulses by the point-by-point technique, without oil-immersion of the fiber, are investigated in detail. Postfabrication spectral monitoring at room temperature showed significant long-term instability of the gratings and stable spectra only after 600 h. The stabilized spectral properties of the gratings improved with increasing annealing temperature. The observed changes in resonant wavelength, optical strength, and grating birefringence were correlated to the laser inscription energy and were further used to study the mechanism of femtosecond inscription. Furthermore, the femtosecond-laser inscribed LPGs were compared to electric-arc fabricated LPGs. Comparison of experimental results with theoretical models of LPGs and laser propagation during inscription indicate that the major processes responsible for the index change are permanent compaction and thermally induced strain, the latter can be significantly changed through annealing. © 2011 Optical Society of America.

In situ diagnostics and prognostics of solder fatigue in IGBT modules for electric vehicle drives

This paper proposes an in situ diagnostic and prognostic (D&P) technology to monitor the health condition of insulated gate bipolar transistors (IGBTs) used in EVs with a focus on the IGBTs' solder layer fatigue. IGBTs' thermal impedance and the junction temperature can be used as health indicators for through-life condition monitoring (CM) where the terminal characteristics are measured and the devices' internal temperature-sensitive parameters are employed as temperature sensors to estimate the junction temperature. An auxiliary power supply unit, which can be converted from the battery's 12-V dc supply, provides power to the in situ test circuits and CM data can be stored in the on-board data-logger for further offline analysis. The proposed method is experimentally validated on the developed test circuitry and also compared with finite-element thermoelectrical simulation. The test results from thermal cycling are also compared with acoustic microscope and thermal images. The developed circuitry is proved to be effective to detect solder fatigue while each IGBT in the converter can be examined sequentially during red-light stopping or services. The D&P circuitry can utilize existing on-board hardware and be embedded in the IGBT's gate drive unit.