Use of concentrated radiation for solar powered glass melting experiments

To investigate the feasibility of using concentrated solar radiation to provide process heat for glass production, a high flux solar simulator was used to melt glass forming batches. Initial experiments involved melting various glass forming batches which demonstrated that rapid and full conversion of the crystalline raw materials into an X-ray amorphous vitreous state was possible. A pure silica batch produced an X-ray amorphous product but it was not possible to refine the melt in these exploratory tests. A powdered, ternary soda-lime-silica (SLS) glass forming batch melted vigorously, with rapid gas removal, resulting in a completely transparent glass. Industrial SLS pellets were subsequently used in semi-continuous melting experiments, whereby the batch was intermittently fed into the melting zone while the beam was kept on. Additional secondary heating and insulation around outlet of the melting zone was required to achieve a semi-continuous flow of molten glass to an output crucible

Thermal Recycling of Waelz Oxide Using Concentrated Solar Energy

The dominating Zn recycling process is the so-called Waelz process. Waelz oxide (WOX), containing 55-65% Zn in oxidic form, is mainly derived from electric arc furnace dust produced during recycling of galvanized steel. After its wash treatment to separate off chlorides, WOX is used as feedstock along with ZnS concentrates for the electrolytic production of high-grade zinc. Novel and environmentally cleaner routes for the purification of WOX and the production of Zn are investigated using concentrated solar energy as the source of high-temperature process heat. The solar-driven clinkering of WOX and its carbothermal reduction were experimentally demonstrated using a 10kWth packed-bed solar reactor. Solar clinkering at above 1265°C reduced the amount of impurities below 0.1wt.%. Solar carbothermal reduction using biocharcoal as reducing agent in the 1170-1320°C range yielded 90wt.% Z

Glass melting using concentrated solar thermal energy

Glass melting using concentrated solar thermal radiation is demonstrated on the kilogramme scale using a high flux solar simulator (HFSS). The melting process involved a novel furnace design utilising a downward orientated concentrated solar beam coupled with back-up integrated electrical heating elements, which provided secondary heating to maintain a melt when the HFSS beam was unavailable (i.e. equivalent to cloudy conditions or at night). With 5·26 kW radiative power from the HFSS input to the furnace through a 6 cm diameter aperture, pelleted soda–lime–silica batches were melted. Repeated additions of ∼300 g of batch pellets were made to the melt with each ∼300 g addition requiring ∼15 min for the reactions to complete and the melt temperature to recover. This is equivalent to a glass batch melting thermal efficiency of 16% at a solar concentration ratio of 1857 suns. The areas of land required for the heliostat field and, for the electrical backup elements, photovoltaic field are shown to be significant for even moderate daily glass production tonnages

Experimental Investigation of the Solar Carbothermic Reduction of ZnO Using a Two-Cavity Solar Reactor

ABSTRACT Zinc production by solar carbothermic reduction of ZnO offers a CO 2 emission reduction by a factor of 5 vis-à-vis the conventional fossil-fuel-based electrolytic or Imperial Smelting processes. Zinc can serve as a fuel in Zn-air fuel cells or can be further reacted with H 2 O to form high-purity H 2 . In either case, the product ZnO is solar-recycled to Zn. We report on experimental results obtained with a 5 kW solar chemical reactor prototype that features two cavities in series, with the inner one functioning as the solar absorber and the outer one as the reaction chamber. The inner cavity is made of graphite and contains a windowed aperture to let in concentrated solar radiation. The outer cavity is well insulated and contains the ZnO-C mixture that is subjected to irradiation from the inner graphite cavity. With this arrangement, the inner cavity protects the window against particles and condensable gases and further serves as a thermal shock absorber. Tests were conducted at PSI's Solar Furnace and ETH's High-Flux Solar Simulator to investigate the effect of process temperature (range 1350-1600 K), reducing agent type (beech charcoal, activated charcoal, petcoke), and C:ZnO stoichiometric molar ratio (range 0.7-0.9) on the reactor's performance and chemical conversion. In a typical 40-min solar experiment at 1500 K, 500 g of a ZnO-C mixture were processed into Zn(g), CO, and CO 2 . Thermal efficiencies of up to 20% were achieved

On the Development of a Zinc Vapor Condensation Process for the Solar Carbothermal Reduction of Zinc Oxide

In the conventional Imperial Smelting Process, the dominating pyrometallurgical zinc production process, zinc vapor is recovered from the furnace off-gas by absorption into an intense spray of molten lead droplets in a splash condenser, followed by separation of zinc from the Zn-Pb alloy upon cooling from 550°C to 450°C by taking advantage of the decrease in the solubility of zinc in lead at lower temperatures. The adaptation of this condenser technology into a solar-driven thermochemical plant using concentrated solar energy faces several drawbacks owing to its mechanical complications and the continuous recirculation of large quantities of lead. An alternative zinc condenser concept involving gas bubbling through a zinc liquid bath of the off-gas evolved from the carbothermal reduction of ZnO is thus proposed and numerically modeled for transient heat and mass transfer. Condensation of bubbles containing 53.5% of noncondensable gases yielded chemical conversions of Zn(g) to Zn(l) in the range of 95.6-99.8% for operation in the temperature range 500-650°C while conversions of Zn(g) to ZnO in the order of 10−6 were obtained, thus predicting successful suppression of Zn(g) reoxidation by CO2 and CO

Phase Chemistry Study of Products from the Vitrification Processes AshArc and Deglor.

AshArc and Deglor are two new complementary vitrification processes for residues from incineration of municipal solid waste. The hazardous fly ash and bottom ash are converted into a glassy product (main product), a heavy metal salt fraction, a metal fraction (AshArc only) and an off-gas. AshArc is a reductive melting process based on DC arc furnace technology, whereas the Deglor process is based on a glass tank furnace with a more oxidizing gas atmosphere. Samples from pilot and technical scale Operations of both processes were analyzed in detail using methods from petrography and chemical analysis by electron microprobe and X-ray fluorescence. Both processes produce homogeneous glassy melts with variable amounts of metal-rich minute inclusions. For the reductive AshArc process with a relatively short retention time in the furnace the melt contains a minor fraction of metal and metal sulfide inclusions enriched in iron, copper and lead, as well as traces of chromium spinel. Deglor samples are either free of inclusions or contain traces of metal sulfide enriched in copper, iron, nickel and lead. The residues contain heavy metal concentrations below those stipulated for inert waste materials according to Swiss legislation except for zinc in some samples