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FP5

SOLZINC Informe resumido

Project ID: ENK6-CT-2001-00512
Financiado con arreglo a: FP5-EESD
País: Sweden

Direct Zn-dust production from the offgas of carbothermic ZnO-reduction

ScanArc's part in the Solzinc project is to develop a process to convert the zinc metal vapor produced in the solar furnace into a zinc powder suitable for electrolytic cell electrode production.

The conventional way to produce zinc powder is to first condense the zinc vapor into zinc metal and then produce the powder according to one of the three alternative routes:
- Atomisation of liquid zinc.
- Condensation of evaporated zinc.
- Electrolytic precipitation.

Since the zinc vapor from the solar furnace is diluted by CO and H2, and if operated at higher carbon utilization also CO2 and H2O, the diluting gas will be oxidizing to the zinc when the temperature drops and the condensation product will be a mixture of zinc metal and zinc oxide. To avoid the zinc oxide formation the zinc from the vapor has to be dissolved into liquid lead and two alternatives were studied: the ISP splash condenser and the ScanArc spray condenser.

Both alternatives are possible to use with some advantage for the ScanArc condenser since it is a true counter-current reactor giving lower sensitivity to oxidizing gases. The condensation into zinc metal followed by powder production is a quite possible and safe route, but rather investment and cost intensive. We have therefor worked along another concept to produce powder direct from the zinc vapor containing gas from the solar reactor.

After a series of introductory tests we managed to produce a zinc powder with a good yield but the content of ultrafine particles made the powder too reactive for electrodes. The powder production was discussed with a commercial powder producer (Harzer Zinc) and the test equipment has been modified with good success. This design was upscaled for the pilot scale offgas system. It performed well and produced a Zn-dust with a typical size of a few microns and with a purity of around 95%, as targeted.

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