Process for the preparation of silicon or ferrosilicon

Claim 1

A process for the preparation of silicon or ferrosilicon by reduction of silicon oxide in the form of silicas or cation containing silicates and oxides, optionally in the presence of iron or iron oxide, by means of a carbonaceous reducing agent in a reaction zone, which reaction zone comprises a zone of energy supply and a zone of subsequent reaction, whereby at least energy and condensed phases from the zone of subsequent reaction are brought to the zone of energy supply while silicon product and a gas phase are leaving the zone of energy supply and whereby at least carbonaceous reducing agent and the gas phase from the zone of energy supply are brought to the zone of subsequent reaction while a gas phase product and condensed phase are leaving the zone of subsequent reaction so that the gas phase product leaves the reaction zone and the condensed phases enter the zone of energy supply and whereby the silicon oxide is supplied in condensed form somewhere in the reaction zone or in gas phase to the zone of energy supply, comprising the steps of: (a) supplying at least 33 percent of the silicon oxide directly into the zone of energy supply through a channel through the furnace wall, or a channel through the charge or a channel through the electrodes, (b) controlling the supply rate of the silicon oxide to the zone of energy supply essentially continuously and in an adjustable way to make the consumption of the silicon oxide in the zone of energy supply independent of the charging of energy to the zone of energy supply so that the temperature in the zone of energy supply can be influenced, and (c) regulating the supply rate of silicon oxide and the supply rate of energy to the zone of energy supply to give a high enough temperature in the zone of energy supply to give a content of silicon monoxide below 5 mole percent in the gas leaving the zone of subsequent reaction.