Collection and conversion of silicon furnace waste gas into higher value products: Phase 3, 6 MW pilot plant dc closed furnace technology. Final report

Abstract

By DISCLAIMER~s repon was pepared as an account of work sponsored b) an agency of the Uruted Sues Govcmmmt Neither the Umted States Government nor an) agency thereof. nor an) of theu employees. makes any warranty. express or imphed or assumes any iegal Labihty orresponshht). for the accuracy, completeness. or usefulness of any m f o m o n . apparatus, product or process d~sclosed. or EXECUTIVE SUMMARYSilicon and Ferrosilicon Industries in North America have been on the decline for more than a decade, primarily as a result of the availability of low cost import silicon and ferrosilicon.Although the world demand for silicon is increasing, the high energy and feedstock costs associated with current production methods continue to place North American producers at a disadvantage.Silicon is conventionally produced by carbothermic reduction of silica in large open submerged arc ac furnaces. The process off-gas, primarily carbon monoxide, is lost by combustion on top of the bed. This loss can be eliminated by enclosing the furnace with a cover and processing the off-gas in a sealed system. Electrode cost, which represents a significant portion of the variable cost for the production of silicon, can be significantly lowered by smelting in a direct current (dc) system; particularly in a closed dc system.The construction and operation of a 6 MW, closed dc furnace for smelting silicon was the primary focus of Phase 111. A 6 MW, dc closed furnace pilot plant was built in East Selkirk, Manitoba, Canada. The furnace is equipped with world's most modern automatic control system used to control and monitor the process variables and operational data. This control system is suitable for commercial applications and could be used with either closed or open dc furnaces for smelting silicon or ferrosilicon. The construction was started in September 1990, and the facility was operational within 18 months. Following successful commissioning of the pilot plant in June 1992, twelve smelting test campaigns were conducted through November 1994.The first three tests designated as "start-up commissioning runs" were made to demonstrate equipment operation, and resolve any operating problems. The furnace-bottom anode, a critical part of the furnace, was successfully developed and a potentially patentable anode design has emerged through three generations of anode modifications. Anode technology is a key element in successful commercialization of dc silicon smelting technology.Test runs 004-01 2 provided the operating experience for managing carbon theory and optimizing feed rate as a function of power input. Managing the flow of raw materials to the smelting zone remains a problem inspite of modifLing the mix-movement system. The issue of mix-movement is considered to be a consequence of a closed furnace operation. In a semi-closed vi or an open dc furnace, the mix-movement should not be a problem and could be handled as with conventional open, alternating current (ac) furnaces.The targets for electrode consumption in...

Silica Fume Formation in Different Gas Atmospheres

“…This could be an option for silicon production but requires closing of the furnace. Previous attempts at closing the furnace have been done by Elkem in 1981 5 and by Dow in the 1990s, 6,7 with a motivation of improving the process and producing a sellable combustion gas, consisting mainly of CO and some H 2 . These efforts showed a wide range of challenges that needed to be solved to make a closed furnace process viable.…”