Leveraging Value and Environmental Gains Through Integrated Steel- and Ferroalloy Plant Slag Cleaning

Abstract

There exists a strong business case to incorporate a pyrometallurgical Slag Cleaning Furnace (SCF) into the process-chain of large ferrochrome producing sites, or into an integrated steel plant where ferroalloy production is in close proximity to the converters.

Recent studies into the design and layout of such SCFs have revealed environmental benefits and attractive pay-back periods for large ferrochrome and integrated stainless steel producers looking to recover valuable components from discard slag, whilst enjoying a stream through which historical waste sources can be recycled.

Transferring the molten discard slag, with its inherent store of sensible energy, directly to the SCF from the primary reduction process means molten feed-to-solid feed ratios can be optimized to yield a ferroalloy at reduced cost. Within the context of a steel producer, molten Electric Arc Furnace (EAF) and converter slags add further “sweeteners” high-in-metallic units that can be recovered to produce alloys of higher value.

The processing of discard slag and historical wastes in a high throughput SCF supports sustainability and circularity. The resulting alloys are produced with a reduced carbon foot-print, the sensible heat of the molten slag can be recovered for heating or electrical generation, the barren slag is well suited to de-classification for use as an aggregate in concrete or as backfill in the construction sector, and a “dustbin” now exists on the site into which troublesome wastes can be fed, converted and neutralized without filling costly and environmentally detrimental landfills.

This paper will introduce the process flow, technology and layout for SCFs designed to work within this context. The furnace metallurgy, M&E balance, furnace parameters and slag cleaning process essentials will be discussed. Options for additional value streams beyond the production of the ferroalloy will be explored, with the key environmental upside as the foundation of the process intent.

Keywords: slag cleaning, ferroalloy, steel plant, green slag, circularity, rectangular furnace