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Turning waste into cash
 By-products generated by the steel and related industries can now be processed and re-used thanks to the AVOID-SOLID project, which has developed a new treatment process yielding an array of valuable commodities.Avoid-Solid is an ideal example of a project that addresses an industrial need by developing appropriate and innovative sustainable technology. By combining waste streams generated by a number of industry sectors it achieves high value products and – as a bonus – a reduction in carbon dioxide emissions.
Zero waste
The so-called ‘ZEro WAste' (ZEWA) process is based on the high-temperature smelting reduction of suitable blends of acid and basic by-products. The process has been designed to cope flexibly with a wide variety of the wastes produced by various steel-making processes such as basic steelmaking slags and dusts or acid residues from scrap metal handling in electric arc furnaces. Acid residues from other industry sectors can also be used including fly ash from the power industry, automotive shredder residues from car recyclers or bottom ash from urban waste incinerators.
The process feeds together appropriate acid and basic inputs with added reductants, such as coal, coke or ferro-silicium, as well as other balancing additives, such as lime and bauxite, into an electrically heated ladle-type furnace. The furnace is designed to allow top-charging of liquid steelmaking slag and coarse solid materials as well as deep pneumatic injection of powdery materials.
The ladle also features bottom stirring to enhance mixing and speed up conversion together with post combustion in the top of the ladle to recover chemical heat and improve process efficiency and integration.
One of two main mineral products of the process is Portland clinker substitute that has a large market for use in cement production. A bonus from making clinker substitute from steelmaking slag provides an overall saving of about one tonne of carbon dioxide emissions for every tonne of slag processed. The second mineral product is metallurgical powders that are used for steel refining in secondary metallurgy.
The process also delivers a hot metal product which, when processing stainless steel by-products, contains high levels of Nickel and Chromium and can be immediately recycled.
Pilot plant
A pilot plant for the process was built at the Vítkovice Steelworks in the Czech Republic adjacent to an existing electric arc furnace to access the existing power supply. The erection of the pilot plant started at the beginning of 2002 with the first hot start-up in early October that year. The plant has shown good control characteristics and its efficiency has improved continuously as more experience is gained with it. The pilot plant ladle has a capacity to hold up to 15 tonnes of hot metal and five tonnes of slag.
The project consortium included representatives from along the value chain in the steel and related industries and was a follow-on from a previous project entitled ‘In-Plant By-Product Melting (IPBM)'. The current project was co-ordinated by the Centre de Recherches Métallurgiques (CRM) from Liège in Belgium and included three companies from the Arcelor steel conglomerate: Usinor of France produce carbon-steel via an integrated blast furnace route, ProfilARBED of Luxembourg use electric arc furnace technology and Belgian company ALZ makes stainless steel. Also involved were Cometsambre of Belgium, an SME involved in the car dismantling business and a Polish Research organisation, the Institute for Chemical Processing of Coal, that provided valuable experience from and contacts to large-scale coal producers and coal-fired power plants.
The world's number one cement producer, Lafarge SA, was also involved as the recipient of one of the primary products of the process and Voest-Alpine Industrieanlagenbau GmbH & Co (VAI) of Austria is an engineering company and plant builder. The ZEWA pilot plant was constructed via a sub-contract with the Vítkovice steelworks.
In addition the associated, but separate, Vítkovice R&D company was added into the Avoid-Solid project as a complementary Newly-Associated State extension project. Their role was a dual one: to capture and assess the environmental emissions from the plant and to facilitate the recycling of the hot metal product by studying and testing a dedicated dephosphorisation operation.
Analysis of off-gas from the various pilot plant tests have shown very low emissions of dust and low levels of carbon monoxide and volatile organic compounds, even when the process was handling scrap residues. | 
