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Processing of awkward by-products through the ZEWA process - Integrated evaluation of needs / potentialities for processing by-products from the steel industry through the ZEWA process

The evaluation of needs / potentialities for processing by-products from the steel industry through the ZEWA process integrates an overview of concerned by-products, including annual production figures, economic aspects (cost for land filling and/or processing by alternative routes) and takes into account local and European regulations (current and future).

The ZEWA process features various charging systems: deep pneumatic injection for dried powdery materials, top chute for coarse materials and a dedicated pouring system for liquid slags. From a technical point of view, a great variety of by-products and materials can thus be charged. This feature was demonstrated during test campaigns were various fine materials (including several types of dusts), sludges, solid slags and scales were processed.

Taking now into account localisation, regulation and economical aspects, first potential sites for process implementation have been selected (C-steel and stainless steel plants), and several processing scenarios have been considered taking into account site constraints.

Former project partners USINOR, ALZ and Profilarbed have been integrated during the course of the project into the ARCELOR group, which is a major player in steel making with an annual production of about 45 Mt of steel.

Regarding the integrated C-steel production route (former partner USINOR), various processing options are under development for slags (especially converter slag), but huge stockpiles and excess production remains to be tackled: current situation is non-sustainable. Regarding the various dusts and sludges, current internal recycling will have to be replaced to a large extent with external processing. Several processes are under development. The ZEWA process allows processing all by-products in only one installation. One drawback is the high P content of the recovered hot metal, which must be re-processed before recycling to the converter. Detailed scenarios have been produced for ZEWA implementation in a Belgian plant (SIDMAR, located in Ghent), including converter slag, various dusts, sludges and scales. Other locations are also considered. Comparison with other alternative processing routes is under way.

For the stainless steel production route (former partner ALZ), the industrial context has profoundly evolved during the course of the project. A plant in France was shut down (Lardoise), another one will be closed (Isbergues), while the capacity of ALZ steel plant (located in Genk, Belgium) has been doubled (with an additional change in the process itself), and a new plant is under construction in Charleroi, Belgium. This led company management to re-consider the by-products problem as a whole. Regarding slags, possible applications (re-use as secondary raw material) are largely dependent on specific regional legislation and, even when allowed, the market is uncertain. As a consequence, stockpiles accumulate and the situation is non-sustainable. For dusts, only one external treatment facility exists in Europe, resulting in high treatment costs and uncertainty for the future. Moreover, hot rolling slam is less and less recyclable due to the increase of its chromium content. Detailed scenario calculations have been performed for the implementation of the ZEWA process in Belgian plants (Genk and Charleroi) with very good economic feasibility when processing slags, dusts, sludges and scales (slam). The ZEWA process is generally seen by stainless steel producers as a very good solution for turning their slags into a sellable product and recovering valuable metals (Cr, Ni, Mo). Therefore, a new project was started within ARCELOR - UGINE & ALZ which aims at re-defining by-products policy. This project notably includes a benchmark review of existing valorisation possibilities and treatment processes. This project started at the beginning of 2005. A meeting is notably planned in June 2005 with VAI representatives for examining the ZEWA alternative. Results / conclusions are expected for the end of the year and decisions for future investment(s) should take place in 2006.

For the EAF C-steel production route (former partner ProfilARBED), the processing of main by-products (slags and dusts) was not considered in the project because of rather low technical and economical incentives. The considered by-product (processed scrap residue, a.k.a. silica-containing aggregates) does not justify erecting a dedicated ZEWA plant, but could be supplied for processing in any such plant erected in reasonable proximity.

Similar studies should be set-up in the future for CORUS plants, first through CRM, then with VAI.

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