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Introduction

Project 1.4 deals with the treatment of fine disperse residuals from metallurgical plants and processes as well as fine-grained raw materials. Research topics focus on a valuable material separation (zinc, iron) from metallurgical dusts and sludge’s and the briquetting of dusts and fine coals to enable a sustainable recycling for agglomerated residuals into existing production processes. Furthermore, the coal briquettes are utilized in coking plants. Beside iron and steel production, residual recycling offers interesting chances for copper industry whereas the agglomerated materials are mainly used in shaft furnaces. 

In many cases, fine-grained oxidizing dusts and sludge’s from a dry and wet based process gas cleaning system can contain metallic iron and burnt lime. Due to this pyrophoric character (possible spontaneous ignition in case of contact with air), these residuals have to be investigated in terms of safety-relevant issues concerning the behaviour inside the dedusting system. This is the case especially for dusts from BOF gas (BOF = Basic Oxygen Furnace) and EAF gas (EAF = Electric Arc Furnace) as well as for residuals from the iron ore pellets production and sludge’s being used for the production of Hot Briquetted Iron (HBI). In this context strategies for a safe handling (transport and further treatment) should be developed in the course of P 1.4 research activities.

Objectives and Motivation

  • The plant engineering of the RecoDust process for residual treatment from iron and steel production as well as development of treatment concepts for dusts from copper industry
  • A development of briquetting concepts for metallurgical residuals and fine-grained coal
  • An investigation of oxidizing dusts concerning their behaviour inside dedusting systems and generation of instructions for a safe handling

Methodology

The realization of experimental laboratory and pilot scale campaigns represents one important method in the present project 1.4. The Flash-Reactor-demo plant being built and put into operation at the Montanuniversität Leoben will be further developed in the course of project 1.4. This demo plant for an industrial realization of the RecoDust process (zinc and iron separation from metallurgical residues such as steel mill dusts) was erected in the recent K1-MET funding periods. Further melting campaigns with new input materials will be performed.

Further experimental lab- and pilot-scale campaigns consider the agglomeration (briquetting) of metallurgical residuals (dusts and sludge’s) from iron- and steel production and copper industry respectively, moreover of residuals from direct reduction processes (MIDREX®) as well as the briquetting of fine hard coal. In this context the choice of the suitable binding agents represents one of the main challenge to produce briquettes of satisfying quality (mechanical stability i.e. density, stability, abrasion resistance as well as suitable chemical properties such as a certain reducibility in case of briquettes utilization for direct reduction processes).

The agglomerated residuals can be reutilized into existing production processes for a material cycle closure. Briquetted hard coal of lower quality being usually not suitable for a metallurgical coke product (low coal rank and poor baking properties) can be added to coking coals. This can help to enlarge the raw material spectrum for a coke production (partial replacement of the critical raw material coking coal) and furthermore a larger independence from current coke market prices can be reached.

Laboratory investigations also represent the basics for the characterization of steel mill dusts and dusts from fine ore pelletizing as well as sludge’s from HBI production concerning their oxidizing character. Due to the metallic iron content of these residuals (pyrophoric character) abrupt oxidation reactions can occur (spontaneous ignition in case of contact with ambient air oxygen) in gas cleaning systems and in the course of further treatment (storage, transport…). This can lead to a damage of the gas cleaning system and downward treatment aggregates respectively. In this context fundamental knowledge of ignition properties (temperature range and concentration limits for a spontaneous self-ignition) represents an important requirement for a safety-related harmless handling.

Accompanying modelling and simulation runs as well as economic consideration activities complete the methodological approach in present project 1.4. E.g. in the course of the further Flash-Reactor development burner concept simulations for a large scale RecoDust-plant as well as a determination of CAPEX (Capital Expenditure) and OPEX (Operational Expenditure) will be performed.

Results and application

The development of concepts and processes from pilot scale to large industrial scale  is a primary target of the research activities within K1-MET project 1.4. In the course of up-scaling activities it is planned to implement the results of the experimental Flash-Reactor campaigns (RecoDust-process) as well as the lab scale briquetting experiments of residuals from iron and steel production and copper industry respectively.

The laboratory investigations of specific chosen metallurgical residuals shall be used for the creation of safety-related recommendations and guidelines especially for the design of dedusting plants. Additionally a procedure for safe handling should be generated (transport, treatment and storage) e.g. in form of technical specifications. One company partner in project 1.4 is currently developing in a further COMET funded K1-MET project (project 1.5 - Gas Cleaning Solutions) a dry based energy optimized dedusting system of steel mill process gases, which is called MERCON®. The planned guidelines and technical support documents to be developed in the current project 1.4 can provide an important safety-related contribution for an implementation of dry based steel mill gas cleaning solutions as future Best Available Technique within the iron and steel industry.