EUROPEAN STEEL TECHNOLOGY AND APPLICATION DAYS 2017 - ESTAD 2017

Industry follows only the agriculture sector as main water consumer, as water is fundamental for all process steps from the cooling to the washing stages, from the product formulation to the mass separation. In particular, steelworks use significant amount of water in cooling and washing systems. However, higher freshwater cost and environmental regulation pressurise industry toward an improvement of the efficiency of water usage, which can be achieved, for instance, by reusing, recycling and regenerating wastewater. These are the principles of water process integration that can allow achieving a reduction of the water footprint of a process chain, such as the steelmaking one. To this aim, the paper presents a work carried out in cooperation with an Italian Steelworks that is focused on the evaluation of the possibility to reuse the wastewater coming from the coke-making area after a regeneration treatment. The work is part of the project entitled "Efficient Use of Resources in Steel Plants through Process Integration” (REFFIPLANT), which is funded by the Research Fund for Coal and Steel of the European Union, and consists of a first modelling and simulation step, of an experimental stage and of an economic assessment. A treatment process that consists of ultrafiltration and reverse osmosis as main steps was assessed in order to remove the main contaminants (e.g. iron and manganese salts, ammonia, free cyanide). Firstly, a model was developed using the WATERint® simulation software in order to have a first idea of the suitability of the proposed process scheme to obtain high quality water to be internally reused. Satisfying results paved the way to the development of a pilot plant and to its use to make real field tests in order to optimize the configuration scheme considering if each step is necessary and if some chemicals additions are required: contaminants amount, pH, electrical conductivity, hardness were monitored. The experimental campaign confirms the simulation results, proving that a process consisting of ultrafiltration, an ammonia removal stage and reverse osmosis allows obtaining a water of suitable quality to be reused in the coke-making area. The obtained simulation and real tests results were finally used to evaluate the economic feasibility of the proposed water treatment process through the payback period analysis depending on the variations of the permeate and retentate streams prices.