In the frame work of this research project the possibility to promote synergetic use of low-value energy rich waste combined with cleaning and preheating of zinc-containing steel scrap has been studied. Result from this study indicate that the new proposed zinc recovery methods make it possible to recover the zinc in the steel scrap in the steel process with reduced or without an increase of energy and environmental load.
In the frame work of this research project the possibility to promote synergetic use of low-value energy rich waste combined with cleaning and preheating of zinc-containing steel scrap has been studied. Zinc coating on steel is used to increase the corrosion resistance of the steel product. The low-carbon galvanized steels normally used in automotive bodies and appliances are a source of high-quality scrap feed for both BOF and EAF steel production. Although there have been development of technology for removal of the galvanized coatings, the protracted delays in achievement of an economically viable solution have forced most BOF operators to implement alternative methodologies to maintain environmental compliance (EAF operations, with higher dust disposal cost, benefit to some extent from the value of the contained zinc units). In all scrap preheating applications the exhaust gases generated can contain difficult compounds which need a dedicated gas cleaning system to handle these. The emission of harmful dust and hazardous air emission is generated regardless of the fuel used since these are originated from the impurities and organic coating on the scrap itself. The suggested combined use of a problematic and complex waste as fuel for a scrap preheating concept is a possibility where the wastes energy content and chemical potential is being explored. Within the project the complete value chain from waste to new steel production via the BOF has been considered. Different technologies have been developed and evaluated: * two techniques for separation and treatment of energy containing waste streams, * two techniques for thermochemical conversion of the solid waste fuels, * a stand-alone scrap preheating concept, * a dedicated gas treatment facility and recovery of valuables. Tests conducted in the project have shown that it is possible to separate waste fractions (plastic, rubber etc.) into various useful streams, to thermo-chemically convert these into a syngas, through separate combustion, use the exhaust gases generated preheat scrap and remove coatings, through a dedicated gas cleaning and recovery system recover valuables. Theoretical evaluations shows that the concept is positive both from environmental and economic standpoint. Result from this study indicate that the new proposed zinc recovery methods make it possible to recover the zinc in the steel scrap in the steel process with reduced or without an increase of energy and environmental load. The extra energy that the recovery process requires is recovered in the steel process and the energy and chlorides used for the zinc recovery can be obtained entirely from waste plastics. It must however be stated that there still are some technological/metallurgical questions remaining open and more research to validate and improve before a large scale demonstration and implementation of the concept can be done. Parts of the research results derived within the project can be implemented and used, into new innovations.
Keywords: Stål, zinkplåts, återvinning, Steel zinc-plate scrap recovery simulationmodels, LCA, LCC
Report number: A2287
Authors: Anders Björk, Klara Westling, Åsa Nilsson, Håkan Fridén, Håkan Stripple
Published in: Research and innovation, 2015 EUR 27201 EN ,ISBN 978-92-79-47496-5, doi:10.2777/018866