Das bei Wuppermann angewandte Verzinkungsverfahren bietet prozessuale Vorteile in Bezug auf die Ökobilanz. Das übliche Kaltbandverzinkungsverfahren fordert das Glühen des Stahlbandes auf eine Temperatur von 750° C in einem großen Glühofen, welcher mit Erdgas oder Hüttengas befeuert wird. Sein Verbrennungsprodukt ist CO2, das in die Atmosphäre abgegeben wird. Anschließend muss das Band dann auf die Verzinkungstemperatur abgekühlt werden. Im Heat-to-Coat-Verfahren von Wuppermann wird mit einem kleinen, induktiv (elektrisch) beheizten Banderwärmungsofen gearbeitet, welcher das Stahlband in Sekunden auf die Verzinkungstemperatur 460 – 480° C erhitzt. Das energieintensive Rekristallisationsglühen bei ca. 750° C entfällt.
The Fraunhofer UMSICHT Institute was commissioned to draw up a greenhouse gas balance for the strip galvanizing process of the Wuppermann Group and to compare it with the cold strip galvanizing process commonly used on the market.
The investigation was based on a life cycle assessment or life cycle analysis according to DIN EN ISO 14040. This provides the framework for assessing the potential environmental impact of a product system over its entire life cycle. The process is divided into four phases: Definition of the objective and scope of the study, Life Cycle Inventory, impact assessment and evaluation. It provides an opportunity to record all relevant potential impacts (with a focus on greenhouse gas emissions) on the environmental media. This climate impact is expressed in kg CO2 equivalents per kg (CO2-eq./kg) of hot-dip galvanized steel strip. The environmental impact of all other greenhouse gas emissions, e.g. methane, is converted via a standardized value into a value comparable to CO2.
In order to be able to assess the total environmental impact caused by the production of one kilogram of hot-dip galvanized steel strip with ø Z214 (zinc coating 214 g/m2) or ø Z558 (zinc coating 558 g/m2), a system room extension is required. The concrete life cycle assessment therefore includes not only the primary data of the galvanizing process itself, but also secondary data of downstream or upstream processes. These primarily include the production of zinc, the provision of electricity and the transport of raw materials to the plants.
For the reference process, publicly available data records were used for the production of hot strip, for the production of cold-rolled steel strip, and for the production of galvanized sheet by means of cold-rolled galvanizing. The latter refers to material with a zinc coating thickness of 275 g/m2.
In order to be able to reference against the zinc layer thickness Z275 in the cold strip galvanizing process, the average zinc layer thickness for WSN (Z214) and WA (Z558) was corrected accordingly in the comparative calculation.
The present LCA is primarily a so-called gate-to-gate consideration. The system boundary is quasi defined by the "factory gate". The focus is on the environmental impact caused by the galvanizing process. Only the minor CO2 input caused by the hot strip transport to the plants is included in the calculation. Since the heat-to-coat process at Wuppermann runs via a combined pickling & galvanizing plant, pickling is also included in the LCA. This is not the case with the reference process, as pickling takes place in a separate step before cold rolling. In a direct comparison of processes, the LCA of Wuppermann is thus additionally burdened by the environmental impact of pickling, i.e. it is presented somewhat too negative.
If the system boundary of the reference process is extended to all process steps that take place between the completion of the hot strip and the finished galvanized steel strip, the advantage of the Wuppermann process even increases to 48 % in the case of the Dutch site and to 56 % in the case of production in Judenburg, Austria.
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