The SDHL-Waelz
oven process

Today, the recycling of steel scrap is as important as obtaining raw or primary steel, in order to preserve natural sources and protect the environment.

Our customers use electric arc furnaces to recycle steel scrap to produce steel. In this process a hazardous waste called “steel dust” is generated. Befesa manages and recycles this hazardous waste.

Compared to the classic Waelz process, the patented “-Waelz SDHL process” technology, applied in the 5 Befesa facilities in Spain (Befesa Zinc Aser SA U), Germany (Befesa Zinc Duisburg GmbH, Befesa Zinc Freiberg GmbH), South Korea (Befesa Zinc Korea, Ltd.), Turkey (Befesa Silvermet SL) and France (Recytech SA), has been named as the best available technique (Best Available -Technique, BAT), due to the great benefits it offers.

The Waelz SDHL process consists of the following stages:

Dusts, sludge, filter cakes and other residues containing zinc, sent by our clients, with different compositions, are initially stored in closed silos or covered niches. The intermediate storage capacity is equivalent to approximately one to two months of production, depending on the facility. In the first phase, these raw materials are mixed and pelletized with water, coke and lime, to guarantee a homogeneous feed to the Waelz kiln. The micropellets feed the kiln either directly or from intermediate storage. The operating temperature of the furnace is approximately 1,200 ºC, at which all volatile compounds, mainly zinc, pass into the gas phase and are re-oxidized to Waelz oxide. By the off-gas treatment facilities the Waelz oxide is recovered and provided afterwards to the zinc industry as a secondary feed material.

By selectively adding air to the charge at the end of the furnace, most of the iron reduced during the process is reoxidized to iron oxide (FeO). The heat produced -in oxidation is used to preheat the fresh air that enters, thus providing the thermal energy necessary for the chemical process in the reaction zone. Thanks to the development of this technology, the SDHL process, it has been possible to optimize the efficiency of this stage, with respect to the conventional Waelz process.

The Waelz plants of Befesa Zinc Aser. Befesa Zinc Freiberg and Befesa Zinc Gravelines carry out the washes – in two or three stages, to purify the Waelz oxide -.

The slag produced can be used as a building material for applications in the cement industry and as bituminous aggregates. In Spain, it is used under its brand name – Ferrosita®.