Global Steel Dust (GSD) deploys the reliable Waelz Kiln technology that successfully processes over 80% of the world’s recycled steel dust. The Waelz Kiln process is an established, energy-efficient and resilient technology used to treat zinc containing materials and residues.
Although Waelz technology has been around for over 80 years, the design and technology surrounding the basic kiln has improved throughout this time. In fact, we believe, that GSD has advanced the design further than any company and now has the best-designed system anywhere in the world. This state of the art Waelz system is now being constructed in Saudi Arabia.
As a result, this continually improving process continues to be the industry’s Best Available Technique (EU BREF notes) and Best Demonstrated Available Technology (US – EPA) for recycling high zinc content EAF dust and other zinc bearing waste.
Energy efficient and clean, the Waelz Kiln technology is especially suited to the increasing demands of environmental laws being implemented globally.
The Typical Waelz Kiln Process
(1) EAF steel dust is transported by road or rail to a steel dust recycling plant.
(2) The feed materials are provided in either dry compact-moist or pelletized form. The compact and pelletized moist materials, coarse fluxes and coke are stored in boxes while the dry dust is transported by pneumatic conveying systems to raw material silos.
(3) Typically 55 meters long with a four-meter diameter, the Waelz Kiln is slightly inclined 2-3% and has an approximate rotary speed of 1.0 rpm. As the moist material moves through the rotary kiln, it is dried and preheated by the kiln gas, flowing in a counter-current pattern. In the reaction zone, reduction of the metal oxides occurs around 1200°C as the zinc is vaporized as metal vapor into the gas cleaning system. Zinc is then re-oxidized in the kiln atmosphere that is operated with excess air (process air is injected from the kiln end). Chlorine and alkalis volatilize jointly with the heavy metals and the dust-laden off-gas is treated in a downstream off-gas system.
(4B) In the first stage, coarse particles mechanically entrained are separated in a dust settling chamber and returned to the kiln. The hot, dust-laden off-gas is cooled and Waelz Zinc Oxide is separated in a high efficiency collector.
(4A) The co-product, Waelz Iron Product, can be used directly in road construction, civil construction (backfilling), cement manufacturing or can be reprocessed to add more value to the iron content which is currently under research and development.
(5) The dust-free off-gas is then treated, filtered and discharged.
(6) The discharged air easily meets strict U.S. and European environmental regulatory standards and is a major supporting factor in the U.S. - EPA's designation as Best Demonstrated Available Technology and the E.U.'s designation as Best Available Technique.
(7) Waelz Zinc Oxide, the main product of the process, is delivered to zinc smelters for zinc production.