The lead recycling plant of Weser-Metall GmbH in Nordenham, Germany is unusual. Not only does its compressed air control unit use volume flow as the reference variable (rather than pressure) it is also uniquely energy-efficient, saving up to 600,000€ in energy costs.
Weser-Metall specializes in recycling lead, especially from battery scrap and battery paste. The plant purchased six new oil-free centrifugal ZB VSD (variable speed drive) compressors from Atlas Copco, which are flow-controlled, within a range of 1500 to 10,000 Nm3 (standard cubic meters) per hour with up to 1.95 bar excess operating pressure.
“Our requirements are totally different”, explained Timo Tesch, manager of design/process engineering/ancillary operations at Weser-Metall. The lance immersed in the furnace in the liquid slag experiences fluctuating counter pressure at its tip. In order to keep the metallurgic process securely under control, it is absolutely necessary for us that we can securely provide a specific constant volume flow at any time. Also, operating conditions change very quickly, requiring rapid intervention and readjustment.”
The new compressed air installation is now so flexible, powerful, and user friendly, that they have met our, admittedly, high demands. As far as I am aware, this kind of installation is unique worldwide. We save € 500,000 to 600,000 on energy costs per year with our new compressed air station.”
The air from the turbos is provided 24 hours a day – blown together
with natural gas and oxygen through a lance immersed in the molten mass,
maintaining the metallurgic process in the immersion melting furnace. Parallel
to this, after-burning air is fed into the furnace via the molten bath to ensure
that no reactive components, such as non-combusted natural gas, end up in
When the Nordenham lead works converted from the coke-fired melting shaft furnace process to the more environmentally-friendly natural gas-fired immersion melting furnace process in 1996, a two-stage turbo compressor (first stage 0.82 bar; second stage 2.8 bar) was installed for processing and after-burning air, but it was always felt this could be more efficient.
Ultimately, rising energy costs and better compressor technology prompted the purchase of the brand new ZB centrifugal air blowers with VSD direct drive from Atlas Copco. The problem for Weser-Metall, however, was the lack of any references for those kinds of applications. Although ZB turbos were used in wastewater treatment plants, they were always pressure-controlled and not flow-controlled.