Recover, reduce, reuse: optimizing metal recoveries from dross Presented by Alan M Peel C.Eng ALTEK Group
Recover, reduce, reuse: optimizing metal recoveries from dross Presented by Alan M Peel C.Eng ALTEK Group
Agenda Dross management Review basic principle of each technology Information on the facility that sponsored trial Testing procedure / protocol Results of trial Summary / Conclusion Questions
The Dross process Process Route Importance of logistics Time Labour Environment
Initial Step SKIM LOGISTICS COOL or HOT PROCESS TIME LABOUR ENVIRONMENT
Two extremes!! 1% per minute Al loss Capture the value at skimming
Dross Process - Which way? Cooling Disconnects the dross generation from secondary recovery and gives TIME Rapid sealing of aluminium Easier logistics Less environmental impact Hot Processing Logistics very important Continued Al burning if dross bins left waiting Difficult if too many furnaces
Prevalent Dross Cooling Technologies Inert Gas Dross Cooler Dross Press
Prevalent Hot Dross Processing Techniques Tilting Rotary Furnace Dross Stirring
Dross Management Dross can account for 5% of a facilities total production Dross can contain up to 80% of aluminum 1% of aluminum can be lost per minute through oxidation The treatment of the dross after skimming is the single most important factor influencing the metal content and the value of the dross
Dross Management In the Furnace Minimising dross in the furnace MUST be the first priority Type of furnace Burner set up Pressure control Door Electromagnetic stirring
Bath surface temperature 782 C The Temperature of the metal is the single most controllable factor that determines dross generation in a furnace.
Dross Management Over the years a number of technologies have been developed to address both economic and environmental issues Dross Stirrers Rotary Dross Coolers Inert Gas Coolers Hot Dross Processing in a Tilt Type Rotary Dross Pressing Systems Many technologies have not gained universal acceptance
Characteristics Required Needs to be safe. Minimal impact on the cast house and not interfere with the day to day operations. Should be easy to use and require minimal maintenance. Should be environmentally sound and meet all local environmental standards. Should maximize the amount of Al recovery. Should be capable of handling a wide variety of dross types including white, black and heavily thermiting dross.
Inert Gas Dross Cooler Developed by Alcan in the mid 1980 s Dross is skimmed into compartmentalized pans Pan is transferred in a cooling station Hood is lowered and the chamber is purged with an inert gas such as argon Pan is kept under the inert atmosphere typically between 4 to 7 hrs until temp falls below 400 deg C
Developed by ALTEK in the mid 1990 s Consists of a steel frame, hydraulic unit, press head and dross pan set Dross is skimmed into to the dross pans Pan is transferred into the dross press Head is slowly lowered into the dross squeezing trapped metal into the sow mold below Head not only extracts metal but also cools the dross preventing further oxidation Dross Press
Dross Stirrer More prevalent in Japan and parts of Asia Uses flux to increase aluminium drain while stirring Large real estate In house environmental challenges
Trial Facility Pennex operate a very efficient billet re-melt facility in Pennsylvania, USA 60 MT static melting/holding furnace that generates approximately 2200 T of dross / year Facility successfully operated several inert gas cooling hoods for many years At another facility in the group they also operated a dross stirrer Had experience with operators recording the weights of dross pans as part of standard working practices
Based on size of furnace and dross generation, ALTEK selected Tardis Generation II Model #500 Dross pans with an approximate capacity of 700 Kg Equipped with many latest features: Air cooled press head Hydraulically operated guillotine door Updated PLC and HMI Pressure feedback control Machine was fully assembled and tested prior to shipment Shipped preassembled to minimize installation time and costs Dross Press
Testing Procedure Dross was skimmed simultaneously into the pans supplied for both technologies. Inert Gas Cooler pan(s) were placed in the hood(s) and left to cool under the inert atmosphere. Simultaneously, the Dross Press pan(s) were processed through the dross press system. Once processed through each technology, every dross pan was weighed to establish the weight of dross as well as the amount of metal captured in the drain pan below. When cooled, the dross from each technology was placed in separate dross bunkers. The dross was shipped to a separate facility where it was processed in a Tilting Rotary Furnace. The secondary facility was aware that a comparative study was being conducted and the loads of dross were segregated accordingly.
Skimming Furnace
Pan being placed in Inert Gas Cooler
Pan being placed in Dross Press
In-house recovery 16 weeks data In house recovery is expressed as a percentage of dross skimmed Data collated per week Dross Press consistently provides a higher recovery than the Inert Gas Cooler
Over the trial period higher in house recovery with press technology In-house recovery
Secondary recovery 16 weeks data Similar results on the secondary recovery from a Tilt Type Rotary Salt Furnace
Total Recovery - 16 weeks data Higher combined recovery ~ 3% from press + Tilting Rotary Salt Furnace
Summary Results Press v Cooler Summary of Pennex Tests:- Higher recovery with Press + Tilt Rotary Salt Furnace Lower transport cost due to less shipped weight of dross Less space required at plant (valuable undercover space) Quicker cycle times of dross to secondary processor Less dross pan inventory SAVINGS from using Dross Press v Dross Cooler > $250,000 per year
Secondary Dross Processing OPTIONS Tilting Rotary Salt Furnace Mechanical crushing/separation People say remove the salt BUT there is more than just the salt to consider You need to consider all the constituents of in dross!
The Dross Processor Dross Skulls need to be recycled in a Tilt Type Rotary Furnace ALTEK 16 MT Tilt Type Rotary Furnace
Tilt Type Rotary Melting Furnace The above 24 Tonne furnace currently being installed in large Middle East smelter
Tilt Type Rotary Melting Furnace Still the most effective way to process dross:- Obtain the highest metal yield Lowest emissions Smallest footprint Most flexible operation BUT requires further processing of the salt slag
Typical solid components of dross Alumina Oxide (Al2O3) Spinels (MgO.Al 2 O 3 ) Aluminium Nitride (2AlN) Aluminium Carbides Aluminium Sulphites (trace) Aluminium Phosphates (trace) Official Host: 33
Possible Gaseous Components of Dross are: NH 3 (Ammonia) H 2 S (Hydrogen Sulphide) H 2 (Hydrogen) SO 2 (Sulphur Dioxide) CO 2 (Carbon Dioxide) CH 4 (Methane) NH 4 OH (Ammonium) Hydroxide) Phosphine Phosgene (possibly) So its not just the salt slag you have to consider! 34
NMP (Non Metallic Particulate) The key is to get the NMP inert Once safe it can then be used and transported safely In Europe this is undertaken by salt wash systems (large Salt Reclamation plants) to ensure the NMP is safe for sale to down stream applications - and will not release the gaseous emissions when wet.
Some end uses of NMP Cement clinker Rock Wool Refractory Ceramics Many companies are selling NMP into these applications
Project - ALUSALT New development project initiated in 2011 Objective local salt recycling at salt slag generation source Demonstration small capacity pilot plant to be operational Q1 2015
Summary 1. Consider dross skimming/cooling logistics 2. Rapid cooling and drain important to maximise Al 3. Disconnect the dross generation process from the secondary dross processing 4. Over 85% of the dross generated in Middle East today is cooled using dross press technology 5. There are markets and uses for the NMP BUT it needs to be inert 6. The Low Salt Tilting Rotary Furnace for secondary recovery still is the most efficient route for highest aluminium recovery