Adam J Gesing Gesing Consultants Inc Lightweighting Summit 19-21May 2014, Detroit, MI

Transcription

1 Adam J G G C Lightweighting Summit 19-21May 2014, Detroit, MI

2 Current state of light-metal recycling from both production facilities and post consumer scrap Use of scrap alloy batching for vehicle production With a focus on: metal losses in collection metal-nonmetal separation parent metal separation melt losses in remelting and refining system constraints required for sustainable recycling potential for improvements in alloy batching and sorting for increased scrap utilization potential for recovery of primary quality Mg-Al and Al-Mg from secondary Al foundry melts 2

3 The use of light metals in vehicular components makes transportation more sustainable by fuel savings due to lightweighting. Lightweight material substitution increases sustainability if the in-use energy savings exceed the extra energy required for production of the lightweight material. Recycling of light metals makes the production of lightweight components more sustainable by reducing the capital and energy costs of metal production - in the case of Al by 95% each. Energy savings are even greater for Mg! This presentation will demonstrate that: The recycling system is currently optimized for the use of all old scrap in a small number of large-volume secondary alloys. As long as all the available scrap is used, it does not matter for system sustainability which markets and which components use the scrap. There is little to be gained by adding scrap to performance-critical automotive alloys. There is more to be gained by maximizing the properties and thus maximizing in-use fuel savings. 3

4 North America (1000 metric tons) Sources: G, A.J., Das, S.K. et al., 2014 USGS 2011, USEPA

5 North America (1000 metric tons) Sources: G, A.J., Das, S.K. et al., 2014 USGS 2011, USEPA

6 New scrap (skeletons, clippings and chips) is: a large, important quantity (typically 30-75% of feed metal) and is mostly ignored in recycling considerations, often omitted from recycling statistics. nearly 100% collected; most of it is easily remelted with low melt loss predominantly separated at source by alloy predominantly used in batching same-value alloy, or in diluting impurities in post-consumer scrap mix mostly recycled in house, or bought back from manufacturer The inability to efficiently recycle new scrap is keeping Al- and Mg-matrix composite materials from the mass automotive market. 6

7 Old scrap comes from the consumer in-use pool with a widely variable time delay (days to centuries; years to decades in transportation). It is difficult to quantify old scrap supply (in transportation often tracked by de-registration). There is no separate collection of old Al or Mg scrap. Old metal scrap is co-collected with nonmetals in a small number of collection streams: curbside (packaging recyclables) recycling depots and scrap yards (white goods, consumer durables) de-polluters and dismantlers (ELVs) demolition waste (buildings, factory equipment and machinery) depots and events (electrical and electronic equipment) repair shops (scrap parts) ELV hulks, demolition metals and scrap yard metals are co-shredded in hammer mills, further mixing parent metals and alloys. Each stream is a mixture of all materials present in a specific collection type: metals and nonmetals different parent metal components different alloys of each parent metal 7

8 At scrap yards and MRFs, collected streams are pre-sorted into ISRI categories traded on the world scrap-metal market. Multi-material items (including ELV hulks) are shredded to liberate an equiaxed, mono-material particle mix. The shredded mixture is separated at both shredders and scrap-metal sorters. A large portion of North American Al old scrap is exported, mainly to Asia. 8

9 Separated Al-alloy shred mix is remelted at secondary smelters/ refiners mainly for use in batching 38X and 319 Al foundry alloys (0.1% Mg). Mg-alloy shred is a small quantity; most often, it is still not separated from Al scrap shred. Excess Mg content is chlorinated out of the 38X/319 melt (loosing >30,000 t of Mg in US in 2011). Mg-alloy scrap is lost in this process. In addition to foundry alloys, 3105 alloy painted sheet for the building market and 3X04 alloy for beverage can body sheet constitute two other major markets utilizing old post-consumer scrap. These combine to provide a ready market for every gram of old scrap. Scrap is sold at a discount to prime that reflects the added cost of scrap processing, cleanup, decoating and melt losses. There is little financial benefit to the user of using scrap instead prime metal. 9

10 A large proportion of Mg recycling takes place as Mg alloying element in Al-based alloys. Al-Mg alloys can consume all the available Mg alloy scrap. Consumptive desulphurization of steel provides a major market for Mg-alloy scrap. Old Al scrap is also consumed as steel de-oxidant. There is little point in diverting Al or Mg scrap from consumptive uses to structural automotive applications as it would have to be replaced by primary metal. 10

11 New manufacturing scrap, if maintained separated by alloy, can be used closed-loop to the same or compatible alloy. Most alloys are not exclusive to automotive applications. Alloy ingots and billets are sold into any market that uses a given alloy. Old post-consumer Al scrap from vehicles, consumer durables and demolition ends up as a shredded mixture feeding mainly foundry alloys used predominantly for cast vehicle components. In this way vehicles provide the largest market for old scrap coming from a variety of sources, many non-vehicular. This free cross-market scrap trade is beneficial to the scrap recycling system allowing low-tech, low-cost recycling solutions and promoting financial sustainability of the entire material recycling system. 11

12 No landfill in North America buries vehicle hulks. Hence endof-life vehicles did not directly contribute to 2.8 million metric tons of Al found by USEPA in landfills in Beverage cans, consumer durables and unprocessed demolition waste were the categories that accounted for most of the Al scrap lost in >200 million metric tons of landfilled waste. The expansion of CDW-MRFs and increased collection of consumer durables for recycling has the potential to supply ~2 million more metric tons of Al from mixed scrap that feeds the shredders and hence provides Al scrap for automotive foundry alloys. 12

13 Metal losses in scrap processing are small when compared with incomplete scrap collection. These losses derive from: Incomplete material liberation: Al attachments in steel shred Incomplete metal nonmetal separation: Al in shredder fluff Comingling of Mg and Al scrap particles in Al scrap product Melt losses: Oxidation of Mg and Al on melting Refining losses: Chlorination of excess Mg from Al melt 13

14 Process step Sizing and mono-material liberation Density separation: Fluff and foam from dense fraction Plastic & rubber from metal Shape separation (wire, sheet) Magnetic separation of ferrous alloys Conductive, non-ferrous alloy separation from dense fraction Stainless from fluff Method Shredding, screening Suction, cyclone, elutriation, rising current, sink-float Inclined, spiked conveyors Drum magnet, overbelt/headpulley magnets Eddy current rotor EC sensor-based particle sorter 14

15 Process step Method Foam, fluff, wood Float at r = 1 g/cm 3 Hollow Al + Mg Float at r = 2 g/cm 3 Light (Al + rock) dense (SS + Zn + Cu + brass) Rock from Al SS - Zn - Cu - brass Shape separation (wire, sheet) Sink-float at r = 4 g/cm 3 or x-ray transmission sensor particle sorter Eddy current rotor (Eddy current coil + color) sensor particle sorter Inclined, spiked conveyors Using these processes it is feasible to cost effectively produce >99% grades of: Al-alloy mix Cu Mg-alloy mix Red (Cu+ brass) Zn-alloy mix Yellow brass Stainless-steel-alloy mix Pb 15

16 Typical industry net melt yields in scrap remelting range between 92% and 95%. Net melt yield on submergence melted decoated UBC shred is >98%. There is 3%-5% of improved melt recovery to be gained by proper scrap cleaning, decoating and submergence melting. 16

17 Sufficient markets to consume all scrap Technology to adequately liberate, separate, clean, melt and refine scrap for market needs Free trade in scrap and secondary alloys between markets 17

18 Secondary alloys compositions are least-cost batched from pre-grouped/pre-sorted scrap categories traded on the scrap market plus prime for dilution and to make up for scrap shortage. Sensor-based particle sorters enable sorting of some simple new scrap mixtures. Long term it is still usually more cost efficient not to mix new scrap in the first place. Sensor-based particle sorters analyzing properly cleaned old scrap are able to determine the elemental composition of each particle with sufficient precision to enable particle-byparticle batching of secondary alloy compositions in real time, thus enabling practical upgrading of old scrap mixtures. HVSC sorted Twitch (Al recovered from shredded NF scrap) into high-mg painted sheet alloy and low-mg 380/319 foundry alloy, thus eliminating significant Mg chlorination costs, and getting a small premium for sheet alloy. 18

19 Mg losses from chlorination of Al melts were >30 kt in US (2011), and prime Mg production was <60 kt. Recovery of this Mg as prime quality Mg-Al hardener would have a significant impact on the US Mg supply. US DOE is funding proof-of-concept of such a Mg recovery process through its ARPA-e program on light-metal production. The proposed process uses electrorefining to preferentially oxidize Mg from the Al melt anode and to reduce it as pure Mg on the cathode. 19

20 Action Separation of recycling by market and closed-loop recycling within each market Closed-loop recycling of old scrap alloys Scrap upgrading or sorting that does not directly impact metal recovery or reduce impurity pickup Development of impurity-tolerant alloys for critical corrosion and structural applications Effect Reduced supply of demolition and consumer durable scrap to the transportation market Not practical, vastly increased sorting costs, reduced properties and hence increased weight of critical structural components Upgrading scrap to simply divert it to an alternative market or application is a waste of money and energy Reduced properties and hence increased weight 20

21 include any action that globally reduces prime-metal consumption, such as: Improvement of metal scrap collection efficiency through: Universal adoption of curbside recycling from MSW Improved depots for collection of consumer durables and demolition residue Additional scrap processing capacity for construction and demolition residue Universal adoption of new scrap segregation by alloy Adoption of cleaning and decoating steps for improved sorting capability, reduced melt losses and reduced impurity pick up Replacement of refining by Mg chlorination by Mg recovery by electrorefining 21

22 Light-metal recycling improves sustainability of the global transportation system The current light-metal recycling system is sustainable (consuming every gram of collected and separated Al scrap) While there is room for improvement in recycling, there are also well-meant actions that are counterproductive 22