Sustainable production of aluminium

Transcription

1 Sustainable production of aluminium The way Qatalum and Hydro do it Presented by Dr. Odd-Arne Lorentsen (1)

2 Recycling Rolling Bauxite Alumina Carbon Energy Primary Casting Products Extrusion Recycling (2)

3 In order to produce 1 kg of aluminium, the following quantities of raw material are consumed: + 4 kg of Bauxite 2 kg 0,5 kg Alumina Carbon g Aluminium Fluoride 50 g Cryolite ~13 kwh 1 kg Electric Power Aluminium (3) kg CO 2

4 Value chain for aluminium (4)

5 Alumina from Bauxite The Bayer Process (5)

6 Major Bauxite areas Global bauxite production in 2007 was approximately 190 million tonnes Source: (6)

7 Bauxite deposits lie an average of 8 meters below the surface Trees Cleared Overburden Removed Ready for Mining (7)

8 The Bayer process Red mud Alumina Source: (8)

9 Aluminium production by electrolysis (9)

10 Aluminium production 1. Cooling of cell superstructure 2. Securing no gas leakage to potroom Alumina Carbon Power ~1% CO 2 ~99% Air Na 3 AlF 6 + AlF 3 +CaF 2 2Al 2 O 3 + 3C = 4Al + 3CO 2(g) Aluminium Heat HF SO 2 CF x (10)

11 Cathode The cathode process is taking place at the surface of the metal aluminium at 960 C (8) Alumina feeding Source: (11)

12 The carbon anode Challenges: The only reducing agent for production of aluminium Cause production of CO 2 - Greenhouse gas Possibilities(?): New knowledge to lower the net consumption Exploit new raw materials to produce high-quality carbon anodes (12)

13 Anode consumed and replaced every 3-4 weeks (13)

14 Two types of electrolysis cells Søderberg VSS, Alcoa Norge Lista Prebake CWPB, Hydro Aluminium, Årdal (14)

15 Aluminium production is a function of DC current supply Production per cell-day [kg] CE = 94% Qatalum Su4 HAL4e More DC current means more aluminium produced per unit Aluminium cell size has increased over the years Hydro: Line current has increased from A to A in 91 years Line Current [ka] (15)

16 Aluminium tapping once per day (16)

17 (17) Environment

18 Red mud waste from the alumina production Red Mud treatment with the most modern environmental technology: Red mud filtration Red mud stacking in sealed areas Alkaline effluent is neutralised, i.e. ph is reduced (18)

19 Tailing pond of dry red mud reforested The waste tanks/ponds are re-vegetated with species native to the region (19)

20 Reforrestation with species native to the region Stocked organic soil spread out where bauxite closed mines used to be Hydro sowing with native leguminous plants inoculated with bacteria Planting of native cuttings and cast seeds by hand (20)

21 Two years after re-planting ~2,500 cuttings planted in each hectare ~100 different species planted per year (21)

22 Anode gas depends on alumina concentration U = Pseudo resistance Anode effect: CF 4 & C 2 F 6 AE CO 2 Normal operation Carbon anode 4Na 3 AlF 6 + 3C = 4Al + 12NaF + 3CF 4(g) (~94%*) 2Na 3 AlF 6 + 2C = 2Al + 6NaF + 2C 2 F 6(g) (~6 %* ) CF x gases are Greenhouse gases * Ref.: Kvande, Nes and Vik, Light Metals [Al 2 O 3 ] (22)

23 Emissions of CO 2 eq is technology dependent REF: IAI, 2009, (23)

24 Emissions very dependent on energy source General Hydro Gas Coal Hydro Gas Coal kg CO2/kgAl kg CO2/kgAl kg CO2/kgAl kwh/kg Al %CO2/kg Al %CO2/kg Al %CO2/kg Al Alumina prod Anode prod Electrolysis Anode effect Casthouse Recycling Hydro Power Gas fired power plant Coal fired power plant Total NOTE: Typical values, not Hydro/Qatalum specific Alumina prod Anode prod. Electrolysis Anode effect Casthouse Recycling 0.00 Alumina prod Anode prod. Electrolysis Anode effect Casthouse Recycling (24)

25 Energy reduction has been a continuous process 50 kwh/kg Al A smelter produces aluminium for years! 2. The technology forefront is about 20 years* ahead of the industrial average Ye ar * excl. China (25)

26 Environment The Årdal smelter case Major improvement over four decades (26)

27 Fume Treatment Plant Cell flue gases (i.e. fluorides, sulphur dioxide (SO 2 ), CO 2 and CF x ) from the reduction cell HF (hydrogen fluoride) from the electrolyte removed by use of primary Al 2 O 3 in dry scrubbers then called secondary alumina secondary alumina are used in the reduction cell SO 2 (sulphur dioxide) from the anode removed by use of seawater in seawater cooling towers (or by using caustic solution) The CF x gases formed during anode effects are not possible to collect (27)

28 Fume Treatment Plant - Typical HF removal SO 2 removal (28)

29 Environment FROM: Karmøy Norway TO: Ziar Slovakia Before potroom was closed (29)

30 Aluminium recycling Part of the Solution Over 70% of all aluminium ever produced is still in use Recycling energy efficient - Saves 95% of GHG emissions - Saves 95% of energy CO 2 /tonne Aluminium Steel (30)

31 Lessons learned today Alcoa (31)

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