Air Emissions During the Thermal Treatment Processing of Aluminium Smelter Spent Potlining (SPL) Material

Transcription

1 Air Emissions During the Thermal Treatment Processing of Aluminium Smelter Spent Potlining (SPL) Material Graham Taylor (AECOM) Kevin Cooper (Regain Services) September, 2010

2 ALUMINIUM PRODUCTION PROCESS 2Al 2 O 3 + 3C 4Al + 3CO 2. Electrolysis Process Molten Cryolite (Na 3 AlF 6 ) Direct electrical current

3 Aluminium Smelting Pot Schematic Ref:

4 How Aluminium and SPL are Produced Ref: ENSR Australia Report 1 May Environmental Assessment: Construction and Operation of a Spent Potliner Processing Facility, Tomago

5 Spent Potlining (SPL) Potlining life 6-7 years Cathode carbon porosity 10-25% Approx 30% of SPL is penetrated salts. Contaminatants include: NA 3 AlF 6, NaF, CaF 2, AIN, Al 4 C 3, NaCN. Fluorides and Cyanides of specific environmental concern; Na( S ) and Al 4 C 3 react with water to form H 2 and CH 4 ; Typically SPL contains approximately 25% fluorides with AlN and Al 4 C 3 approximately 1-2% and NaCN varying between %; Found in both SPL carbon (first cut) and SPL Refractory (second cut); SPL is one of the Aluminium Industry s major environmental concerns. Major recovery potential fluorides and energy content. Landfill disposal has created many problems.

6 Methods for Handling or Treatment of SPL Landfill: - Controlled landfill inland. - Controlled landfill at the seashore. Disposal techniques: - Combustion for power-generating purposes. - Slag additives in iron- and steel industry. - Fuel and mineral supplement in cement manufacture. - Conversion to inert landfill materials. - Red brick ceramic products. Recovery or recycling techniques: - Graphite recovery. - Cathode carbon additives. - Anode carbon additives. - Fluoride recovery from leaching processes. - Pyrohydrolysis. - Pyrosulpholysis. - Silicopyrohydrolysis. Ref: Energeia Vol 5 No 1, 1994 CAER University of Kentucky, Center for Applied Energy Research.

7 In 2009 the SPL global generation rate was estimated to be 1.7Mtpa. In 2008 approximately 35% of SPL reported to be recycled. 60% deposited as treated residue or stored pending final deposition or recycling. Major barrier to supply of SPL as a feedstock has been economics.

8 Uses of SPL Energy savings in the brick and cement industries; Beneficial fluxing properties in the brick, cement and steel industries; Enhances strength development from cement. Recycle into cathodes, and anodes for use in the aluminium ramming paste industry; Fluorides recovery (cryolite).

9 Regain Process 3 Stage process: Preparation (sorting, crushing and grinding); Heat treatment (heat treatment followed by exposure to air and water); Grinding and blending (coal, sand etc) to achieve end user specifications.

10 SPL Treatment Process Flow Diagram Ref: ENSR Australia Report 1 May Environmental Assessment: Construction and Operation of a Spent Potliner Processing Facility, Tomago

11 Environmental Controls Maximum process temperature 850 o C to minimise fluoride emissions. Thermal destruction of CN. Recovery of hazardous gases for use in primary combustion. Control of fugitive emissions by maintaining process buildings under negative pressure. Control of process particulate emissions by use of baghouses. Process interlocks to maintain effective operation.

12 Air Emissions Total Particulates; Fine Particulates; Sulphur Dioxide; Hydrogen Fluorides; Oxides of Nitrogen; Polycyclic Aromatic Hydrocarbons; Dioxins and Furans; Cyanides.

13 Pollutant Emission Concentrations Ref: ENSR Australia Report 1 May Environmental Assessment: Construction and Operation of a Spent Potliner Processing Facility, Tomago

14 Pollutant Emission Rates (Based on a 20,000tpa Plant) Ref: ENSR Australia Report 1 May Environmental Assessment: Construction and Operation of a Spent Potliner Processing Facility, Tomago

15 Air Quality Impact Assessment Assumptions Locate SPL Treatment facility within existing aluminium smelter; Stack Heights metres, temperature of discharge 50 o C. AUSPLUME v6.0 dispersion model; Inputs required include meteorology, terrain, building dimensions, emission source characteristics and emissions inventory.

16 Modelling Results (maximum modelled GLC) Ref: Air Quality Impact Assessment 27Mar09

17 Modelling Results (maximum modelled GLC) Ref: Air Quality Impact Assessment 27Mar09

18 1 Hour Maximum SO2 Isopleths Ref: ENSR Australia Report 1 May Environmental Assessment: Construction and Operation of a Spent Potliner Processing Facility, Tomago

19 24 Hour Maximum HF Isopleths Ref: ENSR Australia Report 1 May Environmental Assessment: Construction and Operation of a Spent Potliner Processing Facility, Tomago

20 1 Hour Maximum Cyanide (as CN) Isopleths Ref: ENSR Australia Report 1 May Environmental Assessment: Construction and Operation of a Spent Potliner Processing Facility, Tomago

21 CONCLUSION Regain s SPL treatment process can operate well with legislative emission limits to produce a valuable mineral product that is suitable for reuse. The operation of the SPL treatment facility does not have an adverse environmental impact. The Regain process converts the hazardous SPL material into a valuable mineral product suitable for reuse.

22 Thank You addresses: