Technology

Process Steps

Figure 1 — Prebaked Carbon Anode production process schematics ^[4]

Step 1 — Raw Material Reception & Storage

• CPC received as purchased feedstock by rail, truck, or ship and stored in enclosed silos or covered stockpiles
• Coal tar pitch received as liquid (heated storage tanks at ~80°C) or as solid blocks for remelting
• Anode butt returns from the smelter potroom received, sorted, and inspected for contamination
• Conditions: CPC stored dry; liquid pitch tanks maintained at 70–90°C to prevent solidification

Step 2 — Crushing, Screening & Milling

• CPC and crushed anode butts processed through jaw crushers and roll crushers, then classified on multi-deck vibrating screens
• Fractions produced: coarse (4–14 mm), medium (1–4 mm), fine (0.2–1 mm), and flour (<0.2 mm)
• Flour produced by ball mill or impact mill to d50 ~50–80 µm
• Conditions: Ambient temperature; dust extraction on all transfer and screening points

Step 3 — Dry Aggregate Proportioning & Preheating

• CPC fractions and anode butt aggregate weighed gravimetrically per the anode recipe using automated batch weighers
• Butt content: typically 15–20 wt% of dry aggregate
• Blended dry aggregate preheated to 150–170°C in a screw preheater or fluidised bed preheater
• Conditions: Recipe controlled for optimum particle size distribution targeting maximum packing density and minimum void volume

Step 4 — Paste Mixing (Kneading)

• Preheated dry aggregate transferred to twin-shaft batch kneader or continuous Intensive Mixing Cascade (IMC, Fives ECL technology)
• Liquid coal tar pitch injected at 160–180°C; pitch content: 14–16 wt% of total paste mass
• Batch mixing time: 10–20 minutes; paste temperature maintained at 155–170°C throughout
• Rhodax^® 4D inter-particle compression technology (Fives) enables homogeneous paste at lower pitch content, improving baked density
• Conditions: Closed mixer with fume extraction; paste temperature monitored continuously

Step 5 — Green Anode Forming (Vibro-Compaction)

• Hot paste discharged at 145–165°C into steel mould on vibro-compaction press
• High-frequency vibration at 40–60 Hz at controlled amplitude consolidates paste into block form
• Green anode typical dimensions: 700–900 mm (L) × 500–700 mm (W) × 550–650 mm (H)
• Target green apparent density: 1.60–1.68 g/cm³
• Dynpac^® advanced compaction control (Fives) monitors and adjusts vibration parameters in real time
• Conditions: Mould temperature controlled; forming cycle 2–4 minutes per anode

Step 6 — Green Anode Cooling

• Green anodes transferred by conveyor to water spray cooling station or water pool conveyor
• Target exit temperature: <60°C before storage or baking furnace loading
• Cooling time: 30–90 minutes depending on anode size and cooling system design
• Conditions: Controlled cooling rate to avoid thermal cracking or pitch migration

Step 7 — Baking

• Green anodes loaded into pits of open-top ring furnace (dominant technology) with packing coke (filler) surrounding each anode block to prevent oxidation and support shape
• Furnace fire travels section-to-section; incoming sections preheated by hot flue gas from active baking sections (heat recovery)
• Baking temperature curve:
  • Drying & pitch softening zone: 100–400°C (slow ramp, ~5°C/h through softening point)
  • Carbonisation zone: 400–800°C
  • Final bake plateau: 1,050–1,200°C
• Full baking cycle duration: 160–280 hours
• Pitch volatiles (BTX, PAH) combusted in flue duct system and treated in Fume Treatment Centre (FTC)
• Conditions: Inert/reducing atmosphere within anode pits; furnace section pressure and temperature monitored continuously; packing coke recovered and recycled

Step 8 — Rodding Assembly

• Baked anodes cleaned by shot-blasting; quality inspected (apparent density, electrical resistivity, crack detection by ultrasonic testing)
• Stub holes pre-cleaned; steel stub/yoke assembly positioned and cast-in using liquid cast iron at ~1,300°C
• Completed rodded anode assemblies dispatched to smelter potroom
• Conditions: Cast iron temperature and pour volume controlled for joint integrity; cooling time before dispatch ~30 minutes

Equipment & Devices

Figure 2 — Prebaked Carbon Anode production block flow diagram ^[3]

References

1. International Aluminium Institute (March 2, 2022). Production process: Anode Production
2. Huanggang Huayao Zhonghui Kiln Company. Production line for prebaked anodes for electrolytic aluminum (Accessed Mar 5, 2026)
3. Mollaabbasi R., Hansen L., Grande T., Taghavi S.M., & Alamdari H. (May 2021). Effect of fine coke particles on rheological properties of the binder matrix of carbon anodes in aluminium production process. The Canadian Journal of Chemical Engineering, 100(S1), S58–S71. DOI: 10.1002/cjce.24108?
4. Fives. Green Anode Plant (Accessed Mar 5, 2026)
5. Riedhammer. Carbon Backing Furnaces (Accessed Mar 5, 2026)
6. Lang Guanghui, et al. Chinese patent CN107235728B: Energy-saving production process of prebaked anode. Jun 22, 2017 — Application filed by Sotong Development Co Ltd
7. Khaji K., & Al Qassemi M. (2015). Role of anode manufacturing processes in net carbon consumption. In Travaux 44, Proceedings of 33^rd International ICSOBA Conference (p. 445). Dubai, United Arab Emirates