Electrode Technology: Baking Furnace/Electrode Design
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: Houshang Alamdari, Laval University

Wednesday 8:30 AM
March 1, 2017
Room: 1B
Location: San Diego Convention Ctr

Session Chair: Donald Ziegler, Alcoa

8:30 AM Introductory Comments

8:35 AM  
Flow Detection Module – A New Model to Predict the Flow in Open Pit Anode Baking Furnaces: Detlef Maiwald1; Domenico Di Lisa1; Frank Heinke1; Florian Krummrich1; 1Innovatherm
    The continuous measurement of the flow inside the flues of baking furnaces is still a challenge and not solved. As a substitute, the draught is measured in one position of each flue to determine the existence of a volume or flow. Knowing the real flow would be of the essence for a more accurate and optimized control of the combustion inside the furnace. A mathematical model for flow detection, based on fuzzy logics was developed to determine the actual flow in each flue. With the introduction of this flow detection module, each flue in a furnace is continuously evaluated. The on-line mathematical model calculates the actual flow in each flue by correlation of the relevant process data available in the firing system. As a result, the baking process is further optimized for lowest emissions and best fuel efficiency. The paper illustrates the mathematical approach and shows the results.

9:00 AM  
Formation of Carbon Build-Up on the Flue Wall of Anode Baking Furnace: Zhaohui Wang1; Arne Petter Ratvik1; Tor Grande2; Stein RÝrvik1; 1SINTEF Materials and Chemistry; 2Norwegian University of Science and Technology
    A hard carbon build-up layer often formed on the flue wall surface in anode baking furnaces. The layer accumulated over thermal circles and regularly needed to be removed mechanically to ensure sufficient space for the anodes between flue walls. The underlying mechanisms are still unknown, but the extent of the carbon build-up varies from plant to plant. Build-up on the flue wall from an autopsy of an open top furnace has been studied. Microstructure and phase compositions of carbon build-up, especially at the refractory interface, have been studied by optical microscopy, X-ray computed tomography, SEM/EDS, and XRD. Pyrolytic carbon was found to be the main carbon source in carbon build-up layer. The transport of silicon source from the refractory material to the flue wall surface is proposed to contribute to the formation of carbon build-up. Proposed formation mechanisms of carbon build-up and the reaction schemes are supported by thermodynamic calculations.

9:25 AM  
Investigation of Spent Refractory Lining in an Anode Baking Furnace: Trond Brandvik1; Zhaohui Wang2; Arne Petter Ratvik2; Tor Grande1; 1Norwegian University of Science and Technology, NTNU; 2SINTEF Materials and Chemistry
    The refractory lining in anode baking furnaces is exposed to harsh chemical environment and thermal cycling. Here, we report on an autopsy of spent refractory lining in an anode baking furnace after 4000 days operation. Variation in the density and porosity across the bricks revealed carbon build up in pores had taken place towards the anode side. The spent refractory bricks were investigated with respect to chemical and mineralogical composition by X-ray diffraction, optical and electron microscopy. No significant change in the mineralogical composition across the brick could be detected by X-ray diffraction. Fluoride was not found in the bricks, while traces of sodium was shown to accumulate together with calcium impurities in the bricks. The changes in the chemical and mineralogical composition across the bricks are discussed in relation to possible chemical reactions taking place during anode baking.

9:50 AM  
25 Years of Naural Gas Purged Infrared Pyrometer Temperature Measurement For The Operation Of Open-Top Anodes Baking Furnaces: Yvon Menard1; 1Retired Process Specialist
    To improve a low flue walls life, a natural gas purged infrared pyrometer system was implemented to replace original thermocouples based temperature measurement system on firing system, in 1991. Flue wall life increased to be over 100 cycles, on Pechiney furnaces, by preventing flue walls overheating. Anodes baking quality is adequate for two burners ramps fire technology. Some problems had to be corrected over time as they appeared: calibration drift, pinched injector tubes, frosted pyrometers lenses, etc. Pyrometers and thermocouples measurement technologies can both successfully bake anodes to specifications, but original cost, ease of operation, ease of maintenance and effect on refractory may favor one system over the other, depending on plant situation.

10:15 AM Break