Electrode Technology: Electrodes: Raw Materials and Anode Quality
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: Houshang Alamdari, Laval University
Tuesday 2:00 PM
February 28, 2017
Location: San Diego Convention Ctr
Session Chair: Christopher Kuhnt, Rutgers Basic Aromatics GmbH
2:00 PM Introductory Comments
Influence of Calcination Temperature and Sulfur Level on Coke Properties: Victor Buzunov1; John Johnson1; 1JCG
The majority of RUSAL’s Russian smelters have to deal with challenges that are created by blending and calcining green cokes with varying chemical and physical properties and especially the problem associated with high-sulfur cokes. It has been widely reported in the literature that desulfurization, which occurs during petroleum coke calcination, negatively affects coke quality. To assess the risks of desulfurization and its influence on the coke physical structure, the Krasnoyarsk Aluminum Smelter RUSAL has run several experimental trials regarding the calcining of petroleum coke in an industrial rotary kiln at different temperatures. This paper discusses the physical changes calcined coke with different sulfur contents in an industrial rotary kiln where the real density and carboxy reactivity of high-sulfur coke are shown to be extremely dependence on temperature of calcination and non-predictable from 1,200oC to 1,350оC.
Pilot Anode Properties of Binder Pitches Softening between 110 and 150°C: Winfried Boenigk1; Christopher Kuhnt1; Jens Stiegert1; Joris Claes2; Les Edwards3; 1RAIN Carbon Inc. (dba) RÜTGERS Germany GmbH; 2RAIN Carbon Inc. (dba) RÜTGERS Belgium N.V. ; 3RAIN Carbon Inc. (dba) RAIN CII Carbon LLC
Today there is a growing trend towards the use of higher melting binder pitches in the manufacture of prebaked anodes. Although 110-112°C Softening point Mettler pitches are still the dominant quality for prebaked anodes, the use of 120M pitches is growing and some anode producers are even using 130M pitches on a routine basis. Due to their increased coking value, higher softening point pitches provide several property benefits over standard binders and total PAH levels are lower. Binders up to 150M can be still produced with conventional distillation technology and processing of these binders should be achievable in modern paste plants with relatively minor upgrades. Today’s generation of paste mixers are already capable of processing carbon paste up to 250°C. The paper gives an overview of binder properties in the range of 112-150M and presents the results of pilot anode testing with these binders.
2:55 PM Cancelled
Uniform Bulk Density for Calcined Petroleum Coke: Ravindra Narvekar1; Gajanan Bandodkar1; Jagmohan Chhabra1; 1Goa Carbon Ltd.
Aluminium Smelters are tightening bulk density specifications for Calcined Petroleum Coke while Refineries are sacrificing green coke densities at the cost of outputs. Previously Apparent Density using Mercury was popular for defining CPC density . But after A.D. testing was discontinued owing to environmental issues arising out of Mercury usage, each Smelter has come out with its own Bulk density measurement method and specs. We have Vibrated Bulk Density, Tapped Bulk Density and that too on a different size fraction viz 1 – 2 mm, -8 + 14 mesh , -20 + 35 mesh, uncrushed, crushed particles etc. The Calciners are confused and GOA CARBON LTD has made an attempt to analyse various Bulk Densities on various size fractions on crushed / uncrushed basis to see if there exists a co-relation internally among all the densities and with Mercury A.D.
Use of Thermally Desulfurized Shaft CPC for Anode Production: Les Edwards1; Kevin Harp1; Christopher Kuhnt1; 1Rain Carbon Inc.
Thermal desulfurization of petroleum coke during calcination is a well-known phenomenon and when practiced in rotary kilns, results in a significant increase in porosity and decrease in bulk density. In 2011, Rain Carbon began experimenting with thermal desulfurization in a shaft calciner. Some results were unexpected, particularly the steady increase in real density as the temperature and degree of thermal desulfurization increases. The paper reports on the results of extensive work to explore the fundamental differences between desulfurization in shaft calciners and rotary kilns. Numerous pilot anode studies have been completed to establish the potential of using thermally desulfurized coke from shaft calciners in anode production. The attraction here is both commercial and operational. High sulfur cokes are more readily available and cheaper than low sulfur cokes and removing SO2 during calcination is much more efficient than removing SO2 from low concentration, high volume potroom exhaust-gas streams.
3:45 PM Break
Anode Carbon Aggregate Packing Description Compared to Relevant Industrial and Engineering Practises: Bjarte Oye1; Lorentz Lossius2; 1SINTEF; 2Hydro Aluminium
The primary aluminium metal production carbon anode is a high volume product even on the global scale, which can benefit from optimising the aggregate packing. The general impression from literature is that the industry employs relatively simple methods for particle sizing, modified and enhanced by specific knowledge about the materials in question. The study lists examples of current and possible methods for measurement and control. The packing of given particle size distribution is substantially affected by surface roughness and particle shape, factors that normally is addressed empirically. The civil engineering sector uses simple methods for particle sizing, relying on empirical knowledge of the materials. Typically, the Fuller curves - which is a based on sieving - are used: Cumulative % finer than= √(((particle diameter)⁄(maximum particle diameter))) ∙100% Ceramic industry generally involves smaller particle size than anode carbon, and liquid content and factors affecting particle surface effects are important.
CPC Testing and Relationship between Coke and Anode Physical Properties: Marvin Lubin1; Kevin Harp1; Les Edwards1; Christopher Kuhnt2; Winfried Boenigk2; 1Rain Carbon Inc. (dba) Rain CII Carbon; 2Rain Carbon Inc. (dba) RÜTGERS Germany GmbH
Rain Carbon completed its 20th global CPC round robin (RR) in 2016 with five CPC samples covering a wide range of chemical and physical properties as well as both rotary kiln and shaft calcining technologies. Twenty-three labs participated in the RR and the paper summarizes repeatability and reproducibility data for the different test methods. Particular emphasis was given to bulk density testing. Pilot anodes were prepared with each coke to examine the relationship between coke bulk density, anode density and other anode physical properties. The study generated some interesting findings with respect to bulk densities measured on naturally occurring coke particles. As coke particle size increases, particle shape has a greater influence on the bulk density result. An alternative envelope density test gives a more reliable indicator of anode density. The paper also provides an update on a new ASTM bulk density test being developed.
Effect of Coke Properties on the Bubble Formation at the Anodes during Aluminium Electrolysis in Laboratory Scale: Wojciech Gebarowski1; Arne Petter Ratvik2; Stein Rørvik2; Lorentz Petter Lossius3; Hogne Linga3; Ann Mari Svensson1; 1Norwegian University of Science and Technology; 2SINTEF Materials and Chemistry; 3Hydro Aluminium
The anodic reaction of aluminium electrolysis cells leads to the formation of CO2 bubbles, which partly screen the anode surface and leads to an increase in the cell voltage. An advantage of these bubbles is that the formation and release contribute to the stirring of the electrolyte, however, the screening of the surface increase in the irreversible energy losses. More profound knowledge about behaviour of gas bubbles related to anode properties is useful for minimize the screening effect and thus reduce the additional cell voltage. This work focus on the voltage oscillations caused by the formation, growth and release of bubbles at different carbon anode surfaces in lab-scale electrolysis experiments. The oscillations are correlated to properties of the cokes and the anodes, like coke isotropy, anode wettability determined by immersion-emersion tests, and coke fractions. Additionally, computed x-ray tomography imaging is used for investigation of post electrolysis anode surfaces.
Coke Produced from Lower-Oxygen Fast-Pyrolysis Oil, a New Approach to Produce Renewable Anode Raw Materials: Yaseen Elkasabi1; Hans Darmstadt2; Akwasi Boateng1; 1Eastern Regional Research Center, Agricultural Research Service, U.S. Department of Agriculture; 2Rio Tinto Alcan
Carbon anodes are presently produced from petroleum-derived coke and coal tar pitch. Upon consumption of these anodes, some 1.5 t CO2/ t Al are generated. This considerable footprint could be reduced by using biomass-derived coke. It was suggested to manufacture coke from biomass char. However, the corresponding cokes typically contained undesired oxidation catalysts (alkali and alkaline earth metals), were high in oxygen (reducing carbon available for electrolysis), had undesired isotropic textures, and low bulk densities. In order to avoid these shortcomings, a new approach was studied: coking of biomass-derived oils from a fast pyrolysis process yielding lower-oxygen oil. The corresponding cokes are very low in undesired impurities (sulphur, vanadium, and nickel). Levels of oxygen, alkali and alkaline earth metals are acceptable. Using appropriate conditions, cokes with desired anisotropic textures can be made.