Aluminum Reduction Technology: Dry Scrubbing, Alumina Transport and Dissolution
Sponsored by: TMS Light Metals Division, TMS: Aluminum Committee
Program Organizers: Mark Dorreen, Light Metals Research Centre, The University of Auckland
Wednesday 8:30 AM
March 1, 2017
Location: San Diego Convention Ctr
Session Chair: Nancy Holt, Hydro Aluminium AS
8:30 AM Introductory Comments
Influence of Handling Parameter on Powder Properties: Peter Hilgraf1; Jan Paepcke2; Arne Hilck2; 1HAW University of Applied Science; 2Claudius Peters Projects
Handling and conveying of powderous material needs a detailed knowledge of the powder properties itself combined with the knowledge how the conveying and handling effects the powder properties. Ideally there is no measurable effect on the powder. For intermediate storage in the plant and Material Distribution Systems alongside the pot room these effects need to be considered. In this paper the influence of various parameter of pneumatic conveying on the material properties is described. Comprehensive tests have been done to evaluate the influence of changes in conveying parameters on the material and vice versa. This paper concludes technical features presented on earlier TMS Annual Meetings and compares them with results from practice. To determine these effects in more depth for Alumina tests have been undertaken with systematically varied material compositions. These data are compared with material data from other industries with the aim to give general conclusions for the material handling.
Spreading of Alumina and Raft Formation on the Surface of Molten Cryolite: Csilla Kaszás1; Laszlo Kiss1; Sandor Poncsak1; Jean-Francois Bilodeau2; Sebastien Guerard2; 1Univeristé du Québec à Chicoutimi; 2ARDC Rio Tinto Aluminium
It is a well-known phenomenon in aluminium industry that alumina powder, fed into the electrolyte, tends to stay afloat on the surface of the bath. This hinders dispersion and direct contact of some of the powder with the electrolyte, therefore delays dissolution. In addition, large clusters of alumina particles sintered together during raft formation might lead to the agglomerate piercing through the bath-aluminium interface, which should be avoided. Since the perturbation of raft formation is so significant, it is a process that deserves more attention. Several experiments were conducted in a small carbon crucible in which cryolitic bath was melted and alumina with different properties was fed. The injections were recorded by a video camera above the bath. The spreading of the powder on the surface, the infiltration of powder by the bath as well as the disintegration or the sinking of the raft was observed and the results analysed.
Fluoride Capture Capacity of SGA: The Interplay between Particle and Pore Size Distribution: Gordon Agbenyegah1; Grant McIntosh1; Margaret Hyland2; James Metson3; 1Light Metals Research Center; 2School of Engineering, University of Auckland; 3School of Chemical Sciences, University of Auckland
The Bayer process, storage and transport of smelter grade alumina (SGA) together contribute to the unique particle size distribution of the SGA as received in a gas treatment facility or in a reduction cell hopper. Pore size distribution analyses of alumina fractions indicate that the +125μm, +90μm -125μm, +63μm -90μm and +45μm -63μm particles possess similar total pore volumes. The total pore volume of -45μm particle size fraction was found to be approximately 15% lower than the remaining bulk. Having earlier studied the evolution of pore size distribution in the bulk SGA during fluoride scrubbing, this work examines the interplay between particle and pore size distributions, with focus on the impact of fines on scrubbing efficiency in a smelter GTC.
Predictive Formula for the Competitive Adsorption of HF and SO2 on Smeltergrade Alumina Used in Dry Scrubbing Applications: Stephan Broek1; Neal Dando2; Stephen Lindsay3; 1Hatch Ltd; 2Alcoa Technical Center (retired); 3Alcoa Primary Metals
Smeltergrade alumina (SGA) is the preferred agent for recovering HF from aluminum smelter ventilation gas streams since the alumina also serves as feed to the electrolysis cells, thereby allowing return of the recovered fluoride to the process. This alumina-based recovery loop includes sulfur, since SO2 evolved from cells is also adsorbed on SGA that is not completely saturated by HF. Previously, Dando and Lindsay reported on the competitive adsorption of HF and SO2 on smeltergrade alumina by investigating the temporal breakthrough behavior of both HF gas and SO2 gas to quantify the two physically different mechanisms behind adsorption of both gases on the same particle of alumina. In this paper follow on work is reported where this research data is converted into usable, empirical formulae and examples of applications that may be useful to engineers and technicians in making predictions on the removal of SO2 in a alumina dry scrubber.
10:15 AM Break
Pot Gas Treatment at High Gas Temperatures: Anders Sorhuus1; Sivert Ose1; 1GE Power Norway
HF regeneration due to submicron fluoride particles trapped inside the filter cloth reacting with the humidity in the pot gas is one likely mechanism that explains why the HF emissions increase with gas temperature and humidity in the dry scrubbers. A significant temperature effect is observed and gas cooling is in many smelters today necessary to keep the emissions under control. The GE heat exchanger (HEX) technology is one of the technologies that are now built and operated in full scale several places in the world. Results from the first full scale GTC installation document the positive effect of the cooling for the Abart GTC technology installed. The HEX cools the temperature with more than 25C down to less than 110C and HF emissions in the range 0,2 to 0,3 mg/Nm3 are measured at ambient temperatures higher than 40C, and high humidity.
Potroom HF Emission Reduction by Anode Inert Tray Technology Performances of ALRO Industrial 1st of Class: Vincent Verin1; El Hani Bouhabila1; Jérémy Neveu1; Serge Despinasse2; Gheorghe Dobra3; Marian Cilianu3; Fabienne Virieux4; 1Fives Solios; 2Fives ECL; 3VIMETCO ALRO; 4Fives Aluminium Division
Today, in the electrolysis area of modern aluminium smelters, pot gas emissions are very efficiently treated by the latest generation of dry scrubbing technologies such as Ozeos, with rates close to 99.8%. As a consequence, stack emissions only represent a very small amount of the total Fluorides emitted over the entire smelter. Indeed, most of the HF is released to the atmosphere directly from the potroom, where in many smelters no specific treatment is provided to limit emissions related to maintenance activities (pot hoods opening, spent anodes removal, etc.). Fives now proposes a solution to eliminate emissions coming from hot spent anodes stored in potroom thanks to an Anode Inert Tray (AIT) which confines butts. This paper presents the performances of the industrial first of class AIT developed conjointly between Fives Solios and Fives ECL and which has been operated by ALRO for several months.