Originally published in... ALUMINIUM 89 (2013) 1/2

Transcription

1 Originally published in... ALUMINIUM 89 (2013) 1/2 Dubal Möller direct pot feeding system for greenfield and brownfield smelters

2 A L U M I N I U M s m e l t i n g i n d u s t r y Möller direct pot feeding system for greenfield and brownfield smelters C. Duwe and T. Letz, FLSmidth Hamburg FLSmidth is a market-leading supplier of equipment and services to the global minerals and cement industries. With more than 15,000 employees, FLSmidth is a global company with headquarters in Denmark and local presence in more than 50 countries including project and technology centres in Denmark, India, USA and Germany. Over the past 130 years FLSmidth has developed a business culture based on three fundamental values: competence, responsibility and cooperation. For the alumina and bauxite industries the company offers complete bauxite handling, storage, crushing, grinding and settling on the red mud side, as well as conveying and storage systems on the white side. Today s aluminium smelter industry requires the most economical, reliable and environmentally friendly systems in each part of the smelter. The electrolysis cells (pots) in all modern greenfield smelters are already or will be equipped with closed pot feeding systems. Brownfield smelters, which still mainly use the open type crane feeding technology, seem more in need of changes to the closed pot feeding system after examining modernisation projects. The Möller direct pot feeding system is an innovative system that ensures constant and reliable feeding of secondary (fluorinated) alumina to each ore bunker of the electrolysis cell. Since the first installations at Vereinigte Aluminium Werke (VAW) in Hamburg, Germany, and at Aluminij Mostar in Bosnia-Herzegovina, the design has continuously been improved in order to fulfill a wide range of requirements. These improvements include a flexibility for use in both greenfield and brownfield smelters. This paper presents the general design and latest improvements of the Möller direct pot feeding. This system will be installed in the Emirates Aluminium (Emal) Phase 2 greenfield project in Taweelah, Abu Dhabi, and in a brownfield project at Alcasa in Venezuela. General description The vent air from the electrolysis cells is evacuated via gas ducts to the Gas Treatment Centres (GTC) where primary (fresh) alumina absorbs many of the emissions. During this cleaning process the primary alumina becomes secondary alumina and is stored in silos, near the potrooms respective GTCs. From the secondary alumina silos the direct pot feeding system transports the secondary alumina pneumatically to each of the electrolysis cells. The fully automatic and absolutely dust-free feeding process can be either continuous or discontinuous, and it works independently from the potroom cranes. The smooth-working Möller direct pot feeding system combines the Möller Turbuflow dense phase and Möller Fluidflow pipe air slide transport system to take the secondary Fig. 1: Process flow diagram, Möller direct pot feeding system complete with Möller Fluidflow pipe air slides FLSmidth Möller

3 S P E C I A L Fig. 2: Möller rotary flow control valve and material trap Fig. 3: Möller Fluidflow pipe air slide from secondary alumina silo to potroom wall; main bin and Möller Fluidflow pipe air slide along potroom (Dubal) alumina from the storage silo to distribution pieces at the electrolysis cells. From there the Möller Fluidflow pipe air slide feeding system takes alumina to each of the ore bunkers of the electrolysis cells. The Möller Turbuflow dense phase conveying and the Möller Fluidflow pipe air slide are both well proven transport technologies which have established itself because of its superior performance record. Highlights of the Möller direct pot feeding system complete with Möller Fluidflow pipe air slides are: Highest possible performance and reliability of continuous feeding of the electrolysis cells for almost all kinds of secondary or primary alumina qualities by Möller Fluidflow pipe air slide Gas-tight pot feeding system by Möller Fluidflow pipe air slide (no dust emission from flange connections) No generation of fines, no segregation and no scaling Lowest possible (over-)pressure Self-regulating system by filling level in ore bunkers of cells Works independently of any slight overpressure or slight under-pressure in the ore bunkers of the electrolysis cell Quickest possible (emergency) refilling of the ore bunkers of the electrolysis cells by Möller Fluidflow pipe air slides and high performance fans or blowers ( bar) Lowest possible emission to GTC gas duct No pulsation in the Möller Fluidflow pipe air slide along the potroom and on top of each cell Independent of the filling level of the buffer silo Minimised energy consumption. Low fluidising air amount and energy consumption by use of frequency controlled fans or blowers Minimised maintenance work as well as minimised amount of spare parts. Functional description and design features Fig. 4: Möller distribution pieces and vent dome Silo discharge including material trap: The secondary alumina is discharged via Möller rotary flow control valve and Möller Fluidflow pipe air slide, generally from the secondary alumina silo at the GTC, and transported to the so-called main bin. A specifically designed material trap is installed to avoid any foreign particles entering the direct pot feeding system. In greenfield aluminium smelters, vibrating screens

4 A L U M I N I U M s m e l t i n g I N D U S T R Y in the GTC system already remove most of the coarse material (e. g. from scaling effects). However, in brownfield aluminium Fig. 5: Single-feed design Fig. 6: and double-feed design of the Möller direct pot feeding system smelters the existing installation situation may not have enough space in which to install vibrating screens. To address this, FLSmidth Fig. 7: Variable design of the Möller Fluidflow pipe air slide on top or inside of the electrolysis cell enhanced the design of the material trap in order to include the process function of a vibrating screen. The Möller direct pot feeding system can generally be installed at every brownfield smelter presently operating with a crane feeding system. Main bin: The main bins normally one main bin is used for each half of a potroom are located right next to the potroom wall. The main bins are always 100% filled, and the resulting material column ensures a continuous mass flow of secondary alumina to all electrolysis cells, especially to the last cell at the end of the Möller Fluidflow pipe air slide along the potroom. Because of the well-defined height of the main bin, the Möller direct pot feeding system is independent of the filling level of the secondary alumina silo. Whether the secondary alumina silo is full, half full or nearly empty, the conveying capacity of the Möller direct pot feeding system stays the same. Given the sufficient height between the outlet flange of an existing secondary alumina silo and the superstructure of the electrolysis cell, then the Möller Fluidflow pipe air slide can also be installed along the potroom with an appropriate declination (downhill slope) without a main bin. Distribution pieces and vent domes: From the main Möller Fluidflow pipe air slide along the potroom the secondary alumina is transported via the distribution pieces into the potroom, and then to the electrolysis cells. According to the design requirements, a sufficient number of vent domes will be installed on top of the distribution pieces. All necessary venting domes are connected to the gas duct of the GTC. Each of the above described distribution pieces can be connected to one (single-feed), two (double-feed) or even more electrolysis cells (multi-feed), as per customer requirements resp. installation situation. Superstructure design requirements: Each superstructure is specially designed as part of the electrolysis cell s technology. Generally, the state-of-the-art electrolysis cell technologies already ensure sufficient space for a direct pot feeding system. However, clients have different requirements regarding free access for crust breakers, dosing devices and the option for removing the ore bunkers during operation, and these factors influence the final design of the Möller Fluidflow pipe air slide to be installed on top or inside of the superstructure of the electrolysis cell. The self-regulating and continuous filling process of the ore bunkers of an electrolysis

5 S P E C I A L A L U M I N I U M s m e l t i n g I N D U S T R Y cell by the Möller direct pot feeding system is simply ingenious. If the ore bunker is full, then the material cone level has reached the filling spout discharge opening of the Möller Fluidflow pipe air slide, and the mass flow is blocked automatically. As soon as secondary alumina is removed from the ore bunker of the electrolysis cell, the pneumatic transport starts again automatically and ensures a constant and reliable mass feed rate to the pots. The fluidising of the secondary alumina inside the Möller Fluidflow pipe air slide works permanently to ensure a constant bulk density. Fluidisation air equipment: The fluidisation air requirements for the Möller Fluidflow pipe air slide along the potroom and on top of the electrolysis cells are different in regard to the fluidisation air pressure and the specific fluidisation air amount. Therefore, the Möller direct pot feeding system uses two different fluidisation air sources which can either be frequency controlled rotary piston blowers or fans. This design allows minimised energy consumption during operation down to the necessary minimum amount as well as minimised fluidisation air vented into the GTC s gas duct. Conclusion The necessary flexibility of a closed pot feeding system to serve greenfield and brownfield aluminium smelters had already to be considered by FLSmidth Hamburg when the Möller direct pot feeding system was introduced at VAW in Hamburg in 1997, and at Aluminij Mostar, Bosnia-Herzegovina in In particular, the latest contracts for Emal Phase 2, Abu Dhabi (greenfield), and Alcasa, Venezuela (brownfield), have proven the system s high adaptability with great success. This system is designed to ensure a constant and a reliable feed into the ore bunkers of the electrolysis cells at the highest possible standard. The lowest possible conveying velocities preserve the particle size distribution as well as the flow ability of the secondary alumina without any scaling effects. This most competitive system is superior by minimising wear and maintenance as well as energy consumption, and last but not least by its high operating reliability. Fig. 8: Self-closed filling spout and filling process of the ore bunker Higher performance with MÖLLER Alumina handling systems DUBAL Through MÖLLER technology, FLSmidth specializes in design, engineering, procurement, erection and commissioning of pneumatic material handling systems for turnkey projects and components for the Alumina Industry. For more than 75 years the MÖLLER brand has stood for high quality standard systems with more than references worldwide. MÖLLER Alumina handling systems - High performance, high efficiency. Visit us at the TMS 2013 in Booth #212 FLSmidth Hamburg GmbH Haderslebener Str Pinneberg, Germany Tel: hamburg@flsmidth.com

6 A L U M I N I U M s m e l t i n g i n d u s t r y Contract Client Smelter Type System description 2001 Aluminij Mostar brownfield 256 pots, 130 kg/h/pot (double-feed), potroom length 600 m 2006 Dubal, Potline 8 greenfield 40 DX pots, 210 kg/h/pot (double-feed) IMIDRO, Hormozal Aluminium Smelter Rusal/Hydro, Boguchany Aluminium Smelter Rusal, Taishet Aluminium Smelter greenfield greenfield greenfield 2012 Emal, Phase 2 greenfield 2012 CVG Alcasa, Potline 3/4 brownfield 228 D20 pots, 170 kg/h/pot (double-feed), potroom length 720 m 672 RA300 pots, 200 kg/h/pot (double-feed), potroom length 1,050 m 672 RA400 pots, 200 kg/h/pot (double-feed), potroom length m 444 DX+ pots, 480 kg/h/pot (single-feed), potroom length 1,520 m 400 pots, 480 kg/h/pot (single-feed), potroom length 700 m Tab. 1: Möller direct pot feeding system references in operation or under construction; all secondary alumina In close co-operation with clients around the world, FLSmidth Hamburg has offered and contracted various tailor-made solutions for the use of a Möller direct pot feeding system. Please contact the authors for more detailed information or to obtain support regarding specific projects. Authors Dipl.-Ing. Carsten Duwe is head of Technical Department and Dipl.-Ing. Timo Letz is area sales manager of FLSmidth Hamburg GmbH, based in Pinneberg, Germany. Contact: carsten.duwe@flsmidth. com; timo.letz@flsmidth.com FLSmidth Hamburg GmbH Haderslebener Straße Pinneberg Germany Tel Fax Hamburg@flsmidth.com