Excellence through innovation. Recent developments of DUBAL aluminium reduction cell technologies

Transcription

1 Excellence through innovation Recent developments of DUBAL aluminium reduction cell technologies

2 Recent developments of DUBAL aluminium reduction cell technologies Michel Reverdy Dubai Aluminium (DUBAL), PO Box 3627, Dubai, UAE Introduction Dubai Aluminium (DUBAL) commenced operation in 1979 with an annual capacity of 90,000 tonnes and has progressively grown to over one million tonnes reached in 2010, predominantly using its in-house developed D18, D20, CD20, DX, DX+ and D18+ cell technologies. The number of cells and annual capacity of these technologies is shown in Table I. DX cell technology started in 2005 with five prototype cells, followed by a 40 cell demonstration potline of 40 cells at DUBAL in Implementation on a large industrial scale was at EMAL Phase I with two potlines and an initial annual capacity of 750,000 tonnes. DX cells have operated at 385 ka at DUBAL since March 2012 and at 380 ka at EMAL since September 2012 [1-3]. Five DX+ cells were started in July 2010 at DUBAL at 420 ka and are now operating at 440 ka now. One potline of 444 DX+ cells is currently under construction at EMAL Phase II, which shall be started in 2013/2014 at 440 ka and is designed for a future potential of 460 ka. D18 cells were recently completely redesigned for 210 ka and low energy consumption, resulting in seven D18+ pilot cells, started up in March 2012 at 200 ka because there is no booster for this group of cells. Recent development and results of DX+ and D18+ cell technologies will be described in this paper. Table I. Cell technologies at DUBAL Reduction cell technology Amperage (ka) Number of cells Capacity (kt/y) D D CD D DX DX TOTAL 1,573 1,039 DX+ Cell Technology DX+ cell technology is an evolution of the DX technology for high productivity and lower capital cost per installed tonne of capacity [4 5]. Five DX+ demonstration cells in DUBAL Eagle Section are shown in Figure 1. The key performance indicators (KPI s) are given in Table II. DX+ cells were designed utilising in-house, commercial software-based mathematical models that were developed in recent years at DUBAL. These comprise thermo-electric, magnetohydrodynamics (MHD), mechanical, cell gas exhaust and potroom ventilation models. The models were originally validated on operational DX cells and re-confirmed on operational DX+ cells [6]. The alignment between the models and measurements is excellent, instilling Figure 1. Five prototype DX+ cells in the demonstration section at DUBAL. confidence to use these models for further optimization and development of DUBAL cell technologies. In addition to increased amperage and higher metal production per day, DX+ technology is optimized in many other ways with respect to its sister DX technology. In spite of increased length and width, the mass of the DX+ optimized potshell was reduced by 21% without any reduction in strength due to improved structural characteristics of the design. The cell superstructure height was lowered by more than 400 mm and in spite of its increased size, its mass was decreased by 12%. The overall volume of the concrete in the potshell and busbar supports was reduced by 35%. Considering the amperage increase to 440 ka, the productivity of potroom in tonnes of aluminium per square meter of covered building was increased by 16% to 7.12 tonnes of aluminium produced per square meter of covered building, calculated for 360 cells and one central passage per potroom. CAPEX improvement is the result of cell productivity, which is proportional to amperage and of the increase of number of cells per potline as the result of higher rectiformer voltage of 2,000 V DC. Further optimisation is under way. The design of DX+ busbars has already been optimized and the results are: decrease of cell centreline distance by approximately 5%, reduction of busbar mass by 20% and reduction of busbar voltage drop by 26%. Reduced cell to cell distance increases the building productivity by 4.6%. In Table I, the actual voltage and corresponding specific energy consumption are corrected for the expected improvements due to design changes in the industrial DX+ cells to be installed at EMAL Potline 3 with respect to demonstration cells. These improvements include larger cross-sections of busbars and cathode collector bars. A substantial voltage gain has been obtained with the introduction of four-stub anodes at the end of 2011 instead of the three-stub 2

3 Table II. KPIs of DUBAL DX+ Technology average of the five cells. KPI Unit Dec 10 to July 11 Aug 11 to Feb 12 Mar 12 to Sept 12 1 Oct 12 to 21 Nov 12 Amperage ka Current efficiency % Metal production kg/pot-day 3,214 3,291 3,345 3,366 Volts per cell V 4.22* 4.22** 4.24*** 4.24*** DC specific energy kwh/kg Al 13.22* 13.25** 13.37*** 13.37*** Net carbon consumption kg/kg Al Fe % Si % AE frequency AE/pot-day AE duration s CO 2 equivalent**** kg/t Al * Based on 4.35 V actual minus 0.13 V for design changes in the industrial version of DX+. ** Based on 4.32 V actual minus 0.10 V for design changes in the industrial version of DX+. *** Based on 4.31 V actual minus 0.07 V for design changes in the industrial version of DX+. **** CO 2 equivalent is calculated as in Reference [4], using the Tier 2 method. anodes previously used. This explains a different voltage correction for DX+ industrial cells for the four periods given in Table II. Excellent performance has been maintained in conjunction with amperage increase. As per tradition at DUBAL, the metal purity is excellent in DX potlines at both DUBAL and EMAL and in DX+ demonstration cells at DUBAL, with low iron and silicon content which did not deteriorate with amperage increase. Anode effect frequency and duration result in very low PFC emissions (expressed in CO 2 equivalent kg/ t Al in Table I) are a benchmark within the industry [7]. DUBAL has developed its own proprietary cell control system, comprising microcomputer based DCCU (DUBAL Cell Control Unit) and cell control software. DCCU has been progressively installed since 2005 in DUBAL and also in DUBAL licensed smelters with 1,276 cells equipped as of November Recently, a new hardware system, based on standard PLC (Programmable Logic Controller), has been developed and installed on the five DX+ demonstration cells. It has been also chosen for EMAL Phase II. Figure 2. Historical data on HMI. Increased Graphical User Interface (GUI) capabilities provide improved and more complete information to cell operators than the original control systems, which were generally text based and black and white. The new Human Machine Interface (HMI) provides the operators access to all required supervisory controls, data entries and information about the cells in the potroom. Two sample screen shots from HMI are shown in Figures 2 and 3. The HMI can also display various trend graphs for a period of 30 minutes to 8 hours (Figure 3). The PLC data are sent to the potline server where they are analysed and displayed in the same way as with Figure 3. Pot voltage trend graph on HMI. 3

4 DCCU based control system. Detailed pot traces and command interface can be obtained from ipots system hosted on a network server. In addition, user specified queries can be used in a new web based Smelter Analytics platform developed in-house to provide data in an exportable format to programs such as MS Excel. The new irpms reporting system, equipped with a web based interface for ease of navigation, provides information to the user from the potlines, carbon plant, casthouse etc., as well as various types of summary overviews to the senior management. D18+ Cell Technology The D18 technology is the result of DUBAL development of the P69 technology first installed in 360 cells in DUBAL in Subsequent additions brought the total number to the current 520. Further significant advances in operating performance are limited mainly by poor magnetic stability, alumina and AlF 3 feeding control and high anode current density. A new cell design, D18+ has been developed to modernise the original DUBAL D18 potlines and improve their performance and economic competitiveness [8]. The objectives behind modernizing the cells through new technology are to reduce the specific energy consumption to below 12.9 DC kwh/kg Al, reduce the anode effect frequency to below 0.10 per cell-day and allow for a possible further amperage increase of 40 ka. The constraints were: maintain the same cell-to-cell centerline distance and the same cell height, keep the amperage availability limits within the same rectifiers and use the same gas treatment centre. Table IV. D18+ and D18 performance comparison (D18+ is average of five middle pots). Amperage ka Current efficiency Metal production % , , Volts per cell V DC specific energy kwh/kg Al Fe % Si % AE frequency AE duration (V>8V) PFC emissions, CO 2 equivalent [4] KPI Unit D18+ D18 Difference kg/potday AE/potday s kg/t Al D18 cells. The test cells are currently being fully evaluated before implementing throughout DUBAL s D18 potlines. Seven D18+ cells were constructed and successfully started-up in March Table III gives a list of changes made during the transition from D18 to D18+ cell design. Additionally, the original potshell was modified to accommodate two more cathode blocks. Figure 3 shows the seven test cells. Table IV gives key performance indicators. The performance of the D18+ cells has now exceeded the original design targets, resulting in significant improvement over the existing Table III. Comparison between D18 and D18+. D18 D18+ Busbar configuration Al 2 O 3 feeding AlF 3 feeding Alumina distribution End risers Pseudo point feed converted from dual centre breaking 10 kg bags added manually Via crane hopper Four side risers with under cell bus Four point feeders with bath sensing breakers Dedicated AlF 3 feeders Dense phase system Number of anodes Anode beam control Number of cathode blocks Collector bar flexible connection Pneumatic Electric Bolted Welded Figure 4. Seven completed D18+ test cells in a D18 potline. Conclusion DX+ cell technology continues to give excellent performance with considerable amperage increase to 440 ka in DX+ pilot cells. The new DX+ Pot Control System is based upon standard market PLCs, which give increased HMI capabilities and insure easy maintenance and future development. The successful test and validation of the D18+ cell technology has proven that it is both technically and practically possible to update and replace the cell technology within an existing operating potline. Study of the feasibility and optimal engineering pathway is currently in progress to enable replacing the remaining 513 D18 cells with the D18+ technology. 4

5 References 1. Ali Al Zarouni et al., DX Cell Technology Powers Green Field Expansion, Light Metals 2010, B.K. Kakkar et al., Commissioning of Emirates Aluminium Smelter Potlines, Light Metals 2012, Ali Al Zarouni et al., The Successful Implementation of DUBAL DX Technology at EMAL, Light Metals 2012, Ali Al Zarouni et al., DX+ an Optimized Version of DX Technology, Light Metals 2012, Michel Reverdy et al., Advancements of DUBAL High Amperage Reduction Cell Technologies, Light Metals Abdalla Zarouni et al., Mathematical Model Validation of Aluminum Electrolysis Cells at DUBAL, Light Metals Abdalla Zarouni et al., Achieving Low Greenhouse Gases Emission with DUBAL s High Amperage Cell Technology, 19th International Symposium ICSOBA, Belem, Brazil, October 25 - November 2, Sergey Akhmetov et al, D18+: Potline Modernisation at DUBAL, Light Metals For more information, contact: Dubai Aluminium ( DUBAL ) P O Box3627, Dubai, United Arab Emirates Tel: , Fax: technology@dubal.ae 5