awj14; dr. joachim heil

24 PRIMARY SMELTING AND PROCESSES

Aluminium Reduction Cell Technology Providers – a 2014 Review

IntroductionThis article is the second, updated edition of a paper published in the context of the European Metallurgical Conference 2011 (EMC2011), organized by GDMB of Germany. Special thanks go to my former colleagues, Dr. R. Minto and T. Heitling, who helped establishing the first edition which has been published in the EMC2011 conference proceedings [1].

Consultation of an article on the topic published in 2000 gave rise to the question who would be providing aluminium reduction cell technology today.

The referenced article elaborates on cell technologies developed by well-known companies which mostly have been in business for a long time, some since inception of the Hall-Héroult process. Potline current values cited in the article are in a range of 250 – 320 kA for the then latest technologies; further tiers of reduction current are the 150 – 200 kA range and anything below

that down to 50 kA, the latter mostly for an illustration of the historical evolution of the electric current as a qualifier for the advancement of reduction cell technology.

Since 2000, the global primary aluminium industry has grown at a remarkable rate of 5,5 % year-on-year: production capacity rose from 23,7 million tpy (Mtpy) in 2000 to 39,8 Mtpy in 2008, with a recess to some 37,5 Mtpy in 2009 in the aftermath of the financial crisis, just to rebound to 47,3 Mtpy in 2013. China has grown its share in the primary aluminium market from about 10 % in 2000 to some 21,5 Mtpy or 45 % of global supply in 2013, which is equivalent to almost all of the above increase in global production tonnage.

The same period has seen an equally unprecedented change amongst the players in the primary business: mergers and acquisition have led to a concentration of the industry into

fewer but bigger players. This trend along with management buy-outs, bankruptcies and changes of business strategy has led to the disappearance of quite a few of the traditional primary producers´ names including some of the long-established cell technology providers.

128 years after Hall and Héroult independently applied for their patents for the still unrivalled aluminium electrowinning process, this paper gives an updated review of who today would be developing and providing aluminium reduction cell technology to primary smelters, be it new greenfield or brownfield expansion projects.

1 Summary of Reduction Cell Technology as at Year 2000In early 2000, Tabereaux published a global review on prebake cell technol-ogy [2] in which he elaborated the then prevailing situation with regard to cell technology developers and operators. The article also included an overview

Company Cell Type UPBN I / kA Pots installed Year Remarks

Alcan A-275 AC-28 280 5 1981/92Test cells in Jonquière, shut down

A-310 AC-31 310 n. inv. n. inv.

Alcoa P-225 AA-23 225 n. inv. n. inv. Massena, Tennessee

A-817 AA-30 300 n. inv. n. inv. Portland

Alusuisse EPT-18 AS-18 180 n. inv. n. inv. Rheinfelden, closed 1991

Comalco-Dubal CD-200 CD-20 200 5 1990 Test cells at Dubal

Hydro HAL-230 HAL-23 230 n. inv. n. inv. Hoyanger, Venalum PL5 (1988), Slovalco (1995)

HAL-250 HAL-25 250 4 n. inv. Test cells in Ardal

Kaiser P-80 KA-18 190 6 1981 Test cells in Tacoma, shut down

Pechiney AP-30 AP-30 300 - 325 2040 + 720* n. inv. Various smelters, global spread

Reynolds P-20S RY-17 170 n. inv. n. inv. Alcasa, Alscon

P-23S RY-18 180 n. inv. n. inv. Test cells at Alcasa

VAW CA-180 VAW-18 180 115 1980 Upgraded Töging version now in Nordural, 120 pots

CA-240 VAW-24 240 5 1980/93 Test cells in Töging, shut down for CA-300 prototype

CA-300 VAW-30 300 3 1992/93 Test cells in Sayanogorsk, shut down**

Venalum V-350 VN-35 320 5 n. inv. Test cells

Russia/VAMIC-255 RU-26 255 n. inv. n. inv. Tajik, Sayansk, Volgograd

C-300 RU-30 300 3 1992/93 Test cells in Sayanogorsk, shut down**

China P-280 CH-28 280 n. inv. n. inv. Qingyang

P-320 CH-32 320 30 n. inv. Test cells, Pingguo

*: 720 cells under construction at that time**: VAW and Sayanogorsk jointly built and operated a test facility in Russia, each partner contributing 3 potsn. inv.: not investigated

Table 1: Most Advanced Reduction Cell Technologies as at the Year 2000, excerpts from [2]UPBN: Universal Prebake Cell Nomenclature, proposed by Tabereaux

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of the developmental steps taken by individual companies. This historic part of Tabereaux´s review will not be repeated here and interested readers are referred to the original source. For this update, only the 2000 spearhead cell technologies, in terms of highest amperage will be quoted as reference points. A condensed summary of those reduction cell technologies is pre-sented in Table 1.

Table 1 shows more than one entry for some companies and countries. The intention is to highlight the develop-ment potential that can be seen in operational test cells.

The original table further included companies Montecatini, Elkem, Sumi-tomo and Egyptalum as cell technology holders. These have been omitted here as their cell technologies are consid-ered outdated at publication in 2000, no progress is recognized since, or due to their solely local significance, all in the context of this article.

The 10 companies in possession of aluminium cell technology mentioned in Table 1 comprise the big traditional industrial names, four of which can even be traced back to the inventors of the Hall- Héroult (HH) process: Al-coa and Alcan are the direct result of Charles Hall´s entrepreneurial ac-tivities in North America while Alusu-isse and Pechiney are the European offspring of Paul Héroult. VAW can be considered a late arrival, founded 1917 to support German armament during WW I but without direct ties to the founding fathers of the industry. Kaiser and Reynolds can be regarded as the generation of heirs as they came into the primary aluminium business in close timely connection to WW II, e. g. by snapping up from Alcoa, in an US government initiated auction, what was considered overcapacity after the war. Norsk Hydro, founded 1905 as a hydro-power company with associated power-consuming assets (fertilizers, explosives), entered the aluminium business even later, after

VAW-led initiatives to build a German production basis in Norway during WW II had not been finished before the end of the war. Although Hydro itself had contemplated aluminium produc-tion repeatedly since 1907 (including failed own process inventions outside Hall-Héroult) only in 1963 did Hydro diversify into the aluminium business by building its first smelter in Karmøy; later in the last century Hydro started buying history through acquisition of older Norwegian smelters [3]. That leaves Comalco-Dubal and Venalum as representatives of an upcoming new generation of more recent birth and, due to the still prevailing lack of detail insight (in 2000), the Russian and Chinese aluminium industries pooled by Tabereaux just under the country names.

Concluding from the above summary, it can be seen that by the year 2000, aluminium reduction cell technology know-how that had been deployed internationally appears to be almost exclusively held by big western enter-prises with a long history in the industry to the extent that the original inventors can still be traced. The Russian and Chinese industries had been contained within their respective borders and, due to their lack of involvement outside of their territories, had remained opaque until way into the 1990s. However, in-ternal cell development had reached a similar amperage level as the western technologies.

The reduction cell development had obviously reached peak line amperages of 300 – 325 kA while a lot of cell tech-nologies still hovered at between 180 and 280 kA. Tabereaux in his outlook mentions, without being specific, that further testing into the 400 kA region was underway and that this amperage was expected to establish the next reduction cell generation.

While in principle aluminium can be produced in cells with either Söderberg (S) or prebaked (PB) anodes, all of the modern high-amperage cells are

based on prebaked anodes. Another distinguishing element of reduction cell construction and operation is the concept of supplying the alumina feed to the electrolyte. Historically, PB cell feeding has been developed from side work (SW) to center work (CW), and finally to point feeding (PF) systems. While SW pots were fed (several) hun-dred kilograms of alumina at a time in intervals of 1 – several hours, CW pot feeding occurred in doses of tens of kilograms several times per hour and PF feeding involves quantities of 1 – 1.5 kg/shot some 2 – 3 times per minute. All modern high-amperage cells exclusively utilize point feeders and can thus be characterized as point-fed pre-bake or PFPB cell types.

Finally, at the bottom line of Tabereaux´s article, his minibio significantly refers to Dr. Tabereaux as working for Reynolds Metals. However, the article was printed just a few weeks before Alcoa finally finished its takeover of Reynolds Metals in May 2000. This leads to the indicated sub-topic of dramatic changes in the primary aluminium industry since pub-lication of Tabereaux´s article which will also be highlighted below.

2 State of the Primary Aluminium Industry at the Turn of theMillenniumThe 1990s had started off with one of the worst economic periods in the primary aluminium industry: as a con-sequence of the fall of the iron curtain, aluminium that would have otherwise been used by the former Soviet Union and its allies was sent into the west-ern markets and particularly into LME warehouses. At that time, the traditional correlation between metal inventory/consumption and price was still intact, so the influx of excess metal sent the LME prices, coming from above 2.000 USD/t (incl. a peak of above 3.500 USD/t) into steep decline down to the 1.100 USD/t range at which level almost all smelters would face losses. It took the industry huge joint efforts in terms of mutually agreed curtailments for the price to escape the 1.100 – 1.300

Dr.-Ing. Joachim Heil MetCons – Metallurgical Project Consultancy

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USD/t range which only succeeded in about mid 1994. Players and individual smelters with less solid balance sheets were forced into shutdowns or became prey for takeovers.

In addition to considerable pressure from marginal product proceeds at low LME prices, cost pressures were also on the rise, particularly from the energy cost end. Smelters faced expiry of their long-term power contracts and more often than not the new contracts included hefty increases of electric power prices. In this context, the Bonn-eville Power Administration (BPA), a US governmental (not-for-profit) power agency, achieved some doubt-ful fame as a result of pressurizing their US aluminium clients for many years, in some instances to the brink of bankruptcy.

Only during the second half of the 1990s did the primary aluminium in-dustry regain enough stability to be able to entertain new developments. In reflection of the tough times, the aluminium industry started forging stronger entities through mergers and by acquiring weaker players.

Figure 1: Monthly Average Primary Aluminium Price, 01/1981 – 04/2014 [4]

3 Aluminium Industry Consolidation at Corporate Level from2000 – 2014

3.1 Western Primary Aluminium IndustryThe new millennium started off with two major reorganizations among the big western players. In May 2000, Alcoa finalized the acquisition of Reynolds Metals in a 4,5 blnUSD deal, almost one year after the offer had been sub-mitted [5]. The merger combined the two biggest aluminium producers of the US, or numbers one and three on a worldwide scale, making Alcoa by far the biggest aluminium producer globally.

Soon after, in October 2000, Alcan (of Canada) finalized its merger with Alusuisse (of Switzerland) [6]. This merger was what remained of an ini-tially contemplated three-way merger that would have included Pechiney (of France) as well. However, the idea of including Pechiney was mutually abandoned as the project faced stiff opposition from regulatory authorities over market dominance in the flat-

rolled products business resulting from Alcan´s 50 % ownership in the giant Alunorf rolling mill in Germany. Alcan now was number two on the global list of primary aluminium producers.

In February 2002, Kaiser Aluminium, then the third largest aluminium pro-ducer in the US, filed for bankruptcy protection under Chapter 11 following a failed debt repayment of some 25 MUSD and facing another upcoming debt repayment of 174 MUSD. The Kaiser bankruptcy was mainly attrib-uted to a failed diversification into the chemical business [7]. However, the weak aluminium business during the 1990s will have contributed its share. Additionally, Kaiser had been hampered by an explosion, in July 1999, at its Gramercy alumina refinery, which took its 1 Mtpy production off the market for 1,5 years [8]. Kaiser was also one of the victims of BPA´s new increased power tariffs which, among others, forced them in late 2000 to contemplate shutting down its Mead smelter and selling the freed power back to BPA at the higher price. Ironi-cally, this idea was opposed by BPA


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(and thus the US government) as they did not entertain a private company making a windfall profit to the tune of 300 MUSD out of a public utility [8]. It actually took Kaiser until 2006 to re-emerge from Chapter 11 protection. Still an aluminium company today, Kai-ser has, however, divested all alumina and primary aluminium assets. Under the new business model, Kaiser is now a producer of engineered aluminium components with an emphasis on the aerospace market [9].

In March 2002, Hydro Aluminium (of Norway) took over VAW aluminium AG (of Germany) from E.ON AG, a Ger-man holding company formed in 2000 through the amalgamation of VIAG AG and VEBA AG, in a 3,1 bln € deal [10]. VIAG had been the holding owner of VAW since its inception. VIAG´s port-folio included basically power produc-ing and power consuming industries whereas VEBA held a portfolio of power producers and chemical plants. The new E.ON strategy was to concentrate on power generation so all industrial holdings, including VAW, were divested as a consequence.

The takeover of VAW promoted Hydro Aluminium to position four, behind Alcoa, Alcan and RusAl, in the global primary aluminium producer ranking. Meanwhile, the new Alcan had obvi-ously not entirely given up the idea of integrating Pechiney since in Septem-ber 2003 they gained clearance from the European Commission, though there was an obligation to divest major parts of the downstream business in-cluding the flat-rolled production [11]. The latter was finally spun-off in 2005 as Novelis which now, since 2007, is wholly owned by Hindalco. The incor-poration of Pechiney boosted Alcan´s primary aluminium output close to that of Alcoa, however Alcan remained in second place.

After almost 2 years of a long unsuc-cessful courting period, Alcoa then made an unsolicited takeover bid to Alcan early May 2007 [12] which was

immediately rejected as it supposedly did not properly reflect the true value of the new Alcan [13]. Alcoa bid 33 blnUSD for Alcan, however, after Al-can management´s rejection of Alcoa, Rio Tinto offered 38 blnUSD. When Vale (CVRD at the time) also entered the takeover-war, Rio Tinto and Alcan settled the deal at 38,7 blnUSD, one of the biggest takeovers ever. In October 2007, the aluminium activities of Rio Tinto, i.e. the Comalco business, were combined with Alcan and are known today as Rio Tinto Alcan or RTA. The combined primary production has put RTA in second place, closely behind the new RusAl.

In May 2010, Hydro Aluminium signed an agreement with Vale to take over Vale´s aluminium business (primary smelters, alumina and bauxite activi-ties) for 4,9 blnUSD [14]. After approval from regulatory authorities, the deal was finalized early 2011 [15], giving Hydro upstream access to bauxite and making Hydro a long alumina pro-ducer.

To summarize, the last decade has shrunk the number of potential western reduction cell technology providers from 10 (or rather 8 + 2, the 2 being Comalco-Dubal and Venalum) to 3 + 2: Alcoa, Hydro Aluminium and Rio TintoAlcan + Dubal and Venalum, see graphic representation in Figure 2.

Dubal appears to have discontinued the joint technology development agree-ment it had with Comalco before 2005 and now has developed its own DX series of high amperage cells. While Dubal is continuing with reduction cell development no similar information is available from Comalco since 2006 - when Comalco reported about five modified CD26 test cells operating at the Boyne smelter, which were being considered for the intended potline 1 and 2 modernization. The so-calledB32 (RTC-28) cell was operating at 270 and 280 kA between 2002 and 2005 [16]. Interestingly enough, for Boyne´s potline 3 construction between

1995 and 1997, Rio Tinto Comalco had already opted for AP-30 technology over the in-house CD technology. De-velopments of Comalco cell technol-ogy have probably been discouraged after the Rio Tinto – Alcan merger in 2007 since this has given Rio Tinto/Comalco direct access to the more advanced Pechiney technology.

3.2 Eastern Primary Aluminium IndustryRussia started primary aluminium pro-duction on an industrial scale in 1929. All Soviet smelter technology R&D was concentrated in the All-Union Alu-minium Magnesium Institute (“VAMI”) founded in 1931 (and re-named All-Russian Aluminium Magnesium In-stitute VAMI in 1993) [17]. Historically, Söderberg technology had long been dominant, and still continues to be largely present, in Russian smelters.

The dissolution of the communist bloc after the fall of the iron curtain brought about unprecedented upheavals in the formerly planned and centralized economies, specifically in the Former Soviet Union (FSU). Both, aviation and armament industries, the biggest con-sumers of aluminium in the FSU, had broken away almost entirely, and do-mestic consumption dropped from 17 kg/capita in 1990 to a mere 2 kg/capita in 1994. Before production out-puts could be adjusted, an overhang of aluminium had been produced which was subsequently shipped westward deluging the global markets. FSU smelters found themselves discon-nected from their alumina supplies which were now situated in foreign countries (i.e. in the now independent previous Soviet republics) and started operating on a tolling basis. In an al-most lawless, mafia-like environment, proverbial aluminium and alumina wars took place with huge profits to be made but also leaving casualties at the wayside. Since the state-owned smelters were effectively ownerless, a major privatisation took place from 1993 onwards.



In this environment, a few individuals started building ownership in individual smelters, then progressing into group-ing individual plants together to form strong groups almost mimicking the earlier communist structures, but now under private ownership. So-called “oligarchs” concentrated aluminium as-sets under the names Sibirsky Alumini (1997, Oleg Deripaska), Sibneft (1999, Roman Abramovich) and Sibirsko-Uralskaya Aluminievaya Kompania (SUAL, 1996, Viktor Vekselberg).

Also in the eastern hemisphere, the new Millennium started with yet an-other major concentration of market share. In 2000, Sibirsky Alumini and Sibneft merged to form Russian Al-uminium (RusAl) with a production capacity of more than 2 million tpy of aluminium representing almost 10 % of global output [18].

During the following years RusAl and SUAL grew independently through further acquisitions of international scope and in 2003, RusAl acquired the All-Russian Aluminium Magnesium Institute VAMI [19].

In 2007, with the merger of RusAl, SUAL and the alumina business of Swiss trading house Glencore, a new industrial giant was born. The new United Company (UC) RusAl was then worth some 30 blnUSD and controlled 4,4 million tpy of primary aluminium output - placing the new RusAl on top of the producer´s ranking and overtak-ing Alcoa [20].

In summary, the Russian primary alu-minium industry is now controlled by UC RusAl. RusAl, after a total disin-tegration, in the 1990s, of the state-owned assets, has almost rebuilt the Soviet-era industry including control of the VAMI R&D facilities, though now under private shareholding owner-ship and with a global reach, through acquisitions.

The early days of the Chinese primary aluminium industry remain obscure

due to a combination of long-lasting shielding of the country and the exis-tence of a multitude of small smelters (down to the 5 ktpy level) which went unrecognized globally or remained unknown due to non-reporting. Accord-ing to Zhongxiu, in 2002 there were still 128 operating Chinese smelters with only 17 smelters having more than 50 ktpy capacity [21]. Taking the IAI-published Chinese production figure of 4,321 Mtpy for 2002 into consider-ation [22], the average output from a Chinese smelter was a mere 33,7 ktpy. By 2013, China had increased primary output to 21,936 Mtpy [23] equivalent to an average of 175 ktpy from each of its 125 operating smelters.

The ownership of Chinese smelters appears to be scattered between the government, semi-public entities and partially or wholly private ownership. The largest single Chinese entity in this context is the Aluminium Corpora-tion of China Ltd. (Chalco), which was formed in September 2001 to oversee the aluminium and alumina business of state-owned Aluminium Corporation of China (Chinalco). Chalco was partly floated on the New York and Hong Kong stock exchanges in December 2001 which reduced Chinalco´s ma-jority ownership to some 44 % while Alcoa picked up an 8 % share of Chalco [21]. Chalco has continued to expand by acquisitions (of other Chinese smelters) and by building new smelt-ing capacity at rapid pace. Despite a production increase from 690 ktpy in 2000 to >4,2 Mtpy in 2012, Chalco´s share of the total Chinese primary alu-minium output has, however, fallen from 25 % to some 21 % [23], [24].

Concluding from company informa-tion collated by Pawlek [26], Chinese aluminium production appears to have started in the 1930s, based on VAMI Söderberg pots, but later Elkem and Japanese technology providers have also been sporadically mentioned. In the 1980s, obsolete Japanese smelter equipment was imported into China (as a consequence of Japan exiting the

primary business after the oil crisis) and the VAW CA 115 from Töging (as a consequence of the smelter shutdown in 1994 after Russian metal flooded the market) had been bought second-hand.

However, the overwhelming majority of Chinese smelters apply home-grown aluminium reduction cell technology which has historically been developed by two institutes: Shenyang Aluminium & Magnesium Engineering & Research Institute (SAMI, founded in 1951) and Guiyang Aluminium Magnesium Design & Research Institute (GAMI). Both are now managed by the China Aluminium International Engineering Corporation (Chalieco), which is a wholly owned subsidiary of Chinalco. These two in-stitutes, SAMI and GAMI, have recently been developing high-amperage cell technologies separately and they are competitors, even though both have the same parent company. SAMI and GAMI designed potlines constitute the bulk of China´s current primary aluminium industry.

Established in 1981 and restructured in 2003, the Northeastern University Engineering & Research Institute (NEUI) has followed a similar tech-nology development path as SAMI, and within a few recent years, NEUI has developed and put into operation a series of high-amperage reduction cell technologies in China.

The historic development of western and eastern reduction cell technology providing companies is graphically summarized in Figure 2.

4 Aluminium Reduction Cell Technology Providers at theTurn of 2013/2014

4.1 AlcoaAlcoa has not reported any progress on their 300 kA cell technology since more than a decade as far as the TMS´s annual Light Metals proceedings are concerned. Actually, it appears that the only industrial application of Alcoa´s


Primary Aluminium – Ancestry

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Figure 2: Historic Timeline of Reduction Cell Technology Providers

own most advanced reduction cell is at Portland Aluminium in Australia.The acquisition of Reynolds by Alcoa in 2000, including their cell technology R&D department, did not bring about any obvious revival of cell technology development activities at Alcoa.

Alcoa´s North American operations, which utilize Alcoa’s own cell tech-nology, are applying line currents of between 120 kA and 245 kA, according to information available from Pawlek´s PASaPoW [26]. Among these there are 3 smelters that exceed 210 kA, namely Mt. Holly (215 kA), Tennessee (245 kA) and Massena (230 kA) while the latter also houses an unspecified number of A-716 type test pots operating at 280 kA and 450 kA (?).

Much of Alcoa´s global assets today have been acquired, i.e. these have an inherent lower probability of using Alcoa cell technology, and actually Al-coa inherited a wide variety of different technologies from the original owners. However, there are again 3 smelters outside of the USA using Alcoa cell technology beyond 210 kA: Point Henry

(215 kA, P-155 cells), Alumar (228 kA, A-697 cells) and Portland (320 kA, A-817 cells). Concluding from PASa-PoW [26], Portland appears to be the only smelter in the Alcoa organization that has been built using Alcoa´s most advanced technology. Portland was commissioned in 1986 with an initial line current of 275 kA, which has obvi-ously been crept to 320 kA.

Since Portland was started up in 1986, Alcoa appears to have reduced activi-ties in terms of building its own new smelter capacity. Only in the second half of the first decade of the new mil-lennium, did Alcoa resort to expand through building new smelters: Alumar underwent 2-step brownfield expan-sions which were commissioned by September 2005 and from November 2005, respectively. Alcoa A-697 cell technology (developed as AA-18, after boosting now operating as AA-23) has been used for the new potline 3 at Alumar. In April 2007, Alcoa started commissioning its new Fjarðaál smelter in Iceland - which presently operates at 380 kA. Interestingly, Alcoa did not implement its own cell technology but

built a one-potline smelter based on Alcan (i.e. Pechiney) AP38 cell tech-nology. Also in Alcoa´s most recent participation in the Ma´aden smelter project in Saudi Arabia Rio Tinto Alcan AP37/39 technology has been imple-mented [27].

The European Economic Commis-sion (EEC) in 2003, on the occasion of the Alcan/Pechiney merger, issued a merger procedure that assessed the concentration of market shares for the new entity. Amongst other items, the market shares of a combined Alcan/Pechiney in the aluminium reduction cell development and licensing busi-ness were investigated in relation to their competitors. One of the competi-tors mentioned by Alcan/Pechiney was Alcoa. However, the EEC assessment found that Alcoa in fact had ceased li-censing cell technology to third parties in the 1980s. Consequentially, Alcoa was regarded by the EEC as a hypo-thetical competitor only [11].

As a conclusion of the above, it seems that Alcoa not only has largely dis-continued implementation of its own



reduction cell technology in smelters they own but has also discontinued licensing to third parties. The latest Al-coa greenfield projects are based upon reduction cell technology licensed from RioTintoAlcan. This together with the total absence of publication of cell technology advances could be interpreted that Alcoa has aban-doned primary aluminium reduction cell development altogether in favour of external licensing.

4.2 Hydro Aluminium (incl. VAW)When Hydro Aluminium acquired VAW in 2002, the VAW cell technology R&D department was also included in the deal. VAW had operated five CA 240 (VAW-24, in Töging) and three 300 kA test cells in Sayanogorsk, the latter project having been hampered by the Russian conditions in the years just after 1990. This experience lead to a VAW decision to replace the VAW-24 cells in Töging with CA 300 (VAW-30) test cells. However, this project was stopped in 1994, shortly after or-ders had been placed and construc-tion work had begun. The so-called Töging potline 2, which was to receive the test cells, was decommissioned (as a result of Russian metal flooding the market depressing the LME ingot price), dismantled and finally rebuilt in Iceland (Century´s Norðurál smelter). The former VAW´s cell technology R&D group (aka VAW-ATG) continued to work on cells, mostly on smelter upgrades, retrofits and the like but the VAW-30 remained shelved. However, Hydro acquired the residual know-how and also the manpower and modeling and engineering tools developed by VAW. Today, the ex-VAW R&D know-how is a vital part of the Hydro Aluminium cell technology development as can be concluded from ongoing Hydro publications including former VAW staff.

Hydro Aluminium had licensed its HAL-23 cell technology to Venalum (potline 5, commissioned 1988) and also to the Slovalco smelter where the HAL technology replaced three

1950s Söderberg potlines. Slovalco commissioned the HAL pots from June 1995 and achieved operational results as presented in Table 2.

Slovalco was expanded by adding 54 pots of HAL250 technology which was commissioned from July 2003. At the same time the line amperage for the existing potline had been increased to match the HAL250 technology of the new pots. Today, Slovalco operates at 258 kA.

In December 2002, Hydro started com-missioning 11/2 potlines comprising 340 pots in its Sunndalsøra smelter (the so-called Sunndal 4 or SU4 proj-ect), also replacing older Söderberg potlines, implementing their HAL250 cell technology. Even during com-missioning the amperage was raised to 275 kA - the reported value when the last pot was energized in August 2004. This cell technology is dubbed the HAL275 (HAL-28) and the Sunndal smelter is the biggest European single site smelter [28], [29]. It has been re-ported that the HAL275 pots at SU4 have been crept to 290 kA (HAL-29) as of April 2007 [26].

It appears that both the Slovalco and the Sunndal SU4 potlines might go down in history as the last newly-built smelters in (Central) Europe, or at least the last for quite some time to come, unless the European energy prices al-low for new smelter projects to proceed again in the future.

The HAL275 cell technology was also licensed to the new greenfield smelter Qatalum, in Qatar, which was started up in December 2009. According to

Cell Technology (UPBN)Parameter

HAL230(HAL-23)

HAL250(HAL-25)

Unit

Amperage (design) 230 250 kA

Amperage (operation) 230,3 258 kA

Number of Pots / Potlines 172 / 1 54 / extension -

Current Efficiency (CE) 96 94 %

Anode Effect Frequency (AEF) 0,044 n.a. AE/(day · pot)

Specific Energy Consumption 13,5 13,2 kWh/kg aluminium

Table 2: Hydro Aluminium Cell Performance Data at Slovalco as per [26]

information available on the Qatalum website, the operation was supposed to start at 300 kA which would allow a production of 585 ktpy of potroom metal from their 704 pots [30]. This would require a current efficiency of 94,5 %. Output in 2012 reached 628 ktpy [31] which would have required an amperage creep to some 320 kA at95 % CE, so the Qatalum pots should now be categorized HAL-32. The rectifi-er-transformers (RTs) installed at Qata-lum (5 x 85 kA) would even have enough rated capacity for future line amperage creep to 340 kA without compromis-ing on the N+1 RT configuration [32].

In its latest development, in June 2008, Hydro Aluminium has commissioned six HAL420 or HAL4e (HAL-42) cells in its Årdal research facility, operating at 420 kA and designed to operate at up to 450 kA. The first commercial imple-mentation of the HAL4e technology was foreseen to begin after 2014 [33]. In 2013, a 70 ktpy pilot smelter applying HAL “next generation technology” to be sited at Karmoy was under study [34]. The pilot HAL-42 cells achieved specific energy consumption of 12,5 kWh/kg in 2012, with a 2014 target of 12,3 kWh/kg and a mid-term target of <11,8 kWh/kg for an extra energy-saving variant called HAL4e ultra [35]. A full set of performance data from the first months of operation of the HAL-42 test cells had been published in 2009, and the results achieved are shown in Table 3.

One distinguishing unique HAL tech-nology feature common to all of the above mentioned variants (except per-haps at Venalum) is that a HAL potline is housed under one common roof.


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Figure 3: Typical HAL-32 Potline, Photo: copyright Qatalum

This is called by Hydro Aluminium the double potroom concept, or al-ternatively the half-potroom concept. Usually, modern PFPB side-by-side potlines consist of two rows of pots. These are traditionally housed in two distinct buildings (potrooms) which are spaced apart by an open courtyard of typically some 60 m open width to keep the reciprocal magnetic disturbance of the two rows at a minimum.

Due to the courtyard, the center-to-center spacing of pots between the

Parameter Value Unit

Amperage 420 kA

Number of Pots 6 Test cells

Current Efficiency (CE) 95 % (assumed)

Pot Voltage 4,1 V

Anode Effect Frequency (AEF) < 0,03 AE/(day · pot)

Specific Energy Consumption 12,83 – 12,93 kWh/kg aluminium

two rows would be of the order-of-magnitude of 80 – 90 m and maybe more for the very high amperage cell technologies. Hydro Aluminium places the two rows of a potline in two half-potrooms which share a common yet unclad central building wall instead of an open courtyard. The center-to-center spacing of HAL pots between the two rows is then only about 30 m [37]. This configuration somewhat resembles the traditional end-to-end potline arrangement where there are 2 potrooms but each of them housing

Table 3: Hydro HAL420/HAL4e (HAL-42) Cell Performance Data as per [36]

2 rows of pots.

This HAL specific potline configuration is very advantageous in terms of land usage, i.e. the annual output per m2 of built-up area is comparatively high. The HAL potline concept also achieves lower potroom construction investment and operating costs.

A satellite image comparison of a tra-ditional vs. a HAL potline arrangement is shown in Figure 4, whereas the yel-low lines are 1000 m and 250 m long, respectively.

Hydro Aluminium also reports that its development will consider pot-shells with forced cooling (with an undisclosed cooling medium) on the sidewalls and usage of the resulting off-heat for power generation. Heat extraction from the pot off-gas in the GTC area for district heating purposes is already a feature of some Norwe-gian smelters. Another topic of Hydro technology development is dealing with concentrating the CO2 content in the pot off-gas (from <1 % to > 4 %) which would reduce the size of gas handling and treatment equip-ment and eventually facilitate future uses, e.g. in CCS (carbon capture and sequestration) [37].

The HAL-32 technology based Qata-lum smelter cost was 9.000 USD/ktpy installed capacity [38].

4.3 RioTintoAlcan (including Comalco, Alusuisse & Pechiney)As already discussed, RTA is now pooling the previous R&D activities of Comalco, Alcan, Alusuisse and Pechiney. The current RTA reduction cell technology is equivalent to the former Pechiney technology (RTA technology is still marketed under the APXX denomination). In the contextof this review, it is assumed that RTA reduction cell technology today is equivalent to Pechiney AP technology and the other technology develop-ments have been discontinued or, if not, at least their contribution remains

1 potline, 360 pots (AP36). 360 ktpy - Aluminium

2 potlines, 2 x 352 pots (HAL275), 585 ktpy - Qatalum © 2010 Google © 2011 LeaDog Consulting© 2011 GeoEye


Figure 4: Land Usage of 1 AP Potline vs. 2 HAL Potlines (yellow lines: 1000 / 250 m long)


invisible to the public (this contrasts with RTA alumina handling and stor-age technology which is still marketed by RTA under the previous Alusuisse brand “Alesa”). Pechiney has a long-standing and well documented track record of reduction cell technology development. Their AP18 (180 kA) technology was commercialized in 1979 and almost 10 years later, the AP30 was first commissioned on an industrial scale in 1986. The first higher amperage applications were both built inside the Pechiney smelter facilities at Saint-Jean-de-Maurienne, France. Extrapolating from this historical path, it was justifiable for Tabereaux to expect the launch of the next generation AP reduction cell about the time he wrote his review in 1999. The next generation was expected to be of 400 kA while he also expected that this required the solution of some technical prob-lems, e.g. wear of cathode lining, heat balance, emissions, cell instabilities, higher magnetic fields and metal loss due to increased cell turn-around time for relining [2].

Tabereaux was not mistaken, since in July 2000, Pechiney indeed present-ed its new cell generation. Pechiney, however, had skipped the 400 kA and immediately went to the AP50 technol-ogy - to be operated at 500 kA [39]. Within about a year, a first project site was identified at Coega/RSA to host a 460 ktpy greenfield smelter, which was to be the first commercial imple-mentation of the AP50 technology on a large industrial scale. Agreements for power supply with Eskom were made and environmental clearance was achieved by early 2003, however Pechiney looked for investment part-ners as they only wanted to retain about 40 % ownership in the project. After Alcan had gained control over Pechiney in late 2003, including the Coega proj-ect, the project was delayed trigger-ing investigation of several alternative scenarios. The whole process was fur-ther protracted due to Rio Tinto then taking over Alcan which, in mid 2007, resulted in a downscaling of the project

to 360 ktpy combined with a decision to implement the project with AP36 cell technology. In the winter of 2007/08, Eskom´s severe shortfall of maintain-ing power generation and distribution systems came to the surface - leading to country-wide blackouts in RSA. This was probably only the last in a string of events that caused RioTintoAlcan to abort the Coega AP50 project finally in October 2009 [40].

Obviously frustrated by the inability to launch the AP50 at Coega, Alcan had started building a semi-industrial short potline of 44 AP50 pots within its own organization, at the Jonquière smelter in Canada. Commissioning of this 60 ktpy potline was envisioned for mid 2008. However, the financial stress caused by Rio Tinto´s 38 blnUSD outlay for Alcan still persisted when the global financial crisis started to hit in 2008. This did not favour the Canadian AP50 project which was then slowed down. During the slowdown, the project was re-engineered and RTA announced that the Jonquière short potline will now receive the latest development, AP60, instead of the AP50 previously announced [41]. In keeping with the 60 ktpy production capacity target, the pilot potline now consists of 38 pots of first generation AP60 cells operating at 570 kA after full capacity

was achieved in December 2013 [42]. Jonquière could later be expanded to 460 ktpy using the second generation AP60 cells which would be operated at 600 kA [43].

RTA still markets its AP30 technol-ogy successfully which has been fur-ther developed stepwise. Due to the creeping amperage this technology is now called AP3X and can be operated

at up to 390 kA. RTA´s AP3X range of reduction cells has so far dominated the reduction cell technology licensing business outside of Russia and China. The AP technology market share of the world’s modern smelters outside of Russia and China is estimated to be at least 80 %. The global application basis of AP3X is summarized in Table 4. Besides that, there is one 405 kA potline under construction at Kitimat.

The latest AP performance data can be characterized as follows (see Table 5), summarizing from various publi-cations in TMS Light Metals and RTA company brochures. This appears to be supported by the RTA confirmations that the AP3X and the AP50 test pots have maintained their performance data level throughout the entire am-perage range.

Cell Technology (UPBN) Parameter

AP3X(AP-30/39)

Unit

Total Potlines (PLs) 19 + 3 * PLs

Total Pots 5274 + 810 * Pots

Average Pots 280 (excl. u/c pots) Pots/PL

Total Installed Capacity 5,25 (excl. u/c pots) Mtpy

Average Output 290 (excl. u/c pots) ktpy/PL

Avg. Potline Voltage ** 1170 (excl. u/c pots) V/PL

*: 3 PLs with 810 pots under construction in Iceland and India; pots not included in below calculations**: assuming 4,2 V/pot

Table 4: Overview of Smelters based on RTA AP Cell Technology as per [44], [45]


Amperage 300 – 500 kA

Current Efficiency (CE) 94,1 – 96 ,0 %

Pot Voltage 4,2 V

Anode Effect Frequency (AEF) 0,23 – < 0,03 AE/(day · pot)


Table 5: RTA AP3X and AP50 Cell Performance Data as per [45], [46], [47]


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The higher amperage range of the AP3X reduction cells is understood to be applied to pots with unchanged outer dimensions with moderate ad-justments to anode size and potlining. This means that at the high amperage end, current density and energy input to the AP3X cells is higher compared to the basic AP30 cell. It is also un-derstood that this will require forced sidewall cooling, which consists of low pressure air blown through chan-nels attached to the sidewalls of the potshells. The resulting heated air is released to atmosphere.

The AP-36 technology based Sohar smelter was built at 6.670 USD/ktpy installed capacity [48], while the AP-60 pilot potline has cost a staggering 18.330 USD/ktpy [42], and it remains to be seen how much this cost can be lowered for a full commercial smelter project.

4.4 United Company RusAl (including VAMI)Most of UC RusAl’s aluminium smelt-ers were built between 40 and 60 years ago, and the majority of these smelters are still based on Söderberg technology [49]. According to RusAl, more than 80 % of Russian primary aluminium originates from Söderberg cells [50] while the international share of Söderberg smelters was only 18 % in 2005 [51]. Modernizing their Söder-berg aluminium production sites has an ongoing high priority for RusAl (dry anode technology, hooding, gas treat-ment, anode gas incineration, alumina

feeding etc.). Prebake smelters have been built in the FSU from around 1975 [26]. An overview of RusAl high amperage reduction cell performance is presented in Table 6.

A year into its existence RusAl started development of a high amperage PFPB reduction cell (in 2001) and five pi-lot cells were commissioned at their Sayanogorsk smelter (SAZ) at the end of 2003. The so-called RA-300 (RA-30) reduction cells have been used for the construction of the Khakas smelter (KhAZ) which was started-up in 2006 and operates 341 (336 + 5?) pots at 320 kA. In 2005, a newly developed RA-400 (RA-40) prototype was commissioned at SAZ, and by 2010, sixteen RA-400 cells were in operation at 435 kA.

As example for a typical Rusal PFPB potroom see a photo from the Khakas smelter in Figure 5.

The RA-400 is to be installed at RusAl´s new Taishet smelter; construction com-menced in 2007 but was suspended by the end of 2008. The Taishet smelter will comprise 672 pots with production capacity of 750 ktpy [57].

BEMO (Boguchanskoye Energy and Metals Complex) is a combined hy-dropower plant (HPP) and aluminium smelter project under construction. The 3 GW HPP project originally started 1979 but was stopped from 1994–2005.

Meanwhile 6 out of 9 generators are



OA-300M1(SU/RA-30)

RA-300(RA-30)

RA-400(RA-40)

RA-500(RA-50)

Unit

Smelter Site IrkAZ KhAZ/ * SAZ/ ** SAZ

Amperage (design) 300 300 400 500 kA

Amperage (operation) 330 320 415 – 435 520 kA

Number of Pots 200 336 + 672* 16 + 672** ?

Current Efficiency (CE) 94 95 > 93,5*** > 93,5*** %

Pot Voltage 4,33 n.a. 4,3 - 4,4*** 4,3 - 4,4*** V

Anode Effect Freq. (AEF) 0,13 0,15 < 0,05*** < 0,05*** AE/(d · pot)

Specific Energy Cons. 13,73 n.a. < 13,8*** < 13,8*** kWh/kg Al

*: under construction (BEMO project, 588 ktpy)**: under construction (Taishet project, 750 ktpy)***: target values

Table 6: RusAl Cell Performance Data as per [52], [53], [54]

Figure 5: Typical RA-30 Potline, Photo: copyright Rusal


operating, and smelter construction would see first hot metal later in 2014. The smelter comprises 672 pots of RA-300 technology for a total output of 588 ktpy [58].

Before their merger with RusAl, SUAL reported that they were operating six OA300M1 type 300 kA test cells (SU-30) at its Ural smelter (UAZ), designed by SibVAMI. Commissioned in 2005, the amperage of the test cells was later increased to 330 kA. In early 2010, a full 170 ktpy potline (potline 5) at Ir-kutsk (IrkAZ) was commissioned with plans to increase the amperage to 330 kA. The IrkAZ potline 5 comprises 200 OA300M1-based pots which are now (after the merger with RusAl) also dubbed RA-300 [55].

During 2007/2008, RusAl further advanced development of a 500 kA reduction cell. However, it remains unclear if a prototype has already been built or if this is yet to happen. There are plans to build an experimental RA-500 potline between 2011 and 2014 [54].

RusAl further reports that it is experi-menting with inert anode technologies in two ways: firstly, as a replacement for prebake carbon anodes in standard Hall-Héroult cells and secondly, in trial cells that implement multiple verti-cal inert anodes and cathodes. The latter trial cells would have a much higher time-volume-related output as compared to standard Hall-Héroult cells. Specific energy consumption

is expected to be < 12 kWh/kg. In the absence of information to the contrary, it is assumed that a cryolite-based electrolyte would be used as opposed to the chloride-based trials that Alcoa conducted in the late 1970s using a similar cell but with multiple horizontal bipolar electrodes [50], [53].

RusAl claims that they can build a smelter in Russia at a cost of 2.300 – 2.800 USD/tpy installed capacity [56]. The Khakas smelter is said to have been built in less than 24 months.

4.5 DubalDubal started operations in 1979 with 3 potlines implementing National Southwire technology (an improved

version of Kaiser P69 (KA-15)) [59]. The reduction cells were modified and retrofitted over the first decade of op-eration by Kaiser and Norsk Hydro [26]. When potline 4 was commissioned in 1990, the first five CD-type test pots, jointly developed with Comalco, were also started at 190 – 200 kA. Potlines 5 (commissioned from 1996) and 6 (1999) both implemented the so-called CD20 cells on an industrial scale. In the Comalco-Dubal nomenclature the number actually represents the number of anodes and only roughly coincides with the amperage level. So, in UPBN terminology, this was a CD-21 (210 kA) cell. In 1997, again five test cells of further advanced am-perage were commissioned, called

Figure 6: Dubal DX Pilot Potline, Photo: copyright Dubal


DX(DU-35)

DX(DU-38)

DX+(DU-44)

Unit

Smelter Site Emal 1 * Dubal Dubal, Emal 2

Amperage (design) 340 340 440 kA

Amperage (operation) 380 380 440 kA

Number of Pots 756 40 5 + 444444 DX+ under commissioningat Emal 2

Current Efficiency (CE) 95,8 95,5 95 %

Pot Voltage 4,2 – 4,22 n.a. 4,24 V

Anode Effect Frequency (AEF) 0,1 < 0,02 < 0,05 AE/(day · pot)

Specific Energy Consumption 13,12 13,04 < 13,4 kWh/kg aluminium

*: Emal 1 values during commissioning phase

Table 7: Dubal Cell Performance Data as per [67], [69], [70]


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CD26 (CD-28). Further expansions into potlines 7 (2003) and 9 (2005), however, deployed the cell type D20 (DU-23) which may be taken as an early indicator that the Comalco co-operation had been put on the “backburner”. In 2006, five independently developed test cells of DX (DU-34) type have been commissioned and, in 2008, the tech-nology was semicommercialized in an in-house 40 pot short potline (potline 8) at Dubal [60], [61]. A photo of this pilot potline is shown in Figure 6.

Between 1997 and 2004, Dubal’s inter-est to expand outside of its UAE Jebel Ali smelter site was also based on com-mercialization of the Comalco-Dubal CD reduction cell technology. Projects for a proposed 530 ktpy smelter in the Gulf, using CD20 technology [62], a 500 ktpy smelter in the Bintulu region of Malaysia [26], and a 520 ktpy smelter in Qatar based on CD26 technology [63] did not progress, however, and Dubal withdrew from the latter proj-ect in January 2004 for undisclosed reasons [64].

The impending split between Comalco and Dubal became evident in mid 2006. On 26th June 2006, Comalco and Gen-eral Holding Corporation (GHC) of Abu Dhabi signed a heads-of agreement for a feasibility study of a 550 – 700 ktpy greenfield smelter at Ruwais/Abu Dhabi whereas a joint venture between Dubal and Mubadala Development Company of Abu Dhabi had, on 28th June 2006, awarded the feasibility study for a 700 ktpy greenfield smelter to be located at Taweelah/Abu Dhabi [65]. While the Comalco–GHC project did not materialize, the Dubal–Mubada-la project, called Emirates Aluminium (Emal), has since been constructed and is fully commissioned since 31st

December 2010 [66].

For the Emal project, Dubal has li-censed its own DX (DU-35) technology. The 2 potline smelter comprises 756 pots and has been started up at 350 kA with key performance indicators keeping up with those of the experi-

mental pots at Dubal (see Table 7). At this amperage, Emal will achieve an output of 740 ktpy.

Meanwhile, Dubal has further chal-lenged its DX cells in potline 8 at the Jebel Ali smelter, Dubai. Originally designed for 320 kA, the DX pots have, since October 2010, been boosted to 380 kA while sustaining the target key performance indicators (see Table 7). Dubal anticipate that, with a modified potshell, the DX cell technology´s operating envelope can be pushed even further to 400 kA before reach-ing physical limitations [67]. This im-provement has already been trans-ferred to the Emal smelter which operates, after a rectifier upgrade, at 380 kA since 2012 boosting the Phase 1 output to 800 ktpy [71].

In an attempt to avoid such physical constraints, Dubal has begun develop-ing a new generation of reduction cell technology called DX+ (DU-44). Five DX+ test cells, built at Jebel Ali, are already being tested at 420 kA since August 2010 and reached 440 kA in February 2012 [68]; the performance data achieved so far are included in Table 7. Dubal is predicting that this new generation DX+ technology can even operate at above 440 kA with good key performance indicators [69].

Emal has meanwhile built an additional potline implementing DX+ technology. FHM was achieved on 15.09.2013, and it is said that the potline current is al-ready set at 440 kA. This single potline expansion comprises 444 pots, and as such is the longest globally, with capacity of 545 ktpy. DX+ technology may be further deployed if and when the Alba Line 6 expansion gets the go-ahead; for now, DX+ technology has been the basis of a recent feasibility study evaluating this expansion.

The DX (DU-35) technology based Emal Phase 1 smelter was built at 8.240 USD/ktpy installed capacity [71], while the DX+ (DU-44) technol-ogy for Emal Phase 2 has cost 7.500 USD/ktpy [72].

4.6 VenalumIn 2000, Corporación Aluminios de Venezuela S.A. (CAVSA) presented a technology website describing its so-called V-350 aluminium reduction cell developed by the CVG Venalum R&D department. The V-350 (VN-35) cell was designed for operation at 320 – 350 kA and test pots were said to be operating at 322 – 325 kA [73]. Further performance data mentioned are presented in Table 8.

In 2004, Berrueta presented a paper at TMS on the planned expansion of the Venalum smelter by two potlines with 240 reduction cells each of V-350 (VN-35) type. Groundbreaking was scheduled for March 2004 and the first of the two potlines (potline 6) was planned to be commissioned from the end of 2006. The additional elec-tric power was to be provided by CVG Edelca, a state-owned power provider within the same CVG group, which was said to have included some generat-ing units in the Caruachi dam project on the Caroni River to provide for the Venalum demand. This hydroelectric power project was supposed to gener-ate energy by 2005.

Berrueta also presented an estimate of the capital expenditure (CAPEX) necessary for one potline, including casthouse, carbon and dock facilities. The estimated CAPEX of 652 mUSD, for a production capacity of 220 – 230 ktpy, would translate into a specific investment of around 2900 USD per tonne installed capacity [74].

However, according to Pawlek´s PASa-PoW [26], no further potline construc-tion activities have been recorded at Venalum, and the V-350 test pots are supposed to have been taken out of service and dismantled.

The author therefore believes that Ve-nalum cell technology development was ceased altogether.

4.7 Chalieco-SAMISAMI had initially developed Söderberg cells (until the mid 1970s) and by the



late 1970s designed a first prebake anode cell for 135 kA (SY-14). Devel-opment was now focused on prebake cells and continued stepwise (SY-16, SY-19/20, SY-23/24, SY-28) until the turn of the millennium. All these cell types have been applied commercially in the Chinese primary aluminium in-dustry. In June 2002, the first full 300 kA potline in China using SY300 (SY-30) cell technology was commissioned after 12 months of potline construction; the 200 ktpy potline is quoted to have been built at 1.707 USD per t installed capacity [75]. By 2007, 13 potlines us-ing SY-300 technology had already been commissioned in China, including 2nd generation pots operating at 317 kA and 3rd generation pots applying 335 kA - with plans to further increase potline current to 350 kA. The invest-ment cost was quoted as being 1.200 – 1.500 USD per t installed capacity for a standard SY300 potline of 200 ktpy capacity [76]. The 350 kA target was obviously achieved by 2010 and SAMI even reported implementation of 350 – 400 kA cells and a first 500 kA potline being under construction. Summarizing from a presentation given by SAMI in November 2010 [77], SAMI high amperage ( 300kA) reduction cell technology had reached more than 5,5 Mtpy capacity in operation


Amperage (design) 320 – 350 kA

Amperage (operation) 322 – 325 kA

Current Efficiency (CE) 95 – 96 %

Pot Voltage 4,1 – 4,2 V

Anode Effect Frequency (AEF) 0,1 – 0,2 AE/(day · pot)


Table 8: Venalum V-350 (VN-35) Cell Performance Data as per [73]

and over 3 Mtpy under construction, exclusively located in China. Further-more, 23 additional operating potlines utilizing SY190 – SY240 reduction cells were mentioned [78]. A fresh com-parison with Pawlek´s PASaPoW [26] reveals a lot of uncertainty regarding the aforesaid as the smelters directly attributed to using SAMI technology do not match. The author, therefore, lumped together explicit SAMI technol-ogy smelters with those mentioned in Pawlek´s PASaPoW as using “Chinese Technology”, clustering the result into 3 amperage categories. The result is presented in Table 9.

So far, only one SAMI cell technology application is known outside China which is the Iralco expansion in Arak/Iran, consisting of 1 potline with 120 ktpy capacity implementing SY200 cell technology which was commis-sioned from mid 2007 - 2009. There is some confusion because Pawlek stipulates GAMI as technology provider [26] whereas SAMI itself mentions it in one of their publications [78]. The following Table 10 summarizes the performance data of SAMI reduction cells as published.

A typical SAMI potline is shown in Figure 7.

4.8 Chalieco-GAMI:GAMI seems to have followed a similar development to SAMI, although there is very little publication. The GAMI development was initially based on a 160 kA cell - first commercialized in the Guangxi smelter in 1994. It appears, from an evaluation of information provided by Pawlek in his PASaPoW directory [26], that GAMI has further de-veloped this technology into the 200 – 280 kA range. A number of potlines are reported to have been commissioned using GAMI reduction cell technology in this amperage range, though there is no primary source that confirms this [26]. In 1998, the GP320 reduction technology was jointly developed by GAMI and the Pingguo Aluminium Company (PGAC). The first GP320 pots came on stream in October 1999, in a 30 cell trial potline. This trial potline achieved a current efficiency of 94,4 % with specific energy consumption of 13,323 kWh/kg Al, operating at up to 325 kA. The cell voltage was reported as 4,18 V with anode effect frequency of 0,3 – 0,4 AE/(d · pot) [79]. Further performance data for GAMI technology appear to be publicly unavailable.

As there is little GAMI publication, Pawlek´s PASaPoW seems to be the only accessible source of information about GAMI. However, due to limited information about Chinese aluminium smelters in general, this directory also remains vague on China and some of the information is contradictory (e.g. there sometimes appears to be a mis-match between amperage, number of pots and output) which cannot be finally resolved by the author. That said, evaluation of PASaPoW for explicit


SY300(SY-30)

SY400(SY-40)

SY500(SY-50)

SY300(SY-30)

SY400(SY-40)

SY500(SY-50)

Unit

Smelter Status operatg. operatg. operatg. u/c u/c u/c -

Total Potlines (PLs) 27 20 4 0 8 8 PLs

Total Pots 6310 5902 1236 0 2256 2584 Pots

Average Pots 240* 290 310 - 275 325 Pots/PL

Total Installed Capacity 4,17 4,84 1,71 - 2,45 3,51 Mtpy

Avg. Potline Voltage ** 1010 1220 1300 - 1160 1365 V/PL

*: excluding 1 short potline of 86 pots/70 ktpy considered an outlier**: assuming 4,2 V/pot

Table 9: Overview of Chinese Smelters based on SAMI Cell Technology 300 kA as per [26], SAMI and “Chinese Technology” lumped together for better match with [77]


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Figure 7: Typical SAMI SY400 Potline, Photo: copyright SAMI


SY300(SY-30)

SY350(SY-35)

SY400(SY-40)

SY500 (u/c)(SY-50)

Unit

Amperage (operation) 300 – 335 348 – 378 400 500 kA

Number of Pots 3074 444 n.a. 288

Current Efficiency (CE) 93,8 – 95,7 94,15 - 94,5 94,16 94 %

Pot Voltage n.a. n.a. 4,19 < 3,94 V

Anode Effect Freq. (AEF) 0,1 < 0,3 0,08 0,05 AE/(d · pot)

Specific Energy Consumpt. 12,9 ± 0,06 12,8 – 13,5 13,26 < 12,5 kWh/kg Al

GAMI high amperage ( 300 kA) reduc-tion cell technology (with one attempt to mend an obvious mismatch and back-calculating some missing data in the directory) has resulted in the following tentative overview of GAMI technology proliferation (to be read with due caution), see Table 11. In ad-dition, > 2,8 Mtpy capacity appear to be based on GAMI 200+ kA cells which seem to have been fairly frequently im-plemented during the past 12 years be-sides the high amperage technologies.

Outside of China, GAMI has licensed its technology to some smelter projects. The GP320 technology has been the basis of an expansion of the BALCO smelter, located in the Korba district, In-dia. The project comprises one potline of 288 GP320 pots with a capacity of

Table 10: Summary of SAMI Cell Technology Performance Data ( 300 kA) as per [77], [78]

250 ktpy; the potline commissioning was started in February 2005. GAMI has also licensed its GP215 technology for the Press Metal smelter project in the Sarawak region, Indonesia. The project consists of one potline with 204 pots and has a capacity of 120 ktpy; commis-sioning began in mid 2009. The Det.Al smelter in Ganja, Azerbaidjan, uses GP240 cells for its 164 pots potline with capacity of 100 ktpy.

4.9 NEUIAs a fairly young entity, NEUI also has little published track record. However in 2010 they reported their latest achieve-ments with the development of high-amperage reduction cells. The NEUI technology portfolio is reported to cover the ranges 200/240 kA, 300/330 kA and 400 kA, while the extent of its

related industrial applications remains largely unknown. The first potline using NEUI400 (NE-40) cell technology has been energized in 2008 at the Zhongfu smelter. The potline comprises 216 pots with capacity of 240 ktpy, now operating at 406 kA with pot voltage of < 3,9 V. Further operating results have been reported as follows: current efficiency of 94 %, specific energy consumption of 12,5 kWh/kg Al and anode effect frequency of < 0,01 AE/(d · pot) [80], [81].

The NEUI 400 kA technology is cur-rently applied in four potlines, built between 2008 and 2010 running at 415 – 460 kA. Six new potlines of 400 kA are said to be under construction without giving any details. The four operating smelters are reported to run with current efficiency around 94 % and specific energy consumption of less than 12,5 kWh/kg Al [82]. Not entirely surprising, also in case of NEUI technology, information provided by Pawlek in his PASaPoW directory [26] does not fully match the aforesaid, see Table 12.

Meanwhile, NEUI has taken their re-duction cell development to the 500 kA level. However it is understood that to date this only covers simulation and modeling, based on the modeling tools used for the development of the NEUI-400 reduction cells [83].

NEUI further reported that they are con-tinuously testing (since March 2008) pots with so-called novel structural cathodes (NSC) which consist of cath-ode blocks with a baffled surface.



There are different shapes and pat-terns of protrusions under test, all with the aim of reducing the metal rotating velocity and ultimately, although not explicitly mentioned, lessening the

ACD. The test pots are reported to op-erate at around 3,7 V resulting in 12,0 kWh/kg specific energy consumption and achieving 93 % CE [84].

5 Summary and ConclusionThe author has highlighted the de-velopments since the turn of the new millennium that have led to a con-siderable concentration of primary aluminium production capacity by way of mergers and acquisitions while some traditional producers have ex-ited the primary aluminium business. This trend is equally observed in the western world as well as in Russia and China. Along with this development, the number of companies developing and licensing reduction cell technol-ogy has shrunk in number, specifically in the western world.

This trend replicates the equally tre-mendous shift of the primary alu-minium production base from west to east.

While for decades Alcoa and the US had been the unchallenged leadersin primary aluminium production, their share of global primary aluminium production today is 7,9 % and 4 %,

respectively, whereas Chalco (8,9 %) and RusAl (8,8 %) are now the big-gest players with almost equal market share and China is the biggest produc-ing region, representing a massive 45 % of global supply. As an update to the reduction cell technology pro-viders presented in Table 1, the fol-lowing Table 13 gives an overview of the remaining and new players at the turn of 2013/2014, together with their

achievements in terms of cell amper-age and the underlying application basis, expressed as the number of operating pots and installed capacity. The reference to new reduction tech-nology players actually only applies to Dubal because the other Russian and Chinese “new” players in fact have quite a history though this went largely unrecognized due to their long-lasting geopolitical isolation. A graphical rep-resentation of pots in operation by technology provider is given in Figure 8.

It can be concluded that two of the remaining technology providers, namely Alcoa and Venalum, appear to be inactive in the field of reduction cell technology development and their technologies would probably not be available for licensing today. This leaves reduction cell technology know-how with only two western companies (RTA and Hydro Aluminium), one each from the Middle East and Russia, and three Chinese research and development institutions.

From the western companies, RTA has


GP300(e.g. GP-30)

GP400(e.g. GP-40)

GP500(e.g. GP-50)

GP300(e.g. GP-30)

GP400(e.g. GP-40)

GP500(e.g. GP-50)

Unit

Smelter Status operatg. operatg. operatg. u/c u/c u/c -

Total Potlines (PLs) 26 2 1 4 0 0 PLs

Total Pots 6322 510 288 840 0 0 Pots

Average Pots 280* 260 290 210 - - Pots/PL

Total Installed Capacity 5,75 0,55 0,39 0,76 - - Mtpy

Avg. Potline Voltage ** 1175 1100 1220 880 - - V/PL

*: excluding some obvious test sections and 2 short potlines of 84 pots/138 ktpy**: assuming 4,2 V/pot

Table 11: Tentative Overview of Chinese Smelters based on GAMI Cell Technology 300 kA as per [26]


NEUI300(NE-30)

NEUI400(NE-40)

NEUI500(NE-50)

Unit

Smelter Status operatg. operatg. operatg. -

Total Potlines (PLs) 1 4 0 PLs

Total Pots 180 1006 0 Pots

Average Pots 180 250 - Pots/PL

Total Installed Capacity 0,15 1,19 - Mtpy

Avg. Potline Voltage * 760 1050 - V/PL

*: assuming 4,2 V/pot

Table 12: Tentative Overview of Chinese Smelters based on NEUI Cell Technology 300 kA as per [26]


Figure 8: Reduction Cell Technology Proliferation (operating pots)

Red

uct

ion

Cel

ls in

Op

erat

ion

7.000

6.000

5.000

4.000

3.000

2.000

1.000

0

*: estimated

NEUI*GAMI*SAMI*Rusal/VAMIVenalumDubalRTAHydroAlcoa

300 - 399 kA400 - 499 kA> 500 kA

39AWJ 2014

Company Cell Type UPBN I / kAPots Capacity / Mtpy

Remarksinstalled u/c installed u/c

Alcoa A-817 AA-32 320 448 none 0,388 none Portland

Hydro

HAL-230 HAL-26 240 - 258 ca. 410 none 0,285 e none Hoyanger, Venalum PL 5, Slovalco

HAL-275 HAL-30 290 - 320 1044 none 0,90 none SU4, Qatalum

HAL4e HAL-42 420 6 none negl. none test cells in Ardal

RTA

AP30/40 AP-30/40 300 - 400 5274 1194 5,25 1.22 various smelters, global spread

AP50 AP-57 570 41 none 0,065 none St. Jean-de-Maurienne, Jonquière

AP60 AP-60 600 none none none none 460 kpty planned for Jonquière

DubalDX DU-38 380 796 none 0,85 none Dubal PL 8, Emal 1

DX+ DU-42 440 449 none 0,55 none Emal 2, Dubal test cells

Venalum V-350 VN-35 325 5 none none none test cells shut down and dismantled (?)

Rusal/VAMI

RA-300 RA-33 330 536 672 0,47 0,59 Tajik, Sayansk, Volgograd

RA-400 RA-44 435 16 672 0,02 0,75 test cells in Sayanogorsk

RA-500 RA-52 520 ? none ? none test cells (to be) in Sayanogorsk (?)

Ch

alco

/ C

hal

ieco

SY300 SY-30-38 300 - 375 4.752 0 4,17 0PASaPoW 05-2013, plus private communications R. Pawlek

SY400 SY-40-45 400 - 450 4.402 2.256 4,84 2,45

SY500 SY-50-52 500 - 520 1.236 2.584 1,71 3,51

CT300/350 CT-30-35 300 - 350 1.558 - 1,32 - unspecified Chinese Technology per PASaPoW05-2013 & private communications R. PawlekCT400 CT-40 400 1.500 - 1,63 -

GP300/370 GP-30/37 300 - 365 6322 840 5,75 0,76 PASaPoW 05-2013, plus private communicationsR. Pawlek, see Chapter 4.8

GP400 GP-40 400 510 0 0,55 0

GP500 GP-50 500 288 0 0,39 0

NEUI

NEUI300 NEU-30 306 180 ? 0,15 ?

NEUI400 NEU-46 415 - 460 1006 ? 1,19 ? 6 PLs u/c: ??

NEUI500 NEU-50 500 ? ? ? ? modeling completed ?

SAMI

Chinaunspec

GAMI

Table 13: Reduction Cell Technology Providers as at the Year 2013

the most widespread global prolifera-tion of their Pechiney-based reduction cells. RTA also licenses its technology independently of project ownership. Their application base of AP3X pots is impressive and is still growing, however this is almost dwarfed by the spread of China-developed reduction cells which, at comparable amperage, all occurred during little more than the last 12 years.

While in the past Hydro Aluminium and RTA have licensed their technolo-gies on a global scale, the application of Dubal, RusAl and the Chinese cell technologies remains, by and large, confined to their respective home-lands, with only a few exceptions. This is, among other reasons, prob-ably due to some persisting questions over the long-term performance of the eastern technology cells. Looking at the performance presented in the tables of the previous chapters, this appears not to be justifiable since the

gap between published eastern and western performance data seems to have narrowed. Other issues are the reported low investment costs and short construction durations in their home countries, which raise the ques-tion of transferability into an interna-tional framework where the specific Russian or Chinese local conditions do not apply. Also, the project scope of facilities and materials/equipment supply sources behind such figures often remain unknown - which makes benchmarking extremely difficult and potentially misleading. Finally, inter-national aluminium smelter projects are often based on project finance with money to be raised on the international financial markets. International financ-ing institutions would normally apply a rigid scrutinization of the project, technically and financially, including compliance checks with international standards such as the World Bank Stan-dards or the Equator Principles. These issues will be much less prominent if

a project is financed out of equity or by a government, as may be the case in the eastern hemisphere.

Coming back to Tabereaux´s expec-tations that future high-amperage reduction cells would require the so-lution of technical problems related to, e.g., wear of cathode lining, heat balance, emissions, cell instabilities, stronger magnetic fields and greater metal losses due to increased cell turn-around time for relining [2], the following general trends can be no-ticed.

The reduction cell technologies have, over the years, undergone a few creep-ing changes that are worth mentioning. Reduction cells are usually developed for a certain amperage. Cells developed up to the 1980s were still very delicate when operating parameters, specifically the cell amperage, were changed and small amperage increases frequently met with major disturbances. It appears



that cells developed in the 1990s and later have a much higher tolerance. For example, this can be concluded from the AP30 creep to AP39/40. This creep has happened within a given potshell with only minor modifications such as the addition of cooling fins or forced (air) cooling systems, adjustments to the anode size and changes in the potlining. While increasing the amper-age (and thus the aluminium output) by about 30 %, the performance fig-ures could be maintained despite the stronger magnetic fields with their potentially detrimental effect on cell performance. This can be taken as evi-dence that the modeling tools applied during reduction cell development have reached a level of sophistication that the behaviour of reduction cells under modified operating parameters can be simulated quite precisely. The same conclusion is applicable for the development of new reduction cells - which seems to happen in ever shorter periods of time with less time required for pilot cell trials.

The creep previously mentioned comes along with an increased energy input to the cell, which up to now is just dissipated as heat into the environ-ment. The crucial issue of the pres-ence (or absence) of a frozen layer of bath (ledge) to protect the sidewall lining is largely left to the success of ventilation enforced by natural draft. Thus, the aluminium reduction cell can be regarded as rare sample of a metallurgical furnace (in German: Elektrolyse-Ofen) operating at just short of 1.000 °C that is left to natural forces for the successful furnace cool-ing as opposed to forced cooling (us-ing media other than air) which would even allow the partial recovery of the dissipated energy.

An achievement of modern PFPB cells that usually goes unnoticed outside the industry is the lowering of the anode effect frequency (AEF) and duration which is due to ever smarter, more reli-able alumina feeding and pot control systems. Obviously, this lowers the amount of energy wasted during anode

effects and disruption of the electrolytic aluminium deposition as well as the thermal cell disturbance related to the additional heat input. Generation of the powerful greenhouse gases CF4 and C2F6 (PFCs) is directly related to the occurrence and duration of anode effects and the industry as a whole has achieved remarkable reductions in the co-production of PFCs. Modern PFPB cells can almost entirely sup-press anode effects which “in the old days” (which started ending maybe only 20 years ago) were considered an indispensable means for good cell operation. Older technologies (SWPB, CWPB, Söderberg) have inherent dif-ficulties in supporting such achieve-ments because the feeding systems do not allow the elimination of anode effects, which means that smelters operating such reduction cells will be under increasing environmental pressure in the future.

Modern high-amperage reduction cells would normally use highly or fully graphitized cathode blocks which are softer than blocks made from an-thracite with low graphite content. As a consequence, one would expect shorter cathode life for cells with graphitized cathodes. Nevertheless it appears that the cathode life is not becoming shorter but indeed longer with a tendency to achieve 2000 days or more on average. Connected to this there should also be no negative effect on productivity (or rather cell availability) from a relining point of view. If cells are not lined in-situ but in a dedicated pot delining/relining facility, turnaround time - and hence loss of metal production - can be kept low and, as a positive side effect, the working environment for the delin-ing/relining activities can be better controlled.

As a summary to the above, today´s computer-based modeling tools (for modeling electro-thermal, electro-mechanical, magnetic, and magneto-hydrodynamic effects) used during reduction cell design are very capable of predicting the behaviour of such

cells. Modern cells designed with such tools have high probability of achiev-ing low energy consumption and, at the same time, high current efficiency because detrimental effects of strong currents and the associated magnetic field can be compensated during de-sign. This results in the required robust cell design necessary for stable cell operation. Sophisticated cell control algorithms (including fuzzy logic) and development of more robust sensors support operation to achieve favourable operating parameters including low AEF. These core reduction cell issues seem to be fairly well controllable even when current intensities well in excess of 300 kA are applied.

From a potline construction point of view, high-amperage cells then require more focus on some rather profane pe-ripheral issues which have been much less important on lower amperage levels. Aluminium reduction cells have, despite some higher anodic/cathodic current densities, almost exclusively grown in one direction with increasing amperage which is the length of the potshell; potshell width and depth have almost remained unchanged over the past 2 – 3 decades. Construction elements affected by a longer pot-shell are the potroom building width; wider crane span combined with heavier lifting loads; consequentially heavier foundations and structural steel el-ements; wider superstructures that need to support more own weight plus more weight from additional anodes without too much sagging, just to name a few.

As has been indicated in the previous chapters on individual reduction cell designs, potlines have grown in number of pots installed per line. Specifically western technologies are now imple-menting potlines with 350 – 400 pots per line whereas eastern technologies seem to only follow this trend more hesitantly (usual pots per potline are still around 200 – 300). While the trend towards longer potlines saves on in-vestment cost for common equipment like the rectifier-transformers (RTs) for


41AWJ 2014

each potline it is also more demanding in terms of voltage level for such units. Recently built long potlines based on Dubal, Hydro and RTA technology now require RTs of 1.700 ± 50 V while this level for eastern technologies is still in the 1200 V range (and below). The RT manufacturers are offering 2.000 V RTs by now, and the Emal 2 potline with 444 pots is the first where this RT technol-ogy is practically applied. The 2 kV RT, however, has two major implications. Firstly, potlines would be able to grow into the 450 pots per potline size which would support 500 ktpy capacity out of just one potline (assumed @ 400 kA). In case of a power failure (generation, transmission, rectification), the entirety of this production capacity would be at risk and it remains to be seen how venturesome the aluminium industry and its financiers will be. Secondly, the 2 kV RT creates higher demands for the electrical insulation of potline buildings and the insulation strength of all affected electrical equipment inside those buildings (motors, cables, PLCs etc.).

Higher metal output per cell also requires more metal handling and more anode carbon to be replaced. An increase of pot interventions (for tap-ping or anode changing) or an increase of potroom and plant traffic would not be welcome by operators so new concepts might have to be devised, e.g. for tapping, there are limitations to increasing the height of the crucible because of the metallostatic pressure that needs to be overcome.

6 Alternatives and OutlookThe Hall-Héroult (HH) cell is a com-paratively inefficient metallurgical reactor, even at the 600 kA level: one 600 kA cell produces only 4,5 t per day or 1.670 tpy, but occupies an area of some 4 m x 18 m = 72 m2. For a commercially viable plant, between 200 and 450 of these cells have to be installed which causes quite a big land usage. In comparison: one single modern iron blast furnace (BF) unit of 10 m hearth diameter, or a footprint of 78 m2, produces 7.260 t per day

or 2.650.000 tpy (2,65 Mtpy!), and there are bigger ones also. HH cells operate at 950 °C or ca. 300 °C above the melting point of pure aluminium and usually yield aluminium of 99,7 % purity or better, whereas the iron BF operates at a tapping temperature of ca. 1.450 °C which is actually some 90 °C below the melting point of pure iron (this is possible because the iron BF does not produce pure iron but an iron-carbon alloy with about 4 % C plus some other metallic impurities which together lower the melting point of the impure, so-called pig iron, which needs to be purified in another step).

So who is to blame for this dispar-ity? In brief, aluminium production is hampered by its very own natural properties, first and foremost its very strong chemical bond to oxygen, but also its trivalence, its low atomic weight and density, plus the fact that common reducing agents like carbon do not work quite well in aluminium metallurgy. These facts required that the harshest of all possible reducing agents had to be deployed to break the aluminium-oxygen bond: pure electrons in the form of electric cur-rent in an electrolytic process, and its industrial manifestation is the HH cell.

Up until now, all investigated or dis-cussed alternatives struggle with some form of fundamental problem related to the strong oxygen-affinity of aluminium and its position in the electrochemical series. Let’s look at some of the potential alternatives:

Electrolysis• Near ambient temperature and/or wa-ter based electrolytic process (maybe similar to copper): aluminium hardly dissolves in aqueous solutions, and if, its position in the electrochemical series favours reduction (= production) of other components of such systems instead of aluminium.

•Electrolytic process closer to aluminium´s melting point of 660 °C, say at around 700 °C (instead of 950

°C): no suitable electrolyte has been found that would combine alumina solubility, electric conductivity etc. like fluoride based cryolite. There are chloride based alternatives which have their own disadvantages, see below.

• Inert anodes: Materials investigated so far are not exactly inert yet, causing co-deposition of more noble metals affecting impurity levels. Widespread industrial application of inert anode materials always seems - at any given time - to be 15 – 20 years away. In prin-ciple, such anodes would just release oxygen, no carbon would be consumed and no CO/CO2 generated, no pot intervention for anode change, and no anode plant would be required. How-ever, the change of the sum reaction would require some 0,5 – 1 V higher pot voltage compared to HH cells.

• Wettable, drained cathode: would reduce magneto-hydrodynamic (MHD) effects and would help avoid the deep pool of liquid aluminium in each cell (15 – 25 cm of dead inventory) required to control the MHD effects; industrial implementation, similar to inert an-odes, always seems far away. A new development from China comprises the mentioned NSC baffled cathode blocks which might help in this context though these NSC cathodes are made of conventional carbon material and therefore are not to be confused with wettable, drained cathodes.

Novel Processes• Carbothermal Reduction (preferably similar to the iron blast furnace process): the quick answer is that thermodynamically, carbon can only reduce alumina above 2000 °C, and that the product is an unwanted and unstable Al4C3 instead of aluminium. However, the issue is much more complicated and can be summarized as follows: up to 2.160 °C, only an alumina-carbide slag (AlO, AlO2, AlC) but no liquid aluminium metal is produced; above 2.160 °C there is also a second phase: something like liquid metal but in fact it is an aluminium-carbon alloy with some 10 % C; at the required



process temperature of > 2.200 °C, additionally there will be considerable evaporation of aluminium in the form of aluminium and aluminium sub-oxide (Al2O) vapors which can amount to up to 25 % of the produced metal and may require a vacuum process stage [85]. Carbothermal reduction is said to be further investigated by an Alcoa-Elkem JV which designed process reactors called Advanced Reactor Process (ARP) and Vapor Recovery Reactor (VRR). While Alcoa-Elkem estimate that Capex and Opex of a commercial ARP + VRR plant would be 30 % less than an equal-sized HH smelter, the authors of [85] also point out that major issues of the carbothermal process still remain unsolved.

In the personal opinion of the author of this review, it appears to be very un-likely that the 50 Mtpy primary smelter community can be convinced to switch from the established HH process (oper-ating at a manageable 950 °C, directly yielding a single, high-quality product without fritting) to a novel carbothermal process that requires extremely high temperatures (> 2.200 °C), and scatters the desired aluminium across 3 product streams, whereby those products are far from being pure aluminium hence requiring some sort of post-treatment for metal purification.

• Alcoa Smelting Process (ASP): it may be argued that this is not a novel pro-cess as it has been developed around 1970 already, that the pilot facility was shut down in 1985, and that it should have been mentioned under Electroly-sis above. Nevertheless, the author of this review wants to point out some of the ASP´s conceptual advantages which may justify its categorization as novel process. Published data on the ASP are scarce, so the below rests on summary information published in [86] and [87], from which also the ASP cell (or rather electrolyser) sketch is taken, see Figure 9.

The ASP consists of electrolysing Al-

Cl3, dissolved in a chloride electrolyte (e.g. NaCl + LiCl), operating at 700 ± 30 °C. No PFCs would be generated/emitted.

HH cells consist of one single, hori-zontal anode-cathode pair (also PB cells where the anode may consist of some 40 individual anode blocks). In contrast, the ASP electrolyser com-prises 12 horizontal bipolar anode-cathode pairs stacked above each other, i.e. the underside of each electrode acts as anode whereas the upper side acts as cathode (see Fig.9). In this way, one ASP electrolyser replaces 12 HH cells.

The 1980s ASP electrolyser is quoted to have produced in excess of 13 tpd; crunching the few available numbers, back-calculation reveals that the am-perage would have been 140 kA (which fits very well with the rectifier capa-bilities of the early 1970s) resulting in 13,2 tpd or 4.820 tpy per single ASP electrolyser (at an assumed CE of 98 %), which is 3 times the output of one AP60 cell.

No dimensions for an ASP electrolyser are available but, based on a num-ber for current density, the author of this review dares an educated guess: the size of one ASP electrolyser was

probably about 3 m x 3 m (W x L) with height between 2 and 3 m. This means, one single ASP electrolyser produces 1,47 t/(m2 day) which is 2350 % of one AP60 cell, despite the ASP only requiring 140 kA or 23,3 % of the AP60 current intensity.

The bipolar electrodes are inert, i.e. no electrode changes would occur (probably, after some time the ASP electrodes would also deteriorate to some extent and would have to be replaced about once every 3 years, which is more similar to cathode relin-ing in HH cells). An ASP smelter would therefore not require any anode plant and no CO/CO2 would be generated/emitted.

The interpolar distance (ACD) is quoted as 1 – 2 cm (HH: ca. 5 cm), and the cathode surface only carries a thin film of aluminium which is swept off by the anodic chlorine gas-induced electro-lyte circulation. As a consequence, MHD disturbances in ASP electrolysers would be minimal which would most certainly allow placing electrolysers much closer to each other in an indus-trial ASP smelter (recap: HH pot rows are spaced some 30 – 90 m apart). A higher CE of (assumed) 98 % seems also justifiable for ASP electrolysers due to lower MHD impact.


Figure 9: Sketch of Alcoa Smelting Process Electrolyser [87]

Feed port

Upcomer

Downcomer

Bipolar

Anode - cathodespace

Aluminiumsump

Terminalcathode

Terminalanode

43AWJ 2014

Due to use of a chloride electrolyte, single-cell voltage (i.e. one anode-cathode pair) is 2,7 V, so one electrol-yser would require some 32 V, plus external busbar losses. ASP´s specific power consumption is quoted as < 9,5 kWh/kg.

Despite the clear advantages that such an ASP based smelter would present, the author does not want to hide that there are obviously major challenges that lead Alcoa to stop this develop-ment 30 years ago. One area of concern is the preparation of the intermedi-ate AlCl3 which is a nasty chemical compound as it is highly corrosive, volatile, hygroscopic (attracts water) and hydrolyses (e.g. with humid air) forming aluminium oxi-chlorides. Both water and oxygen impair the electrolytic process and must be kept at minimum levels. There would also be formation of chlorinated biphenyl which needs to be removed in order to avoid pol-lution issues.

However, the author of this review be-lieves that it may be worthwhile re-visiting the underlying ASP concept again, given some 30 years of scientific progress in material science, process engineering, and computational simu-lation tools.

In order to demonstrate the potential behind the ASP concept let’s make the following thought experiment: Assume it is possible to stack 20 bipolar anode-cathode pairs (instead of 12) in one ASP electrolyser. Additionally you put 2 of these stacks into one electrolyser so one electrolyser would now have dimensions of 3 x 6 x 3,5 m3 (W x L x H), and the increased electrode area would permit 300 kA at only incremen-tally higher current density. Imagine a smelter with 100 ASP electrolyser units, and the capacity would be a whopping 1.720.000 tpy!

Looking forward, it looks as though the Hall-Héroult process at its 128th anniversary is here to stay for quite

some time. Alternative processes are not close to any kind of industrial implementation.

Concluding from this it means that the primary aluminium industry would continue to improve the Hall-Héroult process gradually. How far the increase in potline amperage, one-dimensional growth of cell length and ever lon-ger potlines can be sustained before some kind of optimum configuration is reached remains to be seen.

Aluminium demand growth seems to continue in line with global urbaniza-tion and population growth, and recy-cling efforts should be reinforced as much as possible. However, recycled material will only continue to comple-ment primary aluminium production which will likewise (have to) continue to be the major source of any future aluminium supplies.

7 AcknowledgementsSpecial thanks go to my former col-leagues, Dr. Robert Minto and Thiago Heitling, who helped establishing the first edition. For this second edition, I would like to thank Anne Tappen for her friendly support and Rudolf Pawlek for his private communica-tions regarding latest intelligence on Chinese smelters.

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45AWJ 2014

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Author: Dr.-Ing. Joachim HeilContact Information:[email protected]


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