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R&D Carbon operates a pilotplant and laboratory to studyvirtually all carbonaceousmaterials used for thealuminium and steel industry.Sophisticated research projectsare conducted in parallel withtesting of carbonaceousmaterials. A review is givenabout the activities andcapabilities of the technologycentre in Sierre, Switzerland.By Dr Markus W Meier*,Raymond C Perruchoud* andJean-Claude Fischer*

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January/February 2012 Aluminium International Today

In 1986 Werner Fischer founded R&DCarbon with a management buy-out fromAlusuisse, where he had headed thecarbon research group since 1966.

Werner Fischer defined six areas ofwork, which are still in operation today:– Research and development– Sales of laboratory test equipment and

standards– Technical services– Bake furnace firing and control systems– Technology development– Training and conference

R&D projects have been a veryimportant part of R&D Carbon since itsfoundation 25 years ago. In the past 25years seven PhD dissertations have beencompleted in collaboration withuniversities in New Zealand, Switzerlandand China.

The topics covered fundamentalquestions related to anode raw materialcharacteristics and reactivity behaviour[1],green mill operation[2], heat treatmentduring baking[3], anode properties, anodeburning, dusting and crackingbehaviour[4], as well as an in-depthunderstanding of Chinese raw materials[5].

The results of these extendedinvestigations were published as technicalpapers in renowned journals, for whichR&D Carbon was honoured several timesincluding several Light Metals awards[6, 7,

Testing of Carbon Materials forResearch and Industrial Purposes

* R&D Carbon Ltd

Forming area of pilot plant with vibrocompactor, extrusion press, pilot press and bench scale unit

8]. Comprehensive handbooks werepublished that are considered today asindispensable reference books for everyperson working in the carbon area ordealing with carbon related topics ofaluminium smelters.

To pass on the findings of the extendedresearch and practical developmentprojects, R&D Carbon regularly organisestraining courses for which the companyhas gained a reputation and recognition.

The international training course“Anodes - From Raw Materials to the PotPerformance” is organized in Switzerlandevery second year (the next course isscheduled for October 8 - 12, 2012) withparticipants from all over the world.

Today’s focus of researchIn the two decades since R&D Carbonwaas formed, the aims of the researchactivities were to improve the performanceof anodes to reduce carbon consumptionand thus the aluminium production cost.

These investigations are ongoing, astoday’s changing quality of anode rawmaterials (lower coke density and lower QIin pitch) create new challenges that theindustry has to deal with.

With the introduction of graphitisedcathodes to the aluminium industry, theirlimited abrasion resistance became thedetermining factor for the potlife.

This has activated a new researchprogramme at R&D Carbon to investigatein alternative coke types to be used for

graphitized cathodes with high abrasionresistance [9]. Potential alternatives aretested that have a significantly higherexpected lifetime than ordinary graphitisedcathodes.

The steel industry is suffering from ashortage of needle coke to manufacturegraphite electrodes. Emerging countriessuch as China, India and Russia produceand consume large quantities of graphiteelectrodes. They need ever more premiumneedle coke with a low coefficient ofthermal expansion, as their steel industryinstalls more ultra-high-power electric arcfurnaces (EAF). Western countries andJapan cannot supply much more needlecoke from their scarce feed stocks of lowsulfur decant oil. Therefore thedevelopment and production of first classcoke by delayed coking of coal tar pitch isurgently required in the years to come torespond to the increased demand.

Pilot PlantR&D Carbon operates in its technologycentre in Sierre an advanced pilot plantwith a range of equipment.

Pilot calcinationThe choice of both calcining technologiesand of the corresponding calcinationparameters are of principal importance forcalcined coke quality. In R&D Carbon’spilot plant, green coke can be calcinedeither in a rotary kiln or in a shaft calciner.

The plant can reach a production rate of

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January/February 2012 Aluminium International Today

up to 20kg/h with appropriate heattreatment and residence time to guaranteethe correct degree of calcination for eachof the different applications.

Preparation of green pasteThe dry aggregate is prepared throughcontinuous sieving in fractions andcontinuous grinding in a air jet mill. Thepaste is mixed either in an intensiveimpeller mixer or in a sigma blade mixer.Several batches with different bindercontents are prepared for determining thecorrect binder requirement.

Pilot forming of carbon artefactsDepending on the product type andapplication, the paste is formed in a benchscale press (50mm diameter), pilot scalepress or vibrocompactor (147mmdiameter) or a 400t extrusion press (80mmrod).

Pilot bakingThe formed green carbon artefacts arebaked in an electrically heated pilot bakefurnace to a final temperature between1050 and 1250oC to remove the pitchvolatiles and to increase the real density foroptimum physical and chemical propertiesof the final product.

For Söderberg applications, the greenpaste is baked in a dedicated Söderbergbaking furnace where the paste is bakedunder pressure.

GraphitisationAfter machining the samples to 50mmdiameter rods, the final step is tographitise them. The rods are placed in alengthwise column for graphitisation in an80kW pilot furnace. The cores remainunder pressure during the entire process.

The incremental change in length of thesample provides vital information on thepuffing behaviour in the temperaturerange of 1200 to 1700oC and on thegraphitisation pattern up to 3000oC.

R&D Carbon uses its versatile pilot plantnot only for research purposes, but

regularly conducts assessments oroptimisation trials as part of its technicalassistance of customers who manufactureor use carbon products.

Carbon testingVirtually the entire array of carbonmaterials used for the metallurgicalindustry may be characterised, as thefollowing roster shows.

Green Coke/Anthracite– Ash content (%) ISO 8005– Elements XRF (%/ppm) ISO 12980– Hardgrove grindability index (-) ISO 5074– Sieving analysis (%) ISO 12984– Volatile matter (%) ISO 9406– Water content (%) ISO 11412

Calcined Coke and Crushed Butts– Air reactivity (%/min) ISO 12982-1– App. Hg density (kg/dm3) DIN 66133– Ash content (%) ISO 8005– CHON analysis (%/ppm)ASTM 5291-02– CO2 reactivity (%) ISO 12981-1– Crystallite size Lc (A) ISO 20203– Elements XRF (%/ppm) ISO 12980– Grain stability (%) ISO 10142– Oil content (%) ISO 8723– Real density in xylene (kg/dm3) ISO 8004– Sieving analysis (%) ISO 12984– Spec. electr. resistance ( Ωm)ISO 10143– Tapped bulk density (kg/dm3)ISO 10236– Water content (%) ISO 11412

Pitch– Ash content (%) ISO 8006– Coking value (%) ISO 6998– Elements XRF (%/ppm) ISO 12980– Quinoline insoluble (%) ISO 6791– Real density in water (kg/dm3)ISO 6999– Softening point Mettler (oC)ISO 5940-2– Toluene insoluble (%) ISO 6376– Viscosity (mPas) ISO 8003– Water content (%) ISO 5939

Prebaked, Söderberg Anodes and Butts– Air permeability (nPm) ISO 15906– Air reactivity (%) ISO 12989-1

– Apparent density (kg/dm3)ISO 12985-1– Ash content (%) ISO 8005– Binder content (%) ISO 14423– CO2 reactivity (%) ISO 12988-1– Compressive strength (MPa)ISO 18515– Crystallite size Lc (A) ISO 20203– Dyn. elasticity modulus (GPa)

DIN 51915– Elements XRF (%/ppm) ISO 12980– Flexural strength (MPa) ISO 12986-1– Fracture energy (J/m2) RDC 184– Open porosity (%) ISO 12985-2– Real density in xylene (kg/dm3) I

SO 9088– Spec. electr. resistance ( Ωm)

ISO 11713– Static elasticity modulus (GPa)

ISO 18515– Thermal conductivity (W/mK)ISO 12987– Thermal expansion (10-6/K) ISO 14420

Cathode– Air permeability (nPm) ISO 15906– Apparent density (kg/dm3)ISO 12985-1– Ash content (%) ISO 8005– Compressive strength (MPa)ISO 18515– Dyn. elasticity modulus (GPa)

DIN 51915– Elements XRF (%/ppm) ISO 12980– Flexural strength (MPa) ISO 12986-1– Fracture energy (J/m2) RDC 184– Open porosity (%) ISO 12985-2– Rapoport expansion (%) ISO 15379-1– Real density in xylene (kg/dm3)

ISO 9088– Sodium vapour resistance (%)RDC 192– Spec. electr. resistance ( Ωm)ISO 11713– Static elasticity modulus (GPa)

ISO 18515– Thermal conductivity (W/mK)SO 12987– Thermal expansion (10-6/K) ISO 14420

The company also analyses specialcarbon materials in its laboratory, such as:– Ramming paste– Stub collar paste– Söderberg briquets for Si arc furnaces– Electrodes for steel production

Modern research equipment andcorresponding techniques are applied tolink the macrostructure properties of thecarbon materials to their porosity,crystallinity and macrostructure.

Among them, X-ray spectrometry anddiffractometry, mercury pressureporosimetry and microscopy imageanalyser are proven as efficient tools.

Technical assistance R&D Carbon tests carbonaceousmaterials for customers with differentgoals, but all rely on sound test resultscombined with clear recommendationsfor optimisation.

Routine analysis Prebaked and Söderberg anode plants

Testing with high precision and capacity

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regularly send samples of anodes andraw materials for analysis of the relevantproperties in weekly, bi-weekly ormonthly intervals. These plants also oftenoperate their own laboratory. But the testresults provided by R&D Carbon areusually broader and accompanied withan evaluation of actual trends that arepresented graphically. The short leadtime also makes it interesting for plants,which could send the samples to theircorporate laboratory.

The third party opinion given in thereports is an important support for theresponsible plant personnel in theirdecisions about raw material procurementand plant operation.

Shipment certificationTogether with Aminco Resources R&DCarbon has developed a business modelto produce “Swiss Anodes Made inChina”.

Stringent specifications and technicalsupport starting with raw materialselection and during the entire productionprovided by R&D Carbon allows Amincoto offer quality anodes. Since the late1990s Aminco has supplied more than1.5Mt of baked anodes to customersworldwide. Samples of each shipmenthave been analysed in R&D Carbon’slaboratory to issue the quality certificateand to assure specifications are met.

Suppliers of coke, pitch, prebakedanodes and special products (such asSöderberg briquets or ramming paste)appreciate independent certification oftheir product shipments. The quality sheetas part of the technical report brings anadded value to the product, as theparticular advantages claimed by theproducer get much more transparent.

R&D Carbon is also regularly contactedas an independent party for arbitragequestions. Either suppliers or consumerssend samples for analysis to crosscheckwhether the specifications are met.

Plant audits and optimisation trialsEvery major smelter decides at some stageto conduct an audit of its production siteby an external party with the appropriateexperience.

For audits within the carbon area, R&DCarbon has gained a reputation due to theclarity of information provided[10]. Themethodology used involves taking samplesat every relevant processing step along thematerial stream from the anode rawmaterial intake to the potrooms.

These samples are analysed in itslaboratory for the relevant properties. Thecomparison of the properties with a vastdatabase means each processing step isjudged in relation to the world averageand benchmark. As a consequence, thepotential for improvement can be

quantified for every processing step basedon neutral criteria.

The plant audit may conclude that adynamic process optimisation in the pasteplant (DPO[11]) or bake furnace[12] isjustified. These are powerfulmethodologies to boost production andproduct quality often without anyinvestment in hardware. In either casesystematic tests are conducted that resultin a large number of samples.

The samples generated during a plantaudit and during a process optimisationexceed the capacity of an ordinarylaboratory of a smelter. Therefore thesesamples are analysed in R&D Carbon’slaboratory, which is equipped andprepared for large amounts of samples.

Non-routine testing It is evident that many activities of thelaboratory occur on an irregular basis onshort term notice.

Such activities may include a quick rawmaterial evaluation. The procurementdepartment of a smelter may send somecoke samples of a new supplier to checkthe compatibility with the existing rawmaterials. In such a case a full analysis ofthe new and of the reference cokefollowed by a bench scale test will providevaluable information long before thepotential new coke is processed in theplant.

Preliminary tests may be conducted,when a plant experiences problems in itspotrooms, such as a carbon dusting oranode cracking problem. The informationgained from these tests often give valuableindications of the potential root cause(s) ofthe problem. This means the actualproblem can be resolved more efficientlyduring the subsequent plant visit.

Assuring testing accuracyR&D Carbon regularly conducts roundrobin tests to support other laboratories toensure the accuracy of theirmeasurements. For owners of laboratory

test equipment from the company, asupport service is available formaintenance, repair and certification. Thismeans the comparability of the test resultsfound on carbon materials is assured. �

References[1] Sheralyn Hume, Influence of Raw MaterialProperties, R&D Carbon, Switzerland, 1993/ 1999[2] Kirstine Hulse, Raw Materials Formulation andProcessing Parameters, R&D Carbon, Switzerland,2000[3] Felix Keller and Peter Sulger, Baking of Anodesfor the Aluminium Industry, R&D Carbon,Switzerland, 2008[4] Markus W Meier, Cracking Behaviour ofAnodes, R&D Carbon, Switzerland, 1996[5] Liu Fengqin, Blending of Chinese CarbonMaterials for the Production of Anodes for theAluminium Industry, R&D Carbon, 2004[6] Werner K Fischer and Raymond C Perruchoud,“Influence of Coke Calcining Parameters onPetroleum Coke Quality”, Light Metals 1985, 811- 826[7] Sheralyn M Hume, Werner K Fischer, RaymondC Perruchoud, James B Metson and R Terry K.Baker, “Influence of Petroleum Coke SulphurContent on the Sodium Sensitivity of CarbonAnodes”, Light Metals 1993, 535 - 541[8] Raymond C Perruchoud, Markus W Meier,Werner K Fischer, “Survey on Worldwide PrebakedAnode Quality”, Light Metals 2004, 573 - 578[9] Raymond C Perruchoud, Werner K Fischer,Markus W Meier, Ulrich Mannweiler, “CokeSelection Criteria for Abrasion ResistantGraphitized Cathodes”, Light Metals 2011, 1067 -1072[10] Nils Einar Saue, Jon Ola Ystgaard, Jon-IngeJohannessen, Markus W Meier and Raymond CPerruchoud, “Improvement of Anode Paste Qualityand Performance of Alcoa Lista”, Light Metals2012[11] Raja Javed Akhtar, Saleh Ahmad Rabba,Markus W Meier, “Dynamic Process Optimizationin Paste Plant”, Light Metals 2006, 571 - 575[12] Vinicius Piffer, Ciro Kato, Markus Meier,Raymond Perruchoud, Peter Sulger, “ProcessOptimization in Bake Furnace”, Light Metals 2007,959 - 964

Mobile laboratory shipped onsite for dynamic process optimization DPO of paste plant

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