ISSN 1611-616X VULKAN-VERLAG · ESSEN 22004

HHHHEEEEAAAATTTTPPPPRRRROOOOCCCCEEEESSSSSSSSIIIINNNNGGGGINTERNATIONAL MAGAZINE FOR INDUSTRIAL FURNACES · HEAT TREATMENT PLANTS · EQUIPMENT

MultiMelter© – The new generation ofaluminium melting furnaces

Dr.-Ing. Björn Henning, Jasper GmbH, Borstel-Hohenraden (Germany)Dipl.-Ing. Robert Jasper, Jasper GmbH, Geseke (Germany)

Published in HEAT PROCESSING 2/2004

Vulkan-Verlag GmbH, Essen (Germany)

Editor: Dipl.-Ing. Stephan Schalm, Tel. +49 (0) 201/82002-12, E-Mail: s.schalm@vulkan-verlag.de

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Introduction

In principle construction units fromaluminium can often be melted for theproduction of new products. At presentin Europe is approximately 35 % for thetotal requirement of aluminium availableby recasting. The increased demand foraluminium products and the political andeconomic orientation to the recyclingeconomy requires the advancement ofthe remelting processes, since more andmore scraps (contaminated aluminiumscrap) arrive in this cycle. Thesecontaminated aluminium scrap comespredominantly from the recycling, e.g.aluminium windows with foam core,aluminium profiles with bonded sealsfrom plastic, composite sections fromaluminium and plastic. These scraps arenot to be separated at justifiableexpenditure so far and will be melted asa mixture of different scraps with atremendous effort of energy connectedwith high environmental impact [3]. Inthe rotary furnace contaminatedaluminium scrap is melted by coveringthe melt with salt (NaCl and CaCL), inorder to prevent the oxidation ofaluminium. The dross of salt whichoriginates in the furnace is very complexto recycle. The Closed Well Furnace ortwo-chamber melting furnace is suitablefor melting thin-walled and easily tomedium contaminated scrap. A fixedpartition wall divides the furnace intoHeating Chamber and PyrolysisChamber. The Heating Chamber issuitable for melting clean and blank

scrap. The homogenisation of the bathand good melting capacities are reachedby a circulation pump. However, thepartial highly loaded exhaust gas fromthe Pyrolysis Chamber makes a cleaningprocess necessary. A part of the exhaustgas flow can be supplied to the gasburners. The same effect can beobtained by a TNV (Thermal PostCombustion), in order to cool down theflue gases by a water shower fordecontamination. Fixed particles areseparated in the following filter system.

Dioxins and Furans originateunintentionally during recasting ofcontaminated aluminium scrap inpresence of plastics (chlorine, bromine)under participation of chlorine donors,e.g. carbon, potassium and copper. Thedioxins are formed up to 600 °C anddisintegrate at furnace temperatures by1200 °C into their molecular structures.But with the cooling of the flue gas, anew formation synthesis (de novosynthesis) begins as an unintentionalcycle process up to approximately 300 °C.

MultiMelter© – The new generation ofaluminium melting furnaces

In particular the secondary aluminium industry is in Europe at enormous costpressure. In order to work against the rising costs, on the one hand energy-savingprocesses and on the other hand a minimization of the metal losses are necessary.This will be more difficult due to more contaminated scrap, which arrives into thecycle of the remelting processes. Here is a process engineering demanded, whichfulfil the extreme operating conditions of recasting by specific environmental andfinancial aspects. The MultiMelter© – an advancement of the multi-chamberfurnace combined with the newest technologies – is to be introduced in this article.

Dipl.-Ing. Robert JasperJasper GmbH, Geseke(Germany)Tel. +49 (0)2942 / 9747-14Email: r.jasper@jasper-gmbh.de

Dr.-Ing. Björn HenningJasper GmbH, Borstel-Hohenraden (Germany)Tel. +49 (0)4101 / 801-150Email:b.henning@jasper-gmbh.de

Fig. 1: ECOREG®-Regenerator

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For these contaminated aluminiumscrap are solutions in demand, whichcan help to reduce or eliminate thisproblematic environmental impact andallows an economic mode of operation.

State of art

The main focus for all melting processesis:

• to reduce the metal loss,

• to decrease the energy consumption,

• to prevent dioxins and furans and

• to decrease the CO2-Emissions.

Since more than 20 years the JasperGmbH is involved in the field of buildingplants and furnaces for an economicand environment friendly energy con-sumption. A consistent work in researchand development led to products andprocedures, which consider to thesedemands. In December 1997 a researchproject for a rotating regenerator wassuccessfully finished, which wassupported by the German Government.This rotating regenerator was patentedby the product name EcoReg®

Regenerator. The EcoReg®-Regenerator(Fig. 1) is used for a central heatrecovery in powerful furnaces andreplaces the classic recuperator. The airpiping can be connected to an unlimitedquantity of burners.

The flue gas temperature amountsbetween 1200 °C to 1400 °C. Thisresults in an average combustion airtemperature of approximately 1060 °C to1275 °C (in the High Temperatureversion up to 1400 °C). The exhaust gasof the rotating regenerator (heatexchanger) has a temperature of 140 °C

up to 210 °C, which is suitable as filterinlet temperature. The energy savingamounts up to 62 % in relation to aburner system for cool air with a flue gastemperature of about 1400 °C.

A continuously optimisation of thisrotating regenerator system EcoReg®

and a multitude practical applications inthe aluminium and steel industry was thereason for further developmentconcerning exhaust air purification. Inframe of a research project in 1998 theexhaust air purification was successfullyproven concerning dioxin (quenching ofdioxin). This outstanding effect of thedioxin reduction during simultaneoushigh heat recovery is an environmentfriendly and financially attractive solutionfor the use in melting furnaces.

This combination – a multi-chamberfurnace, in which dirty and contaminatedscrap can be used, with EcoReg® andan internal pyrolysis gas burning –resulted in the plan to the MultiMelter©.

MultiMelter© furnace andapplication

The MultiMelter© is a three chamberfurnace with an integrated pyrolysisprocess. The field of application is theeconomical and ecological melting ofAluminium Scrap heavily contaminatedwith organic coatings and inlets (Fig. 2).The operation of this furnace is withoutsalt.

The newest MultiMelter© (Fig. 3) with acapacity of 120 t/day with a bath contentof 60 t was built for BAGR Aluminium-verwertung in Berlin this year [2]. JasperGmbH got the order on the Therm-process Fair 2003 in Düsseldorf. Thewhole plant was done as a Turn-Key Jobby Jasper GmbH. This job needs fromorder to the first production only 9month. The task was to reach a goodmelting process for dirty andcontaminated scrap with minimal metalloss and the highest possible energysaving through a consequently use ofthe newest available technology.

The technical data of this plant are asfollows:

• Melting Capacity : 5 to/h

• Bath Content: 60 to

• Energy Consumption: < 650 kWh/toaluminium

• Used Aluminium Scrap: blank anpolished srap, painted and de-contaminated scrap, turnings

• Yield: > 98 % for clean scrap

• Yield: > 90 % for dirty and de-contaminated scrap

• Run Time: 550 h per month

• Temperature of Air Preheating: up to1000 °C

• Flue Gas Temperature behindECOREG®: < 220°C

These are the actual data after the firstoperation. Especially the energy

Fig. 3:MultiMelter©

BAGR Aluminium-verwertung GmbHin Berlin, Germany

Fig. 2: MultiMelter© - Regenerator melting furnace

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consumption and the metal loss shall befurther minimised due to an optimisedprocess operation.

The Multimelter© consists of:

• A Heating Chamber (1) to melt cleanscrap, ingots etc. and to heat the bathof liquid aluminium.

• The Pyrolysis Chamber (2) to pyrolysethe organic components of the scrapinto fuel gas and to melt thedecontaminated scrap.

• The PreMelt Inc.– Pumping Chamber(3) with the function of circulating thebath of liquid aluminium and to meltturnings and chips.

The Heating Chamber (1) and thePyrolysis Chamber (2) are equipped withLow NOx Burners with SFI-Technology(Selective Fuel Injection). The SFI-burnertechnology, specially developed byJasper GmbH allows the co-utilisation ofthe pyrolysis gas. In general, all burnersystems of Jasper GmbH are deliveredexclusively in “low emission” version. Asa minimum standard all burners are builtto the German “TA-Luft” requirements,with the following values: NOx < 350mg/Nm3 and CO < 100 mg/Nm3 (5 %O2) [1]. The installation of a specialburner type depends on the applicationof the melting process. The burnersystems (gas or oil) are regulated byoxygen content. The pyrolysis-gasreplaces to a part the main fuel in anefficient and economic way. Differentways are possible to use the pyrolysisgas as substituted fuel. On the one handit can be directly burned in the heatingchamber and on the other hand it can becompletely burned with the natural gaswithin a special burner system.

The pyrolysis gas is formed in thePyrolysis Chamber (2) (Scrap Chamber).

After charging the scrap is lying on abridge. The chamber is heated with aHiTAC-Burner High Temperature AirCombustion) and the convective heattransfer is responsible for the firstthermal treatment of the scrap. Theorganic adhesions releases immediatelywith a temperature above of 350 °Cduring the heating process and the srapis preheated before it slides into thebath. The Scrap Chamber (PyrolysisChamber) is loaded several times perhour due to a uniform heating. Further,this thermal treatment has the effect of adecreasing metal loss due to aminimized oxidation of the aluminiumscrap [4]. The volatiles release and theformed pyrolysis gas is transported intothe Heating Chamber (1). It must beassured that all organic gaseouscomponents completely burned in theHeating Chamber (1). The pyrolysis gascan substitute the main fuel (natural gas)up to 15 %.

A Regenerator System guarantees aneffective heat recovery to preheat the

combustion air (Fig. 4). Further, theregenerator substitutes the quench-cooler to suppress the De-Novo-Synthesis of dioxins and furans. Thefurnace is equipped with a PLC SiemensS7 System with a visualisation of allcomponents, e.g. temperature, pres-sure, oxygen content etc.

Conclusion

The MultiMelter© reach high meltingcapacities with a minimum of meltinglosses. A extreme decrease of energyconsumption is reached by an effectiveheat recovery and the substitution ofnatural gas through pyrolysis gas. Thereducing of metal loss by the pyrolysisprocess and the energy saving throughan effective heat recovery by theRegenerator results in a short time of aReturn of Investment. The MultiMelter©is the profit generating melting furnacefor secondary aluminium melters withrespect to the environment.

Literature

[1] Jasper, H.D.: Low energy and emission intandem: State of the Art HiTA-Combus-tion; 4th International Symposium onHigh Temperature Air Combustion andGasification, Rome 2001

[2] Gansen, H.; Güngör, M.; Jasper, H.D.:Energieoptimierung einer Sekundär-schmlezhütte, Gaswärme International08/2003, Vulkan-Verlag

[3] von Starck, A.; Mühlbauer, A.; Kramer, C.:Praxishandbuch Thermoprozesstechnik,Vulkan-Verlag 2003

[4] Brune, M.; Giese, A.; Mackenstedt, D.:Optimierung der thermischen Prozess-führung von gasbeheizten Schmelzöfenzur Produktion von Sekundäraluminium,Gaswärme-International 05/2004, Vulkan-Verlag

Fig. 4: ECOREG®-Regenerator BAGR Alumi-niumverwertung GmbH in Berlin, Germany