Four-flight technology greatly enhances throughput and quality
BUSS: New Kneader Generation for Anode Paste

Pratteln (Switzerland), May 22, 2012 –  At an in-house show with technical presentations, BUSS presented the first new KX 650 DT Kneader for compounding anode paste used in aluminium electrolysis. Based on more than fifty years of continuous progress, BUSS has taken account of foreseeable market requirements in a long-term development project. The result is an innovative BUSS KX Kneader whose overall concept offers users three decisive advantages:

• 30 % more throughput per machine size, and better mixing of the petroleum coke and pitch used for making anode paste,
• Greater dependability and safety, lower operating and maintenance costs,
• Lower investment costs for plant machinery and buildings, thanks to higher performance.

These KX Kneaders (like their forerunners) also offer another advantage. In contrast to open mixers, the anode paste density so important for quality can be controlled by varying process parameters such as the screw speed and throttling.

Decisive for this quantum leap in performance, product quality and customer benefit is that KX anode paste Kneaders now incorporate the well-proven BUSS four-flight technology introduced ten years ago. The new Kneaders have a higher-capacity processing section and over 30 % more shear-effective surface area. Moreover extensive flow has been increased by about 45 % to improve distributive mixing of the pitch and petroleum coke without damaging the latter’s structure. It goes without saying that the dependability, durability and abrasion resistance of this new KX Kneader generation meet the customary high BUSS standards.

Apart from greater throughput, the new KX Kneaders are also distinguished by the following features:

• New electrical heating of the BUSS Kneader housing instead of the previous heat transfer oil system, with temperature control included in delivery,
• An innovative dynamic throttling system, directly upstream of the anode paste output, which does not require any hydraulically actuated flap dies,
• The KX Kneader housing is now split horizontally, so that the upper half of the housing can easily be removed by crane to the service station included; the Kneader screw and both halves of the housing are optimally accessible thereby for maintenance and upkeep work.

In-house presentation: 60 t/h Buss Kneader KX 650 DT

At an attentive gathering of visitors from all over the world, BUSS presented the first new-generation KX 650 DT Kneader both in theory and practice. The dimensions of the KX 650 DT are impressive: a 6200 mm long housing and 650 mm diameter screw shaft. With a design throughput of 60 t/h, this BUSS Kneader compounds about 52 tons per hour of petroleum coke preheated to about 180 °C. At the beginning of the wetting and transformation zone 8 t/h of pitch, also at a temperature 180 °C, are directly injected into the processing zone through special-version kneading pins. Then the combined rotary and axial screw shaft motion typical of BUSS Kneaders intensively mixes and kneads the petroleum coke and pitch into a homogeneous paste. The innovative dynamic throttling system afterwards builds up the pressure required for extruding the anode paste while at the same time enhancing the mixing effect.

Improvement details

The KX Kneader processing chamber is divided into four different zones, each with optimized screw and housing geometries according to purpose. Petroleum coke preheated to 180 °C is fed to the intake zone and transported to the process zone. The screw flight pitch is greater than the screw shaft stroke to ensure constantly uniform forward flow. Back venting enables drawn-in air to escape without interfering with the incoming petroleum coke feed.

In the wetting and transformation zone immediately after the intake, the pitch, previously liquefied in a separate unit, is injected into the petroleum coke at 180 °C through borings in the special-version kneading pins. This direct injection prevents deposits and clumping as well as the release of volatile components.

In the mixing and kneading zone the kneader screw segments and kneading pins interact to ensure intensive mixing of the petroleum coke and pitch. At the same time the liquid pitch diffuses into the pores of the petroleum coke, which requires an adequate and optimally uniform dwell time of the mix in this zone. This distributive mixing is decisive for the excellent homogeneity of the anode paste.

The final extrusion zone begins with dynamic throttling, an innovative method not requiring any moving parts or hydraulic elements. Dynamic throttling counteracts the transport effect of the kneader screw – thereby increasing the mixing and kneading zone filling degree to further improve mixing – and generates the pressure required for anode paste extrusion without breaking up the coke fraction again just before the end of the mixing process.

Many of the improvements embodied in the BUSS KX Kneader help to save investment and operating costs. Decisive for this is the increase in specific throughput, because the overall investment costs depend above all on:

• The kneader size, 
• The additional equipment required for operation, and
• The plant building size.

An additional cost-saving factor is the extreme compactness of the KX Kneader, which further reduces space requirements.

BUSS focused with this new Kneader generation on maximum dependability and user-friendly operation. The kneader housing therefore has an electrical heating system instead of the previous oil heating system. This type of heating – mainly required during the start-up phase – is not only more dependable, but also safer because it reduces accident risk by eliminating pipes and hoses for the 280 °C heat transfer oil. As an added bonus, it thereby reduces investment and operating costs

Another new feature is the horizontally split kneader housing. This enables the upper half of the housing to be removed quickly and easily by the same crane used for lifting out the kneading screw, and rotated before setting down in the service station that is included in delivery. Also the kneader screw shaft can be lifted out of the bottom half of the housing if necessary. All parts of the kneader are then easily accessible for maintenance and servicing. Thanks to the service station, the necessary workspace is significantly less than for a kneader of the same size in the previous version. The fact that the kneader screw shaft no longer has an external bearing further simplifies servicing, and also reduces structural loading and vibrations in the building.

Christian Hauser, Manager Aluminium & Service, summarizes the advances embodied in the KX Kneader development as follows: “The new BUSS Kneader generation not only meets all current needs for anode paste production, but can also handle future demands for even higher throughputs. Our innovative KX Kneaders are distinguished by a decisively better price/performance ratio with regard to investment, operating and maintenance costs alike, and by a further improvement in anode paste product quality. That is a firm basis for further expanding our strong position in this particularly promising speciality market” 

Contact person for further information:
Marco Senoner, Buss AG
Hohenrainstrasse 10,  CH-4133 Pratteln
Tel.:  +41(0) 61/825 65 51,  Fax:  +41(0) 61/825 66 88
E-mail:  marco.senoner(at)busscorp.com
Internet:  http://www.busscorp.com

Editorial contact and voucher copies:
Dr. Diether Burkhardt, KONSENS Public Relations GmbH & Co. KG,
Hans-Kudlich-Straße 25,  D-64823 Groß-Umstadt
Tel.:  +49(0) 60 78/93 63-0,  Fax:  +49(0) 60 78/93 63-20
E-mail:  mail(at)konsens.de

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