polysius® booster mill – dry agitated bead mill increases cement grinding performance and sustainability

The polysius® booster mill is an additional stage grinding solution, particularly efficient for finer grinding. Therefore, it enables customer to produce ultra-high performance cements or sustainable cements with a lower clinker factor without losing grinding capacity and gaining flexibility. The reduced specific power consumption, the beneficial particle size distribution, higher early strength and short project duration without significant downtime lead to a quick payback. The polysius® booster kit is completed with process know how as well as digital and laboratory services.

Several cement manufacturers are already showing interest in testing and individually optimizing this new type of mill in their plants.

Agitated bead mill – additional stage grinding meets challenges of cement grinding

Throughout the last decades, cement grinding technology shifted from ball mills to combi-grinding systems and vertical roller mills. Compared to ball mills, energy efficiency improved significantly. Especially for vertical roller mills, also flexibility improved (e.g. quick switches between products, drying capacity for additives and supplementary cement materials), while combi-grinding systems can score with a – often preferred – particle size distribution closer to a proven ball mill system.

However, with new challenges, new boundaries are becoming more and more eminent. One challenge is to reduce the clinker factor while maintaining quality. A second challenge and a general trend is to produce high performance cement, in order to meet special market requirements – often also with the goal to reduce the share of cement in mortar composition. For both challenges, the need for finer grinding arises, which means a higher specific energy demand and a consequential loss of production capacity. As a third challenge, markets have become more volatile, so cement producers, even in growing markets, face the task to manage capacity increases at minimum downtimes of the ongoing operations, and obviously, limited investment.

In existing plants, challenges in cement production can arise over time as a result of changing market requirements, including the following:

  • Due to higher quality requirements, the cement must be ground finer than the original design of the plant had envisaged. As a result, the achievable throughput decreases.

  • The market requires the production of a variety of different cements for different applications. However, an optimized grinding of all cement types is hardly feasible.

  • In terms of sustainability and reduction of CO2 emissions, more and more composite materials are being used in cement grinding. The properties of these composites can sometimes differ significantly from cement clinker. The requirement is to grind the right cement constituents to the right fineness to achieve the required quality.

  • New applications require highly specialized binders that significantly exceed the normal cement fineness's. However, relatively small quantities of these binders are in demand. 

A new possibility to meet these challenges and to extend an existing plant with low investment costs is the polysius® booster mill.

  1. The polysius® booster mill, a dry agitated bead mill, has been in development by a cooperation between Netzsch Feinmahltechnik and thyssenkrupp for several years, with the original target application in very fine cement grinding. However, trials and an industrial-size pilot installation turned out to meet a far broader range of interesting scenarios and targets of cement producing companies.

Advantages at a glance:

  • Modular design and small footprint enable integration in existing grinding plants

  • Production increase in range of 10-20 %, depending on the fineness, especially for smaller ball mill systems up to 100 tph

  • Quality improvement by use of the additional grinding stage, for example to improve the early strength while maintaining the original production rate

  • An optional cooling shell enables separation of cooling water and cement material

  • Effective and intensive mixing effect for special compound binders

  • Laboratory trials in thyssenkrupp R&D center

  • Production of reference cement material samples for mortar and concrete testing in a range of 100 to 500 kg

  • Attractive business cases

  • Flexibility of production of a wide variety of cement types at a low specific power consumption

Reference: the polysius® booster mill in operation in an industrial pilot installation

View on the stirrer, mill shell dismantled for maintenance. Bursa Cimento, pilot plant, stirrer , Bursa Cimento, Bursa Cement, wear, maintenance
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In 2017 a pilot installation was commissioned in a grinding plant in Turkey. For two years, the mill operated in fly ash grinding, the results in product quality and high energy efficiency convinced to keep the mill. Since the second half of 2019, this mill upgrades an existing ball mill grinding circuit of the integrated cement production, achieving an increase in production capacity and also in cement quality.

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Several trials were conducted with different cement types. This led to an increase of the CEM I 42.5 N cement production by some 20 percent, up to 56 from 45 tph. Furthermore, a higher compressive strength at nearly the same Blaine surface area indicates an additional potential for production increase by adjusting the cement quality. Second positive result was the significant quality improvement. By switching on the new mill, the compressive strength of the cement was able to meet the CEM I 52.5 R requirement, while maintaining the original production rate. The starting point was the CEM I 42.5 R at a rate of 38 tph.

Beside this reference there are several more for ceramic pigment and white cement grinding.

The benefits of the dry agitated bead mill – the polysius® booster mill
The working principle of the dry agitated bead mill
Material flow through the agitated bead mill.  Inlet, outlet, material flow, operating principle, working principle
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Bead mill working principle for dry cement grinding

One crucial characteristic of this mill is the high energy density, 10-20 times higher than of a ball mill, and the resulting very compact design. The bead-stirring elements on the shaft inside the fixed shell reach a tip speed of 5 times the critical speed. In contrast to a ball mill with a revolving mass of rolling and falling ball inside the rotating shell at a maximum of 0.7 times the critical speed, rather creating a constant cloud of grinding media. Furthermore, the high energy density in the grinding chamber requires a fast material transport and accordingly, a high suction value is needed to get the product through the mill by air. The filter design must fit the mill’s requirements, which are slightly different from typical filter specifications in a cement plant, due to the higher pressure drop. The mill accepts a maximum particle size of about 0.5 mm, while grinding media can vary in a 2-8 mm diameter range.

polysius® booster mill - a further innovation contributing to our vision of a green cement plant

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thyssenkrupp is committed to ambitious climate targets. With our vision of green polysius® cement plant we are already offering green solutions for our customers and playing a leading role in green technologies in the cement industry. We call it #grey2green.

Agitated bead mill services by thyssenkrupp

Focussing on customer’s target cement portfolio and operating result thyssenkrupp services start with the analysis of current operation and market and supports as far and as long as the customer requires. Therefore the polysius booster kit comprises complementary services and supplies around the polysius® booster mill. thyssenkrupp – as a full rang supplier to the cement industry – offers all alternative solutions in their portfolio and consult the customer on the solution with the highest benefit.

The process and mechanical engineering audits of the existing plant and main machines like ball mill, high pressure grinding roll (HPGR), separator and vertical roller mill (VRM) is the basis of the polysius® booster kit.

A grinding plant – including the agitated bead mill, a ball mill, HPGR, combi grinding and VRM - and laboratories within thyssenkrupp R&D center enable offering of polysius® lab services. Here the adaptation and optimization of binder properties by physical, chemical and mineralogical analysis as well as mortar testing are carried on customer’s behalf. For this purpose, calculation models for relevant mortar properties are created on the basis of existing analysis in order to predict the effects of process changes. The use of new measurement technology and equipment and the evaluation of new measurement methods complement the polysius® booster kit.

The digital services being developed will analyse the production data, report on current operation, give hints for process optimisation and predict cement quality (e.g. early strength or workability) and maintenance. The grinding system simulator enables capacity and production planning including new cement types. Services and training can partly be carried out online. Support in the use of new measurement technology and equipment and the evaluation of new measurement methods.

Having the expertise along the entire cement production our approach is to provide a 360° service for our customers to ensure best performance of your current and new installation. For the polysius® booster mill an uptime between maintenance intervals at least matching those of ball mills is currently expected. For the pilot installation almost no wear was experienced after 2000 operating hours. The replacement of wear parts, liners and grinding tools can quickly be executed by trained plant personnel or thyssenkrupp Cement Technologies.