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1 Introduction

The Fives Group celebrates the company’s 200th anniversary this year, which is also the 20th anniversary of the introduc-tion of the Horomill to the market by its subsidiary Fives FCB. The Horomill operates on the principle of a horizontal ring-roller mill. It was built and introduced into the cement industry with a cylinder diameter of 2 200 mm at the Trino cement plant in Italy that belongs to the present Buzzi Unicem cement group. Like the vertical roller mill, the Horomill uses the centrifugal force principle for trans- porting the material, for which the material cylinder is driven above the critical rotational speed. Within a grinding plant system the Horomill is always operated as a closed-circuit bucket elevator mill and is used for producing raw meal and, in particular, for grinding clinker and granulated blastfurnace slag. It is also used in the minerals industry. As far as power consumption is concerned the Horomill ranks between the high-pressure roller press and the vertical roller mill. It undoubtedly has advantages over the high-pressure roller press that was introduced to the market in 1985. It uses substantially lower specific grinding forces in closed-circuit with a high performance separator and fulfils the require-ments for a grinding system for producing finished ground products.

2 The Horomill today

The Horomill was presented to the cement world for the first time at the International VDZ Congress in 1993. In the

20 years of the Horomill – a review*)20 Jahre Horomill – ein Rückblick*)

Figure 1: View of a small HOROMILL® 1600 from the beginning year of 1995

meantime 54 Horomills have been sold, for cement grinding as well as for raw meal production or slag grinding (� Fig. 1). 21 Horomills were installed on the American continent, six of them dedicated to raw material grinding, in particular the biggest ever designed, the HOROMILL® 4400 at the Barroso plant in Brazil. 17 Horomills are running in Europe, 11 mills for cement grinding application. 16 Horomills were installed in Asia, six of them dedicated to slag grinding in China, two so-called Twin-HOROMILL® plants. Two Horomills are equipped with new single shoes, one of the latest development by FCB. Nowadays the Horomill is operating worldwide at most of the major cement manufacturers:

� At Buzzi Unicem that has actively participated to the development of the mill, and whose prototype, a HOROMILL® 2200 is still producing cement in the Trino plant, in Italy. Buzzi Unicem now operate 18 Horomills, including 13 mills installed in the Cementos Moctezuma plants, Mexico, and a very recently commissioned mill at Buzzi Unicem in Maryneal, Texas, USA.

� Five Horomills have been purchased by Holcim, and in particular the biggest one, the HOROMILL®4400 for the Barroso plant, Brazil, with a production capacity of 420 t/h of raw meal.

� Cemex, Vicat are using Horomills for cement grinding in Turkey.

� Lafarge, one of the early Horomill users with currently three units, has recently placed an order for a mill for cement grinding in its Teresa plant, the Philippines.

The Horomill is also an attractive technology for the Asian cement market: four machines are operating in Vietnam and eight machines are installed in China, where six of them are dedicated to slag finish grinding.

3 Energy consumption and product quality

In addition to the use of the material bed compression grind-ing technology the process advantages of the Horomill linked to its specific process and technical design are the following:With a relatively low quantity of material circulating (there are about 10 t of material for a HOROMILL® 3800) rapid and frequent changes of product types are possible within a very short period of about five minutes and without the need of a purge bin to deal with intermediate production grades.

� Thanks to the material centrifugation onto the shell rotat-ing over critical speed, combined with a large grinding contact area, the Horomill is running stably and allows grinding of cements with high finenesses without any need of water spraying.

� The Horomill is not discharged by air, but only dedusted. The ventilation is only needed for the selection circuit. The gas circuit is then devoted 100 % to the classifier operation with relevant cooling or drying effect. Conse-quently, this leads to a high saving in specific electrical energy consumption for the fan compared to the verti-cal roller mill.

*) E. Edet, Fives FCB, Villeneuve d‘Ascq, France

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Hence, the energy consumed by the grinding process is low, high quality of cement can be reached. The energy perfor-mance of the Horomill will be illustrated by some selected industrial results in � Table 1. The Horomill leads to large energy savings, more important with harder to grind ma- terials, such as slag cements or pure slags. In comparison to the classical ball mill, the energy savings are between 30 to 50 %. But also compared to other bed compression grinding technologies, the savings can be estimated between 15 to 30 %, because the ventilation circuit is sized only for classi-fication, and not for the material transport. In addition, it has been measured that strength developments and values are similar to those obtained with ball mill cements, and even with a lower specific surface area! It also applies for both mortar and concrete and for any cement type.

Various cement types meeting all quality targets are pro-duced very steadily due to Horomill process stability and TSV™ classifier proven efficiency. Some plants manufac-ture different types of products with the same Horomill, taking advantage of its flexibility and versatility, with 3 to 4 daily changes of the recipe, depending on production and sales needs like in the Karsdorf plant in Germany. For the standard daily operation, along with the modifications of the cement compositions, every adjustment of process param- eters, and the selection of the cement silos can even be fully automated (Trino, Italy).

4 Easy management of moist materials

As the Horomill is not an air-swept mill, the drying function is ensured in the selection gas loop, mainly in the rising duct

below the TSV™ classifier. The classifier rejects constitut-ing the external material circulation as a dilution for mois-ture, which facilitates material handling in the case of raw mix, but also permits control of the moisture content into the mill. The design and equipment of the grinding plant and of its drying arrangement are selected according to the type of material to be dried and of its grain size distribution and moisture content.

It is important to mention that, in this way, the Horomill eliminates two major inconveniences: high venting speed and water spraying that leaves low operating wear rates in the range of 0.2 to 0.7 g/t. The drying is done by feeding the moist material into the riser duct below the classifier (� Fig. 2). This moist material can be:

� either some wet fine component used in cement, such as pozzolana in the Tepetzingo plant, Mexico, represent-ing 15 % of the composition up to 24 % moisture in the wet season, or blastfurnace slag as in the Karsdorf plant, where up to 100 % of pure slag is fed at 10 % moisture,

� or a part of the mill outlet in the case of moist blended cement mix up to 10 % moisture content or raw ma- terial grinding.

� Figure 3 shows the flow sheet of a plant in Tepetzingo with a plant output in minimum of 230 t/h, where a raw mix with a moisture of about 9 % is processed and 20 to 50 % of the bucket elevator outlet is deviated to a flash dryer.

Whereas the fine particles are dried during their gas lifting to the classifier, the coarsest particles are mechanically fed

Product quality Plant size Machine sizeCapacity

[t/h]Fineness acc. to Blaine

[cm2/g]

Spec. energy consumption [kWh/t]

HOROMILL® Total plant

CEM I 42,5 Çimentas 3 800 76.0 2 890 18.1 27.2

Tepetzingo 3 800 103.0 3 070 18.7 24.6

Ciskovice 2 800 58.7 3 050 16.0

Karsdorf 3 800 72.6 3 860 24.5

RCC 3 600 92.0 3 260 19.9

CEM II/A-L 32,5 CEM II/A-L 42,5

Karsdorf 3 800 105.0 3 850 17.4

Darica 3 600 100.0 3 210 18.7 24.2

CEM II A/M (P-L) Cerritos 3 800 115.0 3 580 15.6

CEM II/A-P 3,25 Tepetzingo 3 800 115.0 4 100 16.1 21.9

Mudanjang 3 800 125.5 3 360 15.1

Konya 3 800 140.0 3 100 15.4 21.2

CEM IV A/P Trino 3 800 129.0 4 920 16.1 22.2

CEM II/B-P 32,5 Çimentas 3 400 81.0 4 210 18.1 25.9

Çimentas 3 400 88.6 3 880 17.3 24.2

Denizli 3 400 81.0 4 210 17.0 22.1

Denizli 3 400 83.2 4 220 16.0 21.7

Darica 3 600 106.0 4 000 17.8

CEM II/A-S 42,5 HanZhong 3 800 78.0 3 330 20.5

CEM III/B 42,5 Karsdorf 3 800 63.3 4 170 28.4

Blastfurnace slags Karsdorf 3 800 55.0 4 800 31.0

Karsdorf 3 800 57.0 4 100 28.0

Karsdorf 3 800 66.0 3 500 23.9

Raw mix Tepetzingo 3 800 230.0 R90 mm < 12 % 7.9 12.3

Table 1: List of industrial results

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back, either to the classifier top feeding via the bucket eleva-tor, or to the Horomill via the classifier reject belt. Improved drying efficiency is even obtained by the use of a so-called aerodecantor (� Fig. 4). For example, in a plant in Jiujiang, China, 100 % of the wet slag with a moisture of up to 12 % is fed firstly to the aerodecantor. Only the aerodecantor coars-est particles and classifier rejects are fed to the Horomill. In a new plant in the Philippines, an aerodecantor will be fed with wet pozzolana of 30 % of the recipe with a moisture of up to 25 %. So moisture up to 10 % has been success-fully practised in industrial plants. Trials realised in representa- tive tests in the Fives FCB testing station indicated that it would be possible to process a moisture of up to 20 % with-out difficulty.

5 Operation stability and flexibility

The operational stability of the Horomill combined with the well-known high-efficiency TSV™ classifier is also a major advantage for the production of even finer cements. While the vertical roller mill needs water addition to avoid roller vibrations, the Horomill can keep the finished product dry. In trials, carried out in the Fives FCB testing station under adequate classifying conditions, high finenesses have been reached by the production of CEM I qualities with finenesses according to Blaine values of more than 7 000 cm2/g.

The operation of a grinding plant with a Horomill is fully automatic, without intervention by the operator after hav-

ing pushed the start button. Thus, automatic changes of the cement composition, adjustments of the plant parameters and selection of the target silo have even been successfully implemented in some plants allowing overnight and week-end operation without supervision. The external material cir-culation loop of the Horomill circuit also brings an advantage with the slag grinding, and in particular in China, where the steel industry is in expansion. The mill system gives access to the material during the grinding process and enables per-formance of an in-line magnetic sorting to eliminate the iron particles from the circulating load. So the accumulation of coarse metallic iron inside the mill is avoided. This is an advantage compared to other mill systems. The low ven-tilation inside the machine also reduces its erosion by the wind-borne hard slag particles. Another advantage of the external circulating load has been successfully exploited in the minerals industry, with the extraction of specific parti-cle size ranges.

The flexibility of the Horomill can be demonstrated with the Twin-HOROMILL® concept (� Fig. 5). This consists of the arrangement of two mills with a single materials feed and a single selection circuit using a TSV™classifier. This per-mits a more compact installation, and easily adapts to the

Figure 2: Basic flow sheet of a grinding plant with Horomill for produc-tion of cement and blended cements

Horomill®

Feed Reject

Final product

Hot gases supply (HGG or cooler)

TSV® classi�er

Bag �lter

Fan

Bucket elevator

Application case:Cement and blended cementsFeed moisture up to 7% Outlet mill moisture < 2%

Figure 3: Flow sheet of a grinding plant with Horomill, equipped with a flash dryer for processing of raw meal, cement or blastfurnace slag

Secondary feed point

Flash dryer

Figure 4: Flow sheet of a grinding plant with Horomill, equipped with a aerodecantor for processing of raw meal or blastfurnace slag with high moistures

Aerodecantor

Figure 5: View of the so-called “Twin HOROMILL®-concept”

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variations of the production level. The grinding concept can be operated either with one Horomill or with both, depend-ing on the market needs. On the other hand it gives room for better maintenance planning. This type of grinding con-cept is not only used for cement grinding as in Cam Pha, Thai Nguyen, in Vietnam, but also for steel slag grinding in China, where two Twin-HOROMILL® plants are operating in the steel industry.

6 The Horomill – a reliable machine

The development of the Horomill was a challenge from pro- cess aspects as well as for mechanical solutions, because the basics were adapted from proven technologies. Twenty years after, many improvements have been carried out, mak-ing the technique mature and giving the mill a high level of reliability. Today innovations are going on in order to answer the evolving needs of the cement industry.

Reliability sometimes comes with simplification: The multi-ple supporting system of the mill cylinder with its four shoe bearings has been replaced by a large and unique bearing (� Fig. 6). By retaining the hydrodynamic shoe bearing tech-

nology, developed by Fives FCB in the 1970s, this new pa- tented supporting system has permitted redesigning of the Horomill shell. As a result, it has become lighter: the shell of the HOROMILL® 4400, dedicated to Barroso plant, has the same weight as the shell of a four shoe supported clas-sical HOROMILL® 3800. This new configuration is already in operation in China, with two HOROMILL® 3800, recently commissioned for steel slag grinding.

With this new supporting system, larger sized machines have been designed up to a shell diameter of 5 m, installed with a power of 4 600 kW. In a similar manner, the machines are equipped with compact parallel gear train gearboxes, not only for their small size compared to stand-ard gearboxes, but also for their high reliability and mechan-ical sturdiness.

A dedicated data-logging system (� Fig. 7) has been devel-oped and was installed in a Mexican cement plant to realise a follow-up of the evolution of the process and of the condi-tion of some mechanical components. The tilting movement of the roller is analysed: it gives information on the struc-ture of the material bed and enables adaptation of the pro- cess parameters accordingly. The free rotation of the swivels is monitored in a predictive oriented maintenance strategy for their potential replacement, since curative maintenance would not only reduce the global reliability of the installation but induce side costs as well. The vibration level and the state of the reducer bearings can also be analysed to allow some anticipation in the control of the machine. All this con-tributes to increasing the availability by implementation of predictive maintenance. Automatic procedure and tooling for hard-welding has been developed and implemented to compensate for the wear of the roller sleeve and shell liner surfaces in case of high prod-uct abrasiveness (� Fig. 8). The strategy consists of main- taining the condition of their structure (rafters) to build up a material layer on the liner surface that protects it and that

cannot slide. The maintenance of the structure is a key point, since the material can slide on the hard material layer surface, if the rafters are not sufficient. This sliding increases the wear rate caused by abrasion by 300 to 400 %. Assuming a regu-lar maintenance and depending on the abrasiveness of the products, for cement applica-tion, a roller sleeve can last 3 to 5 years of operation, and the liners over 8 to10 years.

For raw meal grinding, the results vary according to the specific abrasiveness of the raw components, and to the free silica content. This being said, a sleeve can last 2 to 3 years in the case of very abrasive products, and more than 10 years in the case of soft grinding materials. More than ten years can be expected for the shell liners.

Figure 6: View of the new hydro-dynamic single shoe bearing

Figure 7: Data logging system for monitoring the technological process and mechanical components

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7 Conclusion

The Horomill is one of the latest innovations in comminution technology, with a different design allowing compact instal-lation with a flexible and stable operation.

With more than 50 machines in operation for the finish grind-ing of cement, slag, raw materials and minerals, the technol-ogy has demonstrated the expected energy efficiency and versatility. The Horomill adapted to the coming challenges of the market, is the right decision for the sustainability expec-tations of today.3

Figure 8: View of the shell lining a) and roller sleeve surface b)

a) b)

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cement international

4 processing 4 perForMAnce 4 ApplicAtion no. 4/2013

60217

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Reprint from CEMENT INTERNATIONAL 11 (2013) No. 4, pp. 76–81