8 Static-dynamic Separator Sepol

®

STATIC-DYNAMIC SEPARATOR SEPOL HR® MAKES THE USE OF ® HIGH-PRESSURE GRINDING ROLLS POLYCOM FOR CEMENT AND RAW MATERIAL GRINDING HIGHLY ATTRACTIVE Dr.-Ing. Robert Schnatz

Polysius AG, Beckum/Germany

Summary

The use of high-pressure grinding rolls (HPGR) for the grinding of cement in semi-finish grinding plants is proven pro ven practice not only in India but also around the world. Nowadays usually the cement clinker and the gypsum is preground with a POLYCOM  working in closed circuit with a static and/or dynamic separator. The finish grinding is then made in a subsequent one-chamber ball-mill. Significant energy savings compared to ball mill systems syste ms are achieved. Furthermore a huge variety of cements with fly-ash or slag addition and also including high-Blaine cements cements (> 5000 cm²/g) can be produced easily and with short transition t ransition periods. Up to moderate moisture contents it is also highly recommendable to produce raw meal by HPGRs operated in closed circuit with a static-dynamic separator. separator. Energy savings are even a lot higher than that which can be achieved by using vertical mills. Both applications demand for a static-dynamic separator of the latest design. design. The SEPOL ® HR is the combination of a very compact static separator stage st age with a dynamic rotor part. The advantages of such a separator are its simplicity and robustness against wear caused by the t he abrasive cakes and the ability to produce cements up to 4000 cm²/g. The “HR” has proven its advantages in the first industrial applications at Vasavadatta Vasavadatta Cement Cement for cement and raw material grinding. Throughput and spec. energy values obtained are far better than warranted and are even exceeding ambitious expectations. Meanwhile other clients also decided to use the “HR” t echnology echnology throughout the world. Industrial results proposed slight improvements improvements and confirmed sizing procedures thus enabling to offer a mature product to the market.

1.

Introduction

During the last decade combi-grinding plants (semi-finish grinding plants) have been used more and more for the energy efficient grinding of high-quality cement. Combi-grinding plants are applied for grinding of OPC and cements with composite contents up to 40 %. The biggest size of the POLYCOM series can absorb more than 3000 kW and an appropriate design of the ball mill allow product throughputs of more than 300 t/h OPC with one single combi-grinding-line still achieving a plant power efficiency which is about 30 % higher than that of a closed-circuit ball mill system. The first combi-grinding plants were equipped with a dynamic separator in the Polycom circuit too. These separators were very efficient but suffered from severe wear. In a second step static separators such as the STATOPOL-C® in the POLYCOM circuit were used. The advantages of such a separator are its simplicity and robustness against wear caused by the abrasive cakes. Furthermore it has a good separation efficiency at moderate finenesses and the ability to dry moist feed components. Disadvantages are the limited fineness of the intermediate

product and the deteriorating separating efficiency with increasing fineness. In addition this kind of separator is very voluminous and therefore the required height of the mill building is in any case near to 50 m in total. Worldwide there is a clear trend to the production of high grade cement. Which means that higher finenesses of  4000 or even 5000 cm²/g acc. to Blaine are required. Furthermore in many plants clients intend to upgrade already existing ball mill circuits by the addition of a POLYCOM-separator-circuit used for pre-grinding. In that cases the existing ball mill separator usually is too small to handle the significantly increased throughput of the uprated system. Therefore the separator has to be replaced by a larger unit. Or an additional separator has to be installed in parallel to the existing one . That results in long down-times of the plant during the erection phase which is needed for the installation/replacement of the separator in the ball mill building.

Fig. 1: Flow-sheet of a combi-grinding plant with SEPOL HR® separator, Producing high-Blaine cements of e. g. 4000 or even 5000 cm²/g require intermediate product fin enesses of about 3000 up to about 4000 cm²/g. This level has to be obtained by means of th e separator in the POLYCOM grinding circuit. Plant upgrades are made easier if this separator is able to separate part of the product in order to support the separator in the ball mill circuit.

2.



The SEPOL HR  separator concept

The consequent answer to that demands is the SEPOL HR. A typical flow sheet of a combi-grinding plant with HR shows fig. 2. It is a combination of a very compact static separation stage and a subsequent dynamic part with a horizontally oriented cage rotor. This Rotor gave the newly developed separator its name. HR stands for Horizontal Rotor. A 3D-design sketch of an HR is given in fig. 3.

Fig. 3: 3D-Sketch of the SEPOL HR separator Main features of the SEPOL HR are the high separation efficiency, the ability to achieve a product fineness of up to 4000 cm²/g acc. to Blaine, the possibility for the extraction of fin ished cement from the SEPOL HR and a compact design (only 50 % of the height which is required for the V-Separator) thus r esulting in a significantly lower building height. The simple design allows for local fabrication near to job-site. The housing can be lin ed quite easily resulting in a high robustness of the machine against wear. The feed material transported from the POLYCOM to the separator by means of a bucket elevator and a belt conveyor is entering the static stage via the feed chute (see fig. 4). Partial deglomeration takes place on an impact plate. The material then slides over a steeply inclined aerated floor which is made out of casted wear resistant steel which gives it an excellent wear behaviour.

Intermediate product and air

Aeration floor

Feed material

Aeration floor

Separating air Air supply duct

Grit

Fig. 4: Static part of the SEPOL HR separator The coarse material slides down to the grits extraction chute. The fines are separated out of the feed by the separation air and are transported pneumatically to the horizontal rotor. Fig. 5 shows a sketch of the rotor. The fines out of that material are sucked through the r otor and are collected in subsequent cyclones or a bag-house. As shown here: Two gas exit ducts on each side of the rotor di scharge the product pneumatically. Depending on the rotor diameter and the width of the stati c part an HR can also be equipped with only one gas exit duct.The grits from the dynamic rotor stage can be returned to the Polycom or dir ected to the subsequent ball mill in case of a combigrinding circuit for further grinding. The rotor is driven by a very reliable multi-belt and p ulley drive system which is very compact and do not require an additional coupling. If desired also a gear box, cardanic shaft, coupling combination can be executed. A typical machine layout with two attached cyclones is given in fig. 6.

Outlet end

Product Air

Grit Intermediate product and air

Fig. 5: Sketch of the SEPOL HR rotor

Fig. 6: Typical SEPOL HR installation

3.

Industrial applications of the SEPOL HR

In spring of 2005 Vasavadatta Cement (Kesoram Industries Ltd.) decided to install a new 3000 tpd cement production line in north-east Karnataka. The client already operated a combi-grinding system of Polysius in the plant since 1995. Originally that system was equipped with a SEPOL separator in the POLYCOM circuit which suffered from wear. This separator was replaced in 1999 by a static STATOPOL-C separator. The raw material grinding in the existing production line is carried out by a roller mill. The moisture content of the raw material is quite low with max. 4 %. The raw materials’ grindability is as in most Indian plants high in dicated by a work index of 17.0 kWh/t acc. to Bond. Vasavadatta Cement decided again to build a combi-grinding system for finish grinding from Polysius which is pretty similar to that already in operation. It is designed for the production of 225 t/h at a mass-specific surface area of 3000 cm²/g acc. to Blaine. But instead of a STATOPOL-C separator this is equipped with a SEPOL HR 21/21. The POLYCOM is a type 17/10-7 (1.7 m roller diameter, 1.0 m roller width) with two times 950 kW installed motor power. The ball mill has the dimensions Ø 4.6 x 14.5 m and have an installed motor power of 4,000 kW. This is the first time that a ball mill in India is equipped with the compact and reliable COMBIFLEX® gear box. It is operated in closed circuit with a SEPOL® SV 310/4. The flow-sheet of the system is quite similar to that given in fig. 1. Beside the “normal” combi-grinding operation mode also the discharge of finished product out of the SEPOL HR is possible. This enables to operate the plant without the ball mill circuit. The fines from the POLYCOM® circuit can be directed to the ball mill inlet or to the bucket elevator leading to the ball mill separator. To separate the fines out of the intermediate product is especially advantageous when producing low Blaine cements. The plant went into operation in February of this year. Fig. 7 shows the HR during errection phase. Clearly visible are the rotor bearings which are situated on pillow blocks on the outside thus facilitating maintenance and increasing lifetime. The Fines from the rotor are collected in cyclones attached to the separator by means of a short duct.

Fig. 7: SEPOL HR 21/21 during erection phase

High-pressure grinding rolls are especially suited to grind hard and n early dry raw materials. If that is the case the specific energy consumption is even lower than that of vertical roller mills. A raw meal desired by every kiln operator has an average fineness but no or few coarse particles > 200 µm. That is an obstacle for the use of a static separator for raw material grinding only because that will not be able to produce a product without coarse particles although it is able to do the required drying of the feed material. A proven solution is the u se of a dynamic separator SEPOL® which for sure has to be equipped with liners to withstand the wearing cakes. A better choice therefore is the SEPOL HR which includes a static and a dynamic separation stage. Vasavadatta Cement decided also to go for a POLYCOM® grinding circuit for raw material grinding of the new kiln line. The POLYCOM® 21/16-9 has a roller diameter of 2.1 m and a roller diameter of 1.6 m. An overview of the raw mill building shows fig. 8. The installed power is 2 times 1650 kW. The cakes coming from the high-pressure grinding rolls will be transported to two SEPOL HR 21 by means of two bucket elevators. The machine throughput will be in the range of 1,100 t/h.The plant became operational end of 2006. The desired throughput is 275 t/h at a fineness of R0,09 = 20 %. More than 300 t/h at that fineness were achieved. The energy consumption for the complete system was excellent and only slightly above 14 kWh/t. More info on the grinding systems at Vasavadatta Cement will be given in a presentation held by Mr. Jain.

Fig. 8: Raw mill building at Vasavadatta Cement Ltd.

Meanwhile Drake Cement Ltd. decided to go for Polycom grinding units with SEPOL HR as well. The company is building a greenfield plant near Phoenix, AZ, USA which will come onstream mid 2008. The kiln capacity is 2000 t/h. The desired raw meal throughput 164 t/h @ R0,09 = 15 %. 92 t/h of OPC with a fineness of 3800 cm²/g acc. to Blaine will be ground in a combi-grinding plant with an open circuit ball mill subsequent to the Polycom circuit. In both cases a Polycom 15/8-5 is used with an installed motor power of 2 times 700 kW and a roller diameter of 1.6 m and a roller width of 0.8m. For the raw grinding plant a SEPOL HR 16/27 is foreseen. The width of the static part will be 1.6 m and the diameter of th e separator rotor 2.7 m. For the cement grinding plant an HR 12/21 will be built.

3.

Conclusion and Outlook

Beside the finish-grinding and the standard-combigrinding several other sophisticated applications of the SEPOL HR concept are feasible. One is the combination of the static part of th e HR with a subsequent SEPOL separator taking advantage of the pros of each kind of equipment. Texas Industries Inc. decided to go for a POLYCOM finish grinding plant for the production of raw meal for its new 6000 t/d kiln lin e at Oro Grande, CA, USA. The plant is equipped with a Polycom 20/15-8 having an installed power of two ti mes 1700 kW. Before the Sepol 440/4 (rotor diameter 4.4 m, four detached cyclones) the static part of the HR is used as a drying facilit y and a pre-separation stage for the fresh feed. The operational results obtained at Vasavadatta Cement proposed slight improvements in the design. The u sed sizing procedures were confirmed. Thus Polysius is able to offer a mature product to the market which will boost the attractiveness of POLYCOM installations.