Osman NEMLİ, Ruhi BİLGE, Levent ONAT – Bursa Çimento Fabrikası, Kestel, Bursa
Hakan BENZER, Okay ALTUN – Hacettepe Üniversitesi Maden Mühendisliği Bölümü Beytepe, Ankara
Udo ENDERLE, Hayri ÜNAL – Netzsch Feinmahltechnik, Sedanstr. 70, 95100 Selb, Almanya
Abstract
The cement industry worldwide is facing growing challenges in conserving material and energy resources, as well as reducing its CO2 emissions. Global demand for energy is increasing rapidly, because of population and economic growth, especially in emerging market economies. Rising demand creates new challenges that creates new opportunities like the use of energy efficient systems, machines and the production chains.
During the last years several efforts were made by Netzsch to implement its horizontal bead mill Pamir into cement industry in collaboration with Hacettepe Comminution Group (HCG) initially for grinding Flyash and Cement. Following many laboratory size and pilot scale test work as an industrial partner Bursa cement plant joined the consortium to generate information for cement industry.
An industrial size bead mill was commissioned at a cement line in Bursa cement plant where sampling campaigns were carried out at different streams of the circuit, final product, separator reject, and mill filter return. As a result, various feed size distributions were tested and the performance of the mill was assessed. The sampling studies around the mill was performed when the mill reached to a steady state condition which was understood by
observing power draw and production rate of the mill. Provided that both of the parameters were steady, then the samples were collected and subjected to characterization works. In terms of characterization, size distributions, surface area and strength properties was determined. Additionally, operational conditions were measured and evaluated by Bursa Cement technical staff. This paper is aiming to outline the development stages of the mill and then sharing the latest results obtained from the grinding circuit where 1000 L mill was commissioned. The initial results are promising that the energy saving of 18 % and production rate improvement of 22% have been achieved with the operation of the bead mill at separator feed stream. In addition to the energy savings, 10% quality improvement results on mortar and concrete quality are also observed in comparison to reference measurements. The operational conditions in terms of easiness and difficulties are also outlined in the paper. Further expected advantages of using the new mill in cement industry are also simulated. The findings indicate that the benefits obtained are not limited and further improvements can also be reached for sustainable cement production.
1. Introduction
The cement industry worldwide is facing growing challenges in conserving material and energy resources, as well as reducing its CO2 emissions. Global demand for energy is increasing rapidly, because of population and economic growth, especially in emerging market economies. Rising demand creates new challenges that creates new opportunities like the use of energy efficient systems, machines and the production chains. [1,2].
Cement manufacturing is a process that combines many unit operations including raw meal handling, pyrometallurgical processing and comminution both in raw meal preparation and cement section. Among them, comminution is the most energy consuming part with almost 60% [3,4,5,6,7,8] and globally, all the comminution processes are reported as responsible for 2-4% of the world’s energy consumption [8,9]. Since a considerable amount of energy is consumed in this field focus should be given on the reduction where various alternatives could be considered. These can be either through innovating a new product or through a process optimization that can be accomplished by replacing the old technologies or optimizing the operating conditions/flow sheets of the production. By considering such options, saving about 20% to 50% is possible [4,5,6,7,10].
The development of dry horizontal stirred media mill had started for that purpose and some of the results had been published [11,12,13]. During the last years several efforts were made by Netzsch to implement its horizontal bead mill-Pamir- into cement industry in collaboration with Hacettepe University (Hacettepe Comminution Group) initially for grinding Flyash and Cement. Following many laboratory size and pilot scale test work as an industrial partner Bursa Cement Plant joined the consortium to generate information for cement industry. The first industrial application of Netzsch Pamir mill was done for efficient fine grinding in the 1st line of Bursa C ement Plant.
2. Plant Studies
Industrial trails were carried out in the 1st Cement Grinding Circuit of Bursa Cement Plant during Cem I type cement production. The grinding circuit includes one ball mill operating in closed circuit with an air separator. Ball mill has two grinding chambers, which are separated from each other by a slotted diaphragm through which the particles finer than the size of the slots pass to the second chamber for further size reduction. Technical data of the 1st Cement Mill is given in Table 1.
Table 1 Technical data of the 1st Cement Mill
Figure 1 Simplified flowsheet of the 1st Cement Grinding Circuit
Figure 1 gives the simplified flowsheet of the circuit. From Figure 1, fines in the mill are collected by means of filter then returned to system, the rest of the material in the mill discharges by overflowing. Filter generates a pressure difference between the feed-end and discharge-end of the mill to increase the material transport rate through the mill. The clinker is crushed through roller press before being fed to the 1st Cement Grinding Circuit. The sampling campaign around the circuit was completed at steady state conditions and the size distributions of each stream were measured down to 2 microns. Figure 2 shows the full siz e distributions around the circuit.
Figure 2 Size distributions around Cement Line I during CEM I production
In any sampling operation, some errors are inevitable. These errors result from dynamic nature of the system, the physical conditions at a particular point, random errors, measurement errors and human errors.
Mass balancing involves statistical adjustment of raw data to obtain best fit estimates of flowrates. Then, it is possible to evaluate the performance of a circuit or equipment. By using particle size distributions and the tonnage of fresh feed, mass balancing study was carried out to determine the mass flow of each stream. The agreement between the experimental and calculated size distribution data sets are presented in Figure 3. Calculated flow rates after mass balancing study are given in Figure 4.
Figure 3 Experimental and calculated particle size values
Figure 4 Flowrates around the circuit after mass balancing
3. Bead Mill (Pamir) Implemen tation And Results
Stirred media mills have been used in fine and ultra-fine grinding applications. Successive wet operations raised the question as to whether it is applicable in dry milling which is expected to be prominent in the future due to the environmental reasons. Dry stirred media mill technology can be employed where fine grinding is required. It is possible to develop various circuit alternatives improving energy efficiency of the circuit without deteriorating cement quality.
The Netzsch Pamir®is a type of mill which uses a flow of air to convey the mill feed through the grinding chamber. The balls in the stirred media mill are moved by an agitator and so reduce the size of the mill feed.
Industrial size bead mill-Pamir-(Figure 5) was commissioned at Bursa Cement Plant where sampling campaigns were carried out at different streams of the circuit, final product, separator reject, and mill filter return. The new mill was installed into the cement line to grind the separator feed material. Depending on the capacity of the existing mill only 1/3 of the separator feed could be ground in this system therefore a controlled splitter was also installed into the system to feed the bead mill uniformly. The PID photograph of the system is given in Figure 6.
Figure 5 Photograph and the technical specifications of the bead mill installed at Bursa cement Line 1.
Mill motor (kW) 400
Effective length (m) 1.5
Effective diameter (m) 0.905
Effective volume (m3) 0.96
Figure 6 General PID illustration and magnification of the bead mill position in the system
Various feed size distributions were tested and the performance of the mill was assessed. The sampling studies around the mill was performed when the mill reached to a steady state condition which was understood by observing power draw and production rate of the mill. Provided that both of the parameters were steady, then the samples were collected and subjected to characterization works. In terms of characterization, size distributions, surface area and strength properties was determined. Additionally, operational conditions were measured and evaluated by Bursa Cement technical staff. The results are compared with the reference data as given in the previous section.
Size distribution data are utilized for mass balancing and the results are given in Figure 7 below. The production capacity of the mill is increased to 56 tph from 45 tph. The product size distribution of the circuit is compared for two conditions with and without bead mill application (Figure 8). The size distribution data showed that the production fineness of the two conditions was almost identical. As a result of similar size distribution curves the quality results of the two conditions were also similar (Figure 9).
Figure 7 Flowrates around the circuit with Pamir after mass balancing
Figure 8. The product size distributions of the circuit with and without Pamir
Figure 9. Strength Comparison of the production with and without Pamir
The mill is in operation for more than 6 months and comprehensive results were collected in the operational period. The long term data showed that the bead mill implementation provided 5.38 kWh/t energy advantage which counts for 15.5 % energy savings with 22.7 % capacity improvement (Table 2).
Table 2 Comparison of the results with and without bead mill
Bursa technical staff evaluated the operational easiness, wear properties and maintenance behavior of the system during this long term observation. All these observations addressed a very smooth and high availability unit operation process. These results will be the topic of another technical paper.
4. Conclusion
This paper is aiming to outline the development stages of the mill and then sharing the latest results obtained from the grinding circuit where 1000 L mill was commissioned. The initial results are promising that the energy saving of 18 % and production rate improvement of 22% have been achieved with the operation of the bead mill at separator feed stream. In addition to the energy savings, 10% quality improvement results on mortar and concrete quality are also observed in comparison to reference measurements. The operational conditions in terms of easiness and difficulties are also outlined in the paper. The findings indicate that the benefits obtained are not limited and further improvements can also be reached for sustainable cement production.
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