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Current modernization and maintenance concepts in the cement industry Joachim Harder OneStone Consulting Group, Buxtehude/Germany 1 Introduction In recent years, cement production capacity has risen faster than cement sales [1]. The resultant surplus capacities on numerous cement markets have been highlighted by the global economic crisis and recession. Steps have since been taken to substantially reduce overcapacity by means of permanent or temporary factory closures. These have particularly affected uneconomical factories with wet-process kilns or poor capacity utilization in North America, Western and Eastern Europe and also in parts of Asia and South America. Furthermore, production capacities have been adapted at locations where new cement production lines are due to come on stream in the near future. In some cases, cement works have been temporarily operated only as grinding plants, with the clinker being delivered from other factories. However, the overall situation has shown what an important role production costs play in this scenario. Large cement producing companies are increasingly making use of strict benchmarking methods in order to increase efficiency. This enables a valid comparison of individual factories in spite of their regional differences and enables weak points to be effectively eliminated. The

essential benchmarking parameter is production cost, which differs greatly depending on region, market and plant technology, and is plotted as a function of the accumulated capacity (Fig. 1). The selected example is the Holcim Group, which had a cement production capacity of approx. 210 rnillion tonnes per year (mta) in 2009. Such benchmarking of individual factories is, of course, only valid for a given moment in time, as the costs greatly depend on the energy costs in any given country and the distribution of fixed and variable costs is strongly influenced by the respective plant's capacity utilization. One distinguishes between quartiles with the lowest, medium, high and highest production costs. The production costs of Holcim plants differ by the factor 3. Plants in China and India are benchmarked with US$ 25 per tonne. The plants in the 1st quartile are also situated in this region. The 2nd quartile concerns production costs of US$ 30-35 per tonne. This relates both to plants with modern dry process lines and also to plants in low-cost countries with modern and conventional dry processes without calciners. The 3rd quartile, with production costs of US$ 41- 48 per tonne contains a high proportion of wet process plants and plants with higher energy costs, while the plants in the 4th quartile, with production costs of

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US$ 50-74 per tonne, are in danger of becoming loss makers. On the one hand, this quartile contains wet process plants and conventional dry process plants, and on the other hand relatively small plants (economy of scale) as well as plants with a high cost level, such; as in Western Europe and North America. To enable valid cost comparison, identical approaches are required. The specific production costs include expenses for raw materials (in the case of pure grinding plants this naturally also includes the supply cost of clinker), energy and electricity, personnel, maintenance, servicing, repair, depreciation, financing, transportation, sales and administration (before taxes and duties). Even if the other boundary conditions are identical, the cost structure differs greatly from region to region. Energy costs can make up a proportion varying between 10% and 50%. The expenses for maintenance, servicing and repairs depend to a large extent on personnel costs and hourly rates for employees and outside personnel. As a general rule: the older the plant, the higher the modernization and maintenance costs, because cement factories are subjected to a high degree of wear. 2 Modernization concepts There are many different ways of modernizing cement plants, particularly in view of the fact that such plants have a relatively long service life during which a very large number of technological and economic changes can occur, thereby significantly altering the basic conditions. The most important reasons for modernization projects are: - the refurbishing of complete plants and lines - the elimination of bottlenecks/increases in

capacity/higher availability - measures for energy saving/energy efficiency - upgrading of plants and components - reducing emissions/assuring sustainability A modernization project can thus concern the entire plant or only individual components. There are also differences in the applied concepts and in the employed terms, such as upgrade, retrofit, conversion, changeover, re-equipping, refurbishment, etc. The refurbishment of production lines or entire plants is undertaken after lengthy shutdowns or if the plants only achieving a fraction of its nominal capacity. In

recent years such projects (Fig. 2) became far less common due to the booming construction of new plants. Nevertheless, there is still a great need for such projects, as shown in recent years by countries like Russia and Iraq in particular. In this report refurbishments will not be further considered: Instead, it will deal with the most important targeted measures and concepts for modernization projects. 2.1 Modernization of the kiln system The number of existing wet process kiln lines and dry process plants without calciners is still relatively high. In the case of Lafarge, the world's leading cement producer with 120 integrated cement plants, a capacity of 230 mta and a production quantity of 141 mta, 88% of the kiln lines use the dry process. Due to the high energy costs for wet-process plants, such lines (Fig. 3) are often the first to be closed down if capacity in a specific country has to be adapted as a result of newly constructed plants or a decline in capacity utilization. Conversions from the wet process to the dry process demand a completely new raw material preparation system and are therefore generally very expensive in comparison to new plants. For this reason, semi-dry processes have often been introduced in the last 30 years, so that most of the raw material preparation system can be retained. A plant using the semi-dry process (Fig. 4) can be of advantage if the raw material has a high moisture content [2] or if it contains, for instance, a high amount of sulphur [3], which in a dry process plant would require complex gas scrubbing equipment.

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At present, the most important kiln modernization measures concern increasing the capacity of dry process plants. A large number of dry process plants are still operated without a calciner and with a planetary cooler (Fig. 5). Also, some plants are still operated with a kiln air system, where there is only a limited amount of air for the calciner and it is drawn through the kiln [4]. In such cases, significant capacity increases of 30 to 50 % can be achieved by installing a grate cooler and tertiary air duct, as well as a calciner tailored to the respective plant [5,6]. Figure 6 shows two kiln lines at Gorazdze Cement, where the capacity of one kiln was increased from 3500 t/d to 6100 t/d while simultaneously significantly reducing the heat consumption and emissions. The rotary kiln dimensions can often remain unchanged, because earlier rotary kilns had a rated kiln volume loading of 2.5 t/d per m3 Nowadays, kilns are operated with more than 5 t/d per m3. New plants (Fig. 7) influenced the development of cyclone preheaters and calciners in the last 10 years. The collection efficiency of the cyclone stages has been increased, the pressure drop reduced and service lives improved. Meanwhile, high-performance low-NOx calciner systems are on the market. These employ multi-stage

combustion and split feeding of fuel, combustion air and raw meal to create adjustable reduction zones [7]. There are also solutions enabling the burning of less reactive and solid fuels such as petcoke and anthracite. Market data regarding the development of calciner systems are presented in [8]. Modernization concepts for cyclone preheaters employ these developments. The main objective is to use alternative fuels, which also demands modification of the kiln, the refractory lining and the burner. To enable kiln dust to be returned from the filter to the rotary kiln feed, bypass systems are necessary in order to remove chlorine and alkalis from the system. Kiln modernization projects (Fig. 8) have to take particular account of the raw material properties, the type of precalcination and the employed fuels. Modern 2-support rotary kilns permit L/D ratios ranging from <12 for short kilns up to 15, like classical 3-support rotary kilns. The kiln shell is supported in splined tyres on tilting, i.e. self-centering rollers. The advantages of this system are that the weight of the kiln is tangentially supported on the internal toothing of the tyre, the mode of load transmission reduces the ovality of the kiln shell or even completely prevents it, and that the kiln tyres are practically maintenance-free. Moreover, such a system increases the

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service life of the kiln's refractory lining. For modern kilns the average specific refractory brick requirement is approx. 150-350 g/t of produced clinker, depending on operating mode of the kiln, brick quality, employed secondary fuels and secondary air temperature. Pneumatic kiln inlet and outlet seals also prevent false air inleaks more effectively than conventional spring plate seals. Cooler modernization projects primarily follow three directions and concern the switchover from planetary coolers to completely new reciprocating grate coolers (Fig. 9), the installation of static inlet grates in reciprocating grate coolers and the complete or partial replacement of obsolete reciprocating grate coolers by modern concepts. Current cooler developments are described in [7]. A market study concerning developments in the cement industry up to the year 2013 found that in 2007 and 2008 orders were placed for 82 cooler conversions [9]. Most of these orders came from eastern European countries, the Middle East and Africa. An important objective when replacing planetary coolers with reciprocating grate coolers and tertiary air ducts (Fig. 10), and in all other cooler modernization projects, is to complete the conversion within the shortest possible kiln stoppage period [10-12].This demands very

detailed sequence planning, so that the experience of plant engineering companies is of great value. 2.2 Modernization of grinding plants The modernization and optimization of grinding plants is generally aimed at reducing the power consumption and increasing the throughput. Such projects most often concern clinker/cement grinding plants [13]. In the case of an existing ball mill, the preferred method of upgrading to achieve an increase in capacity and save on energy is to create a combination grinding process with a roller press (also called high-pressure grinding rollers). The roller press/HPGR (Fig. 11) is either installed upstream of the ball mill or operates in conjunction with a ball mill and, depending on the grinding system configuration, enables primary grinding, hybrid grinding and semi-finish grinding [14]. There is a high optimization potential. The higher the proportion of finish grinding performed in the roller press, the greater the energy saving for the process [15]. Reports state that the increase in capacity with combination grinding processes can be as high as 100% and the achieved energy savings can reach 50%. Ball mill modernization projects consist of a wide

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range of measures. Firstly, there are process technological modifications such as the conversion of open-circuit mills to closed-circuit operation with separators. These days, existing separators are increasingly being replaced with highly selective high-efficiency separators [16], which provide considerable energy savings and also minimize the downstream cyclones and filters. Optimization of grinding compartments to suit the required fineness of grinding and improvement of the grinding ball grading [17] are also favoured process-technological methods. Mechanical conversions and optimizations are concerned, for example, with new null end walls, wear linings, intermediate diaphragms and discharge diaphragms with material flow control devices or new mill drive systems. Such conversions usually take place within the context of a complete mill refurbishment. The components often have to be assembled outside the mill building (Fig. 12) due to tight space conditions. In contrast, vertical mills offer less potential for modernization. This is mainly due to the fact that these mills are already very efficient and that

grinding equipment from one manufacturer is not compatible with the system of another manufacturer. The situation is different in the case of the integrated mill separators. For one thing, numerous static separators are converted into so-called dynamic separators by the respective mill supplier (Fig. 13). Another point is that there seems to be considerable potential for the optimization of separators by firms other than the manufacturer. The high-efficiency separator was originally introduced onto the market by Onoda under the proprietary name O-Sepa, but in the meantime numerous copies and improvements have appeared. Such improvements are always concerned with the subjects of sharpness of separation/collection efficiency, pressure drop, wear and electrical power requirement. 2.3 Modernization of automation/electrical systems Automation solutions in the cement industry have developed very quickly. Speaking generally, one can expect new product generations to come onto the market about every 5 years, which means that the lifecycle of electrical and electronic systems is significantly shorter than that of mechanical equipm.ent. For the automation of cement factories a complete range of products and systems is offered these days, a situation that has only existed in the last few years. Due to the fact that a cement plant has a period of operation in excess of 30 years, new possibilities for the modernization of individual automation systems and electrical components repeatedly present themselves. According to a new market study [9], on the cement plant modernization market, electrical systems are responsible for a much greater proportion of business than mechanical equipment, which IS different from the situation on the new plant market.

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One important area is, for instance, the modernization of process control systems [20-23]. Process control systems (PCS or Distributed Control Systems DCS) on the basis of Siemens PCS7, ABB 800xA or, for instance, Rockwell/ AB SLC 500/ ControlLogix® are gaining in popularity because they are less specialized and more universal and internationally available. For the purpose of modernizing a factory it is important that different technology generations are intercompatible and that migration to the la test version requires practically no plant stoppage. A process control system (Fig. 14) collects all the information relevant to the production and ancillary processes by means of more than 50000 signals and performs the required control and synchronization of the processes. Process control systems such as the CEMAT also provide recommendations for modification and modernization of the plant via a weak point’s analysis. When kiln lines are modernized, they are often equipped with new power supply, drive and automation systems, as well as new process instrumentation, which is connected up to the old modules. Increasingly, this is being implemented in accordance with industry standard, which eliminates the need to develop special interfaces for devices and components from other manufacturers. The current trend in kiln drive

solutions is to use variable-speed drive systems. These provide a broad scope for drive modernizations [24]. The automation sector also includes all online analysis systems. Beside exhaust gas analysis, this particularly includes material analysis systems (Fig. 15), which have meanwhile developed from pure quality assurance systems into process control systems [25]. On this field there is still a great need for the modernization and retrofitting of cement production plants. 2.4 Other modernization measures There is a long list of further possible cement plant modernization measures. Generally, plant components such as filters, fans, storage and conveying equipment, loading and packing facilities are modernized in the course of increasing the capacity or performing a major upgrade of a kilnline. However, such modernizations can be carried out separately in order to eliminate specific bottlenecks in the system. Conversion to a high-capacity bucket elevator (Fig. 16) takes place almost exclusively in connection with an increase in the capacity of a kilnline. Just in the feeding of raw meal to the raw meal silo and the preheater, a three-digit kWh figure can be saved when existing pneumatic conveying systems are replaced with these bucket elevators [18]. Silo modernization projects (Fig. 17), however, are usually carried out independently of capacity increase

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considerations. A silo conversion is performed if incrustations of material in the silo drastically reduce the available storage capacity or if there are continual outfeeding problems. 3 Maintenance concepts Repair, maintenance and servicing expenses can vary very considerably from one cement factory to another and depend on a number of influencing factors, such as the age and condition of the equipment and the number and size of individual kiln lines, plant capacity utilization, mode of plant operation, personnel expenses and external costs, as well as the applied maintenance and servicing concept. As a rule, plant repair, maintenance and servicing expenses make up 5-20 % of overall operating expenses or absolute costs of between US$ 4 and 15 per tonne. Annual expenses represent approx. 2-4 % of the asset value or replacement value of a factory. Figure 18 takes the example of a 4.5 m cement factory budget to illustrate the allocation of these expenses [26]. In this example, about 5 % are caused just by the elimination of occurring faults and around 30% each by repairs and maintenance/servicing. The remaining 35 % are allocated to the planned annual plant stoppage and system optimization measures. The figure also shows the planned allocation of expenses for personnel and material to the individual measures and whether the work is expected to be assigned to in-house or outside personnel. The approach to budget planning differs greatly from company to company and in the past year of global economic crisis many companies drastically reduced their planned budgets to a minimum or only included measures that would provide immediate benefits. However, the planning of ll1ainntenance measures is only possible if the current condition of the plant is known as a result of inspections [27]. In practice,

the maintenance programmes of most cement producers are a mixture of planned and unplanned measures. A concept aimed at high plant availability and incorporating preventive maintenance, condition monitoring, proactive and reactive maintenance is depicted in Figure 19. Although preventive maintenance is still the most widely accepted approach in the cement industry, the concept is primarily employed for critical plant components that involve lengthy stoppage periods. In order to ensure high availability of the respective plant components, regular inspections are necessary. The inspection results determine whether the required maintenance can be carried out during the annual plant stoppage or will have to be performed earlier. The reactive maintenance concept involves operating the plant sections or components until a fault or equipment failure occurs. Faults can usually be eliminated without requiring a plant stoppage. The situation is different in the case of critical components like large drive motors, large bearings for mills, gear units and fans. To avoid the replacement of such components too soon before they reach the end of their planned service life, the condition of the units is monitored. Condition monitoring can be implemented in various forms. In practically every case it is based on the recording of different parameters and interpreting them in order to assess the possibility of failure. In recent years such processes have experienced a real boom, promoted by the advance in automation solutions. Condition monitoring of plant components is supported by active maintenance concepts that are aimed at identifying fault mechanisms and consequential damage and determining the possible effects of, for example, operating errors or incorrect maintenance. 3.1 Inspections in the case of preventive

maintenance To enable preventive maintenance, the servicing and inspection staff has to constantly provide comprehensive and up-to-date knowledge of the condition of the plant (Fig. 20). This particularly serves the purpose of avoiding expensive scheduled replacement of components that are still in fully functional condition and have a lengthy residual service life expectation. On the other hand, it is essential to minimize the number of unplanned plant shutdowns, because shutdowns are always problematic and have a decisive effect on the cost-effectiveness of the plant. These requirements are met by inspecting critical plant components, such as the kiln,

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cooler, mills, large fans etc. to determine how smoothly the machines are running, whether vibrations or high surface temperatures occur, whether there is corrosion etc., and by checking oil levels and lubricant conditions. Another purpose of regular inspections is to check that plant safety is assured and that all downstream plant components, such as filters, flue gas conditioning units (Fig. 21) and other environmental systems are functioning properly. Naturally, such on-the-spot checks are only one module of safety organization. It is additionally necessary to have the important parameters, particularly plant emissions, monitored by sensors and registered and displayed in the control room with alarm and shutdown functions. Moreover, inspections and function checks do not provide a view inside the manchines. Despite regular inspections it may happen that a component suddenly such incidents that condition monitoring of machines and plant components is performed. 3.2 Condition monitoring of machines and plants Different effective methods of condition monitoring in cement factories have established themselves in recent years. The most important condition monitoring processes are [29]: - kiln scanning processes - vibration measurements - wear analyses etc. The use of condition-oriented maintenance enables the reliable operation of progressively

more complex cement plant machines and systems with progressively fewer personnel while assuring the operating economy, factory safety and plant availability [28]. One of the longest-used processes in the cement industry is computer-aided thermal imaging of rotary kilns. FLSmidth alone has supplied more than 650 such systems and is continuously improving

the technology. The latest processes sold by numerous kiln vendors and specialists make use of infrared sensors that scan the entire length of the kiln and supply three-dimensional pictures and evaluations (Fig. 22).These provide the required information for decisions on the optimal refurbishment of the refractory lining or for assessing the thermal loading of bearings and drive systems [30]. Due to poor accessibility, it is seldom possible to directly measure the temperature situation and the progress of wear at the machine components themselves. However, it is possible to ascertain damage to components by means of an increase or a change in the machine's vibrations, or by an alteration in the size of metal particles in lubricating oil. The use of vibration measurements for the purpose of monitoring machines has proved particularly effective in the case of blowers and system fans, large motors and large gear units. As a rule, the machines' bearing assemblies are monitored by vibration velocity sensors and accelerometers. Figure 23 depicts the condition monitoring system of a mill gear unit at the Lafarge plant in Dunbar. The vibration measurement system coupled with computer-aided analysis of the frequency spectrum once identified a damaged bearing, which was subsequently replaced during a planned shutdown of the plant.

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Particle size distribution counters are employed for monitoring the metallic contamination of circulating lubrication oil in order to enable early recognition of bearing or gear unit damage. Other examples of condition monitoring processes are alignment checking systems for drive units (Fig. 24) or rotary kilns [31,32]. The condition measurements provide the data for computer-aided condition diagnoses of plant components. The data acquisition itself can take place online or by means of cyclic manual measurements, after which the data are fed to a data collector. The vendors of process control systems nowadays also offer condition monitoring systems (CMS) and remote diagnosis facilities, which enable largely fully automatic monitoring of plant operation and automatic triggering of warnings, alarms or shutdowns. Before such systems are employed, it is wise to perform cause-of-failure analyses (RCFA) and failure mode and effect analyses (FMEA) in order to identity weak points and thus achieve trouble-free plant operation. 4 Industrial solutions and prospects A large number of companies are involved in the

advancement of modernization and maintenance concepts. Firstly, there are the cement producers, who are interested in increasing the reliability of their plants and obtaining maximum machine availability. Then there are the machine and plant vendors, who are also concerned with advancing the reliability of their systems. In addition, there are numerous service providers. Process logical studies and audits (Fig. 25) provide the basis for efficiency analyses concerning entire or partial processes in a cement factory and for possible plant modernization or the elimination of weak points. Machine vendors and service providers also offer audits for the entire field of plant maintenance in order to improve maintenance planning or to analyze the current condition of machines. The Aumund Group, for instance, have been providing their "PREMAS-Service" (PREMAS = Preventive Maintenance Services)' for some years now. This primarily involves the inspection of plants (Fig. 26) with subsequent status reports and proposals for improvement of the situation. Services like this are well received by cement producers as they enable the reduction of maintenance expenses and substantially extend machine lifetimes. Another topic is the management of planned plant shutdowns [33]. The point of this is not only to plan the shutdown itself and to organize the assignment of outside personnel, but al so to simultaneously undertake an improvement of the processes. The trend towards outsourcing the responsibility for plant operation and the performance of maintenance and servicing work demonstrates that there is still a broad scope for services of this kind. The market leaders FLSmidth and Polysius both operate service centers (Fig. 27) on several continents of the world. Literature [1] Harder, j.: The Cement Industry 2013 with Substantial Changes. ZKG INTERNATIONAL, 63 (2010), No. 2, pp. 26-27.

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[2] Holpert, M.: Lägerdorf's Calciner Upgrade. ICR, june 2009, pp. 30-32. [3] Menke, T: A Unique Approach, ICR,july 2001, pp. 45-51. [4] Eckert, C.; Hand, A.: Modernizing, Upgrading and Modifying Rotary Kilns with Cyclone Preheaters. ZKG INTERNATIONAL, 54 (2002), No. 4, pp. 37-49. [5] FLSmidth: Izmir's Speedy Upgrade, ICR, May 2007, pp. 37-40. [6] Jelito, E.: Completing Gorazdze. ICR, january 2004, pp. 69-72. [7] Harder, J.: Trends in Kiln Systems for the Cement Industry. ZKG INTERNATIONAL. 60(2007), No. 7, pp. 38-49. [8] Harder,J.: Development of PrecalciningTechnology in the Cement Industry. ZKG INTERNATIONAL, 54 (2002), No. 10, pp. 34-41. [9] One Stone Intelligence GmbH: "Cement Projects Focus 2013", Multi-Client Market Report, December 2009, Buxtehude, Germany. [10] Blümel, S. et al.: Modernisation of a Kiln Line within Shortest Shut-down Period. ZKG INTERNATIONAL, 63 (2010), No. 3, pp. 67-76. [11] Vos, A.: Bye Bye Tubes. World Cement, December 2009, pp. 53-56. [12] Heyden, W.; Fabian, E.: Mississauga Retrofit. ICR, May 2008, pp. 66-72.

[13] Harder,J.: Grinding Trends in the Cement Industry. ZKG INTERRNATIONAL,63 (2010), No. 4, pp. 46-58. [14] Harder,J.: Developments in the Grinding of Raw Materials, Clinker and Slag. ZKG INTERNATIONAL,60 (2007), No. 3, pp. 33-45. [15] Harder, J.: Advanced Grinding in the Cement Industry. ZKG INTERNATIONAL, 55 (2003), No. 3, pp. 31-42. [16] Pattier, L.; Niel, P: Optimisation with TSV ICR, December 2008, pp. 7-50. [17] Fleiger, P; Woywadt, S.: Optimisation of the Ball Charge in Mills for Cement Grinding. Cement International 6/2009, pp. 43-47. [18] Bojdys, M.: Energy Savings Using Bucket Elevators for Raw Meal Feeding. ZKG International, No. 9/2002, pp. 100-108. [19] K.-P. Sönnichsen: lmproving the Performance of Cement Dispatch Terminals in the Countries of the CIS. ZKG INTERNATIONAL, 55 (2003), No. 7, pp. 66-73. [20] Kling, G.; Walther, T: Transparent Process Integration. World Cement. World Cement, February 2006, pp. 71-76. [21] Luchsinger, M.: Modernisierung von Prozessleitsystemen in Zeementwerken. ZKG INTERNATIONAL, 56 (2004), No. 3, pp. 40-47. [22] Schreiter, K.-D.: New Cemat Version wirt Improved Functionality and Openness. ZKG

INTERNATIONAL, 55 (2003), No. 5, pp. 80-85. [23] Woznuk, T: Plant-wide Control Systems. ICR, March 2010, pp. 80-82.

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[24] Horvath, B.: Variable Speed is the Way to Go. ICR, March 2008, pp. 83-84. [25] Harder,J.: Material Analysis for Process Control in Cement Plants. ZKG INTERNATIONAL,62 (2009), No. 6-7, pp. 58-71. [26] Drexler, J. M.: Wettbewerbsorientierte Budgetierung der Instanddhaltung. In: Biedermann (Hrsg.): Instandhaltungscontrolling und Dudgetierung im Wandel, Kiiln 2005, TÜV- Verlag. [27] Patzke, j.; Krause, K.-A.: Geplante lnstandhaltung, ZKG 3/1994, 128-132. [28] Nowak. R. et al: Condition-oriented Maintenance at Dyckerhoff AG's Lengerich Cement Works. ZKG INTERNATIONAL, 55 (2003), No. 12, pp. 32-43. [29] Rudd, K.; Wesley, l.: Condition-Based Maintenance. World Cement, june 2003, pp. 43-45. [30] Idoux, M.: Scanning Success. World Cement, December 2009, pp. 57-59. [31] Becker, E.: VIBNODE Keeps Kilns Turning, ICR, December 2005, pp. 85-87. [32] Gebhart, WM.: Paradigm Shift in Alignment Technology. World Cement, june 2008, pp. 42-48. [33] Rudd, K.: Sht1tdown Management. ICR. December 2002, pp. 45-48. FUENTE: ZKG Cement Lime Gypsum May., 2010 p 24-28