The plant manufacturer as service partner

The European cement and primary industry has to cope with increasingly limited financial and personnel resources. ­Owing to the global financial crisis, it is at present hardly possible to finance cost-intensive new plants, so that existing plants are being subjected to greater production demands than in the past. The core equipment of the plants is often operated to the very limit of its rated service life or even beyond that. In addition, the high pressure of cost is forcing plant owners to fully exploit the performance reserves of the equipment, while simultaneously minimizing production costs. In the cement industry, for example, this has resulted in the widespread usage of alternative fuels, which place an increased strain on the kiln due to combined thermal loading and chemical attack.

All this inevitably results in constantly increasing maintenance and repair requirements, i.e. the amount of expense and work needed for installing replacement parts and performing repairs in order to assure high plant availability. However, in recent years the already-mentioned pressure of cost has often led to drastic reductions in plaint maintenance personnel and in the outsourcing of necessary maintenance and repair work. The remaining plant personnel and the personnel of smaller local maintenance contractors can generally perform the routine maintenance tasks and minor repairs that are necessary for the upkeep of the plant in a professional manner. But the really experienced personnel that are needed for the planning, preparation and performance of major maintenance and repair jobs are often not available, and there is a lack of the required specialized tools and equipment.

As a consequence, many plants are forced to employ outside companies for the installation of replacement components and the performance of repair work. However, the technical complexity of such major tasks is often seriously underestimated, so that the supposedly reasonably-priced combination of spare parts and services actually turns out to be expensive and often fails to provide the hoped-for long-term restoration of plant performance and stable availability.

Lengthy plant stoppages for the installation of replacement parts and for carrying out repairs require considerable planning and preparation. The performance of a complex job often involves numerous individual tasks at the various subsections, which have to be carried out by different departments and contractors, creating numerous work interfaces that demand a great deal of coordination. All this results in considerable expense, which the plant management has to minimize while simultaneously maintaining a high quality of work.

In this problem environment the plant manufacturer, as the supplier of the machines and systems in the kiln and grinding plants, can provide crucial assistance. It is logical that the plant manufacturer has immense experience in the management of large, complex construction sites when building new factories and extending or upgrading existing plants. The plant manufacturer can therefore be an invaluable service partner for the industry. He possesses all the necessary resources, equipment and know-how for the in-house processing of complex industrial projects.

In addition to these benefits, the plant manufacturer has comprehensive design knowledge of the whole range of machines and plant components, even those of other equipment pro­viders. This enables him to correctly select the spare parts required for the specific application, and to make mechanical improvements through the installation of new components, even in old machines. In addition, the plant manufacturer’s know-how assures first-rate detailed planning of all required measures, correct adaptation of the repair methods used to the case in hand and supervision and checking of the work performed in accordance with predefined measurement reports and tolerances.

If desired, the plant manufacturer is also able to assist and advise the customer during the recommissioning of the plant after maintenance or repair work has been carried out, and to optimize the process technology of the entire plant. To come to the point: spare parts and services from a single source can only be obtained from the plant manufacturer. An actual case study illustrates the advantages of this.

A South-German cement factory contracted Polysius AG to supply and install the following spare parts for a rotary kiln with planetary cooler (Ø 5.2 m x 85/110 m): 

­– Kiln tyre station 1 (comprising tyre-bearing shell section, tyre and tyre fixing elements)

­– Kiln tyre station 3 (comprising tyre-bearing shell section, tyre and tyre fixing elements)

­– Four kiln shell sections (in the area of kiln tyre station 1)

­– Bearing shells for the supporting rollers

­­– Compensating elements (for correcting the inclination of the supporting rollers at stations 1 and 3)

In addition to the flat-rate installation of the above components, the service package included a survey of the kiln, and a mobile machining service for key components that could be reused. The package was rounded off by the employment of professional project management. The implemented service package therefore involved a complex scope of work and had to take account of very restricted space conditions, a demanding schedule and a tight budget. Even before the order was awarded, a detailed appraisal of the plant was carried out on site in combination with detailed coordination discussions with the customer regarding all work interfaces and the range of services required. After placement of the order, work was commenced immediately.

First, a very detailed work schedule was drawn up and discussed/co-ordinated in detail with the customer in view of the fact that the specified time slot between stoppage and restarting of the rotary kiln was very short: the work had to be performed within the regular winter shutdown. The prepared work schedule determined the starting point and execution period of all further work. In addition, a detailed procedure plan was drawn up for the construction site mobilization, crane hiring and personnel requirements. Prior to the actual commencement of the disassembly and reassembly work, the rotary kiln system had to be very precisely inspected by a highly experienced assembly inspector and also surveyed (Fig. 1) with the aid of an opto-electronic measuring system (POLSCAN). The results of the inspection and survey were discussed and evaluated with the experts of the Polysius kiln engineering department and with the customer. The necessary adjustments to the scope of services were thereby agreed and incorporated into the further planning.

A competent and efficient contractor is essential for the practical execution of the assembly work. Selection of the contractor was therefore based on proven criteria, such as occupational health and safety standards, quality of work, experience, adherence to schedules and cost effectiveness. When making such a selection, the special experience gained by a plant manufacturer from his activities in the worldwide construction of new plants and his strategic partnerships with qualified assembly service providers are of immense advantage. In the case in hand, a major German assembly contractor was selected.

Within the framework of the mobilization the construction site was set up at the beginning of November 2009, the required personnel was sent to the site and all necessary tools and equipment were made ready. Parallel to that, diverse organizational measures were implemented with regard to subjects such as occupational health and safety, schedule and cost monitoring, coordination meetings, etc. Subsequently, the extensive preassembly work (mounting the kiln tyres on the shell sections, welding on the fixing elements and joining up the kiln shell sections) could be commenced (Fig. 2).

Within the scope of the previous inspection work, deviations in the geometry of the supporting rollers (uneven wear) had been ascertained at tyre stations 1 and 3. In order to ensure correct contact of the running surfaces after the new tyre stations had been installed, the supporting rollers were returned to the cylindrical form by grinding while the kiln was in operation (Fig. 3). This work was performed by the Polysius mobile machining service for reusable key components (POLGRIND). This service enables expensive components that have long delivery times (supporting rollers, kiln tyres) to be refurbished on site, which considerably extends their service lives. The grinding work took place parallel to the preassembly activities. The intermediate target of concluding all preassembly work before the kiln shutdown was achieved.

After the customer had handed over the rotary kiln for refurbishment, the disassembly work commenced at the beginning of February 2010 (kiln cylinder, tyre-bearing shell sections, roller stations). The support of the remaining shell sections was precisely planned and prepared; after all, support loads in excess of 700 t had to be transferred. The plant manufacturer’s engineering department had calculated the position and load of every single assembly support, taking account of the kiln shell sag. In view of the very short available time slot (26 days for disassembly and reassembly), the schedule situation was monitored on a day-to-day basis. Even small deviations from schedule were analysed immediately and discussed with the parties concerned before introducing appropriate countermeasures.

An example of a disruption of the assembly procedure is provided by the chaotic road conditions in Germany during the cold weather at the beginning of 2010. A crawler crane with a carrying capacity of 400 t that had been ordered for the lifting work at station 3 could not reach the site on time. To deal with this problem, the job planning was immediately altered and alternatives were considered and then implemented (employment of an alternative crane with a carrying capacity of 350 t, Fig. 4). Through this rapid and competent action it was possible to avoid any negative effect on the agreed deadline. Subsequent to the disassembly work, the individual new shell sections were put in place and aligned. This was followed by the execution of all circumferential welds (plate thicknesses of up to 80 mm) using the submerged arc welding process.

At the same time the base plates were adapted (installation of compensation elements for correcting the inclination of the supporting rollers) and the rollers were equipped with new bearing shells. All the complex lifting manoeuvres with load weights of up to 200 t required careful planning and safe, precise work because of the very tight space conditions and due to existing underground structures. The assembly work was followed by comprehensive quality control measures, consisting of surface crack testing, ultrasonic testing and dimension checks, and the customer was given the corresponding quality documentation. After exactly 26 days, at the end of February 2010, the project was brought to a successful conclusion and the rotary kiln was handed over to the customer for installation of the refractory lining.

Within the framework of the recommissioning work the final alignment of the rotary kiln was again checked using the POLSCAN system and documented. Together with the customer’s personnel the fine adjustment of the supporting ­rollers was carried out and the operating data were subsequently moni­tored and logged.

In this case study the order was executed within the agreed time period, within the specified budget, to a high quality and without any accidents. The customer confirmed that the work had been performed “to our utmost satisfaction”. The following factors can be identified as the key to this success:

– supervision and coordination by a single company (one face to the customer)

– minimization of the work interfaces

– machine and process-technological know-how in all phases of the order execution

– inhouse availability of important measurement and refurbishment tools

– assembly and installation know-how derived from previous orders all around the world