Future Grinding Technologies
Grinding accounts for more than 60% of the electrical power demand during cement production while also being of greatest importance for the final product quality. With today’s and tomorrow’s challenges regarding energy and resource efficiency in mind, grinding within the cement industry has to be rethought. New concepts and new technological approaches towards efficient comminution are required.
In 2014 the European Cement Research Academy (ECRA) started its cross-sectoral research project “Future Grinding Technologies” in order to optimise and develop comminution technology for the cement industry and also for other related sectors. As a first step, ECRA conducted a pre-study in which available comminution technologies were analysed and information was collected within a database which documented more than 100 different technologies.
In order to build up a cross-sectoral research community for the first phase of the project, a roundtable event was held in November 2014 which was open to all researchers in the field of comminution and grinding experts from the cement industry and other industries. Besides lectures and plenary discussions, three workshops were conducted with themes ranging from machine-level (micro) with the definition of all its sub-functions, up to the more abstract industry-level (macro) to collect synergies between the cement industry and other industries using comminution.
The discussions and the results produced by the working groups showed that the control of product properties and the flexibility of production are as important as energy efficiency. Furthermore, the need to reduce OPEX short term without high CAPEX was stressed throughout the discussions. This was further confirmed by more detailed evaluations during the workshop phase. Summarised under the topic “quality”, the control of particle size distribution (PSD) and tools for the a priori determination of changes in the PSD were intensively debated. Cement properties, especially water demand and strength development, are strongly dependent on the PSD, but the control of surfaces also plays an important role.
The working groups at the roundtable event achieved largely intersecting results, despite being generally independently led. Discussions in all the working groups automatically led to very common basic points. Outside the cement industry the main challenges are the same: quality and energy. Since material fineness plays a very important role with regard to both quality and energy efficiency, it has to be investigated what possibilities for limiting fineness are available through a product-based approach. For the cement industry this would involve a closer look at cement’s use in concrete and at today’s standards. It should be noted that in order not to limit possible outcomes directly at the start, CAPEX, although of significant importance, was widely excluded from the workshop discussions. Synergies between the cement industry and other comminuting industries can be found, especially regarding basic theoretical knowledge and sub-processes like material transport. Knowledge improvement can result in more efficient, stable and inexpensive grinding processes in the cement industry and also in similar industries
A systematic improvement of the comminution process starts with the benchmarking of the existing equipment, including all auxiliaries. This task involves the reliable determination of the process’s impact on product properties, especially PSD. Therefore, the application of comminution models for the reliable prediction of the particle size distribution has to be tested and the results have to be validated. Models can then be used to benchmark even non-traditional grinding equipment and to derive new technological approaches. Furthermore, the modelling of the process along with better and more reliable test procedures for the characterisation of the materials will allow better controlling of the particle size distribution in the existing equipment and can lead to new operational and control concepts. In order to obtain results that can be applied universally, the developed tools have to be flexibly designed.
Basic modelling approaches required for benchmarking and long term research activities can lead directly to results of high practical relevance. These can be used for the optimisation of existing grinding plants (e.g. ball charge grading in ball mills). This can in the short-term improve throughput, efficiency, reliability, wear rates and other important factors. In a second step, results can be applied to the developed database on comminution technology in order to allow the development of optimum plant layouts using existing technology. The final phase of the research project can then focus on the actual development of new future grinding technologies ready for tomorrow’s requirements on comminution.
In December 2016 a master thesis on modelling approaches for dry comminution was completed by Matthias Haarmann in cooperation between the Institute for Particle Technology at the Technical University of Braunschweig in Germany and ECRA. Besides a comprehensive literature study, two modelling approaches were implemented and applied to a tumbling mill and a dry stirred media mill. The results show the possibilities of modelling but also the challenges for the upcoming phases of ECRA’s Future Grinding Technologies project.