Material analysis for process control in cement plants
Summary: Material analysis is undergoing transformation from a quality assurance measure to a process control tool. This is being promoted not only by the well-known crossbelt/onbelt online analysers, but also by XRF and XRD inline analysers combined with an automatic sample preparation system. Online and inline analysers are hardly in competition with each other because the devices operate at different points of the process in the cement factory where not only the chemical properties but also e. g. the particle sizes of the materials to be analysed are different. Some of these applications do not require sample preparation while for others sample preparation is absolutely essential. Process control systems have hitherto mainly been implemented for raw material blending beds, raw mills and cement mills. Kiln control systems using material analysis are even less widely applied.
1 Introduction
Online measuring methods are indispensable for process control in cement factories. However, while measurements of temperatures, pressures, filling levels, flow rates, motor powers and gas analysis parameters are long established, the online measurement of material parameters for process control purposes is far less common. This may be connected with the fact that material analysis has up to now mainly been regarded as an essential component of quality assurance systems. Furthermore, material analysis for non-online measurements is without doubt relatively complex and the route from the material sampling points via pneumatic delivery systems, material preparation devices and analysis up to the mixture control system is very long.
However, numerous inline measuring methods exist for elementary and phase analysis of the starting materials such as raw materials and fuels, intermediate products such as raw meal, hot meal and cement clinker and the various types of cement as finished products which can also be used for process control. The demands imposed on these result from quality and profitability objectives that can only be attained with more uniform and troublefree plant operation and simultaneous conservation of resources. However, the conservation of resources often runs counter to considerations of quality because it involves the use of poorer or more problematic raw material qualities and more complex secondary materials. Moreover, additional demands are imposed by the trend towards the production of a range of different types of cement.
Joachim Harder
OneStone Consulting Group GmbH, Buxtehude/Germany
