Over the past years, the Research Institute of the Cement Industry has developed a direct-to-practice computer model that realistically depicts the cement clinker burning process.1 At its core, the model illustrates the process from oven meal feed to clinker output from the cooler. The model consists of model segments for the plant components preheater, calciner, bypass, rotary kiln and grate cooler. The plant sections of the external cycle, that is the evaporative cooler, raw meal grinding plant and dust collector, can also be incorporated. All of the individual model segments can be combined in the computer (Fig. 3-1) and facilitate depiction of a stationary state of the entire rotary kiln plant. The modular nature allows a comparatively simple and flexible creation of computer models for different plant configurations.1, 2
It further also allows the various plant sections to be modelled geometrically, which means that different plant sizes can be depicted. Other input variables include the raw material and fuel compositions and mass flows as well as the volumetric flow rates of cooler supply air, secondary air and, if required, tertiary air. The calculations themselves comprise the energy and resource balances for the fuel, dust and gas flows. They take into account not only the fuel combustion calculations and heat transfer, but also include the relevant chemical-mineralogical solids reactions, gas phase reactions and gas-solids reactions. The calculation process is iterative and is repeated until it reaches a stationary state of the kiln plant. The calculation results supply extensive process variables such as mass and volume flows as well as their respective compositions and temperatures. Heat loss and specific energy demand for burning the clinker are also calculated. To obtain foundations for assessment, a reference state of the kiln plant is calculated as part of a survey. The reference state is based primarily on test reports and the owner’s data. It is then used to encode computational changes of the plant, the results of which are in turn compared with the reference state and assessed in an expert report.
1 Klein, H. & Hoenig, V.: Modellrechnungen zum Brennstoffenergiebedarf des Klinkerbrennprozesses, Cement International, 2006, 3, 44- 63
2 Locher, G.: Mathematische Modelle zum Prozess des Brennens von Zementklinker, parts 1- 5, Zement-Kalk-Gips, 2002; 1, 29- 38; 1, 39- 50; 3, 68- 80; 6, 46- 57; 7, 25- 37