Pyrolysis processes are used in the field of the thermal treatment of waste e.g. as a process unit incombination with a gasification or combustion unit realized in the RT21 process in Japan fromMitsui. Furthermore, pyrolysis processes are used for specially prepared waste fractions as athermal pre-treatment unit, e.g. before a power station in the Con-Therm process in Germany orin the steel and cement industry. In principle there is also the possibility to use pyrolysis for thedirect recycling of materials such as Plexiglass or plastics reinforced with carbon fibres.Rotary kilns are often used in the field of pyrolysis.The lumpy starting material is mixed due to the rotation of the rotary kiln. The energy for thepyrolysis can be given to the starting material indirectly, e.g. through radiant tubes from anexternal heater, to the rotary kiln wall or directly through a hot gas flow. The starting material isconverted through the steps of drying, release and conversion of volatile components to apyrolysis coke and pyrolysis gas.To optimize existing plants or to design new ones, mathematical models are important tools tominimize the experimental effort.In order to be able to describe the pyrolysis process in a rotary kiln using a mathematical model,the transport of the solid and the specific conversion processes dependent upon the constructionparameters such as diameter and length of the rotary kiln as well as operating parameters such asangle of inclination, rotational frequency, throughput and course of the temperature over thelength in the rotary kiln must be described. For process models which describe such processes ina reactor, it can usually be distinguished between a reactor model and a so-called basic model.The behavior of the solid in the reactor (residence time behavior) is described using the reactormodel and the material and heat transfer as well as the conversion process with the help of thebasic model.In the following, a mathematical model which considers on the one hand, the residence timebehaviour and on the other hand the heat and material transfer mechanisms (basic model),including unsteady behaviour, is presented. This paper shows a mathematical model and itsvalidation for an homogenous material, such as sand, without and with solid conversion ofpolyethylene and substitute fuels including the evaporation and drying process.
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