PREFORM PRODUCTION 37 PETplanet Insider Vol. 24 granules. The air may well be at the required temperature, but this is no guarantee that the granules in the core have the same temperature - 25-40% of the energy in the granules may thus be unaccounted for. The company ReduPET GmbH has now developed the monitoring system Waste Analysis and Visualisation of Energy (“WAVE”), which works according to the somewhat modified physical law “energy is not consumed - but only transferred in a different form”. The principle shown in three simple graphs In the first step, only three values are entered on an input page, which determines the PET material throughput at the dryer: The number of active preform cavities and the weight of the preform, optionally the material proportion if a different material is fed through a second dryer (e.g. rPET). With the signal of the machine cycle, the throughput can now be determined precisely on a continuous basis. In continuous measurement, the specific energy requirement of the material currently being processed is determined - only by measuring its input temperature. The output temperature is set by the operator - it is, after all, as mentioned, non-measurable. Due to the known enthalpy values of PET, the specific energy value of PET is known and can be determined by the continuous material throughput of the machine. The process air has the advantage that its temperature can be easily measured. The air also has enthalpy values that change in relation to density, pressure and humidity. However, since the air is extremely dry, the moisture content does not need to be taken into account. The common drying systems on the market work with cubic metres of process air volume, which is not sufficient for determining the energy transport into the PET material. The decisive factor is the air mass, which makes it possible to determine the energy transferred to the PET material by means of the measured temperature loss Delta T (process air inlet temperature - process air outlet temperature). In this way, the specific energy requirement of the PET material and the specific energy delivered by the air to the PET material are compared. Losses and the extraction of moisture are taken into account. WAVE now plots the graph of the specific energy demand of the material (blue curve) and the specific energy given off by the air on a graph (green curve). With a dryer running in thermal equilibrium, both curves over-
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