PREFORM PRODUCTION PETplanet Insider Vol. 24 No. 05/23 www.petpla.net 38 lap, indicating that the PET material is energetically saturated (see Figure 1). If the process air flow is now too low, it is obvious that the green curve will drop below the blue curve. The material does not have enough energy, the plasticising and the PET material are thus more stressed, the quality of the preforms decreases (acetaldehyde value, bubbles, unmelts, black specks etc.). The balance of power consumption also increases, as plasticising has a lower energy input efficiency than an extruder. If the process air flow is too high, there is energy left over after the PET material has passed through the drying hopper, which the material is not able to absorb because of the degree of saturation. However, because this air is too hot for renewed drying in the drying cartridges, it has to be cooled down by means of a heat exchanger. This means that the already unnecessarily heated air feeds further energy to the cooling machine via the heat exchanger - the energy loss is therefore reflected twice - in the heat generation - and in the heat dissipation. The software records this energy loss in a specific graph (red curve). In this graph, the energy loss of the process air via the heat exchanger is determined, which is then apportioned to the throughput. Sources: ReduPET The user enters only a few parameters in the setting, number of active cavities, preform weight and the desired pellet temperature - when using two dryers on one system, the material proportion of the respective dryer must also be entered. Figure 1 Before the airflow optimisation, it can be seen that the green graph (energy input) lies on the blue graph and the material is thus energetically saturated. The red graph shows the energy losses via the heat exchanger, which is generated by a much too high airflow. This means that twice as much energy is used here as is necessary. Figure 2 After the airflow optimisation, the PET material is still energetically saturated (optimal for the processing) but the loss has been significantly reduced - by approx. 40Wh/ kg PET. At a throughput of 800 kg/h, for example, this would be a loss of 262,000KWh/a. With optimal filling of the dry hopper, a further reduction in losses would be conceivable. If the machine is switched off while the dryer is still running, the material in the upper area of the drying hopper heats up, while the losses increase. Figure 3 The visualisation with its graphs on the timeline not only shows how optimally the drying process is running, but also the changes. This means that a malfunction in the material feed can be detected immediately - and thus in good time. The effectiveness of the filters for the process air in the drying hopper can also be constantly monitored. This allows the filters to be cleaned when necessary - and not when the maintenance schedule calls for it, which can often be too early - or too late. The graph and display also warn when the heat exchanger is not running as it should. In very many cases, the process air is cooled down too much because the valve is no longer working cleanly - these losses hit twice: on the process air heater and on the cooling machine. These losses are not only unnoticeable, but usually significant. Also, when using two different materials (e.g. mixture with rPET) when using two different dryers, the energy input of both hoppers can be used to determine whether the proportions are plausible - or not. Summary WAVE succeeds for the first time in the preform industry in visualising the energy efficiency of a dryer on a timeline by means of three simple graphs with current data. Especially in times of rising energy costs, the advantages are obvious: the return on investment can be steadily reduced to a few months and employees are constantly made aware of the energy consumption in the drying process through the visualisation. ReduPET GmbH also offers recognised training courses that not only focus on drying, but also consider the PET system as a production unit whose entire energy and process optimisation is in focus. www.redupet.swiss
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