As part of the BEST program run by the Baden-Württemberg State Institute for the Environment, Measurement and Conservation, experts from the Munich-based Steinbeis Transfer Center for Energy and Environmental Process Technology and Eco-Management investigated ways for SMEs in the plastics processing industry to save energy. The aim of this across-the-board analysis? To uncover the use of energy in the company and kick-start the optimization of the production in order to lower energy costs.
Another aim of the project was to improve working conditions for staff at the company by reducing the amount of excess heat generated during production – as well as improve competitiveness by lowering the specific energy costs per ton of product. And last but by no means least, the project also strove to reduce the environmental impact of production.
The middle-sized plastics processing firm in the study produces filaments for the brush and textile industries, as well as sport and leisure applications. During production, polyamides and PET are melted and extruded into filaments, which are stretched in a multi-step process. Next, these filaments are heat treated – ensuring they behave as required in their future application. The energy this requires is supplied mostly as electricity, but steam from a gas boiler also plays a role. Overall, the production process requires substantial amounts of energy. It also generates considerable amounts of waste heat due to its low efficiency.
The Steinbeis team began by undertaking a rough analysis of the plant operations according to the VDI 4075, a guideline of the German Engineering Association. This indicated that filament production consumed the most energy and was thus responsible for the highest energy costs. In a subsequent microanalysis, two typical production lines were assessed in detail. This entailed using specific parameters to estimate the theoretical energy demand while measuring the actual energy demand of each production stage during normal operation. Key variables were the absolute energy demand – electrical and fossil fuel – and the demand per kilogram of raw material processed. All values were extrapolated to forecast annual consumption, then compared with the firm’s actual annual consumption.
Analysis of the energy and material flows revealed that most energy was consumed by the extruders (36 per cent) and tunnel kilns (37 per cent), which heat the filaments. A significant proportion was used for cooling – 9 per cent in total. The energy demand of the extruders could be reduced by insulation, while that of the tunnel kilns could be substantially reduced by narrowing the entrance and discharge gaps and improving insulation. Cooling currently takes place via a cooling tower and several cooling compressors – however, alternative cooling methods using wells and river water were investigated.
Together, all of these optimization measures would result in a potential annual saving of around 320,000 euros – not including revenue from CO2 trading. At current prices, the company’s annual energy consumption costs 1.2 million euros – for around 12 million kWh of electricity and around 5 million kWh of natural gas. These relatively simple measures could slash energy demand – and thus costs – by as much as 25 per cent. In turn, this would lower annual CO2 emissions by around 2500 tons – allowing the firm to optimize energy costs while doing its part for the environment. These aren’t the only benefits of the project. Internal processes are now much more transparent, resulting in considerable improvements in communication and information flows. Staff are also much more conscious of the need to save energy and are committed to implementing the optimization measures.
Prof. Dipl.-Ing. Peter Kleine-Möllhoff
Steinbeis Transfer Center for Energy and Environmental Process Technology and Eco-Management
(München)
stz690@stw.de