The Volkswagen plant in Emden is using a unique technique to save energy during the curing and drying of the vehicle bodies.
At the plant’s gigantic paint shop, 1,200 cars entering each day leave as high-gloss versions of themselves in every conceivable colour. The clear highlights of the finishing lines are the curing ovens, which bake the finishing layer previously applied by painting robots. Vehicle bodies first pass through two radiant heating zones before entering the next three zones, where recirculating air produces a high-gloss finish that will last for many years.
Detert Ackermann, who helps maintain the finishing lines, explains that the painting process accounts for over forty per cent of the energy costs at an automotive plant. VW collaborated with Crone Wärmetechnik, an equipment builder from Rhauderfehn, Germany, and CVET of Clausthal, Germany on a solution that produced huge savings in the curing and drying process.
From a technical perspective, the process has two outcomes: it provides the ovens with thermal energy, while eliminating the harmful substances in the oven waste gas that pose a hazard to human health and the environment. The entire process must keep costs at a minimum without sacrificing the quality of the finish.
Post-combustion techniques have been used for many years to minimise paint residues in waste gas, and the recuperators employed for this job are optimised with respect to their energy balance. Recovering the waste heat from the post-combustion process and using it to preheat the oven intake air represents yet another important way of helping to minimise energy consumption.
The concept code-named LAVA (a German acronym for load-dependent volume flow adjustment) was refined still further, with additional savings focusing primarily on the air volume flow through the ovens. Classic paint-baking ovens and post-combustion equipment are operated at a constant volume flow, which is always set for the maximum load. The maximum load, in this case, refers to the maximum number of vehicle bodies to be dried per day.
The LAVA approach involves adjusting the volume flow to match the current load. This means that less air flows through the system when loads are light, which in turn decreases the amount of air and the paint residues it contains to be returned to the recuperator to be treated. While this reduces the power consumed by the fans, it also generates huge savings by cutting the amount of natural gas used in the recuperator. During its 12+ months of operation at the VW plant in Emden, the system has generated impressive savings of 25 per cent, achieved without compromising the quality of the finish.
All of the equipment parameters are measured and visualised online including the air volume flow. Due to the high temperatures involved in this process, which at times exceeded 300°C, volume flow was measured with a dynamic pressure probe using a method based on differential pressure.
According to Andreas Scherer, who heads the Electrical Engineering Department at Crone Wärmetechnik, they were recommended halstrup-walcher’s measurement solutions for the application. They not only found the measurement point setup, on-time delivery and the company’s ongoing follow-up absolutely flawless, but were also impressed with the automatic zero-point correction that the P26 differential pressure transmitter regularly carried out with the aid of magnetic valves. This feature keeps the measured value completely stable for many years without having to be adjusted. Additionally, the system’s resistance to overload prevents pressure spikes from having any impact on the sensor system.
A family-owned business in Kirchzarten, Germany, halstrup-walcher specialises in technology for measuring pressure and volume flow. In addition to supporting classic differential pressure applications such as filter and fan monitoring, the company also dedicates much of its energies toward sophisticated measurement tasks such as maintaining overpressure in cleanrooms and measuring volume flow in climate control and processing applications. Rounding out this portfolio are halstrup-walcher’s accredited in-house calibration laboratory and the calibration services that the company provides at its customers’ sites.
The paint shop operator is extremely pleased with the results of collaboration with halstrup-walcher as well. Ackermann observes that they haven’t had any problems with their volume flow measurements since starting up over a year ago.
halstrup-walcher’s measurement solutions are available in Australia from Bestech Australia .