Energy on demand for the oven
Rastatt, December 2015 – Dürr has incorporated a new software solution for managing fresh- and exhaust-air flows at Daimler. When drying freshly painted bodies, EcoSmart VEC substantially reduces the gas and electricity consumption at the Rastatt site in Germany. The intelligent air-management system adapts the oven’s energy consumption to its current demand.
As the oven is fed continuously with hot air, any breaks in production, or idle cycles in particular, mean that far more heat is supplied than is necessary. Even if car manufacturers already rely on energy-optimized, exhaust-air purification systems, a great deal of heat is still lost to the environment. From experience, the figure is around 50 percent. To counter this problem, Dürr has developed the EcoSmart VEC air-management system.
In conventional oven systems heated by pure gas, fresh-air intake and exhaust-air removal are operated at a constant volumetric flow. Previous attempts to resolve this problem by adapting the energy budget to the oven utilization level were unsatisfactory in terms of effectiveness and speed of response.
Individual supply of air to each oven zone
EcoSmart VEC works predictively. The air-management system, which is protected by several patent applications, controls the volumetric flow of fresh and exhaust air according to the number and position of the vehicles that are located in the oven at that moment. A body counter is located directly at the air-seal entrance. Based on the conveyor speed, the air-management system calculates in which oven zones bodies are currently located, and how this capacity utilization will develop in the course of production. On the basis of this and other information – for example, the weight and surface area of the car body – EcoSmart VEC can control the fresh- and exhaust-air fans fully automatically. In this way, the system ensures an optimum and individual supply of air to each oven zone at all times.
“With this new approach, we have succeeded in combining the two aspects of energy efficiency and consistently high paint-finish quality,” says Oliver Iglauer, R&D project leader at Dürr responsible for developing EcoSmart VEC. “Due to the potential of EcoSmart VEC to make significant reductions in the flow of fresh and exhaust air, this system is of interest not only for production, but also for the earlier commissioning and ramp-up phases of drying systems. In these cases, the gas and electricity savings can be as much as 50 percent, meaning that the system will pay for itself within this very short time.”
The supply of heat to the drying ovens depends also on the interaction with the exhaust air purification system that is part of the oven installation. The burner in Dürr’s Ecopure TAR system heats the solvents released by the body-drying process, thereby rendering them harmless. The residual heat from the pure gas produced in this way is used to heat the oven zones.
“EcoSmart VEC ensures optimum interaction between process exhaust air purification and process heating. Fewer bodies mean less solvent. This, in turn, means that there is less exhaust air. As a result, the gas burner requires less fuel, since the energy content of the pure gas diminishes. The fans also have to move less air, and so electrical energy can also be saved,” explains Oliver Iglauer.
The integration of EcoSmart VEC in the existing ED oven in the Rastatt plant was a pilot project. Daimler’s TeBIS energy-logging system quickly showed considerable savings in gas and electricity consumption. The paintwork on the dried bodies showed a consistently high quality. Daimler would therefore like to incorporate the system in other oven systems.
Holistic overall concept
The ED oven in the Rastatt plant has a raised design. It already has an effective air-seal system with its A-type seals. However, Dürr still had to overcome one more hurdle before it was able to incorporate EcoSmart VEC in the commonly used straight-through ovens. If the fresh-air supply is reduced here, this generally has a negative impact on the sealing effect of the air seals – with the formation of condensate in this area being a possible consequence. To counteract this effect, Dürr has developed a new, optimized fresh-air seal especially for use in straight-through ovens. A patent has also been applied for this product which requires up to 50 percent less fresh air compared to a standard air seal, but offers an equally reliable sealing effect.
The total volume of fresh air is divided into a variable and a constant flow. The variable flow – which depends on the number of bodies in the oven – is fed to the process via recirculating units. The air seals, on the other hand, are supplied with the constant fresh-air flow. This creates the best conditions for reliable sealing.
“The newly developed air seal means that we have the exclusive capability to offer an integrated concept. EcoSmart VEC can therefore also be used in straight-through ovens,” declares Oliver Iglauer.