Energy-optimised exhaust and filtration system

The long-term evaluation of an industrially used exhaust system and filtration system from SPÄNEX proves the advantages of speed-controlled vacuum systems. This includes the flexible adaptation to the current operating situation as well as the flexibility in the further development of the machinery.

If extensions or restructurings in industrial furniture production are pending, for several years not only the optimization of the core processes, but also increased attention to the economical use of energy has been taken into consideration. Requirements from holistic management systems and the increasing cost pressure move of the exhaust technology into the focus as a significant consumer when planning or evaluating production facilities. Experience gained from innovative plant concepts in recent years therefore is also valuable for future plants.

Vacuum systems with significant advantages

Although speed-controlled vacuum systems are already state of the technology for a long time in trade as well as in the industrial sector, discussions in companies in the furniture sector during the planning stage often show information requirements for the reliability of such systems in multi-shift operation and for larger air volumes. Even in the case of accumulated exhaust volumes starting from 40,000 m³/h, up to a few years ago exhaust systems were often equipped with raw-air side fans. The respective fan is in the material flow in front of the filter device and therefore must inevitably be equipped with suitable raw-air running-wheels.

The paradigm change from over-pressure operation to vacuum operation in industrial plants consists of the installation of the fan behind the filter device. Because the conveyed material is separated in front of the fan, a closed high-performance running-wheel with backward curved blades and significantly higher efficiency can be used. In addition, the vacuum system offers the advantage that the clean-air side fan is practically not subject to wear and is eliminated as a potential source of ignition.

A criterion that is highly underestimated in many planning approaches is the difference between the required exhaust power at the highest production load and at medium load level. While no compromises can be made on the necessary exhaust capacity for quality securing, an adaptation to the respective operating situation must be possible from an energetic point of view. To this end, a speed-controlled exhaust fan in conjunction with a professional planning of the pipework system is particularly suitable. After the first installations of this type have been installed several years ago, it is now possible to check the forecasts at the time of the planning stage for availability and energy efficiency.

Lower required motor capacity

Hobb Holzveredelung GmbH & Co. KG from Bad Bentheim already decided in 2008 for a speed-controlled vacuum system when choosing a new exhaust system. The largest machine connected to the exhaust system is a fully automatic panel sizing saw installed in 2000. Fixed dimensions made from full or half format wood-based panels are manufactured here according to customer order. The company Hobb has direct access to an own large-scale plate storage, in which all common plate types are stored.

In the specifications of the exhaust system, not only the usual demands of the machine manufacturers such as air quantities or machine resistances were determined, also a concept for energy optimization and thermal recycling of the remaining residues was also fixed. The sum of panel sizing saw, press zone, calibration machines and shredding of residual material including particulate dust collection resulted in a required exhaust volume flow of approximately 70,000 m³/h. The volumes of the connected machine groups distribute unevenly from about 8,500 up to 18,000 m³/h. The consideration of a reserve capacity of ten percent resulted in a maximum exhaust flow of 77,000 m³/h. The energetic superiority of a vacuum system compared to a conventional overpressure system with raw-air side installed fans was already quickly undisputed in the planning phase. So the improved efficiency of the pure air fans itself reduced the motor capacity to be installed by approximately 15 percent.

stepless variable exhaust capacity

Especially against the background of 3-shift operation and the variable system charge, the as precisely as possible adjustment possibility to the respective operating situation was searched for the exhaust system. If several fans are used on the clean air side, which switch on or off as required, only the possibility of a gradual coverage of the entire power range would have existed. Even a speed control of one of the fans could not have avoided particularly voltage peaks and additional bearing loads due to the numerous attempts of the individually additionally switched on fans. Therefore, it was decided innovatively to install a 110-kilowatt fan, being automatically and continuously adjusted to the required exhaust capacity by means of a frequency converter. The flexibility of this system deserves special attention. Especially in the case of industrial furniture production and supplier companies, further developments in production processes are often connected to significant changes in the exhaust performance. The company Hobb has also made changes in the calibration department and in the press systems in the meantime. The selected plant technology allowed the required adjustment in the speed range of the fan. After the installation of the new press system and of the new calibration unit, only the pipe connection had to be adapted, the reserve was available at the fan system without further effort. Further advantages round off the positive picture of the investment at that time. In this way, the exhaust fan is located space-saving in the frontal noise protection cabin, which, like the clean-air room, is accessible upright for maintenance and service work. For the presentation of the continuous operation the reverse-air technology already proven in overpressure systems was chosen. This is also an advantage in terms of energy, since the cleaning of the filter hoses during operation averagely results in a lower resistance of the filter system.

The right decision

The chips separated in the filter system are conveyed to the silo via a transport line. On the silo ceiling is a filter system with buffer container including discharging unit and pressure-safe rotary valve. Thus, a material jam is excluded at this sensitive plant position and the downstream automatic firing system is not affected by any possibly entering transport air.

In the meantime seven and a half year have passed since the plant was commissioned. During this time it collected 58,300 motor operation hours at almost maximum availability. Although peak outputs up to 90 kilowatts have been accessed, the average power consumption is currently approximately 50 kilowatts. The company Hobb is accordingly satisfied with its decision at that time.

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