With cream please...

But what does cream have to with compressed air? We’ll explain the connection in the following success story from the Bavarian Dairy Industry Cooperative (BMI - Bayerische Milchindustrie eG) in Zapfendorf. The story is about clean water, but more so about industrial wastewater treatment in a dairy production plant.

Clean water: an essential requirement that needed to be met with machine technology that is easier to use, more dependable and - very importantly - future-compatible. Lower costs were another key factor. An advanced station using rotary screw blowers made this possible.

The BMI (Bavarian Dairy Industry Cooperative) is a dairy cooperative with a long tradition and international experience; currently, BMI’s largest plant is located in Zapfendorf, northern Bavaria. Aside from standard products such as skimmed milk and sweet whey powder, manufacturing is increasingly focusing on specialised products. Highly advanced ultrafiltration processes yield high-quality protein concentrates – products of growing importance for the nutrition, dietetics, child nutrition and health food industries. BMI’s activities also include lactose manufacture and the production of high-fat milk and whey products, as well as the drying of partially de-sugared whey and polyamine concentration. Zapfendorf also houses the modern fresh dairy plant that produces products such as butter, cream, curd cheese and fermented milk products.

Due to rising demand of BMI’s products and the consequent increase in production, planning began in 2014 for a new, larger treatment system for the process water that arises as a by-product of dairy manufacturing. The future system would have four sequential batch reactors in which to treat this process water in batches, to decompose its nutrient load. The system would also use four blowers to supply air to the microorganisms that are involved in this process.

To minimise the operating costs of the water treatment plant, the new rotary screw blowers - which recently launched on to the market at that time – would be used for the energy-intensive production of aeration air instead of rotary lobe blowers that would usually have been used for this purpose in the past. Rotary screw blowers are essentially dry-compression/oil-free rotary screw compressors that are modified for the low-pressure segment and which deliver significantly greater efficiency at differential pressures of 400 mbar and above. Thanks to their screw-shaped rotors, such as the Sigma Profile for example, these machines assure exceptionally efficient operation. In fact, they provide significant energy (and therefore cost) savings in applications with pressure differentials between 600 and 800 mbar, such as at BMI, and for applications that require long blower operating hours, such as in the water technology sector.

The initial plans drafted for BMI still included the use of first-generation rotary screw blowers, i.e. the incomplete machines that were common in the past. These essentially comprised individual mechanical components that required the separate installation of electrical systems and control cabinets by a subcontractor before they could be operated. However, since next-generation rotary screw blowers – i.e. plug & play, complete machines that come with a pre-installed electrical control and power supply – had already begun to redefine this sector of the blower market, the planners’ focus quickly shifted to these newer systems.

It was precisely this “completeness” of the new screw blowers that ultimately swayed the decision in their favour: FBS-M-SFC type screw blowers with integrated frequency converter and additional integrated smart machine control via the SIGMA CONTROL 2 controller were ultimately chosen for BMI Zapfendorf. This advanced controller directly connects the blowers, via Profibus, to the main control centre where operating and status data are visualised. The control centre prescribes the motor speed, which translates into the flow rate, to the blowers – enabling remote control of the blowers via the bus system.

The controllers and complete design also make these machines suitable for applications in Industrie 4.0 or Water 4.0 environments. Also termed the fourth industrial revolution, this sea change in industrial production has now also arrived in the water technology field. As a fundamental prerequisite for Industrie 4.0, comprehensive machine-to-machine communication must be possible, such as by means of a networked, digital master process control system. The goal is to achieve greater flexibility in machine control and to perform diagnostics based on operating and status data in real-time (“condition monitoring”) in order to ensure optimal operation and to be able to take advantage of predictive maintenance capability. This enables, in one direction, comprehensive data regarding the blower’s operating and maintenance status to be read; and in the other, enables the blower to be remotely controlled – ideally with just a single cable (data bus cable).

For example, analogue values can be read in real-time, thereby allowing close monitoring of key data such as: inlet, discharge and differential pressures; inlet, discharge, oil and sound enclosure internal temperatures; pressure drop at the inlet filter; blower speed (in the case of frequency converters), frequency converter power consumption and intermediate circuit voltage. Monitoring includes motor temperature and power consumption, oil level and circuit board temperatures for the power electronics and much, much more.

Each of these values are limit values that trigger warning or fault messages, which can also be implemented into the process control system via bus protocol, making monitoring convenient and straightforward. The system also includes counters for the machine‘s operating hours, as well as the values for its individual components, such as the blower airend, motor, controller, power supply, maintenance parts, etc. Time intervals are also saved for maintenance parts such as the inlet filter, oil, V-belts, etc. which also trigger a maintenance message upon expiry. Status values such as Machine off, Start ready, Operation, Warning and Fault are also shown on the process diagram.

From the operator’s perspective, the decision in favour of such versatile plug & play machines was clearly motivated by a detailed comparison of functionality and cost: compared to the complete machines, the outlay required to implement comparable functionality by means of separate electrical automation of the individual components was simply impractical. It was obvious that not only would components such as the blower, frequency converters and metal control cabinets have to be procured, but many others as well. A detailed comparison of the machine and control functionalities also included costs for switching relays and overcurrent protection to connect electrical auxiliary drives, such as fans, oil pumps and vacuum pumps, as well as transformers and analysis devices for temperature, pressure, oil level and oil pressure sensors. Received sensor signals have to be analysed, limit values have to be stored and logical electrical switching of actions has to be implemented. Because of this decision, there were no loose ends when it came to the many interfaces, and commissioning was performed smoothly and rapidly. Above all, everything is clearly documented, with CE and EMC certification, as required by the Industrial Safety Regulation (BetrSichV). This complete scope of delivery facilitated investment cost planning as well as the comparative energy cost calculations, since validated performance data for the complete, turnkey machine were available right from the outset.

The installed system assures planning and legal certainty, as well as process reliability. The installed system assures planning and legal certainty, as well as process reliability. Should the remote control ever fail, it is incredibly easy to operate the blowers manually, independently of the process control system, by using the simple menu navigation in the SIGMA CONTROL 2 – without the need for rewiring and reconfiguration (as used to be required for connections to an external frequency converter, etc.). In an emergency, these machines form the last remaining functional island, reliably supplying the microorganisms with the air they need to survive.

Looking back on two years of successful operation with the four advanced rotary screw blowers, the project manager has not only been pleased with the outstanding service that has been provided, but is also impressed by everything related to the rotary screw blowers, including the frequency converters, controllers and control centre connection. Another welcome factor is the realisation of the advertised performance values for the rotary screw blowers within the tolerances of the values guaranteed as per ISO 1217 Annex E – the excellent energy efficiency values projected at the outset have therefore also become a reality. Moreover, the project manager explained that the overall “completeness” of these machines also enabled significant investment cost savings.

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