Production processes that run 24/7 need reliable and energy efficient drive systems to maintain a cost effective process. Philip Crowe reports
For one pharmaceutical manufacturer the drive for efficiency led it to replace some existing equipment with the latest IE4 electric motor technology from Bauer Gear Motor; reducing the kW power size by 60% whilst also reducing the weight and improving overall drive efficiency.
Fresenius Kabi Austria is a subsidiary of the international healthcare group Fresenius Kabi and its plant in Linz manufactures active pharmaceutical ingredients (API), such as Lactulose, Hydroxyethyl Starch (HES) and Sinistrin, and houses a pharmaceutical production unit for related finished products.
The production of Lactulose API operates 24 hours a day, seven days a week with an order-related and just-in-time production system that safeguards the delivery of API to its customers with a maximum shelf life. A significant part of the production process involves the product being held in large vats that are continuously stirred by agitators, driven by electric motors.
A need for improved efficiency
It was this process, amongst others, that was under scrutiny in terms of energy efficiency as well as process efficiency. Fresenius Kabi approached Bauer with a request for support in investigating a more efficient drive system. At the same time they wanted to engineer in flexibility that would ensure the solution would continue to perform when some of the process specifications were changed as well.
The initial step was to carry out an assessment of the existing equipment which comprised an IE2 (2-pole) direct on line (DOL) asynchronous geared motor (ASM) rated at 18.5 kW with a stated efficiency of 91.2%. This was connected to the agitator paddles that turned at about 105rpm with an approximate load of 1,632Nm.
Initial measurements showed that this drive arrangement was working at 10.5 kW and therefore had a reduction in energy efficiency due to the partial load conditions. At this point the production engineers explained that they wanted to change the geometry of the agitator and also reduce the speed from 105 rpm to just 53rpm.
Comparing the options
The new design of agitator was trialled at the reduced speed to ensure that the product in the vat was properly mixed and confirmation of this allowed Bauer to continue with the selection process for the new geared motors, using the new parameters. Initially Fresenius Kabi was interested in installing an IE4 asynchronous motor (motor size 132) that had a stated efficiency of 92.6% but after consultation with Bauer, decided to use an IE4 permanent magnetic synchronous motor (PMSM) (motor size 112) to achieve even greater efficiency gains.
Bauer’s consultation started with a comparison of running costs of the original equipment with those of the latest motor technology. This was accompanied by calculations for total cost of ownership (TCO) that provided a clear evaluation of the differences in energy consumption between the ASM and PMSM designs, as well as detailed technical calculations for bearing lifetime. The test and evaluation work was completed together with Bauer’s Gear Center, ESKO in Fohnsdorf, Austria.
As part of the project, Bauer proposed the BF60 and BK60 models of geared motors that would provide a 7.5kW IE4 PMSM with parallel or bevel gearboxes respectively. The most significant advantage when compared to even an IE4 ASM is seen when operating at lower speeds or under partial load.
Although both the ASM and PMSM motors were classed as IE4, the stated efficiencies were 92.6% and 92.1% respectively. However, the ASM efficiency was stated for direct-on-line (DOL) duty and after this was corrected for inverter duty it became 90.2%. There was also a considerable difference in the physical mass of the motors, with the ASM weighing in at 84kg and the PMSM only 31kg; which can make a considerable difference when looking at the design of the application.
The ASM in partial load has a considerably higher decrease in efficiency than the PMSM for the same load conditions. At loads under 50% the differences are extremely high. A further factor to be considered is, when the speed is also variable the efficiency also reduces.
Comparison of IE3 technologies in general
During the consultation period Bauer was able to reference data from a physical comparison test that was carried out on an IE3 ASM and IE3 PMSM. In this example the stated efficiency of the ASM was 89.6% while the PMSM motor was rated at 90.8%. As with the IE4 examples above, there was a considerable difference in the physical mass of the motors, with the ASM weighing in at 56kg (size 132) and the PMSM only weighing 31kg (size 112).
The efficiency charts demonstrate the advantages of the PMSM when the application requires a lower speed or less than full load from the motor. While providing savings for the proposed arrangement, the PMSM also has the scope to deliver continued efficiency in the event of another process change.
These charts show that the efficiency of the ASM is significantly lower than that of the PMSM at lower speeds (6Hz) when operating under partial load. This data is transferable to the IE4 counterparts considered for the application. These are deciding factors which show the client the true efficiency of the motors in a real life application.
The range of geared motors available from Bauer offers total flexibility in power requirements, gear arrangement and mounting options that allow unparalleled integration possibilities. Quiet running and high efficiency are trademarks of all Bauer geared motors, making them ideal for production environments.
The BF and BK series are available in power ratings up to 45kW, producing an output torque from 80Nm to 18,500Nm and speeds from 0.2 to 280rpm. The design is completely enclosed and sealed against dust and water spray to IP65 as standard, with IP66 and IP68 optional. This ensures that all geared motors are dust tight and protected against water jets so that they can be used outdoors or in wet and dusty environments without the use of additional enclosures.
For applications in ‘Explosion Hazardous Areas’, Bauer Gear Motor has also developed a PMSM solution in both IE3 and IE4 efficiency ratings. This allows operators within such industries as mining, with the exception of mines susceptible to firedamp and oil & gas to benefit from similar performance increases.
Reliability is built in with generously dimensioned ball or roller bearings, case hardened, forged and ground gears, as well as internally and externally reinforced gearboxes; all of which ensure a long, low maintenance service life. A hardened wear sleeve and spray ring at the rotor seal allows for reduced sump capacity and reliable lubrication that provide many years of leak free performance.
All of the product lines are well supported through a high level of parts interchangeability for all geared motor components that benefits the customer with increased options, reduced costs and faster deliveries.
While motor nameplates offer the rated efficiency of the motor, it is also important to accurately appreciate the efficiency of the geared section which can be affected by friction in the oil, bearings and seals. Bauer was able to improve the overall drive efficiency by approximately 35% while maintaining the required quality of mixing.
However, these gains in efficiency cannot be at the expense of reliability which is heavily influenced by the running temperature of the drivetrain. With this in mind, thermal imaging equipment was used to provide accurate information on the normal running temperature of both the motor and the gearbox.
The attention to detail provided by the Bauer engineers in providing a comprehensive demonstration of the energy saving potential of IE4 PMSMs and the depth of knowledge relating to the application resulted in the Bauer geared motors being selected by Fresenius Kabi. Furthermore, as the initial units performed to the expected levels, additional units were ordered to complete the comprehensive overhaul of the original process equipment.
Philip Crowe is with Bauer Gear Motor GmbH.