Bioreactores

J. VANAGS and U. VIESTURS: Local Mixing Intensity Measurements, Food technol. biotechnol. 39 (1) 59–65 (2001)

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professional paper

UDC 621.929 ISSN 1330-9862 (FTB-980)

Local Mixing Intensity Measurements for the Food Industry and Biotechnology
Juris Vanags and Uldis Viesturs*
Latvian State Institute of Wood Chemistry, 27 Dzerbenes, LV-1006 Riga, Latvia Received: July 10, 2000Accepted: October 26, 2000

Summary The application of local mixing in food industry and biotechnology is demonstrated. Using a Stirring Intensity Measuring Device, SIMD-f3 and SIMD-s1, specially designed for this purpose, optimum mixing in a bioreactor, loading-flooding transition in the aeration process, and the local mixing level were controlled. The new potentialities of applying an SIMD-type unitoffer its connection with a motor-driven frequence inverter. Key words: mixing, local turbulence, SIMD, electromagnetic drive, dosage, process control

Introduction
For different food industry and biotechnological processes, it is important to know the level and quality of mixing, as it can influence the product quality. Mixing is often characterized as »good« or »insufficient«, implying thelevel of integral mixing which can be quantitatively described by impeller rotational speed, gas flow rate and mechanically introduced power. The above criteria characterize the average hydrodynamic situation in a technological vessel. However, not always do these criteria characterize the mixing character in a technological vessel unequivocally. To characterize the effect of mixing in rheologicallycomplicated and multiphase conditions most properly, we have developed a Stirring Intensity Measuring Device, SIMD (1,2) which ensures measurements of the kinetic energy, E, of flow fluctuations in various points of a technological vessel. The main advantage of the device is that it ensures precise enough measurements in multi-phase media, including fermentation media (3). The data obtainedthereby serve as a base for new industrial applications. For experiments we have developed a laboratory bioreactor FAS-5.2 (produced by the Biotechnical Centre, Ltd., Latvia) with a special electromagnetic drive (2,4). Its application in industry during the candy mass dosage process has been also demonstrated. Application examples show that the use of SIMD can detect the local mixing intensity. Thisinformation can be helpful to hold mixing on an optimum level in different technological processes. The goal of the present work was the development of food and biotechnological processes control based on local mixing measurements.

Material and Methods Stirring Intensity Measuring Device
SIMD units consist of the following basic parts: ¿ a set of piezoelectric transducers, ¿ a data processingunit, ¿ mathematical programs for data sampling. A piezoelectric transducer has two versions: 1. For summary flow fluctuations energy measurements with an ellipsoid type-head (Fig. 1); 2. For one-component flow fluctuation energy measurements with a disk-shaped head part. The data processing unit also has two versions:

* Corresponding author; Fax: ++371 7550 635; E-mail: koks@edi.lv

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J.VANAGS and U. VIESTURS: Local Mixing Intensity Measurements, Food technol. biotechnol. 39 (1) 59–65 (2001)

ring systems, including a counter-flow system, provide an intensive stirring mode which prevents the damage of microorganism populations. Additionally, FAS-5.3 can be completed with a 30 L stainless steel vessel equipped with the same electromagnetic drive. This 30 L vessel is in aseparate frame construction, but uses the same bioprocess controller, pneumatic part and thermostat block.

Bioprocess controller
Besides traditionally measured and controlled parameters (t, pH, pO2, n, foam, etc.) the bioprocess controller ensures measurements of overpressure p, air consumption Q and local stirring energy E by SIMD. The controller is based on a Basic programmable multitasking...