To make beer, brewers combine water, barley, hops, and yeast in an intricate process to allow fermentation. In the beer brewing process, precise volumes of air or pure oxygen is necessary during the fermentation step for the ideal reproduction of yeast cells. Nearly all oxygen is used during the fermentation step. And the remaining dissolved oxygen subsequent steps should be as low as possible to avoid oxidation, thus ensuring a high quality beer. To improve the shelf life and the taste of the beer, the oxygen content requires continuous, accurate monitoring during the steps after fermentation. An in-house gas mixing system allows manufacturers to generate custom reference gas on-demand.
A global leader in high-precision weighing and measuring equipment manufactures oxygen sensors to measure the remaining amount of oxygen in liquids. These sensors are ideal for measuring oxygen content in beer brewing and in other food and beverage production processes. The Swiss engineering company, Clerici Engineering, builds a system to calibrate these oxygen sensors, for which Bronkhorst provides mass flow controllers.
In addition to oxygen (O2), gases such as nitrogen (N2) and carbon dioxide (CO2) will be present in the beer brewing liquid. They may or may not be dissolved into the liquid. So, to calibrate the oxygen sensors accurately, the influence of these other gases must go into account. For this purpose, a broad range of compositions of these gases (oxygen, nitrogen, carbon dioxide, as well as air) will be used to the oxygen sensor.
A gas mixing system generally consists of two compactly built stainless steel boxes. The boxes contain the gas mixing chamber and the control box with touch display, which connect to each other via signal lines. Finally, six thermal mass flow controllers (EL-FLOW Select series) integrate into six gas supply lines. They are able to mix the dry gases (oxygen, nitrogen, carbon dioxide, air) to obtain he necessary composition.
In the case with Clerici Engineering, two of the six mass flow controllers have a flow range of 0.06-3 ln/min. Two have a flow range of 0.006-0.3 ln/min, and the remaining two with 0.0006-0.03 ln/min. Each of these mass flow controllers use air with extra curves for oxygen, nitrogen, and carbon dioxide for calibration. In addition to supplying low gas flows very accurately, our flow controllers allow fewer devices for the setup because each EL-FLOW Select can handle several gases and flows.
In most applications, the the gas mains supplies process gas. And users indicate the gas compositions via the touch display of the control box. The gases enter the gas mixing box and pass through the mass flow controllers into the gas mixing chamber. The flow controllers are in two groups of three devices to maintain high accuracy. The oxygen sensor that requires calibration is downstream of the mixing chamber and outside the gas mixing box. The duration of the calibration tests range from days to weeks. Meanwhile, during these tests, characteristic curves are recorded and analyzed.
The current setup is an improvement of a previous gas mixing setup. Originally, the setup consisted of four lines, but the two extra lines gives higher accuracy. It also offers better resolution, up to three digits after the decimal point, more flexibility, and more mixing options. When comparing the six vs. four lines systems, no additional gases need supplying, but there are different ranges of the flow rate. Overall, this means that there’s a higher accuracy in a typical (lower or higher) flow range.
In addition to a high level of accuracy, the calibration setup is flexible in the sense that up to 27 different gas compositions are programmable. The programmable logic controller (PLC) inside the control box operates via touchscreen interface to generate the gas mixtures. Some of these compositions are preprogrammed in the PLC, so clients can simply press one button to start calibration.
The Profibus protocol for data communication enhances the control of all instruments together in the setup. Certainly, this makes it easy to use and more flexible. Profibus also allows readout of temperature and other parameters such as set point values and measuring values of the flows. Furthermore, measuring data can transfer by USB from the PLC to the client’s PC. In sum, this allows users to log, track, and analyze data using Excel.
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