Pressure measurement


The production of grappa requires a great deal of skill and, above all, experience if the product taste and quality are to remain at a high level over many decades. Additionally, the process itself requires solid, reliable technology, for example in the production of tartaric acid. The process conditions must be stable and precisely maintained – VEGA sensors make a significant contribution to this, as Florian Burgert explains.


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nyone who loves grappa cannot eschew the products of the Bonollo distillery. The distillery Bonollo SpA,


with headquarters in Formigine (MO) and production facilities in Anagni (FR) and Torrita di Siena, is one of the most important wine distillation companies in Europe. Founded in 1908, it produces grappa, brandy, ethanol, grape spirits and liqueurs. Bonollo is one of the first producers of Grappa, the exclusive Italian spirit. Grappa is obtained through the distillation of grape skins, using both continuous and discontinuous stills. Bonollo also produces natural tartaric


acid, an inherent component of grape skins, as a separate product. It is used in a wide range of products, from confectionery to baked goods to pharmaceuticals, wine-making and even in the construction industry. Bonollo uses a fully integrated and sustainable processing cycle. Basically, water, sulphuric acid and calcium tartrate are used to extract tartaric acid. The process itself consists of multiple phases, including separation, concentration, crystallisation, centrifugation, drying and sieving.


Electronic differential pressure measurement is totally


unaffected by the ambient temperature or vibration.


VEGA sensors are used in the


concentration phase. In this phase, the solution is concentrated in vacuum evaporators to obtain a concentration of about 70 per cent tartaric acid. The solution is then returned to the containers for a second separation. The decanted solution is then passed through a continuous concentration process until a suspension consisting of crystal and mother liquors containing 90 per cent tartaric acid is obtained. Accurate level measurement is essential for controlling the continuous concentration phases. This is the only way to achieve the desired concentration.


LEVEL mEAsurEmEnT wiTh ThE conVEnTionAL diFFErEnTiAL prEssurE mEThod dELiVErs inAccurATE rEAdinGs Up until recently, a conventional differential pressure measuring system had been used for level measurement, but it did not work satisfactorily. Let us not forget: Differential pressure measurement is actually a very reliable method. Two oil-filled chemical seals are installed on the tank, one at the top and one at the bottom, and connected together via an oil capillary. The challenge with this measuring principle


however, is its function and accuracy is affected by the ambient conditions. Temperature changes, e.g. caused by sunlight or frost, affect the oil-filled system and have to be compensated for. Another drawback is that the oil-filled


capillary tube is costly to install and also mechanically vulnerable – for example, if the tank is subject to vibration or a forklift brushes past the tank. Setup and commissioning can also prove to be very difficult in some cases. In the distillery there was another


problem that led to measurement inaccuracies. Small crystals kept collecting on the screwed fittings of the capillary. The resulting level measurement was unstable and often inaccurate. For some years electronic differential


pressure measurement has been available. Put simply, this technique replaces the oil-filled tubes with an electric cable. Two sensors (master and slave) are installed directly at the measuring points and electrically connected to each other. The costly installation of impulse lines is eliminated, as are the costs for the necessary electrical trace heating.


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Bonollo is convinced of the value of the plics concept, which made installation, setup and commissioning really easy.


Neither ambient temperatures nor strong vibrations have any affect on the measurement, and sensor installation is extremely quick and easy.


ELEcTronic diFFErEnTiAL prEssurE mEAsurEmEnT wiTh VEGABAr sEnsors Two sensors of type VEGABAR 82 with ceramic measuring cell were deployed. These instruments use an oil-free ceramic measuring cell. It functions exceedingly reliably, without any drift over longer periods, regardless of ambient temperatures. When using conventional oil filled measuring cells, drift can occur, especially under vacuum conditions. Thanks to the flush-mounting, robust ceramic measuring cell, no sensor cleaning or maintenance work is required.


May 2021 Instrumentation Monthly


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