FEATURE FLOW & LEVEL CONTROL


Brendan Robson, project engineer at TÜV SÜD National Engineering Laboratory, stresses how crucial accurate flow measurement is in industries from food and beverage to oil and gas, and how it can affect production, end product quality and profitability


M


easurements are essential in any process requiring quantification. For


example, understanding, monitoring and controlling flow rate, as part of industrial processes, are essential to the viable operation of production systems. Basic principles are the same whether the measurements are for oil and gas or for producing beer and bread. Of course, the product price will dictate


the level of cost and required accuracy of flow measurement. But, again, the processes share a common question: what are the effects of inaccurate measurement of fluid flow to the producer’s profit? For example, within the food and beverage industry, the Scotch Whisky Association reported that 1.3 billion bottles of whisky were exported from Scotland last year, which equates to approximately £4.9 billion in sales. The effects of flow inaccuracy could run to millions of pounds in lost revenue in this sector. In a recent measurement audit of an


alcohol bottling plant the classic offline, manual procedures were used for both sampling and estimating the Alcohol By Volume (ABV). The plant operators were unaware that their existing (and expensive) Coriolis flow meters were also capable of measuring temperature and density simultaneously. So now, ABV can be calculated in real time using these parameters, presenting more effective online monitoring and flow rate control. Food and drink factories require very


specific needs for flow measurement. Flow meter selection narrows when a non- contact design is critical. Electro-magnetic (EM), ultrasonic (including clamp-on designs), Coriolis and thermal mass flowmeters address such needs. The understanding of the benefits and limitations must be assessed at the design stage: the fluid must be conductive for an EM flow meter, for example. If the process can operate in both directions, then a Coriolis meter would be a good choice. Hygiene is a critical part of food and


20 JULY/AUGUST 2020 | PROCESS & CONTROL FROM BEER TO BREAD, THE IMPORTANCE OF FLOW MEASUREMENT


Flowmeters that do not meet an application’s specific needs can prove inaccurate and cost the food industry £millions


beverage production and requires expensive stainless-steel apparatus. The effort required to clean the components, including flow meters, affects the production cost and dictates suitable measurement designs. So, insertion-type flow meter designs which are in contact with the fluid, such as turbines, are avoided. An interesting case was a bottling plant


Brendan Robson, project engineer at TÜV SÜD National Engineering Laboratory


of the most popular soft drink in the world, which regularly used a densitometer that was originally designed for high precision petrochemical laboratories (at a price of £20,000). Unfortunately, the poor cleaning and calibration of the sensitive device affected the product results and corrective measures were very expensive. Other measurements directly affecting


Selecting appropriate flowmeters is crucial in the food industry


flow rate include density and viscosity which change with temperature and pressure. Some products, such as sugar syrup or starch solutions for example, create measurement challenges. As a further complication, multiphase conditions may appear during the transit of concentrated orange juice, where fluid, air and pulp share the pipe run. Some processes use carbon dioxide stored as a liquid and then depressurised


when added to beverages. This can be troublesome to control and maintain a consistent flow supply. Conversely, energy recovery from heat and carbon dioxide processes, like fermentation, is of financial benefit but depends on flow rate measurement and control. Furthermore, the use of steam is a common method in food and beverage production which requires specialised flow equipment. The calibration of flow meters which


ensures accuracy in food and beverage production is certainly not as critical when compared with oil and gas production. The overall calibration and traceability of flow measurement is a pyramid-like organisational arrangement. At the apex is the national flow measurement laboratory, which uses sophisticated facilities to test and calibrate flow meters precisely. Each subsequent level in the pyramid has reducing costs of calibration but a larger effect on measurement accuracy. The food and beverage tier is considerably below that of oil and gas, but a similar link can still be traced in the quality control and good measurement practice. Flow measurement is also needed to


blend ingredients, which requires careful control and quantification if the product quality is to remain constant and production costs optimised. As another example, nitrogen can be used in the final production stage for food preservation during shipping and further extends the diverse range of flow-related measurements. From milk to chocolate, beer to wine,


energy input to recovery, liquids, gases and mixtures; the prevalence of flow measurement and the selection of appropriate metering types should not be overlooked, as it can affect production, quality and profits to a surprising degree.


TÜV SÜD National Engineering Laboratory www.tuv-sud.co.uk/nel


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