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Sweet solution for liquid sugar level control

24 July 2016

One of British Sugar’s beet refineries in the UK has recently installed a new 80ghz radar for use on a challenging level control application. 

VEGAPULS 64 radar with typical heavy condensation on sensor face from the dissolver process.
VEGAPULS 64 radar with typical heavy condensation on sensor face from the dissolver process.

At the first stage of production in the refinery, the raw beet is cut into strips and the sugar content diffused in hot water to form a liquor which is heated and boiled to concentrate before it is mixed with other process streams of varying densities in the ‘dissolver’. It is at this process stage that level is monitored and controlled by a VEGAPULS 64 80GHz radar.

The dissolver consists of several interconnected agitated vessels, each one with a weir allowing the liquor to flow from vessel to vessel. During the dissolving process, sugar byproducts from the downstream refining process are also reintroduced to enable the sugars from those to be recovered and reused.

To ensure a continuous process, a reliable level measurement is required in the tanks, to control heat and product input as well as to maintain consistent output and quality. The liquid density is continually changing, the product is viscous and adhesive and slightly abrasive, so a direct level measurement with a non-contact sensor is preferred. 

The sugar is heated typically at a temperature of between 80 and 90°C, so the surface consists of a continuous ‘rolling’ surface foam. The tanks are vented to atmosphere and there is always heavy condensation present. For maximum vessel and process efficiency, the level runs close to the top of the dissolver. 

Solving challenges
These conditions create many challenges for any contactless level transmitter –even radar based devices – with constant steam and heavy water droplets on the sensor itself. Originally a lower frequency device with 6in antenna was used to overcome the condensation and foam, but did not quite perform as required. With very high liquid levels in the vessel and foaming surface so close the radar antenna, it required regular cleaning of deposits to keep the unit functioning reliably. 

When looking for test sites for the new 80GHz radar ‘Zero series’ sensors from VEGA, this was a perfect application task in a difficult environment. The sensor chosen was a unit with a DN150 fitting, to match the existing nozzle (although the size could be as little as 50-80mm with same performance). The unit was fitted by the end user and commissioned using a PLICSCOM plug in programmer, for in head set up of any VEGA plics transmitter. The performance improvement was immediately apparent, providing continuous, accurate level data, no step changes and no sensor outages for cleaning. 

VEGA engineers attended site shortly after and, with only very minor adjustments for testing and setting up the integrated sensor data logging for the trial, agreed the unit was working very well. The pilot data was monitored and retrieved and the successful unit remains now permanently installed and working well on site over six months later. 

British Sugar is now looking at several other applications where the capabilities of the 80Ghz radar can be utilised in the sugar production process. British Sugar engineers are also evaluating another new innovation from VEGA, a new version of PLICSCOM programmer with Bluetooth, which enables set up and asset management via Smartphone or tablet of any VEGA transmitter. 

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