VEGAPULS 64 provides reliability in the crystallization process in sugar production

According to the American Ministry of Agriculture, about 175 million tons of sugar are produced annually. Household sugar, so-called saccharine, however, is used in relatively small quantities in households. Two thirds of the average annual consumption are processed industrially in beverages, bakery and confectionery, sandwich spreads and dairy products. The South African RCL Foods Sugar and Milling is a specialist for different sugar products. They manufacture brown sugar and refined crystal sugar among other things. The production of different sugar types requires, above all, good timing but also robust components. First, sugar cane is ground before sugar syrup and crystals are extracted by different processes in the next step. In the subsequent evaporation station, water is drained gradually from the juice concentrate until an exactly defined sugar concentration is achieved. Finest sugar crystals are fed into the crystallizer to trigger the crystallization process. By draining off more and more water, the crystals grow to an exactly defined size. Then, the juice and crystals are separated in a centrifuge. The different sugar variants are then stored, packed and are ready for sale.

The crystallization is a hot business. High process and product temperatures of up to 100 °C are just as much a part of the daily routine as steam and condensation. Despite all adversities: High accuracy and repetitiveness are absolutely crucial for the process itself and the key to a high-quality end product. In the plant part, in which VEGA measuring technology is also used, the juice is boiled in a vacuum at 64 °C. The vacuum pressure enables the water to evaporate already at between 65 °C and 80 °C and prevents the sugar from caramelizing and becoming dark at these temperatures. Then the mass is passed on for crystallization. Two crystallizers are available in the RCL plant. The challenge is that the whole content from the boiling process must be filled into one of the crystallizers. To do this, the level of the respective crystallizer must be below 15 per cent because otherwise it could be overfilled. The hot liquid could cause injury to persons in the case of overfilling. In addition, high costs for cleaning and recommissioning the equipment would be incurred.

If, on the other hand, too high a level is indicated, a locking mechanism in the control system is activated and the filling is not even started. This could mean that the whole batch might have to be thrown away. Sugar is very sensitive: If the process conditions, i.e. dwell time and temperature, are not kept exactly, this can have effects on the product properties. Both scenarios cause high downtimes and production losses. This means that measuring instruments must be very robust but must also operate absolutely reliably.

Radar level measuring instruments are also to be used in sugar crystallization but repeatedly had to face process-specific challenges. The crystallizer has an agitator which is intended to prevent crystals forming at the bottom of the container. For this reason, the container is regularly cleaned with steam because sugar crystals would otherwise stick to the container walls and the agitators. These can become as hard as cement. There are therefore valves at the bottom which can be opened to allow the hot steam to flow in. This is a first acid test for the measuring instruments because they come into direct contact with the hot steam. Despite these measures, sugar crystal deposits cannot be totally avoided. But these kept causing interference echoes which could not easily be computed out because the interference signals changed with growing deposits. In addition, moisture repeatedly penetrated the process fitting due to the condensation. VEGA therefore suggested installing a VEGAPULS 64 with a 40-mm process fitting in one of crystallizers as a test. After seeing the echo curves of the new instrument, RCL soon decided to use the VEGAPULS 64 which has been providing reliable level values ever since.

The VEGAPULS 64 solved many problems at once. The Kalrez seal of the VEGAPULS 64 prevents moisture from penetrating the process fitting. In addition, the narrow beam angle of the VEGAPULS 64 ensures that it simply glides past the sugar deposits. This succeeded because the measuring frequency in the VEGAPULS 64 is 80 GHz (formerly 26 GHz). The radiation angle could therefore be reduced considerably. The measuring instrument operates reliably and accurately even in case of deposits on the sensor. And the aggressive process conditions do not disturb the measuring instrument either. Interference signals have as good as disappeared.

RCL has been working with VEGA for more than a decade and admires the Schiltach company, above all, for its excellent services. The reliability and high quality of the instruments are also unbeatable as far as the company is concerned. The VEGAPULS 64 that is now working reliably in the harsh production environment has proven this impressively once again.