The Sweetest Chill: Cooling Sugar Crystals Installation and operation of a bulkflow sugar cooler in Belgium
Bulkflow Technologies is a world leader in the indirect heating and cooling of powder and bulk solids in many industries worldwide (chemicals, polymers, fertilizers, detergents, minerals, oilseeds, grains, food products, sugar and biosolids). In the last few years, Bulkflow has introduced this technology to the sugar industry, where it has been established as a proven and effective method of cooling sugar crystals before storage and packaging. The Bulkflow system can be installed as either a primary or a secondary cooler, and is readily adaptable to plant retrofits.
The Bulkflow Heat Exchanger is a unique piece of equipment that consists of a bank of vertical, closely spaced, hollow, stainless steel plates. The sugar flows slowly, by gravity, between the plates in mass flow. Cooling water flows through the plates, counter-current to the product flow for higher thermal efficiency.
Cooling occurs by heat transfer through the sugar particles, and is exclusively by conduction. Below the heat exchanger, a vibrating discharge feeder creates mass flow and regulates the sugar throughput. The Bulkflow sugar cooling technology is covered by world-wide patents, and also benefits from a strong R&D department that has produced many other patent-pending applications for heat exchange in bulk solids.
Problems at Brugelette
For white crystal sugar to be stored or packed successfully, its moisture content and crystal size distribution must be tightly controlled, as also must the temperature at which it is held. These variables depend on the local ambient temperature and relative humidity, as well as the type of storage silo used (ventilated or unventilated, heated or unheated). The sugar plant at Brugelette in Belgium, operated by the company of the same name, uses a horizontal silo in which the ideal sugar storage temperature is approximately 30 °C.
Brugelette has undergone several modernization projects during its history. One of these projects, the replacement of old centrifuges, caused an increase in the temperature of the sugar leaving the process. As a result, sugar was being sent out to storage at well above the safe temperature of 30 °C.
The plant had previously used a combined rotary drum dryer and cooler. The first section was used as an air dryer and the second as a cooler using ambient air, both sections operating in countercurrent flow.
The existing dryer section could still meet the increased load, drying the sugar to below 0.04 percent moisture. However, the drum’s cooling section could not cope with the resulting increase in temperature and was no longer able to provide the required sugar outlet temperature of 30 °C.
An ideal solution
According to Laurence Philippart, project engineer at Brugelette, the Bulkflow Sugar Cooler was chosen for three reasons:
- a compact design was easily integrated into the existing plant;
- extremely low energy consumption, of approximately 0.33 kWh/t of product;
- the fact that it does not use air eliminated the need for large fans, ducts, and auxiliary equipment such as air filters or cyclones.
The cooling water circuit needed for the exchanger was designed by the plant engineers using a small portion of the beet washing water transported from the settling ponds to the wash plant. The water is filtered and sent through a small plate and frame exchanger, which cools the closed-loop water system for the Bulkflow Heat Exchanger, before rejoining the main water stream on its way to the wash plant. With this design, the Bulkflow unit provides adequate cooling even at the beginning of the production cycle, when the water in the settling ponds is relatively warm.
Since Bulkflow does not use air to cool the product, the plant was able to realize important savings by avoiding the expensive task of installing additional air pollution equipment. The fact that air is not used also increases the product quality, since there is no risk of contaminating the sugar with bad odors or microorganisms.
The operation of the cooler is completely automated, with the unit’s level and temperature control system integrated in the plant’s distributed control system (DCS). In 2006, the Bulkflow unit cooled 80 t/h of sugar from 48 °C to 30 °C using cooling water at 20 °C. The maintenance of the equipment consists of washing the interior of the exchanger at the end of the sugar production cycle. This operation is extremely easy, as large doors allow good access to the plate banks. Both the inlet hopper and the vibrating discharge feeder are also equipped with quick-release openings for inspection and maintenance.
The author is with Bulkflow Technologies Inc., Calgary, Alberta/Canada.