Spray drying is a widely used process for the production of powdered food products. In this process, atomization is used to create fine droplets from feed liquids, which are subsequently dried to particles in a hot air stream. However, drying processes are known to be the most energy consuming processes used in food industry. A good way to reduce their overall energy consumption is the use of alternative concentration methods for the feed liquid. Unfortunately, with rising dry matter content, the feed viscosity increases rapidly. This complicates the drop formation step during atomization. On industrial scale, pressure swirl nozzles are most commonly used, as they provide very efficient atomization. However, the maximum processable viscosity is comparably low. Generally, pneumatic twin fluid nozzles are suitable for atomization of high viscous liquids. But, these atomizers are only used on small scale, due to high gas consumption rates. A possible solution for these limitations could be the use of the Air-Core-Liquid-Ring (ACLR) nozzle in the atomization step of spray drying processes.
In our recent investigations, the applicability of this new atomizer type for energy efficient spray drying of high viscous food liquids was investigated. ... mehrTherefore, spray drying experiments with model concentrates at two different dry matter to viscosity ratios were examined on pilot scale (Werco SD20). Aqueous solutions of reconstituted whey protein concentrate (WPC 80, c = 2 %) and two different maltodextrins (DE = 8.6 and 14, c = 28-48 %) were employed. For comparison, a commercial pressure swirl nozzle was applied. The focus of this work was on overall energy consumption of the spray drying process and on resulting powder characteristics, like moisture content, bulk density, particle size distribution and morphology.
The results show a high potential of the ACLR nozzle for spray drying of high viscous liquids. By use of the ACLR nozzle, the maximum processable viscosity is more than ten times higher than by use of the commercial pressure swirl nozzle. For the model system, this leads to an increase of the processable dry matter content of the liquid from 30 to 47 %. Summing up, an increase of dry matter content by 1 % reduced overall energy consumption of the process by 2 %.