(414c) Drying Kinetics of Single Droplet of Sugar Cane Molasses

Drying kinetics of Single Droplet of Sugar Cane Molasses

Valeria Benalcazar¹,
Paulo C. Narvaez¹, Alvaro Orjuela¹

¹Department of
Chemical and Environmental Engineering, Universidad Nacional de Colombia,
Bogotá, Colombia.

Keywords: Drying, REA model, CDC model, sugarcane
molasses.

Non
centrifugal cane sugar (NCCS) or jaggery is a solid food product
obtained by open evaporation of the sugar cane juices up to nearly 95 °Brix,
followed by cooling down and solidification in molds of different shapes and
sizes. NCCS is mainly composed of sucrose, glucose, fructose and minor content
of minerals, vitamins, and antioxidants; this makes NCCS a nutritional and
functional food product. Currently, NCCS is produced worldwide and it is mainly
consumed as a traditional food or as ingredient for crafted beverages. Despite
its nutritional value makes it a preferable sweetener over refined sugar,
current commercial shapes are not convenient for instantaneous applications;
the blocks require grinding and treatment with hot water for a proper
dissolution. This is a major drawback for the use of NCCS as ingredient in the food
industry and for consumer products.        

In this
regards, granulation and powdering have been identified as alternative
processes to develop instantaneous sweeteners from NCCS. While granulations has
been successfully accomplished by grinding and sieving, powdering is still a
challenge. In general, powdering can be accomplished by spray drying, however
there are challenges with the processing of high sugar content materials. High
viscosity, hygroscopicity, caking and sticky behavior are typical of high sugar
content solids, so the operating window for spray drying is reduced. Thus,
process modeling is required to assess the technical feasibility for the
implementation of a spray drying process in the powdering of NCCS.  

Modeling
of spray drying can be done by mean of different approaches. In particular,
computational fluid dynamics (CFD) has been used as a tool for the rigorous
description of phenomena occurring during the process. In addition to the
models for the calculation of physicochemical properties, CFD requires models
for the determination of inlet drop size distribution and for the drying
kinetics when modeling spray drying units. Specifically, the drying kinetics is
fundamental for the accurate prediction of mass and heat transfer phenomena
during the drying process. The drying kinetics is specific of each material,
and unlike phase equilibria, it cannot be predicted from theoretical models but
must be experimentally measured.

Taking
into account the aforementioned, the aim of this work is to evaluate the drying
kinetics of sugarcane molasses under different operating conditions. Thus,
drying kinetics were evaluated by mean of single drop drying experiments under
controlled conditions of air velocity (0.5-1.5 m/s), temperature (60-140 °C), molasses
solids content (30 to 70 °Brix) and drop size (1 to 10 µL). In
total, 48 single drop drying experiments were carried out, with the
corresponding repetitions to ensure accuracy, reproducibility and reduced
uncertainty. The drying profile was tracked along time by mean of a gravimetric
method using a microbalance, following the drop temperature with a thermal
probe, and the drop size by video recording and image processing. In parallel,
Equilibrium humidity content of NCCS particles at different temperatures was
determined by mean of thermogravimetric analysis. Once the drop/particle
humidity, size and temperature profiles were obtained, they were used together
with the equilibrium conditions to adjust the corresponding parameters of a
theoretical (i.e. RAE) and a semi empirical (i.e. CDC) drying model. According
to results, both models fit well the experimental data, and they can be used
for the further CFD modeling of the spray drying of sugarcane molasses.