Choosing the right spray dryer
GEA Niro has significant expertise within process equipment, including spray drying plants for the Food & Dairy industry. When selecting a spray drying plant, it is important to know the requirement to the end product. Should it be a regular product, or should it be agglomerated and instantly soluble in cold water? Should the spray drying plant be designed for CIP cleaning-in-place?
The spray drying principle
In a spray dryer, water from the feedstock (concentrate) to be spray dried is evaporated from the surface of many small droplets (1 litre of concentrate is atomized to 1,5 x 1010 droplets with a diameter of 50 my with a total surface of 120 m2.) the small droplets are created by an atomizer- either a rotary wheel or a high pressure nozzle. The droplets are introduced into a hot airstream, which - due to the evaporation of the water from the concentrate - is cooled down. This now colder and humid air is discharged from the dryer and after separation of the now dry particles discharged into the atmosphere. The dry particles are - after separation from the process air - further cooled and bagged off.
Spray Dryer Type MSD™/FSD™
The spray drying process depends entirely on the composition of the product. Some are very easy and others very difficult to dry. In this context it should be stated that a GEA Niro spray dryer is designed and the process parameters selected to ensure as long operation time as possible, before it is necessary to stop the plant for cleaning. To support our design engineers when they select the drying parameters, we use the
DRYNETICS™ single particle drying method developed by GEA Niro.
Below some basic principles are given to be used when a GEA Niro dryer is designed:
1. The total moisture content in the exhaust air is one of the most important parameters. It depends on the composition of the product, e.g. a product with high protein content can be dried at high total moisture content in the exhaust air, whereas a high carbohydrate content requires low moisture content to avoid sticking of powder in the chamber, ducts and cyclones.
This is also why the total moisture content in the ambient air is an important parameter to know before the plant is designed, as the "drying potential" is reduced if the ambient total moisture is high.
2. Another important parameter to know is the maximum solids content in the concentrate. This is viscosity-driven and as such also depending on the composition of the product. As a rule of thumb the following applies:
High fat content
• allows higher solids content.
• requires lower drying temperature in order to avoid sticking (i.e. low total moisture content in the exhaust air).
High protein content
• requires lower solids content due to viscosity (except for hydrolysed proteins).
• allows higher drying temperature without sticking (i.e. high total moisture content in the exhaust air).
• The higher protein content, the more difficult becomes the agglomeration process. This is, however, counteracted, if the MSD™/FSD™ or IFD™ dryers are selected.
High carbohydrate content
• Allows higher solids content (except for starch, due to its high viscosity) of the concentrate.
• Allows higher spray drying temperature without sticking, if the carbohydrates are of the high molecular weight type (e.g. maltodextrins and starches), which results in an increase of the glass transition temperature. The moisture content of the chamber exhaust air can be higher when drying powders with higher glass transition temperatures resulting in a more economical drying.
• If the carbohydrates are of the low molecular weight type (e.g. sugar, lactose and glucose syrup), it results in a decrease of the glass transition temperature, which requires lower spray drying temperature in order to avoid sticking (i.e. low total moisture content in the exhaust air)
Spray Drying Plant Type MSD™ with integrated fluid bed
For U.S. Food & dairy dryer inquiries, please visit the GEA Process Engineering Inc website
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