What are the original causes of stickiness in spray dryer drying? How to control?

Spray-dried foods fall into two categories: non-sticky and sticky. Non-sticky ingredients are easy to spray dry with simple Dryer design and free-flowing final powder. Examples of non-sticky materials include egg powder, milk powder, solutions such as maltodextrins, gums, proteins. In the case of sticky foods, there are drying problems under normal spray drying conditions. Sticky food often sticks to the walls of the dryer, or becomes useless sticky food in drying chambers and transport systems, with operational problems and low product yields. Sugary and acidic foods are typical examples.

Stickness is a phenomenon encountered during the drying process of food materials rich in sugar and acid are often sprayed. Powder stickiness is a cohesive adhesive property. It can be explained in particle-particle viscosity (cohesion) and particle-wall viscosity (adhesion). A measure of the force with which powder particles bind is due to their internal property known as cohesion, which forms lumps in the powder bed. Therefore, the force required to break down the powder agglomerates should be greater than the cohesive force. Blocking is an interfacial property, the tendency of powder particles to adhere to the walls of Spray Drying Equipment. The cohesion and adhesion are key parameters for designing drying and drying conditions. The surface composition of powder particles is primarily responsible for stickiness issues. The cohesive force and adhesion tendency of powder particle surface materials are different. Because drying requires a large amount of solute to be transferred to the particle surface, it is bulk. Two sticky characteristics (cohesion and adhesion) can coexist in spray-dried sugar-rich food materials. The cohesion between particles is cohesive force is the formation of fixed liquid bridges, moving liquid bridges, mechanical interlocking and electrostatic attraction between molecules and solid bridges. The main cause of powder particle sticking with drying chamber walls is material loss during spray drying of sugar and acid rich foods. Silty stays longer when lost on wall drying.


lead to stickiness

Spray sugar and acid-rich food drying powder recycling Using spray drying technology, low molecular weight sugars (glucose, fructose) and organic acids (citric acid, malic acid, tartaric acid) have great challenges. Small molecules such as high water absorption, thermoplasticity, and low glass transition temperature (Tg) contribute to stickiness problems. The spray drying temperature is higher than Tg20°C, and these ingredients mostly form soft particles with sticky surface, causing the powder to be sticky, and finally form a paste-like structure instead of a powder. The high molecular mobility of this molecule is due to its lower glass transition temperature (Tg), which causes stickiness problems at temperatures commonly popular in spray dryers. Glass transition temperature The main characteristics of amorphous phase transition temperature. A glass transition event occurs when a hard solid, amorphous sugar, undergoes a transition to a soft rubbery, liquid phase. Surface energy, solid glass has lower surface energy and does not adhere to low energy solid surfaces. As a result of the transition from the glassy to the rubbery (or liquid) state, the surface of the material can be raised, and molecular and solid surface interactions begin. During the food drying operation, the product is in a liquid or cohesive state, and the liquid/cohesive food becomes a glass state due to the removal of the plasticizer (water). If the food raw material does not undergo a high drying temperature transition than the glass transition temperature change, the product will maintain high energy viscosity. If this food comes in contact with high energy solid surfaces will stick or cling to it.

control stickiness

There are many materials science and process-based approaches to reducing stickiness. Materials science-based methods include high molecular weight material liquid drying aids that increase temperatures beyond the glass transition, and process-based methods include machine room walls, bottoms, etc.