Whether you operate in the food, pharmaceutical or chemical industry, learning to control spray drying particle size is important to promise your products’ quality.
In this article, I will introduce the influencing factors and control methods of spray drying particle size, hoping it will be helpful to your production.
What is the Spray Drying Particle Size?
The spray drying particle size refers to the size of the powder particles formed after being atomized and rapidly dried. It is usually expressed in micrometers (μm).
Particle size influences the solubility, fluidity, density and application performance of your product directly, which is one of the important indicators for evaluating the spray drying effect.
What Factors Determine the Spray Drying Particle Size?
The particle size of your spray drying products usually ranges from 10 to 500 μm, and the specific particle size range is related to factors such as material properties, atomization methods, and process parameters, etc.
The following are the core factors that influence the particle size of spray drying:
Atomization Method
The atomization method is the most important factor that determines the particle size. Different types of atomizers will influence the initial size of the droplets directly, thereby determining their final particle size.
Generally, centrifugal atomizers produce larger particles with a wider distribution, pressure nozzles produce particles uniformly, and air-flow atomizers can obtain finer particles.
Material Properties
For instance, your material’s physical properties such as solids content and viscosity, can have a significant impact on particle size.
Generally, the higher the viscosity and solid content, the more difficult it is to atomize the material, and the larger the formed droplets, which results in larger particle sizes. If the surface tension of the material is lower, it is easier to form smaller particle sizes.
Process Parameters
The process parameters during spray drying, such as inlet and outlet air temperatures, atomization pressure, and feed rate, which all can affect the drying speed and particle size of the droplets.
For example, the increased atomization pressure or rotational speed usually reduces the particle size, while increasing the feed rate may result in larger particle sizes.
Dry Air Flow and Dry Tower Structure
The airflow pattern (parallel flow, counter-flow or mixed flow) and the structure of the drying tower will affect the residence time and heat distribution of droplets within the drying chamber, which can indirectly improve the final size and distribution of the particles.
A reasonable design of the drying tower can obtain more stable and uniform particle sizes for your products.
Post-Treatment
In some applications, secondary agglomeration (such as fluidized bed granulation) can be employed to combine fine particles into larger ones, which can enhance its solubility and fluidity.
Consequently, the final particle size of spray drying may also be affected by the post-treatment process.
How to Control the Particle Size of Spray Drying?
There is no fixed standard for the actual particle size of spray drying materials. You should adjust and control it based on the specific application situation.
Select the Appropriate Atomization Method
To control the particle size of spray drying, it is crucial to select the atomizer type which is suitable for your target particle size. Choosing a right atomization method can determine the particle size range directly.
Centrifugal atomization usually results in larger and more widely distributed particles. Pressure nozzles are suitable for producing uniform particles, while air-flow atomization is suitable for preparing ultrafine powders.
Adjusting the Feed Concentration and Viscosity
By increasing or decreasing the solid content and viscosity of your material, you can change the droplet’s size. Generally, the higher the solid content and viscosity, the larger the final particle size.
Therefore, by adjusting the feed properties through pre-treatment, you can control the particle size more easily.
Adjusting the Atomization Parameters
For pressure nozzles and centrifugal atomizers, adjusting the nozzle pressure or the atomization speed can control the particle size precisely.
Adding the pressure or the speed will cause the droplets to dissolve more thoroughly, thereby reducing the particle size.
Control the Feeding Rate and Temperature
The feeding rate and the temperature of the inlet and outlet air will affect the spray drying speed and the particle formation process.
A higher feeding rate may cause insufficient dispersion of the droplets, which will form larger particle sizes. In contrast, right temperature control helps stabilize the drying process and prevent fluctuations in particle size.
Using Agglomeration Technology
When you need larger particle sizes or want to improve the solubility of your product, you can re-agglomerate the small particle sizes into larger particle sizes by a second agglomeration process (such as fluidized bed granulation).
This is widely used in products like milk powder and instant coffee to adjust the final particle size distribution.
Maintain Equipment Stability
If problems such as nozzle wear, unstable feed, or unstable system control occur, it will lead to particle size fluctuations. Therefore, you can maintain and clean the spray dryer regularly, and adopt an automatic control system to achieve long-term stability of the particle size.
Spray Drying Particle Size Requirements in Different Application Industries
| Industry | Typical Product | Particle Size Range(μm) | Core Requirement |
| Food Industry | Milk powder, coffee, seasoning powder | 50-300 | Good solubility, low dustiness |
| Pharmaceutical Industry | API, inhalation preparations | 1-50 | High precision, strict PSD control |
| Chemical Industry | Catalyst, fine chemicals | 20-500 | High reaction efficiency, excellent flowability |
| Agricultural Chemical Industry | Pesticides, fertilizers | 50-300 | Good dispersibility, easy to spray |
| Daily Chemical Industry | Laundry detergent, cleaning agents | 100-500 | High flowability, low dust |
Particle size requirements are different across various industries. If your product has a specific particle size requirement, we can recommend and customize the most suitable spray dryer configuration for you.
FAQ
How to Select a Spray Dryer that Meets Your Particle Size Requirements?
You should consider the particle size you need, material properties, application industry, production volume, etc, so as to choose the appropriate atomization method and spray dryer configuration.
Why is the Particle Size Distribution (PSD) of Spray Drying Important?
The particle size distribution determines the uniformity and stability of your product’s performance. Generally, the narrower the distribution, the more consistent the product quality, it is especially important in the pharmaceutical and food industries.
How to Measure the Particle Size of Spray Drying Products?
Common measurement methods include laser particle size analyzer, sieve analysis, etc. Among them, laser particle size analysis is the most common and highly accurate detection method.
Does the Particle Size Change During the Spray Drying Process?
Yes. During the drying process, droplets may undergo contraction or slight aggregation, thus the final particle size is not exactly the same as the initial droplet size during atomization.
What is the Relationship Between Spray Drying Particle Size and Solubility?
Generally speaking, the smaller particles usually resolve faster. However, if the particle is too small, it will have an impact on its fluidity. Therefore, you need to strike a balance between particle size and its own performance.
Final Thoughts
A thorough understanding of spray drying particle size is especially important for your production. As a professional spray dryer manufacturer, Pilotech can match the most suitable spray dryer for your specific particle size requirements, thereby enhancing your product quality and production efficiency.
Contact Pilotech immediately to obtain professional selection advice! We look forward to cooperating with you!
More Resources:
What are the Functions of a Spray Dryer?
Microprilling VS Spray Drying: Complete Comparison for Industrial Buyers