Choosing the wrong spray dryer capacity can be a costly design mistake for any industrial drying system. At any instance, you must strive to achieve an optimal design range to avoid bottlenecks that come with an undersized unit or unnecessary capital investment in oversized systems.
In this article, you will learn how to calculate the capacity of a spray dryer and how to choose the right size.
What is Spray Dryer Capacity?
Spray dryer capacity is the rate at which a system can convert a liquid into a dry powder. Additionally, spray dryer capacity is measured by its evaporation rate, which is the amount of water the system can vaporize per hour. That is, you can quantify this as kg/hr or lb/hr.
Whenever you are buying a spray dryer machine based on capacity, it is important to confirm the feed composition alongside other operating conditions. For example, a spray dryer rated at 1,000 kg/h feed at 40% solids is different from 1,000 kg/h at 10% solids. We will explain this further in the subsequent sections.
How to Measure Spray Dryer Capacity
· Feed Capacity
Feed capacity is the volume or mass of the liquid solution entering the atomizer per hour [measured in L/h or kg/h]. This value must be matched to the spray dryer specifications and evaporation capacity to achieve efficient drying and consistent product quality. Improper matching can lead to incomplete drying or thermal degradation.
For example, a dryer capacity indicated as 1,000 kg/h feed rate at 20% solids implies incoming solids is 200 kg/h, while water is 800 kg/h. On the other hand, for 1000 kg/h at 50% solids, it simply implies 500 kg/h incoming solids and 500 kg/h incoming water.
It is quite clear that the nominal feed capacity is the same, however, the drying load is quite different.
· Water Evaporation Capacity
Water evaporation capacity is calculated as the mass of liquid feed minus the mass of the final dry powder. It represents the total moisture load the dryer must remove per hour, usually measured in kg/h indicating the dryer’s drying capability and affecting production throughput.
Usually, when comparing spray dryer sizes, most designers emphasize the evaporation capacity over the feed capacity. Of course, they must also consider the residual moisture, which can range from 3% to 5% after the drying process is completed.
· Powder Production Capacity
Powder production capacity is the amount of dry powder produced per hour, depending on the feed rate, water evaporation capacity, and solids content of the feed. It is measured in kilograms per hour and serves as a key measure of actual production output. This value can be compared with the spray dryer’s design specifications to evaluate performance.
For example, if the final powder output from the spray dryer should be 500 kg/h, then the designers must work backwards. By doing so, they will target the moisture and feed solids.
· Air Flow Capacity
Air flow capacity is the volume of drying air circulated per hour, measured in cubic meters per hour [m3/h] or cubic feet per minute [CFM]. It must balance the thermal energy required to vaporize the liquid feed with the need to provide sufficient particle residence time.
Insufficient airflow leads to incomplete drying and wet powder, while excessive airflow reduces residence time and increases operational energy consumption.
Factors Determining the Spray Dryer Capacity You Actually Need
· Feed Material Properties
Factors like heat sensitivity, viscosity, and stickiness influence chamber size, residence time, and the optimal outlet temperature. These properties affect atomization, drying efficiency, and energy consumption. Ensure you optimize these properties to improve capacity while maintaining consistent product quality.
· Moisture Content
Moisture content helps you calculate the amount of water that must be evaporated. High-moisture feeds contain more water, reducing throughput and increasing energy consumption, while lower-moisture feeds are achieved by concentrating the liquid before spray drying, improving production efficiency and powder output.
Putting this into perspective:
Assuming the sprayer design should be such that the production target is 500 kg/h solids. This will imply:
At 20% solids, the feed rate will be 2,500 kg/h. This is from the formula: required feed rate = required dry solids/feed solids fraction.
While at 40% solids, the required feed rate will be 1250 kg/h. Of course, in all these, we have ignored the final residual moisture.
Therefore, the design team must evaluate whether the upstream concentration can economically reduce the spray dryer evaporation duty. This should be before specifying the drying chamber and heating system.
· Drying Temperature
A larger temperature difference generally yields a greater evaporation capacity, provided it does not thermally degrade the product. Drying temperature controls the speed of moisture evaporation, optimizing it maximizes the capacity and product quality without damaging heat-sensitive materials
· Atomization Selection
Atomization plays a fundamental role when determining spray dryer capacity. For example, fine droplets have a larger surface area, allowing moisture to evaporate more quickly for efficient drying, significantly impacting the drying rate and final product quality.
Here is a quick reference table:
| Atomization Method | Typical Throughput | Key Capacity Limitation | Best Fit |
| Pressure nozzle | · Medium to high | · Nozzle size and feed pressure | · High-throughput controlled particle size |
| Two-fluid nozzle | · Low to medium | · Atomizing gas demand | · Pilot or small production, viscous feeds |
| Rotary atomizer | · High | · Wheel speed and atomizer feed limit | · Large-scale, variable-throughput production |
Note: When considering capacity sizing, it is important to select an atomizer that can handle the required feed rate without pushing droplet size outside the spray dryer effective drying range.
· Drying Chamber Design
The spray drying chamber is where the moisture is evaporated from the atomized droplets. It controls the droplet drying time and the overall efficiency of the drying process, increasing the overall production capacity.
When you want to optimize the drying conditions, it is critical to consider the chamber shape, air distribution and system insulation. A properly designed chamber will ensure uniform drying, while preventing the possibility of product sticking or uneven particle size distribution.
· Heat Source
By knowing the heat source, it will be easier to determine the thermal energy available to evaporate water from the feed. When the feed rate is high, it will increase the moisture load, which requires greater heating duty.
It is important to balance both the maximum heat output and the feed rate. This is to ensure the final product has the right moisture content while maintaining the optimal operating conditions for the spray dryer.
Therefore, under continuous production conditions, you must determine the available thermal duty, achievable inlet air temperature, heating stability, and heat-transfer efficiency.
How to Calculate Spray Dyer Capacity
A spray dryer’s capacity is defined by its water evaporation rate [W evaporation], calculated by multiplying the liquid feed rate [M feed] by the difference in moisture percentages.
Capacity [W evaporation in kg/hr.]= M feed *[IMC –FMC]/100
Where: M feed is the liquid feed rate [kg/h], IMC is the initial moisture content [%], and FMC is the final moisture content of the product [%].
FAQs
Does a larger spray dryer improve efficiency?
Not necessarily.
Remember, an oversized system implies a larger initial investment, larger footprint, underutilized equipment and inefficient operation away from the intended design considerations.
On the other hand, an undersized system can always lead to production bottlenecks, limited expansion capacity, excessive operating hours and inability to achieve required output.
Can one spray dryer process different products?
Yes, a single spray dryer can process different products by adjusting operating parameters such as feed rate and thoroughly cleaning the system between batches.
Can you improve spray dryer capacity without replacing the machine?
Yes, spray dryer capacity can be increased by:
- Optimizing operating conditions such as temperature and feed concentration.
- Upgrading key components such as air, fans, and heater.
- Improving heat efficiency.
- Reducing interruptions.
Need Help in Determining the Right Spray Dryer Capacity?
Pilotech engineers will take you through every stage in the spray dryer sizing. Based on your production needs, our team will help you to determine the feed rate, feed solids, moisture removal requirements, and product characteristics.
Send us your inquiry today, and our engineering team will recommend the right spray dryer machine.