If you are looking for an efficient, stable and controllable drying solution, a spray dryer is likely the best choice. You can apply it at various stages, ranging from the laboratory to industrial production.
This article will introduce the working principle, construction, types, pros and cons, as well as applications of spray dryers, helping you find a suitable spray dryer for your products.
What is a Spray Dryer
The spray dryer can quickly turn solutions or slurries into dry powders and is commonly used in fields such as food, medicine, chemical engineering, and biotechnology.
In the long-term spray drying production, you can control the size and moisture content of the output particles, obtaining stable and consistent powder products, thus increasing the product market advantage.
How Does the Spray Dryer Work
Step One: Atomization
The liquid material is rapidly dispersed into uniform and tiny droplets by the atomizer. This increases the surface area of the material, thereby enhancing the efficiency of your subsequent heat exchange.
Step Two: Drying
When the droplets enter the drying tower and meet the hot air, the moisture will evaporate in a very short time. As evaporation takes away a lot of heat, the material itself does not get too hot, so it is very friendly to heat-sensitive materials. The air volume, air temperature and feeding speed during the drying process will affect the moisture content and quality of the final particles.
Step Three: Separate and Collect
The airflow carries the dried powder into the cyclone separator. Under the action of centrifugal force, the powder is pushed against the separator wall and falls into the collection bucket, realizing the separation of powder from exhaust gas. Combined with the bag filter, you can capture finer micro-particles in the airflow, thereby improving the yield.
Main Components of the Spray Dryer
Feed Pump
The feed pump delivers liquid material to the atomizer. And, its feed rate affects the moisture content and particle size of your final product. Common pumps include screw pumps, plunger pumps, and peristaltic pumps.
To enhance your production continuity and reduce maintenance costs, it is advisable to choose an inlet pump that is easy to clean, corrosion-resistant with adjustable flow.
Atomizer
It breaks up materials into small, uniform droplets. The more uniform the droplets, the better the drying effect and the more stable the quality of your powder. Typical atomizers include centrifugal atomizers, pressure nozzles and dual-fluid nozzles.
Heater
The heating system heats the air to your required process temperature. Heating methods involve electric heating, steam heating, and gas heating. A precise PID temperature control system can be used to prevent overheating that could lead to discoloration or loss of active ingredients. Of course, you should also be aware that thermal efficiency is closely related to your electricity bill.
Drying Chamber
Liquid droplets evaporate quickly in the drying chamber and turn into a powder. Drying chambers are generally made of stainless steel, cylindrical with a conical bottom. It ensures that the droplets have enough residence time to complete the drying process and prevents the wet materials from adhering to the walls. Also, proper airflow design can improve your production continuity.
Collection System
This separates and collects the dried powder from the exhaust gas. A cyclone separator can separate the vast majority of powder with high efficiency. You also maintain it easily. A bag filter can capture ultrafine powder, minimizing powder loss. When you combine them, efficiency and throughput improve. If needed, the exhaust gas can be further purified through a wet scrubber.
Types of Spray Dryer
The common classification methods for spray dryers are based on the type of atomizer and the form of hot air flow. By understanding these classifications and advanced technologies used in spray drying, you can compare equipment differences more intuitively and quickly determine which spray drying solution meets your product requirements and goals. It can help you reduce the cost of trial and error.
Classified According to Atomizer
| Atomizer Type | Working Principle | Features | Application |
| Rotary Atomizer | The material is atomized by centrifugal force using a high-speed rotating disc. | Atomize a large amount of material. Work normally at a higher feed rate.
But it is difficult to maintain. |
Ideal for drying highly viscous liquids or solutions containing solid particles, but the cost is higher. |
| Pressure Nozzle | Use a high-pressure pump to atomize the material. | Atomizer structure is relatively simple, easy to repair and replace, operates silently, with low operating costs.
But the nozzle is prone to clogging and wear, so you need to replace the nozzle often. |
Suitable for handling low viscosity liquids, the power consumption is minimal.
Mostly used in spray granulation, spray concentration and other occasions. |
| Two-Fluid Nozzle | Operate at a low pressure.
Suitable for atomizing liquid materials with high viscosity.
|
Suitable for solutions, emulsions, suspensions, and pastes with viscosity or containing some solid particles, but it consumes a lot of power.
|
Depending upon the Airflow Pattern
Co-Current Spray Dryer
Co-current spray dryers are very common. Hot air and the atomized material enter the drying chamber from the same direction, usually flowing from top to bottom.
This enables the atomized droplets to come into contact with the hottest air first. As the moisture evaporates and absorbs heat, the surface temperature of the particles will not be too high, and greatly protects the activity of the material itself. The resulting powder maintains good color and flavor, and is often used in milk powder, coffee, plant extracts, etc.
In a word, if your product is sensitive to temperature, Co-current spray drying machines are a safe and reliable option.
Counter-Current Spray Dryer
In counter-current spray drying, the hot air moves in the opposite direction to the material. Usually, the droplets move downward from the top of the tower, while the hot air moves upward. It allows the material to face the higher temperature air even when its moisture content is very low. So, this method can more deeply dry the material and produce denser particles. Commonly used for ceramic powders and inorganic salts.
It is thermally efficient and more economical for handling materials that are heat-resistant, have high moisture content or large particles. However, it tends not to be used for biopharmaceuticals as it is prone to cause irreversible damage to heat-sensitive materials.
Mixed Flow Spray Dryer
Mixed Flow combines the characteristics of co-current and counter-current. Generally, the atomizer sprays from the bottom upwards, while the airflow enters from the top or forms a circulation within the tower.
It makes some hot air flow in the same direction as the material and some flow in the opposite direction. Thus, it causes the droplets stay longer in the drying chamber and dry more evenly. You will often see it processing larger particles such as detergents and chemical additives.
In short, if you want to prepare coarse powder but the plant height is limited, you should consider the mixed flow spray dryer first.
Advanced Technology in Spray Drying
Fluidized Bed Spray Dryer
It combines spray drying with fluidized bed technology. After spray drying, the material will fall into the fluidized bed at the bottom for secondary drying or granulation. Eventually, you will obtain highly fluid and soluble granular products. Also, because this way of drying materials more thoroughly, you don’t need to worry about uneven drying or wall adhesion problems due to high moisture content in the material. This is currently standard equipment in the instant powder, coffee, and other instant product industries.
If you want your product to have larger particles and better performance, it is best to use a secondary or tertiary drying system with a fluidized bed.
Low-Temperature Spray Dryer
The low-temperature spray dryer reduces the inlet air temperature and dehumidifies the introduced air to dry the materials gently. It can effectively protect heat-sensitive components of materials, such as proteins, probiotics, and enzyme preparations, to prevent biological inactivation and denaturation. Therefore, it is highly suitable for heat-sensitive materials such as Chinese herbal medicines, natural plant extracts, and biological products.
Under the low-temperature environment, materials with high sugar content can also be easily made into powder particles with excellent fluidity and solubility, so that your powder yield can also be guaranteed.
If you are more concerned about product quality and active ingredient retention, then the low-temperature spray dryer is the ideal choice.
Nano Spray Dryer
You can use a spray dryer to prepare sub-micron or even nanometer-sized powder particles. This type of machine typically employs high-frequency vibrating mesh technology or air flow atomization, is equipped with an electrostatic collection system, and has a high powder collection rate. Also, due to its relatively small processing capacity, it is more suitable for preparing inhalants, precise drug delivery, and the production of high-value products.
Spray Freeze Dryer
Spray freeze-drying first atomizes the material and rapidly freezes it into microspheres, then undergoes sublimation for dehydration. This technology can preserve the structure of the material, and the resulting particles have a porous structure with excellent solubility. It is commonly used for the preparation of high-end preparations, vaccines, protein drugs, etc. However, the equipment investment and operating costs are relatively high. So, it’s best for situations where you absolutely need top-notch solubility or you’re working with products that are worth the investment.
Electrostatic Spray Dryer
During the atomization process, the electrostatic sprayer charges the droplets, enabling the materials to dry quickly at a lower temperature. Unlike conventional atomization methods, it can dramatically decrease energy use and ensure more uniform particle distribution. You can use it to encapsulate volatile products such as fragrances and oils. The electrostatic spray can enhance your encapsulation efficiency and prevent the loss of volatile components in your products.
Ultrasonic Atomization Spray Dryer
The ultrasonic spray dryer uses high-frequency vibration to atomize the materials, resulting in fine and uniform droplets that are less likely to clog the nozzle. Therefore, you can use it to handle medium to high viscosity solutions and produce functional materials such as medical particles and precursors. If you are developing new materials and have high requirements for the stability of atomization, then you may consider purchasing an ultrasonic spray dryer.
Functions of the Spray Dryer
Extend Your Product’s Shelf Life
Liquid products such as milk and fruit juices are highly perishable. The cost of cold chain transportation is extremely high, and there is also a risk of leakage. Spray dryers evaporate water quickly and inhibit microbial growth, thus extending the shelf life of your products. The powder after spray drying can be stored at room temperature for 1-2 years.
This not only greatly reduces the loss caused by product expiration, but also frees your products from long-distance restrictions, making it easier to enter international markets.
Convenient for Transportation and Storage
Did you know that most of the time, you’re paying for shipping and storage fees for the water content in your materials? Using a spray dryer allows you to convert liquid or slurry materials into powder, dramatically reducing product volume and weight, and saving you considerable logistics costs.
If you’re a supplier of fruit and vegetable extracts or plant pulps, and your raw materials are highly susceptible to seasonal fluctuations, you can choose to use a spray dryer to process excess material into powder for storage during peak seasons. When market demand is high, your customers can simply add water to obtain a high-quality product. So, a spray drying machine can help you quickly respond to market demands and improve the efficiency of capital turnover.
Get Rid of Complex Processing Procedures
The operation process of the spray dryer is quite simple. The powder particles produced are usually spherical and have good fluidity. Therefore, you can directly use them for tablet pressing and capsule filling without the need for grinding or secondary granulation.
Compared with the irregularly shaped materials produced by traditional oven drying, this method can reduce labor costs and shorten the production process. It is highly suitable for the pharmaceutical and health supplement industries, and can increase your production efficiency by at least 25%.
Expand By-Product Profit Margins
The spray dryer can also help you transform often low-value or discarded by-products into higher-value goods. For instance, in addition to turning milk into milk powder, you can also turn whey liquid into whey powder, which can be used in functional foods and sports health care, bringing you more profits.
Whether it’s herbal residue or chemical by-products, the spray dryer can fully exploit their value. Not only does it boost the profitability of your production, but it also creates a good environmental image for your brand.
Improve Product Safety
Liquid products are susceptible to secondary contamination during the dispensing process, raising health and safety concerns.
During the spray drying process, high temperature can inhibit most of the harmful microorganisms. And when equipped with a closed-loop system, it can avoid the contact between the material and the surrounding environment, which is in line with the hygiene standards of food, medicine and so on.
Compared with natural drying, a spray dryer can dry the material more evenly, reducing its moisture content to an extremely low level and avoiding problems such as local clumping and deterioration. In short, spray drying reduces your risk of returns and earns the trust of your customers.
Advantages of Using a Spray Dryer
High Efficiency and Cost-Effective
The process of atomizing materials into finished powder typically takes only a few seconds to tens of seconds. Meanwhile, spray dryers are durable and stable, capable of continuous, uninterrupted production, so they are ideal for projects with high capacity requirements and tight delivery schedules.
Compared to freeze drying, spray drying generally does not require prolonged low-temperature vacuuming, resulting in lower operating costs—approximately one-fifth that of freeze drying—and lower unit energy consumption. This advantage is even more pronounced in mass production, helping you recoup your investment more quickly.
Consistent Batch Quality
You can adjust the particle size and moisture content of the finished powder by controlling the inlet air temperature, feeding speed and atomization method. Moreover, once the parameters are set, the spray dryer can continuously produce high-quality powder products, ensuring consistency in each batch of materials. It reduces the defect rate, saves your material losses, and is beneficial for keeping your brand reputation.
Suitable for Heat-Sensitive Material
Although the dry air has a high temperature, the rapidly evaporating moisture will carry away a large amount of heat, so the material is heated for an extremely short period of time. Compared to the oven that requires long-term heating, the drying spray can better protect the active substances and nutrients of the material.
Even if it is stored in a sealed environment for a long time, the aroma of the product can still be smelled after the packaging is opened, and the taste does not fade. Thus,it can make your product stand out in the market.
Scalable from Lab to Large Production
If you want to launch a new product, you can first test the formula with a small amount of materials on the laboratory spray dryer to reduce the development risks. Once the parameters are fully optimized, you can transfer them to the pilot-scale equipment to ensure everything is flawless. Then, scale up the process parameters and production scale proportionally and apply it to a large-scale production line. In this way, you can shorten the product launch time and also save your trial-and-error costs.
User-Friendly
After being equipped with a PLC control system, the spray dryer becomes much more convenient to operate. And it diminishes the reliance on skilled operators and helps you save training costs. Through the touch screen, you can monitor the temperature and pressure, and promptly detect faults. What’s more, in conjunction with the CIP system, equipment cleaning and maintenance will become simpler, lowering your downtime. All of this makes your factory management more worry-free and efficient.
Limitations of Spray Dryers
- Yield Losses: The fine powder is prone to being discharged along with the exhaust gas, which will cause product loss. Especially for the low-density powder, additional wet cleaning or electrostatic dust removal is required to ensure the powder collection rate.
- Limited Material Viscosity: The feed is usually introduced by pumping. Therefore, for materials with high viscosity, containing fibers or large solid particles, the processing will be very difficult.
- Higher Maintenance Requirements: Components such as nozzles and filters are prone to wear and require regular cleaning and replacement. If they get clogged or damaged, it will directly affect the quality of your finished products and also shorten the machine’s service life.
- High Initial Cost: The spray dryer consists of numerous components and auxiliary systems, which makes the initial investment very high. If your project has a low output, the payback period will be longer.
- High Energy Consumption: Spray drying demands a large amount of hot air to evaporate moisture, thus resulting in high energy consumption. Also, some of the heat energy will be lost along with the exhaust gas. You can enhance the heat efficiency by using a heat exchanger, but this will also increase your investment cost.
Considerations When Selecting a Spray Dryer for Your Product
Feeding Speed
When the compressed air velocity remains constant, if the feed rate is too fast, atomization will be insufficient, and the droplets will not evaporate completely, leading to wall adhesion problems in the separator and reducing the powder collection efficiency of your product. On the other hand, if the feed rate is too slow, production capacity will be affected, and energy costs will increase.
You can choose a spray dryer equipped with a variable-frequency feed pump, which can ensure both powder quality and continuous production.
Compressed Gas Flow Rate
The flow rate of compressed gas will affect the size of the dispersed droplets. The greater the flow rate of the compressed gas, the smaller the droplets will be, and the faster the drying speed will be. The particle size of the powder will also be smaller. On the contrary, if it is too low, it will lead to poor spray effect and more difficult drying.
Especially for the two-fluid spray drying machine, you should choose a model that can precisely adjust the gas volume to ensure the final product quality.
Material Characteristic
Viscosity
If the viscosity of your material is high, you need to increase the rotational speed of the centrifugal spray dryer to break up the droplets, or use a pressure-type nozzle spray dryer with a higher pumping pressure. If the viscosity exceeds 300 cP, the normal feeding method is difficult to pump, and you need to equip a screw pump or a rotor pump.
Solid Content
According to some research results, the higher the solid content of the feed liquid, the larger the particle size of the output will be. This will also cause difficulties in atomization and clogging of the nozzle. For such high-solid-content liquid materials, a drying spray machine equipped with a centrifugal atomizer or a high shear pump can be used.
Thermosensitivity
The outlet temperature is generally difficult to control; the inlet temperature has a significant impact on the final powder product quality.
When the inlet temperature is too high, exceeding the glass transition temperature of the material, it can cause the material to denature, become sticky, and lose active ingredients. However, if the temperature is too low, the powder will have a high moisture content, making it difficult to store for extended periods.
Therefore, you should choose a spray dryer that can accurately control the temperature, maintaining an accuracy of ±1%, balancing product quality and energy costs.
Production Scale
The hourly water evaporation volume of the spray dryer is a parameter indicator for evaluating production capacity. The small or laboratory spray dryer capacity is not large, commonly used in formula verification. Industrial spray dryers typically have an evaporation volume of over 50 kg/h and are suitable for continuous mass production.
You have to reserve an additional 20% space for model selection according to the actual capacity demand. In addition, the height of industrial spray drying equipment is higher. If your factory height is limited, you can consider using a horizontal spray dryer.
Spray Dryer Material
The part where the spray dryer comes into contact with the materials is usually made of SUS304 stainless steel, which has good corrosion resistance and is cost-effective. However, if your materials are highly corrosive, it is better to use SUS316L, as the molybdenum element enhances its corrosion resistance. You can also install ceramic liners in the separator and other parts with serious wear and tear to extend the service life of the spray dryer.
Areas of Use of Spray Dryer in Various Industries
Food & Beverage
- Milk powder, protein powder, instant coffee
- Carbohydrates, seasonings
- Fruits and vegetables powder
- Animal protein, blood meal, gelatin
- Fish meal, fish paste, fish solubles
- Functional food ingredients (protein peptides, amino acids, etc.)
Spray dryers can quickly convert liquid raw materials into powder that is easy to store. For instance, infant formula milk powder, instant coffee, and protein powder can retain nutrients and flavors to the greatest extent through spray dryers. Therefore, you will obtain high-quality products with a longer shelf life, while maintaining stable output and high production efficiency.
Pharmaceutical
- Antibiotics, vitamins, pharmaceutical excipients, intermediates
- Microencapsulated drugs
- High-value active ingredients
The spray drying machine can help you accurately control the particle size, water content and fluidity, which is convenient for your subsequent tabletting and capsule filling.
Moreover, spray drying can be used to microencapsulate drugs, reducing the impact of gastric acid and smoothly delivering enteric-coated drugs to the absorption site. It can also mask the taste and protect the drug from environmental factors such as light and moisture.
Meanwhile, the whole process can be completed in a closed system, reducing the risk of drug contamination and meeting GMP requirements.
Chemical & Materials
- Detergents, soaps, pigments, dyes
- Catalysts, pesticides, fertilizers
- Ceramic materials, cement, mineral oil concentrates
- Plastics, resins, organic/inorganic chemicals
A spray dryer can realize flexible production from coarse particles to ultrafine powders by adjusting the atomization method and process parameters, such as detergents, pigments, and catalysts. It means you can purchase one machine for many formulations and reduce your investment in equipment.
Biotechnology
Probiotics, enzymes and functional biomaterials are very sensitive to temperature and shear force. With a co-current spray dryer and precise temperature control, you can ensure your drying efficiency while protecting the biological activity of your materials. Also, powdered products are easier to transport and store, and are more likely to be accepted by the market.
Wood Industry
The spray dryer can also rapidly convert bark extracts, wood tanning extracts and cellulose solutions into uniform powders. And it can help you decrease thermal degradation and stabilize the quality of your products. Moreover, the powder form is more convenient for storage and measurement, so it can be directly used in downstream applications such as adhesives, coatings, papermaking and chemical industries.
Laboratory
The lab spray dryer is mainly used for R&D, pilot testing and formulation validation. When developing new products, you can use a small spray dryer to test the feasibility of raw materials, powder forms and process windows, so as to avoid the risk of using large equipment directly.
FAQ
What Are the Most Common Problems with a Spray Dryer, and How to Solve Them?
Nozzle Clogging: Due to high viscosity or crystallization in the material. You can add high-precision filters at the feed end and preheat high-viscosity materials to reduce viscosity.
Powder Stick to the Wall: Often found in materials with low melting points or strong moisture absorption. By installing a jacket cooling system on the tower wall or adjusting the spray speed, you can address it.
Inconsistent Particle Size: Caused by a worn atomizer and unstable feed pressure. A constant current pump should be applied, and you also need to monitor the wear of the nozzle aperture regularly.
Low Energy Efficiency: Select an efficient heat exchanger.
Low Yield: Exhaust gas takes away fine powder. Combining the cyclone and bag collection system is necessary.
What Materials Are Compatible with a Spray Dryer?
Generally speaking, liquid materials such as solutions, emulsions and suspensions are often used in spray drying. The material should have a certain degree of fluidity, and the solid content and viscosity should be within the allowable range of the spray dryer.
How to Clean the Nozzle of a Spray Dryer?
After the machine has stopped and cooled down, remove the nozzle and rinse it with warm water in a circular motion. If you run into stubborn gunk, switch to a cleaning agent that won’t mess with the nozzle’s material. Of course, ultrasonic cleaning is also very effective for some micro-pore residues. Be careful not to wipe the nozzle orifice directly, as this may damage the material and even affect atomization.
What Safety Considerations are Applicable to a Spray Dryer?
Explosion-Proof Device and Monitor Gas Leakage: When handling flammable or organic solvents, spray dryers with inert gas and closed-loop systems are often used to prevent explosions. Even though the gas isn’t toxic, leaks can push out oxygen and create a suffocation risk. Therefore, gas leak detectors and ventilation equipment are necessary to ensure adequate airflow and oxygen levels.
Prevent Dust Explosion: Spray dryers without closed-loop systems tend to dust overflow during operation. Static electricity can be a trigger for dust explosions. Therefore, daily cleaning is important to avoid dust buildup, and humidity monitoring is necessary to reduce static electricity accumulation.
Protect Personal Safety: Inhaling fine particles can get into your lungs, especially with hazardous stuff. Therefore, operators need to wear personal protective equipment, such as respirators and protective clothing, to ensure safe operation.
Can High-Viscosity Material Be Processed Using a Spray Dryer?
Yes. You can choose a high-pressure nozzle or a centrifugal atomizer with a reverse conical hole atomization plate. Pre-treatment can also be carried out before feeding, by dilution or online shearing, to reduce viscosity and add a filtration system to prevent the nozzle from clogging.
How Does the Spray Dryer Last?
A spray dryer can usually last for more than 10 years, depending on the material, operating conditions, and maintenance.
If you are handling corrosive or highly abrasive materials for a long time, it is best to choose a higher grade of stainless steel. Also, regularly check the seals, clean the nozzles, and swap out worn parts fast if you want your spray dryer to last.
Pilotech— Leading Laboratory Spray Dryer Manufacturer in China
Pilotech specializes in manufacturing R&D and pilot-scale spray dryers, which can assist you in validating your formula, optimizing the parameters, and ensuring the stability and reliability of your subsequent mass production. Whether you are engaged in food, chemical, or pharmaceutical, we can provide technical support such as process validation.
Contact us now to get the latest quote.
More Resources:
https://equipsci.com/43-uses-of-spray-dryers-for-your-industrial-application/