A spray dryer can be applied in all kinds of stages, ranging from lab testing to industrial production. However, the operation of the spray dryer is a bit complicated. This article will introduce the main operation steps of spray dryers to you, hoping to help your production line run more efficiently and stably.
Operating Principle of Spray Dryer
A spray dryer system mainly works through three steps: spraying, heating, and separating powder from air.
First, the liquid material is sprayed into many very fine droplets through the atomization structure, enlarging the contact area between the material and air.
Second, hot air is blown in to fully touch the fine droplets . Heat quickly removes the water inside the drops, and the drops will become solid particles instantly.
Finally, the dry powder is separated from the hot air flow with the help of airflow, and the continuous drying process is completed.
Spray Dryer Standard Operating Procedures
Step 1: Raw Material Preparation
You need to make sure the raw materials are properly prepared before spray drying, which is very important for the stable operation of the whole production line.
First, fully mix the liquid raw materials in advance. Then, adjust the concentration and viscosity according to the equipment requirements. The viscosity of the raw materials should depend on the atomizer type to avoid atomization problems or nozzle blockage. For viscous materials, you can reduce the viscosity by dilution or other methods.
At the same time, the raw materials should stay well mixed. This can prevent layering, sedimentation, and air bubbles, which may cause unstable feeding. If the raw materials are heat-sensitive, they also should be gently preheated. This helps avoid damage to the active ingredients.
If this step is done well, the later atomization will be more uniform, the drying will be more thorough, and the powder quality and production efficiency will improve.
Step 2: Preparation for Operation
Preparation before startup is a regular step in every production cycle.
First, check the equipment. Make sure the atomizer and feed inlet are not blocked. The drying chamber and cyclone separator should be clean and sealed. Check that the temperature control and safety systems are working properly. This can avoid many production risks in advance.
Then, preheat the system. Let the drying chamber reach the target temperature. After the temperature becomes stable and the airflow becomes even, you can start feeding.
Starting the spray dryer in this way can help the machine enter a stable working state. This is better for efficient production and risk control.
Step 3: Atomization of the Liquid
Atomization is the most important step in spray drying. It directly affects the drying efficiency and the quality of the final powder.
First, send the pre-treated liquid raw material into the atomizer at a constant speed. The atomizer will break the liquid into small and uniform droplets, which can help achieve drying quickly.
You can choose different atomization methods based on the material properties:
- For high-viscosity and particle-containing materials, use a rotary atomizer. It uses the centrifugal force from high-speed spin to complete atomization.
- For materials that need uniform particle size and good fluidity, use a pressure nozzle. It uses a high-pressure pump to achieve stable spraying.
- For small-batch trials or fine materials, use a dual-fluid nozzle. It uses compressed air to achieve more precise atomization. However, dual-fluid nozzles usually have lower throughput and higher energy consumption.
It is best to let experienced operators do this operation. During operation, the spin speed or pressure must be strictly controlled. This helps make the droplet size uniform. Droplets that are too large will cause incomplete drying. Droplets that are too small will increase the product yield loss.
Step 4: Drying Process
When the drying stage starts, you should pay more attention to controlling three important things: temperature, atomization, and air volume. These will directly affect the moisture content of the powder, the uniformity of the particles, and the stability of the final product.
Temperature Control
After the atomized droplets enter the drying chamber, they will quickly touch the hot air. The water inside the droplets evaporates very fast, and drying is finished within only a few seconds. During this process, you must keep the feed temperature and exhaust air temperature stable. The correct temperature can fully dry the droplets and avoid too much product yield loss. Improper temperature may cause wall sticking and product buildup inside the chamber.
Atomization State
Atomization controls the droplet size. Before the material enters the drying chamber, you must make sure the atomization is stable and not blocked. There should also be no large droplets. This can prevent wet material from sticking to the wall and help the material dry evenly from the beginning.
Air Volume
Stable and even airflow can give enough space for heat exchange during powder drying. Reasonable air volume can help the droplets fully contact the hot air in the drying chamber and stay inside for enough time, which also affects the final moisture content and particle morphology.
Step 5: Powder Collection
In the powder collection stage, the key points are stable powder separation and efficient material collection. These affect the output and loss rate.
After drying, only the larger particles directly fall to the bottom of the drying chamber due to gravity. This is the main source of powder recovery. You need to discharge and collect this main material in time to prevent blockage.
Then, tiny powder carried by the airflow will enter the cyclone separator. In the cyclone separator, centrifugal force separates the powder from the exhaust gas to recover most tiny powder.
At the same time, the bag filter captures the remaining trace of tiny powder. This helps reduce product yield loss.
During operation, you should keep the airflow in the system stable. You should also use the rotary valve of the air lock to discharge materials slowly and constantly. This can help prevent air leakage, blockage, and powder overflow.
Step 6: Post Treatment
The subsequent processing stage is the final shaping step of the spray-dried product. It mainly includes these steps:
Sifting
You need to sieve the collected powder. This removes lumps and impurities and helps keep the powder uniform.
Grinding
Powder with large particles or lumps needs to be ground again. This makes the particle shape more regular.
Mixing
Powder from the same batch should be mixed evenly. This helps the composition and performance of the whole batch remain uniform.
Cooling
The materials need to be cooled. This helps prevent getting damp and clumping up again, caused by residual heat during storage.
Finished product packaging
After all post-processing steps are finished, the product is sealed and packaged. This helps keep the product dry and active. It also makes bulk long-distance transportation and long-term sales easier. In food or pharmaceutical plants, sealed powder packages can be transferred on hygienic plastic pallets where clean handling and regular sanitation are required.
Spray Dryer System Main Parameter Control
There are many parameters that need to be handled with care and attention during the operation of the spray dryer. I have listed them for you below.
- Inlet Air Temperature
- Outlet Air Temperature
- Air Volume
- Feeding Speed
- Atomization Effect
- Hot Air Flow Rate
- Powder Viscosity And Solid Content
- Residence Time
- Final Moisture Content
- Particle Size Distribution
Spray Dryer Operating Safety Regulations
Explosion and Fire Safety Requirements
In actual production, you must strictly control the operating temperature and the concentration of the feed materials. You should also avoid long-term overloading operations.
For materials that can easily catch fire or explode, you must pay special attention to safety. Remove the risks of fire and dust explosion from the source.
Sealed Protection and Inert Gas Safety
Carry out daily maintenance and regular inspections of the equipment. The spray dryer system must stay well sealed. This can prevent dust leakage. It can also prevent outside gas from entering and affecting the process.
When producing materials that are easy to oxidize and highly active, inert gas can be used for internal gas replacement. This helps ensure product quality.
Dust and Static Electricity Protection
Dust in the corners of the equipment should be cleaned regularly. This helps prevent long-term dust buildup and reduces high-risk problems.
The entire machine must also be properly grounded. This can quickly remove the static electricity generated during production. Otherwise, static electricity may ignite the dust and cause an explosion.
Worker Safety Protection
Operators must wear full professional protective gear and make sure they are safe.
When the equipment is running normally, it is strictly not allowed to reach into the machine or perform any other unsafe operations. This is to protect the safety of operators.
Safe Equipment Operation Control
Before starting the spray dryer each time, check the fan, valves, and other parts one by one. Only when everything is normal can production start.
During production, watch all operating parameters closely. If anything is abnormal, stop the machine immediately and check it.
FAQ
What Powder Recovery Rate can be Achieved by the Cyclone Separator and Bag Filter Recovery System?
A combined cyclone separator and bag filter system can typically achieve an overall powder recovery efficiency of 95% to 99%, depending on particle size and operating conditions.
First, the cyclone separator separates most of the dry powder. Then, the bag filter collects the very tiny powder that is left. This greatly reduces product loss.
Which Materials are Suitable For Inert Gas-Protected Closed-Loop Spray Dryers?
Some materials oxidize easily and react easily with oxygen. Some have flammable liquids inside, such as active probiotics and enzyme preparations. We can use inert gas like nitrogen to replace air and keep oxygen out. This stops materials from going bad.
It also stops fire and explosion risks and keeps product quality stable.
How to Set the Optimal Inlet Air Temperature and Outlet Air Temperature for Spray Drying?
You should set the intake air temperature after fully understanding the thermal sensitivity of the material.
For many food and pharmaceutical materials, inlet air temperature is commonly controlled between 140 and 220℃, depending on thermal sensitivity and process requirements. For common chemical materials, the temperature can be increased a little. This helps achieve drying without damaging the components quickly.
The exhaust air temperature is usually kept at 80 to 100℃. If the temperature is too low, the powder will have high moisture content and easily cake. If the temperature is too high, it will waste energy and may damage the material.
What GMP Regulations and Hygiene Standards Must Spray Dryers Follow in The Food and Pharmaceutical Industries?
Spray dryers in the food and pharmaceutical industries must follow GMP standards.
The equipment should be made of food-grade stainless steel. This can help prevent pollution.The system should support CIP cleaning and avoid dead corners that may cause material residue.
At the same time, the spray dryers must meet aseptic production requirements and follow industry hygiene and safety standards.
What Are The Differences in Operation Between Lab Spray Dryers And Industrial Spray Dryers?
The lab spray dryer is mainly used for small-scale research and development. It has a small single-batch input and simple operation. However, laboratory spray dryers should meet the demand for frequent adjustment of parameters like temperature, air speed and atomization parameters. It is mainly used to test material formulas and study process conditions.
The industrial spray dryer is designed for large-scale continuous production. It has a high level of automation and does not need too frequent parameter adjustments. It can also run stably for 24 hours. In operation, the industrial spray dryer focuses more on process start and stop, dust-proof sealing, and hygiene control. It is suitable for mass production and GMP production requirements in the industry.
Final Thoughts
Pilotech is a manufacturer that focuses on all kinds of spray dryers. We can also provide spray drying process testing and validation services for your materials. If you have concerns about the operations of spray dryers in your project, please contact Piltech to get more details.