The nozzles in a spray dryer have a significant impact on production quality. By understanding the causes of nozzle clogging and knowing how to minimize it as much as possible, you can extend the service life of the spray dryer and improve production efficiency.
Causes of Nozzle Clogging in Spray Dryers
Large-Particle Materials
The main cause of nozzle clogging is the presence of particles in the material. These particles come from various sources, like pollution in raw materials, corrosion fragments from the system, insufficient filtration, and environmental impurities. These particles will accumulate inside the nozzle, blocking fluid flow, while larger particles can quickly clog the nozzle and cause erosion.
High Viscosity Issues
The viscosity of the feed liquid has a direct impact on the frequency of nozzle clogging. High-viscosity liquids tend to flow more slowly. Over time, they form significant deposits in the nozzle’s internal channels. These deposits will block fluid flow, causing the nozzle to clog and reducing the efficiency of the spray system.
Crystallization and Sedimentation
If the feed temperature is high, it accelerates moisture evaporation. In this case, materials with high sugar or salt content may crystallize or precipitate when they reach the nozzle tip. Once crystallization begins, it accumulates, gradually narrowing the nozzle until the nozzle becomes completely blocked. This situation is especially common in the food industry.
Changes in Feeding Temperature
Even slight temperature changes can cause nozzle clogging, cooling can cause crystallization or precipitation, while heating can cause the material to dry out too early at the tip of the nozzle.
How to Reduce Nozzle Clogging
Control Appropriate Viscosity and Solids Content
To prevent nozzle clogging in the drying spray machine, you can adjust the solids content and viscosity of the liquid material by diluting, filtering, preheating, and adding a dispersant before drying.
Here is a table of parameters for different types of materials.
| Material Type | Anti-Clogging Solids Content (%) | Anti-Clogging Viscosity (mPa·s) |
| Herbal extract | 15 – 35 | < 1000 |
| Chemical pharmaceutical | 10 – 40 | < 500 |
| High-viscosity protein | 5 – 15 | < 3000 |
| Sugar/gum materials | 8 – 20 | < 5000 |
| Food and dairy | 30 – 40 | Good flowability required |
| Ceramic/inorganic slurry | 50 – 70 | ≤ 100 |
| Chemical/polymer | 20 – 50 | < 2000 |
Use Maximum Free Passage (MFP) Nozzle Designs
Using a maximum-free-passage nozzle can keep the majority of particles passing through smoothly. It can minimize the risk of clogging and maintain a stable spray mode and flow rate, even with high-viscosity liquids that are difficult to handle. However, you should also be aware that some large-diameter nozzles can result in excessive spray volume. These nozzles require appropriate pressure and flow control devices.
Install Strainers
Installing a strainer is a simple and cost-effective solution to prevent clogging. A filter is a mesh device installed in the nozzle system. It traps large particles and prevents solids from entering the spray holes. There are two main types of filters commonly used:
- Integrated strainers: usually serve as integral components of the nozzle. They offer various mesh sizes, with the finest achieving 200 mesh. They are suitable for standard and quick-connect flat spray, hollow cone nozzles, full cone nozzles, and fine spray nozzles.
- T-type strainers: can reduce pressure loss and are easy to clean and maintain. These strainers allow the filtered liquid to flow normally while returning trapped particles, which is suitable for various pressure applications.
Use Self-Cleaning Nozzles
The self-cleaning nozzle is designed to automatically remove residue from the nozzle with various methods, helping to prevent clogging. Installing a self-cleaning nozzle can reduce the need for manpower and cleaning time. The most common types include:
Mechanical Automatic Cleaning
A “cleaning pin” is designed inside the nozzle. It uses physical force to push out adhered and clogged material at a pre-set frequency.
Mechanical cleaning is extremely reliable and is almost necessary for handling materials with high solids content, high viscosity, and a tendency to clump.
However, the design is relatively complex. The cleaning pin and nozzle holes are subject to long-term friction, making them consumable and requiring regular replacement.
Ultrasonic Self-Cleaning
The nozzle operates under high-frequency vibration, using ultrasonic energy to atomize the liquid. So, this vibration itself prevents material from accumulating at the nozzle tip, making the nozzle fundamentally non-clogging.
Additionally, this nozzle can produce extremely uniform, micron-sized fine droplets, which are particularly suitable for applications with high requirements and handling valuable materials.
Self-Cleaning Channel
You can install a cleaning fluid channel inside the nozzle. With the spray dryer running, simply switching a valve can allow water or solvent to flow through, automatically flushing the nozzle interior and tip. This achieves cleaning-in-place (CIP) without disassembling the equipment, and you can save on labor costs and machine downtime.
Use Heated Nozzles and Systems
Heated nozzles and systems are commonly used in applications handling high-viscosity fluids. Heating sticky fluids can significantly reduce their viscosity, effectively lowering the risk of clogging.
Heated automated systems can control the temperature, maintaining stable material temperatures throughout the whole process—from the storage tank to atomization.
It is worth noting that one of our well-known customers customized a heated spray drying system from us, achieving a significant 38% increase in production output.
Regular Cleaning and Maintenance
During production, you can establish a fixed cleaning schedule according to the characteristics of the materials produced. For continuous production, flush the system once per batch. You should immediately clean the system when there is a material change or a shutdown lasting more than 1 hour.
You can cycle hot water and detergent through the nozzles, feed lines, and filters for 5–10 minutes to thoroughly dissolve and remove any residue.
At least once a week, completely disassemble the nozzles and use a small cleaning needle and soft brush to clean away scale buildup.
Regularly check the seals, gaskets, and orifices for any wear. You should replace them immediately if they show deformation or wear.
Pulse Width Modulated (PWM) Flow Control
Pulse-width modulation (PWM) controls the flow rate by causing the liquid to be sprayed in pulses rather than flowing at a constant, steady rate.
During each pulse, the fluid flows faster and with a stronger force than during steady flow, effectively washing away small particles that have just adhered to the tube walls and nozzle opening. This prevents particles from becoming firmly attached between pulses. These nozzles can cycle on and off up to 10,000 times per minute and can be combined with larger-diameter, clog-resistant nozzles to achieve a low flow rate.
Automated Spray Systems
In most automatic spraying systems, spray dryers can automatically adjust their operating parameters in response to production changes. It can significantly reduce nozzle clogging problems in various applications.
You can also install monitoring equipment. If a nozzle becomes clogged, the system will immediately detect the fault and inform operators, helping to reduce waste and prevent production downtime.
In addition to clog prevention and fault detection functions, automated spray systems offer several advantages:
- Accurate detection of nozzle wear
- Real-time monitoring of flow rate and other operating parameters
- Flexible adjustment of spray flow rate and spray mode
- Temperature control to achieve uniform atomization of high-viscosity materials
FAQ
What are the Effects of Clogged Nozzles in a Spray Dryer?
- Product quality decline: This is the main problem. Once the nozzle of the spray dryer becomes clogged, the original shape of the liquid material is destroyed. This will lead to uneven droplet sizes, unstable moisture content, clumping, coking, and color changes in the final powder. In severe cases, the whole batch of products may have to be scrapped.
- Production efficiency decrease: Shutting down the system to clean nozzles leads to a drop in production output, resulting in indirect cost increases.
A factory operates 24 hours a day, 5 days a week, for 52 weeks a year. The loss of downtime is $100 per hour. With 2 hours of downtime per week due to equipment maintenance, the annual loss from clogging amounts to approximately $10,400.
- Accelerated equipment wear: Clogging causes pump pressure to rise, accelerating wear on seals and nozzles.
- Energy costs rise: To make up for insufficient drying, spray dryers are forced to increase the air temperature. With repeated shutdowns to raise the temperature, energy consumption per unit of product has increased significantly.
Which is Easier to Clean: Integrated Strainers or T-Strainers?
T-type strainers are easier to clean.
This is because their installation locations and cleaning procedures are different:
Integrated strainers: These are built inside the nozzle. To clean them, you should remove the whole nozzle first. Then take out the internal filter for rinsing. This involves multiple steps and takes a long time.
T-type strainers: These are installed separately on the feed pipe, independent of the nozzle. When cleaning, you don’t need to remove the nozzle; you can just take the filter out easily. The process is simple.
What is the Suitable Nozzle Type for High-Viscosity Spray Drying Materials?
If your material has extremely high viscosity (such as slurries or pastes), or if you need to produce powders with very small particle sizes and a uniform distribution (down to approximately 5 μm), a two-fluid nozzle is the ideal choice.
If you are handling materials of medium viscosity, such as honey or syrup, or materials containing solid particles, a centrifugal atomizer is a more stable and easier-to-maintain choice.
What Materials are Most Likely to Cause a Spray Dryer Nozzle Clog?
- High-viscosity liquids: syrups, honey.
- Materials containing hard particles: calcium carbonate, quartz sand, and activated carbon.
- Easily crystallizing liquids: sodium chloride solutions, amino acid concentrates.
- Heat-sensitive materials: proteins, yeast, vaccines.
How Can I Quickly Fix the Problem of the Nozzle Clogging Immediately When Replacing the Material?
Clogging following a material change usually results from cross-contamination between old and new materials or residual caking. The quickest and most effective solution is to operate the cleaning needle in a piston motion. This will clear 10–30 seconds.
You can also perform CIP (Clean-in-Place): Switch the valves for the self-cleaning channel nozzles to allow water and solvent to flow through the nozzles and pipes for 5–10 minutes.
How Often Should the Cleaning Pin Be Replaced in a Mechanical Self-Cleaning Spray Dryer Nozzle?
There are no fixed requirements, but the standard method in the industry is to inspect the cleaning needles regularly. If you notice any abnormalities or a decrease in clog-prevention performance, you should consider replacing the cleaning needles.
Does Installing a Filter Affect the Safety of Food-Grade Products?
No, some of the filters are made from materials that meet FDA standards, so you don’t have to worry about safety problems. Just remember to replace and clean the filter regularly, or you may encounter problems.
Final Thoughts
Pilotech is a manufacturer with over 20 years of industry experience. We are focused on all kinds of spray dryers. We can also customize spray dryer parameters to suit your material characteristics. If you would like to learn more, please feel free to contact us.