Spray dryers are equipment commonly used in the pharmaceutical, food, and chemical industries. As one of the most important components of a spray dryer, spray dryer nozzles affect the processing quality of your products. Understanding their structure will help you choose the appropriate atomization method. This article will introduce you to spray dryer nozzle parts.
Different Spray Dryer Nozzle Parts
Spray dryers have three different atomization methods. These three methods are achieved using different dryer nozzles. Since these nozzles have distinct designs, we will describe each one separately to you.
Air Atomizing Nozzle
Air atomizing nozzles are primarily used to achieve pneumatic atomization, which is also known as air atomization. Air atomizing nozzles primarily rely on the velocity difference between the air stream and the feed liquid.
Since the feed liquid velocity is low (generally less than 2 m/s) and the air stream velocity is very high (generally 200–340 m/s), a considerable frictional force is generated between them, causing the feed liquid to atomize rapidly. The pressure of the compressed air used for atomization is typically 0.3–0.7 MPa.
Structure
A typical air atomizing nozzle consists of a liquid nozzle, air cap, mixing chamber, sealing components, and fastening hardware. Depending on the number of fluid channels, air atomizing nozzles are generally categorized as two-fluid, three-fluid, or four-fluid nozzles.
Pressure Nozzle
A high-pressure pump pressurizes the feed liquid to 2–20 MPa and forces it tangentially into the swirl chamber of the pressure nozzle. The liquid then rotates at high speed, creating a strong vortex.
As the liquid moves toward the center, its tangential velocity increases while the static pressure decreases, forming an air core. The liquid is discharged through the orifice as a thin annular film, which is stretched and broken up by aerodynamic forces, ultimately forming a fine spray of droplets.
Structure
Pressure nozzles can be classified into swirl pressure nozzles and centrifugal pressure nozzles.
Swirl pressure nozzles have two main structural features. First, they have a liquid swirl chamber. Second, they have one or more tangential inlets through which the liquid enters the swirl chamber.
A centrifugal pressure nozzle features a built-in nozzle core. This design can help the liquid to rotate at high speed, improving atomization performance.
Rotary Atomizer / Rotary Disc Atomizer
Rotary disc atomizers are used for centrifugal atomization. The feed liquid is fed into a high-speed rotating atomizing disc, where it is flung outward and atomized under the combined effects of centrifugal force and friction. The rotational speed of the atomizing disc typically ranges from 8,000 to 25,000 r/min.
Depending on the structure of the atomizer disc, rotary disc atomizers can be classified into smooth disc rotary atomizers and serrated disc rotary atomizers.
Smooth Disc Rotary Atomizer
The smooth disc rotary atomizer primarily consists of a high-speed motor, an atomizer disc, a bearing system, a speed sensor, and channels. Its design is relatively simple. If you want larger particles or your feed solution has high viscosity, you can use a smooth disc rotary atomizer. However, its production capacity is relatively low.
Serrated or Grooved Disc Rotary Atomizer / Atomizer Wheel
The serrated or grooved disc rotary atomizer, commonly referred to as an atomizer wheel, utilizes an atomizing disc with serrated edges or grooved surfaces. Its basic structure is similar to that of a smooth disc rotary atomizer.
The specially designed disc geometry reduces liquid slippage on the disc surface and increases the velocity at which the liquid film leaves the disc, resulting in more efficient atomization and improved droplet formation.
FAQ
How Do I Choose the Right Spray Dryer Nozzle?
When selecting a nozzle, you must comprehensively consider the viscosity, solids content, and abrasiveness of the feed liquid. Pressure nozzles can be used for low-viscosity feed solutions, while two-fluid nozzles are suitable for medium- to high-viscosity or heat-sensitive materials. Rotary atomizers are used for slurries or materials containing solids.
You also need to consider your desired particle size. Pressure nozzles produce droplets ranging from about 20 to 600 μm, while two-fluid nozzles can produce finer droplets. Rotary atomizers offer a wider range of options.
How Can I Tell If Wear on Spray Dryer Nozzles Is Normal or Abnormal?
Normal nozzle wear gradually enlarges the orifice, leading to coarser atomization. Signs of abnormal wear include an uneven spray pattern, unstable pressure readings, and increased flow rates under the same operating conditions.
Nozzle life is influenced by feed solids content, material abrasiveness, operating pressure, and nozzle materials. Highly abrasive ceramic slurries may require nozzle replacement after 200–400 hours of operation, while nozzles used for less abrasive organic materials typically last much longer.
Why Are the Droplets Coming out of My Spray Dryer Nozzle Uneven in Size?
Possible causes include deformation due to nozzle wear, clogging of the swirl chamber, wear on components that impairs the swirl effect, uneven viscosity or solids content in the feed liquid, and unstable pump pressure. If you notice uneven droplet sizes, we recommend troubleshooting these issues one by one.
How Often Should the Seals on Spray Dryer Nozzles Be Replaced?
You need to inspect the seals on the spray dryer nozzles regularly and replace them immediately if you notice any wear. They operate under high pressure, high temperature, and chemical corrosion, which can easily cause seals to age and fail.
Seal failure may result in leaks, unstable pressure, or even unexpected nozzle failure. It is recommended to maintain a sufficient inventory of seals and replace them after each disassembly and reassembly.
What Is the Difference Between a Spray Dryer Nozzle and a Spray Gun?
The spray dryer nozzles are the core components responsible for atomizing the liquid. They disperse the feed liquid into fine droplets through an orifice or a special structure. The spray gun is typically an assembled system including a nozzle, tubing, connectors, and mounting components.
In two-fluid spray systems, the nozzle is usually mounted inside the spray gun. In pressure or centrifugal spray dryers, there is often only a nozzle or atomizer, without a separate spray gun structure. In summary, the spray gun is the assembly, while the nozzle is the core component that actually performs the atomization.
Final Thoughts
Are you looking for a reliable spray dryer or nozzle factory? Pilotech is a professional spray dryer manufacturer in China. With over twenty years of experience in manufacturing spray dryers, we can provide you with excellent product quality. No matter what industry you’re in, we’ll do our best to provide you with personalized solutions. Welcome to contact us！