Views: 3 Author: Site Editor Publish Time: 2025-01-07 Origin: Site
The spray dryer is composed of an air heater, atomizer, drying chamber, and a powder collection and separation system. The drying chamber is usually composed of a cylinder with a cylindrical body and conical bottom, but there are also square structures. Hot air enters from the bottom or top of the drying chamber, and the liquid is sprayed from the top to form a mist for drying. The atomizer is the core component, normally there are three types: pressure type, air flow type, and rotary type.Choosing the right atomizer is the key to ensuring product quality and production efficiency.
Conditions of comparison | Air flow type | Pressure type | Rotary type | |
Material condition | General solution | Yes | Yes | Yes |
Suspension liquid | Yes | Yes | Yes | |
Paste liquid | Yes | No | No | |
Treatment Capacity | Large adjustment range | Minimum adjustment range | Wide adjustment range, large processing capacity | |
| Feeding way | Pressure | Low pressure～0.3MPa | High pressure 1.0～20.0MPa | Low pressure～0.3MPa |
Pump | Centrifugal pump | Piston pump | Centrifugal pump or others | |
| Maintenance of pump | Easy | Hard | Easy | |
Low | High | Low | ||
Atomizer | Price | Low | Low | High |
Maintenance | Easiest | Easy | Hard | |
Power consumption | Maximum | Smaller | Minimum | |
Final product | Granule granularity | Thinner | Thicker | Microfine |
Granule Uniformity | Unevenness | Even | Even | |
Final moisture content | Lowest | Higher | Lower | |
Type | Advantage | Disadvantages |
Air flow type | Suitable for small production or experimental equipment; Droplets can be below 20um; Can handle high viscosity materials. | Power consumption is high. |
Pressure type | Large drying towers can use several atomizers; Suitable for countercurrent operation; Low cost of atomizer; The product has coarse particles. | When the material properties and handling capacity change, the operating elasticity changes little; The nozzle is easy to wear, which causes the change of atomization performance; Need a high pressure pump; Special materials should be used for corrosive materials; When producing fine particles, there are design limitations. |
Rotary type | Easy operation, strong adaptability to materials, operation flexibility; Can atomize more than two kinds of liquid at the same time; Low operating pressure; Not easy to plug, small corrosion; Product particle size distribution is uniform. | Not suitable for countercurrent operation; The cost of atomizer and power unit is high; Not suitable for horizontal dryers; When preparing coarse particles, there are design limitations. |
An ideal atomizer should have the following basic characteristics:
Simple structure: simple design, easy installation and maintenance.
Easy maintenance: easy to clean and repair.
Strong adaptability: suitable for dryers of all sizes, from small laboratory equipment to large industrial production lines.
Controllability: the droplet size can be controlled by adjusting the operating conditions (such as pressure, speed, etc.).
Flexible feeding method: pumping, gravity or siphon feeding can be used.
Wear resistance: no internal wear when handling materials, extending service life.
Although some atomizers may have some or all of the above characteristics, in actual applications, factors such as whether the operating method matches the feeding system, whether the droplet characteristics are coordinated with the drying chamber structure, and whether there is enough installation space should be considered.
Different types of atomizers have their own advantages in producing droplets with a specific particle size distribution:
Coarse droplets: Normally use pressure nozzles, suitable for products that require larger granules.
Fine droplets: It is recommended to use a rotary atomizer, which can produce finer and more uniform droplets.
Medium size: You can choose a blade atomizer wheel or a pressure nozzle, which is suitable for most conventional applications.
Full atomization capability within the feed range: Rotary or nozzle atomizers (both pressure and airflow) can achieve full atomization within the low, medium and high feed ranges. Rotary atomizers perform better at high throughputs because they have greater operational flexibility.
Atomization efficiency: For most spray drying, power is not a major consideration. As long as the required spray characteristics are met at rated capacity. For example, although three-fluid nozzles are less efficient, efficiency issues are not important for some high-viscosity liquids.
Droplet size distribution: At low to medium feed rates, rotary and nozzle atomizers produce similar droplet size distributions. At high feed rates, rotary atomizers generally provide higher uniformity.
Droplet uniformity requirements: Vane atomizer wheels, two-fluid nozzles or rotary airflow cup atomizers are suitable for producing fine droplets. Smooth disk atomizer wheels or pressure nozzles are suitable for producing coarse droplets.
Operational flexibility: Rotary atomizers have greater operational flexibility and can maintain a stable droplet size distribution over a wide range of feed rates. Nozzle atomizers need to adjust pressure or other parameters according to the feed rate, which may cause changes in particle size distribution.
Adaptability of drying chamber structure: Nozzle atomizers are highly adaptable and can be used in drying chambers operating in parallel, countercurrent or mixed flow. Rotary atomizers usually need to be configured with a rotating hot air flow mode.
Adaptability of material properties: For low-viscosity, non-corrosive, and non-abrasive materials, both rotary and nozzle atomizers are suitable. Atomizer wheels are suitable for handling corrosive and abrasive slurries and powdered materials, especially materials that are difficult to pump under high pressure. Airflow nozzles are suitable for handling liquids with long molecular chain structures (usually high-viscosity and non-Newtonian fluids). For many high-viscosity non-Newtonian liquids, they can be preheated to reduce the viscosity before atomization.
Actual operating experience: For new spray drying equipment, atomizers are generally selected based on existing spray drying experience. For new products, they must undergo laboratory tests and intermediate tests, and then the most suitable atomizer can be selected based on the test results.
Selecting the most suitable atomizer requires comprehensive consideration of multiple factors, including but not limited to droplet requirements, feed range, atomization efficiency, droplet uniformity, operational flexibility, drying chamber structural adaptability, and material properties. By comprehensively evaluating these factors, combined with actual operating experience and test data, the optimal atomizer can be selected for a specific spray drying process, thereby improving production efficiency and product quality.
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