Airflow classifier

Types of airflow classifiers

An airflow classifier, also known as a pneumatic classifier, is a particle separation device based on the principle of air classification. It sorts and separates particles like fine sand, silt, coal powder and cement based on their size and density. The airflow classifier has many applications in the chemical, pharmaceutical, mineral and food processing industries.

The airflow classifier uses flow velocity and drag forces to separate particles. Different types of classifiers exist based on their design. Vertical classifiers are typical in many industries. Their cylindrical bodies mostly have a conical or flat bottom. Airflow is introduced at the bottom section and circulates in the vertical direction. Finer particles exit through the top bag filter or cyclone, while larger particles settle at the bottom and are discharged through an outlet.

Horizontal classifiers are also common. They have a cylindrical body with a conical bottom. They work the same as vertical classifiers, but the airflow goes in the horizontal direction. The classifier’s airflow is connected to a dust collection system. Like vertical classifiers, smaller particles exit through the dust collection system, while larger ones are discharged through an outlet.

Spiral classifiers are also popular and work based on particle settling velocity. They mostly feature a flat bottom with a screw rotating clockwise. Lighter particles settle based on their sedimentation velocity. The screw mechanism rotates and scrapes the settled materials into the trough, while lighter particles continue to flow with the air.

Airflow classifiers are also distinguished based on the method of separation. They can be dynamic or static classifiers. Dynamic classifiers use centrifugal forces to separate different particles. The classifier’s rotating element generates centrifugal forces that push particles outwards. Larger particles with higher weights are forced outwards and segregated. Dynamic classifiers have high separation efficiency. They can operate at high temperatures and pressures. Rugged construction usually allows them to work for extended periods without requiring maintenance.

Static classifiers use baffles and blades to separate particles based on their size and weight. The heavier ones fall down due to gravity, while the lighter ones continue to move with the airflow. Static classifiers normally have low separation efficiency. Additionally, they can only operate under low-temperature and pressure conditions.

Another classifier type separates particles based on the drag force exerted by the air moving in the opposite direction. This velocity-based classification methods include dynamic or rotary classifiers and static or missile classifiers. The dynamic classifier has impellers that rotate at high speed to create a swirling air mass that separates particles. Its impellers can be adjusted to meet different particle size requirements. Rotary classifiers have high separation efficiency, but they require frequent maintenance due to their moving parts. Dynamic classifiers are also known as rotary or centrifugal classifiers.

The static classifier doesn’t have any moving parts. It comprises a cylindrical duct with an inlet for the air–material mix. The air moves upwards through the classifier while the coarser particles fall due to gravity. The finer particles remain suspended in the airflow and exit through a cyclone or bag filter. Although static classifiers have low separation efficiency, they can handle large volumes of material. The classifiers are used to restrict the entry of large particles into mills or other processing equipment.

Specification and maintenance of an airflow classifier

Specifications

Typically, specifications for air classifiers will vary depending on a sample or model. The particular specifications include the classifier's dimensions, the material it is made of, the airflow volume (CMM or LPM), and the electrical requirements.

The following are general specifications found in air classifiers.

• The axis dimension refers to different axis parameters depending on the classifier model and manufacturer. For example, classifiers may have a length of about 12 inches to 48 inches with a standard 6-inch diameter.
• A classifier's housing dimensions and design depend on the model. The housing unit is where the classifier motor is placed. An average housing unit measures about 4 feet in height and 5 feet in width.
• The material of an air classifier is typically steel or stainless steel. Depending on the manufacturer's recommendations, the steel may have varying grades and coatings for durability and resistance to corrosion.
• The airflow volume/Airflow rate: classifiers have a recommended airflow volume that is either in cubic meters per minute (CMM) or liters per minute(LPM). For instance, a Fine Grind Air Classifier Mill will work with an Airflow Rate of about 500-6,000 CFM (2,800-34,000 LPM) depending on the mill size.
• Electrical requirement: an air classifier motor will have a different electrical power requirement depending on the voltage. For instance, a classifier may have a power requirement of 75 HP at 480 VOLTS and 60 HZ.

Maintenance

A classifier needs regular inspection and cleaning to keep it in a usable state. The following are general maintenance steps for an air classifier that will prolong its lifespan and optimize its performance.

• Inspection: Inspection involves examining the classifier to find any worn-out parts, damage, and clogging that adversely affect the classifier's performance. During inspection, check for leakages that may occur along the joining sections of the classifier.
• Cleaning: After inspection, cleaning is the next maintenance step. Use a vacuum truck to remove any dust and debris from the classifier's surfaces. Classification air-volumes may result in fine dust particles' accumulation within the unit, restricting its smooth operation. A vacuum truck simplifies the cleaning process.
• Replacement: Some classifier parts may be damaged or worn-out during inspections. Replace the damaged parts to ensure the classifier operates well and ultimately extend its life span.
• Lubrication: Regular lubrication is needed for moving parts in the classifier, such as bearings. Follow the manufacturer's instructions when applying lubricant to the specified components.

Scenarios for airflow classifiers

• Pharmaceuticals and healthcare:

  Airflow classifiers are essential in the pharmaceutical industry. They are perfect for obtaining pure and uniform particle sizes when working with APIs, excipients, and respiratory medicines. In the meanwhile, the air classifiers' airtight designs and adaptability to containment systems guarantee product protection and compliance with the strictest healthcare regulations.

• Food and nutrition:

  The airflow classifiers also play a vital role in the food and nutrition industry. They are utilized to achieve the desired particle size and distribution in food additives, powdered foods, and nutraceuticals. This ensures not only product quality but also digestibility and absorption for end consumers.

• Material recovery and recycling:

  The air classifiers are commonly seen in waste recovery and recycling facilities, which separate valuable materials from the waste stream. Based on the differences in density and airflow resistance, they can efficiently separate lighter materials such as plastics, papers, and organics from heavier contaminants. As a result, it improves the recycling efficiency and keeps the sustainable development of the circular economy.

• Powder coatings and pigments:

  The airflow classifiers also excel in the field of powder coatings and pigments. They are ideally used to attain uniformity in particle size for pigments, fillers, and coating materials. These air classifiers therefore improve not only product performance but also stability and dispersion, which is quite important for different application industries.

How to choose an airflow classifier

When selecting an air classifier, there are several factors to consider to ensure the chosen machine meets specific requirements.

• Material Characteristics

  Users need to classify their materials by identifying their densities, sizes, shapes, and moisture content. The characteristics of the materials determine the suitable classifier design and operating parameters.

• Desired Cut Size and Range

  Users need to define the target particle cut sizes and size range they want to achieve. Classifiers are available with distinct measuring capabilities, so it is essential to choose one that can meet particular cut-size requirements.

• Throughput

  Users must consider the volume they want to process per unit of time. Keywords classifier and airflow classifier may refer to different classifiers. Therefore, they should choose a classifier that can handle the desired throughput without causing bottlenecks.

• Precision and Accuracy

  Users should consider the classifier's separation accuracy and precision. Different classifiers offer distinct levels of precision, so it's essential to choose one that can achieve the required classification accuracy for the specific application.

• Operational Flexibility

  It is critical to think about the classifier's ability to adjust operating parameters like air volume, rotation speed, and other settings. Flexibility allows for optimization and adaptation to different material classification needs.

• Integration and Compatibility

  Users should consider the classifier's ability to integrate with existing production lines or downstream processes. Ensuring proper connection and compatibility can minimize disruptions and facilitate smooth operations.

• Maintenance and Support

  Consider the classifier's maintenance requirements, accessibility of spare parts, and technical support availability. Choosing a classifier with good support and manageable maintenance can reduce downtime and ensure long-term reliability.

• Budget

  Finally, the classifier's selection is influenced by budget considerations. While it's essential to prioritize the classifier's performance and suitability, it is also crucial to choose one that aligns with budget constraints.

Airflow classifier FAQ

Q1: Can an airflow classifier be integrated into an existing powder processing line?

A1: Many classifiers have been designed to be incorporated into existing powder processing lines. However, the degree of ease of integration will be contingent upon the model and specifications of the classifier as well as the particulars of the existing processing line.

Q2: What maintenance does an airflow classifier require?

A2: Routine maintenance for air classifying mills generally includes tasks like inspecting and tightening components, cleaning the classifier to avoid material buildup, lubricating moving parts, and monitoring classifier performance to preemptively identify maintenance needs or adjustments.

Q3: Are airflow classifiers safe to use with flammable materials?

A3: It is probably not safe to use the classifiers with flammable materials unless they have been specifically designed for this purpose. Such classifiers will possibly have attributes like explosion-proof constructions, grounding arrangements, and anti-static features.