Types and Selection of Glass-Lined Agitators

In stirred reactors, agitators are key components for accelerating reactions, improving heat and mass transfer, and maintaining uniform material distribution. In chemical and pharmaceutical industries, glass-lined agitators are widely used together with glass-lined reactors because they provide excellent corrosion resistance when handling acidic, alkaline, and chemically aggressive materials.

The selection of a suitable agitator depends on several factors, including liquid viscosity, solid content, mixing requirements, heat transfer performance, shear sensitivity, and reaction conditions.

Different agitator designs generate different flow patterns, which directly influence mixing efficiency and energy consumption.

Main Types of Glass-Lined Agitators

Paddle Agitators

Paddle agitators have a simple structure consisting of flat or folded blades.

Flat blades mainly generate tangential flow and usually work better with baffles to improve circulation. Folded blades provide stronger axial flow compared with flat blades.

Typical characteristics:

• Diameter: 1/2–4/5 of the container diameter
• Speed: 20–80 rpm
• Flow pattern: Mainly radial and tangential flow

Paddle agitators are commonly used for fluid circulation, blending, and medium-viscosity materials. They offer advantages such as simple design, low cost, and easy maintenance. However, their axial mixing capability is relatively limited, especially in deep reactors.

Propeller Agitators

Propeller agitators have a design similar to marine propellers and are mainly used to generate strong axial flow.

Typical characteristics:

• High-speed operation
• Tip speed: approximately 7–15 m/s
• Diameter: about 1/4–1/3 of the container diameter
• Strong circulation capability with relatively low shear

Propeller agitators are suitable for low-viscosity liquids that require rapid circulation, such as:

• Liquid blending
• Heat transfer enhancement
• Suspension of low-concentration solids
• Preventing particle settling

For tall reactors, propellers are often combined with draft tubes to improve flow direction and mixing efficiency.

Turbine Agitators

Turbine agitators are among the most commonly used agitator types in industrial reactors. They include open turbine and disk turbine designs with flat or curved blades.

Typical characteristics:

• Speed range: approximately 300–600 rpm
• Balanced shear force and circulation
• Suitable for low to medium viscosity fluids

Turbine agitators are widely applied in:

• Chemical reactions
• Dispersion processes
• Gas-liquid mixing
• Heat transfer operations

Curved blade turbine agitators can reduce power consumption and provide gentler mixing, making them suitable for processes involving shear-sensitive materials.

Anchor and Screw Agitators

Anchor agitators have blades that closely follow the reactor wall, creating strong circulation near the heat transfer surface.

Typical characteristics:

• Large diameter close to reactor diameter
• Low-speed operation
• Tip speed: approximately 0.5–1.5 m/s

They are commonly used for:

• High-viscosity materials
• Crystallization processes
• Heat-sensitive products
• Materials requiring wall scraping

Screw agitators generally consume less power than anchor agitators and are suitable for higher-viscosity materials where efficient axial movement is required.

How to Select the Right Glass-Lined Agitator?

Choosing the correct agitator requires evaluating the actual process conditions rather than simply selecting based on reactor size.

Selection Based on Material Viscosity

Generally, agitator selection follows this trend:

Propeller → Turbine → Paddle → Anchor → Ribbon

• Low viscosity liquids: Propeller or turbine agitators
• Medium viscosity fluids: Paddle or turbine agitators
• High viscosity materials: Anchor, screw, or ribbon agitators

As viscosity increases, stronger circulation and larger torque capacity are usually required.

Selection Based on Process Requirements

Different processes require different mixing characteristics:

For dispersion and gas-liquid mixing

Turbine agitators are preferred because they provide stronger shear and turbulence.

For rapid circulation and blending

Propeller agitators are suitable because they generate high pumping capacity.

For crystallization and high-concentration slurry mixing

Anchor or screw agitators are commonly selected because they provide gentle but effective circulation.

For heat transfer applications

Anchor agitators are often used in glass-lined reactors because their large diameter improves contact between materials and the reactor wall.

Important Accessories for Glass-Lined Reactor Agitation

Baffles

Baffles are commonly installed inside reactors to prevent excessive swirling and improve mixing efficiency.

Typical design:

• Number: 4–6 baffles
• Width: approximately 1/12–1/10 of reactor diameter

Baffles convert excessive tangential flow into axial and radial circulation, increasing turbulence and improving heat and mass transfer.

Draft Tubes

Draft tubes control the circulation path of liquid inside the reactor.

They are commonly used with propeller agitators to:

• Improve vertical circulation
• Reduce dead zones
• Increase mixing efficiency

The opening design should consider liquid level changes during operation.

The Role of CFD Simulation in Agitator Selection

For complex reaction processes, computational fluid dynamics (CFD) simulation is increasingly used to optimize agitator design.

CFD analysis can help evaluate:

• Flow distribution
• Mixing time
• Dead zones
• Power consumption
• Shear conditions

This allows manufacturers and engineers to select a more efficient agitator configuration before equipment production.

Conclusion

The correct selection of a glass-lined agitator plays an important role in improving reactor performance, reducing energy consumption, and ensuring stable production quality.

Propeller, turbine, paddle, anchor, and screw agitators each have different advantages depending on viscosity, mixing requirements, and process conditions. By considering material characteristics, reactor design, and auxiliary components such as baffles and draft tubes, users can achieve more efficient and reliable mixing performance in chemical and pharmaceutical applications.