An anchor agitator is a low-speed, close-clearance mixing device designed for high-viscosity fluids. Its anchor-shaped impeller sweeps close to the vessel wall, continuously renewing the thermal boundary layer and preventing wall buildup. Used in jacketed batch and continuous vessels where gentle, uniform mixing with effective heat transfer is required and conventional agitators cannot circulate the viscous contents adequately.
The anchor blades rotate at low speed, sweeping tangentially along the vessel wall at close clearance. This continuous wall-sweep prevents stagnant fluid layers from forming at the heated or cooled wall surface, improving heat transfer between jacket and batch. The rotation also generates slow bulk circulation throughout the vessel, maintaining homogeneity without imposing high shear on the product.
Challenges
Poor Central Mixing in Large Vessels
The anchor sweeps only the wall region; the vessel centre receives limited agitation, allowing stagnant core zones to develop in large-diameter vessels where the blade reach relative to vessel diameter decreases.
High Torque Demand at Start-Up in Cold Viscous Batches
Starting the anchor in a cold, highly viscous batch places maximum torque demand on the drive system before the batch warms and viscosity reduces, risking motor overload or gearbox damage if the drive is not adequately sized.
Limited Mixing Capability for Multi-Component Systems
The laminar flow pattern generated by the anchor is insufficient to achieve rapid homogenisation of density-mismatched liquids or to incorporate powders and solids that require higher-energy mixing to disperse effectively.
No Gas Dispersion or Emulsification Capability
The anchor cannot disperse gas bubbles or create the droplet size reduction needed for emulsification, restricting its use to single-phase or pre-emulsified viscous systems.
Scale-Up Wall Clearance Management
Maintaining the correct wall clearance as a proportion of vessel diameter during scale-up requires careful dimensional engineering; incorrect clearance at production scale reduces wall-sweep effectiveness and heat transfer performance.
Solutions
- Close Wall Clearance Engineering at Each Scale: Designing the anchor blade tip clearance as a consistent proportion of vessel diameter at each scale ensures effective wall-sweep and boundary layer renewal are maintained from laboratory to production vessel size.
- PTFE or Stainless Steel Scraper Blades on Anchor Arms: Attaching flexible scrapers to the anchor blade tips removes adhering material from the vessel wall during each sweep, preventing fouling and improving heat transfer in products prone to wall deposition.
- Drive System Sized for Cold-Start Peak Torque: Selecting the gearbox and motor based on the maximum torque required to start the anchor in the coldest, most viscous batch condition, rather than at normal operating viscosity, prevents drive overload and mechanical damage at batch initiation.
- Secondary Central Impeller on Independent Shaft: Installing a separate centrally mounted slow-speed impeller or disperser on a second shaft improves bulk circulation in the vessel centre without requiring the anchor to operate at speeds incompatible with the viscosity of the product.
- Variable Frequency Drive:Adjusting anchor speed throughout the batch cycle as viscosity changes with temperature allows the drive system to operate efficiently across the full processing range, reducing unnecessary power consumption during lower-viscosity phases of the batch.
Applications
- Pharmaceutical Ointment and Gel Manufacturing: Gentle uniform mixing of high-viscosity ointment bases, topical gels, and pharmaceutical creams in GMP-rated jacketed vessels where shear-sensitive active ingredients and polymer structures must not be degraded during processing.
- Cosmetic Cream and Lotion Temperature-Controlled Processing: Controlled heating, emulsification support, and cooling of body creams, moisturising lotions, and emulsified cosmetic products in jacketed vessels where wall-sweep agitation maintains uniform batch temperature and prevents wall deposition.
- Food Syrup, Jam, and Chocolate Processing: Mixing of high-viscosity food products including fruit preserves, sugar syrups, chocolate masses, and thick cooking sauces in jacketed vessels where gentle wall-sweep agitation prevents scorching and maintains product homogeneity during heating.
- Chemical Resin and Polymer Processing: Bulk circulation and heat transfer management during synthesis and processing of high-viscosity resins, adhesives, and polymer systems in jacketed reactors where the anchor sweep prevents wall fouling and maintains temperature uniformity.
- Dairy Concentrated Product and Processed Cheese Processing: Gentle mixing of concentrated dairy products and processed cheese masses in jacketed vessels where close-clearance wall sweep prevents product sticking to heated surfaces and maintains uniform temperature throughout the batch.
Models & Capacities
| Model | Scale | Tank Cap. (L) | Motor (kW) | Speed (RPM) | Viscosity Max (cP) | Tip Speed (m/s) | Op. Temp (C) | Op. Press. (bar) |
|---|---|---|---|---|---|---|---|---|
| ANC-LAB-10 | Lab | 10-50 | 0.18-0.37 | 5-50 VFD | 50,000 | 0.05-0.3 | -10 to 200 | Vac to 6 |
| ANC-LAB-100 | Lab/Pilot | 50-200 | 0.37-0.75 | 5-50 VFD | 100,000 | 0.1-0.5 | -10 to 200 | Vac to 6 |
| Anchor-100 | Pilot | 500-1,500 | 1.5-3.0 | 5-50 VFD | 50,000 | 0.2-1.0 | -10 to 200 | Vac to 10 |
| Anchor-300 | Pilot/Prod | 2,000-5,000 | 3.0-7.5 | 5-50 VFD | 100,000 | 0.2-1.5 | -10 to 200 | Vac to 10 |
| Anchor-750 | Production | 6,000-12,000 | 7.5-15.0 | 5-50 VFD | 200,000 | 0.2-1.8 | -10 to 200 | Vac to 10 |
| Anchor-1500 | Production | 15,000-25,000 | 15.0-30.0 | 5-50 VFD | 500,000 | 0.2-2.0 | -10 to 200 | Vac to 10 |
| Anchor-3000 | Large Prod. | 30,000-50,000 | 22.0-55.0 | 5-50 VFD | 1,000,000 | 0.2-2.0 | -10 to 200 | Vac to 10 |
| Anchor-HC | Heavy Duty | 1,000-10,000 | 5.0-22.0 | 5-50 VFD | 2,000,000 | 0.2-2.0 | -10 to 200 | Vac to 10 |