Specifying a Mixer for Nutraceuticals

February 11, 2008




To identify the right mixer (or blender) for your application, begin with a wide-angle look at your overall production requirements. Then, zoom in on each of the steps in your manufacturing process. For example:

• What volume will you need to produce? Considering your throughput requirements, is your process best served by a batch, continuous, or semicontinuous mixer? Looking upstream and downstream from your mixer, will you gain efficiency with such equipment as multiple mix vessels and discharge systems?

• During each process step, what type of agitation is preferable? Does your process require low-shear or high-shear mixing? If you are blending powders or solids, is gentle blending sufficient? Or will you need greater shear to break up lumps?

• Will your batch require heating or cooling to control the batch temperature? During which process steps? How tight are your tolerances?

• Will you require deaeration during mixing? Techniques such as subsurface injection, vacuum mixing, and in-line injection of solids and liquids into the process stream can eliminate the risk of entraining air in the batch. They often accelerate the wetting out of hard-to-disperse powders, as well.

Materials of Construction

Now, let’s get even more specific. Which materials of construction will deliver the right balance between process efficiency and cost efficiency? Most nutraceutical applications require Type 316 stainless steel, but special alloys may be appropriate to address unusual process needs.

Elastomers

Compatibility is always a significant design consideration, and your application will require elastomers that are compatible with all of your raw materials. Many choices are available, including Viton, Teflon, neoprene, and Kalrez.

Shaft Seals

Choices include single or double mechanical seals, special dry-running mechanical seals, lip seals, and more. Which are most appropriate for your application? Double mechanical seals use barrier fluids for lubrication, and these must also be compatible with your product.

Agitators

Many products require multiple steps-and varying types of agitation-to complete. These may include simple, slow agitation to promote gentle blending or heat transfer, or high-speed agitation for particle-size reduction, deagglomeration, dispersion, emulsification, or homo­g­enization.

In addition, many process steps are accomplished most efficiently with mixers that include multiple agitators-with each agitator turning independently on its own axis. Each agitator may accomplish a unique task while they all operate simultaneously.

Which types of agitation will your process require? And which combination of agitators, operating together, will deliver optimal efficiency? As you evaluate a variety of mixer configurations, be sure to factor in the maximum operating viscosity reached by product during mixing, not just the final viscosity.

Polish

How often will a complete cleaning of the internal surfaces be required? Polishes for sanitary applications typically range from 120-grit mechanical polishes to mirror finishes applied mechanically or via deposition processes.

CIP/SIP

Automated or semiautomated cleaning systems are available, along with simple spray balls, to clean your mixer quickly and consistently between batches.

Covers and Cover Openings

Consider how materials will be added before and after each process cycle. This will determine the number, size, and type of openings included in a cover. For example, if you will blend dusty powders, a dust-tight cover with clamps and a vent port with dust sock will be ideal to reduce airborne particulates. To monitor the process, you may also need a sight glass with a light and perhaps a wiper.

Discharge Valve Design

Many discharge valve designs are available, including designs that facilitate complete disassembly for 100% cleaning between batches. For dry blenders, fully automated pneumatic valves can easily be tied into your control system. And if dead spaces at the bottom of your blender/mixer are a concern, flush plug valves provide a simple solution. For nonflowing, viscous products that need to be pressed out of the mixer, a cove-cut plug valve would work well, and it is easier to clean than a ball valve.

Operator Controls

Simple or complex operator controls, along with complete PLC-driven control systems, provide a wide spectrum of choices to accommodate all levels of process automation. What are your requirements for system compatibility?