The Fluid Bed Agglomerator

Industry members have long debated the value of the fluid bed agglomerator and how granulation companies are often gauged on whether they have fluid bed capability. This determination is often done by non-technical personnel, who may be particularly impressed by the investment in high-dollar hardware. However, industry “techies” realize the fluid bed is not only a powerful tool in the granulation arsenal, but one that comes with many limitations.

The high cost of not only the actual fluid bed agglomerator, but also the supporting infrastructure that it requires to operate, make barrier to market entry very high. A new machine costs well into the six figures; add on installation of air handling systems, temperature/humidity control, boilers for steam production, etc., and the costs could go well beyond a million dollars. Before you turn the switch on, there is additional investment in training the R&D formulators, operators and maintenance crew, since people who work with this machine need to be very specialized.

Once entering the fluid bed processing business, there are several pros and cons to consider. The fluid bed will dry previously wet product in 30 to 40 minutes, where traditional tray ovens will dry in 8 hours or more. This difference can prove beneficial to the production timeline.

However, quicker drying by blowing the product around means more granules are broken down and more fines are created. This may or may not be a problem, depending on the product and final dosage form. If it is an issue, then rewetting and redrying of the fines is a necessity.

A fluid bed equipped with spray nozzles affords the ability to granulate right in the machine. This is commonly known as agglomeration, a process by which the product is wet with a binder solution and dried simultaneously.

The operator controls the product’s moisture by adjusting airflow, air heat and solution spray rates. In wet granulation, moisture can reach as high as 30 percent, whereas in agglomeration, you can keep your moisture below the low teens. This, once again, means quicker process time and more volume through the plant. Where the traditional wet granulation and tray drying process will take two days from beginning to end, agglomeration will take 30 minutes to an hour. Following the exact recipe and dryer cycle will guarantee better consistency from charge to charge, with better control and uniformity on end-point moisture. An additional benefit of having kept the moisture low and the product in constant motion is that very few clumps and large granules form, so the final oscillation or sizing step is easier.

However, the flip side is that granules created through agglomeration are formed in midair without any attrition, so they are basically hollow with very low density. Quite often, agglomerated granulations have lower densities than their own starting material. Low-density granules are ideal in situations that require quick dissolution, quick dispersion and an instantizing effect, such as in beverages and certain food applications. Low-density granules are not desirable in solid dosage applications, which have a lot of active(s), very little room for excipients and issues with dosage size.

An area where agglomeration is the clear hands-down favorite is microencapsulation. The microencapsulation process is commonly used in the development of sustained- or modified-release granulations, in taste-masking and in the spraying or layering of non-pareil seeds (sugar spheres). The fluid bed’s ability to suspend a particle in mid-air while spraying it with specialized binder solution or solubilized active component to create consistent, spherical, perfectly coated granules makes the process second to none. 

Emilio Gutierrez, R.Ph., has experience in both the pharmaceutical and nutritional industries. He currently works for BI Nutraceuticals as vice president of technical services where he specializes in the design and production of bulk powder and solid dosages. Gutierrez holds two patents in powder processing.