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How to determine an efficient pneumatic conveying system for cohesive pharmaceutical powders

Active ingredients and excipients with very poor flow properties in pharmaceutical powders place special demands and sometimes great challenges on the conveying systems. In this article, you will learn more about what aspects you should consider when determining an efficient pneumatic conveying system for cohesive pharmaceutical powders.

Pharmaceutical powders often include very poor flowing excipients and API’s (Active pharmaceutical ingredients) which can present challenges not only in material handling but also in areas such as product and process containment, options in design for cleaning and product changeover.

Pneumatic conveying operations can often be incorporated directly into the second-ary process in an effort to ensure a closed and leak-free operation, without any exposure of operator or product. These additional processes include, but are not limited to: direct blender loading, inline conical screen milling or sieving, tablet press loading, granulator loading/unloading, fluid bed dryer unloading, tablet/capsule conveying, refill of screw feeders for loading of continuous processes such as granulation, mixing, milling/micronization, and extrusion, transfer direct to feeders for batch weighing or dispensing of several components in a blend.

When evaluating a proper pneumatic conveying technology, the following key criteria should be considered:

  1. Properly define the material characteristics: Proper evaluation of a pneumatic conveying system for a cohesive, slightly sticky material requires you to define your material's characteristics, such as bulk density, flowability, particle size distribution, moisture content, abrasiveness, and temperature. These characteristics will all affect not only the proper technology to be used, (e.g. dense phase vacuum versus dilute phase vacuum), but will also affect overall system geometries and design, such as angles on receiver and pickup hoppers and additional flow aid requirements.
  2. Define the overall conveying requirements: These definitions will include a general description of your application and purpose, the system's location and environment classification, the conveying rate, the horizontal conveying distance, the vertical conveying distance, conveying line direction changes (bends), a material source description, and a material destination description. It will also include details on the material explosive properties (which may re-quire an inert conveying gas medium) as well as the toxicity of the powder, which will define the levels of containment required not only during the material transfer but also at both the product pickup and discharge points.
  3. If possible, perform bench material testing: If the material can be sent for test-ing, be sure to send a small representative material sample to Coperion K-Tron for bench testing. If the material is too toxic for testing, then sending a placebo with similar flow and material characteristics is also acceptable. We will issue a test report to confirm and complete the material characteristics testing. This test report, along with the conveying requirements provided in the second step, will help determine the best theoretical pneumatic conveying system configuration.

Each of the criteria described above will enable the most efficient choice for pneu-matic transfer. For example, in the case of designing a system for a slightly cohesive material, the optimal pneumatic conveying system configuration may consist of the following:

  • A dilute-phase pneumatic conveying system, which is the most likely system type as it is the most forgiving, given the application
  • A motive gas supply with a positive-displacement blower package or a Venturi for low rate and small space applications
  • A line charger consisting of a blow-through rotary airlock with a nonstick coat-ing and shear protection
  • A conveying line that is properly supported and sized with flexible rubber hose and flexible rubber hose bend
  • A motive gas and material separation filter, which has a small pleated car-tridge filter media with a nonstick coating and is easy to take apart and clean

The above-mentioned aspects serve as a starting point for considering which delivery system best suits your needs. In all cases of material handling, it is important to discuss in detail all of the items above with Coperion K-Tron who is well versed in the properties of a wide variety of pharmaceutical powders. A proper pneumatic conveying technology ensure not only the most efficient means of transfer, but also the safest means of transfer for both operator and final product.

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