There are many industrial applications that require the enlargement of powder or particles for improved handling. Some objectives may be: enhancing flow properties, recycling, de-dusting, densifying, freezing ingredient distribution, improving mold filling properties, etc. Most powders with the ability to fuse or slightly dissolve in the presence of a liquid can be granulated quite easily. Others may be coaxed to form granules by the introduction of a suitable binder such as water, acid, molasses, etc. The binders may act as a medium for the solid particles to adhere to each other, some may form a matrix to capture the particles, and others may involve chemical reactions to achieve the objective.
“Size-enlargement” is more commonly referred to as agglomerating, pelletizing, granulating and briquetting. What follows below is a top level comparison of particle enlargement through a snowballing mechanism (pan/disc) compared to shear action (high shear mixers), and does not address pelletizing with the application of high pressure or extrusion.
Mix-Granulation versus Disc/Pan-Granulation:
Disc granulation (sometimes called pan granulation) is a continuous process. In its simplest form, powders and liquid are fed in steady streams and fixed proportions onto a rotating disc which is tilted at a certain angle to facilitate continuous overflow of the desired granules. Under theoretically steady-state conditions, particle residence time in the disc granulator is constant and relatively uniform-sized granules in the order of 1/2” diameter and larger are the output.
As with many continuous processes, truly steady-state conditions are fleeting for disc granulation, and actual yields are much lower than theoretical yields. Furthermore, disc granulation requires frequent operator attention to try and maintain a balance of mass flow.
Mix-granulation in a Lancaster Products K-series high shear mixer offers a much higher level of control and thus greater yields in the granulation process over disc granulation for several reasons:
- The mixing process is completed in batches and tightly repeatable.
- The ability to produce products of the same characteristics batch-to-batch allows the operation to be automatic, with little operator attendance.
- The process produces a wider spectrum of granule sizes, from micro sizes to as large as 8 -10 mm depending on requirement and feed material.
- Because of higher shearing and configurable tool actions, granules are generally packed more tightly and require less liquid/binder.
- Flexibility in the ability to control properties beyond size specification to a significant degree according to objectives.
- Mix-granulation also has the flexibility of approaching the final moisture content either from the dry end or from the wet end.
- A full mix-granulation cycle can be completed in as little as 3-10 minutes depending on process requirements.
The Lancaster Products mixer is capable of regulating intensity and energy, independent of mixing-granulating time, and a number of factors can be adjusted to influence granule characteristics. These mixer configurable parameters include: rotor design, rotor speed, direction and granulating time and pan speed. In addition, optimizing process parameters such as solids fineness, binder, liquid-to-solids ratio and liquid addition rate can enhance desired granule properties.
Lancaster Products K-series mixers are especially useful for processes where some multi-ingredient solids need to be mixed to complete homogeneity, and then granulated into nominally spherical products. Mixer and process parameters can be controlled to achieve desired properties. Size distribution usually follows a bell-shaped curve, with approximately 90 percent of granules falling within one order of magnitude.
Contact us today to discuss how Lancaster Mixers can provide higher yields and greater efficiencies for your granulating needs.