Continuous blenders

Fig. 4.5. K-G/Shugi vertical continuous blender-agglomerator. (Courtesy of Bepex Corporation.)...

Blending may be accomplished on a batch or continuous basis. Batch blending processes consist of three sequential steps weighing and loading the components, blending, and discharging. Unlike a continuous blender, the retention time in a batch blender is rigidly defined and controlled, and is the same for all of the particles. 

FIGURE 36 Continuous blender (A) and mixing paddles (B). Source Courtesy of Buck Systems Ltd. 

Continuous blenders Figures 36 and 37 contain pictures of two types of continuous blenders, which have been developed for the manufacture of large volume products. They are designed to continuously accept raw materials (input) and provide a uniform blend (output) that can be constantly fed to filling equipment over a sustained period of time. The defined batch size when using such blenders may be determined by... 

FIGURE 37 Continuous blender. Source. Courtesy of Patterson-Kelley. 

The author presents a means for determining how well a continuous blender is operating, as compared to how well it is capable of operating. This takes into account the type of blending cycle used, the ratio of blender volume to batch volume, and for certain cycles, the ratio of inflow rate to outflow rate. 

Fig. 7.31 Schematic representation of a P-K Zig-Zag continuous blender/agglomerator (courtesy Patterson-Kelley, East Stroudsburg, PA, USA).

Fig. 5. Continuous process for producing phosphatidylcholine. 1, Lecithin 2, ethanol 3, blender 4, diffuser 5, thin-type evaporator 6, ethanol-insoluble fraction 7, heat exchanger 8, chromatography column (Si02) 9, prestream 10 and 12, phosphatidylcholine solution 11, circulating evaporator 13, dryer ...

This blender is rated at. 300 ftVh on batchmixing basis 900 ftVh on continuous-mixing basis. Materials rated at 70-lb/fF bulk density. 

Figure 4. Ribbon blender agitator configurations (A) continuous ribbon, arranged for center discharge (B) continuous ribbon arranged for end discharge (C) interrupted ribbon (D) paddle-type ribbon.

Use continuous V-shaped mixer only for handling powder of diameter >0.01mm. For smaller powders, use ribbon blender. 

Root powdering and demineralization. Sixty-five frozen and pulp-free tooth roots were ground in a Waring blender and powdered under liquid nitrogen in a freezer mill (Spex, Edison NJ, USA). The sieved powder (< 450 pm) was demineralized in dialysis bags in 0.5 M EDTA, pH 7.4, at 4°C with regular replacement of the solution. Demineralization was continued until no further calcium release could be detected by atomic absorption spectrometry. 

In summary, it appears that roller compaction pre- and postblends can be NIR monitored during scale-up, independent of batch size and blender type. Using real time NIR monitoring would advance blender unit operations knowledge and provide continuous information and assurance about specific unit operations such as roller compaction, a key FDA Process Analytical Technology goal. 

The data presented in Figure 4.14a are consistent with the following mechanism. The dispersion that emerges from the blender is fundamentally unstable with respect to coagulation and coagulates rapidly to form a volume-filling network throughout the continuous phase. Except for the size and structure of the chains, the situation is comparable to a cross-linked polymer swollen by solvent. In both, the liquid is essentially immobilized by the network of chains, and the system behaves as an elastic solid under low stress. The term gel is used to describe such systems whether the dispersed particles are lyophilic or lyophobic. 

Figure 10.15. Some mixers and blenders for powders and pastes, (a) Ribbon blender for powders, (b) Flow pattern in a double cone blender rotating on a horizontal axis, (c) Twin shell (Vee-type) agglomerate breaking and liquid injection are shown on the broken line, (d) Twin rotor available with jacket and hollow screws for heat transfer, (e) Batch muller. (f) Twin mullers operated continuously, (g) Double-arm mixer and kneader (Baker-Perkins Inc.), (h) Some types of blades for the double-arm kneader (Baker—Perkins Irtc.).

Production must be carried out in an area of controlled (low) humidity. To prevent separation after blending all components should be as similar as possible in particle size and bulk density. The ingredients must be sieved before addition and it is often preferable to prepare a pre-blend of some ingredients to facilitate the addition of small mass items and mixing in. Mixing is earned out in ribbon blenders and can be on either a batch or a continuous basis. Packaging is in sachets or jars. 

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