Liquid paddle mixer

Propeller/paddle mixers are used to blend or agitate liquid mixtures in tanks, pipelines, or vessels. Figure 38.1 illustrates a typical top-entering propeller/paddle mixer. This unit consists of an electric motor, a mounting bracket, an extended shaft, and one or more impeller(s) or pro-peller(s). Materials of construction range from bronze to stainless steel, which are selected based on the particular requirements of the application. 

The propeller/paddle mixer is also available in a sideentering configuration, which is shown in Figure 38.2. This configuration is typically used to agitate liquids... 

Sigma-blade and planetary-paddle mixers are used for solid blending and as a step prior to the introduction of liquids (Figs. 6 and 7. This type of mixer rapidly breaks down agglomerates. 

The paddle mixer can also be used for kneading and for mixing pastes since the kneading action allows phase changes from dry to paste when liquid is added. To evaluate the suitability of such mixers, it is recommended that test trials are conducted on the mixture to judge the duration and the quality of mixing. Paddle mixers are so versatile, they are also used as dryers and coolers for bulk solids. 

Refractory Ramming Mixes. These are noncoherent materials, which are supplied in premoistened status or ready-for-use. After filling them behind a stable shuttering, they are installed by ramming (in special cases by vibrating, too). These materials can also be supplied in dry status together with a separate liquid binder. The ready-for-use consistency will be achieved by using a paddle mixer on-site. 

Dispersion llmmiscible Syslems Turbine Propeller Paddle — 1. Drop Size Conlrol 2. Re-Cireu-lallan 30 1 la 3.5 n H2 in Sloged Mixers Al/or B iow Center Lint of Liquid Chorg ... 

Fig. 23. Some mixers for viscous liquids, (a) Six-blade turbine (b) three inclined-blade paddles (c) helical screw (d) helical ribbon (e) propeller in draught tube (f) anchor. (Reprinted with permission from Chemical Engineering Science, 37, 813, C. J. Hoogendoorn and A. P. Den Hartog, 1967 Pergamon Press pic).

Numerous equipment types can be used for agglomeration, including horizontal ribbon and vertical mixers, rotary drums, zig-zag mixers, and pan agglomerators. Horizontal ribbon mixers as shown in Fig. 36.41 are used primarily for dry mix formulating, where only limited agglomeration occurs. They are comprised of a U-shaped trough and a ribbon or paddle-type agitator. Liquids are sprayed onto the surface of the dry material and slowly dispersed into the mix. Mixer operations can be either batch or continuous. 

With the Flexomix, dry powders are fed into the mixer where the paddles mix the powder with liquid that is introduced close to the paddles, which turn at high speeds. The wet mass which exits the mixer is dried in a fluid bed system. The product from this system is an open structure granulate which exhibits instant behavior upon dissolution. 

The physical model of the reactor is a 350 mm high cylindrical vessel, with a diameter of 200 mm and an elliptical bottom. The operation volume is V = 12 10 m. The entrance of the reactants is placed near the middle of the reactor, more exactly at 130 mm from the bottom. The reactor s exit is positioned on the top of the vessel but below the liquid level. At the vessel centre is placed a mixer with three helicoidal paddles with d/D = 0.33. It operates with a rotation speed of 150 mirnf In order to establish the reactor flow model, this is filled with pure water which continuously flushes through the reactor at a flow rate of 6.6 10 5 m /s (similar to the reactants flow rate). At time t = 0, a unitary impulse of an NaCl solution with a Cq = 3.6 kg/m is introduced into the reactor input. The time evolution of the NaCl concentration at the exit flow of the reactor is measured by the conductivity. Table 3.5 gives the data that show the evolution of this concentration at the reactor exit. 

---