Single-impeller agitator

Toluene and olefinic stock from storage are pumped (at 80°F) separately through individual driers and filters into the alkylation reactor. The streams combine just before they enter the reactor. The reactor is batch operated 4 hr/cycle it is equipped with a single impeller agitator and a feed hopper for solid aluminum chloride which is charged manually from small drams. The alkylation... 

The single-impeller agitator consists of one vertical shaft containing horizontal arms. The shaft may be placed off center in order to create rapid circulation past, or local turbulence at, the point of contact between the nitrating acid and the organic compound. 

Impeller-agitated tanks These can be operated as continuous leaching tanks, singly or in a series. If the sohds feed is a mixture of particles of different setthng velocities and if it is desirable that all particles reside in the leaching tank the same lengths of time, design of a continuous stirred leach tank is difficult and uncertain. 

Mixers for gas-liquid contacting are often equipped with multiple impellers on a single shaft with the gas injected below the lowest impeller. Large commercial systems may use relatively deep cylindrical vessels. The usual ratio of liquid-depth to vessel-diameter lies between 1 and 3 (R3), and the maximum recommended is 4 (P3). In such deep systems, the question arises as to whether the use of multiple impellers would provide more effective contact than a single impeller. It must be kept in mind that if the impellers are spaced too widely the result may be ineffective agitation between the fields of action of the impellers. On the other hand, if they are too close, interference may occur between the flow streams from the adjacent impellers. 

The impeller is the part of the agitator that impacts force to the material being mixed. Propellers, turbines, gates, anchors, and paddles are all types of impellers. Typically, the impeller is a single propeller or turbine blade connected to a shaft that is driven by an electric motor at a fixed speed. There are two classes of impeller agitators axial-flow and radial-flow, and the mixing characteristics are shown in Figure 3.14. 

Specifically, the holdup correlation above was developed from data with air-water systems agitated with a single impeller. However, the correlation will give reasonable results for other systems unless (1) coalescence inhibiting surfactants are present and (2) the viscosity exceeds several hundred centipoise. For higher viscosity liquids, vendors should be consulted. 

Solids suspension is usually carried out in mechanically agitated vessels with or without draft tubes, as shown in Figs. 5 and Dished heads (ASME dished, elliptical, or torispherical heads) are preferred. A single impeller is usually sufficient for off-bottom solids suspension in vessels with dished heads and 7 < 1.3. Dual impellers are recommended for vessels with 13 < H/T < 2.5, which are used for uniform suspension of fast-settling solids. Three or more impellers... 

Markopoulos J., Kontogeorgaki E., Vortex depth in unbaffled single and multiple impeller agitated vessels, Chem. Eng. Technol. 18 (1995), p. 68-74... 

A 50 50 volumetric ratio of acid to hydrocarbons was used 10°C and a large baffled reactor with a single impeller was used for agitation. Calculations were performed using VisiMix 2000 computer model. 

For mass transfer dependent reactions, agitation must promote dispersion, discourage coalescence, and prevent settling. Usually, a single impeller can accomplish these tasks for vessels of H/T < 1.2 and for 0.9 < Pa/Pc < l l- However, additional impellers are used when H/T > 1.2 or when Pa/Pc is outside the limits cited above. The selection of a second impeller was discussed in Section 12-7.2.1. Dispersions of 1 mm drops are easily suspended in square vessels (H = T) and normally do not require use of a second impeller. 

FIG. 15-23 Power for agitation impellers immersed in single-phase liquids, baffled vessels with a gas-liquid surface [except curves (c) and (g)]. Curves correspond to (a) marine impellers, (h) flat-blade turbines, w = dj/5, (c) disk flat-blade turbines witb and without a gas-liquid surface, (d) curved-blade turbines, (e) pitcbed-blade turbines, (g) flat-blade turbines, no baffles, no gas-liquid interface, no vortex. 

Consider a stirred tank vessel having a Newtonian liquid of density p and viseosity p, is agitated by an impeller of diameter D, rotating at a rotational speed N. Let the tank diameter be D, the impeller width W, and the liquid depth H. The power P required for agitation of a single-phase liquid ean be expressed as ... 

---