Power turbine mixer

Figure 7.7. Power number as a function of Reynolds number for a turbine mixer...

Braun, S.S. Power Recovery Pays off at Shell Oil, Oil and Gas Journal, May 21, 1973, p. 129. Abadie, V.H. Turboexpanders Recover Energy, Hydrocarbon Processing, July 1973, p. 93. Casto, L.V. Practical Tips on Designing Turbine-Mixer Systems, Chemical Engineering, Jan. 10,... 

Paszek E., Power characteristics of turbine mixers with inclined blades. Pt. 

We find then that the coefficient P is between 2 and 4 for propellers and pitched blade impellers, and between 1 and 2 for flat disc turbines. That would mean that the latter are the most power-effective mixers. 

Equipment suitable for reactions between hquids is represented in Fig. 23-37. Almost invariably, one of the phases is aqueous with reactants distributed between phases for instance, NaOH in water at the start and an ester in the organic phase. Such reac tions can be carried out in any kind of equipment that is suitable for physical extraction, including mixer-settlers and towers of various kinds-, empty or packed, still or agitated, either phase dispersed, provided that adequate heat transfer can be incorporated. Mechanically agitated tanks are favored because the interfacial area can be made large, as much as 100 times that of spray towers, for instance. Power requirements for L/L mixing are normally about 5 hp/1,000 gal and tip speeds of turbine-type impellers are 4.6 to 6.1 i7i/s (15 to 20 ft/s). 

Fig. 3 shows the experimental apparatus. The feed tank had a 50 gallon capacity and was equipped with a variable speed mixer. The feed pump was a flexible impeller, positive-displacement pump to minimize shearing of the feed emulsion. The pumping rate was regulated by a Graham Variable Speed Transmission. Each flotation tank was 11.5 in. ID with 6.5 in. liquid depth maintained by a CE IN-VAL-CO conductometric level controller with a pneumatically actuated control valve in the effluent line. The fourth cell was not equipped with an air inducer. The outer diameter of the air downcomers was 1.5 in. The rotor in each air inducer was a turbine taken from a 2 in. turbine flow meter. Each rotor was belt driven by a 10,000 rpm, 1/30 hp motor and all three motors were governed by the same variable transformer. Another pulley on each rotor shaft was attached to a non-powered belt connecting all three shafts to ensure that each rotor turned at the same speed. 

For non-Newtonian fluids, viscosity data are very important. Every impeller has an average fluid shear rate related to speed. For example, for a flat blade turbine impeller, the average impeller zone fluid shear rate is 11 times the operating speed. The most exact method to obtain the viscosity is by using a standard mixing tank and impeller as a viscosimeter. By measuring the power response on a small scale mixer, the viscosity at shear rates similar to that in the full scale unit is obtained. 

Espinosa-Solares T., Brito-De La Fuente E., Tecante A., Tanguy P.A., Power consumption of a dual turbine-helical ribbon impeller mixer in ungassed conditions, Chem. Engng. J. 67 (1997), p. 215-219... 

If it is desired to consider axial flow impellers in a gas-liquid system for any reason, it should be remembered that the upward flow of gas tends to negate the downward action ofthe pumping capacity ofthe axial flow turbine. A radial flow turbine must have three times more power than the power in the gas stream for the mixer power level to be fully effective. On the other hand, the axial flow impeller must have eight to ten times more power than in the gas stream for it to establish the axial flow pattern. 

Turbines, propellers, and paddles power = 0.2 to 1.5 kW/m for mixing liquids with impeller discharge rate >20 x liquid flow rate into tank. Heat transfer, 0.4 to 2 kW/m but don t neglect heat input from the mixer mass transfer 2 to 4 kW/mT Turbines, propellers, and paddles power = 1 to 4 kW/m for mass transfer. Air agitation diffused air 0.3 to 0.5 NdmVs-m 1.5 to 6 dmVs m... 

POWER CORRELATIONS FOR SPECIFIC IMPELLERS. The various shape factors in Eq. (9.16) depend on the type and arrangement of the equipment. The necessary measurements for a typical turbine-agitated vessel are shown in Fig. 9.7 the corresponding shape factors for this mixer are Sj = DalD S2 = EID S = L/D , S4 == W /Od. S5 = J/D, and Sg = HfD,. In addition, the number of baffles and the number of impeller blades must be specified. If a propeller is used, the pitch and number of blades are important. 

The action of a turbine or propeller in a Newtonian liquid of low viscosity can be likened to that of the impeller in a radial or axial flow pump respectively. That is, we can regard the mixer as being a caseless pump. The use of the flow rate (or discharge), Q, from a pump and the fluid head, //, is well known. Thus for a pump of unit efficiency these variables can be related to the power input... 

---