Types of Centrifuges

Centrifugal filters are usually characterized as basket and screen centrifuges. All are capable of filtration, washing, and dewatering, in ttiat sequence. Table 3-11 shows ranges of application of centrifugal filters. The most important variables are the concentration of the feed slurry and the size range of the solid particles. 

Slurry Characteristic Continuous, Slip, Screen Continuous, Vibratory, Screen Ccmtinuous Conveyor Sii /e/ Muhistage Pusher Automatic, Batch-PIcm, Horizotttal Automatic Batch- Plow, Vertical Manual, Batch- Plow, Vertical 

Washing ability Fair Poor Fair Good Good Excellent Excellent 

Discharged-cake condition Dry, granular Dry, granular Dry, granular Dry, granular Dry, granular Firm, granular Pasty, anular 

Liquid darity Fair Fair Poor Good Good Excellent Excellent 

---

The simplest type of centrifugal device is the cyclone separator (Fig. 3.4), which consists of a vertical cylinder with a conical bottom. The centrifugal force is generated by the fluid motion. The mixture enters in a tangential inlet near the top, and the rotating motion so created develops centrifugal force which throws the particles radially toward the wall. 

These concepts are used to analyze separations in the botde centrifuge, the imperforate bowl centrifuge, and the disk centrifuge. Separation by density difference in other types of centrifuges can be analyzed by analogy. 

The Z-concept permits scale-up between sinulat centrifuges solely on the basis of sedimentation performance. Other criteria and limitations, however, should also be investigated. Scale-up analysis for a specified sohds concentration, for instance, requires knowledge of sohds residence time, permissible accumulation of sohds in the bowl, G level, sohds conveyabihty, flowabihty, compressibihty, limitations of torque, and sohds loading. Extrapolation of data from one size centrifuge to another calls for the apphcation of specific scale-up mechanisms for the particular type of centrifuge and performance requirement. 

Power, Energy, and Drives. Centrifuges accomplish their function by subjecting fluids and soHds to centrifugal fields produced by rotation. Electric motors are the drive device most frequently used however, hydrauHc motors, internal combustion engines, and steam or air turbines are also used. One power equation appHes to all types of centrifuges and drive devices. 

This type of centrifuge is also used on borax and boric acid, -xylene, sodium bicarbonate, and sodium chloride from glycerol or electrolytic caustic. 

Experience in using the Z concept has demonstrated that the calculated Z factor should be modified by an efficiency factor to account for some of the aforementioned effects which are absent in the theoiy and, as such, this factor depends on the type of centrifuge. It is nearly 100 percent for simple spin-tube bottle centrifuge, 80 percent for tubular centrifuge, and less than 55 percent for di centrifuges. The... 

Type of centrifuge Inside diameter, in Disk diameter, in/niimher of disks Speed, r/min 2, value, units of 10 fF Recommended scale-up factors"... 

These scale-up factors are relative capacities of centrifuges of the same type hut different sizes when performing at the same level of separation achievement (e.g., same degree of clarification). These factors must not he used to compare the capacities of different types of centrifuges, f Approaches 2.5 at rates helow mL/min. fLong howl configuration. 

Type of centrifuge G/g Minimum feed sclids ccncentraticn by wt. Minimum mean particle size, im Minimum Vy, m/s... 

Rotary-Siphon Peeler Centrifuges In this type of centrifuge, a partial vacuum is drawn on the outer diameter or tne filter such that the filtrate flows through the cake under both centrifugal force as well as a positive pressure difference of about I atm or less. Thus, a higher rate of filtration takes place due to the increased driving force. 

Purchase Price Typical purchase prices, including drive motors, of tubular and disk sedimenting centrifuges are given in Table 18-16. The price will vary upward with the use of more exotic materials of construc tion, the need for explosion-proof elec trical gear, the type of enclosure required for vapor containment, and the degree of portability, and this holds for all types of centrifuges. 

There are many different types of centrifuges, classified according to the way in which the transport of the sediment is handled. The... 

There are numerous types of centrifuge and several ways of classifying them. Construction... 

The turbine is a special type of centrifugal pump (Figure 3-14) and has limited special purpose applications. 

This represents the linear effect of tip speed and the square of impeller size on the flow of a specific impeller. Referring to Figure 12-46, very low flow coefficients for a specific type of centrifugal or axial flow machine cause excessive wall friction or leakage losses, and very high-flow coefficients tend to he subject to turbulence losses due to insufficient flow guiding. ... 

The three types of centrifugal fan blades—radial, backward, and forward—give three characteristic performances. Table 12-12B gives a quick comparison. 

Centrifugal There are two major types of centrifugal compressors used in industrial applications in-line and bullgear. 

Centrifugation can be operated on a semi-continuous or continuous basis and there are several different types of centrifuges. Large scale tests have to be performed to choose the proper centrifuge (unloading speed, capacity, separation performance etc). 

The dimensionless quantity toQ 2/(ghf/A is a characteristic for a particular type of centrifugal pump, and, noting that the angular velocity is proportional to the speed N. this group may be rewritten as ... 

---