Rotary valve feeder

Rotary V lve Feeders. Devices known as rotary valve feeders are commonly used for circular or square configured outlets. These are particularly useful when discharging materials to a pneumatic conveying system where a seal is required to prevent air flow through the hopper outlet. The discharge rate is set by the speed of rotation of the vanes or pockets of the valve. 

Proprietary designs for rotary valve feeders (star valves) capable of continuous feeding of certain pelleted and granular materials into low velocity, dense phase systems, having system pressures up to 200 kPa (2 bars) have been developed. 

Figure 5.3. Basic equipment arrangements of pneumatic conveying systems, (a) Vacuum system with several sources and one destination, multiple pickup (b) pressure system with rotary valve feeder, one source and several destinations, multiple discharge (c) pressure system with Venturi feed for friable materials (d) pull-push system in which the fan both picks up the solids and delivers them [after F. J. Gerchow, Chem. Eng. [17 Feb. 1975, p. )].

For proper operation of a dilute-phase, pneumatic conveying system the solids fed into the pipeline must be carefully controlled. Two common types of feeders are the venturi feeder and the rotary valve or star feeder, illustrated in Figure 3.31. The venturi feeder is only suitable for low-pressure systems. The rotary valve feeder, also known as star feeder as described previously in this chapter is widely used for feeding medium-pressure conveyors. This feeder is efficient and simple in principle, but requires careful design in order to minimize air leakage. Excessive air loss from feeders, wastes power, causes dust, and leads to system instability. Rotary feeders work well on free-flowing, nonabrasive powders and special types are available for more difficult materials. 

For higher pressures (up to 1.4 bar) so-called rotary gate (or rotary valve) feeders may be employed (Fig. 25), which function as air-locks. Similar devices may be used also for the discharge of the material from the pneumatic handling system. A special form of such feeders is intended for dealing with sticky materials which tend to remain adhering in the compartments or pockets of the rotor and is equipped with air jets that dislodge the material by blasts of air. 

Six 7.9 m diameter by 22 m. tall silos were used to store high density polyethylene fluff and pellets. Below each cylinder section was a 30° cone terminating at a rotary valve feeder. A radial hopper seam split open on one silo, spilling one million pounds of material onto the ground. The cause of this failure was determined to be mass flow loads. The silo was structurally designed only for funnel flow. See Figure 5. 

Fig. 4. Typical drop-through rotary valve feeder and drop-out box for granular materials...

Rotary valve feeder similar to Fig. 4, rotor speed = 6 rpra, swept volume = 0.0495 m per rev. 

Fig. 11.1.2. Rotary Valve/Feeder components. Courtesy Koger Air...

Volumetric Feeders. Examples of volumetric feeders are screws, belts, rotary valves, louvered, and vibratory. 

FIG. 17-16 Solids-flow-control devices, a) Slide valve, (h) Rotary valve, (c) Table feeder, (d) Screw feeder, (e) Cone valve, (f ) L Valve. 

FIG. 21-1 Typical feed arrangements for screw conveyors, a) Plain spouts of chutes, (h) Rotary cutoff valve, (c) Rotary-vane feeder, (d) Bin gate, (e) Side inlet gate. (FMC Corporation, Matetial Handling Systems Division. )... 

Material Choke A mass of bulk solids or powders in a rotary valve or screw feeder that prevents a flame from being transmitted. 

At the downstream end of the pipeline it is necessary to disengage the solids front the gas and this is most usually carried out in cyclone separators (See Volume 2, Chapter 8). However, there may be a carry-over of tine particles which must be eliminated before the gas is vented, and gas filters or electrostatic precipitators may be used for this purpose (See again Volume 2, Chapter 8). At the upstream end, the particles must be introduced using some form of positive feeder, such as a rotary valve or a blow tank. 

Rotary valves have been specified for the receivers of the vacuum pneumatic conveying systems (RV-601 and RV-602) and for the feeders (RV-40 1) and receivers (RV-501) of the positive-pressure system transferring powder from the dryers to the extruders. Perry72 gives some recommended sizes for rotary valves. The power required by all these valves will probably not exceed 2 kw and will be ignored. 

Equipment for solids transport which is usually needed in fluidized bed processes will also add to the overall attrition rate. In screw feeders or rotary valves, the particles can be crushed or sheared between the vanes and the housing. The contribution of pneumatic conveying lines is discussed in Sec. 6. 

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