Venting feeder

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. 

The rate of pulp lay-down F on a paper machine is controlled by controlling both the pressure P and the height of slurry h in a feeder drum with cross-sectional area A. F is proportional to the square root of the pressure at the exit sHt. The air vent rate G is proportional to the square root of the air pressure in the box P. Feedback controllers set the inflow rates of air Gq and slurry Fq to hold P and h. The system is isothermal. 

Rotary, star valve feeder used especially as solids feeders for dilute-phase pneumatic conveying to provide an air lock and to feed solids. Seal/wear depends on Ap and abrasiveness of powder. For pressure systems keep Ap <80 kPa for vacuum systems Ap <40 kPa. Provide an air vent to take the air loss away from the gravity flow of the solids and to control the filling of the star. 

Flash dryer with disintegrator A, paddle x)nveyor mixer B, oil-fired furnace C, hammer mill D, cyclone separator E, vent fan F, star feeder G, solids flow divider and timer. 

Drilling has delineated two major massive sulfide lenses in the Bent Hill area (Fig. 28). The Bent Hill Massive Sulfide HMS) deposit (Zierenberg et al. 1998) consists (from top to bottom) of 93 m of massive sulfide, 100 m of sulfide feeder or stringer veins in highly altered sediments, a stratiform deep copper zone of chalcopyrite and pyrrhotite in a totally altered sandstone, and basaltic lava flows and sills at about 500 mbsf An additional sulfide deposit, or possibly an extension of the BHMS deposit, occurs 400 m to the south at the ODP mound (Fig. 28). The ODP mound has an active 264°C hydrothermal vent on top (Butterfield et al. 1994a), three separate massive... 

Other conveying systems, such as elevators, drag chains, vibrating tubes, screw feeders, pneumatic conveyors, and air slides are generally enclosed. Any air displaced from them should be vented to a suitable dust collector. 

FIGURE 29.4 Isometric view of centrifugal fluidized bed drying system. (1, dryer cylinder 2, drive pulley 3, aspiration feeder 4, feeder blower 5, discharge chute 6, air blower 7, air discharge damper 8, steam coil heater 9, plenum 10, air vent 11, vent port 12, recirculating duct 13, make-up air 14, blower intake). (From Hanni, P.F. et al., J. Food ScL, 41(5), 1172, 1976. With permission.)... 

The cold water feed can be provided by direct coimec-tion to the mains (in which case all components must be able to withstand mains pressure) or from a feeder tank (which is in an elevated position and filled from the mains through a float valve similar to the water closet-cistern float valve). For mains pressure systems most utilities or water supply authorities require the installation of a nonreturn valve. Whereas low pressure (feeder tank) systems are open to the atmosphere through a vent pipe, mains pressure systems must be protected against overpressure (due to thermal expansion of water as heated) by a pressure relief valve, as well as against collapse (implosion), which could be caused by a suction effect (vacuum formation) in case of an aceidental water discharge, by an air intake (or breather) valve. 

The flame arresters described above are not suitable for use in equipment and pipework where the hazard of a dust explosion exists. Other procedures must be adopted there. Among the devices used for isolation figure star-wheel feeders or rotary valves, active barriers with extinguishing media, rapid-closing valves (explosion isolation valves) and doors, as well as explosion vents. These are described in detail in [19]. 

Solids flowrate Jrom feeder does not increase with increasing speed of feeder FRI < required flowrate/solids diameter small enough to form a limited rate into the feeder caused by the upflow of air a hopper exit/air injection location too low. Solids flowrate does not increase when rpm of rotary valve is increased moderately low FRI/air introduced by the rotary valve at hopper outlet/venting the returning high-pressure cavity is insufficient. 

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