High-pressure feeders

With the advent of high-pressure feeders after World War II (e.g., blow tanks, screw pumps), many designers and users began to apply pneumatic conveying to much greater distances and/or capacities (e.g.,... 

Supplying solid biomass into a hydrothermal gasification reactor at high pressure is a di icult problem. The pressure in the hydro ermal reactor is much higher than the screw feeder can withstand. Moreover, it is difficult to apply a fluidized bed at the high temperatures and pressures encountered in supercritical water reactions. 

The HTW technique, developed by Rheinbraun, utilizes increased pressure (up to 3.0MPa) and operating temperature. In this process, a lock hopper and screw feeder are used to feed the coal particles into the reactor from a high-pressure charge bin. Due to the increases in both temperature and pressure, coal conversion in the HTW process is much higher than in the Winkler process. 

Figure 397. Dry, high pressure granulating system in which the rollers are positioned vertically and material is fed into the nip by means of a horizontal screw feeder. (Courtesy of Alexanderwerk, Remscheid, FRG)...

Materials characterized by curve (1) in Fig. 10.16a require high energy input during the entire densification cycle. This can be readily accomplished with hydraulically driven ram and punch-and-die presses. It is difficult to process such materials with roller presses. As coarse monosized materials are not easily pulled into the nip between the rollers, large diameter rollers and high force feeder pressures would be needed. 

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. 

Screw feeders provide a convenient way to deliver solids to a gas-solid transport system or process, and they can also be used as metering devices. These units permit accurate delivery of precise amounts of solids. Generally, these units do not work on high-pressure systems but can work adequately up to about 2 atm pressure. 

This high pressure type of feeder, however, is only suitable for fine materials, such as cement and fine grades of fly ash, that are capable of being compressed to a higher bulk density in the reducing pitch section of the screw, since this is how the air seal is achieved. As a consequence of this the power required to drive the screw is quite high. 

The scheme of the jet vortex mill is shown in Fig. 1. The gas under high pressure is injected tangentially through flat nozzles located in the external chamber wall. Coarse particles with low velocities are injected through the orifice in the center of the upper cover of JVM. It is reasonable to carry out the injection of a raw by an ejector through a spiral channel (volute) that provides uniform solid feeding on a circle of a small radius Ri. However, because of the cylindrical zone with radius Rp in the chamber center is zone of rarefaction, the raw can be put into the chamber also by means of a pouring feeder. Coarse particles are accelerated by... 

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