Feeders with process function

Processes such as cooking, steaming, and sterilizing, are often enhanced by live steam injection. Similar construction allows de-gassing, inerting, and gas contact reactions to be effectively undertaken. An injection ring, with multiple entry points surrounding the screw, provides the inlet gas or steam close access to penetrate into the product. 

A feature of some feeder operations is that the product is delivered to a region that has a slightly different pressure to that in the supply zone. Other feeders deliver into ambient conditions that are unfavourable to sustained exposure of the feeder mechanism or to the product. Common examples are feeding from dust filters, into reaction vessels that have vapour-laden atmospheres and into the high-temperature atmospheres of kilns and driers. Discharge end bearings and seals of conventional screw feeders are vulnerable to such adverse atmospheric conditions. Exposed contact surtaces suffer condensation from steamy environments, and 

In some process operations a de-gassing hopper is used to change to ambient atmosphere of the void gas in a bulk material. Typical applications 

For constant volume reduction the feed may be controlled by prior equipment, or the feeder served by a flooded hopper, provided the product is conditioned by nature or a consistent flow channel to a consistent 

An alternative approach is to accept whatever rate of feed reaches the compacting screw and press this against a constant resistance to produce a controllable compacting force. This is done by a form of plug seal screw, either with a fixed form of construction, or with the provision of a variable resistance device to increase or decrease the compacting force. Linking the discharge resistance to the drive unit allows the compaction force to be optimized to the drive capacity. 

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Other examples of screw feed/process devices are feeders with pre-breaker sections, granulating, and/or sieving functions. An example of a pre-breaker with a screening section and an integral feed screw is shown in Fig. 7.4. 

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