Recycling stickies

Bubble columns in series have been used to establish the same effective mix of plug-flow and back-mixing behavior required for Hquid-phase oxidation of cyclohexane, as obtained with staged reactors in series. WeU-mixed behavior has been established with both Hquid and air recycle. The choice of one bubble column reactor was motivated by the need to minimize sticky by-products that accumulated on the walls (93). Here, high air rate also increased conversion by eliminating reaction water from the reactor, thus illustrating that the choice of a reactor system need not always be based on compromise, and solutions to production and maintenance problems are complementary. Unlike the Hquid in most bubble columns, Hquid in this reactor was intentionally weU mixed. 

Thermal pyrolysis for upgrading plastic wastes is one of the better methods for recycling plastics in terms of its perspectives for industrial implementation. The conical spouted bed reactor proposed in this paper may be a solution to the problems arising in fluidized beds handling sticky solids, as particle agglomeration phenomena, which can cause defluidization. In order to avoid defluidization, experiments have been carried out in batch mode in the temperature range of 450-600 °C. A good performance of the reactor is proven under the conditions of maximum particle stickiness. 

Pulsed sieve-plate columns have shown good efficiencies for frequencies between 60 and 150 strokes/min and amplitudes under 1 cm. In general, a plate spacing of 10 cm is considered most favorable. However, these columns operate well in only a limited load range and are also susceptible to fouling, particularly with sticky products. To some extent, the reduction in efficiency at underload can be compensated by changing the pulsation characteristics the load can also be artificially increased by recycling the raffinate. 

Generally, the recycle is similar to mechanical pulping operations but product can be higher quality. De-inking and adhesive ( stickies ) removal are peculiar to recycled pulp. 

For handling large quantities of granular solids, a cascading rotary dryer is often the equipment of choice. If the material is not naturally free-flowing, recycling of a portion of the final dry product may be used to precondition the feed, either in an external mixer or directly inside the drum. Hanging link chains and/or scrapper chains are also used for sticky feed materials. 

Flash Drying Special designs of pneumatic conveyor dryers, described in Sec. 12, can handle filter and centrifuge cakes and other sticky or pasty feeds to yield granular size-enlarged products. The dry product is recycled and mixed with fresh, cohesive feed, followed by disintegration and dispersion of the mixed feed in the drying air stream. 

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