Scraped-surface mixers

Scraped surface heat exchangers (SSHE) have been used as tubular reactors for plastics pyrolysis. SSHE overcome coking and carbon deposits forming on heat exchanging surfaces when the plastic pyrolyzes to hot gases. A tubular reactor with a special internal screw mixer has been developed in Poland [5]. The purpose of the specially shaped internal mixer is to mix the molten plastic and to scrape coke from the internal surface... 

The mixing technique should be such that all the surfaces of the vessel and mixing utensils are well scraped off and that the curative is well mixed in. For smaller batches, a spatula-type instrument is normally used. Poor mixing is evident by the formation of striations in the mix. These are lines of different color or intensity that are evident in both the unpigmented and pigmented mixtures. The hand mixing should be such that the color or clarity of the mix is completely even. For large batches, an electric mixer may be used, but in this case care must be taken that air is not sucked down and whipped into the mix. 

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