Crystallization of Pastilles from Molten Paraffin-A New Design Method Based on Temperature Effects.

Abstract

Crystallization of pastilles from molten paraffin was investigated by measuring (1) the layer thickness growth rate, (2) the secondary crystallization rate, and (3) the shape change during the transformation from a paraffin droplet to a pastille. The molten paraffin was dropped from a heated nozzle onto the smooth horizontal plane of the crystallizer, which was cooled by coolant circulated through the inside of the crystallizer, and the progress of the crystallization of molten drops into pastilles was monitored. Changes of shape and size of the droplets during solidification were analyzed, and a relationship between coolant temperature and reasonable operation time has been obtained to better design the melt crystallizer. Furthermore, the effects of cooling and storage temperature on secondary crystallization rate were examined. The secondary crystallization rate, which was determined from the slope of the relationship between the storage time and the change of X-ray peak intensity of products, had a maximum in a specified range of storage temperatures, around 293 K, independent of coolant temperature.Judging from droplet height and layer thickness changes, the transformation from a paraffin droplet to a pastille could be divided into (I) cooling of droplet, (II) formation of a pastille, and (III) heat withdrawing of a pastille. The formation time was approximately four times as long as the cooling time. Based on these temperature effects, a new design method for a steel-belt crystallizer is proposed to obtain a reasonable operation time.