Tugas Besar CFD - Josiah Enrico S

Introduction

Plastic pellets, also introduced as nurdles, are the building blocks for almost every product made of plastic. About the size of a lentil, plastic pellets are produced by petrochemical chemical companies and transported to plastic manufacturing facilities where they are melted down and shaped into a final product. In 2015, it is estimated that 270 million metric tons of plastic are produced around the globe every year, much of which begins its life as a plastic pellet.

One typical problem along this industry is that producing plastic pellet always comes with some contaminants or dust which need to be removed. Those matters occur naturally in products like minerals, food, tablets, and other bulk solids, while others are caused by the way the products are handled. Impurities in plastic pellets, both fines (dust) and angel hair (streamers), are generated by the friction in conveying lines. Dilute phase systems create large amounts of dust and streamers; the higher the velocity, the larger the amounts of impurities.

For instance, as depicted in figure 1, these bends cause pellets to hit the inner wall of the elbow. Depending on the resin properties, elbow design, and air velocities, some resins get deflected to other areas of the elbow and some get deflected back to the air stream. Most slide against the elbow wall. This sliding generates frictional heat. pellets with low melting points, soften and smear along the wall. This smearing happens fast, and once started, it often grows as incoming pellets rub against the existing smear. Incoming conveyed pellets randomly break off the smeared plastic into long, ribbon-like strands, almost like loose bird’s nests which are called angel hair. 

Cleaning bulk solids in the plastics industry is important to improve the quality of both the pellets and the finished plastic product. Dust and angel hair can contaminate resins at the receiver, including changing the resin’s properties and color. This problem also leads to lower quality end products such as weak spots in fibers, blurry surfaces resulting from vaporized dust particles, flaws in wire insulation, etc. the mixture of these impurities with unaffected resin often plugging a feed area and eventually starving a receiver. These clogged vent or duct resulting in shorter machine and equipment lifespan wherein increasing factory cost.