Cablevey Conveyors Hop Pellets

September 2, 2016

The product tested was hop pellets. Hop cones are processed to make pellets. The pellet is a very convenient form for breweries to use in making beer. Typical pellets were  1/4″ diameter X 1/4″ to 3/4″ long. They had a measured bulk density of 34.3 pounds per cubic foot. The slip angle on stainless steel was 22°. The pellets were received packaged in sealed metalized plastic bags to retain freshness. As received, the pellets were slightly moist and sticky. Upon drying they became dusty.

Testing was conducted using a 4 inch diameter tube conveyor that had a horizontal inlet immediately followed by a 180° sweep to take the product upward and then back to horizontal. Then a discharge directly above the inlet facilitated recycling the pellets through the system. Representative samples of the pellets were subjected to sieve analysis prior to conveying, after one pass through the conveyor, and after 17 hours of conveying. Results of the sieve analyses are shown in the table below. A video camera was used to inspect the conveyor’s interior at the conclusion of the test.

HOP PELLETS BEFORE AND AFTER CONVEYING

SAMPLE TOTAL > #6 #6 – #20 < #20
  MASS(g.) MASS(g.) % MASS(g.) % MASS(g.) %
BEFORE CONVEYING 197.7 196.3 99.29 0.6 0.30 0.8 0.40
AFTER ONE PASS 162.7 161.4 99.20 0.4 0.25 0.9 0.55
AFTER 17 HOURS (EST. 1,600 TRIPS) 256.9 204.9 79.76 35.3 13.74 16.7 6.50

The sample generally conveyed well. As indicated in the table the pellets gradually broke down to smaller pieces and fines. Where the pellets were dragged along the tubes’ interiors, hop residue accumulated. Because there was buildup on the disc and cable the residue even transferred to the tubes of the return side that were not directly exposed to the pellets. The only rollback in the vertical lift section was the fines. Supplemental tests revealed that the size, shape, and friction characteristics of the pellets cause them to pull relatively hard when conveyed upward.

Because hop pellets tend to leave sticky, sugary residues they are not an ideal material for any type of conveyor. A 4″ Cablevey conveyor could convey these pellets provided that the system is kept clean. Systems will need to be equipped with a brush box, wiper disc, and water ports for frequent cleaning. Minimizing the elevation changes in vertical sections and/or replacing vertical sections with sloped sections in the conveyor’s design may improve the operation especially as residue starts accumulating in the tubes.