Improved mill capacity and performance with larger-diameter feeding rollers

The diameter and peripheral speed of the grooved roller pressure feeder (GRPF) and under feed roller (UFR) on a six-roller mill, as a percentage of the mill roller, has a great influence on the capacity and efficiency of the mill. The capacity increases, mainly due to an increase in the peripheral speed and an increase in the allowable width of a Donnelly chute, due to increases in the GRPF and UFR diameters. The bulk density of prepared cane in a Donnelly chute is fundamentally constant for a given Preparation Index (PI) of cane. Accordingly, a larger allowable Donnelly-chute opening and a higher peripheral speed increase the throughput capacity of a mill, other things being equal. The mill capacity also increases due to the improved feedability of the UFR as the contact arc with the bagasse blanket increases. An increased arc of contact reduces the possible slip during cane feeding. Increasing the UFR arc of contact allows it to operate at a higher speed relative to the other rollers. This increases the density at the feed opening entry, resulting in improved extraction at the feed nip and reducing the juice load on the discharge side of the mill. Greater GRPF and UFR diameters increase the capacity of the mill at the same operating speed or the mill can operate at reduced speeds for the same crush capacity with an improved extraction level. This paper highlights the results achieved in two sugar mills in India for increasing the crushing capacity from 3800 to 5200 t cane/day in Shri Chhatrapati SSK, Kagal factory by installing a larger diameter GRPF and UFR (30% higher than mill roller size) and from 3500 to 4200 t/day in Kareli sugar factory by installing a larger diameter UFR (30% higher than the mill roller). Key words Larger-diameter grooved roller pressure feeder (GRPF), larger-diameter underfeed roller (UFR), mill capacity, mill performance